Bidirectional EV Charging Explained: V2G, V2H and ISO 15118-20

What is bidirectional EV charging?

Bidirectional EV charging allows electricity to move both into and out of an electric vehicle battery. A conventional charger only sends energy from the grid to the car. A bidirectional system can also return stored energy to a home, building or electricity network.

That turns a parked EV into a controllable energy resource. It can still charge as normal, but it may also help reduce a building peak, use more locally generated solar power, provide backup energy or support a flexibility service.

The word “may” is doing useful work there. Bidirectional charging is not a feature delivered by the wallbox alone. It needs compatible equipment and a service model around it.

V2G, V2H, V2B and V2X: the acronyms explained

Bidirectional charging covers several use cases:

• Vehicle-to-grid (V2G) sends energy from the vehicle into the public electricity network. A utility, aggregator or energy service normally controls when this happens.

• Vehicle-to-home (V2H) supplies a house from the vehicle battery. It can reduce electricity bought during expensive periods and, where the electrical design permits it, provide backup power.

• Vehicle-to-building (V2B) uses one or more EV batteries to support a workplace, depot, apartment building or commercial property.

• Vehicle-to-load (V2L) powers individual appliances or equipment directly from the vehicle. This usually does not require a connected EV charger.

• Vehicle-to-everything (V2X) is the umbrella term for all these uses.

For CPOs and CPMS providers, V2G and V2B are usually the most relevant. They bring charging operations into the energy system, where tariffs, grid limits, flexibility contracts and availability commitments start to matter.

How does bidirectional charging work?

A working system needs five layers.

1. A compatible vehicle

The vehicle must allow energy to leave its battery. For AC bidirectional charging, its onboard power electronics must also convert battery DC into grid-compatible AC. Many EVs cannot do this today, even if they use the right connector.

2. A bidirectional-ready charger

The charger needs the communications hardware, safety controls and electrical design required for two-way operation. It must exchange limits and instructions with the vehicle, while monitoring the connection and disconnecting safely when required.

3. Vehicle-to-charger communication

ISO 15118-20 defines communication messages and sequences for bidirectional power transfer between the EV and charging equipment. It allows the two sides to exchange information such as charging needs, limits, schedules and control status.

4. Energy and backend control

An energy management system decides when importing or exporting energy makes sense. A CPMS or CSMS manages the charger and connects the charging session with tariffs, users, reporting and other services. For network-level control, OCPP 2.1 adds functions for bidirectional charging, distributed energy resources and improved smart charging.

5. Permission to export

The installation must comply with local grid codes, connection agreements, metering rules and market arrangements. Exporting a few kilowatt-hours is still exporting generation. The distribution system operator tends to take an interest in that sort of thing.

AC and DC bidirectional charging are not the same

In DC bidirectional charging, the charger contains the power conversion equipment. Energy moves between the battery and the grid through an off-board converter. The charger is larger and more expensive, but it controls the conversion process directly.

In AC bidirectional charging, the vehicle normally performs the conversion through a bidirectional onboard charger or inverter. The AC charge point provides the connection, communication, metering, current limits and safety controls.

This distinction matters for amina. amina C2 and M2 are AC chargers. They provide the charging-side foundation for ISO 15118-20 communication and bidirectional operation, but the connected vehicle must also support AC power export. A charger cannot make a one-way onboard converter run backwards through optimism.

AC is particularly relevant for homes, workplaces, depots and multi-residential sites, where vehicles remain connected for longer periods and high-power DC equipment would be difficult to justify. It also means procurement teams must check the exact vehicle and charger combination, not simply the presence of a Type 2 plug.

What does ISO 15118-20 do?

ISO 15118 is the family of standards governing high-level communication between an EV and charging station. The 2022 edition of ISO 15118-20 defines the messages and sequences required for bidirectional power transfer. It also supports Plug & Charge, where the vehicle and charging service handle authentication automatically.

The standard is an essential common language. It is not the whole system. It does not decide an energy tariff, obtain grid approval, create a flexibility contract or guarantee that two products behave identically in every situation.

That distinction has become more important as the market moves from demonstrations to real deployments. At the CharIN Testival Europe in May 2026, both AC and DC bidirectional power transfer were tested. CharIN also noted that V2G implementation and EU grid-code compliance remain at an early stage. Progress, yes. Finished, no.

Where does OCPP 2.1 fit?

ISO 15118-20 handles communication between the vehicle and the charger. OCPP handles communication between the charger and its management system.

OCPP 2.1 adds native support for ISO 15118-20, a bidirectional-charging function block and controls for distributed energy resources. This allows a CPMS or CSMS to coordinate the charge point as part of a wider energy service rather than treating it as a device that only consumes power.

