6.11 Geothermal Energy

What is geothermal energy?

Geothermal energy comes from heat stored inside the Earth, generated by radioactive decay and residual heat from planetary formation. This heat can be tapped to generate electricity or provide direct heating, using steam or hot water reservoirs found near tectonic boundaries, hot spots, and volcanic regions.

Geothermal power plants

Power plants use underground steam to spin turbines connected to generators. Dry steam plants use naturally occurring steam directly; flash steam plants convert hot water to steam by reducing pressure; binary cycle plants transfer heat to a secondary fluid with a lower boiling point, allowing use of cooler reservoirs.

Benefits and limitations

Geothermal energy is renewable, produces low greenhouse gas emissions, and offers a reliable, constant power supply unlike solar or wind. However, it is geographically limited to areas with accessible heat sources, has high upfront drilling costs, and can trigger minor seismic activity or release trace gases like hydrogen sulfide.

Key terms

Geothermal energy

Heat energy from within the Earth, generated by radioactive decay and residual formation heat, used for electricity and heating.

Dry steam plant

Geothermal plant that uses naturally occurring steam directly to spin a turbine.

Flash steam plant

Geothermal plant that reduces pressure on hot water to convert it into steam.

Binary cycle plant

Geothermal plant that transfers heat to a secondary fluid with a lower boiling point to drive turbines, useful for cooler reservoirs.

Advantages vs. limitations of geothermal

Renewable and reliable with low emissions, but limited to specific geologic locations and has high drilling costs and minor seismic/gas risks.

Try an AP-style question

Where does geothermal energy come from?

1. Sunlight stored in rocks
2. Burning underground coal
3. Heat from Earth's interior
4. Ocean tides