From the Sun and the wind to the grid. Learn how the world makes power, step by step.
Solar · Wind · Hydro · The Grid
Hi, I'm Barry the Beaver. I will be with you on every page. We start from the very beginning, so you can understand the big ideas at the end.
★
Welcome
Welcome, energy explorer
START HERE
1How this book works
Clean energy is a big subject, so we build it brick by brick. We start with what energy is, then electricity, then how power stations work. Only after that do we meet the three biggest clean sources: solar, wind and hydro. At the end we see how they all connect through the grid.
Every chapter has three parts
Learn it. Short sections, big pictures, and equations explained in plain words.
See it. Real examples from India and the world.
Check it. 10 questions on what you read, then 2 harder stretch questions.
You will never be asked about anything the chapter has not taught. Every question has a Look back tag. Answers, with reasons, are at the back of the book.
Don't worry if the maths looks scary. Every equation gets the same treatment: words first, then a picture of the idea, then a slow worked example. If you can multiply and divide, you can do this.
2Boxes you will meet
Word box
New words, explained in plain English.
Big idea
The one thing to remember from a section.
Did you know?
A surprising fact, always true.
Equation cardname
Every equation has words first, then symbols, then the idea behind it, then a worked example.
Brain stretch
A think-about-it question. Not graded.
Try it safely
A small, safe experiment. Always optional.
Workshop link
Points back to something you saw in a Gridovators workshop.
Look back: p.12
Tells you which page taught the idea in a question.
3Safety first, always
Read this before any experiment
Never touch wall sockets, bare wires, chargers with damaged cables, or anything plugged into the mains. Real mains electricity can seriously hurt you.
Never open, cut, heat or puncture a battery. Never short-circuit one with a wire.
Never look straight at the Sun, even through sunglasses or a magnifying glass.
Never go near dam walls, canals, rivers in flood, rooftops, or electricity poles and towers.
Always tell an adult first. The experiments here use only paper, string, water in a bowl, torches and tiny batteries.
4The journey in one picture
Foundations first, then three clean sources, then how it all joins up.
Gridovators Clean Energy WorkbookWelcome, energy explorer
Chapters 1 to 5 build the ideas. Chapters 6 to 8 use them on solar, wind and hydro. Chapters 9 to 11 join everything into a working system. Chapters 12 to 14 look at the modern world.
How to study
Read one chapter at a time.
Do the questions without peeking.
Mark with the answers. Read the reason for every wrong one.
Redo any question you missed, a day later.
Skipping ahead is allowed, but later chapters use words from earlier ones. If you get stuck, follow the Look back tags.
Gridovators Clean Energy WorkbookContents
∑
Maths toolkit
Maths toolkit, part 1
TOOLKIT
1Rates: what "per" means
"Per" means "for each" and you find it by dividing. 60 kilometres per hour means 60 km for each hour. A bus that goes 120 km in 2 hours goes 120 ÷ 2 = 60 km per hour. We will meet the same idea as watts (energy per second), rupees per unit and litres per second.
Rule of thumb
If you see the word "per", think "divide". If you see "for each" or "in every", think "multiply".
2Squared and cubed: area and volume in disguise
Squared means a number times itself: 3² = 3 × 3 = 9. Picture a 3 by 3 tile floor: 9 tiles. Cubed means three times: 2³ = 2 × 2 × 2 = 8. Picture a cube made of 2 × 2 × 2 little blocks: 8 blocks.
Squared makes flat things grow quickly, cubed makes solid things grow even faster.
Why this matters: if you double the side of a square, its area becomes 2 × 2 = 4 times bigger. Double the side of a cube and its volume becomes 2 × 2 × 2 = 8 times bigger. Wind power will follow this exact pattern.
3Big and small numbers: the ladder of 1,000
Energy numbers get huge, so we use prefixes. Each step up the ladder is 1,000 times bigger. Going up, you divide by 1,000. Going down, you multiply by 1,000.
milli · basic · kilo · mega · giga
You have
Change to
Because
3,500 W
3.5 kW
up one step, ÷ 1,000
2 MW
2,000 kW
down one step, × 1,000
0.4 GW
400 MW
down one step, × 1,000
Remember: k = kilo = 1,000. A kilometre is 1,000 metres. A kilogram is 1,000 grams. A kilowatt is 1,000 watts.
Gridovators Clean Energy WorkbookMaths toolkit 1
∑
Maths toolkit
Maths toolkit, part 2
TOOLKIT
4Percentages: "out of 100"
Percent means "out of 100". 20% means 20 out of every 100. To find 20% of a number, multiply by 0.20 (move the decimal point two places left). 20% of 1,000 is 1,000 × 0.20 = 200.
To turn a part into a percentage: part ÷ whole × 100. If 30 of 40 lights are LEDs, that is 30 ÷ 40 = 0.75, so 75%.
5Reading a graph
A graph is a picture of a table. The horizontal axis (x) usually shows time or the thing you change. The vertical axis (y) shows what you measure. To read it: find a value on one axis, go across or up to the line, then read the other axis.
Line going up: the value is growing.
Flat line: no change.
Steeper line: faster change.
6The triangle trick for equations
Many equations are three quantities tied together, like Distance = Speed × Time. Draw a triangle with D on top and S, T at the bottom. Cover the one you want:
Cover D: S × T, so D = S × T.
Cover S: D over T, so S = D ÷ T.
Cover T: D over S, so T = D ÷ S.
We will use this trick for energy, power and time, and for current, voltage and resistance.
7The five-step maths routine
Do this every time
Write the equation in words.
Put in the numbers, with their units.
Check that the units match (change kW to W, or hours to seconds, first).
Calculate.
Ask: does my answer feel sensible?
Quick practice (answers are in bold)
1) 150 km in 3 hours is how many km per hour? 50 2) 4² = 16 3) 5³ = 125 4) 2,500 W in kW = 2.5 5) 25% of 400 = 100 6) 18 out of 24 as a percentage = 75%
Gridovators Clean Energy WorkbookMaths toolkit 2
1
Part A · Foundations · Chapter 1
What is energy?
Energy is the reason anything happens. Even your yawn. Let's find out what it really is.
LEARN IT
By the end of this chapter you can
Explain energy in your own words and name eight forms
Trace an energy chain from the Sun to a cricket ball
State the law of conservation of energy
Calculate efficiency as a percentage
Tell renewable energy from non-renewable energy
1.1What is energy?
Energy is hard to see, so scientists describe it by what it does. Energy is the ability to make something change or move. A kettle cannot heat water without energy. A bulb cannot glow without energy. You cannot even yawn without energy.
Where something changes, energy is at work.
Energy is not a thing you can hold in a jar. It is a number we calculate that tells us how much change is possible. Think of it as the bank balance of the universe: you can spend it and move it between accounts, but you can never print more.
When a rickshaw driver says "no fuel, no go", he is giving you the whole chapter in five words. Something has to supply energy for anything to happen.
1.2Eight forms of energy
Energy shows up in different forms, a bit like water can be ice, liquid or steam. Same stuff, different costume. You need these eight.
Word box
Kinetic
energy of movement. A faster, heavier object has more.
Potential
stored energy, like a ball held high or a stretched rubber band.
Thermal
the energy of jiggling particles. Hotter means more jiggling.
Chemical
stored in the bonds between atoms: food, petrol, batteries.
Gridovators Clean Energy WorkbookChapter 1: What is energy? · page 6
1
Part A · Foundations
What is energy?
LEARN IT
1.3Energy changes form
Energy is rarely used in the form it arrives. It is transformed (changed from one form to another) again and again. We draw this as an energy chain. Follow your samosa: sunlight becomes the chemical energy in a plant, then the chemical energy in you, then the kinetic energy of a cricket ball.
Two energy chains. Orange arrows show the form the energy changes into.
When energy simply moves from one place to another without changing form (hot tea warming your hand), we call it transfer. Both happen in every machine in this book.
1.4The law of conservation of energy
Here is one of the most important rules in all of science: energy can never be created or destroyed. It can only change form or move. Add up all the energy before and after, and the total is always the same.
A swinging ball. At the top it has only stored energy. At the bottom it has only movement energy. The grey part grows because the air and the string take a little as heat.
So why does a swing eventually stop? The energy has not vanished. A tiny bit becomes heat in the air and the string on every swing, until all of it has been spread out as warmth. We call this energy "lost", but a better word is spread out: it still exists, it is just too thinly spread for us to use again.
Big idea
When people say "we use up energy" they really mean "we change useful energy into spread-out heat". Energy is not used up. It is downgraded.
Try it safely (optional): swing and watch
Tie a small, light object (a ball of paper) to a 50 cm piece of string.
Hold the top of the string steady and pull the object to one side. Let go.
Count the swings before it stops, once with a big push and once with a small one.
Which went on longer? Where did the energy go in the end?
Gridovators Clean Energy WorkbookChapter 1: What is energy? · page 7
1
Part A · Foundations
What is energy?
LEARN IT
1.5Efficiency: how much do you actually get?
No machine turns all its energy into the thing you wanted. The part you wanted is useful energy. The rest, usually heat, is wasted energy. Efficiency tells you the useful share, as a percentage.
Old filament bulb: roughly 5% becomes light
LED bulb: roughly 40% becomes light
Equation cardEfficiency
Efficiency (%) = useful energy out ÷ total energy in × 100
both energies in the same unit, such as joules (J)
useful outthe energy you actually wantedJtotal inall the energy put into the machineJ
The idea: It is the same as asking "what share of my pocket money turned into the thing I wanted?". Spend 100 rupees, get a 70 rupee snack, and your efficiency is 70%.
Worked example:A fan motor takes in 60 J of electrical energy and gives out 42 J of movement.Efficiency = 42 ÷ 60 × 100 = 0.7 × 100 = 70%. The other 18 J became heat.
Machine
Efficiency (roughly)
Petrol engine
25%
Coal power station
35 to 40%
Solar panel (normal)
20%
Wind turbine
35 to 45%
Hydro turbine
90%
Electric motor
90%
Notice the pattern. Machines that burn something and make heat first are poor at the job. Machines that move something directly (water in a turbine, magnets in a motor) are very good.
We will use this later to compare clean and dirty power.
1.6Chains multiply their losses
Real systems pass energy through several machines in a row. Each one wastes some, so the losses multiply. Take 100 J. Machine A is 80% efficient, so 80 J gets through. Machine B is 50% efficient, so only half of that, 40 J, comes out.
Overall efficiency = efficiency A × efficiency B, with each written as a decimal: 0.80 × 0.50 = 0.40, or 40%. The chain is always weaker than its weakest machine.
Energy shrinks at every step.
Gridovators Clean Energy WorkbookChapter 1: What is energy? · page 8
1
Part A · Foundations
What is energy?
LEARN IT
1.7Where does energy come from?
Nearly all the energy we use began as sunlight. The Sun heats the air (wind), lifts water into clouds (rain and rivers), and grows plants (food, wood and, millions of years ago, the plants that became coal and oil). Only three sources do not come from the Sun.
Follow the orange arrows: wind, water, plants and fossil fuels are all stored or moved sunlight.
Renewable energy refills quickly compared with how fast we use it: sunshine, wind, flowing water. Non-renewable energy took millions of years to make and cannot refill in our lifetime: coal, oil, gas and uranium. Think of a tank with a tap. If water pours in as fast as it pours out, the tank never empties. Renewables are that tank. Fossil fuels are a tank someone filled once, long ago, with no pipe to refill it.
Word box
Efficiency
the useful share of the energy you put in.
Renewable
refills naturally, in about the time we use it.
Non-renewable
used far faster than nature can make it.
Fossil fuel
coal, oil or gas: ancient plants and animals, squeezed over millions of years.
Remember this chapter in a nutshell
Energy is the ability to make something change or move, and it comes in eight forms.
Energy changes form in a chain, and the total is always conserved. "Lost" energy is spread-out heat.
Efficiency = useful out ÷ total in × 100. Direct movers (turbines, motors) beat heat-makers.
Almost all energy traces back to the Sun. Renewables refill, fossil fuels do not.
Gridovators Clean Energy WorkbookChapter 1: What is energy? · page 9
1
Part A · Foundations
What is energy?: check it
CHECK IT
Try every question before you peek. The small Look back tags show which page taught the idea. Answers start on page 71.
1
Energy is the ability to make something or move.Look back: p.6
2
True or false? A ball sitting still on a high shelf has kinetic energy.Look back: p.6
TrueFalse
3
Which form of energy is stored in a stretched rubber band?Look back: p.6
KineticPotentialSoundLight
4
Match each form of energy to an example. Write the letters.Look back: p.6
1. Chemical
2. Kinetic
3. Thermal
4. Light
A. A moving rickshaw
B. A battery
C. A glowing bulb
D. A cup of hot tea
1 – 2 – 3 – 4 –
5
Number these from 1 to 4 to make the energy chain from the Sun to a cricket ball.Look back: p.7
You eat the plant
The plant grows
You hit the ball
Sunlight reaches the plant
6
In your own words, say what the law of conservation of energy states.Look back: p.7
7
A bouncing ball finally stops. Where did its energy go?Look back: p.7
It disappearedIt became spread-out heat and soundIt went back to the SunIt became new energy
8
A motor takes in 200 J of energy and gives out 150 J of useful movement. What is its efficiency?Look back: p.8
Working: Answer: %
9
Machine A is 80% efficient and passes its energy to machine B, which is 50% efficient. What is the overall efficiency of the pair?Look back: p.8
Working: Answer: %
10
True or false? Wind and flowing water both get their energy, originally, from the Sun.Look back: p.9
TrueFalse
Stretch it: extension questions
11
Explain why solar panels, wind turbines and coal power stations all depend on the Sun. Use the idea of an energy chain.Look back: p.7Look back: p.9
12
Draw an energy chain for a torch powered by a battery. Label every form of energy and say where energy is wasted. Then work out the efficiency if 10 J goes in and 4 J comes out as light.Look back: p.7Look back: p.8
Gridovators Clean Energy WorkbookChapter 1: What is energy? · page 10
2
Part A · Foundations · Chapter 2
Power, energy and units
Energy is the amount. Power is how fast. Mix them up and you will pay too much for electricity.
LEARN IT
By the end of this chapter you can
Explain the difference between energy and power
Use joules, watts, kilowatts and kilowatt-hours
Work out stored energy from height and speed
Calculate the energy and cost of running an appliance
Explain what a capacity factor tells you
2.1Energy is the amount. Power is how fast.
People mix these up all the time. Energy is the total amount of change you can get, like the 10 litres of water in a bucket. Power is how fast you use or deliver it, like how quickly the tap fills the bucket.
The unit of energy is the joule (J). Lift a small apple (about 100 grams) up by one metre and you have used roughly 1 joule. The unit of power is the watt (W), and 1 watt means 1 joule every second. A 60 W bulb uses 60 joules of electrical energy every single second.
Energy is the bucket. Power is the tap.
Equation cardPower
Power = Energy ÷ Time
or, rearranged: Energy = Power × Time
Ppowerwatts (W)Eenergyjoules (J)ttimeseconds (s)
The idea: The word "per" tells you to divide. Watts are joules per second, just like speed is kilometres per hour. If you know any two of E, P and t, the triangle trick from the toolkit finds the third.
Worked example:A 60 W bulb is on for 2 minutes. First change the time to seconds: 2 × 60 = 120 s.Energy = Power × Time = 60 × 120 = 7,200 J.
Cover E: P × t, so E = P × t.
Cover P: E over t, so P = E ÷ t.
Cover t: E over P, so t = E ÷ P.
Gridovators Clean Energy WorkbookChapter 2: Power, energy and units · page 11
2
Part A · Foundations
Power, energy and units
LEARN IT
2.2Two ways energy is stored: height and speed
Two stored-energy formulas will come back again and again, in hydro (falling water) and in wind (moving air). Learn them here, slowly, with a jug and a cricket ball.
Height matters in a straight line. Speed matters twice over.
