Geothermal Energy (College Board AP® Environmental Science): Study Guide

Using geothermal energy

• Geothermal energy is heat energy stored beneath the Earth's surface

• This heat is generated by the natural radioactive decay of elements like uranium, thorium, and potassium, as well as residual heat from the Earth's formation and tectonic activity

How geothermal energy is harnessed

Geothermal reservoirs

• Hot water and steam are trapped in permeable rocks or in underground reservoirs

• These reservoirs are usually near volcanoes or tectonic plate boundaries

Energy extraction

• Direct use: hot water from geothermal reservoirs is used directly for heating buildings, greenhouses, or industrial processes by drilling into the reservoir

• Electricity generation:

  • Dry steam plants use steam from underground reservoirs directly to spin turbines connected to generators

  • Flash steam plants extract high-pressure hot water from underground, which 'flashes' into steam as it reaches the surface, which then drive the turbines

  • Binary cycle plants use hot geothermal water to heat another fluid that boils at a lower temperature. The vaporized fluid drives the turbines

Geothermal power station

Advantages & disadvantages of geothermal energy

Advantages of geothermal energy

• It is a renewable resource; providing the Earth generates heat, geothermal energy will be available

• Environmentally friendly, it produces low greenhouse gas emissions compared to fossil fuels

• Reliable and consistent, it provides a constant energy supply regardless of weather conditions, unlike solar or wind power

• They are an efficient use of land as they take up less land space than other renewable power plants

• Geothermal has diverse applications and can be used for generating electricity and direct heating

Disadvantages of geothermal energy

• Geothermal energy depends on tectonic activity, so there are few suitable locations on Earth

• Geothermal power stations are expensive to build

• Geothermal power stations are small so they are not suitable for large-scale electricity production

• Geothermal power stations are not very efficient (around 12%)

• Overuse of reservoirs can lead to depletion if the heat extraction rate exceeds natural replenishment

• There are environmental risks if harmful gases like hydrogen sulfide is released

• Mineral-laden wastewater can contaminate nearby water sources

• Drilling and water reinjection can sometimes trigger small earthquakes