Development of a spectral dependent electrical & thermal model for high concentrating photovoltaic (HCPV) receivers

Abstract

High concentrating photovoltaic (HCPV) systems employ III-V multijunction (MJ) solar cells. Such solar cells are monolithically connected in-series and therefore present a strong dependence on the solar spectrum variations. In addition, the concentrated solar flux contributes to the heat generation within the solar cells and, in combination with the current mismatch between the subcells, can force the device to operate in elevated temperatures. It is important therefore, to investigate the influence of the atmospheric parameters on the electrical performance of HCPV and also to quantify the cooling requirements based on the spectrum changes. In this thesis, a spectral dependent electrical model has been developed to calculate the electrical characteristics and quantify the heat power of a multijunction solar cell. A three-dimensional finite element analysis is also used to predict the solar cell's operating temperature and cooling requirements for a range of ambient temperatures. The combination of these models improves the prediction accuracy of the electrical and thermal behaviour of triple-junction solar cells. The convective heat transfer coefficient between the back-plate and ambient air is quantified based on input spectra. A theoretical investigation is performed to analyse the influence of air mass (AM), aerosol optical depth (AOD) and precipitable water (PW) on the performance of each subcell and whole. It has been shown that the AM and AOD have a negative impact on the spectral and electrical performance of 3J solar cells while the PW has a positive effect, although, to a lesser degree. In order to get a more realistic assessment and also to investigate the effect of heat transfer coefficient on the annual energy yield, the methodology is applied to four US locations using data from a typical meteorological year (TMY3). The integrated modelling procedure is validated experimentally using field measurements from Albuquerque, NM. The importance of the effect of atmospheric parameters on the solar spectrum and hence the performance of HCPV systems is highlighted in this work. The outdoor characterisation provides with useful insight of the influence of spectrum on the performance of a HCPV monomodule and the current CSOC and CSTC ratings are evaluated based on different spectral filtering criteria