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E-cars as electricity storage: How do V2H and V2G work?

Renewable energies are on the rise and are paving the way for the energy transition. But electricity production from wind and sun is volatile, i.e. subject to fluctuations. Depending on the time of day and weather, a lot or little green electricity is generated. Electric cars could help to compensate for fluctuations at home or in the grid – by using the batteries of electric cars as mobile electricity storage devices.

Electric cars as electricity storage – can that work? From a purely mathematical point of view, e-cars sit around unused for a large part of the time, usually full of energy. This could be used sensibly in the future, for example to supply one's own household appliances with electricity. This could increase self-consumption and reduce electricity costs. We take a look at the current state of the art and clarify whether vehicle-to-home (V2H) and vehicle-to-grid (V2G) represent the future of the energy transition and electromobility.

"Vehicle-to-Home": Connecting the e-car to the home grid

The approach of integrating the e-car into the home grid as an electricity storage system is not new. Research has been carried out on the so-called "vehicle-to-home" (V2H) technology for several years now. The prerequisite for this is that the electric car supports bidirectional charging (more on this below). This means that they can not only charge themselves, but also use the electricity to power the house and the electrical devices on it. This is practical, for example, to be able to supply the house with emergency power in the event of power outages. But also in general, the car can be used as an energy storage device to temporarily store electricity, which can be produced by the solar system at the very moment, but cannot be consumed. This means that the self-generated energy can be used completely by yourself. This saves money and also makes you less dependent on rising electricity prices. Another advantage of bidirectional charging is that electric vehicles can charge each other if one of them breaks down due to an empty vehicle battery.

What seems quite simple at first glance is difficult to implement in practice. However, there are a number of research projects that are promising. For example, Audi and Hager Group – a company specialising in intelligent building networking – have modified an Audi e-tron so that the electric car can be used as a mobile electricity storage system. In a short video, the partners explain the technical structure:

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How it works

First of all, it is important to know that e-cars are powered by direct current, but alternating current comes out of the socket. During normal charging at the wallbox, the alternating current must therefore be converted into direct current via a rectifier before it is stored in the car battery. To ensure that bidirectional charging works, a lot of technology is used in the project: A domestic power plant that provides the necessary DC technology serves as the basis. A photovoltaic system produces its own solar power, which then flows either into the home storage system or towards the car. Charging is carried out by a suitable charging station, which is responsible for the flow of energy to and from the car. An intelligent energy management system watches over everything, protecting both the vehicle and the building network from overloads. The e-car also needs a bidirectionally chargeable battery that can both absorb and release electricity. In addition, a charging cable is needed that can quickly transmit large amounts of electricity. Under these conditions, the e-car can be used as a home storage system.

Solar plant

Generating electricity with the solar system and storing surpluses in the electric car – V2H technology makes this possible.

Important with V2H: Not the entire battery capacity can be available as electricity storage. As a driver, you have to rely on the fact that you have enough range at all times when you drive off. For this reason, the "i-rEzEPT" research project – a cooperation between Nissan, Bosch.IO and Fraunhofer Institutes IAO and IFAM – made sure that only 10 to 30 percent of the battery capacity was used for feeding it back into the home grid. If necessary, for example before starting a longer journey, a full charge of the e-car could also be ensured. Of course, this severely limits the possibilities of storing energy for domestic use.

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Canadian supplies house with electricity from his electric car for two days

How practical bidirectional charging can be in the event of a power outage was proven by a Canadian in December 2022. When parts of the USA and Canada were hit by a heavy snowstorm and large-scale power outages occurred, he supplied his house in the Canadian province of Ontario with electricity from the battery of his electric car for two whole days. Due to a lack of a suitable house connection, he laid extension cables from his Ford F-150 Lightning parked in the garage to the other rooms and thus supplied refrigerators, lamps, the WLAN and the TV with energy. When the power supply was restored after 44 hours, the battery of his electric car was still 65 percent full.

Which e-cars can be used as electricity storage?

