Shading that did not exist during planning usually develops gradually – growing trees, more rarely a new building. It can be recognised in the annual comparison of yields before it is taken seriously by eye. Solutions range from pruning to technical adjustments and talking to the neighbour – on the other hand, an enforceable «right to sun» exists only within narrow limits. (As of: July 2026)
Key points in brief
- Subsequent shading is a slow-motion problem: barely visible per year, clearly measurable over five years.
- The yield comparison over several years discovers it more reliably than looking from the garden.
- Even the shadow on a few modules can have a disproportionate effect depending on the wiring.
- Your own trees are the simplest building site; with the neighbour, the conversation counts first, the law sets narrow limits.
- Technically, a lot can be cushioned – optimisers and rewiring – but none of this replaces light.
How do you recognise subsequent shading?
The tricky thing about growing trees: No one notices two per cent less yield per year. After five years, there is a noticeable lack of production, but the tree looks like it «always has». Therefore, the most reliable path is via numbers instead of appearance:
1. Compare annual values. Those who note their yields – as recommended in the annual check – will see a creeping downward trend that cannot be explained by weather years. For classification: The normal ageing of modules is well below one per cent per year (degradation); a multi-year trend above this has a different cause. 2. Look at monthly profiles. Shading rarely affects all months equally. A tree in the southeast mainly depresses morning production, low winter sun lengthens every shadow – if the winter yield drops disproportionately, this is an indication. 3. String comparison where possible. If the monitoring app shows individual strings, the comparison reveals which roof area is affected (Measurement and monitoring). 4. Observe shadow progression. On a sunny day, take a photo of the roof in the morning, at midday and in the afternoon – repeated three times a year, this results in simple, meaningful documentation.
Why does partial shading have a disproportionate effect?
Modules in a string are connected electrically – the shadow on one module can therefore depress the output of the whole string depending on the wiring, similar to a kink in a garden hose. Modern systems mitigate this with bypass diodes and thoughtful string planning; how strongly the effect punches through depends on the specific system. The technical basics for this are in the article Assessing shading correctly.
Practically this means: A small, new shadow in the wrong place can cost more than a large shading taken into account during planning. That is exactly why it pays to take changes in the environment seriously.
What options do you have with your own tree?
The simplest constellation: The tree is on your own property. Then it is a trade-off between tree and yield – with two notes from practice:
Pruning before felling. Often it is enough to thin the crown or maintain the critical height; a regular cut is cheaper than years of reduced yield.
Observe municipality rules. Tree protection is regulated locally – in quite a few municipalities, felling and sometimes even heavy pruning of certain trees require a permit. A call to the municipality before the chainsaw saves trouble.
And if the tree belongs to the neighbour?
First adjust expectations here: There is no general, enforceable right to unshaded solar irradiation in Switzerland. The neighbour law does have rules on plant distances and heights – they vary by canton and can give rise to claims depending on the case. But those who start with the legal situation instead of the conversation have usually already lost: proceedings take time, cost money and poison the relationship at the fence for years.
The proven sequence is:
1. Seek the conversation early – ideally before the shadow hurts. Many neighbours simply do not know that their tree hits a system. 2. Be specific instead of demanding. A proposal («Thin the crown by two metres, we will share the costs») is received differently than a complaint. 3. Document in case it does get formal: Yield data, photos, date of the conversations. 4. Have the legal situation checked, only if nothing works – distance rules and limitation periods differ by canton; this is a case for legal advice, not assumptions.
For the new building next door, something similar applies more soberly: Anyone who builds in conformity with zoning is allowed to do so – even if your system is in the shadow afterwards. All the more important to follow planned building projects in the neighbourhood early and to take a look during the public notification procedure.
What can be done technically?
If the shadow remains, there are adjusting screws – with honest classification:
Retrofit power optimisers. They decouple the modules electrically from each other, so a shaded module drags the others down less. The most effective retrofitting for clearly defined partial shading; they are not a substitute for sun either.
Rewire strings. Sometimes the wiring can be adjusted so the shaded modules form their own string and no longer brake the rest. A manageable intervention for the specialist company.
Relocate modules. For heavily affected single modules, moving them to another roof surface can make sense – an individual calculation shows whether this pays off.
Which of these works for your system depends on inverter, wiring and shadow pattern – it's an hour of analysis, not a catalogue decision.
The classic in the region are trees that seemed harmless during installation and ten years later take half the morning sun. What is striking is that the cases that end well almost always have the same beginning – the system owner came with annual figures instead of a suspicion, and the neighbourly conversation took place before the annoyance was big. One case from a consultation remains in memory: The solution in the end was neither legal nor technical, but a jointly paid tree pruning – a fraction of what optimisers would have cost.
Frequently asked questions
Do I have a right for the neighbour to cut his tree?
A general right to sun does not exist. The cantonal neighbour law has rules on distances and heights of plants, which can give rise to claims in individual cases – whether this applies to you is clarified by legal advice. The practically more successful path is almost always the early, concrete conversation.
Is retrofitting optimisers worthwhile?
For clearly defined partial shading frequently yes, as a blanket rule no. Crucial is how many modules are affected and how the system is wired. We calculate this through based on your yield data before we recommend anything.
How much yield does a growing tree cost?
This ranges from negligible to a noticeable double-digit percentage share – depending on direction, distance and season. It becomes measurable via the annual comparison; estimable via an on-site shading analysis.
The tree is on municipality land – who do I contact?
The municipality, usually specifically the civil engineering or parks department. Here too: documented yield data and a concrete proposal accelerate the matter more than a general complaint.
Can I do anything about a planned new building next door?
During the public notification procedure you can view the project and submit your objections; zoning-compliant building can generally not be prevented with this. It is more realistic to technically adapt your own system afterwards – or to include the shading in the planning beforehand.
Free initial consultation
Shadow where there was none?
We analyse your yield data, assess the shading on site and show which adjustment pays off – and which does not.
Prefer to talk? +41 78 830 83 35
Have a photovoltaic system installed →
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: EnergieSchweiz, Swissolar, ecoEn consulting practice.
Last updated: 9 July 2026 · Author: ecoEn editorial team
