Whether powered electrically or via internal combustion, private vehicles have one thing in common: Statistically speaking, they are parked for an average of 23 hours a day. However, due to their drive system, e-vehicles could also be used in other ways – namely as additional electricity storage, for example for the household power grid. The vehicle stores the electricity that is generated by the solar power system but not directly consumed during the day. In the evening or at night, this stored energy could then be fed back into the household power grid and thus supply all household appliances with electricity. This is made possible by bidirectional charging, which means that the electric car must not only be able to recharge itself but must also be able to release the stored energy. And the potential of these electricity storage devices on wheels is growing continuously.
Around seven million BEVs were sold worldwide in 2022
When comparing January to September 2021 to the same time period in 2022, the number of new registrations of electric drive vehicles, known as BEVs (battery electric vehicles), grew in China from 1,748,000 to 3,378,000. In the US, the trend is similar, albeit on a different scale: From 164,000 newly registered BEVs in 2021, the number of new registrations rose to 550,000. Europe, the second largest market region, also reached a record level of just over one million new BEV registrations. At over 470,000, the German sales market accounts for the lion’s share. In Norway, the electric vehicle market share of new registrations was around 80 percent in 2022. This should make Norway the first country to achieve “Zero Emission” in new registrations by 2025. Even if experts believe that the growth momentum in Europe is slowly moderating, the global trend toward growth in electromobility is unmistakable. According to estimates by the Center of Automotive Management (CAM), around seven million BEVs were sold worldwide in 2022, representing a year-on-year increase of 63 percent.
The approach of integrating e-cars as electricity storage units into the home grid or into the public grid is not new. What initially sounds quite simple is not that trivial, both technically and in practice. Research into this technology has been ongoing for a number of years. There are several approaches. “Vehicle-to-home” (V2H) technology is concerned with connecting e-cars to the home network. The “vehicle-to-grid” (V2G) approach takes on a larger dimension. Here, as many electric cars as possible are meant to be integrated into the public energy grid. The advantage being that the energy generated at peak times can be stored temporarily and called up during consumption peaks in the evening. This “swarm battery” approach could absorb the overproduction of renewable energies and help reduce the energy supply with fossil fuels. At the same time, this way of using electric vehicle batteries also provides a source of income for their owners. When demand exceeds electricity production, e-vehicle batteries stand by as a reserve. By releasing a small portion of the stored energy to the grid, their owners receive compensation without essentially limiting their range and thus their mobility.
Enable bidirectional charging
The integration of vehicles into the overall power grid could also offer flexible storage options to compensate for the volatility of energy generated by solar or wind power plants. The potential of e-mobility not only offers a sustainable option for mobility through V2G, but could also contribute to grid stability and grid security. However, many challenges must be overcome in order to technically implement this potential, which is promising in theory. To enable bidirectional charging, BEVs must be equipped with special chargers and control software. The power grid must also be configured to handle the energy input from many different sources without becoming unstable. The charging software must switch from charging to discharging (or vice versa) within milliseconds, so that the grid frequency remains around 50 hertz at all times and the power grid runs stably. Another technical aspect lies with the vehicle itself, as Michael Ringleb, Product Manager Electrical Engineering and E-Mobility at DEKRA, explains: “An electric car only runs on direct current, because the battery is designed this way. It requires a converter that converts direct current back into alternating current. The converter can either be installed directly in the vehicle or integrated into a DC wallbox, which is advantageous for PV systems.” Additionally, there are still some regulatory requirements that must be met. For example, grid operators must approve the e-cars as “rolling electricity storage units”.
Despite these challenges, various research projects in the USA, Japan, and some European countries are working on implementing bidirectional charging. Vehicle manufacturers, grid operators, and research institutions are investigating, among other things, how bidirectional charging affects vehicle batteries. A common argument against V2G is the stress that batteries are subjected to during charging and discharging, and the resulting aging. However, practical experience shows that the stress on batteries during grid-serving applications is significantly lower than during a traffic light start or fast charging.
Positive effects of intelligent swarm power storage
“DEKRA is primarily involved with its e-mobility laboratories in Arnhem, the Netherlands, and Concord, California, to help manufacturers and regulators eliminate the technical and regulatory hurdles. Both labs have the necessary facilities to simulate the impact on the power grid and the communication between vehicle and charging station using the recently published international V2G standard ISO 15118-20. For this very purpose, the DEKRA Vehicle Grid Innovation Lab in Concord – ViGIL for short – is supported by the California Energy Commission (CEC) to reduce regulatory hurdles in California and create a uniform standard for bidirectional charging, so that in the near future every vehicle can participate at every charging station as a dynamic storage device,” explains Beat Kreuter, Vice President, Business Line Safety Testing, Service Division Product Testing at DEKRA.
Even though there are still some technical and regulatory challenges to be overcome, a few calculated examples show how great the positive effects of intelligent swarm power storage are: If the roughly one million electric cars registered in Germany were simultaneously connected to a wallbox with 11 kilowatts of charging power each, their batteries could deliver or absorb up to 11 gigawatts of power. This corresponds to the short-term flexibility of at least 2,500 modern wind turbines, 30 gas fired power plants, or all German pumped storage power plants combined.