Solar energy is more or less free once the equipment is operational. But it is intermittent. It is available only in sunny hours. V2G or Vehicle-to-Grid is a system wherein a vehicle can connect directly to the grid either to buy power (battery charging) from the grid or to sell power to the grid. It is not basically the vehicle, but the already present large battery storage that is being used. In the solar or wind energy context a grid connected vehicle can serve two main purposes.
Vehicle-to-grid and grid load balancing
Electrical vehicles have large battery capacities which can be gainfully used in balancing grid demand variations. The battery capacity can be used to store energy when the grid is overproducing. This would be typically at night when the demand is below the base production level.
This is sometimes referred to as valley filling (a ‘valley’ in the demand curve). The stored energy can be supplied to the grid when the demand is more than the base demand. This is called ‘peak shaving’ - indeed, a vehicle can hardly make ‘cut’, but can only ‘shave’ a little off the peak.
The utility company has to meet peak demands by switching in smaller generators which can quickly come online in response to a rising demand. Such generators are invariably more expensive to maintain and operate.V2G can help meet the peak demand at a relatively lower cost. This concept is being encouraged by most governments. When the source of battery charging is wind or solar, it has the additional benefit of increasing the proportion of clean energy.
An electric vehicle can store up to 50 KWh currently. For comparison: this is sufficient to service two days’ consumption of a household requiring 1 KW average power. Such batteries can help overcome the limitations of the solar- and wind-power which are intermittent in nature.
As battery capacities increase, this role of vehicle-to-grid will gain greater significance or may yield to H2G (Home to Grid). A lot of research is afoot to increase battery capacity and power density, and safety.