Comparative Analysis of Low Global Warming Working Fluids for Geothermal-Solar Hybrid Cycle

Abstract

Low quality brine discharged from the separator at Olkaria II power plant is normally reinjected back into the ground. Utilizing waste brine in an organic rankine cycle technology can result in cycle efficiency of around 12%. The efficiency can further be improved by the integration of parabolic trough collector to the geothermal cycle. Previous studies on geothermal-solar hybrid cycles have been analyzed using higher global warming potential working fluids such as R134a and R245fa. These organic working fluids pose danger to the environment and contravene protocols such as the Montreal Protocol, Kyoto Protocol and Paris Agreement which insist on the substitution of harmful substances that are accelerating global warming. In this study R-600a (isobutane), R-290 (propane), R-1150 (ethylene) and R152a (difluoroethane) which are low global warming potential organic working fluids are analyzed in terms of pump power, power output and net power output using geothermal-solar hybrid cycle for waste brine at Olkaria II power plant in Kenya. The results obtained show that R1150 produces the highest power output and net power followed by R290, R152A and R600A. Keywords— Organic Rankine cycle, Parabolic trough, Global warming potential, Cycle efficiency.