The technology of generating electricity from hot water and steam collected from geothermal reservoirs has been around for more than a century. These power plants has until recently only been useful in areas near continental plate boundaries where naturally occurring water is combined with a high rock permeability (a material’s ability to transport fluid).
The majority of the geothermal reservoirs exist in hot dry rocks (HDR) with too low permeability, which you can find all over the Earth. This is where enhanced geothermal systems (EGS), also known as engineered geothermal systems, come in; allowing us to extract geothermal energy from resources that otherwise would not be possible.
Injection wells are drilled out several kilometers into the Earth. High-pressure water is sent down the same wells to fracture the rock; a process, which creates thousands of tiny pathways where water can gain heat from the geothermal energy that naturally, is stored at these depths.
This is the same water that is piped to the surface through one or several production wells. It then is lead into a turbine (or transfers its thermal to another working fluid through a heat exchanger), which converts thermal energy to electricity with a generator. The water is then sent back down the injection wells where it regains heat, completing the cycle.
With enhanced geothermal energy systems, the potential of geothermal power is extended from areas near continental plate boundaries to pretty much everywhere. It is not an overstatement to say that EGS pushes the potential of geothermal energy to practically unlimited.
Recent estimations claim that with the recent additional resources of EGS, there is a total annual geothermal potential of 14 million EJ (exajoules) in the United States alone, in other words, 140 000 times more energy than what this country currently consumes.
Earthquake Risks of Enhanced Geothermal Systems
Geothermal power is in general very reliable, which makes it an excellent choice for a base load energy source. However, there are some risks involved with establishing enhanced geothermal energy systems:
Developing enhanced geothermal systems (EGS) possess a potential risk in triggering earthquakes, which is exactly what happened in Basel, Switzerland. This what we called induced seismicity by hydrofracturing (the technique that is used to develop EGS reservoirs). The risks for this happening is very low, if the process is properly monitored, compared to the risks of natural earthquakes occurring.
There are currently operational enhanced geothermal systems installed in France and Germany, with more under construction in Australia (in the picture above), Japan, the United States and Switzerland.