Parametric modeling of life cycle greenhouse gas emissions from photovoltaic power

From 2007 to 2017, global installed solar photovoltaic power capacity grew by a factor of 50. Practices that were minor, including solar tracking, inverter overloading, and Chinese module manufacturing, became mainstream. Countries including the US and India installed large amounts of solar in warm regions with mean temperatures above 20 °C. The impacts of these developments on greenhouse gas emissions from photovoltaic power have not been analyzed by life cycle assessment in depth. This study helps to fill that gap. A modeling tool is built that integrates photovoltaic life cycle inventories, background emission factors, known physical correlations, and modern photovoltaic performance modeling, including temperature-dependent performance ratios. Using this tool, four novel findings are produced on life cycle greenhouse gas emissions from photovoltaic power, referred to here as carbon intensity. Firstly, reversible temperature effects on modules raise the carbon intensity of silicon photovoltaic power installed in warm regions, including by 10% in the southwestern US and 13% in western India. All temperature effects raise silicon photovoltaic carbon intensity by ∼23% in southern India (from 35 to 43 gCO2e/kWh). Secondly, emission impacts of tracking, relative to stationary mounting, depend on installation location and module type. For multi-crystalline silicon and cadmium telluride modules, respectively, adding tracking changes carbon intensity by −11% and −3% in the southwestern US, and by −4% and +5% in eastern Australia. This dependence on location and module type, and the novel result that tracking can increase emissions intensity, is explained by interactions between tracking energy gain, tracker production emissions, and module production emissions. Thirdly, Chinese manufacturing of multi-crystalline silicon modules emits ∼25% more greenhouse gases than European manufacturing, due not only to higher carbon intensity of upstream electricity, as previously reported, but also to more electricity and fuel input per module produced. Fourthly, inverter overloading as practiced slightly diminishes photovoltaic carbon intensity, by less than 2 gCO2e/kWh. Finally, mainstream photovoltaic power in all its forms has significantly lower life cycle greenhouse gas emissions than fossil power.