The electrification of vehicles does not only constitute a revolution in the field of mobility, but could also profoundly transform the electrical system.
A good hundred kilowatt-hours (kWh) stored directly in your garage: that is the unsuspected energy potential offered by your new electric car. To put this figure in perspective, recall that an average Swiss household (composed of 2.23 people) consumes between 3,000 and 4,000 kWh of electricity per year. The electrification of vehicles therefore not only constitutes a revolution in mobility, but could also deeply transform the electrical system thanks to a simple technology: bidirectional charging.
Still limited to certain models, this innovation allows the car not only to draw energy from the grid to recharge, but also to use its battery flexibly to return part of that energy, thus becoming a storage source. In the jargon, this is called V2G (Vehicle-to-Grid), and sometimes more precisely V2H (Vehicle-to-Home) for powering a house, or V2L (Vehicle-to-Load) when it is about powering external devices.
Given that a car spends most of its life parked, this new way of using it is of particular interest. In the sensitive context of the transition to non-fossil energy sources, it is in any case the subject of sustained attention from public authorities. "The reinjection into the electricity grid of energy stored in electric vehicle batteries can improve grid stability, thereby reducing the need for costly investments in additional infrastructure or reserve capacities to manage peak loads," indicates a report published by the Confederation in mid-December 2024.
The first estimates are promising. "Using as a basis an average battery capacity of 60 kWh per electric vehicle in 2035, two million electric vehicles would represent a total capacity of 120 gigawatt-hours (GWh), or nearly half of the maximum usable energy contained in Swiss pumped-storage plants," reads the federal report.
However, Confederation experts qualify this figure, aware that not all vehicles will necessarily be compatible with bidirectional charging. The potential nevertheless remains colossal: "A hundred thousand electric vehicles equipped with V2G technology could already, in theory, quickly inject into the grid a power equivalent to that of the Leibstadt nuclear power plant."
Last summer, the Mobility group unveiled the results of a large-scale test carried out in collaboration with several partners, including the Federal Office of Energy (FOEN). For a year and a half, the car-sharing company operated and tested 50 bidirectional electric cars. The results proved more than conclusive: the vehicles were able to supply electricity within seconds on simple signal from the local grid operator.
"If bidirectional charging is possible within car sharing, it should be everywhere," explains Pascal Barth, electrical engineer at Mobility.
"This experience allowed us to study what is probably the most complex application case: cars parked across Switzerland, with different electricity providers, and that must remain available at any time for shared trips," explains Pascal Barth, electrical engineer at Mobility on the company's website. He is convinced that "if bidirectional charging is possible within car sharing, it should be everywhere."
These mobile storage sources would fit perfectly with the most prominent renewable energy source of the moment: photovoltaics. "Electric mobility could play a decisive role in the future energy system by facilitating better integration of photovoltaic production," confirms the Swiss report.
The concept is relatively simple to understand. When solar panels are producing at full capacity, any excess energy is stored in the car battery, then reinjected into the system after sunset according to daily needs. For households equipped with solar panels, bidirectional charging is not only synonymous with increased energy self-sufficiency, but also a potential source of income.
Beyond a much more optimal return on investment for one's solar installation, the possibility of transforming one's vehicle into a mobile battery could also generate new sources of revenue. Provided the system is adapted, in the case of V2G, the owner could benefit from a reduction in the price of their own electricity, but also from compensation for injecting energy into the grid. In the long term, this would reduce their bill and even slightly offset the purchase of a 100% electric vehicle.
On the Swiss Solar Energy Society website, Karin Schäfer, director of sun2wheel, explains that she amortized her photovoltaic installation and bidirectional charging station in 7.5 years. "With an annual electricity consumption of about 16,000 kWh, we were able to save about 4,500 francs per year in electricity costs," says the head of this young pioneering company in the installation of bidirectional charging stations.
In its report, the government also mentions these forms of monetization, specifying however that the power of a single electric vehicle would be too small to participate in the market. "It would be more appropriate to consider fleets of electric vehicles grouped by an aggregator, who would be responsible for compensating vehicle owners for the use of their batteries."
"With an annual electricity consumption of about 16,000 kWh, we were able to save about 4,500 francs per year in electricity costs," explains Karin Schäfer, director of sun2wheel.
For reasons mainly related to vehicle prices and the cost of installing a charging station, this solution does not yet present a truly sustainable economic model. "For the moment, there is a lack of an economic model to assess the economic impacts of this technology," estimates Mario Paolone, head of the Distributed Electrical Systems laboratory at EPFL.
The experiment conducted by Mobility reached the same conclusion, since the car-sharing company clearly stated that an "economically viable exploitation of this bidirectional technology does not yet exist at present."
Money is not the only obstacle to the current development of bidirectional charging. This technology notably faces a persistent misconception: its impact on battery health. Similar to those who continue to believe that a battery is a major source of pollution, many people fear an accelerated depletion of it.
Research carried out in recent years is nevertheless reassuring, as it has demonstrated the robustness of current solutions. "Modern batteries also have sufficient residual capacity after several hundred thousand kilometers. The battery of a privately owned electric vehicle, so to speak, never needs to be replaced. If it is, moreover, used for bidirectional charging, this increases its total usefulness," write the authors of the federal report.
According to the Touring Club Switzerland, unlike driving, which requires the battery to deliver very high power, bidirectional charging only requires a low discharge capacity. "On the contrary, bidirectional charging even has the potential to extend the battery's lifespan, because it is often in an ideal state of charge," reads the association's website.
The main problem, however, is not ideological but practical. Today, too few electric vehicles are still equipped with the capacity to reinject energy into the grid. The same goes for the number of installations offering this possibility.
"On the contrary, bidirectional charging even has the potential to extend the battery's lifespan, because it is often in an ideal state of charge," indicates the Touring Club Switzerland.
But the law of the market remains the same: if demand increases, supply will follow. On the manufacturers' side, it is highly likely that all future vehicles will ultimately be equipped with software allowing this bidirectionality of electrical flows. As for charging infrastructures, logic suggests the same direction.
This evolution should eventually reduce the pressure on the bills of early adopters and make this technology increasingly attractive. As the Confederation's report states: "A wider diffusion of bidirectional charging and a greater supply of electric vehicles supporting this technology should, however, lead to a strong drop in the prices of suitable charging stations."
This article has been automatically translated using AI. If you notice any errors, please don't hesitate to contact us.
"If the Federal Council is now considering abolishing the program — or at least withdrawing the federal contribution — it is mainly because of the windfall effects it generates," explains Philippe Thalmann, professor of environmental economics at EPFL.
"Today, 70% of our results come from abroad, while 70% of our investments are made in our historic service territory in Switzerland," says Cédric Christmann, Chief Executive Officer of Primeo Energie.
Interview with Philip Mäder, head of media relations at BKW.
At this stage, the investigations reveal an overvoltage problem that led to the failure, but do not yet allow its root cause to be identified.