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What the Solar Simulator cannot know
The calculator makes scenarios comparable. However, it knows neither your building in detail nor the weather of the coming years. Read the result as a guide, not as a guaranteed yield.
Shading is only a flat-rate allowance
Trees, dormers, chimneys, antennas and neighbouring buildings cast shadows that change with the time of day and the season. The slider in the simulator reduces the yield by a flat rate. It does not calculate three-dimensional shadow paths or electrical effects on individual module strings.
A typical year is not a weather forecast
PVGIS TMY data describe typical hourly conditions from a multi-year historical dataset. Real years can be sunnier or cloudier. Long-term climate change and exceptional events cannot be derived from them as an exact annual forecast either.
Local system technology remains simplified
Among other things, the model takes into account module temperature, general system losses and optional inverter clipping. However, it does not automatically know:
- specific module and inverter characteristics, string planning or mismatch,
- cable runs, soiling, snow, ageing and maintenance condition,
- ventilation and mounting type of the modules,
- grid limits, curtailment or local connection conditions,
- structural capacity, fire protection, heritage protection and building regulations.
No economic or consumption advice
The calculated AC yield does not tell you how much electricity is used on site. That requires at least a time-resolved load profile. Battery storage, electricity tariffs, the feed-in tariff, financing, taxes, maintenance and price trends are not part of the yield simulation.
The calculator therefore makes no statement about payback, return or optimal battery size and is not investment, energy or tax advice.
For an investment decision: have the roof, shading, layout, structural capacity, electrical design and grid connection checked by qualified professionals and compare reliable quotes.
How to use the estimate sensibly
- Calculate several plausible variants instead of a single figure.
- Record pitch, azimuth and usable kWp as accurately as possible.
- Compare conservative and optimistic loss assumptions.
- Look at annual yield, monthly distribution and daily curve together.
- Compare the result with an on-site quote and its yield forecast.
More on the calculation method is in the PVGIS methodology. The example calculation for a detached house gives a sense of the orders of magnitude.