Abstract
Photovoltaic-thermal (PVT) collectors combine photovoltaic modules and solar thermal collectors, forming a single device that receives solar radiation and produces electricity and heat simultaneously. PVT collectors can produce more energy per unit surface area than side-by-side PV modules and solar thermal collectors. There are two types of liquid-type flat-plate PVT collectors, depending on the existence of glass cover over PV module: glass-covered (glazed) PVT collectors, which produce relatively more thermal energy but have lower electrical yield, and uncovered (unglazed) PVT collectors, which have relatively lower thermal energy with somewhat higher electrical performance. In this paper, the experimental performance of two types of liquid-type PVT collectors, glazed and unglazed, was analyzed. The electrical and thermal performances of the PVT collectors were measured in outdoor conditions, and the results were compared. The results show that the thermal efficiency of the glazed PVT collector is higher than that of the unglazed PVT collector, but the unglazed collector had higher electrical efficiency than the glazed collector. The overall energy performance of the collectors was compared by combining the values of the average thermal and electrical efficiency.
Highlights
The overall efficiency of a PV system, which has relatively lower efficiency among renewable energy systems, depends on the efficiency of the solar cells and the PV modules themselves
The heat from PV modules can be removed in order to enhance the electrical performance of the PV module; this heat can be converted into useful thermal energy
The two different types of PVT collector were tested at solar radiation above 790 W/m2 and a flow rate of 0.02 kg/sm2, based on ASHRAE standard 93-77 [20] and PVT performance measurement guidelines of ECN (Energy Research Centre of The Netherlands) [21]
Summary
The overall efficiency of a PV system, which has relatively lower efficiency among renewable energy systems, depends on the efficiency of the solar cells and the PV modules themselves. In general, silicon-based PV modules have an electrical efficiency of about 12∼16% under standard test condition (STC: air mass 1.5, irradiation intensity 1000 W/m2, and cell temperature 25◦C). The photovoltaic/thermal (PVT) concept offers an opportunity to increase overall efficiency by the use of waste heat generated in the PV module of the BIPV system. It is well known that PVT systems enhance PV efficiency by PV cooling, where PV cooling may be achieved by circulating a colder fluid, water, or air, at the underside of the PV module. Among the various types of PVT systems, liquid-type PVT collectors combine a photovoltaic module and a solar thermal collector, forming a single device that converts solar energy into electricity and heat simultaneously. PVT collectors can generate more solar energy per unit surface area than can side-by-side photovoltaic modules and solar thermal collectors
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