Method and sources

Where the site's numbers come from, how the calculator works, and what it cannot do.

How the calculator calculates

Weather: two full years, 2024 and 2025, day by day, at the spot you place on the map. Solar radiation and mean temperature come from Open-Meteo (Copernicus ERA5 reanalysis).
Production: the radiation is brought onto your panels according to their tilt and orientation (Liu and Jordan method), with about 80% real efficiency for heat, wiring, dust and the controller. On freezing days, part of the production is lost depending on the installation (snow on a roof, not on a wall).
Simulation: day by day over the two years, the production, what your appliances use, the battery level, and every generator start when the reserve gets too low.
The proposed size: the cheapest system over 15 years (equipment, fuel, maintenance, lead-acid batteries replaced twice) that meets the chosen level of self-sufficiency. Panel and battery sizes are the ones that really exist at suppliers.
Prices: real products, with their real specifications taken from the manufacturers' data sheets, and the prices shown by suppliers on the day they were checked. A product with no public price is marked “price on request”.

It is not a quote. The numbers are ballpark figures to rough out a project, not an estimate.
It does not count installation, wires, fuses, mounts or taxes. The wire and fuse guides help with that part.
Shade is estimated in three levels (open, a little, in the forest), not measured tree by tree.
Prices move. Each price carries the date it was checked; confirm with the supplier before buying.
Anything touching a building's 120 V or 240 V is an electrician's job. The site replaces neither the electrical code nor a permit.

Open-Meteo, ERA5 reanalysis archive (Copernicus): radiation and temperature.
OpenStreetMap, Nominatim service: address and place search.
Esri, Maxar and Earthstar Geographics: the map's satellite imagery, displayed with Leaflet.
Manufacturers' data sheets: power, voltage, capacity, dimensions and weight of each product.
Suppliers' websites: the displayed prices, checked on the date shown.

Prices checked on October 23, 2026.

The calculation runs in your browser. Nothing is stored with us: no account, no email asked.
Two things leave your browser: the chosen location, sent to Open-Meteo for the weather, and the text you type in the address search, sent to OpenStreetMap.
“Keep the link to my answer” puts your answers in the page address, and nowhere else. Whoever has the link sees the answers.
Your answers stay in your browser's memory so you find them again when you come back. “Start over” erases them.
Fonts are hosted on the site: no call to Google when the page displays.

Solunaire receives nothing for the product links, for now. If that changes, it will be written here and next to the links.
No supplier pays to be in the list. The suggested products are the cheapest of their category at the time of the check, from a real supplier before Amazon.