Bidirectional Charging Standards: CHAdeMO, CCS, ISO 15118 and OCPP

Bidirectional charging is the smart charging and discharging of an electric vehicle: power flows into the car's battery, and, when the household or the grid needs it, power flows back out¹. The Climate Change Committee describes the wider capability as V2X, allowing electric vehicles to charge from the grid but also discharge to the grid, a building or a home as needed². In practice it lets an EV either draw or supply power to your home or the grid³.

The catch is that the ability to export is not decided by the car alone or the charger alone. It is decided by standards: the connector on the vehicle, the communication protocol that lets the car and the chargepoint negotiate, and the back-office systems that let an energy company manage the flow. Today, only the CHAdeMO connection has a valid protocol for V2G charging to feed electricity into the public grid, while the CCS standard that dominates new cars in the UK is still catching up⁴. That single fact explains most of the history of UK vehicle-to-grid, and most of what is coming next.

Understanding two way charging: V2G, V2H, V2B and V2L

The umbrella term is bidirectional charging, but the industry splits it by where the power goes. V2G, vehicle-to-grid, means the car exports into the public electricity network, usually through an energy supplier or aggregator that pays for the service. V2H, vehicle-to-home, means the car powers the house itself, backing up the home during a power cut or supplying the evening peak from cheap overnight charge. V2B, vehicle-to-building, is the same idea at the scale of an office block or depot. V2L, vehicle-to-load, is the simplest: a socket on the car that runs an appliance directly, no charger or supplier involved.

There is also V2V, vehicle-to-vehicle, where one electric car charges another directly using energy from its own high-voltage battery⁸. It exists more as a concept than a commonly available real-world solution, especially in Europe: it is not supported by most series-production vehicles, it lacks standardised implementation, and there is no specific UK regulation prohibiting or permitting it, though manufacturers currently do not enable the feature in Europe⁸. Its advantages are real but narrow, emergency backup when an EV is stranded, saving towing time and cost, and it is not officially supported or warranted by most manufacturers⁸.

For a household, the distinctions matter because each route needs different equipment. V2L needs nothing but the car. V2H and V2G need a chargepoint that can accept power flowing backwards, and V2G additionally needs an arrangement with an energy partner. Our page on vehicle-to-home and vehicle-to-load covers the home side in detail, and the bidirectional charging page explains the whole idea from scratch.

The case for a common standard: agreements needed before reverse power flows

Charging a car one way is comparatively simple: the charger supplies, the car takes. Reversing the flow is harder, because the car becomes a power source connected to a building's wiring and, through that, to the distribution network. Before a single watt can flow backwards, several things have to agree: the connector must physically carry current both ways, the car and charger must negotiate over a shared communication protocol, the installation must meet wiring rules that recognise two-way energy flow, and the network connection must satisfy grid codes.

On the wiring side, the UK's wiring regulations now address this directly. Amendment 4 (2026) to BS 7671:2018, published in April 2026, sets out comprehensive requirements relating to system design, power conversion equipment, bidirectional or hybrid inverters and the suitability of protective devices for two-way energy flow⁹. Protective devices and switchgear designed for one-way flow are not automatically safe when current reverses, which is why the standard had to change.

On the communication side, several standards must line up. ISO 15118-20 is the international communication standard that defines V2G communication for bidirectional charging and discharging of electric vehicles and charging infrastructure¹. ISO/IEC 63110 covers the terminology, use cases and architecture for the management of bidirectional charging infrastructure, including communication between e-mobility stakeholders and data exchange with the electricity grid¹. In the EU, RfG 2.0 sets the minimum standard for connecting bidirectional charging infrastructure to distribution networks, though national requirements in member states may go further¹.

Equipment makers state the dependency plainly. Enphase's IQ Bidirectional EV Charger is compatible only with EVs that are ISO 15118-compliant and support bidirectional power flow¹⁰. If the car does not speak the protocol, the charger will not export, whatever its hardware can do. Standardisation of charging equipment has been a recognised international project for years, with the SMMT reporting on progress towards standardising charging equipment for pure-electric and plug-in hybrid vehicles as far back as 2016¹¹. The rules on connecting an export device to the network are covered in our page on grid connection rules for bidirectional charging.

