Your electric car may have the biggest battery in the house – why do we only use it for driving?
Electric vehicles could become an important part of the future energy system. The technology to send electricity both ways already exists. But how do we get the car, the home and the grid to work together?
The car, home and grid can work together
Conceptual diagram: solar panels can supply the home and car. The car can charge from the home and, with compatible bidirectional charging, supply energy back. The home can buy from the grid and potentially export if the installation and agreements allow it. No actual measurements are shown.
Imagine coming home from work and parking your electric car in the driveway.
The battery still has a 60 percent charge. That is plenty for tomorrow's driving, yet the car will simply sit parked for the rest of the evening.
Meanwhile, electricity is expensive, the washing machine is running, and the house is buying electricity from the grid.
It seems a little strange.
Because just outside the house there may be a 60, 80 or 100 kWh battery. In many cases, a battery substantially larger than one you would install as a home battery.
Why can't the house just borrow a little electricity from the car?
That is exactly the idea behind V2H and V2G.
And the technology is further along than many people think.
Three ways to use an electric vehicle's battery
Three abbreviations often come up when discussing intelligent EV charging: V1G, V2H and V2G.
They sound technical, but the difference is quite simple.
V1G – the car charges when it makes the most sense
V1G is intelligent charging.
Electricity still flows in only one direction: from the grid or the home's own production to the car.
But charging can be planned around electricity prices, solar production and when the car will be needed again.
If the car needs to be ready at seven the next morning, it does not necessarily need to start charging at five in the afternoon.
It can wait for a cheaper time, if there is enough time available.
This already makes the electric vehicle a flexible part of the home's energy consumption.
V2H – the car supplies electricity to the home
V2H stands for Vehicle-to-Home.
Here, electricity can flow both ways between the car and the home.
When electricity is cheap, or the solar panels produce more than the home uses, the car can charge.
Later, some of the energy can be sent back to the home.
This means the car's battery could potentially cover consumption during expensive hours.
It might be the oven, washing machine or heat pump using the energy.
For the home, it is still just electricity.
But the energy system suddenly has a new opportunity: a large battery that has already been paid for and is parked for a considerable part of the time.
V2G – the car supplies electricity back to the grid
V2G stands for Vehicle-to-Grid.
Here, the car can supply electricity not only to the home, but also to the public grid.
This could be useful when electricity prices are high, for example, or when the electricity system needs flexibility.
Imagine thousands of parked electric vehicles, each able to make a small part of its battery capacity available.
Together, they could represent a substantial energy reserve.
That does not mean every car should be emptied when the grid needs electricity.
On the contrary, the system must respect that a car is first and foremost a means of transport.
But the portion of the battery the owner does not expect to need could, in principle, become a resource.
How much energy is actually sitting in the driveway?
Let's take a hypothetical example.
An electric vehicle has an 80 kWh battery.
A home battery has a capacity of 10 kWh.
That means the car's battery is eight times as large.
Even if the owner only wants to make 10 kWh available to the home, that equals the capacity of an entire home battery.
Of course, this does not mean the car can always replace a home battery.
It must be at home, connected and compatible with bidirectional charging. Energy losses, power limits, battery condition and the next journey also need to be considered.
But the difference in size is interesting.
We already have large batteries sitting in driveways. The question is how to use them best.
80 kWh compared with 10 kWh
8times the capacity
An example day
Illustrative sequence, not a calculated Fluks plan or a price forecast. The car must be connected when used for energy management. Bidirectional operation and export require compatible equipment, installation and agreements, and driving needs come first.
Night
00–06
The car can charge when electricity is cheap, if it needs energy.
Morning
06–09
The home uses electricity, and the car needs energy for the day's driving.
Day
09–16
Solar panels produce electricity. The car can charge from any surplus if it is at home.
Evening
16–22
A compatible car can supply energy to the home if it can spare it and doing so makes economic sense.
Night
22–24
Any export to the grid requires support and must be worthwhile after costs.
The hardware exists – but it is not just a matter of plugging in
Bidirectional charging is no longer just a theoretical idea.
