Design and performance evaluation of a low concentrating line-axis dielectric photovoltaic system
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This thesis presents a detailed investigation of the design optimisation and performance analysis of a dielectric concentrator for building façade integration at high latitudes (>55°). Considering the seasonal variation of the sun’s position at these latitudes, a concentrating photovoltaic (CPV) system with stationary concentrators of large acceptance angle and low concentration ratio is a suitable alternative to conventional flat plate photovoltaic (PV) modules. A well designed dielectric asymmetric compound parabolic concentrator (ACPC) is a suitable choice to achieve optimum range of acceptance angles and concentration ratio for building façade integration in the Edinburgh and higher latitudes. A theoretical study of the optical performance shows that a truncated dielectric ACPC with acceptance half-angles of 0o and 55o (termed as DiACPC-55) is the optimum design, when compared to the dielectric ACPC designs with acceptance half angles of (0o and 66o) and (0o and 77o) in Edinburgh and higher latitudes. An increase in the range of acceptance angles is achieved by truncating the concentrator profile. Ray tracing simulations show the DiACPC-55 exhibits the widest range of acceptance angles compared to the other designs. The maximum optical efficiency of the DiACPC-55 is found to be 83%. In addition it is found to have a better intensity distribution at the receiver and a higher total annual energy collection, compared to the other designs. Thermal modelling of a CPV system with the DiACPC-55 concentrator shows that the solar cell and rear plate temperature can reach up to 41.6oC for 1000 W/m2 irradiance, when operating with an average ambient temperature of 10oC. The maximum power ratio of the CPV module (fabricated using the DiACPC-55 concentrator) to a similar non-concentrating counterpart is found to be 2.32, when characterised in an indoor controlled environment using a solar simulator. An average electrical conversion efficiency of 9.5% is measured for the entire range of acceptance angles. The optical loss analysis shows that incident light can escape from the parabolic sides and concentrator-encapsulation interface. The outdoor characterisation of the CPV module with the DiACPC-55 concentrator shows that a maximum power ratio of 2.22 can be achieved on a sunny day. In comparison, a maximum power ratio of 1.9 is observed on a rainy day. These results reveal that the designed dielectric concentrator is capable of collecting 68% of the diffuse radiation. The maximum electrical conversion efficiency of the CPV module in outdoor condition is found to be 9.4%. Module degradation due to the delamination of the solar cell is observed in the long term investigation study, which reduces the module efficiency to 8.6% on a clear sunny day. The fabricated CPV system with the DiACPC-55 concentrator is found to be £190.3/m2 cheaper than similar sized conventional glass-glass laminated modules. Therefore the cost of the CPV module is found to be £0.53/Wp cheaper than the conventional glass-glass laminated modules for building facade integration at high latitudes.