A comparative study on life cycle analysis of 20 different PV modules installed at the Hokuto mega-solar plant

The purpose of this study was to identify a suitable type of mega-solar system from an environmental viewpoint. The authors evaluated six types of 20 different PV modules by life cycle analysis (LCA) with actual equipment data and output. The types were single crystal silicon (sc-Si), amorphous silicon (a-Si)/sc-Si, multicrystalline silicon (mc-Si), a-Si, microcrystalline silicon ( μc-Si)/a-Si and CIS. The boundaries of LCA were from the mining stage to that of waste management. Mining, manufacturing and waste management information was taken from an LCA database, while data on transport, construction and amounts of equipment were obtained from actual systems. Since the irradiation figures and electricity output were also actual data, we could avoid the difficulties of making assumptions for values such as the actual output power of thin films. In addition, installation at a single plant provided suitable conditions for comparing PV systems. The results showed an energy requirement ranging from 19 to 48 GJ/kW and an energy payback time of between 1.4 and 3.8 years. CO₂ emissions were from 1.3 to 2.7 t-CO₂/kW, and CO₂ emission rates ranged from 31 to 67 g-CO₂/kWh. The multicrystalline (mc-Si) and CIS types showed good results because mc-Si and CIS PV modules have high efficiency and a lower energy requirement. In particular, the CIS module generated more electricity than expected with catalogue efficiency. The single crystal silicon PV module did not produce good results because, considering their energy requirement, installed sc-Si PV modules do not have high efficiency. However, the operation data used covered only 1 year; data from a longer period should be collected to obtain long-term irradiation figures and clarify degradation.