Energy balances for photovoltaic modules: status and prospects

Previous work has demonstrated that photovoltaic modules are net energy producers. Based on empirical analysis of utility bills and production records at Siemens Solar Industries, energy payback time for crystalline silicon is of the order of three years and for thin film copper indium diselenide ranges from ten years in research mode to under two years in production. About half of the energy content is process energy, half is embodied energy in incoming raw materials. This paper explores the energy balance implications of ongoing and longer-term development efforts. Future prospects for both crystalline silicon and copper indium diselenide are discussed, including production scale and yields, new processes and equipment, waste reduction and reclamation, of existing equipment reconfiguration, and product design.