S4.9.7 Chapter 7

Energy resources

Which resource gives electricity at any hour, and gives out no carbon dioxide while it runs?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

A Coal
You picked A. Read on. At the end, the chapter comes back to your guess.
B Solar power
You picked B. Read on. At the end, the chapter comes back to your guess.
C Wind power
You picked C. Read on. At the end, the chapter comes back to your guess.
D Nuclear power
You picked D. Read on. At the end, the chapter comes back to your guess.

By the end you can

Compare fossil, nuclear, solar, wind, hydro and biofuel resources
Judge which resources suit a sunny, windy or hilly place

Every home, factory and train needs energy from somewhere. An energy resource is a source we can get energy from. Some resources will run out. Others will not. Each has good points and bad points.

A renewable resource is one that is used up no faster than it is replaced, or that never runs out. A non-renewable resource is one that will run out, because it is used far faster than it forms.

Fossil fuels are coal, oil and natural gas. They formed from dead plants and animals over millions of years. They are non-renewable. Burning them gives out carbon dioxide, which adds to the warming of the Earth.

Nuclear fuel is uranium, which is mined. There is a limited amount, so it is non-renewable. A reactor gives out no carbon dioxide while it runs. It makes radioactive waste, which must be stored safely for a very long time.

A fossil fuel power station. A generator then turns the turbine's movement into electricity. A nuclear station is the same, but its heat comes from the uranium.

The other four resources are renewable. Solar panels turn sunlight into electricity. They give out no carbon dioxide and use no fuel. They work only in daylight, and less well under cloud.

A sunny place with clear skies is a good place for solar panels.

Wind turbines use moving air to turn a generator. They also use no fuel and give out no carbon dioxide while they run. They work only when the wind blows. In a very strong wind they are switched off to protect them.

A place with steady wind is a good place for a wind turbine.

Hydroelectric power uses falling water. A dam holds water in a lake high up, called a reservoir. The water runs down a pipe and turns a turbine. It gives out no carbon dioxide while it runs. The stored water can be used at any time.

A hilly place with plenty of rain is a good place for hydroelectric power.

Water high up holds energy in its gravitational potential store. Chapter 1 gave the sum for it.

Worked example

A dam lets 1 000 kg of water fall 50 m every second. How much gravitational potential energy does the water lose each second, and what power is that? Use g = 9.8 N/kg.

Ep = m × g × h.
Ep = 1 000 × 9.8 × 50 = 490 000 J.
This happens each second, so the power is 490 000 J ÷ 1 s = 490 000 W = 490 kW.

Answer: 490 kW

A real station gets a little less than this, because the pipe, the turbine and the generator waste some energy. The sum gives the most that is possible.

A biofuel is a fuel made from plants or from animal waste, such as wood, plant oil or biogas. It is renewable, because new plants can be grown. Burning it gives out carbon dioxide.

The plants took in carbon dioxide as they grew. So the carbon dioxide from burning can roughly balance over time. But growing, drying and moving the fuel use energy too. And land used for fuel crops cannot grow food.

Now put the six side by side. Always say what a table cannot: each one has good points and bad points, and the best choice depends on the place.

CO₂ means carbon dioxide given out while running. Fossil means fossil fuels. Biofuel gives out CO₂ when burnt, but growing plants took it in.

Carbon dioxide is not the only harm. Burning coal, oil and wood also makes smoke that harms the lungs. A nuclear station costs a great deal to build and to take apart. An accident is rare, but it can close land for many years.

Wind turbines are noisy close up and can harm birds. Today, batteries and pumped water storage can keep solar and wind energy for the night or a calm day, at extra cost.

Other harms besides carbon dioxide and waste. Every resource has some.

Solar and wind depend on the weather. Hydro works while the lake holds water. Fossil fuel and biofuel stations can be started when needed. A nuclear station runs day and night but is slow to start or stop.

Solar panels give electrical power. The energy from a panel is E = P × t, with the time in seconds, as in Chapter 4.

Worked example

A solar panel delivers 200 W in full sunshine. How much energy does it deliver in 5 minutes?

E = P × t.
5 minutes = 5 × 60 = 300 s.
E = 200 × 300 = 60 000 J = 60 kJ.

Answer: 60 kJ

To judge a place, ask three questions. Is it sunny for most of the year? Is the wind steady? Are there hills, rivers and rain? The answers point to solar, wind or hydroelectric power.

A wrong idea many people have

Renewable energy has no bad points.

Why it feels right: Sunshine, wind and rain cost nothing, and none of these runs out.

The test that breaks it: Think of each one. Solar panels give no power at night. Wind turbines stand still in a calm. A hydroelectric dam floods a valley and changes the life of the river.

What is true: Renewable resources do not run out, but each has costs. They may depend on the weather, take up land or harm wildlife. Choose by looking at the place and the need.

A wrong idea many people have

Nuclear power gives out no carbon dioxide while it runs, so it must be renewable.

Why it feels right: Clean and renewable both sound like the same good thing.

The test that breaks it: Ask where the fuel comes from. Uranium is mined from the ground, and the supply is limited.

What is true: Renewable means the resource is replaced or never runs out. Nuclear fuel is not replaced, so nuclear power is non-renewable, even though a reactor gives out no carbon dioxide while it runs.

Try it

A sun and wind diary

You need: a stick or a pole, a strip of light cloth or a plastic bag torn into a ribbon, string, paper and a pencil.

Be safe: Never look at the Sun to see if it is out. Look at your shadow instead. Keep plastic bags away from small children.

Tie the strip of cloth to the top of the stick. Push the stick into the ground in an open place, away from walls and trees.
Make a table with three columns: day, sun and wind.
Three times a day, look at the sky and at the cloth. Write yes or no for sun. Judge it by whether you have a sharp shadow.
Write none, light or strong for the wind. Hanging down is none. Waving is light. Streaming out flat is strong.
After a week, count the days with sun and the days with strong wind.

What you will see: Many days with sun and a sharp shadow mean solar panels would work well in your place. Many days with the cloth streaming out mean a wind turbine would turn well. If the cloth hangs down most of the week, wind power would give little. One week is only a start. Engineers measure for a year, high up where the blades would turn.

If you cannot try it, this is what happens.

Key words

renewable: a resource that is replaced as fast as it is used, or that never runs out.
non-renewable: a resource that will run out, because it forms far more slowly than it is used.
fossil fuels: coal, oil and natural gas, formed from dead plants and animals over millions of years.
biofuel: a fuel made from plants or animal waste, such as wood or biogas.
reservoir: a lake held behind a dam, where water is stored high up for a hydroelectric station.

Back to your guess

The answer is D: Nuclear power

Nuclear power gives steady electricity day and night, and a reactor gives out no carbon dioxide while it runs. Coal gives out carbon dioxide. Solar and wind depend on the weather.

Keep it

Copy this into your exercise book.

Renewable: replaced or never runs out. Fossil fuels and uranium are not. Solar needs sun, wind needs wind, hydro needs hills and water. Every resource has a cost. Choose by the place.

Draw: Three small pictures: a sun over panels, a turbine in wind, a lake on a hill with a pipe.