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V2G |
Vehicle-to-grid (V2G) describes a system in which power can be sold to the electrical power grid by an electric-drive motor vehicle that is connected to the grid when it is not in use for transportation.1 Alternatively, when the car batteries need to be fully charged, the flow can be reversed and electricity can be drawn from the electrical power grid to charge the battery.
Vehicle-to-grid can be used with such gridable vehicles, this is, plugin vehicles (this is, electric vehicles as Battery Electric Vehicles (BEV) or Plug-in hybrid electric vehicles), with grid capacity. Since most vehicles are parked an average of 95 percent of the time, their batteries could be used to let electricity flow from the car to the power lines and back, with a value to the utilities of up to $4,000 per year per car. Since power companies only buy power in blocks of 1 MW, at least 20,000 vehicles need to be connected to the grid.2
One notable V2G project in the United States is at the University of Delaware, where a V2G team headed by Dr. Willett Kempton has been conducting on-going research. Their goals are to educate about the environmental and economic benefits of V2G and enhance the product market.>3 Other investigators are PG&E, XCel Energy, and the federal National Renewable Energy Laboratory.4
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The company AC Propulsion Inc. coined the term V2G for vehicle-to-grid.5
V2G is a version of Battery-to-grid power applied to vehicles. There are three different versions of the vehicle-to-grid concept:
The concept allows V2G vehicles to provide power to help balance loads by "valley filling" (charging at night when demand is low) and "peak shaving" (sending power back to the grid when demand is high). It can enable utilities new ways to provide regulation services (keeping voltage and frequency stable) and provide spinning reserves (meet sudden demands for power). In future development, it has been proposed that such use of electric vehicles could buffer renewable power sources such as wind power, for example, by storing excess energy produced during windy periods and providing it back to the grid during high load periods, thus effectively stabilizing the intermittency of wind power. Some see this application of vehicle-to-grid technology as a renewable energy approach that can penetrate the baseline electric market.
It has been proposed that public utilities would not have to build as many natural gas or coal-fired power plants to meet peak demand or as an insurance policy against blackouts6 Since demand can be measured locally by a simple frequency measurement, dynamic load leveling can be provided as needed.7
V2G could also be used as a buffer during power outages. As the New York Times explains:
| “ | [After a power outage, a Florida man] plugged his Toyota Prius into the backup uninterruptible power supply unit in his house and soon the refrigerator was humming and the lights were back on. “It was running everything in the house except the central air-conditioning” ... As long as it has fuel, the Prius can produce at least three kilowatts of continuous power, which is adequate to maintain a home’s basic functions. 4 | ” |
However, at the present time many electric vehicle conversion owners, whose battery of choice is still lead acid with limited cycle lives and capacity, would prefer to use them to power their cars rather than load-balance the electricity grid.
Future battery developments8 may change the economic equation, making it advantageous to use newer high capacity and longer-lived batteries in BEV/PHEVs and in grid load balancing and as a large energy cache for renewable grid resources. Even if cycled daily, such batteries would only require replacement/recycling every 55 years or so. Since BEVs can have up to 50 kWh worth of battery storage they represent somewhat more than the average homes daily energy demand. Even without a PHEV's gas generation capabilities such a vehicle could be utilized for emergency power for several days (V2H or Vehicle-to-home). As such they may be seen as a complementary technology for intermittent renewable power resources such as wind or solar electric.citation needed
These utilities currently have V2G technology trials:
There is some skepticism among experts about the feasibility of V2G. As the New York Times states:
| “ | An analyst at the Minneapolis-based utility Xcel Energy, [explained] a “pie-in-the-sky vision” for V2G in which a company would offer incentives to its employees to buy plug-in hybrids. The parking lot would be equipped with recharging stations, which could also return power to the grid from the vehicles.4 | ” |
A Environmental Defense representative stated: "It’s hard to take seriously the promises made for plug-in hybrids with 30 miles (48 km) all-electric range or any serious V2G application any time soon. It’s still in the science project stage."4
The Vehicle-to-grid potential of Honda’s full hybrid vehicles is unexplored, but Honda is doubtful of using them to power homes. "We would not like to see stresses on the battery pack caused by putting it through cycles it wasn’t designed for," said a Honda spokesman. "Instead, they should buy a Honda generator that was made for that purpose."4
Not all skepticism is warranted. Federal Energy Regulatory Commissioner Jon Wellinghoff points out that partial grid regulation (absorbing excess surges, but not supplying peak power) can be done without decreasing the life of the battery. This can be done "without affecting the charge whatsoever." 9
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