• In V2GHalf, PHEV/BEV charging is varied to absorb the additional imbalance from the wind generation, but never feeds power back into the grid. This scenario is highly desirable to automotive manufacturers, who harbor great concerns about battery warranty if vehicle-to-grid discharging is allowed.

• V2GFull varies not only the charging of the vehicle battery, but also can vary the discharging of the battery back into the power grid. This scenario is currently less desirable to automotive manufacturers, but provides an additional resource benefit to PHEV/BEVs by theoretically doubling their capacity value to the grid.

The report examined grid conditions in the Northwest Power Pool, which covers Idaho, Montana, Nevada, Oregon, Utah, Washington and Wyoming; many of them home to abundant wind resources and wind energy projects. In particular, the PNNL report examined the implications of adding another 10 Gigawatts of wind to the region’s grid by 2019, which regulations such as the Renewable Portfolio Standards require.

Key findings of the report include:

1. While a V2GFull operating mode may have some market acceptance barriers to overcome, V2GHalf would not be encumbered with these issues. V2GHalf strategies only require a modulation of the charging current without violating the users’ desire to have the battery fully charged at a certain time. If about 13% of the existing light-duty vehicle stock (about 2.1 million vehicles) were PHEVs with a 33-mile electric range and applied V2GHalf charging strategies at home and at work, all of the additional balancing requirements of 3.7 GW could be provided by the electric vehicles.

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2. There is a strong relationship of the availability of charging stations throughout the day (“charging at work”) on the total number of vehicles required to meet the balancing requirements. The results reveal a behavior of diminishing returns after the vehicle stock is offered a certain amount of charging stations at work. Almost 80% of the improvements by offering public charging stations at work can be achieved with about 10% of public stations (i.e., a public to residential charging station ratio of 1:10).

3. A comparison between V2GFull and V2GHalf confirmed that the individual larger capacity that V2GFull service offers to the grid (6.6kW=3.3kW – (-3.3kW)), which is theoretically double the capacity of V2GHalf (3.3kW), requires a smaller number of vehicles to meet the additional balancing constraints. The V2GFull service requires, on average, about 30 to 35% fewer vehicles than the V2GHalf approach, across all scenarios.

4. The size of the vehicle battery matters for supplying balancing services. For the home-only charging option, the larger battery (BEV) reduces the number of required vehicles in the range of 17% to 30% over that for a PHEV33, while for home and work charging options, the improvement potential is only between 7% and 10%.

5. A comparison between Level 1 and Level 2 charging revealed very little differences. This suggests that the apparent advantage of higher electricity demand of Level 2 charging (3.3 kW) compared to Level 1 charging (1.7 kW), does not reduce the number of vehicles to meet the balancing requirements in the proportion of the charging limits, the authors concluded.

6. A limiting case was defined that postulated that all electric vehicles be available 24x7 performing V2GFull services—i.e., a case identical to a distributed stationary energy storage system dedicated to perform balancing services. For this limiting case, a total number of about 560,000 vehicles (4% of light-duty vehicle stock) would be necessary with a Level 2 (3.3 kW) charging/discharging technology to provide all of the additional balancing services.

The results indicate that the emerging electric vehicle fleet could make a substantial contribution toward meeting the new balancing requirements associated with the grid integration of growing wind technology deployment. To what degree this potential can be realized in the future will depend on the economics of the implementation and a viable and compelling business model either for the individual electric vehicle owner, or a third-party service provider. Other demand response technologies, particularly residential electric hot water heaters and large industrial customers, are likely to compete for the same market share.

While several million hot water heaters are already installed in residential and commercial buildings, electric vehicles still have to prove their market acceptance. However, the international automotive industry has made significant investments in battery and electric vehicle technology, giving rise to the anticipation that electric vehicles will play a role as transportation means. With an optimistic outlook of future market adoption of PHEVs and EVs in the US, 10% of the light-duty vehicle stock could be achieved by about 2030.

—Tuffner and Kintner-Meyer

This research was funded by the Department of Energy.

Resources

• Frank Tuffner, Michael Kintner-Meyer (2011) Using Electric Vehicles to Meet Balancing Requirements Associated with Wind Power (PNNL-20501)