Simulation and economic analysis of a CPV/thermal system coupled with an organic Rankine cycle for increased power generation

Abstract

In concentrating photovoltaic (CPV) systems the incident solar radiation is multiplied by a factor equal to the concentration ratio, with the use of lenses or reflectors. This is implemented, in order to increase the electric power production, since this value has a linear dependence from the incident radiation. Therefore, the specific energy production of the cells (kWh/m 2) radically increases, but due to this high intensity CPVs consequently operate at elevated temperatures, because heat dissipation to the environment is not so intense and heat produced cannot naturally convected. This temperature increase not only leads to a reduction of their electric efficiency, but also it must be dissipated, since issues regarding their degradation and reduction of their lifetime might arise. There are many reported ways of removing this heat, either by adding a cooling unit on the back side of the CPV module, or by recovering with possible uses in buildings, industry, additional power production or even desalination of seawater. The current work is actually a feasibility study, concerning a concentrating photovoltaic/thermal (CPV/T) system, where the heat produced is recovered by an organic Rankine cycle (ORC) for additional power production. A pump drives the organic fluid of the cycle, which is evaporated in the tubes of the CPV/T and driven to an expander for mechanical power production. For the condensation of the organic fluid several possible alternatives can be applied. That way, the PV cells can be cooled effectively and increase their electrical efficiency, while the recovered heat is designated to produce additional electric energy through the organic Rankine process, when the expander of the Rankine engine is coupled to a generator. The scope of the present work is to investigate an alternative application of concentrating PV modules through exploiting the generated heat by the ORC process and combining both technologies into an integrated system. The design of the system is presented in details, along with an optimization of some main parameters. The performance of the system will also be examined and compared with an equivalent conventional CPV system, referring to their design points. Finally, the annual and daily performance will be studied, which is a more realistic indicator, concerning the increased efficiency this integrated system is expected to have, followed by a cost analysis, in order to examine its economic feasibility as well.