Electric vehicles can do more than just prevent carbon dioxide emissions. They can also serve as power storage units, stabilize electric grid levels and possibly make money for EV drivers via the so-called vehicle-to-grid (V2G) concept.
With the vehicle-to-grid (V2G), power flows from the electricity grid to the car’s battery and back, ensuring steady power levels and stable frequency generation for grid operators. Electric vehicles can act as mediators between supply and demand to balance fluctuations in energy needs.
And, for EV owners, there is the added benefit of a car that actually makes you money.
The University of Delaware, a forerunner in V2G research, published a study in the March 2007 issue of Science Direct journal examining the possible profits for fleets of vehicles equipped with V2G. According to a projection model, a fleet of 100 Th!nk City vehicles gained an annual net profit of $7000 to $70,000 and a fleet of 252 Toyota RAV4s brought in $24,000 to $260,000 of net profit under a V2G scenario.
Led by Professor Willett Kempton, the University of Delaware research team is made up of professors and graduate students from the marine policy, mechanical engineering and computer and information sciences departments. There are also a number of collaborating researchers from other universities and companies.
You have to balance the value for the vehicle owner with the balance for the grid operators.
–Jackie Piero, member of University of Delaware V2G Research Team
The university is currently testing five Toyota Scions on its vehicle-to-grid system.
The V2G vehicle could also make money for its owner through acting as a frequency regulator for the grid operator.
1 megawatt EV aggregates needed
To maintain electricity production at 60 Hz (the best frequency), small adjustments are made throughout the day to either ramp up or decrease production. This is done through a market in which electricity generators bid on providing one megawatt increases or decreases at a given time.
An aggregate of vehicles can participate in this market if it has a threshold capacity of one megawatt, potentially winning bids to provide this service and paying back the owners of the vehicles as a group.
For a V2G system to be effective, there needs to be an aggregate of vehicles whose storage capacity equals one megawatt of power, explains Jackie Piero, a masters of marine policy student at the University of Delaware and member of the U. of Delaware V2G research team.
These vehicles do not need to be close to each other to form an aggregate. They just need to be in the same Independent System Operator (ISO) boundaries and need to be part of the same frequency regulation market.
There are seven ISOs in the U.S., covering about two-thirds of the country. These ISOs can extend across several states.
The University of Delaware is in the territory of an operator called PJM, which goes from New Jersey south to Virginia and as far west as Chicago.
There are areas in the southeastern and western U.S. that do not have ISOs, which makes V2G incompatible with their utility systems.
Minimum of 67 EVs plugged in
An electric vehicle battery has about 15 kilowatts capacity of power storage. That means a minimum of 67 EVs with 15 kW batteries need to be parked and plugged in to a given sector of the electric grid at all times.
Since driver habits are different, it is unlikely that all 67 vehicles would be parked at the same time. The University of Delaware research team generally figures at least one-third would be unavailable. They assume an aggregate of 100 potential V2G vehicles is necessary to make up for those vehicles not plugged in at a given time, said Piero.
The U. of Delaware team is working with a company called AC Propulsion, which is developing the communications and control systems to make V2G technology possible.
The technology involves plugging an electric vehicle, plug-in hybrid or fuel cell car into an electrical outlet and setting it to the V2G mode. This allows the vehicle to be in constant communication with grid operators to maintain a steady level of power between the car and the electric grid.
V2G does not need “smart grid” technology to operate successfully, since all the necessary communications hardware can be installed in the vehicle itself, notes Piero.
The V2G system is best adapted for the frequency regulation market, she explains.
The frequency regulation market is the minute-to-minute communication between the electricity load (how much power is needed in the grid) and the grid operator (who controls the amount of electricity put out onto the grid). This system ensures that under normal operating conditions, there is a balance between the load needed and the energy put out.
Average car parked 23 hours a day
Since the average vehicle is parked 23 hours a day, there is a long period of time it could be helping to regulate the general electric grid load and generation balance.
However, not all electric vehicles, plug-in hybrids and fuel-cell vehicles have the capability to be adapted to V2G. The power electronics unit has to be capable of a two-way energy flow, or so-called bi-directional power flow. If the car is not built with this innate bi-directional capability, the technology cannot be added later.
According to Piero, only one power electronics unit currently on the market — the unit manufactured by AC Propulsion, called the AC150 — has this innate ability. Power electronics technology such as the AC150 includes hardware, software and a special plug with communications wiring built in. The hardware and software additions cost a few hundred dollars, and the appropriate plug can range from a few hundred to a few thousand dollars.
As far as she knows, says Piero, these are the only manufacturers whose vehicles currently have V2G capability off of the assembly line.
Pure electric cars best for V2G
There is a difference in the V2G capability of vehicles that run solely on electricity and those that run on a combination of electricity and gasoline, says Piero.
A pure electric vehicle has a much larger battery than a plug-in hybrid. The plug-in hybrid vehicle has about one-fourth to one-third the capacity of the EV battery, which makes it less useful as a V2G car, she said.
Any home can be used with a V2G vehicle. The V2G car simply needs to be plugged into a 240 volt, 80 amp socket to be effective storing power, which most homes have.
“The house isn’t the issue,” explains Piero. “It’s the car.”
Energy utilities and grid operators have been receptive to the idea, adds Piero.
Auto manufacturers are more hesitant about the concept, their main concern being the use of the battery for a purpose other than driving, she says.
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The effect of V2G on the battery life of a vehicle is still uncertain.
However, the system does not involve deep recycling of the battery. There will be some effect on battery life, Piero explains, though the fact that the battery is not drained when plugged into V2G mode may lessen this effect.
There is a driver-controlled setting onboard the V2G vehicle to regulate how low the battery can get before cutting the vehicle out of frequency regulation and the passage of electricity.This helps balance the possible effect on battery life, owner driving habits and schedule and the needs of the frequency controller.
“You have to balance the value for the vehicle owner with the balance for the grid operators,” Piero explains.
For V2G to take off, EVs need to become more popular, Piero says. And for this to happen, major automakers need to increase involvement in EV production.
This may mean V2G will be seen as technology for future generations of EVs, once they have become an established part of the auto market.
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