Equation cardPotential energy
PE = m × g × h
mass × gravity × height
mmasskilograms (kg)ggravity, about 10 (exact: 9.8)newtons per kghheight liftedmetres (m)
The idea: To lift something you push against gravity. Lift twice the mass, or lift it twice as high, and you store twice the energy. It is a straight-line relationship.
Worked example:A 2 kg water jug on a shelf 3 m high.PE = 2 × 10 × 3 = 60 J.
Equation cardKinetic energy
KE = ½ × m × v²
half × mass × speed × speed
mmasskilograms (kg)vspeedmetres per second (m/s)
The idea: Speed is squared, so it counts twice. Double the speed and the energy is 2 × 2 = 4 times bigger. That is why fast crashes are so much worse than slow ones.
Worked example:A 0.16 kg cricket ball at 30 m/s.v² = 30 × 30 = 900. KE = ½ × 0.16 × 900 = 72 J.
Why this matters later
Falling water has potential energy that turns into kinetic energy. Moving air has kinetic energy. Hydro and wind are these two formulas at work.
The little "g" is the pull of the Earth. We round 9.8 up to 10 to keep the sums easy. Your answers will be about 2% too big, which is fine for understanding.
Gridovators Clean Energy WorkbookChapter 2: Power, energy and units · page 12
2
Part A · Foundations
Power, energy and units
LEARN IT
2.3The power ladder: watts to gigawatts
Small machines use watts. Cities use gigawatts. Every step up the ladder is 1,000 times bigger, just like in the toolkit.
Typical values. Real machines vary, so these are round numbers to give you a feel for the sizes.
2.4The kilowatt-hour: the unit on your electricity bill
Joules are tiny. A single 60 W bulb uses 216,000 J in one hour. So power companies use a bigger unit: the kilowatt-hour (kWh). It is the energy used by a 1 kW machine running for 1 hour. On your bill it is called a "unit".
Because 1 kW is 1,000 W and 1 hour is 3,600 s, one kWh = 1,000 × 3,600 = 3,600,000 J. Notice that kWh is a unit of energy, not power. The "h" is there because it is power multiplied by time.
Equation cardEnergy in kWh
Energy (kWh) = Power (kW) × Time (hours)
change watts to kilowatts first: divide by 1,000
Ppower of the machinekilowatts (kW)ttime it runshours (h)
The idea: It is the same E = P × t as before, with units that suit everyday life. Big, long-running machines cost the most. Cost = kWh × price per unit.
Worked example:A 75 W fan runs for 8 hours. Power = 75 ÷ 1,000 = 0.075 kW.Energy = 0.075 × 8 = 0.6 kWh. At an example price of ₹7 per unit, the cost is 0.6 × 7 = ₹4.20.A 1.5 kW air conditioner for 8 hours: 1.5 × 8 = 12 kWh, which costs 12 × 7 = ₹84. That is 20 fans!
Gridovators Clean Energy WorkbookChapter 2: Power, energy and units · page 13
2
Part A · Foundations
Power, energy and units
LEARN IT
2.5Capacity and capacity factor
A power plant has a capacity: the most power it can give at one moment, such as 2 MW. But a solar panel makes nothing at night, and a wind turbine slows when the wind drops. Over a year it delivers less energy than "capacity × all the hours". The share it really delivers is its capacity factor.
Capacity is the size of the tap. Capacity factor tells you how often it is running full.
Equation cardCapacity factor
Capacity factor (%) = actual energy ÷ (capacity × hours) × 100
both energies in the same unit, such as MWh
actualenergy really produced in the periodMWhcapacity × hoursenergy if it ran at full power the whole timeMWh
The idea: It is like asking: "what share of the year was this plant effectively working flat out?" A 30% factor means about 30% of the year at full power.
Worked example:A 2 MW turbine could make 2 × 8,760 = 17,520 MWh in a year but really made 5,256 MWh.Capacity factor = 5,256 ÷ 17,520 × 100 = 0.30 × 100 = 30%.
Source
Typical capacity factor
Solar panels (India)
18 to 25%
Wind turbines (India)
25 to 35%
Hydro (India, varies with rain)
35 to 45%
Nuclear
80 to 90%
Brain stretch (not graded)
Why does an air conditioner cost so much more than a fan if they both run for 8 hours?
Word box
Joule (J)
unit of energy. 1 J is about an apple lifted 1 m.
Watt (W)
unit of power. 1 joule per second.
kWh
unit of energy. 1 kW for 1 hour.
Workshop linkWind is not steady. In the wind workshop we saw why a turbine beside a road sees bumpy, changing wind, and what that does to its output.
Remember this chapter in a nutshell
Energy (joules, kWh) is the amount. Power (watts) is how fast. E = P × t.
PE = m × g × h and KE = ½ × m × v². Speed is squared.
Each step in W, kW, MW, GW is × 1,000. 1 kWh = 1 kW for 1 hour = 3,600,000 J.
Capacity factor = actual ÷ possible × 100. Solar and wind are well below 100%.
Gridovators Clean Energy WorkbookChapter 2: Power, energy and units · page 14
2
Part A · Foundations
Power, energy and units: check it
CHECK IT
Try every question before you peek. The small Look back tags show which page taught the idea. Answers start on page 71.
True or false? Energy and power mean exactly the same thing.Look back: p.11
TrueFalse
3
A 100 W bulb stays on for 30 seconds. How much energy does it use?Look back: p.11
Working: Answer: J
4
A 5 kg bag is lifted 2 m. Using g = 10, how much potential energy does it gain?Look back: p.12
Working: Answer: J
5
A 0.5 kg ball moves at 4 m/s. What is its kinetic energy?Look back: p.12
Working: Answer: J
6
A rickshaw doubles its speed. Its kinetic energy becomes:Look back: p.12
2 times bigger4 times bigger8 times biggerthe same
7
Change these units. 3,200 W = ______ kW. 0.6 MW = ______ kW.Look back: p.13
Working: Answer:
8
A 60 W fan runs for 10 hours. How many kilowatt-hours (units) does it use?Look back: p.13
Working: Answer: kWh
9
A 1.5 kW air conditioner runs for 4 hours. Electricity costs ₹8 per unit. How much does it cost?Look back: p.13
Working: Answer: ₹
10
A 5 MW solar farm makes 8,760 MWh in a year (8,760 hours). What is its capacity factor?Look back: p.14
Working: Answer: %
Stretch it: extension questions
11
Fan A uses 75 W. A more efficient Fan B uses 40 W. Both run 10 hours a day for 30 days. At ₹7 per unit, how much money does Fan B save?Look back: p.13
12
A wind turbine has a capacity of 2 MW but its average output is only 0.6 MW. Explain, in words, why the two numbers are different. Then work out its capacity factor.Look back: p.14
Gridovators Clean Energy WorkbookChapter 2: Power, energy and units · page 15
3
Part A · Foundations · Chapter 3
Electricity
Electrons are tiny delivery riders. Let's follow them round a circuit and find out what pushes them.
LEARN IT
By the end of this chapter you can
Describe an atom and the two rules of electric charge
Tell a conductor from an insulator and say why
Draw a simple circuit and explain series and parallel
Explain voltage, current and resistance with the water-pipe idea
Use V = I × R and P = V × I
3.1Atoms and electric charge
Everything is made of tiny atoms. In the middle of each atom is a nucleus holding protons (positive charge, +) and neutrons (no charge). Zipping around the outside are electrons (negative charge, −). Normally an atom has equal + and −, so the charges cancel.
Charges follow two simple rules: opposites attract and likes repel. Electrons are light and can leave their atom, but protons are stuck in the nucleus. So when we talk about electricity, electrons are the ones that move.
Static electricity is a build-up of charge. Rub a balloon on your hair and electrons jump from your hair to the balloon. The balloon is now negative, your hair is positive, and since opposites attract, your hair rises to meet it.
Electrons are tiny delivery riders. They carry energy from the battery or power station to the machine. They do not get used up. It is the energy they carry that gets used.
3.2Conductors and insulators
In a conductor such as copper, some electrons are loose and free to wander between the atoms. Push them from one end and a flow starts. In an insulator such as rubber or plastic, the electrons are held tightly, so almost nothing flows.
Conductors: copper, aluminium, iron, graphite, salt water, wet skin. Insulators: plastic, rubber, glass, dry wood, dry air.
That is why a wire is copper inside, plastic outside. Water makes things conduct, so wet hands and electricity are a dangerous mix.
Free electrons let metals carry current.
Gridovators Clean Energy WorkbookChapter 3: Electricity · page 16
3
Part A · Foundations
Electricity
LEARN IT
3.3A circuit is a loop
Electricity only flows when it has a complete loop to travel round: a circuit. The battery (or cell) gives the push. The wires are the road. The bulb is where the energy gets used. The switch opens or closes the loop. Open the loop and the flow stops everywhere at once.
The flow of charge is called current. Engineers draw current going from the + side of the battery round to the − side. Electrons actually travel the other way, but the maths comes out the same, so we keep the old drawing rule.
Symbols engineers use to draw circuits
Closed loop: current flows, the bulb lights.
Open loop: no path, no current, no light.
3.4Series and parallel
There are two ways to connect two bulbs. In series there is only one path: the same current goes through both, and if one bulb breaks the loop breaks and both go out. In parallel each bulb has its own path: if one breaks, the other stays on.
Why homes use parallel
Home sockets and lights are wired in parallel, so switching off the fan does not turn off the fridge.
Try it safely (optional): a lemon is not enough
Look at a torch (not plugged into anything). Open the battery cover with an adult.
Find the two metal contacts. Draw the circuit with the symbols above.
Never use mains sockets for circuit experiments. Only use small torch batteries.
Gridovators Clean Energy WorkbookChapter 3: Electricity · page 17
3
Part A · Foundations
Electricity
LEARN IT
3.5Voltage, current and resistance
Three ideas run all of electricity. The water loop below makes them easy. A pump pushes water round a pipe. A battery pushes charge round a wire.
Left: a water loop. Right: the matching electric circuit. Pump = battery, pipe = wire, narrow pipe = resistor.
Voltage (V) is the push, like the pump pressure. Unit: the volt (V).
Current (I) is the flow, how much charge passes each second, like litres per second. Unit: the ampere or amp (A).
Resistance (R) is the squeeze, how much the part fights the flow. Unit: the ohm (Ω).
Resistance depends on the material, and also on the wire: longer wires resist more, thinner wires resist more. That is why thick copper cables carry big currents safely.
Equation cardOhm's law
Voltage = Current × Resistance
V = I × R so I = V ÷ R and R = V ÷ I
Vvoltage, the pushvolts (V)Icurrent, the flowamps (A)Rresistance, the squeezeohms (Ω)
The idea: A bigger push gives a bigger flow. A bigger squeeze gives a smaller flow. Same pump, narrower pipe, less water per second. Use the triangle: cover the one you want.
Worked example:A 12 V battery is connected across a 4 Ω resistor. Find I.I = V ÷ R = 12 ÷ 4 = 3 A.Now use a 6 Ω resistor on the same battery: I = 12 ÷ 6 = 2 A. More resistance, less current.
Gridovators Clean Energy WorkbookChapter 3: Electricity · page 18
3
Part A · Foundations
Electricity
LEARN IT
3.6Power and staying safe
Chapter 2 gave us power in watts. Electricity has its own way to find it: push times flow.
Equation cardElectrical power
Power = Voltage × Current
P = V × I (watts = volts × amps)
Ppowerwatts (W)Vvoltagevolts (V)Icurrentamps (A)
The idea: Push times flow is the rate at which energy is delivered. It connects this chapter to Chapter 2: the same watts, the same kWh.
Worked example:A 2,000 W kettle runs on 230 V. Find I.I = P ÷ V = 2,000 ÷ 230 = 8.7 A. That is a big current, so kettles need thick wires and a proper plug.
Higher voltage can push a current through your body. Low voltage cannot.
Electricity safety rules
Never touch a fallen wire or a power line. Stay away and tell an adult.
Never use water near plugs, sockets or switches.
Never poke anything into a socket.
Only use small torch batteries for experiments.
What is a fuse?
A fuse is a thin wire that melts if the current gets too big. It breaks the loop on purpose, before the wires overheat. Homes also use circuit breakers, which do the same job and can be switched back on.
Did you know?
Your body is a conductor. Even a few hundredths of an amp through your chest can be dangerous, which is why we treat mains as a serious matter.
Remember this chapter in a nutshell
Atoms have protons (+), neutrons and electrons (−). Electrons move, opposite charges attract.
A circuit needs a complete loop. Series has one path, parallel has several.
Voltage is the push, current is the flow, resistance is the squeeze. V = I × R.
Power P = V × I. High voltage can hurt you, so never touch mains or power lines.
Gridovators Clean Energy WorkbookChapter 3: Electricity · page 19
3
Part A · Foundations
Electricity: check it
CHECK IT
Try every question before you peek. The small Look back tags show which page taught the idea. Answers start on page 72.
1
Which particle moves through a copper wire to carry an electric current?Look back: p.16
ProtonsNeutronsElectronsAtoms
2
True or false? Two negative charges attract each other.Look back: p.16
TrueFalse
3
Which of these is a good electrical insulator?Look back: p.16
Copper wireRubberIron nailSalt water
4
Why is a wire made of copper inside and plastic outside?Look back: p.16
5
What must a circuit have for current to flow?Look back: p.17
A bulb onlyA complete loopTwo switchesA thick wire
6
Two bulbs are wired in parallel. One bulb breaks. What happens to the other?Look back: p.17
It goes outIt stays onIt gets brighter and burstsIt becomes a battery
7
Match each idea to its meaning. Write the letters.Look back: p.18
1. Voltage
2. Current
3. Resistance
A. How much the part squeezes the flow (ohms)
B. The push on the charge (volts)
C. How much charge flows each second (amps)
1 – 2 – 3 –
8
A 12 V battery is joined across a 4 Ω resistor. What current flows?Look back: p.18
Working: Answer: A
9
A torch bulb has 3 V across it and 0.5 A flowing. What is its resistance?Look back: p.18
Working: Answer: Ω
10
A heater draws 5 A from a 230 V supply. What is its power?Look back: p.19
Working: Answer: W
Stretch it: extension questions
11
A 2,300 W heater runs on 230 V. Find the current. Then use the water-pipe idea to explain why it needs a thick wire.Look back: p.19
12
Draw a circuit with one battery and two bulbs, where each bulb has its own switch so you can turn them off separately. Say which type of connection you used.Look back: p.17Look back: p.17
Gridovators Clean Energy WorkbookChapter 3: Electricity · page 20
4
Part A · Foundations · Chapter 4
Magnets, generators and turbines
Almost all the electricity in the world is made by something spinning. Let's see why.
LEARN IT
By the end of this chapter you can
Describe a magnetic field and an electromagnet
Explain how a moving magnet makes a voltage
Say how a generator works and what AC means
List what can spin a turbine, and which source needs no turbine
4.1Magnets and their invisible field
A magnet has two ends, a north pole (N) and a south pole (S). Around it is an invisible region called a magnetic field, where it can push or pull iron. The rules look like those for charges: opposite poles attract and like poles repel.
Pour iron filings (tiny iron pieces) near a magnet and they line up along the field lines. The field is real, we just cannot see it.
4.2Electricity can make a magnet
In 1820 a scientist noticed that a wire carrying current made a compass needle move. Current makes a magnetic field. Wind the wire into a coil, put an iron nail inside, and you have an electromagnet.
It is a magnet you can switch on and off. More turns of wire or more current make it stronger. Scrapyard cranes, doorbells and electric motors all use electromagnets.
If electricity can make magnetism, can magnetism make electricity? Yes. That question gave us power stations.
Did you know?
A compass needle is a tiny magnet. It points north because the Earth itself acts like a giant bar magnet.
Gridovators Clean Energy WorkbookChapter 4: Magnets, generators and turbines · page 21
4
Part A · Foundations
Magnets, generators and turbines
LEARN IT
4.3Making electricity: induction
In 1831 Michael Faraday pushed a magnet into a coil of wire and the needle on a meter jumped. A changing magnetic field pushes the charges in a wire. This is electromagnetic induction. Nothing touches, nothing burns: movement turns into electricity.
