Making the most
of the sunshine.

For each complete day, household electricity (kWh) × that day’s mean grid carbon intensity gives the all-grid comparison. Recorded imports × the same factor gives the grid-import estimate. Dividing grams by 1,000 gives kg CO₂. The supporting carbon figure is the difference between those estimates, summed over the same available days.

Household demand after installation comes from Sigenergy daily totals. Where the Octopus history is connected, imports come from complete smart-meter half-hours; before solar, those imports also represent household demand. Grid intensity comes from NESO’s historical national estimates for Great Britain. We average its half-hourly “actual” estimates over each Europe/London calendar day, including the clock changes. We assume the energy provider’s daily totals follow that same day boundary. We don’t substitute forecasts or fill missing readings with zero.

This first version uses a daily average, not the intensity at the exact time we consumed electricity. It assumes the same household demand without the system. Grid imports include battery charging; battery discharge isn’t counted again as a saving. Energy stored across days and battery losses affect the comparison, so a single day can be higher as well as lower.

This covers electricity-generation CO₂ associated with grid supply. Panel and battery manufacture, other lifecycle impacts, heating fuels and travel are outside this estimate. Export isn’t an automatic carbon offset. The difference is a modelled comparison, not proof of the emissions our installation caused the wider grid to avoid.