Bidirectional charging: The e-car as an electricity storage unit for your home
With bidirectional charging, the electricity in your electric car battery is there for more than just driving. You can also use the energy for household use or to charge an electric scooter on the go, for example. In this article, you'll learn exactly how bidirectional charging works, where you can use it, and which electric cars support it.
How bidirectional charging works
Bidirectional charging turns your electric car into an energy storage device. Instead of just one direction, i.e. from the grid to the battery, this technology allows the electricity to flow in both directions.
An example: The photovoltaic system on the roof produces more electricity on a sunny summer's day than the household consumes. Bidirectional charging means that you can store the excess electricity in the car battery and feed it into the home grid or the public power grid at night or on days when there is little sun.
For this, you need a wallbox and an electric vehicle, each equipped with a bidirectional charging device.
What you need to know about direct and alternating current
In the household network, alternating current (AC) is used, while electric cars run on direct current (DC). When the car battery is charged, the alternating current from the grid is converted into direct current by means of a rectifier.
In order to feed the energy stored in the battery back into the power grid, the reverse process is necessary: the direct current is converted back into alternating current with the help of an inverter.
This is how you can continue to use the electricity from your electric car
There are various ways to feed electricity from the electric car back into the grid. These are usually marked with abbreviations such as V2X (Vehicle-to-Everything) or V2H (Vehicle-to-Home).
Via a user interface, which can be accessed either directly on the wallbox or via an associated app, you can control exactly how much electricity your electric car battery should feed back into the grid.
For example, you can set the battery never to drop below a certain charge level, so that even after a week with little sunlight, you still have enough juice for planned trips or spontaneous trips.
We have put together an overview of the 3 most popular V2X variants for you here:
V2H: Vehicle-to-Home
With V2H, the electric car is used as a battery storage system to supply the house.
You connect your electric car to the wallbox in the garage as normal. The battery is charged and as soon as you need the electricity in the house, it can feed the energy back into the house grid.
This is particularly interesting for homeowners with a solar system, as they can store their own electricity and thus become less dependent on the power grid.
Example: A 4-person household needs about 5,200 kWh per year in a single-family house. The largest car batteries currently available store about 100 kWh. Consequently, a car battery can store about as much electricity as the family of four needs for a week.
V2L: Vehicle-to-Load
The V2L variant enables the supply of external devices. A conventional socket with 3.6 kW can be used to charge devices such as a laptop or e-bike battery. You will need a V2L adapter that allows you to connect normal electrical devices directly to the vehicle.
V2G: Vehicle-to-Grid
With the V2G solution, the discharge is fed into the entire power grid in a targeted manner. If too little electricity is produced by solar or wind energy, car batteries can be used. This helps to stabilize the power grid.
However, either the car has to convert the direct current into alternating current or it needs a wallbox that takes care of the conversion.
There are now various V2G options. In Switzerland, however, the whole thing is still in the development phase and is currently not very widespread.
The wallbox must fit: prerequisite for bidirectional charging
In order for you to be able to charge bidirectionally, the charging infrastructure must be right. This means that not only your electric car, but also your wallbox must support this technology. The problem: Such a wallbox is very expensive.
For example, a bidirectional V2H wallbox with 10 kW costs a good 18,000 francs. An EM2GO unidirectional wallbox with AC charger and 22 kW is available for less than 1,000 francs.
We recommend that you inform yourself comprehensively about the costs before making your decision and check whether a bidirectional wallbox can be installed at your premises.
Which electric cars support bidirectional charging?
Not all electric cars support bidirectional charging. You should check whether your car can be used for this purpose with your trusted dealer before buying. With these models it is currently possible (list not exhaustive):
Tip: However, if the electric car is equipped with a CHAdeMO charging port, you already have a good indication that it supports bidirectional charging. This is the case with many electric cars from Asian manufacturers.
Load management: How bidirectional charging supports the entire power grid
Electric cars can serve as flexible electricity storage systems that can be used to compensate for fluctuations in production and demand and to break power peaks in the distribution grid. After the peak, the battery is recharged.
Bidirectional charging thus makes electromobility grid-friendly and helps to reduce the need for grid expansion. In this way, e-cars can make an important contribution to more efficient energy use.
This is because if all companies start their machines at the same time in the morning or all households use their electrical appliances at the end of the day, so-called load peaks occur in the power grid. In other words, short periods in which a particularly large amount of electricity is consumed.
At present, they are compensated for by so-called peak-load power plants, but this is associated with high costs. An alternative to this is peak shaving – the smoothing of load peaks. During the peak, an alternative power source, such as car batteries from electric cars, is used.
Bidirectional charging in Switzerland
In Switzerland, it is permitted to install and operate bidirectional charging stations and wallboxes. However, this requires the approval of the local distribution system operator. Since 01.01.2022, bidirectional charging stations can be registered regularly with the distribution grid operator by means of an updated technical connection request (TAG).
Standardised standards simplify bidirectional charging
In April 2023, the international standard ISO 15118-20 was introduced. It defines how electric cars and charging devices for bidirectional charging communicate with each other. It also determines how the data about the battery charge level and the current flow possibilities are transmitted between the vehicle and the charging infrastructure.
This makes it easier to implement bidirectional charging, as manufacturers and infrastructure developers now have a clear guideline on how to design the exchange of information.
Technical challenges and possible solutions
Although there are many advantages to bidirectional charging, there are some technical challenges:
- Battery: More frequent charging and discharging can shorten the life of the battery. As a result, you will have to repair or replace them ahead of time. One possible solution is intelligent battery management systems. You can precisely control the load on the battery, minimizing wear and tear.
- Electricity grid: Feeding excess energy back into the grid can lead to overloads or voltage fluctuations and affect the stability of the power grid. To prevent this, smart grid technologies must be used more frequently. These enable intelligent control of energy flows throughout the power grid.
- Law: The legal framework for bidirectional charging is not yet fully developed, as electric cars are currently legally only considered PWs and not battery storage systems. In order to enable the integration of electric cars as energy storage systems in the mobility market, an adjustment of the legal framework is necessary.
Conclusion: Bidirectional charging has a lot of potential
The advantages that bidirectional charging offers for the energy landscape and for electric car owners are great. As mobile energy storage systems, electric cars can help to manage peak loads and reduce dependence on traditional energy sources.
The expansion of the necessary infrastructure and the creation of a clear legal framework are crucial in order to exploit the full potential of bidirectional charging in the future.
In Switzerland, however, there are still a few steps to go before it becomes standard. Seasonal problems, such as a possible electricity shortage in winter, are also not solved by bidirectional charging.