Geothermal Energy

Geothermal energy is thermal (heat) energy from inside the Earth. It is one of the few energy resources not powered by the Sun (the others are nuclear and tidal). Hot rocks underground heat water, which we can use for heating or to generate electricity.

Where the heat comes from

Heat inside Earth comes from radioactive decay and leftover heat from Earth’s formation. This heat moves upward by conduction through rocks and by convection in hot water and steam found in some regions.

How a geothermal power station works

• Production well: Cold water is pumped down, or hot water/steam is brought up from deep, hot rocks.
• Boiler/heat exchanger: Hot geothermal fluid heats water to make steam (sometimes the steam comes straight from the well).
• Turbine: Fast steam pushes turbine blades, giving them kinetic energy.
• Generator: The spinning turbine turns a generator to produce electrical energy.
• Condenser/cooling: Steam is cooled back into water.
• Reinjection: Cooled water is pumped back underground so the resource is sustainable.

Direct uses (no electricity)

Geothermal heat can warm buildings (district heating), greenhouses, or water for bathing. Ground-source heat pumps use the steady temperature of shallow ground for heating and cooling; they are a heating technology, not an electricity source.

Advantages

• Renewable: Earth’s internal heat is constantly produced.
• Reliable: Available day and night, not dependent on weather.
• Low emissions: Very low carbon dioxide compared with fossil fuels.
• Small running costs: After drilling, fuel is essentially free.

Disadvantages

• Location-limited: Best in volcanic or tectonic areas (e.g. Iceland, New Zealand, Kenya).
• High upfront cost: Drilling deep wells is expensive and risky.
• Environmental issues: Can release trapped gases (e.g. hydrogen sulfide), mineral-rich water can corrode pipes; careful management is needed.
• Scale: Large power output needs the right geology; not every place can build big plants.

Energy transfers to remember

Internal (thermal) energy in hot rocks → heating water (by conduction) → kinetic energy of steam → kinetic energy of turbine → electrical energy in the generator.

Common misconceptions

• It is not solar-powered; it comes from Earth’s internal heat.
• It is renewable, but local reservoirs can cool if overused without reinjection.
• Ground-source heat pumps do not “make” electricity; they move heat for buildings.