Renewable and non-renewable
A renewable resource is replaced as fast as it is used, so it will not run out: examples are solar, wind, hydroelectric, tidal, wave, geothermal and biofuels. A non-renewable resource is used faster than it forms and will eventually run out: the fossil fuels (coal, oil, natural gas) and nuclear fuel (uranium).
Generating electricity
Most power stations turn a turbine that drives a generator. Fossil fuels and nuclear fuel produce thermal energy to boil water into steam, which spins the turbine. Wind and moving water can turn turbines directly. Solar cells transfer energy from sunlight straight into electricity without a turbine.
Key idea
The Sun is the source of most of Earth's energy. It drives wind, waves, the water cycle (hydroelectric) and, in the past, plant growth that formed fossil fuels. Tidal energy comes mainly from the Moon; geothermal and nuclear do not come from the Sun.
Worked example
A wind turbine has a useful power output of 300 kW and receives 1000 kW of power from the wind. Find its efficiency.
efficiency = useful power out ÷ total power in = 300 / 1000 = 0.30 = 30%.
Remember
- Fossil fuels give reliable large-scale power but release CO₂.
- Renewables are cleaner but many depend on weather.
- Nuclear needs no fossil fuel but produces radioactive waste.