Environmental impact of thin-film GalnP/GaAs and multicrystalline silicon solar modules produced with solar electricity

摘要

Background, aim, and scope The environmental burden of photovoltaic (PV) solar modules is currently largely determined by the cumulative input of fossil energy used for module production. However, with an increased focus on limiting the emission of CO_2 coming from fossil fuels, it is expected that renewable resources, including photovoltaics, may well become more important in producing electricity. A comparison of the environmental impacts of PV modules in case their life cycle is based on the use of PV electricity in contrast to conventional electricity can elucidate potential environmental drawbacks in an early stage of development of a solar-based economy. The goal of this paper is to show for ten impact categories the environmental consequences ofrnreplacing fossil electricity with solar electricity into the life cycle of two types of PV modules.rnMaterials and methods Using life cycle assessment (LCA), we evaluated the environmental impacts of two types of PV modules: a thin-film GalnP/GaAs tandem module and a multicrystalline silicon (multi-Si) module. For each of the modules, the total amount of fossil electricity required in the life cycle of the module was substituted with electricity that is generated by a corresponding PV module. The environmental impacts of the modules on the midpoint level were compared with those of the same modules in case their life cycle is based on the use of conventional electricity. The environmental impacts were assessed for Western European circumstances with an annual solar irradiation of 1000 kWh/m~2. For the GalnP/GaAs module, the environmental impacts of individual production steps were also analysed.rnResults Environmental burdens decreased when PV electricity was applied in the life cycle of the two PV modules. The impact score reductions of the GalnP/GaAs module were up to a factor of 4.9 (global warming). The impact score reductions found for the multi-Si module were up to a factor of 2.5 (abiotic depletion and global warming). Reductions of the toxicity scores of both module types were smaller or negligible. This is caused by a decreased use of fossil fuels, on the one hand, and an increased consumption of materials for the production of the additional solar modules used for generating the required PV electricity on the other. Overall, the impact scores of the GalnP/GaAs module were reduced more than the corresponding scores of the multi-Si module. The contribution analysis of the GalnP/ GaAs module production steps indicated that for global warming, the cell growth process is dominant for supply with conventional electricity, while for the solar scenario, the frame becomes dominant. Regarding freshwater aquatic ecotoxicity scores associated with the life cycle of the GalnP/ GaAs module, the cell growth process is dominant for supply with conventional electricity, while the reactor system for the cell growth with the associated gas scrubbing system is dominant for the solar scenario.rnDiscussion There are uncertainties regarding the calculated environmental impact scores. This paper describes uncertainties associated with the used economic allocation method, and uncertainties because of missing life cycle inventory data. For the GalnP/GaAs module, it was found that the global warming impact scores range from -66% to +41%, and the freshwater aquatic ecotoxicity scores (for an infinite time horizon) range from -40% to +300% compared to the default estimates. For both impact categories, the choices associated with the allocation of gallium, with the electricity mix, with the conversion efficiency of the commercially produced GalnP/GaAs cells, and with the yield of the cell growth process are most influential. For freshwater aquatic ecotoxicity, the uncertainty concerning the lifetime of the reactor system for the GalnP/GaAs cell growth process and the gas scrubbing system is particularly relevant.rnConclusions Use of PV electricity instead of fossil electricity significantly reduc