Electric cars (EVs) have very powerful batteries. In fact, when the car is simply parked, its battery can also be used to store energy for a building or the power grid. The benefit? Energy costs can thus be significantly reduced.

But how does this happen? And what problems arise?

What is two-way charging?

In addition to meeting the energy needs of the vehicle itself, the battery of an electric car can also be used to power external devices, such as a refrigerator on a camping trip, or to charge other electric vehicles. These additional capabilities are called V2D (Vehicle-to-Device) and V2L (Vehicle-to-Load).

Some models can meet the energy needs of entire buildings (V2H, Vehicle-to-Home). And some others can even supply power to the public grid itself (V2G, Vehicle-to-Grid).

A “two-way charging” station is needed to return electricity from the car’s battery. This station can both charge a car, but also conversely take the energy stored in the car’s battery and transfer it to a building or the power grid. So far, however, there are few electric car charging stations that offer this possibility.

How much energy can a car battery store?

The impressive thing is that the batteries of electric cars usually hold enough energy, which could cover the weekly energy needs of a small household – in Germany, a house with two people consumes an average of 54 kilowatt-hours per week, while the batteries of most electric cars medium-sized vehicles start with a capacity of around 60 kilowatt-hours.

In addition, with bi-directional charging and the use of solar panels a house can generate electricity during the day, store it in the car battery and consume it again at night. Thus, not only will they be able to consume energy that they produced themselves at a very low cost, but at the same time they will save the costs of purchasing special batteries for its storage, which cost several thousand euros.

Two-way charging “is not per se harmful to the car battery,” Robert Kors, an expert on “smart” energy networks at the ISE Institute, told DW. “If done correctly, controlled charging and discharging of the battery can even increase its life by 5 to 10 percent.” And the owner of an electric car can monitor his car’s battery, as well as when and for how long it can be charged, quite easily, through an app on his mobile phone.

Improvement of the electrical network?

In Germany people drive their car less than an hour a day on average. While the electric cars are parked, the electric grid managers can use their batteries as energy storage areas and in this way also deal with fluctuations in the electric grid.

In many countries there is often a surplus of renewable energy (mainly wind and solar energy). Exactly this surplus could be stored in electric car batteries and from there fed back into the grid when demand increases. Thus, on the one hand, natural gas plants or coal power plants will not be burdened more, on the other hand, the number of required batteries for energy storage will be reduced – and of course the electricity grid will be stabilized.

According to recent research carried out on behalf of the European environmental organization Transport & Environment, in the EU savings through energy storage and electric car batteries could reach up to €22 billion per year.

Based on this research, electric cars could cover up to 9% of the EU’s electricity needs, occasionally even up to 20%, thus contributing the most to the smooth operation of the electricity grid.

What is the benefit for drivers?

This will also benefit car owners, who will be able to save between 31 and 780 euros per year.

In France, there has already been a relevant offer for owners of the Renault R5 electric model since October. By plugging their car into a two-way charging station for an average of 15 hours a day, drivers get free electricity for 10,000 kilometers in return.

Early on, “there is a lot of demand” for this particular offer, as Thomas Refiner of Mobility House, which promotes the flexibility of electric car batteries in energy markets, told DW. According to him, within the next two years there will be similar offers in Great Britain and Germany. In a related poll conducted on behalf of the energy group EON, 77% of respondents said they would like to use this method to meet their own energy needs, while 65% said they were willing to participate in the project to support the electric grid.

Will two-way charging be introduced?

To date, the electrification of buildings and electrical networks with energy from car batteries has been tested in more than 150 projects worldwide. And in the coming years, more and more electric cars will be available on the market that will offer this possibility.

Experts agree that the more private and public charging stations that can work both ways, the better. The initial additional cost for the construction of such stations would range from 100 to 250 euros per station. Due to the economic benefits of these stations, however, the payback will be within a few months.

In order for this technology to dominate globally, a relevant transnational communication framework would have to be established that would allow the exchange of data on vehicles, charging stations, electric network operators and costing. Both the car industry and many companies, public authorities and politicians are pushing for uniform standards.

And according to the German Directorate of Charging Infrastructure, in the coming years two-way charging will be established as an important piece of the puzzle for climate-neutral energy supply in Germany and other countries.

Edited by: Giorgos Passas