Modelling the impact of spectral irradiance and average photon energy on photocurrent of solar modules

Photocurrent generated by a solar cell depends on environmental conditions as well as electrical and technological parameters of the cell. During this research, a holistic assessment of the performance of solar cell technologies is performed. Measurement of the solar spectrum is carried out from sunrise to sunset using a calibrated spectrometer. Temporal variations in the solar spectrum, spectral content and average photon energy (APE) are discussed. A model is developed to assess the impact of spectral irradiance and temperature on photocurrent from planar pn junction cells. Effect of irradiance, temperature and average photon energy on the photocurrent generated by a poly-Si solar cell is simulated and analysed. Discussions on the performance of other cell technologies are also made. Results show that the APE was 1.94 eV for the 300-1050 nm bin, 1.91 eV for the 350-1050 nm bin and 1.84 eV for the 400-1050 nm wavelength bin of the AM 1.5 solar spectrum. At low intensity of light, the solar spectrum is rich in photons within near Red - IR wavelengths and hence the APE is 1.75 eV. The APE then increases proportionally with an increase in irradiance until a saturation level is reached at approximately 1.95 eV when irradiance exceeds 700 W/m2. Photocurrent is computed for varying spectral irradiance and temperature conditions. First, at low irradiance levels when the solar spectrum is rich in photons from Red-IR regions, the photocurrent is linearly proportional to the APE. Secondly, as the intensity of light increases and Visible-UV components of light increases, an exponential relationship between the photocurrent and APE is exhibited.