CHAdeMO: the protocol behind UK V2G to date

The awkward truth of UK vehicle-to-grid is that it has run almost entirely on a connector that most new electric cars no longer use. Only for the CHAdeMO connection is there currently a valid protocol for V2G charging in order to feed electricity into the public grid⁴. Cenex put it more bluntly in its commercial viability work: CHAdeMO is currently the only protocol that supports V2G¹².

That is why the pioneer vehicles were what they were. The Nissan LEAF and e-NV200 were, for years, the only battery electric vehicles that supported V2G, and they did so via the CHAdeMO standard¹². The Nissan LEAF has been able to charge bidirectionally for several years and is described as the pioneer of the technology⁴. Most V2G systems use a CHAdeMO connector, though some models can also use CCS¹³. Our pages on the Nissan LEAF and vehicle-to-grid and on Project Sciurus, Britain's largest domestic V2G trial, tell that story.

The reason CHAdeMO got there first is architectural rather than accidental. CHAdeMO was designed from the outset as a DC standard with the car's onboard charger out of the path, which made defining a DC export protocol comparatively straightforward. CCS arrived later and with a different design philosophy, and its bidirectional extension, built on ISO 15118, has taken longer to reach products. Meanwhile Type 2 connectors are the standard for EVs in the UK and Europe for home and public AC charging⁵, and CCS connectors are the standard for rapid DC charging in the UK and Europe⁵, so the connector most drivers actually have is not the one that currently exports to the grid.

For a household choosing a car today, this is the practical consequence: a CHAdeMO-equipped vehicle is the proven route to grid export, but it is a shrinking share of the new market, and betting a home energy plan on one connector has its own risks. The cars that support bidirectional charging page lists where each model stands.

CCS and ISO 15118: the direction of travel for the dominant standard

The mainstream answer to bidirectional charging is being built on CCS and the ISO 15118 family. ISO 15118-20 is the international communication standard which, amongst other things, defines V2G communication for the bidirectional charging and discharging of electric vehicles and charging infrastructure¹. It is the successor to ISO 15118-2, and it is the protocol that lets a CCS car and a CCS charger agree, securely and over the charging cable itself, that power may flow out of the vehicle.

Products are arriving. Enphase's IQ Bidirectional EV Charger is designed for ISO 15118-2, 15118-20 and EN 50549, and supports OCPP 2.1, V2H and V2G¹⁰. The same maker states it will support both AC and DC bidirectional charging¹⁰. On the AC side, bidirectional power can flow through the car's own onboard charger, which is the route several new models take for vehicle-to-home; on the DC side, the chargepoint does the conversion, as CHAdeMO V2G does today.

The gap is closing but has not closed. The CCS standard, which is widespread in Europe, is yet to master V2G feeding electricity into the public grid, and is described as having a lot of catching up to do⁴. The practical position for a UK household is therefore split: CCS-based vehicle-to-load and, increasingly, vehicle-to-home are arriving in current models, while CCS-based vehicle-to-grid that earns money from the grid is still moving from pilots toward products. The bidirectional chargers page tracks the equipment as it reaches the UK market.

OCPP: communication between chargepoint and management system

The protocols between car and charger are only half of the picture. A chargepoint also talks to a charge point management system, the back office that an operator or energy company uses to start sessions, bill, monitor faults and, crucially, schedule charging and discharging. The international standard for that link is OCPP, the Open Charge Point Protocol.

OCPP 2.1 is the latest version of the international communication standard for connecting charging infrastructure to charge point management systems, and from version OCPP 2.1 onwards, bidirectional use cases are supported, ensuring seamless communication between charging infrastructure and the management systems that control it¹. Earlier versions of OCPP were built around one-way charging, so a V2G charger on an older back office could physically export but not be managed as an export asset.

