Analysis of a Low Concentration Solar Plant with Compound Parabolic Collectors and a Rotary Expander for Electricity Generation

In the last decade many studies have been carried out on low temperature solar compound parabolic collectors (CPC) that are able to collect solar direct and diffuse radiation without the need of a tracking system, especially if coupled with small scale Organic Rankine Cycles for electricity and heat combined production. This paper presents a study on a thermal power plant that uses an expansion device driven with pressurized vapor generated with the heat collected by a CPC solar field. The numerical model of the expansion device was developed with the simulation tool AMESim v.12 and allowed the simulation of the indicated cycle of this machine for the evaluation of delivered power, isentropic efficiency and specific working fluid consumption. At the same time in this paper an analytical model of the evacuated solar CPC is presented for the evaluation of the collected heat as a function of sun incidence angle, external temperature, inlet carrier fluid temperature and mass flow rate. These two models were used in conjunction for the analysis of the electricity that may be generated as a function of the ambient and working conditions. This study was performed in steady state conditions and with several working fluids to evaluate the power that would be delivered by a given displacement expander rotating at a fixed speed. The results are given in terms of delivered power, thermal efficiency and amount of collecting surface needed for a given displacement expansion machine, calculated for several working fluids and different operating conditions.