A new approach to extracting energy from hot underground rocks has been developed that avoids the earthquake risks posed by the current technology. It relies on a new type of heat exchanger at the bottom of a deep borehole rather than breaking open solid rock.
There have been questions raised over the financial and geological risks posed by the current approach The technology, known as Enhanced Geothermal Systems (EGS), has the potential to trigger earthquakes and contaminate aquifers – rocks which contain and transmit groundwater. In 2009 in Basel, Switzerland, a project caused seismic events large enough to damage property and had to be cancelled.
The new system, developed by Conneticut based start-up ,GTherm, uses a solid-state heat exchanger at the bottom of wells called a “heat nest”. The nest draws heat away from the surrounding rocks more efficiently using a highly conductive grout that encases the heat exchanger. To generate power the fluid travels up the well carrying heat from the nest to the surface. Here, the heat is used to turn a second fluid into gas, which in turn drives an electricity-generating turbine.
Conventional geothermal energy generation requires a combination of underground heat, water and rock permeability. EGS provides a source of clean power generation in areas that lack these conditions by engineering the required environment. However, doing this involves fracturing rocks and creates problems associated with “induced seismicity”. The initial rupturing of rocks creates micro-earthquakes that could be felt at the surface and produce damage. The pressure forced onto the rock could even interact with existing deep faults and generate large quakes.
GTherm’s system also uses thin holes up the length of the well, around 100 feet long and lined with heat-conducting material which further enhances heat recovery and increases power output. GTherm’s CEO and founder, Michael Parrella describes the system as: “basically a heat pump on steroids.”
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