Your electric car as solar storage for your home

In bidirectional charging, the vehicle battery is used as an intermediate storage of electrical energy (e.g. to store surplus solar power). In contrast to monodirectional charging, which is still common today, a bidirectional charging station can be used to feed electrical power and energy back into the building (V2H/V2B) or the electrical supply network (V2G) as required.

Bidirectionally chargeable e-cars can not only store electrical energy for driving purposes, but also feed it back into the home. Vehicle-to-home thus makes it possible to supply one’s own household with the stored electrical energy from the e-car. The entire charging and feeding back processes take place behind the house meter and is often used to increase the self-sufficiency rate by means of solar power systems.

In principle, bidirectional charging is equivalent to the operation of stationary batteries. If the charging infrastructure complies with the VSE recommendation on grid connections for energy generation systems (NA-EEA) and the technical standards for electrical safety and electromagnetic compatibility, it can be authorised when registering with the distribution grid operator.

From 1 January 2022, bidirectional charging stations can be registered regularly with an updated technical connection application (TAG).

The following vehicles are enabled for bidirectional charging as of February 2024:

• Honda: Honda e > read more
• Nissan: Leaf (from 2014), Evalia and e-NV 200
• Mitsubishi: i-MiEV, Outlander and Eclipse Cross > read more
• Peugeot iOn and Citroën C-Zero
• VW: ID.3, ID.4, ID. Buzz and ID.7

Listed are all vehicles that allow vehicle-to-home via a suitable charging station. Vehicle-to-load, such as the Hyundai Ioniq 5, must be considered separately. Here, you can only draw a limited amount of power via an onboard plug (single-phase, up to 3.6 kW), but you cannot supply a house with electricity.

Further information: In principle, all Japanese electric vehicles can charge bidirectionally because this is mandated by the Japanese government. So far, bidirectional charging is primarily possible for vehicles with CHAdeMO plugs. The Honda e is an exception, it can do bidirectional charging via the CCS plug. Bi-directional charging requires approval from the vehicle manufacturer and certification of the charging station for the specific vehicle type.

Several vehicle manufacturers have announced that their vehicles will be enabled for bidirectional charging in the near future. In general, the introduction of an international standard ISO 15118-2020 is expected by 2025, which will also regulate bidirectional charging with CCS charging plugs in a binding manner.

Years of practice and scientific research have shown that lithium batteries are very robust. In addition, the latest technical developments have resulted in an even longer battery life. Since the discharge power during bidirectional charging is much lower compared to driving (factor 10 and more), the additional aging of the battery is extremely low. The approval of vehicle models for bidirectional charging operation by their manufacturers also includes the retention of full warranty services.

Yes, a bidirectional charging station must be registered with the local network operator just like a simple charging station. The technical connection application, which may be completed and submitted by an electrician, for example, is used for this purpose.
How do I notify the grid operator of a bidirectional charging station?

The “technical connection request” form is used for this purpose. This may only be filled out by a certified person such as an electrician. Only the section “Charging facilities for electric vehicles” is filled in. The following data must be entered:
Type of device: “bidirectional charging station”.
Manufacturer of the device: “sun2wheel AG”.
Device type: “two-way-digital” or “two-way-10
Connection: 3x400V
Rated current device: 16 A
Rated power device: 10 kVA
Cos Phi: 1
DC charging of the vehicle
Max. Mains draw power: 10 kVA
Max. Mains withdrawal power: 0
Adjustable power by TSO: 0 kVA to 0 kVA
Controllable power by operator: 0 kVA to 10 kVA
Active power controllable: No
Interface between charging pole and distribution grid operator available: No
Comment of the submitting company: “For the regulation of charging as well as discharging, the balance energy is measured. This guarantees that no energy is fed back into the grid.”

The “technical connection request” form, or TAG for short in German, is used for this. This may only be completed by a certified person such as an electrician. Only the section “Charging facilities for electric vehicles” must be completed. The following data must be entered:

Type of device: “bidirectional charging station”
Device manufacturer: “sun2wheel AG”
Device type: “two-way digital” or “two-way 10”
Connection: 3x400V
Rated current device: 16 A
Rated power appliance: 10 kVA
Cos Phi: 1
DC charging of the vehicle
Max. Mains power consumption: 10 kVA
Max. Mains power consumption: 0
Controllable power by VNB: 0 kVA to 0 kVA
Adjustable power by operator: 0 kVA to 10 kVA
Active power controllable: No
Interface charging station to VNB available: No

Comment from the submitting company: “The balance energy is measured to regulate charging and discharging. This guarantees that no energy is fed back into the grid.”

No, the bidirectional charging station is not yet island-capable and cannot operate in the event of a power failure. Likewise, our charging station is not yet compatible with a self-sufficient building. We are working to ensure that our systems can be used in an island system in the near future.

Advantages: Optimisation of energy use and support for the energy transition. The self-consumption of the PV system can be significantly increased, thereby reducing electricity costs. Renewable energy is stored and therefore utilised optimally and efficiently. The idle times (usually an average of 23 hours/day) of the e-vehicles can be utilised. The car has multiple uses and is not just a means of transport. The power grid is relieved. Possible price fluctuations in electricity costs can be balanced out.

Disadvantages: The regulatory requirements are not yet fully in place. At present, the electricity from the car battery can only be used for personal consumption. The price of the bidirectional charging station is higher compared to a monodirectional wallbox. However, the cost of a stationary battery should be taken into account when making a comparison. Only a few vehicles are currently approved by the vehicle manufacturers for bidirectional charging