How much does installing solar photovoltaic (‘PV’) panels reduce domestic electricity bills? Despite over 800,000 households with solar panels in the UK today, we do not have a firm answer to this simple question. This is because the empirical data necessary to calculate solar self-consumption is not widely available; an issue common to many countries. Without electricity metering that records solar PV generation, imports and exports, it is impossible to know exactly how much solar power is being used directly in the household, and as a result, how much solar panels actually reduce electricity bills. As many countries reduce state subsidies, the revenue stream from avoided grid imports (i.e. self-consumption) becomes increasingly critical for the economic viability of PV. Quantifying this potential revenue is also vital for the solar industry to evaluate the potential benefits of battery storage and flexibility services. This paper will help to address this knowledge gap by analysing a previously unused dataset of electricity readings from over 1,300 households with solar panels located across the UK, USA, Australia, Germany, the Netherlands, and Belgium. The results show there is considerable variation in self-consumption between different households, but this is relatively well explained by differences in the amount of solar electricity generated and the amount of electricity consumed during the day (r-squared 0.915), and that the factors affecting self-consumption are similar between the different countries analysed here. The findings will be relevant to regulators for making evidence-based decisions about solar energy policy, provide better information about potential self-consumption to people interested in adopting solar panels, and highlight the importance of improving data availability for ‘behind-the-meter’ micro-generation.