Bidirectional Charging

More than just charging: the electric car as a flexible energy storage solution

With bidirectional charging – or ‘BiDi’ for short – the electric car becomes a flexible energy storage solution: it can not only draw energy but also feed it back into the grid, thereby reducing the cost of electricity consumption and increasing self-consumption.

Most electric cars spend the majority of the day unused in garages or car parks. This is precisely where bidirectional charging comes in: the vehicle’s battery is integrated into the energy system and can store surplus electricity or make it available again when needed.

What does this new technology mean for you?

Solar power can be utilised to the full: Instead of feeding surplus PV electricity into the grid for comparatively low remuneration, it can be stored in the electric car. It is then available again later – for example, in the evening for domestic or business use when the sun has gone down. This time lag significantly increases self-consumption. The vehicle’s battery offers sufficient capacity for this. In purely mathematical terms, a 50-kilowatt-hour battery in a medium-sized electric car can supply a four-person household in a detached house for 3–4 days (based on an annual consumption of 4,700 kWh, including electric water heating).
Targeted reduction in electricity costs: With a dynamic electricity tariff, the electric car charges when electricity is cheap. If prices rise, it can feed the stored electricity back into the home. This means less expensive electricity needs to be drawn from the grid.
Energy can be used flexibly: Even in a commercial setting, the vehicle battery can help to cushion periods of unusually high electricity demand within a business and ensure compliance with available grid capacity. Operators with load profile monitoring can thus ensure they do not have to pay the more expensive tariff for an entire month due to a single exceedance. This advantage is particularly evident during longer periods when a connected fleet of electric vehicles is stationary at charging points.

A key component of the energy system of the future

Through Vehicle-to-Grid (V2G), many vehicles can collectively contribute to stabilising the electricity grid. This creates a decentralised energy storage system comprising many individual batteries, which can offer both spare battery capacity to store surplus energy from the grid and energy to feed back into the grid. A key component of the energy transition. Owners of vehicles capable of bidirectional charging will in future benefit from several advantages simultaneously: on the one hand, they can optimise their energy costs; on the other, they can participate in energy trading via an intermediary – known as an aggregator – and offer V2G services to the grid operator.

AC or DC: two technical approaches

In principle, bidirectional charging can be carried out using direct current (DC) or alternating current (AC). Whilst with DC charging a large proportion of the power electronics is located within the charging infrastructure, AC BiDi utilises exclusively the power components already present in the vehicle. This is why AC solutions are more cost-effective, particularly in private and commercial settings, and are therefore more scalable.

Market forecasts predict that, from 2027 onwards, the share of bidirectional vehicles with AC charging capabilities will continue to grow, eventually leading to AC technology occupying a dominant position in the mass market.

Standards and market conditions: bidirectional charging with clear rules and common standards for a mass-market

Bidirectional charging is already a reality. However, regulatory and technical frameworks still need to be established for widespread market adoption. Many key standards and regulatory frameworks are already being implemented. The years 2026 and 2027 are regarded as a crucial phase for the market ramp-up of bidirectional AC charging.

As soon as a vehicle feeds energy back into a building or the electricity grid, it is treated, together with the charging infrastructure, as a generation plant for regulatory purposes. This gives rise to new requirements regarding electrical safety, communication and grid connection. A certified solution is tested for compliance with the required standards and integrates seamlessly into the bidirectional ecosystem.

Important questions about bidirectional charging technology

Is the technology already available?

Yes, the technical foundation already exists.

Bidirectional charging functions are supported by an increasing number of vehicle manufacturers, and the first solutions are already in use. Research projects and field tests have shown that Vehicle-to-Home (V2H), Vehicle-to-Building (V2B) and, in the future, Vehicle-to-Grid (V2G) work from a technical perspective. in 2027 and onwards new OEM platforms will push sales for bidirectional electro mobility.

What standards are required?

The aim is for all components to speak the same language. Bidirectional charging involves the interaction between the vehicle, the wallbox, the energy management system and the electricity grid. Uniform standards are required to ensure that these components can communicate across different manufacturers.

These include, amongst others

For grid connection & grid stability

RfG 2.0 (Requirements for Generators) as the European basis for systems capable of feeding power back into the grid
EN 50549-1, amongst other things, as the reference standard for feed-in verification and grid security
VDE-AR-N 4105 for grid connection in Germany (and other norms in other European countries accordingly)

For communication & control

ISO 15118-20 for communication between the vehicle and the charging infrastructure

For the basic framework and electrical safety

IEC 61851-1 with Annex F on general requirements for conductive (cable-based) charging, including power feed-back
ISO 5474-2 as an extension of the standards to include all functions required for bidirectional AC operation

Standards such as these lay the groundwork for interoperability and, through the certification of charging infrastructure, provide investment security for the future.

What regulatory hurdles remain?

The regulatory framework is constantly evolving. To ensure that vehicles can feed energy back into the grid in a cost-effective and legally compliant manner, a wide range of issues are currently being discussed at both German and European level and are being finalised with increasing success.

Grid connection and energy feed-in
Metering and billing schemes
Grid charges, taxes and levies
The roles of grid operators and energy suppliers
Certification and authorisation processes

The year 2027 is regarded as a key turning point for the further opening up of the market.

When will Vehicle-to-Grid become economically viable?

Vehicle-to-Grid becomes an interesting prospect as soon as there are enough vehicles, standards and market mechanisms in place.

The greatest potential arises when many vehicles can make their battery capacity available on a flexible basis. This makes it possible to reduce peak loads, better integrate renewable energy and create additional flexibility for the electricity grid. With the increasing uptake of vehicles capable of bidirectional charging and a clear regulatory framework, Vehicle-to-Grid is gradually evolving from a pilot project into a commercially viable application. Experts see considerable potential here for consumers, businesses and the energy system as a whole, and anticipate the emergence of a mass market from 2027/2028 onwards.

What you should consider now

Anyone investing in charging infrastructure today should not just consider current needs. It is important to choose a solution that also takes future requirements into account.

The key points are:

When planning, ensure you opt for certified, future-proof solutions
Expand your systems: compatibility between existing unidirectional and new bidirectional systems
Bidirectional communication standards to ensure seamless data exchange between the vehicle, the charging point and the grid
Compatibility with energy management systems

Compleo views BiDi as a comprehensive system

Bidirectional charging is more than just a charging point. The key lies in the interaction between the vehicle, the charging infrastructure, energy management and the electricity grid. Under the new regulations, grid operators will scrutinise whether local grid requirements, protective functions and flexibility requirements for operation are met. That is why Compleo consistently develops its solutions in line with open standards and future regulatory requirements: for an infrastructure that is ready for the next stage electro mobility.

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