The calibration and measurement of spectrally resolved terrestrial solar irradiance using a low-cost laboratory grade spectrometer.

This thesis aims to produce methods and tools that allow the acquisition of spectrally resolved data in a low-cost manner from which the calculation of spectral influence on electrical energy production of different photovoltaic technologies can be evaluated. For this purpose it was necessary to design a reliable cosine correcting coupler to reduce the error on the angular reading of the fibre optic which inputs the light to the spectrometers. This work produced a paper that demonstrated an improvement over the state of the art instrumentation for fibre coupled irradiance measurement. The second stage focused on the calibration of the spectrometer for long term outdoor spectral data acquisition. This was achieved using the solar terrestrial irradiance as light source. From empirical data acquired by a pyranometer specific time points with near to clear sky were selected to be later used to produce calibration curves. The low-cost method of calibration presented in this thesis is demonstrated to be reliable for low resolution measurements used for solar spectral characterisation. The spectral time series data acquired allowed a quantitative characterisation of the impact of the climatological conditions of the region on solar irradiance through spectral distributions and clearness indices. The results in spectral variation were used to calculate the influence of the solar spectra difference on the performance for different photovoltaic materials. A small difference in spectral variance was found between seasons, since a-Si presented a gain from summer to winter of +4.0% in contrast to the other technologies which had spectral effects of -5.0%, -5.4%, -6.3% and -7.0% for CdTe, c-Si, high efficiency (HE) c-Si and CIGS respectively. It is shown that the impact of spectral variation is minor when compared with the influence of other performance loss factors such as degradation and temperature, within the UK.