There are different ways of feeding electricity back from the car battery

V2L: The vehicle has a socket to connect devices (e.g. tools)
V2B or V2H: The vehicle can supply parts of a building. However, the supplied power grid is not connected to the public power grid.
V2G: The vehicle can supply the building and, if necessary, also feed electricity into the public grid.
V2X: Collective term for all the above variants.

As of 09/2023, there are some car models that are capable of V2L. Since the vehicles have a separate plug, it is possible to operate devices independently of a wallbox.
To feed back electricity via a wallbox, the car and the wallbox must be able to communicate via ISO 15118, which usually requires special PLC (Power Line Communication) hardware in the wallbox. Our wallbox models do not currently have this hardware. However, we are evaluating whether we can offer a retrofit board when the topic becomes marketable. Various promises are made with regard to ISO 15118 for electric cars, but very few of them are kept.

There are two possible standards

1. The car has a 1-phase or 3-phase inverter that generates the necessary 230 V voltage compatible with the household grid. The wallbox then only switches its contactor and the car can feed into the household grid.
2. The car feeds its CCS plug directly from the battery back to the wallbox. For this, the wallbox must have an inverter or be connectable to an external inverter.
Which standard will prevail is currently (as of 09/2023) not clear. We are monitoring this.

Benefits of V2G

A private household needs an average of approx. 7 kWh per day, of which 3-4 kWh are needed during the time when the PV system is not producing electricity. This means that a storage unit with 3-4 kWh capacity is needed for this time. The cheapest storage units with 4 kWh are currently around 260 €/kWh, i.e. a little over 1000 € plus installation (tendency decreasing). In order to satisfy the need for self-sufficiency, a V2H solution should therefore not cost more than an additional €1000 plus installation, otherwise one could also buy a stationary storage unit, which would also have the advantage of not being "gone" in between.
Use of V2G as a virtual power plant:
As the number of electric cars increases, a lot of distributed battery capacity is created. E-cars could be linked together to form a virtual power plant to serve grid stability and to compensate for gaps in supply. For this purpose, each e-car owner could make a certain contingent of his e-car battery and/or stationary storage available (against payment) to the virtual power plant. Appropriate signalling protocols on when who feeds in or charges how much electricity are a prerequisite. There would have to be a corresponding legal framework for this. We believe that this will come sooner or later and find the topic very interesting. In the cFos Charging Manager, there is a charging rule with which it is already possible to charge in a way that at least serves the grid.

Regulatory

The feeding back of electricity from the car battery, which is electrically connected (via wallbox) to the household grid, requires the approval of the grid operator. However, the current legal situation in Germany prohibits feeding electricity back into a grid that is electrically connected to the public grid (as of 09/2023).