Design for energy: Modeling of spectrum, temperature and device structure dependences of solar cell energy production

Abstract

Solar photovoltaic energy generation can benefit from high efficiency, environment specific design. In this work, a model is developed to assess the electrical energy produced by concentrator solar cells during specific time frames with varying realistic weather conditions and cell temperatures. The model is applied to a comparative study of the spectral and temperature sensitivities of efficiency and energy production for tandem junction and spectrally split parallel junction solar cell structures. Direct normal solar spectra in a representative sunny site, Tucson, Arizona are calculated using the SPCTRAL2 model at 15-minute intervals throughout a year with real-time meteorological data input. The corresponding efficiencies of the two devices under 500 times concentration at cell temperatures deduced from thermal modeling with real-time ambient temperatures are computed. Both device structures comprise the same materials, InGaP, GaAs and Ge, and each device design is optimized to standard operating conditions (AM1.5D spectrum and a cell temperature of 25°C). The two devices are compared for their efficiencies and power/energy output at (i) 15min intervals (instantaneous values), (ii) daily and (iii) yearly time spans. Despite efficiency loss due to series resistance that is three times as high as that for the tandem junction, the parallel junction has a higher daily averaged efficiency every single day, and its yearly averaged efficiency is 1.2% absolute higher, meaning an additional annual energy production of 19.2MWh per m2 cell area. Besides energy forecast and assessment, the developed method can be used to obtain optimum solar cell designs for maximum energy production under varying geographical and climatic conditions.