The Future of Energy: Rocks Are Hot

Geothermal

How Does It Work?

Geothermal energy uses the heat of the Earth’s crust to produce energy. The natural heat of the Earth originates from the radioactive decay of certain radioactive isotopes which release heat in the form of radiation. Some heat also continues to be released from the formation of Earth billions of years ago.

The process of extracting heat to produce energy can occur in multiple ways:

· Direct Use – Directly, geothermal can be used to heat buildings, warm greenhouses, or dry crops. The method is to drill a well into a geothermal reservoir, providing access to hot water and steam. The hot fluid is pumped to the surface for its intended use. After extraction, cooling fluid can be placed into the reservoir to maintain the balance.

Photo by Gaelle Marcel on Unsplash

To find these geothermal sources, a resource assessment has to occur. Resource assessment combines geological mapping, surface expression, geophysical surveys, geochemical analysis, temperature gradient, heat flow measurements, remote sensing, and aerial surveys all before exploration drilling can occur.

After, any impurities or non-condensable gases in the geothermal reservoir need to be removed. From here, thermal energy is converted into mechanical energy via steam-turning turbines.

If geothermal isn’t accessed directly, there are three different variations of geothermal power plants used to produce electricity:

· Dry Steam Power Plants – Drives a turbine using steam directly produced by geothermal reservoirs, to then power a generator and produce electricity.

· Flash Steam Power Plants – High-pressure hot water from geothermal sources is brought to the surface. It then enters a pressure-reduction system, and the change in pressure causes the hot water to evaporate into steam. The steam drives the turbine and powers the generator.

· Binary Cycle Power Plants – The Binary Cycle power plant uses lower temperature geothermal sources by using a binary fluid with a boiling point lower than water. The binary fluid is a hydrocarbon or organic fluid. The temperature difference between the binary fluid and the geothermal reservoir causes the binary fluid to heat up. From here, it evaporates, and the steam created drives a turbine and generates electricity.