Performance analysis and characterisation of a high concentrating solar photovoltaic receiver
Maka, Ali Omar Mohamed
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Solar energy is deemed to be one the most efficient and clean energy resources to generate electricity. Photovoltaic technologies have a promising future in space and terrestrial applications. Photovoltaic concentrating is a technique to increase the conversion efficiency of high-efficiency solar cells. Multi-junction solar cells are designed to exploit a larger range of solar spectrum photons and convert to electricity. In this study, triple-junction III–V solar cells compound consisting of GaInP/GaInAs/Ge semiconductor materials is considered. This work investigates terrestrial multi-junction solar cells performance characterisation, which is important for the design of high concentration photovoltaic systems. The research has developed a model of a III–V solar cell operating at high flux conditions induced by light concentration. The thermal management on such an assembly is a focus of this work. This research also presents the effects of Air Mass (AM) on solar cell performance. This atmospheric parameter has a strong influence on the behaviour of high concentrating photovoltaic solar cells. As air mass increases, the corresponding Direct Normal Irradiance (DNI) and Cell Temperature (Tc) decrease. The effects of air mass (AM =1–10D) atmospheric changes on triple-junction solar cells have been assessed. For High Concentration Photovoltaic (HCPV) the light concentration on to a relatively small solar cell area leads to high power densities. Effective thermal management is essential to avoid damaging high temperatures. A thermal model by using a convergent iterative technique has been developed; the predicted convergent cell temperature limit is ≤ 80oC. The proportion of the incident radiation not converted to electricity leads to the generation of heat; this is a function of material temperature coefficients and current mismatch in variable atmospheric conditions and results in an increase in cell temperature. The rate of heat loss by convective transfer is also considered for air mass values AM =1.5, 4 and 8D. In addition, a Finite Element Method (FEM) model is developed in COMSOL Multiphysics® in order to predict the temperature distribution of the PV cells and thermal behaviour of the receiver assembly. Furthermore, in this study, a transient model of the HCPV cell has been developed using MATLAB® Live-Link with COMSOL Multiphysics. In order to characterise the behaviour of a triple-junction solar cell, it is essential to find the transient cell operating temperature. The behaviour of electrical parameters of the Jsc, Voc, FF and conversion efficiency are considered. However, in the proposed model, a dynamical efficiency is compared with constant efficiency and the error is about 12%. The research has given a better understanding of the overall daily/annual performance prediction of CPVs and is important for future system design in variable environment conditions. At higher values of DNI, Tamb and lower AM the thermal response needs enhanced/forced convection to maintain cell operation within/below safe operating temperature and to optimise energy yield. For long-term performance evaluation, the average of monthly variations of atmospheric parameters throughout the year is considered. Thus, during the summer months, a higher record of the atmospheric parameters values in which need more consideration. The annual cell operating temperature of ˃ 80oC represents about 13% of the time, which happened during the Summer season. As is noted, the cell temperature between 65 – 70oC is predominate in the Spring and Autumn seasons and represent about 24%, (the highest frequency).