There are already vehicles and charging equipment that support different forms of bidirectional energy.
But that does not mean every electric car with a large battery can automatically supply electricity to the home.
Support is needed throughout the chain:
- The car must allow discharge through the charging connection.
- The charging equipment must handle electricity in both directions.
- The home's electrical installation must handle the energy safely.
- Metering and any export must be set up correctly.
- The car, charger and control system must be able to communicate.
So it is not enough for the car and charger each to advertise modern features.
They also need to work together in the actual installation.
And once the technical side is in place, another question arises: how should the energy be used, and who makes that decision?
When the technology is ready, the rules need to keep up
Although V2H and V2G are technically possible, taxes, grid tariffs and settlement remain a challenge in several European countries.
Imagine charging the car cheaply at night and using that electricity for the washing machine the next evening. How should that energy be taxed if charging was covered by special tax rules?
This is particularly relevant in Denmark, where EV charging has been eligible for electricity tax refunds, while the ordinary electricity tax has temporarily been reduced in 2026 and 2027.
The issue is not only Danish, however. The rules also need to account for electricity being stored, used locally or sent back to the grid – without incorrect double charges.
Source: Danish Tax Agency – temporary electricity tax reduction in 2026 and 2027
But what about battery life?
A natural question is whether V2H and V2G cause extra wear on the car's battery.
And yes, additional charging and discharging can cause additional wear.
How much depends on factors including battery chemistry, temperature, state of charge, power and the number of cycles.
That is why selling electricity from the car is not necessarily a good idea just because the price is high.
The economic benefit needs to exceed the relevant costs and drawbacks.
The vehicle manufacturer's warranty terms may also matter.
This is another argument for intelligent energy management.
Because the best decision is not necessarily to use the battery as much as possible.
It is to use it when doing so makes sense overall.
What if the car is needed tomorrow?
This brings us to something fundamental.
An electric vehicle is first and foremost a car.
If the owner needs to drive 200 kilometers the next morning, using the necessary energy to keep the washing machine running the evening before is not particularly intelligent.
A good energy management system must therefore take the car's expected needs into account.
These can include:
- How much charge the car has in its battery.
- When it is expected to be disconnected.
- How much energy it needs to have available.
- How quickly it can charge and discharge.
- What electricity prices and solar production are expected.
Considering these factors alongside the rest of the home makes it possible to plan energy use more sensibly.
That is the difference between simply switching charging on and off and actually optimizing energy consumption.
Intelligent charging makes sense today
Although V2H and V2G are not yet a straightforward standard solution for every EV owner, you do not need to wait for bidirectional charging to benefit from intelligent energy management.
There is already much to gain from planning when the car charges.
Imagine a home with solar panels, a home battery and an electric vehicle.
If the car needs 20 kWh before the next morning, it may be tempting simply to start charging straight away.
But cheaper electricity might be expected later in the night.
The home battery might hold energy that should be saved for household consumption during expensive hours.
Or there may still be solar production that could usefully be consumed directly.
The interesting question is not how to find the cheapest hour for the car in isolation.
It is how to find the best plan for the whole home.
Where does Fluks fit in?
Fluks was developed to coordinate the home's energy consumption across devices.
Instead of letting the battery, car and heating system each make separate decisions, Fluks works with a combined energy plan.
The system uses available measurements, electricity prices, forecasts and learning about the home's actual behavior.
The aim is that users should not need to know all the technical details to get their devices working together.
The electric vehicle of the future is more than a means of transport
Electric vehicles have already changed how we think about transport.
Perhaps they will also change how we think about energy.
When a large battery is parked outside the house, it makes sense to ask whether it could do more than power the next journey.
The technology makes this possible in more and more situations.
But for V2H and V2G to become commonplace, compatibility, settlement and regulations need to keep up.
We should be able to buy electricity, store it and use it again without becoming experts in electrical installations, tax rules and the energy market.
Because it really ought to be quite simple:
If the car has electricity the house needs, and using it makes economic sense – why should it be so difficult?
Fluks – Your energy. Decides together.