Determining the consequential life cycle greenhouse gas emissions of increased rooftop photovoltaic deployment

Increased power flows on electricity distribution networks, caused by growing photovoltaics (PV) uptake, can result in the implementation of solutions to maintain network function. This study takes a consequential life cycle assessment (LCA) approach to assess the greenhouse gas emissions (GHG) of aggregated PV electricity generation at the distribution network level. The study also considers how future changes in the manufacturing phase of Chinese and Malaysian PV modules, over the period of increasing PV deployment, may affect their GHG emissions. The study finds rooftop PV life cycle values of 21-107 gCO2e/kWh, for various UK PV output yield estimates and module types (Chinese made mono-crystalline (c-Si) and multi-crystalline silicon (Mc-Si), and Malaysian made cadmium telluride (CdTe)) installed in 2015. Prospective assessment of proposed future material efficiency and grid decarbonisation reduces the range to 21 to 87 gCO2e/kWh for modules installed after 2030. Consequential life cycle emissions from network solutions to accommodate growing PV generation shows increased GHG emissions attributable to PV by up to 13% (c-Si and Mc-Si) and 17% (CdTe) where 100% of network users connected install rooftop PV. There is however only a negligible increase in emissions if <60% of network users install PV. Voltage control solutions to network constraints caused by PV are found to minimise the contribution of network solutions to aggregated PV life cycle emissions to 2% (c-Si and Mc-Si) and 6% (CdTe) at 100% user uptake. The study concludes that even with network solution for high penetrations of rooftop PV, there is a minimal (<6% with voltage control) increase in PV GHG emissions when assessed at a network level. Future changes in PV manufacturing could offset the effect of network solutions.