This is the plain-language summary of a much longer and more technical deep dive, Europe’s most reliably parked power plant keeps different hours in every market. The deep dive carries the full method, 13 charts, the 2030 scenario model and 91 sources. Everything here is drawn from it; if a number needs its footnote, it is there.
Every few months someone announces that Europe's electric cars are a giant battery waiting to save the grid, and that owners will be paid handsomely for letting it happen. We wanted to know whether that is true, so we did the boring thing: we measured how many cars are actually plugged in at each hour of the day, worked out who might pay for them and how much, and then ran the numbers forward to 2030. The answer is that the battery is real, it is mostly parked in the right place at the right time, and it is worth a few hundred euros a year per car. Most of that is a saving on the electricity bill, not an income. Here is how we got there.
First, is anyone actually plugged in?
Nobody meters a parked car, so we used the next best thing. Chargalytics tracks 408 000 public AC charging bays across eleven European countries, and we can see, hour by hour, whether each one has a car on it. Public bays are a minority of all charging, but they are the part we can measure, and they told us something clear: the cars keep three different timetables. In Amsterdam and Oslo, where people park on the street, the car goes on the cable at six in the evening and sleeps there; at midnight one Dutch public bay in five has a car on it, and on Oslo's kerbs it is more than a third. In Stockholm and Helsinki the cars charge at work, so the bays fill at nine in the morning and empty by five. In Switzerland they fill in the daytime and are gone before the evening peak. Which timetable a country keeps is set by who owns the car and where it sleeps, not by the price of electricity.
Night shift: kerbside residential: share of public Type 2 bays with a car, by weekday hour, August 2026
Fixed panel of public AC bays present in both July and August 2026, weekday average, local time. Plugged in = charging or blocked seconds ÷ bays × wall-clock. Norway, Sweden and the Netherlands are corrected for our own measurement caps.
That matters because the grid does not need the cars at just any hour; it needs them at its peak. In summer the peak comes in the evening or, in solar-heavy countries, at midday, and in almost every market the public bays are full at that hour. In the Nordic winter the story flips: the grid peaks on a January morning, and that is exactly when the cars are leaving. Scaling the public bays up to the whole fleet, on assumptions borrowed from charging trials, we estimate that 12 to 20 GW of car charging capacity is on a cable at the August grid peak today. Only a small part of that, 2 to 3 GW, sits in cars that could actually feed power back. By 2030 that capable slice grows to somewhere between 10 and 16 GW. For scale, Norway's entire peak demand is about 25 GW.
Who would pay for it, today?
A plugged-in car can earn money in two places. The first is the grid operator's frequency and balancing markets: the operator pays for the right to call on your battery for a few seconds or minutes when the grid wobbles. The rules for cars to do this already exist in the Nordics, Germany, France, Switzerland and the Netherlands, and Danish cars have been doing it since 2016. The problem is that these markets are tiny. A few tens of thousands of cars would fill the whole of any of them, and big stationary batteries got there first. Sweden's main reserve price is down 91 percent since 2022; Britain's is down 79 percent; Germany has more than twice its need already queued up in batteries. A car nets 150 to 350 euros a year in most markets at last year's prices, about 680 in the last expensive corners, and about 50 once the market is saturated. Every market saturates.
What one bidirectional car nets a year selling reserve capacity, at 2025 prices and at a saturated price, EUR
Modelled: 7 kW bid per car (5 kW in Britain and Norway), 3 000 hours a year on the cable with headroom (the 250 hours a month Elli requires), aggregator keeps 40%. “Saturated” = 4 EUR/MW/h, roughly where Britain has settled and below Sweden’s FCR-D low. Prices: TSO auction results, 2025 averages; French aFRR is the 2025 Energy Pool estimate. No energy payments, no degradation, no metering cost.
The second place is behind your own meter. If your electricity price changes by the hour, the car can charge when power is cheap and run the house when it is more expensive. We built an hourly model of a commuter household in each of the eleven countries, using a full year of real prices. Smart charging alone, just choosing the cheap hours to fill the car, is worth about 150 euros a year. Letting the car also power the house adds about the same again, 144 euros a year in the median market, because a house only uses so much electricity in the expensive evening hours and the battery losses eat part of the gain. Solar panels do not help much: a car that leaves at eight cannot store the noon sun. The one case that pays properly is a building with a car park, where fifty cars can shave the building's peak demand charge; a German office can save 500 to 750 euros per car a year that way.
