A series of speakers at the California Air Resources Board Zero Emissions Vehicle Symposium explored a potential accelerated adoption scenario for plug-in hybrid (PHEV) and battery electric vehicles (BEV) that exploits the capabilities of vehicle-to-grid charging.
The premise is that the additional cost to consumers of full-function zero-emission vehicles (ZEV) or near zero-emission vehicles—whether full battery electric vehicles, plug-in hybrid vehicles or fuel-cell vehicles—can be partially offset by providing grid power support to utilities or major power consumers.
The dual use of ZEVs for clean transportation and grid power support with some form of shared capital cost or chargeback offset could thus encourage the earlier adoption of ZEVs.
The need is not trivial on either side of the equation. Utilities that are incorporating—voluntarily or by mandate—more renewable power will be looking for mechanisms to help them manage the variability of that power source. Several of the presentations took a back of the envelope approach to calculating the potential benefit of ZEVs in that role—and it appears potentially substantial.
Unintentionally underscoring the discussion, California Governor Arnold Schwarzenegger signed into law on the same day a bill (SB 107) that requires the state’s three major utilities to provide 20% of their electricity from renewable sources such as solar, wind and geothermal energy within four years.
Grid-connected vehicles can provide four types of benefits, argued Jasna Tomic from WestStart-CALSTART:
Profitable Grid Management—Ancillary Services (A/S). Ancillary Services maintain grid reliability by balancing supply and demand. This is the role of the ISO. (Earlier post.)
Ancillary services include on-line generation synchronized to the grid to keep frequency and voltage steady, ready to be increased/decreased instantly (~ 2-3 min) via automatic generation control (AGC); and spinning reserves—additional generating capacity synchronized and ready to respond for ~10 min in case of failures.
Emergency power supply. One vehicle with 20kW line connection could power 12 houses at average load of 1.5 kW/house. V2G offers very fast response, with a clean power source that can replace diesel generators.
Storage and integration with renewables (e.g. wind power). Several new studies are highlighting (and were discussed in more detail at the ZEV symposium by one of the authors, Willet Kempton) the potential for PHEVs and BEVs to augment the use of wind resources, in some case doubling the effective power generation, or even enabling a 50% wind mix.
Electric transit power support. V2G can power traction spikes for local rail, and use a variety of billing/charging schemes to encourage customers participation. This was discussed in more detail by Eugene Nishinaga from BART—the Bay Area Rapid Transit organization.
Tomic discussed the analysis of the potential of two fleets of EVs for ancillary services: 100 Th!nk City EVs in New York, and 252 Rav 4 EVs in California.
Both studies, each in different markets, showed significant economic potential for V2G providing ancillary services. Important parameters in the assessment were the market value of the ancillary services, the kW capacity of the vehicles nd electrical connections, and the kWh capacity of the vehicle battery.
Willett Kempton from the University of Delaware then spoke on a project done with SMUD (Sacramento Municipal Utility District) on modeling V2G for a utility with a high wind generation portfolio.
Dr. Kempton developed the electric vehicle-to-grid (V2G) concept. His two current research, speaking, and publishing foci are V2G and offshore wind power. (Earlier post.)
Wind is wonderful low-cost, low-CO2 power, but it fluctuates. For utility operators, a heavy reliance on wind thus raises the problem of ancillary services needed to handle the minute-by-minute and hourly fluctuations.
Kempton and his partners at SMUD are proposing a paradigm shift: the use of the customers’s vehicle fleet to provide responsive charging (G2V when too much wind) and discharging (V2G when not enough wind).
As a more modest first step, the V2G-capable vehicles could provide A/S, especially short-term regulation, to manage wind fluctuations and match to ramp rates of gas-fired generators.
A more aggressive approach would be to use V2G as storage to move summer night wind energy to serve the next day’s peak load.
SMUD serves some 570,000 households, and has a peak summer-time load of 3,300 MW and a minimum load of 750 MW.Assuming:
- A robust electric vehicle with a 30 kWh battery, 220v and a 20 kW line;
- ½ of households have V2G-capable cars (this is not a short-term scenario), of which ½ are available when needed, each with ½ storage, then
- V2G power = 570,000 * ½ * ½ * 20 kW = 2,850 MW
- V2G energy = 570,000 * ½ * ½ * ½ * 30 kWh = 2,138 MWh
In other words, V2G could power 86% of SMUD’s peak load with no other generation, and hold it for 45 minutes (2,850 MWh/1,425MW= .75 hour)
SMUD currently has 39 MW of wind power, but plans to grow it. Kempton and co-author Cliff Murley from SMUD calculated the vehicle numbers required to support three scenarios—39 MW, 250 MW and 850 MW—assuming that 100% of wind capacity was needed for regulation, but for less than 1/2 hour.
|V2G for Summer Wind Regulation|
|39 MW Wind||250 MW Wind||850 MW Wind|
|BEV, 20 kW||1,950
|PHEV, 2 kW||19,500
In a scenario with full BEVs, they found that only 0.3% of households would need to be online (1.950) to provide summer wind regulation for 39 MW. With PHEVs, the requirement was higher—3%.
They concluded that BEVs could offer all wind regulation and storage needed. PHEVS could provide regulation but may not be large enough for diurnal wind storage.
More detailed studies and modeling are needed, but the emerging picture is that there is an economic incentive for utilities to electrify transportation and to capture value back to the utility. Money that would have gone to pumped storage or combustion turbines instead goes to ZEVs.
Eugene Nishinaga from BART took that further, with an analysis that suggested it might be in BART’s interest to fund the conversion of hybrids to PHEVs and establish charging stations at BART stations.
BART schedules power in advance and buys, in essence, in bulk. If BART demand is lower than projected, it still pays for the scheduled power; excess power required above the scheduled levels costs more than three times the base amount.
Having commuter fleets of PHEVs at BART stations for charging and discharging could save the transit company more than $260,000 per year by reducing extra energy purchases, according to Nishinanga’s analysis.
V2G: Vehicle to Grid Power (University of Delaware)
W. Kempton and J. Tomic, 2005 “Vehicle to Grid Fundamentals: Calculating Capacity and Net Revenue" J. Power Sources Volume 144, Issue 1, 1 June 2005, Pages 268-279. doi:10.1016/j.jpowsour.2004.12.025”
W. Kempton and J. Tomic, 2005 “Vehicle to Grid Implementation: From stabilizing the grid to supporting large-scale renewable energy”. J. Power Sources Volume 144, Issue 1, 1 June 2005, Pages 280-294. doi:10.1016/j.jpowsour.2004.12.022.