The main energy sources we use are fossil fuels (coal, oil and natural gas), nuclear fuel, bio-fuel, wind, hydro-electricity, the tides and the Sun. A renewable resource is replenished as fast as it is used, so it will not run out. A non-renewable resource is used up much faster than it forms, so the supply is limited.
Fossil fuels and nuclear fuel are non-renewable. Fossil fuels are burnt to release heat, which boils water to make steam. The steam turns a turbine and generator to produce electricity. Oil is also refined into petrol and diesel for vehicles, and natural gas is burnt for heating and cooking. Burning fossil fuels releases carbon dioxide into the atmosphere, which adds to global warming. Nuclear power stations use uranium or plutonium. The fuel gives out heat as its nuclei split, and this boils water in the same way. No carbon dioxide is released, but the waste is radioactive and must be stored safely for a very long time.
Renewable sources are used in different ways:
- Bio-fuel is made from plants or animal waste. It can be burnt in power stations or vehicles, and the plants grown for it take in carbon dioxide as they grow.
- Wind turns the blades of turbines connected to generators. It needs no fuel, but only works when the wind is blowing.
- Hydro-electricity uses water from a dam flowing downhill through turbines. It can respond quickly to demand, but building the dam floods land.
- Tides make water flow in and out of a barrage across an estuary, turning turbines. Tides are predictable, but a barrage is expensive and harms wildlife.
- The Sun gives energy to solar cells, which make electricity directly, and to solar panels, which heat water. They work less well at night or in cloud.
When comparing, non-renewable sources give a reliable, large output on demand, but they run out and cause pollution or waste. Renewable sources will not run out and release little pollution while running, but several depend on the weather or the place, and they can be expensive to build.