Push the magnet in and out and the bulb flickers. Stop moving and the voltage stops.
speedhow fast the magnet moves pasttimesstrengthhow strong the magnet istimesturnsloops of wire in the coiltimes
The idea: Each of the three works like a multiplier. Double any one and the voltage doubles. Double two of them and it becomes four times bigger.
Worked example:A coil gives 100 V. Now spin the magnet 2 times faster and use 3 times as many turns.Voltage = 100 × 2 × 3 = 600 V.
4.4The generator, AC and 50 Hz
A generator is induction on repeat. Instead of pushing a magnet in and out, we spin it inside coils of wire. Each half turn the magnet's north and south poles swap sides, so the push flips direction. This gives alternating current (AC). A battery gives direct current (DC), which flows one way only.
One full spin of the magnet makes one full wave, called a cycle.
Indian mains goes through 50 cycles each second. We say the frequency is 50 hertz (Hz). One cycle takes 1 ÷ 50 = 0.02 seconds, far too fast for your eyes to notice your bulb flickering.
Why AC?
AC is easy to step up to high voltage and back down with a transformer (Chapter 10). That makes it cheap to send over long distances.
Gridovators Clean Energy WorkbookChapter 4: Magnets, generators and turbines · page 22
4
Part A · Foundations
Magnets, generators and turbines
LEARN IT
4.5What spins the turbine?
A turbine is a wheel with blades, built to catch a moving fluid and spin. The turbine turns the generator. So the real question for every power station is: how do we make the blades turn?
Different fuels, same ending: blades turn a shaft, the shaft spins a generator.
Coal, gas and nuclear make heat. The heat boils water into high-pressure steam, and the steam spins the turbine.
Wind pushes the blades directly.
Falling water from a dam pushes the blades directly.
Solar panels are the odd one out. Light knocks electrons loose inside the panel, so nothing spins at all. (Solar thermal plants do use mirrors to make steam, but panels are far more common.)
Steam plants waste heat
A coal or gas steam plant turns about 35 to 40% of the fuel energy into electricity. The rest leaves as heat. Wind and water skip the steam stage, so they avoid that loss.
4.6The same trick in reverse: the motor
Put electricity into a generator and it becomes a motor: the coil becomes an electromagnet that gets pushed round by the permanent magnet. A fan, a washing machine and an electric train all use motors. A generator and a motor are the same machine run in opposite directions.
Remember this chapter in a nutshell
A magnet has a field. Opposite poles attract, like poles repel.
Current makes a magnetic field, and a changing magnetic field makes a voltage (induction).
A generator spins a magnet inside coils. It makes AC, 50 cycles a second in India.
Coal, gas and nuclear boil water for steam. Wind and water spin the blades directly. Solar panels need no spinning.
Gridovators Clean Energy WorkbookChapter 4: Magnets, generators and turbines · page 23
4
Part A · Foundations
Magnets, generators and turbines: check it
CHECK IT
Try every question before you peek. The small Look back tags show which page taught the idea. Answers start on page 72.
1
Two magnets are placed with their north poles facing each other. What happens?Look back: p.21
They attractThey repelNothingThey become electromagnets
2
An electromagnet is a coil of wire that becomes a magnet when flows through it.Look back: p.21
3
True or false? An electromagnet becomes stronger when you wind more turns of wire.Look back: p.21
TrueFalse
4
Which pair is needed to make a voltage by induction?Look back: p.22
A battery and a bulbA magnet and a coil of wire that move relative to each otherTwo coils with no magnetA switch and a resistor
5
Name two ways to increase the voltage from a generator.Look back: p.22
6
A coil gives 50 V. You spin the magnet 3 times faster and double the number of turns. What is the new voltage?Look back: p.22
Always chargingAlternating current: it keeps changing directionAir conditioningA strong battery
8
Indian mains has a frequency of 50 Hz. How long does one cycle take? (Time = 1 ÷ frequency)Look back: p.22
Working: Answer: s
9
Put these in order for a wind turbine. Write 1 to 4.Look back: p.23
Generator makes electricity
Wind pushes the blades
The shaft spins
Electricity goes to the grid
10
Which source of electricity does not need a spinning turbine?Look back: p.23
CoalHydro (dam)WindSolar panels
Stretch it: extension questions
11
A steam power station turns 38% of its fuel energy into electricity. If the fuel contains 1,000 MJ, how much electricity is made and how much is lost as heat? Why does a wind turbine avoid this loss?Look back: p.23Look back: p.5
12
A generator and a motor are the same machine run in opposite directions. Explain what goes in and what comes out for each.Look back: p.22Look back: p.23
Gridovators Clean Energy WorkbookChapter 4: Magnets, generators and turbines · page 24
5
Part A · Foundations · Chapter 5
Fossil fuels and climate
Fossil fuels powered the modern world, but they have a catch. Let's find out what it is.
LEARN IT
By the end of this chapter you can
Say what fossil fuels are and where they come from
Explain what happens to the carbon when fuel burns
Describe the greenhouse effect and why extra CO₂ matters
Compare how much CO₂ different sources make per kWh
Explain net zero in your own words
5.1A short history of power
For most of history people used muscles, wood and wind. About 300 years ago, coal changed everything. Burning coal boiled water, steam pushed engines, and factories, trains and ships took off. Later, oil and gas joined coal. Together they are called fossil fuels.
Fossil fuels powered two centuries of growth. Clean sources have a much shorter history.
Fossil fuels are cheap, easy to store and carry a lot of energy. That is why we still use them. But they come with two big problems that this chapter explains.
5.2Where fossil fuels come from
Fossil fuels are made from ancient plants and tiny sea creatures that lived hundreds of millions of years ago. They stored sunlight as chemical energy. When they died they were buried under mud and rock. Heat and pressure slowly turned them into coal, oil and gas.
It takes millions of years to make fossil fuels. We burn them in a few hundred.
This is why fossil fuels are not renewable: we use them far faster than nature makes them. It is also why they hold carbon, the building block of all living things.
Did you know?
A coal lump is stored sunlight. When a power station burns it, it releases energy that a plant caught from the Sun 300 million years ago.
Gridovators Clean Energy WorkbookChapter 5: Fossil fuels and climate · page 25
5
Part A · Foundations
Fossil fuels and climate
LEARN IT
5.3What happens when carbon burns
Burning means joining with oxygen and releasing energy. Carbon from the fuel joins with oxygen from the air to make carbon dioxide (CO₂). It goes out of the chimney as an invisible gas.
Equation cardBurning carbon
Carbon + Oxygen → Carbon dioxide
C + O₂ → CO₂ so 12 kg of carbon makes 44 kg of CO₂
Ccarbon in the fuel12 mass unitsO₂oxygen from the air32 mass unitsCO₂carbon dioxide44 mass units
The idea: The carbon picks up oxygen, so the CO₂ is heavier than the carbon you started with. 44 ÷ 12 is about 3.67, so each kilogram of carbon makes about 3.67 kg of CO₂.
Worked example:A fuel contains 6 kg of carbon. How much CO₂ does it make when burnt?CO₂ = 6 × 44 ÷ 12 = 22 kg.
5.4The greenhouse effect
Sunlight warms the ground. The warm ground gives out heat, which would normally escape into space. Greenhouse gases such as CO₂ and methane act like a blanket: they trap some of this heat.
A little of this is good. Without it Earth would average about −18 °C. With it we get about 15 °C. The trouble is that burning fossil fuels adds extra CO₂, so the blanket gets thicker and the planet warms.
The greenhouse effect: gases hold some heat in.
CO₂ was about 280 ppm before factories. Now it is above 420 ppm.
ppm means parts per million: out of every million bits of air, how many are CO₂. A rise from 280 to over 420 sounds small, but it is about a 50% increase, and Earth has already warmed by more than 1 °C.
Weather and sea
A warmer planet means more heat waves, heavier rain at times, drier spells at others, melting ice and rising seas. India feels this in its monsoon and its long coastline.
Gridovators Clean Energy WorkbookChapter 5: Fossil fuels and climate · page 26
5
Part A · Foundations
Fossil fuels and climate
LEARN IT
5.5How much CO₂ per unit of electricity?
Scientists measure carbon intensity: grams of CO₂ released for each kilowatt-hour. This counts the whole life of the power plant, including making and building it.
Coal is the worst. Gas is lower but still high. Solar, hydro, nuclear and wind are tiny by comparison. Switching from coal to a clean source cuts emissions by more than 90%.
Typical values (IPCC lifetime estimates).
Equation cardCO₂ from electricity
CO₂ = Energy used × Carbon intensity
grams of CO₂ = kWh × (g CO₂ per kWh)
kWhenergy usedkilowatt-hoursintensityCO₂ per kWh for that sourceg per kWh
The idea: Intensity is a price tag measured in CO₂ instead of rupees. More units used times a higher tag means more CO₂, just like a shopping bill.
Worked example:A 1 kW heater runs for 10 hours, so it uses 10 kWh. Find the CO₂ from coal power (820 g per kWh) and from wind (11 g per kWh).Coal: 10 × 820 = 8,200 g = 8.2 kg. Wind: 10 × 11 = 110 g = 0.11 kg.
5.6Other costs, and the way forward
Burning fuel also releases smoke and tiny particles that damage lungs. Air pollution makes asthma and heart disease worse, which is a big reason cities want cleaner power. Mining coal and drilling for oil also scar land and sea.
Net zero means that the CO₂ we add to the air equals the CO₂ we take out again, for example by forests. India has set a goal of net zero by 2070. To get there we must replace fossil electricity with clean sources. The next chapters cover the three biggest: solar, wind and hydro.
Remember this chapter in a nutshell
Fossil fuels are ancient plants and sea life, turned into coal, oil and gas over millions of years. They are not renewable.
Burning carbon makes CO₂. Each 1 kg of carbon makes about 3.67 kg of CO₂.
Extra CO₂ thickens the greenhouse blanket, so Earth warms.
Coal makes about 820 g of CO₂ per kWh. Wind, hydro and solar make a tiny fraction. Net zero means adding no more than we remove.
Gridovators Clean Energy WorkbookChapter 5: Fossil fuels and climate · page 27
5
Part A · Foundations
Fossil fuels and climate: check it
CHECK IT
Try every question before you peek. The small Look back tags show which page taught the idea. Answers start on page 73.
1
Fossil fuels such as coal and oil mostly come from...Look back: p.25
Old rocks onlyAncient plants and sea creaturesVolcanoesWind and water
2
True or false? Fossil fuels are renewable because new coal forms every year.Look back: p.25
TrueFalse
3
Which gas is released when carbon in a fuel burns?Look back: p.26
OxygenCarbon dioxideHeliumNitrogen
4
A fuel contains 6 kg of carbon. Using 12 kg of carbon makes 44 kg of CO₂, how much CO₂ does it make?Look back: p.26
Working: Answer: kg
5
Greenhouse gases act like a blanket because they trap in the atmosphere.Look back: p.26
6
Why is a little greenhouse effect actually good for life on Earth?Look back: p.26
7
Before factories, CO₂ in the air was about 280 ppm. It is now above...Look back: p.26
100 ppm280 ppm420 ppm2,000 ppm
8
A home uses 100 kWh of electricity made from gas (490 g CO₂ per kWh). How many kg of CO₂ is that?Look back: p.27
Working: Answer: kg
9
Put these in order from most to least CO₂ per kWh. Write 1 to 4.Look back: p.27
Wind
Coal
Solar panels
Gas
10
Besides CO₂, what is another harm of burning coal?Look back: p.27
It makes the air too cleanSmoke and tiny particles that damage lungsIt makes the Sun dimmerIt adds oxygen
Stretch it: extension questions
11
A house uses 300 kWh a month. Find the CO₂ in kg if the electricity comes from coal (820 g per kWh) and from solar (48 g per kWh). How much CO₂ is saved by switching?Look back: p.27
12
In your own words, explain how burning coal today is linked to sunlight from millions of years ago and to a warmer planet.Look back: p.25Look back: p.26
Gridovators Clean Energy WorkbookChapter 5: Fossil fuels and climate · page 28
6
Part B · Solar · Chapter 6
Solar power
The Sun gives us more energy in an hour than we use in a year. Let's learn how to catch it.
LEARN IT
By the end of this chapter you can
Say how much energy sunlight delivers and how long it takes to reach us
Explain how a solar cell makes electricity
Describe the path from cell to panel, inverter and home
Use the panel power and daily energy equations
List the good and hard parts of solar power
6.1The Sun: a free power station
The Sun is a ball of burning gas 150 million km away. Its light takes about 8 minutes 20 seconds to reach us. In one hour, the Sun sends the Earth about as much energy as all of humanity uses in a whole year.
On a clear noon, every square metre facing the Sun receives roughly 1,000 W.
So there is plenty of energy. The challenge is catching it. A solar panel catches sunlight and turns part of it into electricity. Today's panels convert about 20%, which is our efficiency idea from Chapter 1.
6.2Inside a solar cell
A solar cell is a thin slice of silicon, a material made from sand. It has two layers. When sunlight (tiny packets of energy called photons) hits the cell, it knocks electrons loose.
The two layers are made so the loose electrons are pushed in one direction. Join the cell to a bulb with wires and the electrons flow round the loop: that is a current. This is called the photovoltaic effect. Photo means light and voltaic means voltage.
No moving parts, no noise, no fuel.
Remember Chapter 4? Turbines need something to spin. A solar cell needs nothing to spin. Light does the whole job.
Gridovators Clean Energy WorkbookChapter 6: Solar power · page 29
6
Part B · Solar
Solar power
LEARN IT
6.3From cell to panel to array
One cell gives only about 0.5 V. That is not much, so we join many cells in series, as in Chapter 3, and their voltages add up. About 60 cells in a row make roughly 30 V. A group of cells in a frame is a panel. Several panels joined together are an array.
More cells add voltage. More panels add power.
Equation cardPanel power
Power = Area × Sunlight × Efficiency
P = A × 1,000 W/m² × η (η is the Greek letter eta, for efficiency)
Ppower from the panelwatts (W)Aarea of the panelsquare metres (m²)ηefficiency, as a decimal0.20 means 20%
The idea: Start with all the sunlight landing on the panel (area × 1,000). Then keep only the share the panel can convert. A bigger panel catches more light, and a better panel keeps more of it.
Worked example:A panel is 2 m² and 20% efficient. Find its power at noon.P = 2 × 1,000 × 0.20 = 400 W.
6.4The inverter and the whole system
Panels make DC, but your home and the grid use AC (Chapter 4). A box called an inverter changes DC into AC. Then the power can run your lights, or flow through a meter to the grid. Some homes add a battery to keep extra for the evening.
The inverter is the translator between panels and home.
Did you know?
Some houses with rooftop solar send extra power to the grid and get credit on their bill. This is called net metering. India's PM Surya Ghar scheme (2024) aims to put rooftop solar on 10 million homes.
Gridovators Clean Energy WorkbookChapter 6: Solar power · page 30
6
Part B · Solar
Solar power
LEARN IT
6.5What changes the output?
A panel's rating, such as 500 W, is for perfect conditions. Real life is messier:
Time of day: no sun at night, weak sun at dawn and dusk.
Clouds and monsoon: less light, less power.
Shade and dust: even one shaded corner cuts power. Clean the glass.
Tilt and direction: in India, face south and tilt about as much as your latitude.
Heat: very hot panels are a bit less efficient.
The curve is sunlight over a typical day. Its area equals about 5 hours at full strength.
Because sunlight changes all day, engineers add it up into peak sun hours: the number of hours at full 1,000 W/m² strength that would give the same total energy. India gets about 5 peak sun hours a day on average. This is why a solar farm's capacity factor (Chapter 2) is only about 20 to 25%.
6.6Solar maths: sizing a home system
Equation cardDaily solar energy
Energy per day = Size × Sun hours × Performance
E = P × h × 0.8 (kWh per day)
Eenergy made in a daykWhPrated size of the systemkilowatts (kW)hpeak sun hours per dayhours (about 5)0.8performance ratio: losses in wires, heat, dustabout 80%
The idea: A 1 kW system is like a worker who is at full strength for 5 hours a day, then loses 20% to everyday losses. So 1 kW makes 1 × 5 × 0.8 = 4 kWh a day.
