The numbers behind it

How to read this

Every row is built from settled half hours: a meter reading joined to the tariff price in force at that moment, joined to what the inverter was doing. Half-hours is how many went into the row — a month showing fewer than it should have is missing data, and the figure beside it is short by however much is missing.

Would have paid costs the same household demand with no panels and no battery, at the rate actually in force. Total benefit is that minus what was really paid net of export, so it already contains the export earnings — which is why saved on bills and earned are shown separately and sum to it, rather than being added on top.

EV charging is excluded from savings: the charger is grid-only and invisible to the inverter, so its energy costs the same in every scenario and is reported on its own. Heating is not excluded — the radiators sit behind the inverter, so solar and the battery genuinely offset them. Standing charges are excluded throughout; you pay them either way. For this period they came to £16.35.