Modelling and experimental analysis of low concentrating photovoltaic for use in building integrated and attached photovoltaic (BIPV/BAPV) systems

Abstract

This thesis studies stationary, low concentration ratio, non-imaging reflective concentrators to generate power at a lower cost for applications in Building-Integrated Photovoltaics (BIPV). Stationary solar energy concentrators are a promising option for decreasing the price of photovoltaic electricity in BIPV. Two geometrically equivalent non-imaging concentrators parabolic V-trough and CPC are investigated routes to increasing the efficiency of solar cells employed in BIPVs. In this work V-trough and CPCs concentrators were modelled in COMSOL at various geometries and configurations. Each configuration was separately studied at various light angles of incidence. In addition, the effect of CPC truncation and V-trough side wall angle for BIPV implementation was also studied. The results showed big increases in angle of acceptance, reductions in height profile and V-trough-like characteristics past the original CPC design acceptance angles, with consequence in reducing material consumption for the manufacture of CPC and therefore reduction in the cost of the system. For ray tracing analysis a variety of direct and iterative solvers were tested and the generalized minimal residual method (GMRES) was used for 2D and 3D analysis of concentrators. A drop of performance was observed for both concentrators at increased light incidence angles; however, V-trough showed a better ability to dampen the loss as incidence angle increased. In terms of net concentration ratio, a truncated CPC at equal height shows a net concentration ratio of 𝐶𝑜𝑝𝑡=2.70 whilst V-trough hovered around 𝐶𝑟𝑛𝑒𝑡=2.37−2.70 resulting in a net performance increase of 31% for CPC adoption. Results showed V-trough having lower concentration ratios but better performance at high angles of incidence compared to CPCs. Truncated CPCs showed equal optical efficiency to their full height parents but a lower concentration ratio due to a reduction in inlet aperture size. The modelled 50mm CPC concentrator designed for BIPV shows a greater overall concentrating performance, with significantly improved concentration up to the acceptance half angle, a small loss compared to the V-trough from the acceptance half angle to around 30° light incidence, and again an improvement over the V-trough from ~30° onwards. All truncated CPCs also show V-trough-like behaviour past their acceptance angles, making them suitable for BIPV incorporation. On the other hand, the V-trough concentrator showed better uniformity of flux distribution, this was especially pronounced at lower light angles of incidence. The experimental investigation was carried out on two candidates compound parabolic concentrator and a V-trough reflector on the optical and energy conversion characteristics. Two prototype LCPV systems based on dimensions of the selected concentrators have been manufactured and placed through outdoor testing conditions. The aim was to measure the solar radiation incident at the aperture and the PV cell surface using a pyranometer for times 10:00 to 14:00 equivalent to light incidence angles of -30° to +30°. The analysis of the experimental data showed good correlation with ray tracing simulations, showing similar behaviour with changing light angles of incidence. Experimental analysis showed that CPC had an overall 2.4% higher power output compared to V-trough concentrator. This agreed with the ray tracing studies. Although this was lower than the difference predicted by modelling analysis, this was put down to the non-uniformity of the concentrated light on the CPC absorber area and differences between the ideal and manufactured parabolic reflector. Based on these complexities some future work was recommended.