Numerical and experimental investigation of the energy and exergy performance of solar thermal, photovoltaic and photovoltaic-thermal modules based on roll-bond heat exchangers

Abstract

This paper presents numerical and experimental energy and exergy performance assessments of solar thermal (ST), photovoltaic (PV) and photovoltaic/thermal (PV/T) modules based on roll-bond heat exchangers having three different channel geometries: serial, parallel and bionic. The validation of a coupled numerical simulation encompassing the thermo-hydraulic and electrical properties shows that 78% of all the data lies within a ± 10% uncertainty. The thermo-hydraulic simulation shows that the lowest outlet-water temperature inside the absorber is for the case of the bionic absorber (average 44.1 °C vs. 46.5 °C for the serial). This geometry is also beneficial when considering pressure losses, since compared to the parallel configuration (average 778 Pa) the bionic has significantly lower pressure losses (average 385 Pa). The simulation of the electrical properties of PV/T with all three absorber types showed the highest average solar-to-electrical efficiency (14.5%) in the case of the bionic absorber compared to the PV/T with parallel and serial absorbers (14.4% and 14.3%, respectively). Finally, a set of experiments using the ST, PV and PV/T2 (the index 2 denotes a PV/T collector variant with a foil thickness of 0.3 mm, compared to the thickness of 0.4 mm for PV/T1, positioned between the absorber and the PV cells) modules showed that the PV module, coupled with a bionic absorber plate, achieves the highest average electrical (PV – 8.5% vs. PV/T2 – 9.9%) and exergy (ST – 4.4% vs. PV – 9.2% vs. PV/T2 – 12.7%) efficiencies. Only in terms of the thermal efficiency, the PV/T is at a disadvantage to the ST (PV/T2 – 33.5% vs. ST – 61.4%) due to the air gap between the front glass and the absorber of the latter module.