Munty Labs
How close is the standard solar estimate to a real roof?
The roof made 20 % more than PVGIS said
20.0 % more
Measured against modelled (an average year)
108 days, 5 July 2026 to 22 Oct 2026, one house
Every solar quote comes with a number. It is how many kilowatt-hours the panels should make in a year. A common source for that number is PVGIS, the European Commission's free solar estimate. It gives an average year, built from the sun over your area from 2005 to 2023.
This house has a 12.96 kWp roof on two faces, east-south-east and west-north-west. PVGIS says it should make 8,843 kWh in an average year. The house's inverter keeps its own daily total of what the roof really made. So the two can be set side by side, day by day.
PVGIS says 3,291 kWh for these 108 days. The roof made 3,951 kWh. The roof made 20.0 % more.
Month by month
- July, from the 5th: PVGIS 1,111 kWh. The roof made 1,474 kWh, 33 % more.
- August: PVGIS 1,051 kWh. The roof made 1,258 kWh, 20 % more.
- September: PVGIS 804 kWh. The roof made 810 kWh, 1 % more.
- October, to the 22nd: PVGIS 326 kWh. The roof made 409 kWh, 25 % more.
Each month's PVGIS figure is spread evenly over its days. A month with only a few days says very little. 2 days in this window left out because the record was incomplete or the panels were off: 4 Aug 2026, 12 Oct 2026.
Why the roof beat the average
- PVGIS is an average year. This was not an average summer.
- So the extra power is most likely extra sun. That is our reading, not a measurement.
What this means for your estimate
- A PVGIS figure for your roof is an average year. A sunny summer can beat it by a lot. A dull one can fall short.
- One summer is not a year. Winter could still pull the whole year back towards PVGIS.
- No model gets every roof right. Shade, dirt and faults it cannot see can take a roof well below any estimate.
One house, not a promise
The roof's figures are measured on one house. PVGIS's figures are an estimate of an average year. Your roof will be different. It depends on the weather each year, shade and how the panels are fitted. Use this as a guide, not a promise.
How it was checked
PVGIS's monthly figures for this roof come from PVGIS's own service, with a standard 14 % allowance for losses. The roof's figures are the inverter's own daily totals. Only days with a full record are counted.
On record: the validation results, entry "E4 — the roof, standard figure: PVGIS beside the certificate", and the inverter's own daily totals as the nightly re-freeze writes them (E3's scored days). Updated each morning, to 22 Oct 2026.