Vehicle-to-grid
Vehicle-to-grid describes a system in which plug-in electric vehicles sell demand response services to the electrical grid. Such services are either backfeeding electricity to the grid, or reducing the rate of charge from the grid at different times of the day. Demand services reduce demand peaks for grid supply, and hence reduce the probability of disruption from load variations. Vehicle-to-load and vehicle-to-vehicle are related concepts, but the AC phase is not synchronised with the grid, so the power is only available to "off-grid" loads.
Plug-in electric vehicles include battery electric vehicles and plug-in hybrid electric vehicles. They share the ability to store electricity in their on-board battery modules, which are typically used to propel the vehicle's electric engine. V2G allows some of this energy storage to be sent to the grid, turning the vehicle into a small-scale grid battery that is eligible for claiming feed-in tariffs. A 2015 report found that vehicle owners could receive significant payments by charging their EVs at off-peak times when grid electricity is cheaper, storing it in their car battery, and selling it back to the grid at peak times when electricity prices are higher due to congestion pricing.
Rechargeable batteries have a finite number of charge cycles, as well as a limited shelf-life, so V2G can reduce battery longevity. Battery capacity is a complex function of battery chemistry, charge/discharge rates, temperature, state of charge and age, but is improving as technology improves. Most studies of the effects of V2G on battery life show that slower V2G discharge rates lessen degradation, while one study suggested that using vehicles for grid storage could improve longevity.
Some hydrogen fuel cell vehicles are also equipped with V2G functions. HFCVs with fuel tanks containing of hydrogen fuel can deliver more than 90 kWh of electricity. Vehicle batteries may hold 100 kWh or more.
Uni-directional V2G charging is technically simpler than delivering power from an EV battery, which many PIEVs are not equipped to do., most EVs require a separate inverter than the one used to power the propulsion motors in order to output AC power from the battery. UV2G can be extended by throttling other activities such as air heating and cooling.
History
V2G began as vehicle-to-vehicle charging, as introduced by California company AC Propulsion in the early 1990s. Their two-seater Tzero car featured two-way charging. V2G allows charging and discharging between vehicle and grid.Applications
Peak load leveling
V2G vehicles can provide power to help balance grid loads by "valley filling" and "peak shaving". Peak load leveling supports regulation services and provides spinning reserves. Coupling these services with "smart meters" enables V2G. V2G could buffer variable power sources by storing excess energy and providing it to the grid during high-load periods.It has been proposed that public utilities would not have to build as many coal-fired and gas-fired power plants to meet peak demand or as an insurance policy against power outages. Local demand is easily measured, so dynamic load leveling can be provided as needed on a highly local basis.
Carbitrage, a portmanteau of 'car' and 'arbitrage', is sometimes used to refer to the process of buying and selling power stored in a vehicle.
Backup power
Electric vehicles can generally store more than an average home's daily energy demand, and supply emergency power to a home for several days, using vehicle-to-home transmission.Though the concept of V2H charging is simple, putting it into action requires a technologically complex system. Charging stations must integrate software that communicates with the central grid to monitor real-time system demand.
Types
California's grid operator, CAISO, defines four levels of Vehicle-Grid Interface :- Unidirectional power flow
- V1G with aggregated resources
- V1G with fragmented actor objectives
- Bidirectional power flow
V1G/Unidirectional V2G
Bidirectional local V2G (V2H, V2L, V2B, V2X)
Vehicle-to-home, vehicle-to-load, vehicle-to-vehicle, and vehicle-to-building —sometimes collectively termed vehicle-to-everything —use the vehicle to provide power during a power outage or to displace grid energy with energy from possibly other energy sources stored in the vehicle's battery. The source energy may be renewable; for example, vehicles charged using solar power at work during the day could power a home through the night, without pulling power from the grid.By 2022, V2X had not yet reached market deployment, except in Japan where commercial V2H solutions have been available since 2012. In 2022, Utrecht was installing thousands of bidirectional chargers in anticipation of the arrival of vehicles that support bidirectional energy flows.