Worked example:A home uses 10 kWh a day. What size system covers it?Each 1 kW makes 4 kWh, so size = 10 ÷ 4 = 2.5 kW.With 500 W panels that is 2,500 ÷ 500 = 5 panels.
Workshop linkThe workshop shows why the evening matters: solar only works in daylight, so storing the energy is the next puzzle (Chapter 9).
Gridovators Clean Energy WorkbookChapter 6: Solar power · page 31
6
Part B · Solar
Solar power
LEARN IT
6.7Sunlight for heat too
Not all solar uses silicon. A solar water heater has dark pipes under glass. Sunlight heats the water directly, with no electricity needed. Millions of Indian homes use one, and a solar cooker works the same way. Heating water straight from sunlight is more efficient than making electricity first.
6.8Cost, trade-offs and India
Solar panels have become much cheaper: the price has fallen by about 90% since 2010. In many places solar is now the cheapest new electricity, which is why India has added over 100 GW of it. Huge parks such as Bhadla in Rajasthan (about 2.2 GW) and Pavagada in Karnataka (about 2 GW) send power across the country.
Panel price index, 2010 = 100 (approximate)
The good
Free fuel and no smoke or noise
Works on a rooftop or in a desert
Small systems can reach villages with no grid
Very little maintenance
The hard parts
Only works in daylight, so storage matters
Output drops in monsoon and haze
Big solar parks need land
Old panels must be recycled properly
Remember this chapter in a nutshell
The Sun sends about 1,000 W to each square metre. A cell uses the photovoltaic effect: light knocks electrons loose.
Cells in series add voltage. Panel power = area × 1,000 × efficiency.
An inverter changes DC to AC. Output changes with time of day, cloud, shade, dust and heat.
Daily energy = size (kW) × peak sun hours × 0.8. Solar is cheap, clean and daytime only, so it needs storage.
Gridovators Clean Energy WorkbookChapter 6: Solar power · page 32
6
Part B · Solar
Solar power: check it
CHECK IT
Try every question before you peek. The small Look back tags show which page taught the idea. Answers start on page 73.
1
About how long does sunlight take to reach the Earth?Look back: p.29
1 secondAbout 8 minutesAbout 8 hoursAbout 8 days
2
On a clear noon, each square metre facing the Sun receives about watts.Look back: p.29
Stores heat in a tankTurns light directly into electricitySpins a turbineBurns silicon
4
True or false? Solar panels make AC electricity, so a home can use it with no other equipment.Look back: p.30
TrueFalse
5
One cell gives 0.5 V. A panel joins 60 cells in series. What is the panel voltage?Look back: p.30
Working: Answer: V
6
A panel has an area of 2.5 m² and an efficiency of 20% (0.20). What power does it give in full sun?Look back: p.30
Working: Answer: W
7
Which of these will not reduce a panel's output?Look back: p.31
Dust on the glassA tree's shadowCleaning the glassA thick cloud
8
A 2 kW system gets 5 peak sun hours. Using a performance ratio of 0.8, how much energy does it make in a day?Look back: p.31
Working: Answer: kWh
9
A home uses 6 kWh a day. Each 1 kW of panels makes 4 kWh a day. What system size is needed?Look back: p.31
Working: Answer: kW
10
Give one good thing and one hard thing about solar power.Look back: p.32
Stretch it: extension questions
11
A home uses 300 kWh a month (10 kWh a day, 30 days). Using 4 kWh per kW per day, find the system size. If the tariff is ₹7 per unit, how much money does the home save in a month if solar covers all its use?Look back: p.31
12
Solar farms have a capacity factor of only about 20 to 25%. In your own words, explain why it is far below 100%.Look back: p.31
Gridovators Clean Energy WorkbookChapter 6: Solar power · page 33
7
Part B · Wind · Chapter 7
Wind power
Wind is the Sun's energy in motion. Let's see how big turbines catch it.
LEARN IT
By the end of this chapter you can
Explain what causes wind and how the monsoon works
Use the wind power equation and the cube rule
Name the main parts of a wind turbine
Explain cut-in, rated and cut-out speeds and the Betz limit
Find the yearly energy from a turbine
7.1Where does wind come from?
Wind is moving air, and the Sun drives it. The Sun heats land faster than sea. Warm air above the land rises, and cooler air from the sea rushes in to fill the gap. That moving air is a sea breeze.
The Indian monsoon is a giant sea breeze that lasts for months.
In summer the whole Indian land mass heats up and pulls in wet air from the Indian Ocean. In winter the pattern reverses. So wind is solar energy in disguise, stored for a while as moving air.
7.2The energy inside moving air
Air has mass, and anything with mass that moves has kinetic energy, which you met in Chapter 2: KE = ½ × m × v². A turbine slows the wind down a little and takes some of that energy. To find the power, we ask: how much air arrives each second?
Imagine the rotor as a giant hoop. The air that passes through it in one second forms a long tube.
Gridovators Clean Energy WorkbookChapter 7: Wind power · page 34
7
Part B · Wind
Wind power
LEARN IT
7.3The wind power equation
Mass per second = air density × area × speed.
Equation cardPower in the wind
Power = ½ × Density × Area × Speed³
P = ½ × ρ × A × v³ (ρ is the Greek letter rho, for density)
Ppower in the wind passing the rotorwatts (W)ρair density1.2 kg/m³Aswept area of the rotor = π × r²m²vwind speedmetres per second (m/s)
The idea: Mass per second is ρ × A × v. Each kilogram carries ½ × v² of energy. Multiply them: ½ × (ρ A v) × v² = ½ ρ A v³. Speed shows up three times, once for the amount of air and twice for the energy in each kilogram.
Worked example:A rotor has radius 40 m and the wind is 10 m/s. Find the wind power.A = π × 40² = 3.14 × 1,600 = 5,024 m².P = ½ × 1.2 × 5,024 × 10³ = 0.6 × 5,024 × 1,000 = 3,014,400 W, about 3 MW.
The cube rule: double the wind speed and the power goes up 2 × 2 × 2 = 8 times. That is why a windy hilltop or coast is worth so much more than a calm valley.
Power compared with 5 m/s
Gridovators Clean Energy WorkbookChapter 7: Wind power · page 35
7
Part B · Wind
Wind power
LEARN IT
7.4Inside a wind turbine
The blades are shaped like aeroplane wings. Moving air creates lift that turns the rotor slowly, about 15 turns a minute. A gearbox speeds this up so the generator (Chapter 4) spins fast enough to make electricity. The whole top section, the nacelle, turns to face the wind.
A turbine is a generator on a tall stick, with a lot of clever controls.
7.5How much can a turbine really catch?
A turbine only works within a range of wind speeds. Below cut-in (about 3 m/s) there is too little force to spin it. At rated speed (about 12 m/s) it reaches full power. Above that the blades twist away to hold power steady. At cut-out (about 25 m/s) it stops for safety.
No turbine can take all the wind's energy. If it did, the air would stop behind it and block new wind. Physics sets the best case at 59%, called the Betz limit. Good real turbines reach about 40 to 45%.
Power rises with the cube of speed, flattens at rated power, then switches off.
Gridovators Clean Energy WorkbookChapter 7: Wind power · page 36
7
Part B · Wind
Wind power
LEARN IT
7.6Wind maths: yearly energy
Equation cardEnergy from a wind turbine
Energy = Rating × Hours × Capacity factor
E = P × 8,760 × CF
Eenergy per yearMWhPrated powerMW8,760hours in a yearhoursCFcapacity factor (Chapter 2), as a decimal0.30 means 30%
The idea: A 3 MW turbine that ran flat out all year would make 3 × 8,760 MWh. In real life the wind comes and goes, so it makes only the CF share of that.
Worked example:A 3 MW turbine has a capacity factor of 30%. Find its yearly energy.E = 3 × 8,760 × 0.30 = 7,884 MWh (about 7.9 million kWh).A home using 3,000 kWh a year needs 7,884,000 ÷ 3,000 = 2,628 homes.
7.7Wind farms, India and trade-offs
Turbines are grouped into wind farms, placed far enough apart so they do not steal wind from each other. India has about 50 GW of wind, mostly in Tamil Nadu, Gujarat, Maharashtra, Karnataka and Rajasthan. The Muppandal area in Tamil Nadu is one of the largest wind clusters in the country.
Wind blows hardest in the monsoon months, just when solar is weakest. It also often blows at night. So wind and solar complement each other.
Typical pattern (illustrative).
The good
No fuel and no smoke
Farmland under turbines can still be used
Works day and night when the wind blows
The hard parts
Output goes up and down with the wind
Noise and some risk to birds and bats
Best sites can be far from cities
Workshop linkThe Treeva workshop explores bumpy, turbulent wind. Smooth wind is easiest for a turbine to use, bumpy wind is harder.
Remember this chapter in a nutshell
Wind comes from uneven heating by the Sun. The monsoon is a giant sea breeze.
P = ½ρAv³. Double the speed and the power is 8 times bigger.
Betz limit: at most 59% of the wind's energy can be captured. Real turbines get 40 to 45%.
Yearly energy = rating × 8,760 × capacity factor. Wind and solar balance each other across the year.
Gridovators Clean Energy WorkbookChapter 7: Wind power · page 37
7
Part B · Wind
Wind power: check it
CHECK IT
Try every question before you peek. The small Look back tags show which page taught the idea. Answers start on page 74.
A turbine must be 100 m tallNo turbine can capture more than about 59% of the wind's energyWind never blows above 12 m/sTurbines make 59 W each
9
A 3 MW turbine has a capacity factor of 30% (0.30). How much energy does it make in a year? (8,760 hours)Look back: p.37
Working: Answer: MWh
10
Why do wind and solar power work well together in India?Look back: p.37
Stretch it: extension questions
11
A turbine has a rotor of radius 40 m and the wind is 10 m/s. The turbine captures 40% of the wind power. Find the power it produces. (Use the answer from the worked example.)Look back: p.35Look back: p.36
12
Engineers choose hilltops and coasts for wind farms. A site has a wind speed that is twice as high as another. How many times more power is in the wind there? Explain why this matters.Look back: p.35
Gridovators Clean Energy WorkbookChapter 7: Wind power · page 38
8
Part B · Hydro · Chapter 8
Hydropower
Water falls, a turbine spins, a light comes on. Let's see how rivers become electricity.
LEARN IT
By the end of this chapter you can
Explain how the water cycle makes hydropower renewable
Name the parts of a hydropower plant
Use P = ρ × g × Q × H × η and explain each part
Say which turbine suits which site
Weigh up the good and hard parts of dams
8.1Hydro is the Sun again
Hydro means water. The Sun heats the sea, water evaporates, clouds form, and rain falls on high ground. Rivers then carry the water back downhill. Water on the hills has stored energy. Hydropower catches that energy on the way down.
The water cycle is a giant free pump, powered by the Sun.
So hydropower, like wind, is solar energy in disguise. It is renewable because the Sun keeps refilling the hills with rain.
8.2The energy of falling water
From Chapter 2, anything high up has potential energy: PE = m × g × h. Falling water turns this into kinetic energy, which spins a turbine.
Water is heavy. One cubic metre (1 m³) weighs 1,000 kg. Let it fall 50 m and: PE = 1,000 × 10 × 50 = 500,000 J. A river carries many cubic metres every second, so the energy adds up quickly.
Heavy water plus a big drop equals a lot of energy.
Remember: we use g = 10 to keep the maths friendly. The exact value is 9.8, so our answers are close but a touch high.
Gridovators Clean Energy WorkbookChapter 8: Hydropower · page 39
8
Part B · Hydro
Hydropower
LEARN IT
8.3Inside a hydropower plant
A dam holds back a river and builds a reservoir. Water is let into a large pipe called a penstock. It rushes down and spins a turbine connected to a generator (Chapter 4). Then the water flows on down the river. The height difference between the reservoir surface and the turbine is called the head.
A plant is a controlled waterfall. Open the gate for power, close it to save water.
8.4The hydropower equation
Equation cardHydropower
Power = Density × g × Flow × Head × Efficiency
P = ρ × g × Q × H × η
Pelectrical powerwatts (W)ρdensity of water1,000 kg/m³ggravity (we use 10)m/s²Qflow: cubic metres per secondm³/sHhead: height of fallmetres (m)ηefficiency, about 0.9decimal
The idea: Each second Q cubic metres arrive, and each weighs 1,000 kg. Their weight is 1,000 × g × Q newtons, and they fall H metres. Weight times height is energy, and energy per second is power. Then η keeps the share that turns into electricity.
Worked example:A plant has a flow of 20 m³/s, a head of 50 m and η = 0.9. Find the power.P = 1,000 × 10 × 20 × 50 × 0.9 = 10,000,000 × 0.9 = 9,000,000 W = 9 MW.
Double the head, or double the flow, and the power doubles. Unlike wind, there is no cube here: the answer grows in step. That is why engineers look for a high drop and a strong river.
Gridovators Clean Energy WorkbookChapter 8: Hydropower · page 40
8
Part B · Hydro
Hydropower
LEARN IT
8.5Which turbine for which site?
Different rivers need different turbines.
Pelton: very high head, small flow, such as a steep Himalayan stream. Water jets hit spoon-shaped buckets.
Francis: medium head and flow. The most common type.
Kaplan: low head, huge flow, such as a wide slow river. It works like a ship propeller.
Pick the turbine from the head and the flow.
8.6Kinds of hydro and India's dams
Storage hydro uses a big dam and reservoir. The water can be kept for when it is needed. Run-of-river hydro uses the natural flow with a small weir and little storage. Small and micro hydro power a village or even a single mill. In the Himalayas, families have used water mills called gharats for centuries.
India has about 47 GW of large hydro, roughly a tenth of its generating capacity. Tehri in Uttarakhand has India's tallest dam at 260 m.
Some large Indian hydro plants (MW)
Nathpa Jhakri (HP)1,500 MW
Sardar Sarovar (Gujarat)1,450 MW
Tehri (Uttarakhand)1,000 MW
Idukki (Kerala)780 MW
Gridovators Clean Energy WorkbookChapter 8: Hydropower · page 41
8
Part B · Hydro
Hydropower
LEARN IT
8.7Trade-offs and the clean mix
The good
Water can be stored, so power can start in minutes
Plants last 50 to 100 years
No fuel and no smoke while running
Reservoirs also give irrigation and drinking water
The hard parts
Big dams flood land and move people from their homes
Dams change river ecosystems and block fish
Dry years mean less electricity
Large plants take many years to build
Because hydro can be turned up and down quickly, it is a perfect partner for solar and wind. When the Sun sets or the wind drops, water can fill the gap. This ability to supply power on demand is one reason engineers value it.
8.8Hydro maths: bigger plant, yearly energy
Equation cardYearly energy from a hydro plant
Energy = Power × 8,760 × Capacity factor
E = P × 8,760 × CF
Ppower from the equationMWCFcapacity factor (Chapter 2)decimal
The idea: The plant is not always at full flow: rivers rise and fall with the seasons. The capacity factor says what share of the year it effectively runs flat out.
Worked example:The plant that makes 9 MW has a capacity factor of 40%. Find its yearly energy.E = 9 × 8,760 × 0.40 = 31,536 MWh.
Workshop linkThe Cassetex workshop is about storing energy in batteries. Water behind a dam is storage too, and Chapter 9 compares the two.
Remember this chapter in a nutshell
Hydro is solar energy in disguise: the Sun lifts water and rain refills the hills.
Pelton suits high head, Kaplan suits big flow, Francis sits between.
P = ρ × g × Q × H × η. Double the head or the flow and the power doubles.
Hydro can be switched on quickly, but dams change land, people and rivers.
Gridovators Clean Energy WorkbookChapter 8: Hydropower · page 42
8
Part B · Hydro
Hydropower: check it
CHECK IT
Try every question before you peek. The small Look back tags show which page taught the idea. Answers start on page 74.
