Solar photovoltaics for buildings: Development and performance assessment

Abstract

This thesis studies the design, technological, economic and environmental performances of three low concentrating photovoltaic (LCPV) systems for building application. Non-tracked LCPV systems are identified as viable alternatives to the commercially available flat photovoltaic (PV) panels considering weather in the UK, where the diffuse component of solar radiation is predominant. The studied LCPV systems were comprised of a Compound Parabolic Concentrator (CPC), an Asymmetric Compound Parabolic Concentrator (ACPC) and a V-Trough concentrator. LCPV geometries were designed and simulated using the ray trace module in COMSOL Multiphysics to predict the optical efficiency at various levels of truncation whilst varying the angles of incidence. The geometric concentration ratios of LCPVs investigated were 1.53x, 1.46x, and 1.40x for ACPC, CPC, and V-Trough respectively. The ray trace simulations of the ACPC achieved the highest optical efficiency as compared to the other configurations studied. Furthermore, the thermal modelling of the ACPC concentrator when placed in an enclosure was performed to predict the cooling required to maintain the diurnal operating temperature of the module below the ambient temperature. For an irradiance of 945 W/m2, the average cell temperature of the ACPC module without the effect of cooling was found to be 84.85 °C. The predicted average cell temperature of the ACPC module at a cooling flowrate of 40 m3/h was 30.2 °C. Small scale prototypes of ACPC, CPC and V-Trough concentrators in conjunction with low cost solar cells such as mono-crystalline silicon cell (mono-C Si) and poly crystalline solar cell (poly-C Si) were manufactured and tested under OAI solar simulators. Measurements showed that ACPC concentrator with mono-C Si generated higher power as compared to the other configurations and flat PV panel. An analytical model was developed in this study to predict the annual energy output for the LCPV compared to an equivalent area of the flat PV panels. The measured optical efficiencies at various angles of incidence of the LCPV geometries were inputted to the model for realistic predictions. The analytical model is inputted with the weather data adopted from EnergyPlus weather datasets. Analytical modelling results showed that ACPC concentrator with mono crystalline silicon solar cells (mono-C Si) generated highest energy output per unit area of 177 kWh/m2 as compared to the other configurations. Full scale concentrators consisting of ACPC, CPC and V-Trough in conjunction with mono-C Si solar cells were manufactured, assembled and equipped for the deployment on the roof of a building at Brunel University London. The performances of the prototypes have been monitored every 15 min over 16 months and analyzed on an hourly, daily, and monthly basis. Performance parameters such as reference yield, array yield, performance ratio, electrical conversion efficiency and the generated energy output per unit area have been derived and presented. Payback periods have been estimated considering two scenarios. The scenarios consider LCPV module costs 15% and 35% higher than a flat PV module. Measurements have shown that the ACPC integrated LCPV achieved the highest annual optical efficiency generating the highest amount of electrical energy per unit cell area of 393 kWh/m2 compared to the CPC, V-Trough and conventional flat modules which produced 373 kWh/m2, 331 kWh/m2 and 306 kWh/m2 respectively. One particular conclusion of the study is that the ACPC based LCPVs achieved higher energy output in locations where the diffuse component of solar radiation is predominant as in the case of the UK. Consequently, ACPC based LCPV modules are recommended for the building retrofit in such locations.