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Could EVs Be the Secret to a 100% Renewable Grid?

The Mitsubishi Outlander PHEV | Image credit: Mitsubishi

It is possible to unlock a 100 percent renewably powered grid — without any coal, nuclear or gas storage baseload — within the next several years. And any driver or homeowner could contribute to the solution by using electric vehicles (EVs) as mobile batteries that charge at one location when there’s a surge of renewable energy and deliver it back to the grid at another when it’s needed.

The storage potential of EVs is striking. Aggregating energy across one million EVs amounts to 50 to 100 GWh of storage capacity, according to industry analysts Brattle Group. Putting that into perspective, Tesla’s “big battery” in South Australia, currently the largest battery in the world, stores less than 1GWh.

With electric cars storing and transporting renewable power, we wouldn’t need to continue building expensive storage infrastructure. For utilities, this vast mobile power source could be a savior — or their downfall. 

Batteries on wheels

EVs have more capacity than they need on a daily basis: The average daily car trip in the U.S. is about 30 miles, while most EVs have a range of 124 to 310 miles. Current base model vehicles with a 186.4-mile range on a 60 kW battery pack could run a typical house, including air conditioning, for four to five days. And despite some car owners’ concerns, discharging the battery won’t cause noticeable wear, because a typical battery’s life is longer than the lifetime of a vehicle.

Using vehicle-to-grid (V2G) technology, which allows vehicle batteries to store surplus energy from intermittent renewable resources like solar and wind, EV owners could power their homes with energy stored in car batteries or sell it back to utilities, balancing fluctuations in energy demand. Using real-time rates, utilities could encourage EV owners to charge up during the day, when there is excess (and therefore cheap) solar energy, and sell back to the grid during times of high demand.

EV owners would charge their vehicles using a high-powered charger (already coming on the market) while at work or out shopping, and then drive home and plug the car into their home charger. As demand for energy ramped up in the evening, utilities could purchase a bit of power from the full EV battery. There would still be plenty of power left in the vehicle, which could be topped up the next day. Meanwhile, drivers would earn more from selling their battery power than they paid for it.

Going with the flow

Two things need to happen to make this vision a reality. The first is widespread availability of bidirectional charging — technology that allows power to flow between an EV battery and the charger or power grid. Whereas EVs today only import electricity, and EV charging stations can only send electricity to the vehicle, V2G-enabled EVs could feed electricity from their batteries to the grid using bidirectional charging stations.

Japanese EVs already support bidirectional charging (Japan sees it as a disaster preparedness feature, allowing cars to provide energy if the grid goes down). Mitsubishi launched the V2G-enabled Outlander PHEV car in Denmark last year, and Honda recently invested in bidirectional charging at its European R&D site.

In the U.S., the National Renewable Energy Laboratory (NREL) is experimenting with V2G car and charger capabilities. On the charger side, Tritium is engineering a bidirectional DC charger (we assume our competitors are as well), and standards are en route: The Institute of Electrical and Electronics Engineers (IEEE) Electric Vehicle Charging Conformity Assessment Steering Committee is creating technical standards for a DC bidirectional EV fast charger.

Staying current: The utility opportunity

Second, utilities must develop grid-balancing programs that fulfill the potential of this new resource. Utilities hold the key to unlocking EV-to-grid capabilities, and there’s ample reason for them to use it.

Electric vehicles can increase the energy consumption of an average home by 25 to 30 percent, according to Duke Energy, and the NREL found up to a 38 percent increase in U.S. electricity consumption due to EV adoption. Further, Bloomberg New Energy Finance projects that EV electricity consumption will increase to about 33 terawatt-hours per year by 2025 and 551 terawatt-hours by 2040.

The business opportunity is clear, but utilities will have to act fast to hold on to it. Once home batteries coupled with rooftop solar become widely accessible and discharge from EV batteries can fill in any energy shortage, a large number of EV owners may choose to leave the grid in favor of powering their homes with a combination of solar energy and battery storage.

Incentivizing EV drivers to sell power back to the grid is the way to keep them hooked up. If utilities make it financially attractive, drivers will give them access to all those big, mobile battery packs when the sun isn’t shining. Most likely this means demand response using a real-time pricing signal, possibly targeted at whatever transformer the driver is connected to. If the incentives are right, drivers will be better off selling power back to the grid and charging according to grid needs than using their EV to top off their home battery.

In a 40 percent renewable energy penetration scenario, managed charging — which allows a utility or third party to control vehicle charging based on the grid’s needs — could also reduce the cost of delivering electricity to an EV in California from $1,400 to less than $600 per vehicle.

Challenges to charging

Even when bidirectional charging is market-ready, we’ll face a stack of interlocking regulatory barriers to deploying EVs as mobile batteries. For instance, most utilities are not allowed to operate generation assets, and presumably, a bidirectional EV would legally count as a generator. But most utility-scale generators have a minimum allowed size for power resources that can go into a regulated electricity market. A 10kW EV is too small, so EVs would have to be aggregated and operated as one large virtual device — the problem there is that many metering and utility regulations don’t allow aggregation.

These barriers can be overcome, however. Once people realize they can go off-grid entirely using their EVs and a solar array, utilities will press regulatory bodies for policies that will allow them to retain customers and revenue from the EV market. Letting this opportunity slip is a major risk to utilities. If they don’t create a price signal to interact with EVs during peak charging times, they won’t be ready for the strain of EV uptake on the grid.  

A roadmap to renewable profitability

There’s an alternative future in which EVs become a grid resource, and it’s on the horizon. Once bidirectional charging becomes available and utilities incentivize customers to feed energy from their vehicles back to the grid, the transition to on-demand renewable power will occur.

States across the U.S. — including California, Texas and New Jersey — are busy rolling out EV charging infrastructure. Using EVs to help balance the grid, instead of simply adding energy demand to it, should be an easy choice for utilities as well as drivers.


James Kennedy is co-founder and engineering director of Tritium, an Australia-based global manufacturer of DC fast chargers for electric vehicles. @tritiumaus

[Read more about James Kennedy]


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