Load management for electromobility
Managing charging points and avoiding peak loads
By 2030, the German government intends to support the installation of one million charging points for six million electric vehicles. If these charging points are connected to the existing infrastructure, peak loads will quickly occur, and the energy supplier will charge an annual demand fee for them. For this reason, either new contracts will have to be concluded with the energy supplier or a new charging infrastructure will have to be developed. This is expensive: a new low-voltage main connection that may become necessary can cost up to 100,000 euros alone. For the fast charging points a completely new charging infrastructure will be required, as the charging capacity usually can't be covered by the conventional power grid.
In November 2019, several energy supply companies in the European Union declared that they would ration electricity at private charging stations in the event of peak loads (for example in the evening) so that there will be no grid overload. This could happen as early as next year. Based on the charging capacities for a normal charging point described above, the regular eleven or 22 kilowatts could be reduced to half or a quarter. Accordingly, the charging time would be doubled or quadrupled.
The problem is quite real because the distribution networks to which the charging points are connected to have little in the way of reserves to absorb such peaks. In addition, not every consumer of electricity can call up the power he or she requires at every charging point. The reason for this is simple: the distribution grids were designed at a time when electromobility had not yet been thought of. They are adapted according to needs, such as population growth or the construction of new business parks. But not on the basis of a growing number of electric cars.
It all depends on the output at the actual location
The output at the site where the charging points are to be set up is therefore crucial when it comes to solving this problem. It is only on the basis of this output that the number of possible charging points and their output can be calculated - without the need to install a new infrastructure.
If the available capacity is not sufficient for the desired number of charging points, but there is no desire to do without them, the only option is to generate and possibly store electricity in-house. This can then be accessed from the charging points.
A further possibility would be to choose a charging point which itself identifies the imminent loads as well as the possible charging capacities and regulates itself. The simplest way here is to ensure that the available power is distributed equally for all the charging points of the charging station (usually two). However, this principle can also be regulated more intelligently. In this way, the charging station can detect how far charging of the battery has progressed. If it is also known what distance a vehicle has to cover and when, a hierarchy can be defined to determine who may be able to access a higher charging capacity, as they are travelling earlier and longer. This principle is very practical for vehicle fleets, for example.
The charging times during the day must also be taken into account. These can overlap with the peak loads that already exist (8:00, 11:00 and 17:00 on weekdays in Germany). Charging at night would therefore be ideal. However, during the day, for example on the company premises, charging can overlap. This is where a peak load management system helps, which regulates loading in such a way that no additional costs arise. This can delay the charging process. However, in the available time frame of eight hours that an employee remains in the company, this would normally not be a problem.
If there is a threat of peak loads, the charging stations can also be completely shut down, for example if the company's power supply has priority. However, this solution is always the worse one, as the traction batteries in electric cars cope better with continuous charging processes. Multiple switching on and off of charging processes has a negative effect on the service life of these batteries.
Intelligent load management
But how does peak load management work? It ensures that the amount of electricity is distributed equally among all vehicles to be charged. Such systems are software-based and can therefore be expanded as required.
Load management can be subdivided into three forms:
1. Integrated load management: here, the total power can be distributed to several vehicles. If only one vehicle is charged, it receives the entire charging capacity and can be charged correspondingly faster.
2. Static load management: with this variant, the connected load is distributed to the charging stations. The same power is always available at each charging station.
3. Dynamic load management: here, there is an interaction with the current power consumption in the network in which the charging point is integrated. Whatever power is left below the peak loads is distributed among the vehicles to be loaded.
In addition to load management, charging times are also determined by the charging technology in the vehicle. A 22-kWh battery is fully charged again in about one and a half hours at a 22-kW charging point. A 40 kWh battery takes about two hours. The computationally longer charging times result from the fact that the charging capacity is not constant during the charging process, but depends on the condition of the battery.
In-house power and batteries offer solutions
These peaks can also be avoided with in-house power generation, which is then used directly for charging. A photovoltaic system, for example, which can be installed on many company buildings, is sufficient here. If this can be supplemented with a battery storage unit, the charging requirement would even be covered to a large extent by in-house generated electricity. By the way, the peak load problem would be solved at the same time.
Exactly such solutions are mentioned and promoted in the new building energy law (GEG). For photovoltaics and energy storage, for example, no monthly offsetting of the electricity used by the company itself will be necessary in future. A flat-rate figure based on the output of the PV system is sufficient. This figure is capped at 20 percent of the total annual primary energy requirement without and 25 percent with battery storage. This is a clear advantage for solutions in which in-house generated electricity is stored in batteries and delivered to electric cars, for example.
Energy storage and a PV system significantly reduce the amount of electricity drawn from the grid and thus not only reduce the risk of peak loads, but also one’s own costs. After all, in-house generated and stored electricity today costs around 15 to 20 eurocents per kilowatt hour today. Grid purchases cost 31 eurocents. If peak loads are generated that are not covered by the existing contract with the supplier, the price of purchasing electricity will rise significantly.
Conclusion: peak loads must be avoided
If charging facilities are to be installed in public and semi-public areas, the existing and future requirements for charging power, both for normal and fast-charging areas, must be calculated first and rather generously. The next step is to analyse the possible maximum power output on site, without getting into the peak load range. This results either in the possibility of an installation without upgrading the grid or in the necessity of such an installation. When planning the system, it is important to consider how load peaks can be avoided. Is load management sufficient here or is it advisable to generate the charging current yourself, including its storage?