Bidirectional charging: what it is and how it works
Electric cars no longer simply absorb energy from the grid: with bidirectional charging, they can also return it, becoming an active energy resource.
This is a significant change in perspective for anyone considering an electric vehicle and wanting to understand whether this technology can really make a difference in their home or in their relationship with the power grid.
What is meant by bidirectional charging?
Traditional electric charging works in one direction only: the current flows from the power grid to the vehicle battery. Bidirectional charging reverses this logic, also allowing the opposite flow, from the car battery to the home electrical system or to the public grid.
For this to be possible, the charging station must be equipped with a bidirectional inverter, which converts the direct current stored in the battery into alternating current that can be used by household appliances and electrical systems. Not all wallboxes support this function: both the vehicle and the charging point must be compatible with the required technical standards.
The concept falls within the scope of smart charging: an intelligent management of Energy flows that goes beyond the simple charging operation, integrating the vehicle as an active element of the Energy system.
How it works: energy flow in both directions
In a normal electric charging session at home, Energy follows a linear path: from the grid to the meter, from the meter to the wallbox, and from the wallbox to the vehicle battery. Charging times depend on the available power and battery capacity.
With bidirectional charging, the wallbox can manage the flow in both directions. The car communicates with the management system through a specific charging socket and dedicated protocols (such as CHAdeMO or the more recent CCS Combo), which digitally regulate the amount of Energy supplied, the timing and the safety conditions.
To better understand how charging systems work in general, it is useful to start from how electric charging works in its fundamental elements: power, current and communication between the vehicle and the infrastructure.
The vehicle battery thus becomes part of a broader Energy storage system: it can store Energy when the cost is lower (for example, during night-time hours or when Photovoltaic production is available) and supply it when demand increases. Everything happens automatically, according to parameters set by the user or managed by a home automation system.
Bidirectional charging modes: V2G, V2H and V2L
Bidirectional charging is divided into three main modes, which differ according to the destination of the Energy returned by the vehicle.
Vehicle-to-Grid (V2G)
The vehicle supplies Energy directly to the public power grid. In this scenario, the car acts as a balancing element for the national Energy system: at times of peak demand, the batteries of connected vehicles can help stabilise the grid. In return, the owner may receive financial compensation from grid operators, in a model that is still under development in Italy.
Vehicle-to-Home (V2H)
The Energy stored in the battery is supplied to the home electrical system. This scenario is particularly interesting for those who have a Photovoltaic system: the car becomes a sort of mobile Energy storage system, storing solar Energy during the day and supplying it back in the evening. Combined with a heat pump or other significant household loads, the potential savings are considerable.
Vehicle-to-Load (V2L)
This mode makes it possible to directly power electrical loads through a socket integrated into the vehicle, without the need for a bidirectional wallbox. It is useful for powering electrical tools on construction sites, camping equipment or other devices when a stable power grid is not available. Some car manufacturers have already integrated it into their models.
Which cars and wallboxes are compatible?
Compatibility with bidirectional charging depends on two factors: the vehicle and the charging point. Not all electric models currently on the market support this function; its availability varies depending on the battery architecture and the communication protocol adopted by the manufacturer.
As for the infrastructure, the wallbox must be specifically designed to manage flows in both directions. New-generation wallboxes for home charging are progressively integrating this capability, but at present their adoption remains limited compared with the overall installed base.
When choosing a charging point, it is useful to consider not only its current technical compatibility, but also its readiness for future upgrades, in a rapidly evolving sector.
Advantages and current limitations
The main advantages of bidirectional charging
Reduced dependence on the grid during peak periods, with potential savings on the Energy bill;
integration with Photovoltaic systems to maximise self-consumption;
possible remuneration for those participating in V2G programmes with grid operators;
contribution to the stability of the national Energy system.
Specific limitations that are important to consider
The number of vehicles compatible with V2G or V2H is still limited;
bidirectional wallboxes have higher purchase and installation costs than standard models;
the Italian regulatory framework is still evolving and V2G remuneration models are not yet fully operational;
the additional battery cycling could affect its lifespan in the long term, although manufacturers tend to design batteries to handle these cycles.
The regulatory context and adoption in Italy
In Italy, bidirectional charging is a technology at an advanced stage of adoption but not yet fully established. ARERA and the relevant authorities are defining the rules for the participation of electric vehicles in flexibility markets, which are necessary for the V2G model to become economically advantageous for private individuals.
Some pilot projects are already active, in collaboration between grid operators, car manufacturers and Energy operators. The direction is clear: the Integrated National Energy and Climate Plan (PNIEC) envisages an increasingly significant role for smart charging in load management and the integration of renewable sources.
Those approaching this technology today are positioning themselves ahead of a market that, in the coming years, will likely be much more mature and accessible.
Frequently Asked Questions
Additional charging and discharging cycles can, in theory, affect battery degradation over the long term. In practice, manufacturers design modern electric vehicle batteries to handle this type of use, and many guarantee the V2H or V2G function without affecting the warranty, provided that the system is used within the specified parameters. It is nevertheless advisable to check the specific conditions for your vehicle model.
It depends on the capacity of the vehicle battery. A car with a 60 kWh battery, for example, could supply between 20 and 40 kWh without dropping below a minimum reserve threshold, an amount sufficient to cover the average daily Energy needs of a home. These thresholds are generally managed automatically through the wallbox or vehicle control system.
No additional contract is required for V2H mode, as the Energy is used within the home electrical system. V2G, on the other hand, involves supplying Energy to the public grid and therefore requires an agreement with an aggregator or grid operator. These contractual models are still being defined in Italy and are not yet widely available to private individuals.
V2G in Italy is mainly still at the experimental stage. Active pilot projects are in place, but the regulatory framework for the participation of private vehicles in Energy markets has not yet been fully defined. ARERA is working on the regulation of flexibility systems, which will pave the way for wider adoption in the coming years.
Not necessarily. Operation in island mode, i.e. when the grid is unavailable, requires both the wallbox and the home electrical system to be configured to disconnect from the grid and operate independently. Not all bidirectional systems support this mode. Without this function, even if the battery is charged, the system switches off for safety reasons when a blackout occurs.
The connector depends on the standard adopted. CHAdeMO, developed mainly by Japanese car manufacturers, was the first to support bidirectional charging and is still the most widely used for V2G. CCS Combo 2, which is predominant in Europe, is developing bidirectional support through the ISO 15118-20 standard. Some vehicles use proprietary connectors for V2L. Before purchasing a bidirectional wallbox, it is essential to check compatibility with the connector used by your vehicle.
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