Energy and exergy analyses of PV, solar thermal and photovoltaic/thermal systems: a comparison study

Compared with photovoltaic (PV) or solar thermal (ST) system alone, the hybrid photovoltaic/thermal (PV/T) system has many advantages such as simultaneous production of electrical and thermal energies, efficient utilization on solar energy, space reduction and so on. However, there is limited data on both the energy and exergy performance comparisons of these three solar systems, especially for annual performance data. This paper aims to present a comparative study on the performances of the PV, ST and PV/T systems by a series of full-day experiments. Energy and exergy performances of these three solar utilization systems were all calculated and analyzed. Moreover, two typical evaluation methods, i.e. semi-empirical system efficiency model method and input-output method, were also used for evaluating the performances of these systems. Finally, based on the input-output method, the annual performances of the PV, ST and PV/T systems under typical meteorological conditions of Hong Kong region were predicted. The results show that the ST system has the highest total energy gain and energy efficiency and the PV system has the highest total exergy gain and exergy efficiency of these three systems. However, by a comprehensive consideration on the energy and exergy performances, the PV/T system has the best overall performance of these three solar systems.