V2G meaning in General ?

Vehicle-to-grid (V2G) describes a system in which plug-in electric vehicles (PEV), such as battery electric vehicles (BEV), plug-in hybrids (PHEV) or hydrogen fuel cell electric vehicles (FCEV), communicate with the power grid to sell demand response services by either returning electricity to the grid or by throttling their charging rate. V2G storage capabilities can enable EVs to store and discharge electricity generated from renewable energy sources such as solar and wind, with output that fluctuates depending on weather and time of day.

V2G can be used with vehicles that can be connected to an electric plug. These are generally referred to as plug-in electric vehicles (PEV), which includes battery electric vehicles (BEV), and plug-in hybrids (PHEV). Since at any given time 95 percent of cars are parked, the batteries in electric vehicles could be used to let electricity flow from the car to the electric distribution network and back. A 2015 report on potential earnings associated with V2G found that with proper regulatory support, vehicle owners could earn $454, $394, and $318 per year depending on whether their average daily drive was 32, 64, or 97 km (20, 40, or 60 miles), respectively.

Batteries have a finite number of charging cycles, as well as a shelf-life, therefore using vehicles as grid storage can impact battery longevity. Studies that cycle batteries two or more times per day have shown large decreases in capacity and greatly shortened life. However, battery capacity is a complex function of factors such as battery chemistry, charging and discharging rate, temperature, state of charge and age. Most studies with slower discharge rates show only a few percent of additional degradation while one study has suggested that using vehicles for grid storage could improve longevity.

Sometimes the modulation of charging of a fleet of electric vehicles by an aggregator to offer services to the grid but without actual electrical flow from the vehicles to the grid is called unidirectional V2G, as opposed to the bidirectional V2G that is generally discussed in this article.