Determining the potential solar electricity and heat yield from your own roof at the click of a mouse - that is the aim of a solar roof register. The Bonn solar roof register, which has been in operation since 2010 and was one of the first in Germany at the time, was replaced at the end of September 2023 by the NRW solar register of the State Agency for Nature, Environment and Consumer Protection (LANUV), which is more modern in many functions and in terms of the user interface.

In addition to a solar cadastre for roof areas, the LANUV also offers a cadastre for open-space photovoltaic potential. The "Solarkataster.NRW" is part of the digital "Energieatlas.NRW", which also contains other online maps, for example on wind energy potential and a heat register. The NRW solar cadastre can be accessed via the following link: www.energieatlas.nrw.de/site/karte_solarkataster

Building-specific roof area potential

As with the Bonn solar roof cadastre, citizens can also use the NRW solar cadastre to query building-specific roof area potential for photovoltaics and solar thermal energy, including the installable output in kilowatts peak and the installable absorber area in square meters, by entering the address or coordinates - with either maps or an aerial photo as a background. Yield calculators are connected, with which the expected solar power yield or heat yield in kilowatt hours per year and the associated lower CO2 emissions can be calculated. It is also possible to make profitability forecasts.
The NRW solar cadastre classifies roof areas suitable for solar modules by color according to south/north/west and east orientation as well as the category "flat roof" (with a roof pitch of ten degrees or less). This makes it easier to create partial area potentials.

Potential for ground-mounted photovoltaics

The NRW solar cadastre also offers detailed maps of the potential for ground-mounted photovoltaic systems - which Bonn would like to enable in the order of 200 megawatts peak according to the climate plan. For example, according to the German Building Code (BauGB), ground-mounted photovoltaic systems are privileged in a 200-meter perimeter strip around Bonn's freeways and railroads - this means that no development plan has to be drawn up, but a building permit is sufficient.
Within a 500-metre perimeter strip around freeways and railroads, ground-mounted photovoltaic systems are eligible for subsidies in accordance with the Renewable Energy Sources Act (EEG-2023), but require a development plan. According to the NRW solar cadastre, Bonn also has potential for agrivoltaics on agricultural arable land and grassland, for example - although this is also subject to the prior preparation of a development plan.

Data basis for the NRW solar cadastre

The NRW solar cadastre was created on the basis of high-resolution laser scan data available throughout the state. This was used to create a comprehensive digital surface model with a resolution of 0.5 meters for the roof area analysis and three meters for the open area analysis. In a second step, data from the German Weather Service was used to calculate the solar irradiation and the percentage shading of the roof surfaces - taking into account the daily and seasonal changes in irradiation. Shading can be caused by trees, adjacent buildings, roof structures or elevated terrain.

Which roofs are suitable?

Suitable areas are roof surfaces on which a solar power yield of at least 650 kilowatt hours per kilowatt peak (i.e. with an irradiation of approx. 814 kilowatt hours per square meter and year) can be expected and which are less than 20 percent shaded. In addition, pitched roof surfaces are at least seven square meters in size. For flat roofs, it is assumed that 40 percent of the area can be used if the roof is elevated to the south. Flat roofs must therefore be at least 17.5 square meters in size in order to be classified as suitable. The LANUV updates the data regularly - the next update for the southwest of NRW, including Bonn, is planned for early 2024.

Structural factors such as the condition and statics of the roof or building cannot be recorded on the basis of solar cadastre data. This requires a separate expert examination in each individual case.