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Renewable energy
Dutch windmill     


       House with PV panels


Windy dayWhere can you get energy, free and forever? Just look up above you when you’re outside on a sunny day … Yes, the Sun gives our planet far more energy than people make from fossil fuels. Its heat drives the mightiest engine of all: the Earth’s climate. It makes you hot when it shines but it also makes winds, waves and rain. How? And people can use all these things to make electricity or heat energy for homes. And most important, unlike fossil fuels, this sort of energy doesn't damage the Earth and will last for ever!

Sun, wind, waves and rain
The Sun drives our planet's weather. It does this by heating the air and hot air rises – which is why hot air balloons work. The rising hot air sucks in cooler air to replace it and this is what we call WIND. And the wind, when it blows across the sea, makes WAVES. The rising hot air also forms clouds as it expands and cools again. And clouds make RAIN. But it's the Sun which drives all of the wind, waves and rain making what people call WEATHER.

Sun power (solar power) can make electricity by using things called photovoltaic cells (often just called PV – easier to say) which fit on the roofs or walls of your houses or apartment blocks. Some special cars can run on PV electricity and there’s even a race across Australia in which the cars run only on solar power
PV panels on a house in the USA
Sun power can heat water in solar panels (like radiators but instead of giving out heat, they grab it from the Sun). This is then stored in a big tank so you can have hot showers and so on. Solar collectors can pick up the sun's heat even on cloudy days
Solar hot water panels on a hotel roof in Greece
Solar power can also directly heat houses in cold countries – when they’re properly designed to make best use of it. So far, not many are. This is called passive solar energy

This glass conservatory captures the sun's heat and warms this farmhouse in Wales

Hydroelectric power makes electricity by using the energy from falling water. The water comes from big dams across rivers, and flows down great tubes to drive electricity generators. Most of the world’s biggest rivers are already used for this
The Three Gorges Dam in China is the largest hydro-electric power station in the world
Wind power can drive a turbine with a propeller (like some airplanes have) and make electricity. Wind power is getting really important in some countries. Here's a cartoon video (like Wallace and Gromit!) about wind turbines which I rather like!

A big wind turbine in Denmark. Can you make out the door at the bottom?

Wave power can also drive generators but this is still a very new idea. Just a few experimental machines are in use today.

Pelamis wave machine in operation off Portugal

Whoops! The tide's come inTides – you know, when the sea goes up and down twice a day – can drive generators too. There's just one example of this in action at a place called La Rance in France. Other parts of the world with big tides could be useful too, but a big dam has to be built to trap the moving seawater
Tidal power plant on the estuary of the Rance River, Bretagne, France
Biogas (methane) for cooking and heating can be made from human sewage and farm animals' waste. (Phew! Yuk! … but very useful.) It's made in special tanks called biodigesters. Landfills – that's where people's garbage gets dumped – also produce methane gas as the rubbish rots. Usually this is collected and used to make electricity
A working biodigester on a farm in Germany

Is this food or fuel?Biofuels: Because plants and trees soak up CO2 like sponges, making the carbon into wood and putting back oxygen into the air, people can ‘grow’ fuel without adding CO2 pollution to the air. It's called 'carbon neutral'. In Brazil, people pioneered growing sugar cane plants to make alcohol which they use to power almost half the country’s cars. In other countries, people plant special trees (like willow) which grow fast and you can cut them down without killing them – so they keep on re-growing. This is called coppicing. You can use the wood for burning to make heat as well as other things.

Other biofuels like ethanol and palm oil seemed like a good idea at first but they've turned out to be a bit of a disaster. Why?

Sugar cane, cut and ready for processing
Ethanol is a type of alcohol. To make it, people are turning food crops like maize (corn) into fuel instead of food.
Palm oil comes from vast plantations of oil palms in some tropical countries.
Fuel cells make electricity directly from hydrogen, a very light gas. The cells don’t burn the hydrogen. Instead it reacts with oxygen (in the air) to make electricity. The only ‘waste’ is water. Soon cars will run with fuel cells powering electric motors so they are silent and make no pollution. They can also make power for houses so there’d be no need for big polluting power stations. One way people can make hydrogen is by using sunlight to split water into hydrogen and oxygen gases. Scientists are still searching for a good way to do this.
Problems with hydrogen
Hydrogen when mixed with air is highly explosive. It is also very difficult to store which is a big problem if it is to be used for powering transport. And producing it needs a lot of electrical energy.

A hydrogen fuel cell public bus in Australia
Geothermal energy is energy tapped from inside the Earth. It's the only renewable energy source which has nothing to do with the Sun. Deep down, it's very hot. Sometimes these hot rocks break through the surface to form volcanoes. By drilling holes down into areas where hot rocks are close to the surface, people can generate electricity and heat buildings. One type of geothermal energy uses geothermal heat pumps to make hot water for home heating. A heat pump is a sort of reversed refrigerator. A different sort of heat pump takes its heat from the air outside a house and warms the air inside. Sounds impossible, doesn't it, but it works!
Geothermal power plant in Iceland
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