Sooner or later, in every debate about electric cars, two arguments arise: “Where should all the electricity come from?” and “If everyone loads at the same time, the network collapses”. In both cases, controlled charging can help. The charging capacity is based on the electricity supply or the network load. However, consumers, energy suppliers and network operators sometimes have conflicting interests.
The pure amount of electricity is not the central problem. According to Agora Verkehrswende, e-cars accounted for just 0.4 percent of electricity generation in Germany in 2022. By 2030, their share is expected to increase to around five percent. Not a little, but not dramatically either.
More critical is the question of when exactly this charging capacity is called up. If it is not to lead to bottlenecks in the electricity market, it should be postponed to phases in which there is a large supply or low demand in the electricity grid. This would also bring economic benefits: “As a result of market-oriented charging, the demand for electricity will shift from times when prices are high to times when prices are lower,” says a current Agora paper. “Since the price for the ‘last’ kilowatt hour sets the price for all kilowatt hours in the time unit (merit order), market-oriented charging across the board lowers electricity prices for all consumers.”
There are also economic benefits if the charging capacity of e-cars can be reduced when the network is heavily loaded. In this way, for example, more charging stations could be installed more quickly without having to expand the network at the same pace.
conflicting interests
The crux of the matter, however, is that these two variants of “controlled” charging – one based on the electricity supply, the other on the grid load – sometimes contradict each other. “For example, if there is a high level of renewable energy throughout Germany, it may be desirable to encourage high charging rates, while at the same time the load in some places on the network is already so high that charging rates have to be limited,” writes Agora Verkehrswende. Therefore, market and grid-oriented charging would have to be better coordinated.
At the moment, however, there is nothing to notice. There are currently completely different instruments for both variants of controlled charging: For market-oriented charging, these are – in addition to controllable wall boxes – above all networked meters and flexible tariffs. The controllable wall boxes are already available. Smart meters and flexible tariffs, in principle, too, but now they should finally be available across the board. “According to the law passed in May 2023 to restart the digitization of the energy transition, all electricity suppliers are obliged to offer variable prices for electricity purchases and sales from 2025,” says the Agora Verkehrswende fact sheet.
Grid-oriented charging
When it comes to network-oriented charging, on the other hand, there are still many unanswered questions. According to a proposal by the Federal Network Agency, distribution network operators should be given the right to temporarily reduce the charging capacity of e-cars to 3.7 kW if there is a risk of network overload. However, it is unclear under what conditions this should be the case, how long such throttling can last, and how it can be ensured that the network operators really only use it in extreme emergencies and not to save on network expansion. As long as this has not been clarified, customers can no longer rely on their wagons being charged as planned.
To make matters worse, the operators usually don’t even know what the situation is like at the lower network level. In the low-voltage network and the local network stations, they “generally did not have sufficient real-time measured values that would enable a complete observation and forecast of the network status for the precise detection of impending overloads,” notes the Agora. She therefore calls on the Federal Network Agency to “urge network operators to improve the measurement equipment at these network levels”. This is already possible with “a few additional measuring points at critical points”.
The question of how to deal with additional network load extends far beyond the electric car. Heat pumps are also affected. A solution here could be time-varying network charges. “From the user’s point of view, this approach is clearly to be endorsed, since it is based on a voluntary basis and price incentives and reserves the option of not reacting to the price signal in the event of short-term mobility needs, but instead charging a car at full power immediately,” says the Agora . But so far there has only been one “non-binding hearing” by the Federal Network Agency.
increase in self-consumption
If you charge with your own photovoltaic system, you can approach the topic in a more relaxed manner. According to energy supplier E.on, a regenerative car battery with 42 kilowatt hours can more than double the self-sufficiency rate to 51 percent. “Winter, cloudy days and nights are already included here,” reports E.on. For comparison: Most home storage systems only have five to ten kilowatt hours.
However, this “bidirectional charging” requires, among other things, an inverter, which is only on board a few car models. The Agora paper cites the Nissan Leaf, Nissan e-NV200, Hyundai Ioniq 5 and Kia EV6 as examples. Volkswagen has also announced that in future all ID models with a 77 kWh battery will be able to be charged bi-directionally. The Agora also expects that the necessary inverters will be installed as standard in the charging infrastructure in the future. This would mean far more car batteries would be available to relieve the electricity market and grid.
Anyone who increases their PV self-consumption with bidirectional charging not only saves money, but also smoothes out their consumption profile, which leads to better utilization of the generation system. The Agora estimates the associated economic benefits at 25 to 45 euros per car and year – more than twice as much as with unidirectionally controlled charging (each based on the electricity prices of 2020).
According to the Agora, the battery wear and tear should be kept within limits, since the charging power will “usually be in the low single-digit kW range” – peanuts compared to the usual power at a charging station.
(bsc)