Analytical study on integrating downhole thermoelectric power generation with coaxial borehole heat exchanger in geothermal well

Abstract

Geothermal power generation with ORC technology is a traditional and popular way to utilize geothermal energy. A new design of downhole thermoelectric power generation combined with a coaxial borehole heat exchanger is proposed, where the geothermal well is isolated into power generation section and heat exchanging section from the top of the target zone with a packer. A cold fluid is injected to downhole through an insulation pipe, parts of the injected fluid flows reversely in casing-tubing annulus above the packer, and others flows into casing-tubing annulus below the packer and upwards in tubing. These flowing design provides cold source and hot source for thermoelectric generator, respectively. Analytical models of downhole temperature distribution for thermoelectric power generation are established. A case study for a geothermal well with 3000m length of power generation section and 500m length of heat exchanging section is performed. The results show that a substantial generating capacity could be realized with a higher wellhead temperature, and the payback period under different carbon tax scenarios is about 6 – 8 years.The proposed method realizes geothermal energy harvesting and power generation at the same time and can be operated all year round.