1
Where does the energy in hydropower come from originally?Look back: p.39
The MoonThe Sun, which drives the water cycleCoal under the riverWind inside the dam
A plant has a flow of 40 m³/s, a head of 60 m and η = 0.9. Find its power in MW. If its capacity factor is 40%, find the yearly energy in MWh.Look back: p.40Look back: p.42
12
Explain why hydropower is called "solar energy in disguise", and why a long drought is a problem for a hydro plant.Look back: p.39Look back: p.42
Gridovators Clean Energy WorkbookChapter 8: Hydropower · page 43
9
Part C · The system · Chapter 9
Storing energy
The Sun sets, but the lights stay on. Storage is how.
LEARN IT
By the end of this chapter you can
Explain why electricity needs to be stored
Describe how a battery stores energy and measure its size
Use E = V × Ah and round-trip efficiency
Explain how pumped hydro works
Compare the main storage methods
9.1Why store energy at all?
Solar makes the most power at noon. Wind comes and goes. But people use the most electricity in the evening, when lights, fans and cookers are all on and the Sun has gone. If we cannot save noon power for the evening, we waste it or fall back on coal.
The red line is demand. The yellow shape is solar. They do not line up, so we need storage.
Storage works like a water tank for electricity: fill it when there is plenty, drain it when there is not. The tank can be a battery, a lake on a hill, or a tank of hot water.
9.2Ways to store energy
Method
How it stores energy
Good for
Round trip
Battery
Chemical energy
Homes, vehicles, a few hours
about 90%
Pumped hydro
Water lifted uphill (potential energy)
Whole cities, many hours
about 75 to 80%
Heat store
Hot water or molten salt
Heating, solar thermal plants
varies
Hydrogen
Chemical energy in a fuel
Days to months, heavy industry
about 30 to 40%
Round trip means the share you get back for what you put in. It is always less than 100%, because every energy change wastes some as heat (Chapter 1).
Gridovators Clean Energy WorkbookChapter 9: Storing energy · page 44
9
Part C · The system
Storing energy
LEARN IT
9.3How a battery works
A battery stores energy as chemical energy. Inside a rechargeable battery, such as the lithium-ion type in phones and electric vehicles, tiny charged particles called ions move between two layers. When you charge, the charger pushes the ions to one side, storing energy. When you use the battery, the ions move back and electrons flow through the outside wire as current.
Charging stores energy. Using it releases the energy.
Batteries are labelled with volts (V) and amp-hours (Ah). Amp-hours say how much current the battery could give for one hour. Multiply them and you get the energy.
Equation cardBattery energy
Energy = Voltage × Amp-hours
E (Wh) = V × Ah then ÷ 1,000 for kWh
Eenergy storedwatt-hours (Wh)Vbattery voltagevolts (V)Ahcapacity in amp-hoursAh
The idea: Remember P = V × I from Chapter 3. A battery giving I amps at V volts delivers V × I watts. Run it for Ah ÷ I hours, and energy = power × time = V × Ah.
Worked example:An e-rickshaw battery is 48 V and 100 Ah. Find its energy.E = 48 × 100 = 4,800 Wh = 4.8 kWh.The motor uses 1.2 kW. Run time = energy ÷ power = 4.8 ÷ 1.2 = 4 hours.
9.4Round-trip efficiency
Equation cardRound-trip efficiency
Efficiency = Energy out ÷ Energy in
efficiency (%) = (energy out ÷ energy in) × 100
outenergy you get backkWhinenergy you put inkWh
The idea: Think of a leaky bucket. You pour in 10 litres, some leaks, and you pour out 9. The efficiency is 9 ÷ 10 = 90%.
Worked example:A battery takes in 10 kWh and gives back 9 kWh.Efficiency = 9 ÷ 10 × 100 = 90%.To get 9 kWh out you must put in 10 kWh.
Gridovators Clean Energy WorkbookChapter 9: Storing energy · page 45
9
Part C · The system
Storing energy
LEARN IT
9.5Pumped hydro: the big water battery
When there is spare electricity, a pump lifts water from a lower lake to an upper lake. Later, when power is needed, the water runs back down through a turbine and makes electricity (as in Chapter 8). The same machine often works as both pump and turbine. Most of the world's grid storage is pumped hydro.
Energy is stored as the height of water.
How much is stored? Use PE = m × g × h again. 1,000,000 m³ of water (1,000,000,000 kg) lifted 100 m stores 1,000,000,000 × 10 × 100 = 1,000,000,000,000 J, which is about 278 MWh. That could run about 28,000 homes for a day, at 10 kWh each.
9.6Choosing storage
Short and long storage
Batteries react in a fraction of a second and are good for a few hours. Pumped hydro stores far more but needs hills and water. Hydrogen is for very long storage but loses a lot of energy on the way.
Did you know?
A battery storing energy for one small village can be about the size of a shipping container. A pumped hydro plant can hold as much energy as thousands of those.
Try it safely (optional): read a battery label
Ask an adult for a phone or power bank with the label showing volts and mAh.
Change mAh to Ah by dividing by 1,000.
Multiply V × Ah to find its energy in Wh.
Never open, puncture or heat a battery. Only use the charger that came with it.
Workshop linkThe Cassetex workshop uses battery swapping: a charged battery goes in, a flat one comes out, and the flat one is charged when power is cheap. That is storage at work.
Remember this chapter in a nutshell
We store energy because supply and demand peak at different times.
Batteries store chemical energy. Energy (Wh) = volts × amp-hours.
Round-trip efficiency = energy out ÷ energy in. It is always below 100%.
Pumped hydro lifts water uphill when power is spare, and lets it fall when power is needed.
Gridovators Clean Energy WorkbookChapter 9: Storing energy · page 46
9
Part C · The system
Storing energy: check it
CHECK IT
Try every question before you peek. The small Look back tags show which page taught the idea. Answers start on page 75.
Solar makes more power than any other sourceSolar peaks at noon but demand peaks in the eveningThe Sun does not shine in IndiaSolar panels explode at night
2
True or false? A battery creates new energy from nothing.Look back: p.45
TrueFalse
3
A battery is 12 V and 100 Ah. How much energy does it hold in kWh? (E = V × Ah, then ÷ 1,000)Look back: p.45
Working: Answer: kWh
4
A battery holds 4.8 kWh and runs a 1.2 kW motor. For how many hours can it run? (time = energy ÷ power)Look back: p.45
Working: Answer: h
5
A battery takes in 10 kWh and gives back 8 kWh. What is its round-trip efficiency?Look back: p.45
Working: Answer: %
6
A battery has a round-trip efficiency of 90%. You put in 20 kWh. How much do you get back?Look back: p.45
C. Whole cities for many hours, needs hills and water
1 – 2 – 3 –
10
Name two ways to store energy for the electricity grid.Look back: p.44
Stretch it: extension questions
11
A home has a 10 kWh battery. It powers a 1.5 kW load. How long does it run? The battery has a round-trip efficiency of 90%. How much solar energy is needed to charge it enough to give 10 kWh out?Look back: p.45Look back: p.45
Gridovators Clean Energy WorkbookChapter 9: Storing energy · page 47
10
Part C · The system · Chapter 10
The grid
Power plants are far away. Let's see how electricity makes the trip without wasting itself.
LEARN IT
By the end of this chapter you can
Name the stages from power station to home
Explain why high voltage means lower losses
Use P loss = I² × R
Explain what a transformer does
Explain why supply and demand must match, and what frequency tells us
10.1From power station to your socket
A power station is usually far from your home. The grid is the network of wires, transformers and control rooms that links them all. Electricity goes through generation, transmission (long distance) and distribution (local), and the voltage is changed several times on the way.
High voltage for the long trip, low voltage for your home.
10.2Why send power at high voltage?
Wires heat up when current flows (Chapter 3), and that heat is wasted energy. The wasted power depends on the current, squared. And from P = V × I, for the same power a higher voltage means a smaller current.
Equation cardHeat lost in a wire
Power lost = Current² × Resistance
Ploss = I² × R (and current I = P ÷ V)
Plosspower wasted as heat in the wirewatts (W)Icurrent in the wireamps (A)Rresistance of the wireohms (Ω)
The idea: Squared means current has a double effect. Cut the current to a tenth and the loss falls to a hundredth. So send the same power at 10 times the voltage and you waste 100 times less.
Worked example:Send 1,000,000 W along a wire with R = 5 Ω.At 10,000 V: I = 1,000,000 ÷ 10,000 = 100 A. Loss = 100² × 5 = 50,000 W.At 100,000 V: I = 10 A. Loss = 10² × 5 = 500 W. Ten times the voltage, a hundredth of the loss.
Gridovators Clean Energy WorkbookChapter 10: The grid · page 48
10
Part C · The system
The grid
LEARN IT
10.3Transformers change the voltage
A transformer has two coils of wire wound on an iron core. AC in the first coil makes a changing magnetic field (Chapter 4). That field passes through the core and pushes a voltage in the second coil. No wires join the two coils.
It only works with AC, because the field must keep changing. This is why the grid uses AC.
More turns on the output coil gives a higher voltage out.
Equation cardTransformer turns rule
Voltage out ÷ Voltage in = Turns out ÷ Turns in
Vout = Vin × (Nout ÷ Nin)
Vinvoltage into the first coilvolts (V)Voutvoltage from the second coilvolts (V)Nnumber of turns of wire in a coilturns
The idea: The voltage out copies the turns ratio. Twice as many turns on the output means twice the voltage. Fewer turns means a lower voltage. (Power stays about the same, so a higher voltage means a smaller current.)
Worked example:The input coil has 100 turns, the output coil has 2,000 turns, and the input is 11,000 V.Vout = 11,000 × 2,000 ÷ 100 = 220,000 V. This is a step-up transformer.
10.4The balancing act
Electricity is hard to store, so the grid must make exactly as much as people use, every second. Control rooms watch the frequency, the 50 Hz heartbeat from Chapter 4.
Demand higher than supply: the generators slow down and frequency falls.
Supply higher than demand: the generators speed up and frequency rises.
In India the frequency must stay between about 49.9 and 50.05 Hz. Too far outside, and power stations trip off to protect themselves.
The grid is a giant see-saw that must stay level.
Gridovators Clean Energy WorkbookChapter 10: The grid · page 49
10
Part C · The system
The grid
LEARN IT
10.5India's one big grid
India has one of the largest connected grids in the world. For years it was split into regions. In 2013 the last region joined, creating One Nation, One Grid, One Frequency. Now a surplus of wind in the south or hydro in the north can help a shortage somewhere else.
Very long lines can also carry DC at extremely high voltage. This is called HVDC, and it loses even less power over very long distances.
The blackout of 30 and 31 July 2012
Across northern and eastern India the grid went down. About 620 million people, roughly half of the country, lost power. The cause was too much demand and a chain of lines tripping, which is exactly the balancing problem above. It led to better monitoring and stronger links.
10.6Who runs the grid, and the losses
Control rooms call on power stations in a merit order: cheapest first. Solar and wind, which have no fuel cost, go first. Hydro and batteries respond fast when demand jumps. Coal and gas fill the rest.
Not all electricity that is generated is delivered and paid for. In India, roughly 15 to 17% is lost in wires or not billed. Cutting these losses is as good as building new power stations.
Try it safely (optional): spot the grid
From a safe place far away, look at an electricity pylon or pole near you. Never go close and never climb.
Notice the strings of discs (insulators). More discs means higher voltage.
Draw the path: power station, pylon, local pole, your home.
Never touch, climb or fly kites near power lines.
Remember this chapter in a nutshell
The grid is generation, transmission and distribution. Voltage goes up for the trip and down near homes.
Loss = I² × R. Ten times the voltage means a tenth of the current and a hundredth of the loss.
A transformer changes AC voltage in the ratio of its coil turns.
Supply must equal demand every second. The frequency of about 50 Hz tells operators if they are out of balance.
Gridovators Clean Energy WorkbookChapter 10: The grid · page 50
10
Part C · The system
The grid: check it
CHECK IT
Try every question before you peek. The small Look back tags show which page taught the idea. Answers start on page 75.
1
Put these in order from the power station to a home. Write 1 to 4.Look back: p.48
Step-down transformer near the home
Power station makes electricity
High-voltage transmission lines
Step-up transformer
2
Why does the grid send power at high voltage?Look back: p.48
It makes the wires thickerFor the same power, a higher voltage means a smaller current and less heat lostIt makes electricity travel fasterIt makes AC into DC
3
A line carries 1,000,000 W at 10,000 V. What current flows? (I = P ÷ V)Look back: p.48
Working: Answer: A
4
A current of 100 A flows in a wire of resistance 5 Ω. How much power is lost as heat? (P = I² × R)Look back: p.48
Working: Answer: W
5
The voltage on a line is made 10 times higher for the same power. By how many times does the heat loss fall?Look back: p.48
AC is stronger than DCIt needs a changing magnetic fieldDC is too dangerousIt needs a battery
7
A transformer has 100 turns on the input coil and 2,000 turns on the output coil. The input is 11,000 V. What is the output voltage?Look back: p.49
Working: Answer: V
8
True or false? If demand is higher than supply, the grid frequency rises.Look back: p.49
TrueFalse
9
The Indian grid frequency should stay close to hertz.Look back: p.49
10
In your own words, explain why supply and demand must match every second.Look back: p.49
Stretch it: extension questions
11
A line carries 2,000,000 W through a wire with R = 4 Ω. Find the power lost at 20,000 V and at 200,000 V. Which is better and why?Look back: p.48
12
Give one benefit of joining all regions into One Nation, One Grid.Look back: p.50
Gridovators Clean Energy WorkbookChapter 10: The grid · page 51
11
Part C · The system · Chapter 11
The clean mix
One source is never enough. Let's see how a team of sources keeps the lights on.
LEARN IT
By the end of this chapter you can
Compare solar, wind and hydro side by side
Explain variable and dispatchable power
Name four ways to balance a clean grid
Describe a village microgrid
Work out the clean share and carbon intensity of a mix
11.1No single hero
Each clean source has strengths and weaknesses. Solar is cheap but works only by day. Wind is strong in the monsoon. Hydro can be turned up on demand. Put them together and they cover each other's gaps.
Source
Works when
India capacity factor
Can be turned up on demand?
Solar
Daytime
about 20 to 25%
No (variable)
Wind
When the wind blows, especially monsoon
about 25 to 35%
No (variable)
Hydro with a dam
When water is stored
about 30 to 45%
Yes
11.2Variable versus dispatchable
Variable sources, such as solar and wind, change with the weather. Dispatchable sources can be switched on or turned up when the grid asks. Dam hydro and batteries are dispatchable. So a strong grid uses variable sources for cheap energy and dispatchable ones to fill the gaps.
Solar carries noon, wind and hydro share evening and night, and storage helps in between.
Gridovators Clean Energy WorkbookChapter 11: The clean mix · page 52
11
Part C · The system
The clean mix
LEARN IT
11.3Four ways to balance a clean grid
None of these needs a new invention. They need good planning.
Storage (Chapter 9) moves noon solar into the evening.
Flexible demand means using power when it is plentiful. A factory or a washing machine can run at noon. Some places charge less for power at noon, which is called a time-of-day tariff.
Better forecasts predict tomorrow's sun and wind, so operators prepare.
More links let one region share surplus with another (Chapter 10).
A grid that uses these tools well is called a smart grid. It uses sensors and computers to match supply and demand more finely.
11.4Microgrids: small grids with big uses
A microgrid is a small local grid, often with solar panels and a battery, that can work on its own or join the main grid. It is useful where the big grid is far away or unreliable. In 2014 the village of Dharnai in Bihar got a solar microgrid that lit homes, shops and a school.
The controller decides when to charge the battery and when to give power to homes.
Did you know?
A microgrid can keep a hospital running during a storm that breaks the main lines. That is one reason many cities are building them.
Gridovators Clean Energy WorkbookChapter 11: The clean mix · page 53
11
Part C · The system
The clean mix
LEARN IT
11.5Mix maths: clean share and carbon intensity
Equation cardShare of a mix
Share (%) = Part ÷ Total × 100
share = (clean ÷ total) × 100
partthe amount you are asking aboutGW or TWhtotalthe whole mixsame units
The idea: It is the percentage idea from the toolkit. How many parts out of every 100?
