Having your own mains connection is essential
Most grid operators recommend generally installing charging stations via your own mains connection and a separate energy meter. Customers remain free to choose, however, whether to use grid-friendly control in accordance with section 14a of the German Energy Industry Act (EnWG). For the wallbox, and therefore the charging process, to be controlled by the grid operator, it is vital to have your own mains connection. If this requirement is met, electric car drivers can benefit from innovative charging concepts and significant savings, for example using the electric car as a storage battery in the future— we will elaborate on this later on. In addition, using the own mains connection EV drivers can already make use of the special car electricity tariffs that some electricity suppliers offer. The savings this provides can be significantly more than 100 euros a year, depending on the mileage and the electricity provider.
Controlling charging processes — various models
To control the charging processes, almost all grid operators currently use so-called ripple control receivers. This analogue technology has been in use for decades, for example to control storage heaters. The second energy meter that is needed, and the receiver unit, generally entail costs of roughly 40 euros a year. However, this is compensated for several times over by the savings brought about by less expensive tariffs. Ripple control technology basically functions as a remote control for the grid operator: the central ripple control transmitters send the control signals to the decentralized ripple control receivers through the power grid.
There are only a few exceptions: Stromnetz Hamburg, for example, requires a digital OCPP interface for the control of private wallboxes (or OpenADR for charging and energy management systems, as offered by The Mobility House with its intelligent system ChargePilot®), connected via mobile network. As required, for example in an underground garage with bad reception, Stromnetz Hamburg provides an outside antenna free of charge. Westnetz, on the other hand, enables not only ripple control but also the use of a (lead-sealed) timer switch that interrupts the charging device’s flow of electricity for several hours at set times of day.
Certain grid operators, such as Netze BW (grid operator of power supply company EnBW), specify a set schedule for ripple control that reduce the energy supply without cutting it off entirely: at set times, currently in the evening between 7 and 11 p.m., the grid operator issues a ripple control signal to reduce the charging power to 8 amperes per phase. For an electric car with 3-phase charging, this reduced rate still corresponds to a maximum charging power of 5.5 kW. This is enough to fully charge an empty battery with 60 kWh overnight, for example.
Netze BW configured the schedule and the reduction on the basis of findings from various real-life projects (“grid labs”). They revealed that most charging processes take place in the evenings between 7 and 11 p.m. This means that the charging power can be reduced in a reliable and scheduled way to help keep the grid stable. In its grid labs, the electricity provider claims to have found that this reduction barely causes any restrictions for the drivers of electric cars: as the average charging process requires roughly 20 kWh — and not even every day — the charging power remains sufficient for providing a full charge in four hours even when it is throttled to 5.5 kW.
As there are at least 800 grid operators in Germany and each has its own procedure for controlling charging processes, electricians are often unsure how to configure the individual customer’s connection:
|As mentioned above, the majority of grid operators use ripple control receivers. In most cases, the grid operator supplies the ripple control relay itself, and will often even install it (and lead-seal it). If electricians have any questions or uncertainties, they should always contact the relevant grid operator. For initial information they can also consult the connection conditions, which most companies make available on their websites.
A brief guide to control via ripple control receiver
In practice, direct control of a charging station via ripple control receiver works as follows: the receiver, a relay in the control cabinet, registers the pulse sent by the grid operator, basically as either “signal on” or “signal off.” This signal can normally be processed by the wallbox via a potential-free contact. This allows the wallbox to know whether it can provide the full power or just the reduced power. If the wallbox does not have a potential-free contact, it needs to be controlled indirectly, for example via a power contactor. In this case, it is not possible to throttle the capacity to 5.5 kW in the reduced period, and instead the wallbox is then disconnected from the grid and the electric car cannot be charged. Another option, for example, is control via ChargePilot® with the add-on module “Grid Optimized Charging”. It enables multiple charging stations to be controlled intelligently by the grid operator. The system translates the ripple control receiver’s signal to OCPP to enable control.
Controlled charging is just the beginning
Many grid operators, charging station suppliers, and car manufacturers are also currently trying out more innovative strategies, such as digital electricity meters and additional control boxes, and investigating how photovoltaic systems could be incorporated into the overall system efficiently.
The question of how to bring together electric mobility, grid control, and charging behavior in the best possible way is currently being addressed by Bayernwerk Netz, for example, in collaboration with the automotive manufacturer AUDI, and also with The Mobility House. An EnBW project in Künzelsau is primarily focusing on controlling charging devices with EEBUS as digital interface. The communication interface EEBUS, which is used for energy management in the “Internet of Things,” enables continuously adjustable control of the charging power and bidirectional communication with the charging station. A similar project that is also looking into the potential of vehicle-to-grid (=V2G) was recently started by the automotive manufacturer BMW with roughly 20 electric cars and various partners from the energy industry.
The Mobility House has also been working for years on finding sustainable and intelligent ways to connect the worlds of mobility and energy. Multiple pilot projects have proven that this is technically possible, that it can increase the use of renewable energy in the grid, and that electric vehicle drivers can achieve high yields by making a small portion of their electric car battery’s energy available for grid-friendly applications. In a pilot project, a Nissan Leaf was able to “earn” 20 euros a week in this way — which would amount to at least 1000 euros over a year.