Operators should still separate protocol readiness from deployed functionality. The charger, firmware and CPMS must support the relevant OCPP functions, and the complete combination must be tested. Our guide to OCPP versions for EV charging explains the protocol path, while the EV charging management software guide covers the backend itself.

What does AFIR mean for bidirectional charging?

AFIR, the EU Alternative Fuels Infrastructure Regulation, is often mentioned in the same sentence as ISO 15118-20 and V2G. This can make it sound as though every European charger must soon feed electricity back to the grid. That is not what the regulation says.

Commission Delegated Regulation (EU) 2025/656 adds ISO 15118 requirements to the technical specifications supporting AFIR. It sets a path towards ISO 15118-20 support for newly installed or renovated public and private Mode 3 and Mode 4 charging points from 01/01/2027.

Bidirectional charging remains an optional service under the standard. AFIR readiness therefore does not mean that every installation will export energy on day one. It means the hardware and software need the right communications foundation for compliant, interoperable services as they arrive.

This is the practical procurement point. Chargers installed now may remain in service well beyond 2027. Choosing hardware without the required communications components can create an expensive replacement programme later. Software cannot add a missing chip with an update.

Why bidirectional charging matters to CPOs

For operators, the value is less about a single clever charging session and more about what a connected portfolio can do over time.

More control over site demand

V2B can reduce the load a depot or workplace draws during expensive or constrained periods. Combined with smart EV charging, it gives the energy system another controllable resource.

Access to flexibility services

Aggregated vehicle batteries may provide services to utilities, energy retailers or grid operators. The commercial model depends on the country, market rules, vehicle availability and the cost of orchestration. Revenue is possible. Automatic profit is not included in the standard.

Better use of local generation

A site can store surplus solar energy in connected vehicles and use some of it later, provided driver mobility needs are protected. This can reduce curtailment and increase the share of locally produced energy used on site.

Longer-lived infrastructure decisions

The immediate value may be readiness rather than active V2G revenue. CPOs can install a charger platform prepared for ISO 15118-20, then activate services as compatible vehicles, backends and regulations mature. That protects the physical investment and avoids replacing chargers purely because their communcation hardware was designed for yesterday.

What bidirectional readiness should mean in procurement

The phrase “V2G ready” needs follow-up questions. Quite a few of them.

• Does the charger contain the hardware required for ISO 15118-20 communication?

• Is bidirectional support for AC, DC or both?

• Which vehicles and firmware versions have been tested?

• Which functions work today, and which depend on later firmware?

• Can every relevant component be updated over the air?

• Which OCPP versions and bidirectional functions does the CPMS support?

• Can the charger connect directly to the chosen CPMS, or is a manufacturer cloud required?

• What happens if internet connectivity drops?

• Which meter records imported and exported energy, and can the data support billing or settlement?

• How are vehicle mobility needs, minimum state of charge and departure times protected?

• Who is responsible for grid approval, energy orchestration and customer consent?

The answers should describe a system, not a logo. Direct OCPP architecture also matters here because bidirectional services already have enough participants without adding an unnecessary cloud in the middle.

How amina C2 and M2 prepare operators for bidirectional charging

amina C2 and amina M2 include the charging-side hardware needed to support ISO 15118-20, Plug & Charge and bidirectional charging. Both are AFIR-ready AC platforms designed around direct integration and remote operation.

That creates four practical advantages for CPOs.

Install the communications hardware once

Bidirectional communication needs dedicated components inside the charger. By choosing C2 or M2 at the initial deployment, operators avoid planning a wallbox replacement merely to add the missing hardware later. Activation still depends on the vehicle, firmware, CPMS and energy service, but the physical foundation is in place.

Keep control of the backend

amina chargers use local OCPP rather than forcing every command through a proprietary manufacturer cloud. Operators can integrate with their chosen CPMS and develop the energy layer around their own commercial model. This reduces dependency and keeps future migrations possible.

Maintain the connection

amina C2 uses 4G LTE Cat 1 bis and dual-band Wi-Fi. amina M2 adds Ethernet for sites where a wired connection is preferred, alongside 4G and Wi-Fi. Both support over-the-air updates. amina C2 also stores offline data for later synchronisation and provides detailed diagnostics. These operating basics matter more as V2G services add data and moving parts.

Choose the metering and site controls the use case needs

amina M2 adds MID-certified metering, local load balancing, Ethernet and Modbus for multi-residential, workplace and commercial installations. amina C2 provides a connected 22 kW AC platform for home and commercial programmes. The right model depends on whether the project needs compliant billing, local controls and wired integration.

This is amina’s value proposition in fairly plain terms: prepare the charger for what comes next, keep the architecture open and avoid paying for extra dependencies that do not improve the charging session.