Improved Testing of PVT Hybrid Technologies

Report Number



PV Modules; Photovoltaics; Solar Thermal


PV/Thermal (PVT) collectors are being designed and manufactured by numerous companies as a way to improve overall performance of solar energy systems. PVT collectors generate both electricity and usable thermal heat at the same time from one panel. These systems combine a photovoltaic module which converts solar radiation directly into electricity, with a solar thermal absorber, which captures much of the remaining thermal energy. PV generation is increased due to lower cell temperatures and waste heat is captured for utilization. The performance of PV modules as a function of temperature and other operating conditions (such as irradiance, tilt and azimuth, etc.) is well understood. However, the impact of the PV energy production on the thermal performance of PVT products is not well understood and few data are available to contribute to performance model predictions and development of test standards. PVT products require the same level of testing and certification as solar PV and solar thermal products. Previous thermal performance testing of PVT products was done with the PV inoperable -the PV left in either open circuit or short circuit. In either operating mode, the net power output from the PV module is zero. When operating under a maximum power point (MPP) tracking algorithm, as any inverter tied PV module will do in-situ, 10% - 20% of the energy available from the sun will leave the system as electricity. This change in the energy balance will impact the performance of the solar thermal collection. Current testing standards and performance models used for certifying solar thermal products include very minimal provision for PVT products. This paper presents data showing a decrease of about 8% in the thermal performance of a PVT collector when the PV is operated at MPP conditions when compared with the thermal performance of the same collector with the PV not connected. Recommendations for testing as well as overall energy production of a sample PVT system are also presented.

Date Published



Photovoltaics; PV Modules; Solar Thermal

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