Thermoelectric Generator Application and Pilot Test in a Geothermal Field

Thermoelectric generators (TEG) are solid state devices that convert heat directly into electrical energy. A TEG produces electrical voltage when there is a different temperature on each side of the material. TEGs function like heat engines, though not as efficiently, but are less bulky and have no moving parts. TEGs are typically applied to power small devices, such as space probes and wine coolers. This project sought to develop a TEG apparatus that could produce electricity using heat generated form a geothermal field in The Geysers in northern California. While there have been many studies on TEG power output under varying conditions, there are no known studies of adapting TEGs to a geothermal resource. To this end, we designed a geothermal-TEG apparatus that has a modularized design to allow expanded power production by increasing the number of layers. After demonstrating the TEG’s performance in the laboratory, the apparatus was tested in the field at a well located in the Bottle Rock geothermal field. A 6-layer TEG field-scale device could generate about 500 W electricity with a temperature difference of about 152 °C between the hot and cold fluid manifolds, while each individual TEG chip could generate about 3.9 W. The steam pressure at the inlet of the TEG apparatus was about 122 psi, close to the wellhead pressure of 125 psi. After optimizing the field infrastructure, the TEG device could generate electricity without any leak at the wellhead pressure of 125 psi and the temperature over 176 °C (349 °F). The field test of the TEG field device at Bottle Rock geothermal power plant was considered successful. The work demonstrated that geothermal-TEGs can produce electricity in an economically competitively range similar to solar PV panels when external factors such as capacity factor are considered.