The biggest disadvantage of Geothermal Energy for the production of electricity is that it requires a natural geothermal reservoir and thus it cannot be widely used. These geothermal reservoirs are available in only some areas of the world and particularly near the tectonic places where there is also high volcano activity.
Enhanced Geothermal System
Enhanced Geothermal System (EGS) also known as Engineered Geothermal Systems is a new type of geothermal energy system that does not require the use of geothermal reservoir. Instead, EGS extract the heat from hot dry and impermeable rocks. In order to heat up the water EGS make use of natural cracks in the rocks that allow enough water to flow. If cracks are not available or not big enough an injection well is used that will allow the water to be injected into the rock. The injected water will travel through the cracks of the rock, capturing its heat (from the contact with the rock) and come out to the surface as very hot water with the use of production wells.
The process of an Enhanced Geothermal System:
- Injection Well. An Injection Well is drilled into a hot dry and impermeable rock (if a natural crack is not available).
- Injection of Water. Pressurized cold water is injected into the well. The water will flow through the fractures of the rock or create new fractures (from its pressure) inside the rock.
- Hydro-fracture. Pumping of pressurized water continues to extend the fractures inside the rock extending the fractures throughout the rock creating a developing reservoir inside the rock
- Production Well. A production well is drilled at another point of the rock that extracts the hot water from inside the developed reservoir, allowing the water to circulate.
In this way the hot water is extracted from the reservoir, and turned into steam that will be used to generate electricity from steam turbines. Cold water is then re-injected inside the well creating a “closed-loop” circulation of water from the injection well (cold water) to the production well (hot water). Depending of the size of the rock and the power generation requirements, multiple production wells may be drilled.
EGS has a useful lifetime of 20 – 30 years before the temperature of the rock drops to a point where the system will no longer be economically viable. In order to create an EGS system we first need to choose the location carefully. Good locations are deep solid dry rocks (like granite) insulated by a thick layer of sediment (that will act as an insulator in order to prevent heat loss).
The leading countries using and developing EGS are United States, UK, France, Germany and Australia. The biggest project in the world is Cooper Basin in Australia with a potential to generate 5 – 10 GW of power.