Comparative Investigation of Solar Photovoltaic (PV) and Photovoltaic/Thermal (PV/T) Systems by both Laboratory and Field Experiments

Abstract

Photovoltaic (PV) semiconductor degrades in performance due to temperature rise. Therefore, a super thin-conductive thermal absorber was developed to retrofit the existing PV panel into a photovoltaic/thermal (PV/T) panel with multiple benefits including dual outputs of increased electricity and additional hot water, and potential savings in installation cost and space. The thermal absorber regulates the PV temperature by creating trade-off between PV efficiency and thermal output. This chapter presents the parallel comparative investigation of the PV and the PV/T panels through laboratory and field experiments. The laboratory evaluation consisted of one PV and one PV/T panel, while the overall field system involved 15 stand-alone PV panels and 15 retrofitted PV/T panels. The total electric installation capacity of the field system was around 6 kWp, and all the PV or PV/T panels were connected to the national grid through an electric inverter. The laboratory testing results demonstrated that this PV/T panel could achieve an electrical efficiency of PV cells at about 16.8 % (about 5 % increase), and produce an extra amount of heat with thermal efficiency of nearly 65 % under standard testing conditions. The nominal mass flow rate of the working fluid is recommended at 50 Lh−1m−2. The thermal absorber was measured at an extremely low pressure drop of less than 20 Pa. The field-testing results indicated that the hybrid PV/T panel could essentially improve the electrical return of PV panels by nearly 3.5 % in practice, and meanwhile increase the overall energy output (both electricity and heat) by nearly 324.3 %. Such synergetic integration of PV and thermal absorber not only results in improved PV efficiency but also generates more energy per unit area when compared with stand-alone PV panel. To replace with conventional electric water heating system, the 15 PV/T panel’s payback periods were estimated at less than 5 years and the corresponding CO2 emission reduction was about 440 t throughout their life span of 25 years. Further opportunities and challenges in the built environment were discussed from aspects of different PV/T stakeholders to accelerate the development of such technology. It is expected that such a dedicated technology could become a significant solution to yield more electricity, offset heating load freely and reduce carbon footprint in contemporary energy environment.