4.6 - Geothermal Power

How geothermal power works

• Geothermal power uses the thermal energy of hot rocks deep underground.
• Much of this energy comes from the slow decay of radioactive elements (such as uranium) deep inside the Earth.
• It's only practical where hot rocks lie fairly near the surface, such as in volcanic regions.

Generating electricity

1. Water is pumped down pipes to the hot rocks, where it heats up and returns to the surface as steam.
2. The steam turns a turbine, which drives a generator to produce electricity.
3. Thermal energy from the rock is transferred to the turbine as kinetic energy, then carried away electrically.

Heating buildings directly

Hot water brought up from underground can also be piped straight into buildings for heating, without generating electricity.

Reliability, environment and drawbacks of geothermal

• Geothermal is a very reliable energy source because the hot rocks supply energy constantly, regardless of the weather.
• Once built, there are no fuel costs.

Environmental impact

• Geothermal does very little damage to the environment.
• It can release some carbon dioxide trapped underground, but far less than a fossil-fuel power station.
• It produces no polluting waste from burning fuel.

Drawbacks

• Few suitable locations - It only works where hot rocks are close enough to the surface to reach.
• High build cost - Drilling down several kilometres and building the plant is expensive compared with the energy it produces.

Biofuels are renewable fuels from plants and waste

• Biofuels are a renewable energy resource made from plant materials or animal waste.
• They can be solid, liquid or gas, and are burnt to release the chemical energy they contain.

Uses

• Generating electricity - Burnt in power stations to drive a turbine and generator, just like fossil fuels.
• Running vehicles - Used in transport in place of petrol and diesel.

Sources of biofuels

• Specially grown crops - Such as sugar cane, vegetable oils or fast-growing trees.
• Waste products - Such as farm waste, animal droppings and landfill rubbish.