Intermittent and non-dispatchable, renewable energy sources can cause sudden and significant variations in production, creating imbalances between supply and demand on the electrical grid.
As part of the ongoing energy transition, one problem repeatedly arises among the concerns of actors in the sector: what to do with surplus solar energy, particularly common during summer peaks? The rapid development of photovoltaics poses a real management challenge because of its intermittent nature.
Renewable energies are indeed intermittent and non-dispatchable, their production being dependent on often uncertain weather conditions. This can lead to sudden and significant variations in production, creating imbalances between supply and demand on the power grid. This situation constitutes a real challenge for the integration of renewable energies, requiring appropriate flexibility solutions to ensure a stable, balanced and reliable electricity supply.
At this stage, no truly optimal solution has yet emerged to absorb these massive volumes of electricity produced in summer. In the event of excess production and in the absence of sufficient demand, this electricity must be evacuated, or even destroyed. This is then referred to as "wasted energy", that is to say energy produced but not utilized.
One of the main challenges lies at the network level. In Switzerland, they are not yet sufficiently adapted to absorb the growing volumes of solar electricity. Heavily stressed, they will need to be developed and reinforced according to future needs — an adaptation that is costly, with annual expenditures likely to more than double by 2050, rising from 4 to 9 billion francs per year.
One of the increasingly serious options under study is the curtailment of installations. "Even curtailing 3% of the annual production of PV installations leads to a reduction in costs," indicates AES. In its static form — consisting of permanently limiting production to a certain percentage of installed capacity — this measure would already save 2 billion francs by 2050. And in the case of demand-based, so-called dynamic curtailment, costs are reduced by an additional half-billion.
"Overflow is a device that, once connected to the electrical grid, allows the grid to be regulated while recovering wasted energy as heat," explains Luca Juillerat, venture builder at Romande Énergie.
"This option of throttling installations is clearly not optimal, because it amounts to throwing energy in the trash," deplores Luca Juillerat, venture builder at Romande Énergie. Together with his employer, he wanted to give a second life to this wasted energy.
In recent months, he has thus developed a solution called Overflow. "It is a device that, once connected to the electrical grid, allows the grid to be regulated while recovering wasted energy as heat. Decarbonized, this heat can then be used by infrastructures such as public swimming pools, thermal baths, agricultural greenhouses or industries with high heat consumption, such as cement plants," he explains.
With the support of Swissgrid, Romande Énergie intends to help strengthen the flexibility necessary for the integration of renewable energies, and to avoid excessive destruction of wasted energy.
Converting excess electricity into heat represents one solution among others currently being explored in the field of storage — a strategic lever in Switzerland, notably to cope with the winter months during which the country remains structurally deficient and dependent on electricity imports.
The alternative most seriously considered is batteries. To date, available technologies, notably lithium-ion batteries — the most widespread in Switzerland — offer short-term solutions, but remain costly.
Electric vehicles could also play an important role in storage, provided that infrastructures evolve to allow bidirectional charging, that is to say the possibility for cars to return electricity to the grid when they are not in use.
For long-term storage needs, hydrogen is a promising avenue, particularly in its so-called "green" version, produced from renewable energies — unlike "gray" hydrogen, still largely dominant, derived from fossil energies.
Hydrogen could help strengthen the security of energy supply. "It can be used to produce electricity and feed the grid with CO₂-neutral power during the winter, when the supply situation is tight," note the experts in a report by the Federal Office of Energy (OFEN) published at the end of 2024.
However, one of the main obstacles lies in its low overall efficiency: a large portion of the energy is lost between its production, storage and reconversion into electricity. Added to this are the logistical challenges related to its transport, due to its lightness, flammability, and the high pressures required to store and move it safely.
Ultimately, the best solution for Switzerland's energy future could simply lie at a scale no longer national, but local. Called Local Energy Communities (CEL) or Groupings for Own Consumption (RCP), these structures make it possible to pool electricity production between several households or buildings and to optimize the use of solar energy in the immediate vicinity of its production. This approach favors collective self-consumption and helps smooth production peaks.
Although these initiatives are still not widespread in Switzerland, there are already some notable examples such as the participatory Solar Exchange of Renens. This one allows residents to collectively finance photovoltaic installations on local roofs, even if they do not own a roof themselves.
Another concrete example is in Lugaggia, in Ticino, where a self-consumption community brings together 18 houses equipped with solar panels, heat pumps and a shared battery. The whole is managed by blockchain technology, allowing the optimization of local energy management.
These projects demonstrate that solar communities offer a concrete solution to strengthen energy autonomy, involve citizens and accelerate the transition to renewable energies. With the improvement of the legal framework — CELs will be authorized in 2026 — one can expect a gradual generalization of these initiatives in the years to come.
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