Solar roof check: what your roof can really deliver, based on official data instead of estimates

"Your roof has room for 200 kWp" is not an analysis but an assumption, as long as nobody has calculated geometry, orientation and irradiance. The difference between an estimate and an analysis lies in the data sources. Two of them are official, freely accessible, and make a roof check verifiable.

Source 1: The LoD2 building model of the state surveying authorities

The German state surveying authorities (Landesvermessung) maintain 3D building models in the LoD2 standard ("Level of Detail 2"): every building with its real roof shape, ridge direction, pitch and height, captured through airborne laser scanning. For a roof check, LoD2 provides:

• the actual roof geometry instead of a rectangle assumption derived from an aerial photo,
• pitch and orientation of every roof segment, decisive for the yield per module,
• structures such as dormers and offset roof levels that reduce the usable area.

The geometry determines the module layout: how many modules fit in which orientation, minus edge clearances and maintenance walkways. The result is a kWp figure with a documented derivation instead of a rule of thumb like "one kWp per seven square meters".

Source 2: PVGIS for irradiance

PVGIS (Photovoltaic Geographical Information System) is the yield calculator of the European Commission: long-term satellite irradiance data, location-specific, corrected for pitch and orientation. For the same roof area, PVGIS delivers the specific yield in kWh per kWp per year; in Germany, typical values range between 900 and 1,100 kWh/kWp, depending on location and roof position.

Together, LoD2 and PVGIS produce the core statement of every roof check: this many kWp fit on the roof, this many kWh they deliver per year. Both sources are public, and every figure can be recalculated.

What official data cannot see

A serious roof check also names the limits of remote analysis:

1. Structural capacity. LoD2 knows the roof shape, not the load reserve. Whether the roof can carry the additional load is determined by an on-site structural assessment.
2. Roof condition. The age and condition of the roof membrane decide whether a refurbishment belongs before the installation.
3. Grid connection. The available connection capacity limits the project regardless of the roof potential. The grid connection request to the distribution network operator (Verteilnetzbetreiber) belongs at the start of the project.
4. Detailed shading. Trees and neighboring buildings are only partially represented in the model; the detailed analysis adds a shading simulation.

Anyone who gives you a yield commitment without these four points is selling an estimate as an analysis.

From potential to a bankable number

For the investment decision, and even more so for financing, the potential figure alone is not enough: banks expect a robust yield forecast, a cash flow model and verified project parameters. NEXA ONE therefore carries the roof check directly into the economics: yield forecast from LoD2 and PVGIS, load profile matching, then a comparison of the three operating models NEXA Own, NEXA Lease and NEXA Zero, with an explainable score for each property. What the numbers mean economically is covered in the article Is photovoltaics worth it for commercial roofs in 2026?, and the remuneration side in the overview of the feed-in tariff 2026.

The roof check for your property is free of charge: enter the address, receive the result with a full derivation. Start the analysis