Economic investigation of low cost organic rankine cycle incorporated in a combined solar photovoltaic cum thermal plant

Abstract

Current rise in small scale solar thermal combined electricity generation water heating in Kenya has corresponded with demand growth for power supply in areas poorly served by the national grid. The potential technical approach to this increasing demand encourages the use of PV (Photovoltaic) solar collectors coupled with ORC (Organic Rankine Cycle) system. This paper uses Aspen plus software in modelling ORC system. Thika (00, 370, 41’E) climatic conditions is selected for the present case study to examine performance and cost of the system. The system comprises of PV collectors, oil storage unit, pump, and a small scale ORC engine using an expander. The model evaluates the performance of the system under the change in environmental temperature (Thika town conditions adopted) or varying the mass flow rate of heat transfer fluid (HTF). The results indicate that using Therminol oil 55 as HTF and R245fa (1,1,1,3,3-pentafluroropropane) as the working fluid and a collector heat source temperature of 163.50C delivered an output power of 15kW with the overall efficiencyattained as 8.5%. The proposed system is intended to be potentially suited in Kenyan counties with good solar irradiation and without (or with high cost) access to the national grid electricity supply. Detailed cost analysis of the system was carried out in using Levelized Cost of Electricity (LCOE) order to determine the system viability and payback period and Depreciated Payback Period (DPP). For super heater outlet temperature of 1300C, mass flow rate 3000kg/h, the specific cost of 2kW system is 12,073 $/kW with a LCOE of 13.5c$/kWh and a payback period of 10 years. While for 15kW system with the LCOE of 12.2 c$/kWh, specific installed cost is about 8,068 $/kW; the payback period is approximately 6 years.