Electric car as storage: bidirectional charging picks up speed

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It takes a particularly long time from announcement to reality for bidirectional charging. Renault, for example, says that the electric R5 will become a power storage unit. But because it won't be officially unveiled until the end of 2024, charging technology that works in both directions isn't likely to actually be available until 2025. It's no better at Volkswagen. Whenever the Wolfsburg company presents a new model in the ID series, there is talk of bidirectional charging. Nothing has been delivered yet. But Volkswagen, too, will soon be moving from promise to action, according to experts. Renault and Volkswagen are interesting because the brands stand for different vehicle-to-grid (V2G) concepts. Let's take a look.

The R5 is to get a bidirectional charger in the electric car itself, according to a Renault announcement. It handles vehicle-to-load (V2L), meaning it can power external devices. It's an approach that's quite popular with buyers of Hyundai Group electric cars. In addition, there will be the so-called Mobilize Powerbox, a wallbox that matches the R5 and is provided by Munich-based system partner The Mobility House and is designed to market the delivered electricity. The output of this wallbox is stated to be between seven and 22 kW. When asked, Renault confirms our assumption that it is a three-phase AC unit.

Renault's electric cars as participants in the electricity market

Simply put, the Renault is equipped with an emphasis on the electric car as a participant in the electricity market, so it is economically controlled. The Mobilize Powerbox can be installed at any home. The R5 and other future Renault electric cars can charge depending on the market price. For example, the electric energy is particularly cheap when there is a lot of electricity available from photovoltaic plants at noon on a summer weekend. Or also at night, when demand is low. Charging is therefore beneficial to the grid.

But with a dynamic electricity tariff, this is possible with any electric car anyway. In addition, the R5 can either supply the electricity to the household grid or sell it to the general grid when the price is high again. The vehicle owner determines how much energy should remain in the traction battery. The Mobility House handles the marketing for the surplus.

The Renault concept is not necessarily linked to a photovoltaic system or a buffer storage in the house. It is an option. What the cooperation between Renault and The Mobility House shows is an extremely sensible and presumably cost-effective integration of the electric car into the electricity grid and electricity trading. The really amazing thing is that there is still no mass-produced product that follows this idea in a simple and comprehensible way.

Volkswagen: DC instead of AC

Volkswagen wants to take a slightly different approach. One that is designed more for efficient integration into a house with a photovoltaic system. At Volkswagen - and this is the rule rather than the exception in the auto industry's V2G research projects - charging and discharging is done with direct current (DC = Direct Current instead of AC = Alternating Current).

Those who have an electric car from the ID series with current software will find that bidirectional charging is already provided for. The ISO 15118-20 standard must be installed here, a common communication solution that also enables automatic identification at charging stations (plug and charge). For the time being, however, ISO 15118-20 has only been implemented for bidirectional DC charging; on the AC side, it is planned to incorporate it into ISO 15118-20 by the end of this year.

Volkswagen will first implement V2G in electric cars with the frequently sold traction battery with 77 kWh net energy content. A maximum of 60 percent of this will be released, i.e. 46.2 kWh. This is significantly more than with conventional stationary storage systems in single-family homes. However, the DC concept is usually not intended as a replacement but as an addition to the home storage system. The advantage of DC is that both a photovoltaic system and the traction battery as well as the stationary battery work with it. So there are no conversion losses from DC to AC and back; the system has a high internal efficiency. The problem, again, is the cost of the DC wallbox. Volkswagen has not yet quoted a price. Marketable DC wallboxes are considerably more expensive than AC wallboxes and are today usually over 5000 euros.

Deregulation urgently needed

Nevertheless, Volkswagen will not be long in launching an offering. We speculate that a presentation will still take place in the summer and the market launch in the first half of 2024. The well-known system provider E3/DC from the Hager Group has outlined what a DC-based V2G hardware solution could look like: E3/DC plans to sell the S10M DC vehicle-to-X wallbox in 2024. Both for customers who also want other products from E3/DC and for those who are only interested in the DC wallbox. S10M connects to the AC grid in the garage and can be an integral part of a home grid with a photovoltaic system and buffer storage. The company does not yet specify a price.

So the industry is about to get started. What is still missing is deregulation by the German Federal Ministry of Economics and Climate Protection: Mobile storage - i.e. traction batteries in electric cars - is not exempt from apportionments and levies, unlike buffer storage in the home. Although this is planned, it has not yet been implemented. The BMWK should take urgent action here.

(mfz)