Worked example:A state has 20 GW solar, 10 GW wind, 5 GW hydro and 25 GW coal. What share is clean?Clean = 20 + 10 + 5 = 35 GW. Total = 35 + 25 = 60 GW.Share = 35 ÷ 60 × 100 = 58.3%.
Equation cardCarbon intensity of a mix
Mix intensity = add up (share × intensity) for each source
mix = (share₁ × g₁) + (share₂ × g₂) + ...
sharefraction of the electricity from that sourcedecimalintensityg CO₂ per kWh from Chapter 5g per kWh
The idea: It is a weighted average. A source that supplies more of the power counts for more.
Worked example:A grid is 40% coal (820 g per kWh) and 60% wind (11 g per kWh).Mix = 0.40 × 820 + 0.60 × 11 = 328 + 6.6 = 334.6 g per kWh.Replace the coal with solar (48 g) and it falls to about 30 g.
11.6India's direction
India has set a goal of 500 GW of non-fossil capacity by 2030 and net zero by 2070. It has reported that about half of its installed capacity is already non-fossil. Capacity is not the same as energy, though: coal still makes most of the electricity, because solar and wind capacity factors are lower. The challenge now is the whole system: storage, grids and flexible demand.
Remember this chapter in a nutshell
Solar, wind and hydro cover each other's gaps. Dam hydro and batteries are dispatchable.
Four balancing tools: storage, flexible demand, forecasts and more links.
A microgrid is a small grid, often solar plus battery, that can run alone.
Share = part ÷ total × 100. Mix intensity is a weighted average of each source's intensity.
Gridovators Clean Energy WorkbookChapter 11: The clean mix · page 54
11
Part C · The system
The clean mix: check it
CHECK IT
Try every question before you peek. The small Look back tags show which page taught the idea. Answers start on page 76.
Its output changes with the weatherIt can never be usedIt runs on coalIt only works in winter
2
True or false? A hydro plant with a dam can be turned up when the grid needs it.Look back: p.52
TrueFalse
3
Which of these helps balance a grid with lots of solar and wind?Look back: p.53
StorageFlexible demandMore links between regionsAll of these
4
A small local grid that can work on its own is called a .Look back: p.53
5
Why does a village solar microgrid usually include a battery?Look back: p.53
6
A state has 20 GW solar, 10 GW wind, 5 GW hydro and 25 GW coal. What percentage is clean, to one decimal place?Look back: p.54
Working: Answer: %
7
A country makes 120 TWh of electricity and 30 TWh is from renewables. What share is that?Look back: p.54
Working: Answer: %
8
A grid is 50% coal (820 g/kWh) and 50% solar (48 g/kWh). What is the mix intensity?Look back: p.54
Working: Answer: g/kWh
9
Using the mix above (434 g per kWh), how many kg of CO₂ come from 100 kWh?Look back: p.54
Working: Answer: kg
10
By which year has India said it aims for net zero?Look back: p.54
2030205020702100
Stretch it: extension questions
11
A grid is 60% solar (48 g/kWh), 30% hydro (24 g/kWh) and 10% gas (490 g/kWh). Find its mix intensity. Compare it with coal at 820 g/kWh by working out the percentage fall.Look back: p.54
12
Plan a day for a clean grid. Say which source (solar, wind, hydro or storage) mainly supplies noon, evening and night, and why.Look back: p.52Look back: p.52
Gridovators Clean Energy WorkbookChapter 11: The clean mix · page 55
12
Part D · The modern world · Chapter 12
Using less, wasting less
The cleanest unit of electricity is the one we never need to make.
LEARN IT
By the end of this chapter you can
Explain what efficiency means for lamps and appliances
Calculate the energy and money saved by a better appliance
Find which appliances use the most energy in a home
Work out a home's CO₂ and name habits that cut energy use
12.1The cheapest energy is the energy you never use
Efficiency (Chapter 1) means getting the same job done with less energy. An LED bulb gives the same light as an old bulb using about one-sixth of the power. In India, the BEE star label on fridges and ACs tells you how efficient they are: more stars, less electricity.
Less power for the same light.
Equation cardMoney and energy saved
Saving = (Old power − New power) × Hours × Price
kWh saved = (Pold − Pnew) ÷ 1,000 × hours
Poldpower of the old appliancewatts (W)Pnewpower of the new appliancewatts (W)
The idea: Energy = power × time (Chapter 2). Power saved × time is energy saved. Times the price gives rupees.
Worked example:Replace a 60 W bulb with a 9 W LED used 5 hours a day. Tariff ₹7 per unit.Saved per day = 51 × 5 = 255 Wh = 0.255 kWh. Per month: 0.255 × 30 = 7.65 kWh, so 7.65 × 7 = ₹53.55.
12.2Where does a home's energy go?
Use E = P × t for each appliance (kWh per day, example home):
Air conditioner (1.5 kW × 3 h)4.5 kWh
Fans (3 × 75 W × 8 h)1.8 kWh
Fridge (150 W × 8 h)1.2 kWh
TV (100 W × 4 h)0.4 kWh
LED lights (4 × 9 W × 5 h)0.18 kWh
The AC is over half of the day's 8.1 kWh, though it runs for only 3 hours. Big power times many hours drives the bill.
Gridovators Clean Energy WorkbookChapter 12: Using less, wasting less · page 56
12
Part D · The modern world
Using less, wasting less
LEARN IT
12.3Your electricity footprint
A carbon footprint counts the CO₂ caused by what you do. For electricity we use Chapter 5's equation: CO₂ = kWh × intensity. India's grid average is about 700 g of CO₂ per kWh because coal still makes most of our power. Rooftop solar is about 48 g.
Equation cardFootprint of a home
CO₂ = kWh used × grid intensity
kg CO₂ = kWh × 0.7 (India average, kg per kWh)
kWhelectricity usedkWh0.7kg of CO₂ per kWh, India averagekg per kWh
The idea: A bill in kWh can be turned into kilograms of CO₂ by multiplying. Cleaner power means a smaller number.
Worked example:The example home uses 8.1 kWh a day, so about 243 kWh a month.CO₂ = 243 × 0.7 = 170 kg a month.On rooftop solar (0.048 kg per kWh): 243 × 0.048 = 11.7 kg.
Yearly CO₂ from energy, per person (approximate).
India's average person causes less than half of the world average. Rich countries cause far more, which is part of why fairness matters in climate talks (Chapter 14).
12.4Habits that matter
Set the AC to 24 to 26 °C. Each degree higher saves about 6% of its energy.
Use a fan first. A 75 W fan uses a twentieth of what a 1.5 kW AC uses.
Switch off at the wall. Chargers and TVs on standby still sip power.
Choose star-rated appliances and LED lights.
Keep heat out: shade, white roofs and curtains cut cooling needs.
Try it safely (optional): a 10-minute home energy audit
List five appliances at home. Read the watt rating on the label.
Estimate hours used per day, and multiply to get Wh.
Rank them. Which uses most? Which could you use less?
Do not open appliances. Read labels only, and ask an adult before moving anything.
Remember this chapter in a nutshell
Efficiency: same job, less energy. LEDs and star-rated appliances are great examples.
Energy saved = power difference × hours. Big power times many hours is what costs most.
CO₂ from electricity = kWh × grid intensity. India's grid average is about 0.7 kg per kWh.
Small habits add up: set the AC higher, use fans, switch off standby.
Gridovators Clean Energy WorkbookChapter 12: Using less, wasting less · page 57
12
Part D · The modern world
Using less, wasting less: check it
CHECK IT
Try every question before you peek. The small Look back tags show which page taught the idea. Answers start on page 76.
1
Why is the cheapest energy often the energy you do not use?Look back: p.56
It costs nothing to make and nothing to buyIt is always renewableIt makes appliances last foreverIt lowers voltage
2
An old bulb uses 60 W and an LED giving the same light uses 9 W. How much power is saved?Look back: p.56
Working: Answer: W
3
The 51 W saving is used for 5 hours a day. How much energy is saved per day in kWh?Look back: p.56
Working: Answer: kWh
4
Over 30 days at ₹7 per unit, how much money does the bulb swap save? (Use 0.255 kWh per day.)Look back: p.56
Working: Answer: ₹
5
A fan of 75 W runs for 8 hours. How much energy does it use in kWh?Look back: p.56
Working: Answer: kWh
6
An air conditioner of 1.5 kW runs for 3 hours. How much energy, and what does it cost at ₹7 per unit?Look back: p.56
Working: Answer: ₹
7
A home uses 200 kWh in a month. India's grid average is 0.7 kg of CO₂ per kWh. How much CO₂ is that?Look back: p.57
Working: Answer: kg
8
Which statement about CO₂ per person is correct?Look back: p.57
India's average person causes more than the USA'sIndia's average person causes less than half of the world averageAll countries cause the same amountThe world average is below India's
9
True or false? Setting the air conditioner to 24 to 26 °C instead of 18 °C saves electricity.Look back: p.57
TrueFalse
10
Name two habits that reduce a home's electricity use.Look back: p.57
Stretch it: extension questions
11
A home uses 243 kWh a month. Find the CO₂ in kg at the India average (0.7 kg per kWh) and on rooftop solar (0.048 kg per kWh). How much CO₂ does solar save?Look back: p.57
12
Compare a 1.5 kW air conditioner and a 75 W fan, each run for 3 hours. How much energy does each use, and how much money is saved at ₹7 per unit by using the fan?Look back: p.56Look back: p.57
Gridovators Clean Energy WorkbookChapter 12: Using less, wasting less · page 58
13
Part D · The modern world · Chapter 13
Transport, buildings and industry
Cars, trains, houses and factories all need energy. Let's see how they can go clean.
LEARN IT
By the end of this chapter you can
Explain why electric vehicles use less energy than petrol vehicles
Work out the cost and CO₂ per kilometre of a vehicle
Describe how trains, buses and e-rickshaws fit in
List ways to keep a building cool with less electricity
Say why steel and cement are hard to make clean
13.1Why electric vehicles use less energy
A petrol engine burns fuel to make heat, then turns a small part of that heat into movement. It wastes about three-quarters as heat. An electric motor (Chapter 4) turns about 85% of its electricity into movement. This is the efficiency idea from Chapter 1 again.
Petrol engine (fuel to wheels)25%
Electric motor (battery to wheels)85%
Share of energy that reaches the wheels (approximate)
So an electric vehicle (EV) needs far less energy for each kilometre. An EV also makes no smoke at the road, which helps city air. Where the electricity comes from decides how clean it is overall.
13.2EV maths: cost and CO₂ per kilometre
Equation cardCost and CO₂ per km
Per km = Energy per km × Price (or Intensity)
cost per km = kWh per km × ₹ per kWh CO₂ per km = kWh per km × kg per kWh
kWh/kmenergy a vehicle uses each kilometrekWh per kmpricecost of one kWh₹ per kWhintensityCO₂ per kWh (Chapter 5)kg per kWh
The idea: A trip is just energy used. Multiply that energy by what it costs, or by the CO₂ each unit causes. The same recipe works for any vehicle.
Worked example:EV: 0.15 kWh per km. Tariff ₹7. Cost = 0.15 × 7 = ₹1.05 per km. On the India grid (0.7 kg per kWh), CO₂ = 0.15 × 0.7 = 0.105 kg per km.Petrol car: 15 km per litre. 1 litre of petrol holds about 9.4 kWh, so energy = 9.4 ÷ 15 = 0.63 kWh per km. At ₹100 per litre the cost is 100 ÷ 15 = ₹6.67 per km. Each litre makes about 2.3 kg of CO₂, so 2.3 ÷ 15 = 0.153 kg per km.
The EV uses about 4 times less energy and costs far less to run. On today's grid its CO₂ is about a third lower. As the grid gets cleaner, the EV gets cleaner too, without changing the car.
Gridovators Clean Energy WorkbookChapter 13: Transport, buildings and industry · page 59
13
Part D · The modern world
Transport, buildings and industry
LEARN IT
13.3Trains, buses and e-rickshaws
A train carries hundreds of people on one pair of rails, so energy per person is low. Almost the whole Indian Railways broad-gauge network is now electrified, and the railway aims to reach net zero by 2030. Electric buses, metros and e-rickshaws clean up city streets.
A big question is charging. Plug in at noon and an EV can use cheap solar power. Plug in at 8 pm and it adds to the evening peak (Chapter 9). Some systems swap a flat battery for a full one in minutes. Parked EVs could also feed power back to the grid.
The cleaner the grid, the cleaner the EV.
Workshop linkThe Cassetex workshop is about swapping batteries, which keeps an e-rickshaw earning while its flat battery charges elsewhere.
13.4Buildings: keep the heat out first
India is getting hotter and more people can afford air conditioning, so cooling demand is expected to grow many times over. The cheapest cooling is the heat you stop from getting in. Smart building design uses little or no electricity.
Design the building first, then add a fan or an efficient AC.
Gridovators Clean Energy WorkbookChapter 13: Transport, buildings and industry · page 60
13
Part D · The modern world
Transport, buildings and industry
LEARN IT
13.5Industry: the hard part
Factories use a large share of the world's energy. Making steel, cement and fertiliser needs very high temperatures, and some processes release CO₂ from the materials themselves. These are the hardest sectors to clean.
Save first: better furnaces and waste-heat recovery.
Electrify: electric furnaces and heat pumps for lower temperatures.
New fuels: green hydrogen, made by splitting water with clean electricity.
Solar heat for hot water and steam in food and textile factories.
13.6The big picture
Electrify, then clean the grid
The pattern is the same everywhere: save energy, switch to electricity where we can (vehicles, trains, cooking, some heat), and make the electricity clean with solar, wind and hydro. That is why Chapters 6 to 11 matter for every part of life.
Remember this chapter in a nutshell
Electric motors waste far less energy than petrol engines. An EV uses about 4 times less energy per km.
Cost per km and CO₂ per km = energy per km × price, or × intensity.
Trains, buses and e-rickshaws cut city pollution. Charge EVs when power is cheap and clean.
Keep buildings cool with design. Steel and cement are the hardest to clean, and need new methods.
Gridovators Clean Energy WorkbookChapter 13: Transport, buildings and industry · page 61
13
Part D · The modern world
Transport, buildings and industry: check it
CHECK IT
Try every question before you peek. The small Look back tags show which page taught the idea. Answers start on page 77.
1
Why does an electric vehicle use less energy per kilometre than a petrol car?Look back: p.59
Its motor wastes far less energy as heatIt is always lighterElectricity has more energy than petrolIt has no wheels
2
True or false? A petrol engine turns most of the fuel energy into movement.Look back: p.59
TrueFalse
3
1 litre of petrol holds 9.4 kWh. A car travels 15 km on one litre. How much energy does it use per km?Look back: p.59
Working: Answer: kWh/km
4
An EV uses 0.15 kWh per km. The tariff is ₹7 per kWh. What does 1 km cost?Look back: p.59
Working: Answer: ₹
5
Petrol costs ₹100 per litre and the car does 15 km per litre. What does a 30 km trip cost?Look back: p.59
Working: Answer: ₹
6
An EV uses 0.15 kWh per km on a grid of 0.7 kg CO₂ per kWh. How many kg of CO₂ per km?Look back: p.59
Working: Answer: kg
7
The same EV (0.15 kWh per km) is charged from rooftop solar at 48 g of CO₂ per kWh. How many grams per km?Look back: p.59
Working: Answer: g
8
Which of these helps keep a building cool without using electricity?Look back: p.60
A white (reflective) roofA second air conditionerA dark roofClosing all shade
For 100 km, compare a petrol car (15 km per litre, ₹100 per litre, 2.3 kg CO₂ per litre) with an EV (0.15 kWh per km, ₹7 per kWh, 0.7 kg CO₂ per kWh). Find the cost and the CO₂ for each, and the savings.Look back: p.59
12
Give two reasons why making steel is harder to clean than charging an EV.Look back: p.61
Gridovators Clean Energy WorkbookChapter 13: Transport, buildings and industry · page 62
14
Part D · The modern world · Chapter 14
Energy for everyone
Clean energy only matters if it reaches everyone. Let's finish with fairness and your future.
