V2G — bidirectional charging and the installation requirements that come with it

The 722-ev-charging guide and the guide on the Control Pilot signal cover regular, unidirectional charging of an electric vehicle: energy flows from the grid to the car, and the installation requirements are comparable to any ordinary final circuit. This article covers what changes once energy can also flow the other way: from the vehicle's battery back into the installation or the grid.

V2G, V2H and V2B — the distinction

V2G (Vehicle-to-Grid): the vehicle actively feeds power back into the public grid, for example for frequency regulation or peak shaving.
V2H (Vehicle-to-Home): the vehicle feeds the owner's own household installation, often specifically during a grid outage (a backup-power function).
V2B (Vehicle-to-Building): the same function, but for a commercial or utility installation, often combined with peak shaving alongside a large-consumer connection (see the guide on grid congestion and battery storage for the comparable, stationary application).

All three variants require that the charge point and the vehicle can transfer power bidirectionally — an ordinary unidirectional charge point and on-board charger cannot do this, regardless of the physical connector.

From unidirectional to bidirectional: the standards status

ISO 15118-20 is the communication standard that governs bidirectional power transfer (DC BPT — Bidirectional Power Transfer) between vehicle and charge point, as the successor to the unidirectional-only ISO 15118-2. Without this (or an equivalent) communication layer, the charge point has no way of knowing how much power the vehicle can safely return and under what conditions.
IEC 61851-23:2023 added explicit requirements for bidirectional DC charging systems in this edition — earlier editions described unidirectional DC charging only.
CHAdeMO has supported bidirectional power transfer since an early version of the protocol and was therefore used in many early V2G pilots, while CCS-based bidirectionality only became practically available with the more recent standards mentioned above.

Why the vehicle becomes a generator the moment it exports

Once a vehicle exports power, it functions electrically as a distributed generator within the installation — with the same category of requirements as a PV inverter (see the [guide on PV inverter anti-islanding](/guides/nen-1010/pv-omvormer-anti-eilandbedrijf-nen-en-50549)):

Anti-islanding: the bidirectional charging unit must detect a grid outage and stop exporting power immediately, to prevent the grid from unintentionally remaining live during maintenance or a fault elsewhere.
RCD type: the power electronics of a bidirectional charger can, like a PV inverter, cause DC components in the residual current — a standard type A RCD is not sufficient for that; a type B RCD or an equivalent, continuous DC residual current monitor (RDC-DD, see the guide on IEC 62955) is required.
Bidirectional metering: the grid operator needs a metering device that correctly registers both consumption and export — an ordinary one-directional meter is not sufficient for a connection with V2G functionality.

V2H as backup power: the same backfeed rule as a generator

When a V2H installation feeds the household installation during a grid outage, exactly the same requirement applies as for a portable backup generator or an automatic transfer switch (ATS): the installation must be physically separated from the public grid before the vehicle supplies power, for example via a transfer switch that connects "public grid" and "V2H supply" alternately, never simultaneously. Without this separation, the vehicle would feed energy back into a grid that the grid operator assumes to be de-energised during a fault — with the same dangers for technicians as an incorrectly connected backup generator.

Note: this article covers the electrical installation requirements. The practical availability of V2G/V2H tariffs, subsidies, and the extent to which a specific vehicle and charge point are actually certified for bidirectional operation varies by manufacturer and changes quickly — verify this per project.

Practical relevance

When assessing a V2G/V2H/V2B installation, it is not sufficient to check only whether the charge point and vehicle are labelled "bidirectional" by the manufacturer — the installation must actually be equipped with anti-islanding protection, a suitable RCD type, and, for backup use, a demonstrable physical separation from the grid, in the same way as for any other form of distributed generation.

Common mistakes

"Making" an ordinary unidirectional charge point and installation V2G-capable by only replacing the vehicle — the charge point, wiring and protective devices must be rated and certified for bidirectional power.
Applying a type A RCD to a bidirectional charging unit — the same consideration as for a PV inverter: the power electronics can cause DC residual currents that a type A device does not detect.
Using V2H as a backup supply without a certified transfer switch — this creates the same backfeed hazard as an incorrectly connected backup generator.
Assuming any vehicle with a CCS connector can charge bidirectionally — this depends on the vehicle, the charging unit, and the supported communication standard (ISO 15118-20 or equivalent).