Review of high concentration photovoltaic thermal hybrid systems for highly efficient energy cogeneration

Concentrated photovoltaic/thermal hybrid systems are a combination of concentrated photovoltaics and photovoltaic/thermal hybrid systems which capture waste heat for later application. Higher concentrations lead to higher energy fluxes over smaller areas which is beneficial for several reasons. Firstly, less photovoltaic material is required, instead using relatively cheap optics. This allows more efficient types of PV material to be used effectively. Secondly, the concentrated heat flux easily allows for a high outlet temperature which in turn increases the applicability. Point focused systems have experimentally achieved cogeneration efficiencies of 86.47% (excluding system losses) and concentrations of over 1000 suns, but the technology still faces challenges. The design of the cooling system must be optimised to maximise both electrical and thermal efficiency. Furthermore, the optics and cell interconnections must mitigate the effects a non-uniform focal image for high electrical efficiencies. These challenges must be faced while minimising the thermal stresses the system undergoes to ensure the system has a substantial lifetime. This review provides an in depth understanding of the challenges and function of point focused concentrated photovoltaic/thermal systems. From the literature, it is clear more focus should be put on microchannel/impinging jet hybrid cooling systems for use in dense array concentrated photovoltaic/thermal systems. More physical experimentation is needed, especially full model systems which include the output image of the optics, along with consideration to alternative cooling fluids (particularly nanofluids).