The amount of thermal energy stored away inside the Earth is immense. The heat generation, per year, is 8.6x10^20 Joules (Rybach 2007). This is about 1.3 times the global annual consumption in 2018 (International - U.S. Energy Information Administration (EIA) n.d.). This makes the Earth’s internal energy a great renewable source for the global population. With the right methods of extraction, it can be a carbon neutral, environmentally friendly alternative to fossil fuels and even less reliable methods of green energy such as wind and solar.
While there are a few different ways to bring the Earth’s thermal energy to the surface and change it into electrical or mechanical energy, the premise is the same. Two wells are drilled into the heat reservoir (usually, but not always, hot water) - a production well and an injection well. The heat is brought to the surface through the production well, either via steam or hot water that then heats another substance to its boiling point. The steam or gas is then used to spin a turbine, which powers an electrical generator. After the thermal energy has been extracted, cooler water is then injected back into the ground via the injection well. This water is again heated by the Earth and pumped back up to the surface.
While Earth’s wide range of thermal energy can be directly to heat homes and businesses, to make electricity, only the higher ranges of temperatures can be used. Temperatures in excess of 150⁰ C are needed. While there is certainly high enough temperatures being generated by the Earth, this makes extracting those temperatures a little tricky. There are 3 basic methods for doing this: Conventional, Enhanced Geothermal Systems (EGS), and Advanced Geothermal Systems (AGS) (Roberts 2020) . All have their benefits and drawbacks. Please navigate to the “Methods of Implementation” to learn about them.