Energy and exergy analyses of a bifacial photovoltaic/thermal system with nanofluids

In this study, a novel hybrid bifacial photovoltaic-thermal (bPV/T) system is proposed, which can effectively absorb the sunlight from both sides to generate more power and heat simultaneously. An integrated mathematical model of the hybrid system is developed firstly by coupling optical, electrical, and thermal models. Meanwhile, the whole system characteristics are then simulated after validation. Results show that the short-wavelength sunlight is transmitted, while the long-wavelength is absorbed due to selective absorption. A high overall energy efficiency of 85.74% is achieved due to high transmissivity and good insulation, while the overall exergy efficiency is only 12.26% due to low-grade heat generation. Meanwhile, the daily performance demonstrates that the bPV/T system can make better use of the irradiance from both sides to produce power and thermal output simultaneously at a high stage, though the power output is lower than that of the bPV itself due to some optical losses. It is assumed that the power output from the bPV/T system would be higher than bare bPV when transmittance for glass and nanofluid both got closer to 1. For future development, thicker nanofluids with higher mass flow rate and smaller nanoparticles under AM 1.5 solar spectrum could achieve higher overall energy efficiency on the Earth. While for higher overall exergy efficiency on the Earth, thicker nanofluids with lower mass flow rate and bigger nanoparticles under AM 1.5 solar spectrum are recommended.