The “Cash-back car”: Danish EV owners to sell power back to the grid

US company Nuvve will use Denmark as the first test market for a new technology allowing electric vehicle (EV) owners to sell energy stored in their EV batteries back to the grid.

The first pilot will consist of 30 cars. According to Nuvve, individual EV owners could make $10,000 over the lifetime of a vehicle (estimated at 8 years) depending on market price and owner commitment.

The EV owner makes the battery available to Nuvve during a given time period and, depending on supply and demand in the grid, the company uses the car as a short-term energy storage resource to help regulate the power frequency of the grid. Frequency regulation involves adding or reducing power in real-time to match demand.

Although EVs have been discussed for some time as a possible electricity storage solution, the technology wasn’t expected to be deployed in practice for at least another five years. Since most EVs, like other cars, are stationary 95 percent of the time, this could be a good deal for both owners and utilities.

Not all EVs are capable of  the bi-directional power flow that allows energy to be drained from the battery back to the grid. Other EVs will still be able to participate by relieving the grid of surplus power when needed. The 2012 Mitsubishi MiEV, 2012 Daimler Smart E, BMW Mini E, Detroit Electric e63 and Luxgen 7 MPV and SUVall support bi-directional power flow.

Denmark is an obvious choice for Nuvve given its high volume of wind-power and the problem of maintaining a constant energy supply in the presence of large volumes of intermittent power such as that generated by wind. Wind generation tends to reach a maximum at night when demand is at its lowest, making storage necessary. Renewable energy sources like wind also cause voltage rises which can result in grid instability when a large amount of renewable power is feeding into the grid, such as on a stormy night.

Nuvve’s V2G (vehicle to grid) solution was developed at the University of Delaware under the supervision of Professor Willet Kempton who now serves as Nuvve’s CTO. The owner indicates how far he wants to drive on a particular day and the periods during which the car is available to the grid. A computer embedded in the EV measures the power absorbed and fed back to the grid and communicates with Nuvve’s servers.

V2G systemThe servers aggregate multiple EVs into a small “virtual storage network”. Many utilities participate in power regulation markets to buy and sell relatively small amounts of power in real-time so they can match demand. When the market requests a specific amount of power, Nuvve matches the request with the power available in the batteries of its car fleet and sends the required power back into the grid instantly. Utilities pay a premium for access to this instant power supply. It can cost 3 times more than the retail electricity price.

Current storage solutions include Gas turbines, pumped hydroelectricity, compressed air, fly wheels and large battery installations but all of these required a large capital investment from the utility. Nuvve’s system is more like storage as a service.

There are concerns that frequent charging of the EV’s battery could cause it to degrade more quickly. According to Nuvve this is true for full cycles but not if you stay close to a 50 percent charge. Nuvve is giving an incentive to car owners to plug in their cars as often as possible, offering a higher level of battery management.

Nuvve is based in San Diego but plans to establish a Danish headquarters in Horsens. The company was founded in 2010 and is privately funded.

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