Vehicle to Grid

Vehicle-to-grid

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. 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, pluginable vehicles as Battery Electric Vehicles (BEV) or Plug-in hybrid electric vehicles (PHEV), 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.

Many various V2G projects are going on throughout the USA. Notably, at the University of Delaware, 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.

History

The company AC Propulsion Inc. coined the term V2G for vehicle-to-grid.

Three versions

V2G is a version of Battery-to-grid power applied to vehicles. There are three different versions of the vehicle-to-grid concept:

A hybrid or Fuel cell vehicle, which generates power from storable fuel, uses its generator to produce power for a utility at peak electricity usage times. Here the vehicles serve as a distributed generation system, producing power from conventional fossil fuels.
A battery-powered or hybrid vehicle which uses its excess rechargeable battery capacity to provide power to the electric grid during peak load times. These vehicles can then be recharged during off-peak hours at cheaper rates while helping to absorb excess night time generation. Here the vehicles serve as a distributed battery storage system to buffer power.
A solar vehicle which uses its excess charging capacity to provide power to the electric grid when the battery is fully charged. Here the vehicle effectively becomes a small renewable energy power station. Such systems have been in use since the 1990s and are routinely used in the case of large vehicles, especially solar-powered boats.

Peak load leveling

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 unreliable nature 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 blackouts Since demand can be measured locally by a simple frequency measurement, dynamic load leveling can be provided as needed.

Backup power solutions

V2G could also be used as a buffer during power outages. 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.

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.

Future battery developments 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.

Utilities

These utilities currently have V2G technology trials:

PG&E, USA, converting a number of company-owned Toyota Prius to be V2G PHEVs at Google's campus
Xcel Energy, USA, converting six Ford Escape Hybrids to PHEVs with V2G

Skepticism

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.

A Environmental Defense representative stated: "It’s hard to take seriously the promises made for plug-in hybrids with 30-mile all-electric range or any serious V2G application any time soon. It’s still in the science project stage."

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."

Not all skepticism is warranted. Federal Energy Regulatory Commissioner Jon Wellinghoff points out that it is a myth that vehicle to grid necessarily decreases the life of the battery. When V2G is used to fill valleys of demand, it stabilizes the grid by absorbing surges in capacity. This can be done "without affecting the charge whatsoever."

References

External links

Diehl, Stephen "Study suggests electric cars could pay their owners back". Green Mountain College

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Kempton, Willett (2005). "Automobiles: Designing the 21st century fleet". Seattle V2G Technical Symposium, University of Delaware [PDF]
Penney, Terry; Jennifer Elling (2005). "The Race to Connect Cars, Communities and Renewables". Geotimes.org
Woody, Todd (2007). "PG&E's Battery Power Plans Could Jump Start Electric Car Market". Blogs.business2.com – ^{Scholar search}

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Woolsey, Jim; Sexton, Chelsea; Brilliant, Larry "RechargIT: Plug-in Hybrids and V2G". Youtube.com

"20kW DC/AC Power Inverter Preliminary Specifications, For Distributed Power Applications". UQM Technologies, Inc. – ^{Scholar search}

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