Geothermal slim holes for small off-grid power projects

Abstract

Economically viable, small (100 kW e to 1000 kW e), geothermal power generation units using slim holes are available for the production of electrical power in remote areas and for rural electrification in developing countries. Based on borehole data from geothermal fields in the United States and Japan, slim holes have been proven as adequate fuel sources for small-scale geothermal power plants (SSGPPs) and can deliver enough geothermal fluid to the wellhead in a baseload mode to be of practical interest for off-grid electrification projects. The electrical generating capacity of geothermal fluids which can be produced from typical slim holes (150-mm diameter or less), both by conventional, self-discharge, flash-steam methods for hotter geothermal reservoirs, and by binary-cycle technology with downhole pumps for low- to moderate-temperature reservoirs are estimated using a simplified theoretical approach. Depending mainly on reservoir temperature, the numerical simulations indicate that electrical capacities from a few hundred kilowatts to over one megawatt per slim hole are possible. In addition to the advantage of price per kilowatt-hour in off-grid applications, SSGPPs fueled by slim holes are far more environmentally benign than fossil-burning power plants, which is crucial in view of current worldwide climate-change concerns and burgeoning electricity demand in the less-developed and developing countries.