Thermodynamic evaluation of solar-geothermal hybrid power plants in northern Chile

Abstract

A thermodynamic model was developed using Engineering Equation Solver (EES) to evaluate the performanceof single and double-flash geothermal power plants assisted by a parabolic trough solar concentratingcollector field, considering four different geothermal reservoir conditions. The benefits ofdelivering solar thermal energy for either the superheating or evaporating processes were analyzed inorder to achieve the maximum 2nd law efficiency for the hybrid schemes and reduce the geothermalresource consumption for a constant power production. The results of the hybrid single-flash demonstratethat the superheating process generates additional 0.23 kWe/kWth, while supplying solar heatto evaporate the geothermal brine only delivers 0.16 kWe/kWth. The double-flash hybrid plant simulationresults allow obtaining 0.29 kWe/kWth and 0.17 kW/kWth by integrating solar energy at the superheaterand evaporator, respectively. In this context, the hybrid single-flash power plant is able to produceat least 20% additional power output, depending on the characteristics of the geothermal resource.Moreover, all of the cases analyzed herein increased the exergy efficiency of the process by at least 3%.The developed model also allowed assessing the reduction on the consumption of the geothermal fluidfrom the reservoir when the plant power output stays constant, up to 16% for the hybrid single-flash,and 19% for the hybrid double-flash. Based on the results obtained in this study, the solar-geothermalhybrid scheme increases the power generation compared with geothermal-only power plants, being anattractive solution for improved management of the geothermal reservoir depletion rates. The studyshows evidence of existing optimum configurations for the hybrid systems. A relative performancemap was developed in order to determine the best operation approaches according to the reservoir conditionsand solar field size.