Performance testing of thermal and photovoltaic thermal solar collectors

Abstract

This work details a methodology to characterize the performance of solar thermal and photovoltaic thermal (PVT) collectors using an indoor solar simulator. In this study, several cases have been compared to show that the methodology can be used to extract fundamental performance characteristics from a solar collector. In the first case, a serpentine collector was compared against a header riser collector using the same mass flow rate. It was found that the header riser was less efficient, with a 34% increase in the overall loss coefficient. The experimental results were compared with commonly used empirical models and showed a close agreement. In the second case, the impact on performance of using a polycarbonate cover is presented. The results show that the optical efficiency of the collector is reduced by 12% when using a cover; however, because the loss coefficient is reduced by 53%, the covered collector performs better when there is a large temperature difference between the absorber and the ambient. The third case investigates the combined performance of a PVT collector, that produces both heat and electricity from a single device. By placing photovoltaic (PV) laminates on top of the serpentine absorber, the thermal efficiency is reduced by 15%. When electricity is generated by laminates, the thermal efficiency is reduced by a further 3.5%; this drop in thermal efficiency is a result of the incident radiation producing electricity before reaching the thermal absorber. The combined efficiency of the PVT collectors was compared at controlled inlet temperatures. The serpentine design had the highest combined efficiency of 61% with 8% electricity at the lowest inlet temperature (21°C). The dominant form of loss in the PVT system is temperature driven; as the thermal efficiency decreases, electricity generation makes up a larger percentage of the combined output. This study highlights the potential for manufacturers of bespoke thermal absorbers and PV devices to combine their products into a single PVT device that could achieve improved efficiency over a given roof area. 311

Thermal and electric performances of roll-bond flat plate applied to conventional PV modules for heat recovery

“…About thermal efficiency calculation, some authors [8,17] extended the typical linear dependency on reduced temperature of solar panels to the PVT concept according to the following equation:…”

“…The measured thermal efficiency was 28.2% which is a promising results since it was determined in winter time. Allan et al [17] experimentally measured the performances of PVT panels built by placing the PV laminates on the top of an aluminum sheet. Results indicated that the PVT laminates reduces the thermal efficiency of a pure thermal collector by about 15% and a further 3.5% drop is found when electrical power is generated.…”

Experimental studies of temperature channel efficiency for solar energy systems

“…The efficiency coefficient evaluation is based on polynomial linear regression and requires additional costs for changing the SC lighting angles. Experimental studies of various SC designs using indoor solar simulators showed that the standard methodology of the SC main characteristics could be realized with errors up to tens of percent [8]. The analysis showed [9] that the relative experimental error of the SC coefficient efficiency practically is determined by the sum of relative measurement errors of the temperature difference δΔ T and the total surface radiant flux density δ G .…”

Design, Simulation and Experimental Investigation of a Solar System Based on PV Panels and PVT Collectors

“…In this analysis for calculating the thermal losses of collectors, constant loss coefficient (U L ) and transmission coefficient (τ) are used. Note that the model implemented in Type 50 is based on an extension of the Hottel-Whillier model for the analysis of combined photovoltaic/thermal flat plate collectors (actually there is no official standard testing for PVT collectors [29]). The characteristics of such method are the collector fin efficiency factor, F', and the overall transmittance-absorptance product, τα, whose parameters are reported in Table 1.…”