Solar potential in Vienna: does a panel make sense on this roof?
The City of Vienna has calculated every roof in the city from a 25 cm surface model — including the shade cast by neighbours, trees and terrain. This page explains what the figures mean; the address check reads them for one roof.
Most solar calculators start with the roof’s orientation and its tilt. In a city that is the smaller half of the answer: what decides a Viennese roof is what stands next to it. A south-facing roof with a five-storey neighbour eight metres away can be worse than a flat roof three streets on. Vienna measured exactly that — the whole city, from the air, once — and published the result.
Look up your roof →Four classes, and what they mean
A roof is rarely one class. It usually carries several: a very good south pitch, a good east pitch, a shaded strip behind the stairwell. That is why the useful figure is not the average — it is how many square metres lie above the good threshold. A large roof with one perfect surface beats a small evenly mediocre one, and the average hides exactly that.
For the example house on Schrankgasse in the 7th district the cadastre gives 1,138 kWh/m²·a as the roof average, 99 m² in the good and very good classes together, and up to 6 kWp — around 5,700 kWh a year by the rule of thumb. Two houses further on the figures are different, and that difference is the whole point of a cadastre.
Frequently asked
How does the City of Vienna calculate this?
From a digital surface model at 25 cm resolution — a laser-scanned image of the city including roofs, trees and terrain. For every square metre the model works out how much solar energy arrives over a year, with everything that stands in the way already subtracted. That is why the figure differs from a simple orientation rule: the neighbouring building is in it.
What does kWp mean, and what comes out of it?
kWp is the rated output of the array, not its yield. In Vienna a well-built array delivers roughly 950 kWh per kWp per year — so a 6 kWp roof produces around 5,700 kWh. That figure is a rule of thumb: tilt, orientation, module quality and shading move it, and only a planner’s calculation replaces it.
Does this work for a single flat?
Not on your own. The roof belongs to the building, so an array needs the owners’ association — which is exactly why the figure is more interesting before a purchase than after. For a whole house, a Zinshaus or a new development it is a number with money attached.
What does the cadastre not know?
Statics, the state of the roof covering, monument protection, the grid connection and who owns what. It answers one question — how much sun arrives up there — and that question is the precondition for all the others, not a substitute for them.
Where do I see the figure for my address?
In the light check: enter the address, and the roof of that building is looked up in the cadastre — square metres per suitability class, mean irradiation and the possible output. It also lands in the PDF report.
Source: solar potential cadastre of the City of Vienna (2022), calculated from the 25 cm surface model — data.wien.gv.at, CC BY 4.0. Suitability classes as published by the City. The yield rule of thumb (950 kWh per kWp per year) is an estimate, not a measurement. No planning and no offer: statics, monument protection, the owners’ association and the grid connection all have a say.