Car batteries for grids, the Duke way

Will car batteries really work as a distributed grid storage medium? Duke Energy says: “Yes, but not in the way everyone is thinking.” Photo credit: FIAMM
Will car batteries really work as a distributed grid storage medium? Duke Energy says: “Yes, but not in the way everyone is thinking.” Photo credit: FIAMM
Will car batteries really work as a distributed grid storage medium? Duke Energy says: “Yes, but not in the way everyone is thinking.” Photo credit: FIAMM

Will car batteries really work as a distributed grid energy storage medium? Duke Energy says: “Yes, but not in the way everyone is thinking.” Photo credit: FIAMM

Duke Energy, America’s biggest utility, is working on a way to use vehicle batteries for grid energy storage that could sidestep the concept’s biggest drawback. Electric vehicle batteries have long been mooted as a potential sink for distributed renewable energy sources, helping to mop up excess power in times of plenty.

Similarly, the thinking goes, utilities might be able to tap into some of that stored energy to help stabilise output and deal with peak demand. After all, industrial and residential consumption tends to spike when people are at work or at home, not while they are driving. But the disadvantage of this idea is clear to anyone who has a car: would you really give a utility the ability to empty your tank?

Offering incentives

A power company might address this issue by offering car owners an incentive to make a percentage of their charge available. Alternatively, you could use policies and smart data analytics to make sure you will never draw charge off a battery just as the car owner is about to make a trip.

Pretty much any idea you come up with, though, would presumably come up against the need to have a car owner’s consent to draw power. A low or non-existent consumer take-up would stymie the whole thing. Duke’s approach is not to bother.

Speaking exclusively to Energy Storage Report while in Barcelona for the Internet of Things World Forum, Duke vice president of emerging technology David Mohler said it makes more sense to pick up batteries after users have finished with them.

Second-hand assets

“We think batteries will be second-life assets,” he says, adding that while it is in a vehicle the usefulness of a battery as a grid storage device will in any case be limited by warranty considerations. Mohler confirms Duke is currently carrying out tests on used FIAMM sodium-nickel bus batteries and is also aiming to evaluate other grid battery storage systems such as GE Durathon units.

The idea of redeploying second-hand vehicle batteries makes sense. Electric bus fleets around the world are already sitting on a pile of aging batteries. And using them primarily for slow-discharge applications such as frequency control, which Mohler believes would be an important initial use, could allow them to have a useful lifespan of years.

Introducing applications with different load profiles would be “one of the technical challenges,” Mohler says, but that could be dealt with by having ‘storage portfolios’ where different battery technologies are used for specific tasks on the grid.

Cheaper than new

Furthermore, used batteries will be much cheaper than new ones. Duke reckons it could bag these assets at half to a third of the cost. Right now it gets them free from FIAMM, which is also interested in reusing vehicle batteries on the grid. This augurs well for a vibrant secondary market in vehicle batteries but other business models could arise as well.

Southern California Edison and the now-defunct charging station start-up Better Place, for example, looked into the potential for the utility to effectively own the car battery and lease it to car owners on a usage basisChina Southern Power Grid is considering something similar, according to Mohler.

Whether Duke would be tempted to go down a route like this remains to be seen but it is clear that the utility sees storage as an integral part of its future plans. While speaking at the Internet of Things event, Mohler also described how Duke had used a cheap computer technology called Raspberry Pi to marry its battery storage systems to its PV control systems in a bid to even out power supply.

The setup allows batteries to cut in a mere 20 milliseconds after output from the solar panel drops, effectively eliminating the problem of PV intermittency… for USD$35 a pop.

Written by Jason Deign

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