Design and performance study on a large-scale hybrid CPV/T system based on unsteady-state thermal model

A hybrid CPV/T unit designed in this work concentrates solar radiation by a compound parabolic concentrator (CPC) and converts solar energy into electrical and thermal energy by a PV/T module. The CPC eliminating multiple reflections of solar radiation is defined as the ‘EMR-CPC’ in our previous work, which improves photoelectric and thermal conversion efficiencies. Two similar CPV/T units were tested with two-axis tracking device and south-north single-axis tracking device respectively, and the average photoelectric conversion efficiencies were 13% and 12%. A large-scale south-north tracking hybrid CPV/T system with sunlight collecting area of 810 m² was built to explore practical application of this CPV/T unit. The whole-day thermal efficiency and total thermal output of the large-scale hybrid CPV/T system were 55% and 1,730,039 kJ respectively on April 14, 2017. The steady-state and unsteady-state thermal models of the hybrid CPV/T system were established and the energy loss was analyzed. The calculated whole-day comprehensive thermal efficiencies of the unsteady-state thermal model and the steady-state thermal model were 55.3% and 55.0% respectively, which were close to the measurement 55.8%. However, the steady-state thermal model failed to accurately predict the whole-day thermal efficiency variation of the system. In comparison, the unsteady-state thermal model accurately predicts instantaneous thermal efficiency of the system varying with meteorological conditions and its total daily heat output.