|Percentage of super-peak and peak reserve power grid capacity that could be replaced by a PHEV fleet with V2G. Click to enlarge. Source: NREL|
Pacific Gas and Electric Company, California’s biggest utility, showcased the first-ever utility demonstration of Vehicle-to-Grid (V2G) technology during an alternative energy solution summit in Silicon Valley.
V2G technology allows for the bi-directional sharing of electricity between Electric Vehicles (EVs) and Plug-in Electric Hybrid Vehicles (PHEVs), and the electric power grid. The technology turns each vehicle into a power storage system, increasing power reliability and the amount of renewable energy available to the grid during peak power usage.
PG&E, using a Prius converted to a PHEV in partnership with the Bay Area Air Quality Management District and Energy CS, showed the reverse flow of energy from the vehicle back to the outlet—a first public showcase for any utility.
PG&E then ran several lights and appliances to show how V2G could benefit its customers. Although PG&E’s PHEV is currently in prototype form, the company sees the possibility that its customers will be able to take advantage of V2G technology and PHEVs by providing power to their home or businesses during hot summer days to avoid high energy prices and help prevent outages.
PG&E’s V2G demonstration marks an important milestone for plug-in vehicle technology. Using a grid-connected car’s battery as distributed energy storage for homes or businesses expands the economic and environmental benefits of plug-in vehicles.—Felix Kramer, Founder of CalCars.org
Research has suggested that the most promising utility markets for V2G power are for the ancillary services for which hourly wholesale markets exist: power-regulation and spinning reserves.
These services require fast and accurate responses to electric grid operator signals, and typically are used for short durations. Grid operators across the country require each of these services for every one of the 8,760 operating hours in a year, and they represent a multi-billion-dollar combined market.—“Electric and Hybrid Vehicles: New Load or New Resource?”
Regulation (frequency response) services today are used to increase or to decrease grid power in a specific area. If demand is greater then supply at any given moment, then regulation up is required. If demand is less than supply, then regulation down is required. With a PHEV in the loop, regulation up would discharge the battery, and regulation down charge the battery.
Spinning reserves are used to deliver fast power to the grid in case of a sudden contingency, such as a scheduled generator tripping offline, or the failure of a transmission or distribution facility. Spinning reserves, when called upon, are required for only a short period.
Central to these schemes is having the utility have control of the timing of the charging and the discharging, and therefore the use of intelligent grid technology.
This excess capacity could potentially provide electricity to PHEVs provided the utilities have some control over when charging occurs. We did not evaluate system-wide effects of uncontrolled charging; however, we would anticipate significant negative impacts if this were allowed at a large scale.—Denholm and Short, NREL report
In a scenario outlined by PG&E, vehicle owners will select a price threshold at which they are willing to sell energy, and when the price reaches this point the utility will be able to automatically draw energy out of the vehicle, leaving enough for the drive home if necessary. The utility’s customers would then earn credit in the amount of energy used by the utility toward their monthly energy bill.
V2G technology also serves as a way to increase the amount of renewable energy used during peak energy hours. During times of maximum demand, electrical utilities have to buy power from expensive and less efficient fossil fuel power generating sources. PHEVs will charge their batteries at night when energy is inexpensive and is generated with a larger percentage of renewable resources.
When demand is high the next day, instead of turning on a fossil-fuel based generator, the utility can purchase the renewable energy stored in the vehicle batteries.
“Vehicle-to-grid power fundamentals: Calculating capacity and net revenue”; Willett Kempton, Jasna Tomić; Journal of Power Sources Volume 144, Issue 1, 1 June 2005, Pages 268-279
“Vehicle-to-grid power implementation: From stabilizing the grid to supporting large-scale renewable energy”; Willett Kempton, Jasna Tomić; Journal of Power Sources Volume 144, Issue 1, 1 June 2005, Pages 280-294
“Electric and Hybrid Vehicles: New Load or New Resource?”; Steven Letendre, Paul Denholm, and Peter Lilienthal; Public Utilities Fortnightly, pp 28-37