For a household this matters less as a specification and more as a question: can my energy partner actually control my charger? A V2G service depends on the supplier or aggregator being able to tell the charger when to charge, when to discharge and how much, in real time. That needs OCPP 2.1 or an equivalent proprietary link on both ends. Enphase's bidirectional charger supports OCPP 2.1 alongside the ISO 15118 standards¹⁰, which is the combination to look for in any V2G-ready product.

Household requirements for V2G

The equipment list is short but each item is essential. To use V2G, you need a smart meter, a compatible V2G charger and a car that supports the technology¹³. Government guidance on registering energy devices in homes says the same from the other direction: a Vehicle-to-Grid enabled EV chargepoint is able to draw power to charge the vehicle and export the electricity from the car battery back to the home or the grid, and this requires a bi-directional chargepoint and for the car to be V2G compatible¹⁴.

The three conditions for bidirectional charging in general are an electric car, suitable charging infrastructure, meaning public chargers and wallboxes that support bidirectional charging, and a uniform software language⁴. In other words: car, charger, protocol. Miss any one and the power stays one-way.

In the UK today, V2G is still not widely available, and access has run through trials rather than open enrolment¹³. Trials often require specific EV models and compatible chargers and may involve a selection process; applying typically means online registration, eligibility verification and coordination with installers and energy suppliers¹³. Energy Saving Trust notes that bidirectional charging is currently being trialled in some places but is not widely available³.

A household putting itself forward therefore needs, in order:

1. A car that supports V2G, which in the UK has meant CHAdeMO models¹²
2. A bidirectional chargepoint, of which there were four models available in the UK through different suppliers as of 2021, with new suppliers entering regularly¹²
3. A smart meter, so imports and exports can be measured half-hourly¹³
4. An energy partner, a supplier or aggregator running a V2G service or trial¹³

The v2g-earnings-and-tariffs page covers what the energy partner side looks like in practice.

The value of V2G: income for homes and benefits for the grid

The money a household can earn from V2G depends heavily on how often the car is plugged in, and the studies diverge for exactly that reason. Cenex modelling of Sciurus trial data found V2G could make around £410 per year compared with unmanaged charging¹². The V2G Britain feasibility study found that a 7kW V2G charger used by a high plug-in rate driver, plugged in 75% of the time, could capture annual revenues of around £436, four times what the average plug-in rate achieves⁶. A UK average estimate from Cenex is lower, at £150 to £200 per year⁷. The EV-elocity project reports commercial users could save £400 per vehicle per year¹⁵.

Set against that is the cost of the hardware. In 2021, Cenex estimated the premium for a V2G charger above a smart charger at around £4,000¹². The V2G Britain report projects that premium falling to between £656 and £1,164 by 2030¹⁵, and Cenex predicts V2G charger cost to fall to £1000 by 2030⁷. At those levels, a high-usage household could close the gap in a few years; an average one could not.

There is also a sobering comparison. Smart charging, which only shifts when the car charges and needs no bidirectional hardware, can capture around 80% of the value of V2G for low plug-in scenarios, or 24% for high plug-in cases, with grid services excluded⁶. Our page on bidirectional charging vs smart charging works through that trade-off.

Why networks and government back the technology

The reason officials keep promoting V2G is that the value to the electricity system is far larger than the value to any one household. National Energy System Operator estimates that in 2050, vehicle-to-grid, effectively batteries on wheels, could offset as much as 85% of the residual EV demand that remains in peak periods, after smart charging has already shifted the majority of EV demand outside peak hours¹⁶.

The system numbers stack up quickly. Cenex reports V2G could defer network upgrades of £5bn, or £180 per household, and that reduced renewable curtailment could amount to a saving of 6 MtCO₂e per year⁷. A Cenex case study puts the nearer-term figures at £200m of cumulative distribution network investment saved by 2030, plus an additional £40 to £90M saved annually in GB by 2030¹⁷. An Ofgem case study projects that if 50% of the UK's EVs were V2G enabled by 2030, they could provide around 16GW of daily flexible capacity to the grid¹⁸.

