Methodology
How the Solar Simulator calculates PV yield
The estimate combines typical hourly weather data with the geometry of your roof and a transparent PV model. The result is a guide in kWh, not an expert yield assessment.
1. Weather data from the EU Joint Research Centre
The precise data source is PVGIS, the Photovoltaic Geographical Information System of the European Commission's Joint Research Centre. For the selected location, the simulator loads a typical meteorological year (TMY) with 8,760 hours. Among other things, it contains global, direct and diffuse irradiance as well as air temperature and wind speed.
A TMY is not a single calendar year and not a forecast. It combines representative months from a multi-year dataset into one typical year. This makes it suitable for long-term comparisons, but it does not represent any particular future weather year.
2. From the location to the module surface
The position of the sun is determined from latitude, longitude, day and time. The horizontal irradiance is then converted to the tilted module surface. This takes into account:
- Roof pitch: 0° is horizontal, 90° vertical.
- Azimuth: 0° is north, 90° east, 180° south and 270° west.
- Direct and diffuse light: Diffuse irradiance reaches the modules even under an overcast sky.
- Ground reflection: A small share of the irradiance is reflected onto the surface from the surroundings.
3. From DC power to usable AC yield
The system size in kWp describes the rated power of the modules under standard test conditions. Real modules heat up; as the cell temperature rises, their output falls. The model estimates the module temperature from irradiance, air temperature and wind and reduces the DC power accordingly.
The specified system losses are then deducted, for example for the inverter, cables, soiling and electrical deviations. An optional inverter limit models clipping. The annual yield shown is the sum of the hourly AC energy in kWh.
kWp and kWh are not the same thing. kWp is the rated power of the system. kWh is the amount of energy produced. Depending on location and roof, a 5 kWp system in Germany can produce roughly several thousand kWh per year.
4. Fine-tuning for Germany and fallback
For locations in Germany, the monthly irradiance is additionally aligned with the DUETT climatology 1991-2020 of the DWD (Deutscher Wetterdienst, Germany's national weather service). If PVGIS is temporarily unavailable, the simulator can use a simplified climatological model. The interface explicitly labels this quick estimate.