At the beginning of 2025, violent storms swept across Western Europe. It was not the first such event recently. Does this increase the demands on the stability of solar roof installations?
After all, wind and snow - unlike with ground-mounted systems - is the big challenge. „In terms of wind loads, this does not mean that the average wind speeds are increasing. It's more about the frequency of events such as thunderstorms. These are usually unpredictable,“ says Cedrik Zapfe, CTO of the Schletter Group, a manufacturer of mounting systems.
He also refers to the increase in powerful winds such as tornadoes in recent years. „Including a tornado in the planning is neither possible nor sensible,“ he says. „Because if you wanted to implement a tornado design, the substructures would be incredibly heavy and massive, making it economically unfeasible – apart from the fact that the roofs would reach their limits rapidly with their residual load-bearing capacity. In such cases, you have to accept the residual risk.“
A turbulent wind
A tornado not only causes increased load but also presents entirely different forces to normal wind. Normally, winds pull the photovoltaic installation upwards as well as horizontally. This is countered by its own weight and ballasting. If the wind speed increases, the ballasting needs to increase disproportionately. „If the wind speed increases by ten per cent, the load affecting the system increases by 21 per cent,“ explains Cedrik Zapfe.
Compliance with applicable standards
This principle only applies to normal winds with a high harmonic proportion and few turbulences. By way of contrast, a tornado has far more turbulence, which means that wind forces act on the roof in a completely different way. It is also true that turbulence is also triggered by the under- and overflows in normal winds. However, these are much lower than those of a tornado, making planning ahead of time a seemingly impossible challenge.
Cedrik Zapfe advises that applicable static standards should always be respected. These specify the values for wind and snow loads for the static calculation of a photovoltaic system for each region. „The consequences of climate change are already factored in,“ says the Schletter expert.
While wind and snow load zones cover very large areas, the winds do not blow in the same manner across these vast expanses. As such, extra buffers have to be planned to be able to cover areas within the zones that are confronted with stronger winds. In addition, Eurocode 1, which is valid for Europe, is continuously adapted every three to five years. This affects not only photovoltaics but also the entire construction industry, which works with the same wind and snow load values.
Avoiding planning errors
The standards not only take into account the region in which the system is located, but also the surrounding area. If the building with the solar installation is located in an open landscape or on the outskirts of a town, higher wind loads are estimated than within built-up areas. „The problems are borderline cases and grey areas: In practice, it happens time and again that systems are planned and calculated in a risk class that is too low for cost reasons. In the event of damage, no insurance will pay,“ warns Cedrik Zapfe.
If systems are planned in accordance with standards, the damage will also be recognised by the insurance company. „This is because with consistent structural planning, proof has been provided that the system will last 25 years over its service life,“ emphasises Cedrik Zapfe. „If the service life is shortened, there are two main reasons: Either mistakes were made in the planning or the corrosion protection was inadequate,“ says the Schletter CTO.
Pay attention to corrosion protection
As with all steel structures, mounting systems made of steel also need to be protected against corrosion. Here, the thickness and quality of the anti-corrosion coating are particularly important factors. Special corrosivity maps exist that show how thick the coating of the components – usually a galvanised coating – must be if the system is located in a certain region.
For example, steel components must have a thicker anti-corrosion coating if the system is built in a coastal area or in a region with a lot of industry than if the generator is located in a purely residential area or an open field.
In the first part of our series, you can read about the effects of extreme weather on ground-mounted solar installations. In the second part, we will show you how you can prevent any damage. (su)
