Photovoltaic thermal module and solar thermal collector connected in series: Energy and exergy analysis

Abstract

The photovoltaic thermal (PVT) module generates electricity with low temperature thermal energy while the solar thermal (ST) collector outputs only thermal energy without electricity. The combination of PVT module and ST collector in series is able to output high temperature thermal energy together with electricity simultaneously. In this research, the novel concept of series-connected PVT-ST is firstly introduced, and a two-dimensional transient mathematical model is developed to study four cases of the PVT-ST system with or without glass cover. Based on the numerical results, the series-connected PVT-ST system can output high temperature thermal energy with outlet water varying from 63.00 °C to 95.15 °C in different cases. Daily energetic and exergetic performance of four cases is also studied in this paper, revealing that case 1 (glazed PVT and glazed ST) obtains the highest overall energy and exergy efficiency of 41.51% and 17.63%, respectively. Due to the effect of glass cover, thermal energy and exergy output in case 1 can reach 4.10 kWh and 0.38 kWh on a selected day. However, case 4 (unglazed PVT and unglazed ST) has the lowest energy efficiency (28.97%) among four cases, but it performs best in the generation of electricity, which reaches 1.41 kWh during the experimental time. Moreover, a comparative study between the PVT-ST system and typical systems is conducted, and the results indicates that the PVT-ST system performs better than most conventional systems in terms of individual and overall efficiency from the viewpoint of energy and exergy.