Study of the Performance of Solar–Enhanced Closed Loop Geothermal Systems

Abstract

Geothermal energy is becoming a competitive renewable resource, comparable to solar and wind sources of energy. The critical factor is the high initial investment associated with drilling a geothermal well, as it can comprise over 50% of the cost of the entire project. By coupling a geothermal system with a solar heat collector, a resource can supply more heat per metre of borehole thereby reducing the required depth of borehole. Compared to a standalone geothermal system, the solar-geothermal hybrid system injects thermal energy into the geothermal resource during the summer period when geothermal heat is not required. In this study, a finite element model was developed to establish the feasibility of storing solar energy in the ground, so as to restore energy the geothermal resource during the summer period. Using insitu gathered information, the model is used to study effects of rate of heat extraction, rate of solar radiation, solar collector size, outlet fluid temperature, and thermal conductivity of ground on the performance of the system. The unsteady state simulations are carried out over a period of 15 years, in order to assess how much the solar collector can benefit the rejuvenation of the geothermal resource. Additionally, the solar-geothermal hybrid system is compared against a standalone geothermal system. Finally, economic advantages of retrofitting closed loop geothermal systems with solar collectors are assessed and highlighted.