LEARN IT
By the end of this chapter you can
Say what energy access means and why it matters
Explain energy fairness in your own words
Size a solar system for a village
Name some clean energy careers
Write down your own next steps
14.1Energy access
Energy is not only about machines. It decides whether a child can study after dark, whether a clinic can keep vaccines cold, and whether a farmer can pump water. Yet about 700 million people in the world still have no electricity, and more than 2 billion cook on smoky fuels such as wood and dung. The smoke harms lungs, especially for women and children.
India has made big steps. The Saubhagya scheme (2017 to 2019) connected about 28 million homes to electricity. PM Ujjwala (from 2016) has given LPG gas stoves to about 100 million households. The next challenge is not only having a connection, but having power that is reliable and clean.
14.2Fairness: who uses, who pollutes
The average person in India uses far less electricity than the average person in rich countries. People rightly want more energy so that they can have fridges, fans, light and jobs. Climate change was mostly caused by rich countries burning fossil fuels in the past (Chapter 12), but its effects fall on everyone.
Energy fairness means that everyone gets enough affordable energy, and that the move to clean energy is paid for and shared in a fair way.
Electricity use per person per year (approximate)
India1,400 kWh
World average3,500 kWh
USA12,000 kWh
Gridovators Clean Energy WorkbookChapter 14: Energy for everyone · page 63
14
Part D · The modern world
Energy for everyone
LEARN IT
14.3India and the International Solar Alliance
India has more than 300 sunny days in most regions. In 2015, India and France launched the International Solar Alliance (ISA) in Paris. It now has more than 100 member countries, mostly in the sunny belt around the equator. The aim is to share know-how and lower the cost of solar so that every country can afford it.
14.4Village maths: how big a solar plant?
From Chapter 6, a 1 kW solar system makes about 4 kWh a day (5 sun hours × 0.8). Over a year that is 4 × 365 = 1,460 kWh. So to find the size we divide the yearly energy by 1,460.
Sizing a village system.
Equation cardSolar size for a village
Size (kW) = Yearly energy ÷ 1,460
size = (homes × kWh per home per year) ÷ 1,460
sizerated solar power neededkilowatts (kW)yearly energytotal electricity used in a yearkWh1,460kWh made per kW per yearkWh per kW
The idea: Each kW of panels is like a worker who delivers 1,460 kWh a year. Divide the job by what one worker does and you get the number of workers you need.
Worked example:A village has 200 homes, each using 500 kWh a year.Yearly energy = 200 × 500 = 100,000 kWh.Size = 100,000 ÷ 1,460 = 68.5 kW. With 500 W panels: 68,500 ÷ 500 = 137 panels.
Gridovators Clean Energy WorkbookChapter 14: Energy for everyone · page 64
14
Part D · The modern world
Energy for everyone
LEARN IT
14.5Careers in clean energy
Clean energy is a fast-growing field, with more than 16 million jobs worldwide in renewable energy. You do not have to be an engineer. The work spans many skills:
Technicians, engineers, scientists and analysts all help.
Subjects that help: maths, science, computing and design. Skills that help just as much: curiosity, patience, teamwork and clear communication. If you enjoy explaining things, you could become a teacher or a policy writer.
14.6What you can do now
Learn it: you have just done 14 chapters. Teach one idea to someone at home.
Measure it: do the home energy audit (Chapter 12) and share the results.
Save it: use fans first, switch off standby, ask for LED lights.
Ask questions: where does our school's electricity come from? Could it use solar?
Remember this chapter in a nutshell
Energy access means reliable, clean power for everyone. About 700 million people still lack electricity.
Fairness means enough affordable energy for all, and sharing the effort of the clean energy move.
Village solar size (kW) = yearly kWh ÷ 1,460. Each kW makes about 1,460 kWh a year.
Clean energy offers many careers. Maths, science and curiosity are great starting points.
Gridovators Clean Energy WorkbookChapter 14: Energy for everyone · page 65
14
Part D · The modern world
Energy for everyone: check it
CHECK IT
Try every question before you peek. The small Look back tags show which page taught the idea. Answers start on page 77.
1
About how many people in the world still have no electricity?Look back: p.63
About 7 thousandAbout 7 millionAbout 700 millionAbout 7 billion
2
True or false? The average person in India uses more electricity than the average person in the USA.Look back: p.63
TrueFalse
3
In your own words, what does energy fairness mean?Look back: p.63
4
The International Solar Alliance was launched in 2015 by India and .Look back: p.64
5
A village has 200 homes, each using 500 kWh a year. How much electricity does the village use in a year?Look back: p.64
Working: Answer: kWh
6
Each kW of solar makes 1,460 kWh a year. What size system covers 100,000 kWh a year? (to one decimal place)Look back: p.64
Working: Answer: kW
7
A 70 kW system uses 500 W panels (0.5 kW each). How many panels?Look back: p.64
Working: Answer: panels
8
The USA uses about 12,000 kWh per person a year. India uses about 1,400 kWh. How many times more does the USA use? (one decimal place)Look back: p.63
Working: Answer: times
9
Match each job to what the person does. Write the letters.Look back: p.65
1. Solar technician
2. Grid engineer
3. Battery scientist
A. Keeps supply and demand balanced
B. Designs better storage
C. Fits and repairs panels
1 – 2 – 3 –
10
Name two ways electricity improves life in a village.Look back: p.63
Stretch it: extension questions
11
A village has 300 homes using 600 kWh each per year. Find the yearly energy, the solar size needed (÷ 1,460) and the number of 500 W panels.Look back: p.64
12
Explain why a fair clean energy future needs both more access for people who lack power and cleaner ways of making that power.Look back: p.63Look back: p.63
Gridovators Clean Energy WorkbookChapter 14: Energy for everyone · page 66
★
Final project
Design your clean energy plan
DO IT
You are the energy planner for a small village. Use the equations from the book to design a clean plan. This is not graded, so work in pencil and compare with Barry's check on the next page.
Your village: Surya Nagar
200 homes, each using 500 kWh a year. Street lights and a water pump add 20,000 kWh a year.
Sun: 5 peak sun hours a day. A 1 kW system makes about 1,460 kWh a year.
Stream: flow 0.2 m³/s, head 15 m. It runs low in the dry season.
Wind: average 5 m/s. A rotor of radius 10 m would be the biggest that fits.
Evening: 40% of the day's electricity is used between 6 pm and 11 pm.
Today: power from the grid is mostly coal, about 0.7 kg of CO₂ per kWh.
1
Demand. How much electricity does the village use in a year? How much per day (divide by 365)? Ch 2
Working: Answer: kWh a year
2
Solar. What size solar system covers the whole yearly demand? (size = yearly energy ÷ 1,460) Ch 6, Ch 14
Working: Answer: kW
3
Hydro. Find the power of the stream with P = 1,000 × 10 × Q × H × 0.9. Then find the yearly energy if its capacity factor is 50%. Ch 8
Working: Answer: kW
Working: Answer: kWh a year
4
Wind. Rotor radius 10 m (A = 3.14 × r²), wind 5 m/s. Find the power in the wind, P = ½ × 1.2 × A × v³, and what a turbine at 40% can catch. Ch 7
Working: Answer: W in the wind
Working: Answer: W caught
5
Storage. How many kWh are used in the evening each day? A battery has 90% round-trip efficiency. How many kWh must it hold to give that back? Ch 9
Working: Answer: kWh evening
Working: Answer: kWh battery
Gridovators Clean Energy WorkbookFinal project · page 67
★
Final project
Design your clean energy plan
DO IT
★Make your plan
6
Choose your mix. Fill in your plan. The sizes must add up to enough energy for 120,000 kWh a year.
Source
Size (kW)
Yearly energy (kWh)
Share of demand (%)
Hydro
Solar
Wind (if any)
Battery
holds ___ kWh
7
Draw your plan. Sketch the village, your sources, the battery and the wires. Label each part. Ch 11
8
CO₂. With coal-based grid power at 0.7 kg per kWh, 120,000 kWh makes how many kg of CO₂? If your mix averages 30 g per kWh, how much? How much do you save? Ch 5, Ch 11
Working: Answer: kg coal
Working: Answer: kg your mix
Working: Answer: kg saved
9
Dry season and fairness. What happens when the stream runs low? Who in the village might struggle to pay, and how could the plan help them? Ch 8, Ch 14
Barry's check (do your own maths first!)
Demand: 100,000 + 20,000 = 120,000 kWh a year, about 329 kWh a day.
Solar to cover all: 120,000 ÷ 1,460 = about 82 kW.
Hydro power: 1,000 × 10 × 0.2 × 15 × 0.9 = 27,000 W = 27 kW. Yearly: 27 × 8,760 × 0.5 = about 118,000 kWh, nearly all the demand, but the stream runs low in the dry season.
Wind: A = 314 m². P = ½ × 1.2 × 314 × 125 = about 23,550 W. At 40%: about 9,400 W, so a weak site.
Evening: 0.4 × 329 = about 132 kWh. Battery size = 132 ÷ 0.9 = about 146 kWh.
Check your plan: does supply meet demand every hour, and is there a way to cope with a bad week of weather? That is exactly what real energy planners do.
Gridovators Clean Energy WorkbookFinal project · page 68
G
Back of the book
Glossary (1 of 2)
AC (alternating current) Electric current that keeps changing direction. Mains power is AC, 50 times a second in India. (Ch 4)
Ampere (amp, A) The unit of electric current. (Ch 3)
Array Several solar panels joined together. (Ch 6)
Atom A tiny particle with a nucleus of protons and neutrons and electrons around it. (Ch 3)
Battery A device that stores energy as chemical energy and releases it as electricity. (Ch 9)
Betz limit The most a wind turbine can ever catch: about 59% of the wind's energy. (Ch 7)
Capacity factor The share of the year a plant effectively runs at full power, for example 25%. (Ch 2)
Carbon footprint The CO₂ caused by what a person or place does. (Ch 12)
Carbon intensity Grams of CO₂ released for each kWh of electricity. (Ch 5)
Circuit A complete loop that current can flow round. (Ch 3)
Conductor A material that lets current flow easily, such as copper. (Ch 3)
Current The flow of electric charge, measured in amps. (Ch 3)
DC (direct current) Electric current that flows in one direction only, as from a battery. (Ch 4)
Dispatchable A source that can be turned on or up when needed, such as dam hydro. (Ch 11)
Efficiency The share of energy put in that ends up doing the job you want. (Ch 1)
Electromagnet A coil of wire that becomes a magnet when current flows through it. (Ch 4)
Electron A tiny negative particle. Electrons moving make an electric current. (Ch 3)
Energy The ability to make things change or move. Measured in joules. (Ch 1)
Fossil fuels Coal, oil and gas, made from ancient plants and sea life. (Ch 5)
Frequency Cycles per second. Indian mains is 50 hertz (Hz). (Ch 4)
Generator A machine that spins a magnet inside coils to make electricity. (Ch 4)
Greenhouse effect Gases such as CO₂ trap heat in the air and keep Earth warm. (Ch 5)
Grid The network of wires and transformers that carries electricity. (Ch 10)
Head The height of the fall of water at a hydro plant. (Ch 8)
Induction Making a voltage with a changing magnetic field. (Ch 4)
Insulator A material that stops current, such as rubber. (Ch 3)
Inverter A box that changes DC from panels into AC. (Ch 6)
Gridovators Clean Energy WorkbookGlossary · page 69
G
Back of the book
Glossary (2 of 2)
Joule (J) The unit of energy. (Ch 2)
Kilowatt-hour (kWh) The energy of 1,000 watts used for one hour. One "unit" on a bill. (Ch 2)
Kinetic energy Energy of movement. KE = ½ × m × v². (Ch 2)
Microgrid A small local grid that can run by itself. (Ch 11)
Nacelle The housing at the top of a wind turbine. (Ch 7)
Net zero Adding no more CO₂ to the air than is taken out. (Ch 5)
Ohm (Ω) The unit of resistance. (Ch 3)
Peak sun hours Hours at full sunlight strength that equal the day's total sunshine. (Ch 6)
Penstock The big pipe that carries water to a turbine. (Ch 8)
Photovoltaic effect Light knocking electrons loose in a solar cell to make electricity. (Ch 6)
Potential energy Stored energy, for example because of height. PE = m × g × h. (Ch 2)
Power How fast energy is used or delivered. Measured in watts. (Ch 2)
ppm Parts per million. Used for CO₂ in the air. (Ch 5)
Pumped hydro Storing energy by pumping water uphill and letting it fall later. (Ch 9)
Renewable A source that nature refills, such as sunlight, wind and rain. (Ch 1)
Resistance How much a part fights the flow of current. (Ch 3)
Round-trip efficiency The energy you get back from storage divided by what you put in. (Ch 9)
Series and parallel Joined in one path, or joined on separate paths. (Ch 3)
Swept area The circle that wind turbine blades sweep through. A = π × r². (Ch 7)
Transformer Two coils on an iron core that change AC voltage. (Ch 10)
Transmission Carrying electricity long distances at high voltage. (Ch 10)
Turbine A wheel with blades that spins when steam, wind or water pushes it. (Ch 4)
Variable A source whose output changes with weather, such as solar and wind. (Ch 11)
Volt (V) The unit of voltage, the push on the charge. (Ch 3)
Watt (W) The unit of power. One joule each second. (Ch 2)
Yaw The turning of a wind turbine to face the wind. (Ch 7)
Gridovators Clean Energy WorkbookGlossary · page 70
A
Back of the book
Answers
1Chapter 1: What is energy?
1
change.This is the working definition: where something changes, energy is involved.
2
False.A still ball is not moving, so it has no kinetic energy. It has potential (stored) energy because of its height.
3
Potential.Stretching stores energy ready to be released, like a ball held high.
4
1 – B, 2 – A, 3 – D, 4 – C.Batteries store chemical energy, a moving rickshaw has kinetic energy, hot tea has thermal energy, and a bulb gives out light.
5
1: Sunlight reaches the plant. 2: The plant grows. 3: You eat the plant. 4: You hit the ball.Light becomes chemical energy in the plant, then in you, then kinetic energy in the ball.
6
Energy cannot be created or destroyed, only changed from one form to another or moved.A good answer might add an example, such as a swing turning stored energy into movement and a little heat.
7
It became spread-out heat and sound.Energy is never destroyed. Each bounce turns a little into heat and sound, until it is all spread out.
8
75%.150 ÷ 200 = 0.75, and 0.75 × 100 = 75%. The other 50 J is wasted as heat.
9
40%.Efficiencies multiply along a chain: 0.80 × 0.50 = 0.40, which is 40%. The chain is weaker than either machine alone.
10
True.The Sun heats the air, which moves as wind, and it drives the water cycle that fills rivers.
11
Marking guide.A good answer says: solar panels use sunlight directly; wind comes from the Sun heating air unevenly; coal is made from ancient plants that stored sunlight as chemical energy.
12
Marking guide. Efficiency = 40%.Chain: chemical (battery), electrical, then light, with heat wasted at the bulb and in the wires. 4 ÷ 10 × 100 = 40%. The other 6 J is heat.
2Chapter 2: Power, energy and units
1
1 joule per second.A watt is a rate: energy divided by time. 1 W = 1 J every second.
2
False.Energy is the amount (joules, kWh). Power is how fast it is used or delivered (watts).
3
3,000 J.E = P × t = 100 × 30 = 3,000 J.
4
100 J.PE = m × g × h = 5 × 10 × 2 = 100 J.
5
4 J.v² = 16. KE = ½ × 0.5 × 16 = 4 J.
6
4 times bigger.Speed is squared in KE = ½mv². Doubling the speed gives 2 × 2 = 4.
7
3.2 kW and 600 kW.Going up from W to kW divides by 1,000. Going down from MW to kW multiplies by 1,000.
8
0.6 kWh.60 W = 0.06 kW. Energy = 0.06 × 10 = 0.6 kWh.
9
₹48.Energy = 1.5 × 4 = 6 kWh. Cost = 6 × 8 = ₹48.
