Mitigating the uncertainties in life cycle assessment of photovoltaic cells

Abstract

LIFE cycle assessment (LCA) of photovoltaic (PV) electric power generation investigates the energy requirement over the whole manufacturing and operational phases. Existing LCA results of PV have been based on process LCA method which considers the material and energy flow on physical level. This method has an obvious shortcoming of limited boundary. Many processes over the life cycle of PV are excluded from the process LCA, such as producing chemicals, manufacturing facilities and equipment, services and transportation. This paper proposes a step-by-step hybrid LCA method to mitigate the error induced by process LCA of PV. Besides the energy requirement analyzed by process LCA, there are energy requirements analyzed by economic input-output (EIO) LCA. In EIO LCA, the energy requirements fall into two categories--additive and remaining value. The gross energy requirements (GER) from the hybrid LCA result is 3240MJ/m2 for multi-crystalline silicon PV module. This result is higher than previous results: 2300MJ/m2 [1] and 3600MJ/m2 [2]. It is not surprising, because the hybrid LCA covers the whole spectrum from direct energy requirement in manufacturing process, embodied energy in chemicals and equipments to transportation and services, as well as the energy requirements in upstream manufacturing process. While the LCA results of previous study are from process analysis with a limited boundary.