Reflections from photovoltaic arrays / solar panels

by Dr. David Hofstetter

1. facts

On January 9, 2023, the Federal Supreme Court handed down a judgment regarding the reflections emitted by a photovoltaic system (solar system) (judgment 1C_686/2021). In dispute were reflections from a photovoltaic system installed on a multi-family house. The plant consists of 18 solar panels with a total area of 35 m2.

After commissioning of the plant, neighbors complained about light reflections of the photovoltaic plant on their balconies. They demanded that the municipality initiate proceedings to restore the legal situation. The municipality then obtained an expert opinion on the solar reflections and issued a decision in which it requested the owners of the photovoltaic plant to restore the lawful condition with regard to the violation of the Environmental Protection Act. For this purpose, the owner had to submit a building application for the elevation of the existing plant as well as a report on the reflection effect or to dismantle the plant.

Against the decision of the municipality, the owners of the photovoltaic plant unsuccessfully appealed to the cantonal administrative court and subsequently to the Federal Supreme Court. The Federal Supreme Court dismissed the appeal.


2. considerations of the federal court

The Federal Supreme Court states that sunlight which is altered, e.g. reflected, by the construction or operation of installations, falls under the concept of radiation according to Art. 7 para. 1 USG and is thus considered an impact in the sense of Art. 7 para. 1 USG (E. 3.1). For the protection against visible light, there is no binding regulation under federal law so far, which is why the authorities applying the law have to directly apply Art. 11 to 14 USG and Art. 16 to 18 USG in compliance with Art. 12 para. 2 USG. In doing so, they can rely on the information provided by experts and specialist bodies (E. 3.2).

Then, in E. 3.3, the Federal Supreme Court comments on the question whether a remediation of the photovoltaic system is indicated if environmental protection regulations are violated. It states that a remediation in the sense of Art. 16 ff. USG is out of the question because the photovoltaic system in question is a system that does not comply with regulations that were already in force when the system was built (original defectiveness). In contrast, remediation under the Environmental Protection Act refers to installations that are older than the regulations they do not comply with (subsequent defectiveness). According to the Federal Supreme Court, even if no remediation of the facility is indicated, this does not exclude the possibility that a condition that does not comply with the regulations must be subsequently corrected. The examination of the subsequent ordering of measures to limit emissions seems particularly appropriate in those cases where the immissions were not foreseen or not fully foreseen when the permit was granted, or where a reliable forecast is difficult. According to the Federal Supreme Court, this applies all the more if no building permit is required for the installation in question (see Art. 18a RPG and Art. 32a RPV for solar installations).

In the case of existing installations that have been legally approved, the principles of the protection of legitimate expectations and legal certainty must be taken into account in particular. The principle of legal certainty can stand in the way of a complete revocation of an order. On the other hand, it does not carry the same weight if the encroachment on the legal position of the affected parties is less severe because the plant can continue to be operated with certain structural or operational modifications.

In the concrete assessment of the reflections, the Cantonal Administrative Court, on the occasion of an inspection on the balcony of the neighbors, considered the light intensity to be extremely disturbing and unpleasant based on their own perception. According to the administrative court, it was impossible to look into the glare and the view had to be averted. According to the expert called in by the municipality, the luminance (measured in candela/m2 [cd/m2]) on the occasion of a measurement on the neighbors' balcony was between 31,000 and 230,000 cd/m2. From about 100,000 cd/m2 onwards, there is so-called absolute glare, i.e. it is no longer possible for the eye to adapt to the light conditions. According to the expert, in the specific case, reflections with a light reflection brightness of far more than 100'000 cd/m2 were present for more than 50 minutes per day and for several weeks, i.e. far more than 30 hours per year.

According to the FOEN's implementation guide "Recommendations for the avoidance of light immissions", in the absence of empirical bases on the nuisance potential of reflected sunlight, it is still necessary to decide on the basis of on-site inspections and the subjective assessment of experts whether a reflection is excessive or reasonable in individual cases. The assessment of the experts consulted is therefore of great importance. Regarding the duration of the glare, the Federal Supreme Court has so far not defined any limits beyond which a disturbing reflection is to be assumed. In the cited judgment, it states with reference to the previous case law in this context that a reflection for a period of four and a half months up to a maximum of 50 minutes per day and with a light intensity of up to 30 % of the sunlight is suitable to disturb persons in their well-being. According to the FOEN implementation guide, exposure times of just under 20 to 30 minutes per day are considered reasonable.

In the facts to be assessed by the Federal Court, the expert came to the conclusion that the duration of the reflection was high above the masses and that an unacceptably high glare occurs on the balcony. He therefore concluded that there was a significant and no longer permissible nuisance caused by light reflections. According to the expert, the glare can only be avoided by turning one's back to the emission point. The Federal Supreme Court left open whether the effects had to be qualified as excessive in the sense of Art. 14 lit. b USG, because in any case precautionary emission limitations were rightly ordered according to Art. 11 para. 2 USG.

As a result, the Federal Supreme Court upheld the ruling of the Administrative Court and thus the procedure of the municipality regarding the order of emission-limiting structural measures (modification of the installation, i.e. change of the angle for reflected sunlight). It considered the costs for the structural measures for the adaptation of the plant as acceptable, whereby adaptation costs of just under CHF 12,000.00 were in question, with construction costs of CHF 25,000.00.


3. conclusion

Conflicts over reflections from photovoltaic systems will inevitably increase in the future because the expansion of solar energy systems on buildings will increase and is now legally required (Art. 45a EnG). Case law on this subject, however, is still developing. It will be interesting to see, for example, how the courts judge the duration of glare in the future, and the fact at which locations the glare occurs. In our opinion, significant aspects are still unresolved here. But the aforementioned decision of the Federal Supreme Court clarifies that absolute glare on balconies of almost one hour per day over several months basically requires measures and that these measures are still proportionate even if they amount - in the case of smaller installations - to almost half of the construction costs.

From a practical point of view, it should be noted that the assessment of the excessiveness of reflections from photovoltaic systems must be carried out by expert opinions. These are of considerable importance because there is a lack of empirical data on the nuisance potential of reflected sunlight. Then the disturbance is to be determined by an on-site inspection. In this regard, the practical problem arises that although eye visits are planned and scheduled for a long time in advance, they can only meaningfully take place when the sun is shining and the reflections occur. This fact can delay the proceedings not inconsiderably.

In order to prevent such problems from arising in the first place, it would probably make sense to check the glare effect as early as the planning stage of the installation and to contractually oblige the company that builds the installation to build an installation that does not lead to excessive glare or glare that can be avoided without great technical effort.