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The rapid growth of photovoltaic (PV) installations in recent years has largely been driven by government incentive schemes that make PV an attractive option for building owners seeking to reduce their greenhouse gas emissions and energy costs. As government incentives are reduced or withdrawn the incorporation of battery storage, to lower building electricity grid imports through increased on-site PV self-consumption, is an option to sustain rooftop PV uptake. This study combines a life cycle assessment approach and discounted cash flow analysis to assess the CO 2 and financial impact of adding battery storage to a PV assemblage in the context of future incentive withdrawal, electricity system decarbonisation and changing technology costs. An example non-domestic building in the UK with a 20 kW mono-crystalline silicon PV and lithium-ion battery storage is modelled. With electricity grid decarbonisation in line with the Paris Climate Change Agreement, the PV and battery system here reduces the building's CO 2 emissions by 17% (19tCO 2 ) compared with the grid-only reference over a 30year lifetime. The analysis also highlights that adding battery storage does not necessarily increase C0 2 savings achieved by PV alone for the building, if grid decarbonisation is considered. PV systems without batteries in the UK are however found to be viable in 2020 without government incentives. For system considered here the battery costs of <£334/kWh available capacity are needed in 2020 for batteries to positively affect the financial performance of PV. The study therefore concludes that UK battery costs have to continue to reduce rapidly, or additional revenue from providing electricity system services is needed to make batteries financially attractive in lower insolation areas like the UK. Policy to reduce electricity system CO 2 through building integrated battery uptake requires better understanding of the net system CO 2 impact in line with other changes in electricity generation and demand. [ABSTRACT FROM AUTHOR]