What a household saves per year with the car as a home battery, by market, EUR, September 2025 to August 2026 prices
Modelled on hourly day-ahead prices for the year to August 2026 (Energy-Charts), a spot-indexed household contract with each country’s energy tax, volumetric grid fee and VAT, a 60 kWh car home on weekday evenings and nights and all weekend, driving 7 kWh on weekdays, 6 kWp of rooftop solar in the “with solar” case. Perfect foresight over each 24-hour window, so an upper bound. Smart charging = shifting the car’s own charging to the cheapest hours; V2H = additionally discharging into the house. Values are the increment each step adds.
Will it get better?
The grid is changing in ways that sound tailor-made for cars. Europe's wind and solar capacity goes from about 650 GW to over 1 000 GW by 2030. Solar produces at noon whether anyone wants it or not, so cheap hours get cheaper and the expensive hours get more expensive; the gap between the two, which is the whole of the home-battery case, has grown five to seven times since 2019 in most markets we track, and Germany went from 69 hours of negative prices in 2022 to 573 in 2025. At the same time the grid is losing the spinning mass of old power stations that used to steady its frequency, so operators need faster responses than before.
The daily spread a car can capture: average gap between the four most expensive and four cheapest hours of each day, day-ahead, EUR per MWh, 2019 to 2026
Chargalytics from Energy-Charts day-ahead prices (bidding zones NO1, SE3, FI, NL, DE-LU, FR, IT-North, CH, ES, GR). For each day the mean of the four highest hourly prices minus the mean of the four lowest, averaged over the year. 2026 to end of August. This is the raw material of behind-the-meter arbitrage before tax, grid fee and VAT.
Two things cut the other way. The frequency problem is being solved with hardware, not with cars: Britain has bought 36 GVA·s of big spinning machines, Germany opened a market for inertia in January 2026 that only transmission-connected plants can serve, and the fast-reserve products a car could bid into stay small. And the stationary batteries keep coming: more than 80 GW are expected in Europe by 2030 against 17 GW today, and they arbitrage exactly the same hours a car would. The Mobility House, the German company that prequalified the first car for grid reserve back in 2018, now makes its money selling tariffs: it pools cars, trades their flexibility in the wholesale market, and gives the driver a fixed price or free charging. That is where the value went.
So what is a car worth in 2030?
Nobody can forecast this precisely, so we ran three scenarios: one where the battery pipeline is built in full and the grid needs little more, one in the middle, and one where the grid gets volatile and half the batteries are late. In all three, the reserve markets in the seven countries with a serious battery pipeline are worth a few tens of euros per car a year by 2030. Only in Norway, Sweden, Finland and Switzerland, where batteries are capped or expensive to connect, does a car still earn a few hundred, and that number measures a rule rather than a business. The home-battery saving goes the other way: it rises with the spread, to 150 to 350 euros a car, and it is the only line that grows with the fleet instead of being divided by every new participant.
What one bidirectional car could net in 2030, reserves plus household arbitrage, EUR per year, three scenarios
Modelled. Reserves: 2025 pool × need growth; price anchored on the 2025 auction result and falling as batteries plus participating cars outgrow need, floor 4 EUR/MW/h; cars take their share, aggregator keeps 35–40%. Arbitrage: today’s V2H saving × spread growth. Scenario parameters and per-country results in the deep dive, Part 4.
Add it up across the eleven countries and cars could take between roughly 40 and 360 million euros a year from the reserve markets in 2030, and 120 to 570 million from household arbitrage. Against 24 million electric cars, that is pocket money per car. Against 10 to 16 GW of capable inverters that cost nothing to build, it is worth having.
What to take from this
If you own an electric car: bidirectional charging is a tariff feature, worth having when the wallbox costs little extra, and not a side business. Expect a few hundred euros a year, most of it as a lower bill. If you run a fleet, a depot or a building with a car park: this is where the real money is, because you own the car, the meter and the peak all at once. If you sell electricity: the cars will come to you through aggregators and tariffs, not through the reserve auctions, and the operators who move first, as Renault and The Mobility House have in France and Germany, set the terms. And if you build grids: the plant exists, it is parked where you need it in summer and not in winter, and it grows with the fleet at no cost to you. The full analysis, with every chart, assumption and source, is in the deep dive.