Vehicle-to-grid (V2G), translated from English as "from the vehicle to the grid", describes a system in which energy can be sold to the electrical grid by the driver of an all-electric or plug-in hybrid vehicle, when it is connected to the grid when it is not used for transportation. Alternatively, when the car batteries need to be recharged, the flow will be reversed and electricity will flow from the grid to the vehicle.

V2G can be used with electric vehicles (BEV) or hybrids that have a plug. Most vehicles remain parked 95% of the time, their batteries could be used by letting the electricity flow from the car to the power lines and vice versa.

• A combustion vehicle (hybrid or powered only by fuel) that generates energy from stored fuel, using its generator to produce the energy when there is a very great need for electricity.

• A battery or hybrid vehicle that uses its excess energy by giving it to the grid at times of greatest need. These vehicles can be recharged during off-peak hours at cheaper rates, helping to absorb energy generation during the night.

• A solar vehicle that uses its excess energy to give it to the grid. Such systems have been in use since the 1990s and are routinely used in the case of large vehicles, such as rockets.

An important project on the V2G system is being carried out in the United States at the University of Delaware. The team of researchers includes Professor Willett Kempton, a pioneer of V2G technology, also collaborating with the Californian company AC Propulsion, creator of the term V2G, to improve both charging systems and cars and their storage systems.

The Danish island of Bornholm, with 40,000 inhabitants, through a European project, called EDISON (Electric Vehicles in a Distributed and Integrated Market using Sustainable Energy and Open Networks), will serve as a test bed. They intend to use the batteries of the island's vehicles (in the future they want all cars to be electric) to make better use of wind energy. Those responsible for the project estimate that currently 20% of Bornholm's energy comes from wind. With this V2G system, they believe that wind utilization could reach up to 50%.

Some electricity companies are also studying V2G projects. San Francisco-based Pacific Gas and Electric Company (PG&E) uses several Toyota Priuses it owns in a V2G system on Google's campus in Mountain View, California. For its part, Xcel Energy, based in Minneapolis (USA), is experimenting with six Ford Escape hybrids.

The Grid for Vehicle consortium (G4V), with the support of EURELECTRIC"),[1]​ has organized a Conference in Brussels to present the final result of its European research project.[2]​.