"By constantly looking at the surfaces that could still accommodate solar installations, we may be overlooking one possibility: roofs that are already equipped," points out Alban Bitz, director of SI-REN.
For fifteen or twenty years, solar has been advancing all over Switzerland. On schools, public buildings, industrial halls, shopping centers, or apartment blocks. And that’s a good thing.
During all those years, we mainly looked for available roofs. Large ones first, of course. A few thousand square meters well oriented, a suitable structure and an electrical connection nearby were then the ideal playground.
Those large roofs still exist, and there is a lot to be done in terms of photovoltaics in Switzerland. But the easiest to equip and the most interesting are now well covered, especially in regions that took an early lead in solar energy.
So we started to look elsewhere: building façades, parking lots, agricultural surfaces, various infrastructures and smaller or more complex roofs. But by constantly looking at surfaces that could still host solar installations, we may be overlooking one avenue: roofs that are already equipped.
Among investors and operators who got into photovoltaics relatively early, some plants have now been operating for well over ten years and are even approaching twenty. They continue to produce energy satisfactorily, and there is obviously no question of sending them to the scrap heap simply because they have several years on the clock.
But photovoltaics has evolved a lot. Take a simple solar panel: in the early 2010s, a 200 to 250 Wp module was quite common. Today, some reach 500 Wp without their surface area having doubled.
So, let’s take out the calculator! A 1.5 MWc plant installed about twenty years ago. With the modules available today, the same roof could, for example, accommodate a capacity of 2.4 MWc. Without using an additional square meter, annual production could thus increase by about 60%, or nearly 900,000 kWh more, at comparable energy yield.
A roof equipped fifteen to twenty years ago has not exhausted its solar potential. Far from it. But its efficiency has clearly declined, on the order of 0.5 to 1% per year, with variations depending on technologies and operating conditions. This is where repowering comes in: modernizing an existing plant by assessing what still works, what must be replaced and, above all, what could be produced today on the same surface.
With an existing plant, you’re not starting from scratch: you know the roof and the owner, you have the production history and a relationship of trust is already in place.
This issue will become all the more relevant as installations supported by the cost-covering remuneration for injected electricity (RPC) reach the end of their support period. For years, their economic model was fairly simple: they produced electricity and benefited from a pre-set remuneration tariff.
At the end of this period, operators can simply continue operating and sell the electricity produced under current market conditions. However, it would be worthwhile to anticipate this deadline by assessing the profitability of the installation in light of its yield and its operating and maintenance costs. It would also be useful to estimate the site’s energy needs for the coming years and to examine the feasibility and benefits of a storage system.
Developing a new solar plant requires a lot of work. You have to find a roof, contact its owner, convince them, study the building, negotiate a contract, check the load-bearing capacity of the structure, obtain permits, plan access and find a grid connection solution. And sometimes, after several months of work, the project simply does not come to fruition.
With an existing plant, you’re not starting from scratch: you know the roof and the owner, you have the production history and a relationship of trust is already in place. Of course, that doesn’t solve everything. If you increase capacity, the grid will need to be able to cope and the building structure must be checked. While standards have evolved, the roof waterproofing has also aged.
On paper, the equation seems almost too good. Panels are much more powerful than fifteen years ago. You remove the old ones, install the new ones and produce much more. In practice, of course, it’s a bit more complicated. Module dimensions have also evolved (they are about 20% larger today), which may require adapting the mounting system and the supporting structure.
Repowering will therefore not replace new installations: it will complement them. And this contribution will be welcome!
The operation seems obvious. Environmentally, however, it deserves reflection. Because old panels do not stop functioning at the end of their RPC support period nor simply because they are dismantled. And the manufacture of new modules obviously has an environmental impact. The right reflex is therefore not to systematically replace a plant as soon as more efficient panels arrive on the market. One must weigh the expected production gain against the remaining lifetime of the existing installation.
One must above all ask: what becomes of the old panels? If they can be inspected and then reused on sites where space is less constrained, repowering takes on another dimension. The most favorable roof hosts modern modules and produces more, while the old panels continue their life elsewhere.
Unfortunately, the low price of new panels complicates the profitability of the second-hand market. The challenge of repowering will therefore also be that of the circular economy. And in this area, there is still significant room for improvement.
Ultimately, there remains a significant potential for solar to be built in Switzerland. According to a study by FOEN published in 2024 and cited by Swissolar, roofs and façades could produce about 75 TWh per year. The association estimates that annual solar production could reach 10 TWh in 2026. Repowering will therefore not replace new installations: it will complement them. And this contribution will be welcome!
So, before always looking further afield, it may be worth going back to where it all started. To look at those first plants and ask a very simple question: if we had to build this installation today, what would we do differently? The answer could well open a new chapter for Swiss solar.
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