How SolarClair calculates
Every figure comes from an hour-by-hour calculation over nineteen years of real weather, with published models and dated reference values. This page says which ones, and where the calculation stops.
Weather data
Beam and diffuse irradiance, air temperature and wind, hour by hour from 2005 to 2023, from PVGIS 5.3, the tool of the European Commission's Joint Research Centre (JRC): SARAH3 satellite data and ERA5 reanalysis. The terrain horizon around the address is PVGIS's. The data are read once per location and kept with their retrieval date. SolarClair is an independent service, not affiliated with the European Commission.
From the sun to the panel
- Sun position: NOAA solar calculator algorithm, after J. Meeus, Astronomical Algorithms.
- Light on the panel: beam, diffuse with the Muneer (1990) model used by PVGIS, and ground reflection with an albedo of 0.2.
- Reflections on the glass: Martin and Ruiz (2001) angular losses.
- Module temperature: Faiman (2008) model, with the JRC coefficients for the mounting.
- Power: Huld et al. (2011) model per technology, then PVGIS monthly spectral factors.
- Losses and ageing: 14 % system losses by default, a conservative value; 0.5 % degradation per year, counted separately.
Two parameters are not published by the JRC: the angular loss coefficient (0.155) and the factor applied to the 10 m wind speed (0.7). They are inferred from PVGIS hourly results and labelled "calibrated".
Consumption and battery
Without a meter reading, consumption follows the average French household profile published by Enedis (RES1, 2025, Licence Ouverte), scaled to your yearly total. This profile is smoother than a real home: the share of production used on site may be overestimated. Heat pumps and air conditioning are spread by SDES degree-days (17 °C and 21 °C on the daily mean temperature). The battery charges from the panels' surplus only and starts empty.
A car's consumption starts from its approved WLTP value, measured at the socket, charger losses included: the high value of the version chosen, or of the model. 276 battery and plug-in hybrid models registered in France from 2016 to 2025, from the data of the European Environment Agency (EEA, CC BY 4.0, European Commission, DG CLIMA; 2025 provisional; read on October 31, 2026). Values come from cars of 2020 onwards: before, the range is not reported and the consumption follows the old NEDC cycle. For a plug-in hybrid, the declared consumption is weighted by the utility factor of Regulation (EU) 2017/1151; the site derives the consumption in electric mode and the energy of one full charge, and limits each session to one charge. A missing model is typed in.
Finance
Cash flows are calculated year by year: electricity no longer bought, surplus sold, fees, replacements, loans. The net gain compares the installation with a risk-free savings account, the Livret A, in today's euros. The electricity price stays constant by default, as a precaution. No installation price is assumed: it comes from your quote. Reference values in force:
Validation against PVGIS
205 cases at 30 locations are recalculated and compared with the answers of the official JRC API at every engine change. Accepted deviation on yearly energy: 2 %. Deviation with engine 0.7.0: at most 0.95 %, 0.08 % on average.
| Category | Cases | Max. deviation | Mean deviation |
|---|---|---|---|
| Fixed, crystalline silicon | 84 | 0.95 % | 0.10 % |
| Fixed, CdTe | 16 | 0.20 % | 0.07 % |
| Fixed, CIS | 20 | 0.14 % | 0.07 % |
| Fixed, recent silicon (2025) | 15 | 0.05 % | 0.02 % |
| Trackers (PVGIS yearly calculation) | 32 | 0.13 % | 0.07 % |
| Trackers (PVGIS hourly series) | 10 | 0.08 % | 0.05 % |
| Optimal tilt and azimuth | 18 | 0.31 % | 0.07 % |
| Horizon entered | 10 | 0.16 % | 0.07 % |
Engine versions
Every result keeps the version that calculated it: an old link or report stays reproducible.
- 0.7.0November 1, 2026ADR 0013
Break-even thresholds: the installation cost not to exceed and the electricity price needed; the mean production day, hour by hour.
- 0.6.0November 1, 2026ADR 0028
Each complete weather year gets its own production, to set a quote's promise against the best year since 2005.
- 0.5.0October 31, 2026ADR 0023
Plug-in hybrids: a charging session takes at most one full battery.
- 0.4.0October 30, 2026ADR 0012
The yearly consumption entered includes the equipment given: the national profile carries only the rest.
- 0.3.1October 29, 2026ADR 0014
Heating and air conditioning spread by SDES degree-days, on the daily mean temperature.
- 0.3.0October 29, 2026ADR 0013
Finance: cash flow, net gain, yield, payback, cost per kWh, P90 and battery value.
- 0.2.0October 29, 2026ADR 0008, 0009
Every mounting and the trackers, horizon, CdTe and CIS, optimal tilt and azimuth; 205 validation cases.
- 0.1.0October 28, 2026ADR 0003, 0004, 0005
First hour-by-hour calculation for fixed planes; 20 validation cases, maximum deviation 0.31 %.
Known limits
- No near shading yet: trees, chimneys, neighbouring buildings.
- The "9 years out of 10" range (P90) covers weather only, not model uncertainty.
- Battery ageing before the end of its warranty and income tax on the sold surplus are not counted.
- Reference data for France only; other countries will follow with their own sources.