sonnendach.ch shows you free of charge how well your roof is suited for solar energy – calculated by the federal government from 3D building data and solar radiation values. In practice: Even the 'good' class is usually sufficient for an economical system. It only becomes binding after a site visit, because the tool does not know the roof condition, superstructures and the actually usable area. (As of: July 2026)
Key points in brief
- sonnendach.ch is a free tool of the SFOE – enter the address, click on the roof area, done.
- The suitability classes range from 'low' to 'excellent' and are based on the annual solar radiation per square metre.
- In addition to the class, the tool shows the area, pitch, orientation and an estimated electricity yield – broken down into the summer and winter half-year.
- The displayed roof area can practically never be fully covered: Chimneys, skylights and edge distances reduce the module area.
- The tool is an initial assessment instrument, not a planning tool. It replaces neither structural nor condition testing.
What is sonnendach.ch and where does the data come from?
sonnendach.ch is the official solar potential map of Switzerland, operated by the SFOE. You enter an address and see how well each individual roof area of the building is suited for photovoltaics or solar thermal energy – colour-coded, from blue ('low') to dark red ('excellent').
There is no estimate behind this, but a simulation: The federal government combines the 3D building data from swisstopo with the radiation data from MeteoSwiss and calculates the course of the sun over the year for each roof area. Shadowing from neighbouring buildings and terrain shapes is included. Since the beginning of 2023, the tool calculates with a module efficiency of 20 percent – which corresponds to today's standard.
For facades, there is also the sister project sonnenfassade.ch, which works on the same principle.
What do the suitability classes mean?
The classes are based on the average annual solar radiation on the roof area:
| Suitability class | Radiation per year | Classification from practice |
|---|---|---|
| Low | under 800 kWh/m² | rarely makes sense – mostly heavily shaded north-facing locations |
| Medium | 800–1,000 kWh/m² | worth examining if self-consumption is right |
| Good | 1,000–1,200 kWh/m² | solid basis – typical for east-west roofs |
| Very good | 1,200–1,400 kWh/m² | very good prerequisites |
| Excellent | from 1,400 kWh/m² | Ideal location, mostly south-facing roofs with favourable pitch |
As of: July 2026, classification according to the SFOE. The current representation on sonnendach.ch is authoritative.
The most important note on this: Do not let the scale deceive you. 'Good' sounds like mediocrity, but it is not – the difference between a 'good' and an 'excellent' roof is often only a fifth to a quarter in terms of annual yield. Whether the system pays off is less determined by the class than by the question of how much of the solar power you consume yourself. The connections are explained in the article Is a solar system worth it in Switzerland?
What information does sonnendach.ch show for your roof?
A click on the roof area opens the detailed view. There you will find:
Area, pitch and orientation. The key data of the roof area as calculated from the 3D model. Why these three values shape the yield – and why east-west roofs are better than their reputation – is shown in the article Orientation and pitch.
The estimated electricity yield. A kilowatt hour figure per year if the entire area were covered with modules. The breakdown into summer and winter half-years is interesting: Those who heat or want to heat with a heat pump should pay attention to the winter value – that is when consumption is highest and production is lowest.
The possible heat yield. This relates to solar thermal energy, i.e. solar collectors for hot water – a different technology to photovoltaics. The two figures must not be confused or added together.
Profitability scenarios. The tool runs through different self-consumption shares and shows rough yield estimates. These scenarios work with flat-rate assumptions for tariffs and prices; useful as an order of magnitude, not as a basis for decision-making.
Where are the limits of the tool?
sonnendach.ch is excellent for the first check – as long as you know what it doesn't see:
The coverable area is smaller than the one displayed. The tool calculates with the entire roof area. In reality, chimneys, skylights, dormers, snow guards and the necessary edge distances are deducted. How many modules actually fit is only shown by the planning – the rules of thumb for this are in the article How many solar modules do I need?
Vegetation is a snapshot. Neighbouring buildings and terrain are reliably recorded in the model. Trees, on the other hand, continue to grow or are felled – the tree that is in the model today can be twice as high in five years. In critical cases, it is worth taking a closer look: Estimating shading correctly.
Condition and statics remain outside. Whether the roofing will last another twenty years, whether the roof will bear the additional load, whether asbestos is involved – the map says nothing about this. On Eternit roofs from the 70s, we first clarify the asbestos question before planning even begins.
Legal aspects are missing. The tool does not recognise core zones, monument protection or inventory objects. In the City of Zurich, the same roof area can be exempt from authorisation or require authorisation depending on the zone.
In addition: The data bases are updated in stages. New buildings are sometimes still missing, and for recently converted roofs the model can be outdated.
In initial consultations, sonnendach.ch is almost always our common starting point – and the most frequent surprise is the area question. On the map, the roof looks large, but after deducting chimneys, skylights and edge distances, noticeably less module area remains than thought. Conversely, we regularly experience owners prematurely writing off their 'only good' east-west roof, even though precisely this profile delivers electricity evenly during the day and accommodates self-consumption. Both can be clarified in half an hour on site.
From the sonnendach check to the concrete project: What next?
A sensible procedure looks like this:
1. Look at all sub-areas, not just the best one. Often the combination of two areas (such as east plus west) results in a better system than the one south-facing area alone. 2. Note the winter half-year value, if a heat pump is present or planned. 3. Estimate rough system size – the sonnendach values together with your own electricity consumption are sufficient for this. The calculation steps: Calculate PV system size. 4. Arrange a site visit. Only on site do the coverable area, roof condition, cable routes and shading become binding – and from this a serious quote is created.
Those who go into the consultation with this preparatory work, by the way, quickly recognise whether a provider works cleanly: A quote without a look at the roof – whether on site or at least based on concrete documents – is a warning signal.
Frequently asked questions
My roof is only 'medium' on sonnendach.ch – is PV still worth it?
More often than thought. The class only describes the radiation, not the profitability. A 'medium' roof with high self-consumption – for example with a heat pump and e-car – can perform better than a 'very good' roof whose electricity is almost completely fed in. The calculation is individual.
Why does the quote differ from the sonnendach yield?
Because the quote calculates with the actually coverable area, concrete modules and the real shading, while sonnendach.ch calculates the full roof area with standard assumptions. If the two values are far apart, ask – a serious provider can explain the difference position by position.
Are trees and neighbouring buildings taken into account?
Buildings and terrain yes, they are reliably depicted in the 3D model. Vegetation corresponds to the status of the last data collection – a tree that has grown or been felled in the meantime is missing from the model. For trees close to the border, we recommend a shading assessment on site.
What does the information on the winter half-year give me?
It shows how much of the annual production falls into the high-consumption season. Pitched roofs with a south orientation perform relatively better in winter because the low sun hits the modules more steeply. For households with a heat pump, this value is often more informative than the annual yield.
Is the tool also available for facades?
Yes – sonnenfassade.ch shows the potential of facade areas according to the same principle. Facade systems deliver less annual yield per square metre, but a higher winter share. In practice, they are an issue for large, unshaded facades without ribbon windows.
Free initial consultation
What does sonnendach.ch say about your roof – and what does the roof itself say?
We look at both: the data situation and the reality on site. Free of charge, without obligation and without glossing over the figures.
Prefer to talk? +41 78 830 83 35
Your photovoltaic system from a specialist company →
Swissolar-certified specialist company · ESTI installation authorisation (Art. 14 NIV) · in Zurich since 2017 · over 150 systems completed · a personal answer from the specialist company, no call centre
Sources: sonnendach.ch (SFOE), swisstopo, MeteoSwiss, geo.admin.ch.
Last updated: 9 July 2026 · Author: ecoEn editorial team