10
20%.Possible energy = 5 × 8,760 = 43,800 MWh. 8,760 ÷ 43,800 = 0.20, so 20%.
Marking guide. Capacity factor = 30%.Capacity is the most power it can give. The wind is sometimes too weak, so on average it gives less. 0.6 ÷ 2 = 0.30, which is 30%.
Gridovators Clean Energy WorkbookAnswers · page 71
A
Back of the book
Answers
3Chapter 3: Electricity
1
Electrons.Protons are stuck in the nucleus. Electrons are light and free to move.
Rubber.Rubber holds its electrons tightly, so almost no current flows. The other three conduct.
4
Copper is a conductor that carries the current. Plastic is an insulator that stops the current leaking out and keeps you safe.Both parts are needed: one to carry, one to protect.
5
A complete loop.Open the switch and the loop is broken, so the flow stops everywhere.
6
It stays on.Each bulb has its own path, so the other path is still a complete loop.
7
1 – B, 2 – C, 3 – A.Voltage is the push, current is the flow, resistance is the squeeze. Water pump, flow rate, narrow pipe.
8
3 A.I = V ÷ R = 12 ÷ 4 = 3 A.
9
6 Ω.R = V ÷ I = 3 ÷ 0.5 = 6 Ω.
10
1,150 W.P = V × I = 230 × 5 = 1,150 W, which is 1.15 kW.
11
10 A.I = P ÷ V = 2,300 ÷ 230 = 10 A. A thick wire is like a wide pipe: low resistance, so a large current flows without the wire getting dangerously hot.
12
Marking guide.A correct drawing has two parallel branches, one bulb and one switch on each branch, joined to one battery. It is a parallel circuit.
4Chapter 4: Magnets, generators and turbines
1
They repel.Like poles repel. Opposite poles attract.
2
current (electricity).Current makes a magnetic field. Switch the current off and the magnet turns off.
3
True.More turns, or more current, make a stronger electromagnet.
4
A magnet and a coil of wire that move relative to each other.A changing magnetic field pushes the charges in the wire. If nothing moves, there is no voltage.
5
Any two of: spin the magnet faster, use a stronger magnet, use more turns of wire.Voltage grows with speed, magnet strength and turns of wire.
6
300 V.50 × 3 × 2 = 300 V. Each change multiplies the voltage.
7
Alternating current: it keeps changing direction.The magnet's poles swap sides every half turn, so the push flips direction.
8
0.02 s.1 ÷ 50 = 0.02 seconds.
9
3, 1, 2, 4 (in the order the items are listed).Blades turn the shaft, the shaft turns the generator, the generator feeds the grid.
10
Solar panels.Light knocks electrons loose inside the panel, so nothing spins.
11
380 MJ electricity, 620 MJ lost as heat. Wind pushes the blades directly, so there is no heat-to-steam step.38% of 1,000 = 380 MJ. The rest, 620 MJ, is waste heat. Wind skips the boiler stage.
12
Generator: movement in, electricity out. Motor: electricity in, movement out.Spinning a magnet in a coil gives voltage. Sending current through the coil makes it an electromagnet that gets pushed round.
Gridovators Clean Energy WorkbookAnswers · page 72
A
Back of the book
Answers
5Chapter 5: Fossil fuels and climate
1
Ancient plants and sea creatures.Their remains were buried and slowly changed by heat and pressure over millions of years.
2
False.Coal takes millions of years to form, far slower than we use it, so it is not renewable.
3
Carbon dioxide.Carbon joins with oxygen from the air to make CO₂.
4
22 kg.6 × 44 ÷ 12 = 22 kg. Carbon picks up oxygen, so the CO₂ is heavier.
5
heat.Sunlight warms the ground and greenhouse gases hold some of that heat in.
6
Without it Earth would average about −18 °C. With it the average is about 15 °C, warm enough for life.The problem is the extra CO₂ we add, which makes the blanket too thick.
7
420 ppm.It has risen about 50%, mostly from burning fossil fuels.
8
49 kg.100 × 490 = 49,000 g, and 49,000 g ÷ 1,000 = 49 kg.
9
4, 1, 3, 2 (in the order the items are listed). That is coal, gas, solar panels, wind.Coal 820, gas 490, solar 48, wind 11 grams of CO₂ per kWh.
10
Smoke and tiny particles that damage lungs.Air pollution worsens asthma and heart disease.
11
Coal 246 kg, solar 14.4 kg, saved 231.6 kg.Coal: 300 × 820 = 246,000 g = 246 kg. Solar: 300 × 48 = 14,400 g = 14.4 kg. Saving = 246 − 14.4 = 231.6 kg.
12
Marking guide.A good answer says: plants caught sunlight and stored carbon, they were buried and became coal, burning releases the carbon as CO₂, and extra CO₂ traps more heat.
6Chapter 6: Solar power
1
About 8 minutes (8 min 20 s).The Sun is 150 million km away and light is very fast, but that distance still takes about 8 minutes.
2
1,000.This is the standard strength used to rate solar panels.
3
Turns light directly into electricity.This is the photovoltaic effect. Nothing spins and nothing burns.
4
False.Panels make DC. An inverter changes it into AC.
5
30 V.In series, voltages add: 60 × 0.5 = 30 V.
6
500 W.P = 2.5 × 1,000 × 0.20 = 500 W.
7
Cleaning the glass.Cleaning removes dust, so output goes up. Dust, shade and cloud all cut the light reaching the cells.
8
8 kWh.E = 2 × 5 × 0.8 = 8 kWh.
9
1.5 kW.6 ÷ 4 = 1.5 kW.
10
Good: free fuel, no smoke, cheap now, works on rooftops. Hard: only works in daylight so needs storage, drops in monsoon, needs land.Any one good and one hard point from the chapter earns the mark.
Marking guide.A good answer says: the Sun is only at full strength for a few hours a day. There is no sunlight at night, and clouds, shade and dust cut output further.
Gridovators Clean Energy WorkbookAnswers · page 73
A
Back of the book
Answers
7Chapter 7: Wind power
1
Uneven heating of land and sea by the Sun.Warm air rises and cooler air moves in to replace it.
2
True.Land is hotter, its air rises, and cooler sea air flows in to take its place.
1 – B, 2 – C, 3 – A.Gearbox speeds up the shaft, the generator makes electricity, the yaw system points the turbine into the wind.
8
No turbine can capture more than about 59% of the wind's energy.If a turbine took all the energy the air would stop behind it and block new wind.
9
7,884 MWh.3 × 8,760 × 0.30 = 7,884 MWh.
10
Wind is strongest in the monsoon months when solar is weaker, and wind often blows at night when solar makes nothing.Their weak times and strong times are different, so together they smooth each other out.
11
About 1.2 MW.Wind power is about 3,014,400 W. 40% of that is 0.4 × 3,014,400 = 1,205,760 W, about 1.2 MW.
12
8 times more. Windier sites give far more energy from the same turbine, so they are worth a lot more.Power depends on speed cubed: 2 × 2 × 2 = 8.
8Chapter 8: Hydropower
1
The Sun, which drives the water cycle.The Sun evaporates water, rain falls on hills, and rivers carry it down.
2
3, 1, 4, 2 (in the order the items are listed).Evaporation, clouds, rain, then rivers.
3
500,000 J.1,000 × 10 × 50 = 500,000 J.
4
Penstock.The penstock is the strong pipe that takes water to the turbine.
True.P grows in step with H, so doubling H doubles P.
8
1 – B, 2 – C, 3 – A.Pelton suits steep streams, Francis the middle ground, Kaplan wide slow rivers.
9
It can be switched on quickly when needed.The stored water is ready to use, so a plant can start in minutes.
10
Any two of: flood land and move people, change river ecosystems and block fish, give less power in dry years, take years to build.These are the main hard parts of large hydro.
11
21.6 MW and about 75,686 MWh.P = 1,000 × 10 × 40 × 60 × 0.9 = 21,600,000 W = 21.6 MW. E = 21.6 × 8,760 × 0.40 = 75,686.4 MWh.
12
Marking guide.A good answer says: the Sun evaporates water, rain falls on hills and rivers carry it down, so the Sun keeps refilling the reservoir. In a drought there is less rain, so less flow and less electricity.
Gridovators Clean Energy WorkbookAnswers · page 74
A
Back of the book
Answers
9Chapter 9: Storing energy
1
Solar peaks at noon but demand peaks in the evening.Storing noon power lets us use it after the Sun has set.
2
False.A battery only stores energy as chemical energy and releases it later.
3
1.2 kWh.12 × 100 = 1,200 Wh = 1.2 kWh.
4
4 hours.4.8 ÷ 1.2 = 4 hours.
5
80%.8 ÷ 10 × 100 = 80%.
6
18 kWh.90% of 20 = 0.9 × 20 = 18 kWh.
7
As the height (potential energy) of water in the upper lake.Spare electricity pumps water uphill. Letting it fall later gives the energy back.
1 – B, 2 – C, 3 – A.Batteries suit homes and vehicles, pumped hydro suits big grids, hydrogen suits very long storage.
10
Any two of: batteries, pumped hydro, heat stores, hydrogen.These are the four methods in the table.
11
About 6.7 hours. About 11.1 kWh of solar energy.Time = 10 ÷ 1.5 = 6.67 h. Energy in = energy out ÷ efficiency = 10 ÷ 0.9 = 11.1 kWh.
12
Marking guide.A good answer: batteries react fast and fit anywhere (homes, vehicles) with high efficiency. Pumped hydro stores far more energy for many hours and lasts decades, but needs hills and water.
10Chapter 10: The grid
1
4, 1, 3, 2 (in the order the items are listed).Station, step-up, transmission, step-down.
2
For the same power, a higher voltage means a smaller current and less heat lost.From P = V × I, higher V gives lower I, and the loss depends on I².
3
100 A.1,000,000 ÷ 10,000 = 100 A.
4
50,000 W.100 × 100 × 5 = 50,000 W.
5
100 times.Current falls 10 times. Loss depends on current squared, so it falls 10 × 10 = 100 times.
6
It needs a changing magnetic field.A steady DC field does not push a voltage in the second coil.
7
220,000 V.11,000 × 2,000 ÷ 100 = 220,000 V.
8
False.When demand is higher than supply the generators slow down and frequency falls.
9
50.The 50 Hz heartbeat is what operators watch.
10
Electricity is hard to store. If supply and demand differ, frequency drifts, and if it goes too far power stations trip off and the grid can black out.The frequency is the warning sign of an imbalance.
11
20,000 V: I = 100 A, loss 40,000 W (2%). 200,000 V: I = 10 A, loss 400 W (0.02%). Higher voltage is better.I = P ÷ V and loss = I² × R. 100² × 4 = 40,000 W. 10² × 4 = 400 W. A tenth of the current gives a hundredth of the loss.
12
Marking guide.A good answer: surplus power in one region (for example wind in the south or hydro in the north) can help a shortage in another, which makes supply more reliable.
Gridovators Clean Energy WorkbookAnswers · page 75
A
Back of the book
Answers
11Chapter 11: The clean mix
1
Its output changes with the weather.Solar and wind rise and fall with sunshine and wind.
2
True.Stored water makes it dispatchable.
3
All of these.Storage, flexible demand, forecasts and more links all help.
4
microgrid.A microgrid can run alone or join the main grid.
5
Solar only makes power by day. The battery stores some so the lights and fans can run at night.Storage moves daytime solar into the evening and night.
6
58.3%.Clean 35 GW out of 60 GW: 35 ÷ 60 × 100 = 58.3%.
7
25%.30 ÷ 120 × 100 = 25%.
8
434 g per kWh.0.5 × 820 + 0.5 × 48 = 410 + 24 = 434.
9
43.4 kg.100 × 434 = 43,400 g = 43.4 kg.
10
2070.India's stated net zero goal is 2070.
11
85 g/kWh. A fall of about 90%.0.6 × 48 + 0.3 × 24 + 0.1 × 490 = 28.8 + 7.2 + 49 = 85. Fall = (820 − 85) ÷ 820 × 100 = 89.6%, about 90%.
12
Marking guide.A good answer: solar at noon; hydro and stored energy in the evening when the Sun has gone and demand peaks; wind and hydro at night.
12Chapter 12: Using less, wasting less
1
It costs nothing to make and nothing to buy.Saving a unit avoids both its cost and the CO₂ from making it.
India's average person causes less than half of the world average.About 2 tonnes against about 4.7 tonnes for the world.
9
True.Each degree higher saves about 6% of the AC's energy.
10
Any two of: set the AC to 24 to 26 °C, use a fan, switch off standby, buy star-rated appliances, keep heat out with shade or white roofs.These are the habits in the chapter.
11
170.1 kg, 11.7 kg, saving about 158.4 kg.243 × 0.7 = 170.1. 243 × 0.048 = 11.66, about 11.7. 170.1 − 11.7 = 158.4 kg.
Gridovators Clean Energy WorkbookAnswers · page 76
A
Back of the book
Answers
13Chapter 13: Transport, buildings and industry
1
Its motor wastes far less energy as heat.An electric motor is about 85% efficient. A petrol engine is about 25%.
2
False.About three-quarters is wasted as heat.
3
About 0.63 kWh per km.9.4 ÷ 15 = 0.627, about 0.63.
4
₹1.05.0.15 × 7 = ₹1.05.
5
₹200.30 ÷ 15 = 2 litres. 2 × 100 = ₹200.
6
0.105 kg.0.15 × 0.7 = 0.105 kg.
7
7.2 g.0.15 × 48 = 7.2 g.
8
A white (reflective) roof.It reflects sunlight so less heat enters the building. Shade and cross-ventilation also help.
9
1 – C, 2 – A, 3 – B.Trains run on electrified tracks, buildings use passive cooling, and steel needs new methods for high heat.
10
An EV's CO₂ per km equals its energy per km times the grid intensity. As the grid's intensity falls, the CO₂ per km falls, with no change to the car.The recipe CO₂ = energy × intensity shows it.
11
Petrol: ₹667, 15.3 kg. EV: ₹105, 10.5 kg. EV saves about ₹562 and 4.8 kg.Petrol: 100 ÷ 15 = 6.67 L, cost ₹667, CO₂ 6.67 × 2.3 = 15.3 kg. EV: 15 kWh, cost ₹105, CO₂ 15 × 0.7 = 10.5 kg. Savings ₹562 and 4.8 kg.
12
Marking guide.A good answer: steel needs very high temperatures that electricity cannot easily supply, and some processes release CO₂ from the materials themselves.
14Chapter 14: Energy for everyone
1
About 700 million.Hundreds of millions still lack electricity, and over 2 billion lack clean cooking.
2
False.India uses about 1,400 kWh per person per year. The USA uses about 12,000.
3
Everyone gets enough affordable energy, and the change to clean energy is shared in a fair way.Fairness covers access for everyone and a fair share of the effort.
4
France.It was launched at the Paris climate talks.
5
100,000 kWh.200 × 500 = 100,000 kWh.
6
68.5 kW.100,000 ÷ 1,460 = 68.49, about 68.5 kW.
7
140 panels.70 ÷ 0.5 = 140.
8
About 8.6 times.12,000 ÷ 1,400 = 8.57, about 8.6.
9
1 – C, 2 – A, 3 – B.Technicians fit and repair, grid engineers balance, battery scientists improve storage.
10
Any two of: light for study after dark, vaccines kept cold at a clinic, pumps for water, fans, cleaner cooking, jobs.These are examples from the chapter.
11
180,000 kWh, about 123.3 kW, about 247 panels.300 × 600 = 180,000 kWh. 180,000 ÷ 1,460 = 123.3 kW. 123.3 ÷ 0.5 = 246.6, so 247 panels.
12
Marking guide.A good answer: people need energy to live well and to grow, so access matters. If that energy came from coal it would add CO₂ and harm the climate, so it needs to be clean.
Gridovators Clean Energy WorkbookAnswers · page 77
Keep asking why
Clean energy is built by people who understand it. Now you do.
Gridovators
Well done, you finished the whole workbook! Come to a workshop and try these ideas with your hands. I will be there.