Theoretically, a large number of electric cars could already serve as private electricity storage systems today. The catch is that the vehicles are almost exclusively Japanese models that are charged via CHAdeMO plugs. But this is not a standard in Europe. The following models with bidirectional charging capability are available from us:

  • Mitsubishi Eclipse Cross Plug-in Hybrid
  • Honda e
  • Kia Soul Electric
  • Mitsubishi i-MiEV / Citroën C-Zero / Peugeot iOn
  • Mitsubishi Outlander
  • Nissan LEAF
  • Nissan e-NV-200

In Japan, household appliances such as refrigerators and washing machines are already powered by Mitsubishi's electric car batteries. In the next step, the system is to be supplemented by an external battery, which stands as an additional charging unit between the electric car and the household. Mitsubishi plans to offer such a system in Germany in the future. The Ford F-150 Lightning electric truck is so far only available in America. Thanks to the high storage capacity of the battery, the e-car can be used as battery storage in the event of a blackout and supply a household with electricity for up to 3 days.

The Hyundai Ioniq 5 goes in the same direction, although not quite as far yet. It was one of the first models to be equipped with the Vehicle-to-Load (V2L) function. The electric car has a 220-volt socket in the interior, which draws its power from the batteries and to which you can connect your smartphone or laptop – even when the car is switched off. The charging socket can also be converted into an external socket (by means of an adapter), for example to charge an e-bike or e-scooter - and with an output of 3.5 kW you could even connect a hair dryer or a TV. If the battery level drops below 15 percent, the function is deactivated for safety. V2L features have also already been announced for upcoming electric cars such as the Kia EV6, the Genesis GV6 and G80 models and the Toyota bZ4X.

Nissan Leaf is charging

The Nissan LEAF has been offering bidirectional charging since 2010.

First wallboxes with bidirectional charging capability

So far, only a few wallboxes are available that enable bidirectional charging, for example the wallbox from the Spanish company Quasar. It charges with direct current via CHAdeMO plug and can be combined with a photovoltaic system via an energy management system. In conjunction with renewable energy sources, the environment is also protected when charging the electric car. The price for such a wallbox is around 6,000 euros. However, since it only has a charging capacity of 7.4 kW, you will not receive any state subsidies for it. So far, there has been no test from the ADAC, but a practical use of EnQS was positive.

And there is a lot going on in the market. Sono Motors, for example, which is developing an innovative solar car with the Sion, has announced its own bidirectional wallbox. It is to charge by alternating current with 11 kW. The highlight: The conversion of direct current into alternating current takes place in the Sion itself and not in the wallbox, which reduces the technical effort. The Sono Wallbox is therefore said to cost up to 70 percent less than comparable competing products. Sales are scheduled to start in 2023 parallel to the Sion.

Pros & Cons of Bidirectional Charging

Advantages:

  • Renewable energy sources can be better utilized, thus saving fuels.
  • Your own PV or wind power system can be used more efficiently thanks to the intermediate storage system.
  • If the e-car is used as an electricity storage system, this means more independence from the power grid and rising electricity prices.
  • E-cars can charge other e-cars, e-scooters and e-bikes.

Disadvantages:

  • The electric car battery must enable bidirectional power exchange and (still) have a CHAdeMO charging plug.
  • The selection of models that enable bidirectional charging is not yet large.
  • For bidirectional charging, a wallbox is required to support the technology. This is more expensive than conventional wallboxes.
  • After a certain number of charging cycles, the performance of the battery decreases. If the battery is used as a power storage device, this means a higher load and correspondingly faster wear and tear.

Breakthrough could come soon

So far, bidirectional charging has been a niche phenomenon. Could the technology celebrate the breakthrough to mass technology? The chances of this are increasing. This was ensured by an announcement by Volkswagen in the spring. Starting next year, the Group will convert all models that use the Modular Electric Drive Toolkit (MEB) to ISO 15118. Then, in one fell swoop, hundreds of thousands of new e-cars from VW, Audi, Skoda and Seat will be able to charge bidirectionally. Existing models, such as the ID.3 or ID.4, are to receive the function via update.

 
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