There are engineering caveats. The Energy Systems Catapult notes that exploiting the full capability of smart EV charging, demand side response flexibility and V2G can support decarbonisation targets, reduce operating costs and enhance system resilience¹⁹. But it also observes that the focus of EV charging and V2G technology design is customer needs and cost, doing just enough to meet grid-related regulations such as fault ride-through and high and low voltage withstand¹⁹, and that V2G lacks inertia and power system stabiliser capability and will offset low-frequency demand disconnection operation¹⁹. In plain terms: V2G is valuable flexibility, but it is not the same as a spinning generator, and the grid codes it must meet are the floor, not the ceiling.

The current state of UK V2G

The UK has been a lead market rather than a follower. Cenex's introduction to V2G records that the UK and France are currently the lead markets for V2G, with strong emerging opportunities elsewhere¹⁵. The UK's V2G trials were publicly funded: an Ofgem case study records the support of the Office for Low Emission Vehicles (OLEV, now OZEV) and the Department for Business, Energy and Industrial Strategy (BEIS)¹⁸. Across the trial programme, 330 V2G devices were installed in the UK²⁰.

The commercial picture is still early. V2G is in pilot and early commercial projects in select countries⁸, and Energy Saving Trust's position is unchanged: bidirectional charging is being trialled in some places but is not widely available³. Four V2G charger models were available in the UK through different suppliers as of 2021, with new suppliers entering regularly¹². Smart V2G chargers such as the Wallbox Quasar 1 and Indra V2G units enable bidirectional energy flow, allowing the EV to charge and discharge to the grid¹³; our pages on the Wallbox Quasar and on Indra, the UK bidirectional charger maker, cover both.

The direction of travel is set by the car makers. Toyota is planning V2G integration as it expands its energy collaborations to additional countries, which will allow EVs to not only draw energy from the grid but also return it when needed²¹. Meanwhile the UK market has more than a hundred electric models available to buyers²², and the charging stock is growing: devices rated 8kW to 49kW represented 26% of UK charging devices as of 1 July 2025²³. The standards question, not the car count, is what decides how many of those vehicles can ever export.

V2G and household energy self sufficiency

Bidirectional charging is one of the few emerging technologies that turns a purchase a household was making anyway, a car, into an energy asset. With V2G, energy flows both to and from the vehicle, turning it into a portable battery store²⁴. A V2G chargepoint acts, and looks, very similar to a standard charging point²⁴, but it can use the EV battery to shift demand and cut electricity costs, supply energy to energy markets, and increase the use of localised renewables²⁴. Paired with solar, storing generation from a 4 kWp domestic solar PV system in an EV battery over a weekend with 6 hours of sun per day could save over 600 kgCO₂e per year⁷.

The independence is real but bounded. A V2G household still depends on the grid as its counterparty, on an energy supplier or aggregator to run the service, on the chargepoint maker's protocol support, and on the car maker enabling export in the first place. Exports are metered and paid through the supplier, not owned outright. And the battery in the car is a shared asset: managed well, Cenex reports capacity fade can be reduced by 9.1% over a year through battery management, extending usable battery life by 10% and giving an annual depreciation saving of £230⁷, and the EV-elocity project found V2G could extend battery life by about 10%, around one extra year of use¹⁵. Our page on V2G, battery degradation and vehicle warranties examines that evidence.

For homes with solar, one interaction is worth knowing: under the Smart Export Guarantee, your exports and therefore your payments reduce if you have a storage battery, and a storage battery may render you ineligible for some SEG tariffs²⁵. Whether an EV battery used for V2G counts in the same way depends on the tariff's terms, and Solar Energy UK's tariff listings show varying treatment of battery storage²⁶. A V2G setup can also reduce the need for a separate home battery: Enphase's IQ Bidirectional EV Charger can provide backup and export functions, without a home battery, when used with the IQ Grid Switch¹⁰. The choice between the two routes is worked through in our vehicle-to-grid or a home battery comparison.

The honest summary is that the standards, not the marketing, decide what a household can do. CHAdeMO can export to the grid today; CCS with ISO 15118-20 is where the market is heading; OCPP 2.1 is what lets an energy partner manage the flow. A household that understands which of those its car and charger speak knows exactly how much of its energy independence it has actually secured.