By 2023, several vehicles supporting V2X energy transfer had come onto the market. The Ford F-150 Lightning supports 9.6 kW of V2L or V2H power. Tesla began deliveries of a new light truck Cybertruck offering 11.5 kW of V2H or V2L capability.
Bidirectional V2G
V2G allows vehicles to supply electricity to the grid, with energy paid for by the operator of the utility or transmission system. In many jurisdictions meeting power demands during periods of peak demand is much more expensive than at other times. Power from EVs is potentially a cheaper alternative. In addition, EV power can facilitate ancillary services such as load-balancing and frequency control, including primary frequency regulation and secondary reserve.V2G requires specialized hardware, has significant energy losses and limited round-trip efficiency, and the charge/discharge cycling may shorten battery life. A 2016 V2G project in California was done as a pilot by Southern California Edison and found that revenues from the project were lower than project administration costs, eliminating its economic benefits.
Bidirectional DC-charging
EVs typically allow fast DC-charging, with the transformer in a charging station connected directly to the vehicle battery. Technology is being developed for bidirectional DC-charging to and from the station, without needing extra hardware in the car, having the DC-to-AC converter in the station. In principle, EVs without hardware support for V2G could gain bidirectionality capability with only a software upgrade.Efficiency
Most modern EVs use lithium-ion cells that offer round-trip efficiency greater than 90%. Efficiency depends on factors like charge rate, charge state, battery state of health, and temperature.Most energy losses are from system components other than the battery, particularly power electronics such as inverters. One study found round-trip efficiency for V2G systems in the range of 53% to 62%. Another study reported efficiency of about 70%. Overall efficiency depends on many factors and can vary widely.
Implementation by country
According to a study by the U.S. Department of Energy, the increasing use of plug-in electric vehicles and other electricity-dependent technologies could increase the strain on US power grids by as much as 38% by 2050. Coping with this heightened demand presents a significant challenge for both power companies and government agencies.United States
In July 2022, eight electric school buses in the San Diego Gas & Electric service territory were part of a five-year pilot V2G project to boost reliability during electricity failures. Using V2G software from Nuvve, the bus batteries are aggregated with others in a nearby school district to form a participating resource under the Emergency Load Reduction Program, which was initiated in 2021 by the California Public Utilities Commission. SDG&E, Pacific Gas and Electric and Southern California Edison to manage the pilot.In September 2022, the BIDIRECTIONAL Act was introduced in the US Senate, to "create a program dedicated to deploying electric school buses with bidirectional vehicle-to-grid flow capability”. The bill died in committee.
In North America, at least two major school-bus manufacturers—Blue Bird and Lion—are working on proving the benefits of electrification and V2G technology. As of 2020, school buses in the U.S. used $3.2B of diesel a year. Their electrification could help to stabilize the electricity grid, lessen the need for power plants, and reduce gas and particulate pollution and carbon dioxide from exhaust emissions.
In 2017, at the University of California San Diego, V2G technology provider Nuvve launched a pilot program called INVENT, funded by the California Energy Commission, with the installation of 50 V2G bidirectional charging stations around the campus. The program expanded in 2018 to include a fleet of PEVs for its Triton Rides shuttle service.
In 2018 Nissan launched a pilot program under the Nissan Energy Share initiative in partnership with V2G systems company Fermata Energy to use V2G technology to partially power Nissan North America's headquarters in Franklin, Tennessee. In 2020 Fermata Energy's bidirectional electric vehicle charging system became the first to be certified to the North American safety standard, UL 9741, the Standard for Bidirectional Electric Vehicle Charging System Equipment.
Japan
Japan planned to spend $71.1 billion to upgrade existing grid infrastructure. Average Japanese homes use 10 to 12 kWh/day. The Nissan Leaf's 24 kWh battery capacity, could provide up to two days of power.In November 2018 in Toyota City, Aichi Prefecture, Toyota Tsusho Corporation and Chubu Electric Power Co., Inc initiated V2G demonstrations with electric vehicles. The demonstration examined how V2G systems balance demand and supply and power grid impacts. Two bidirectional charging stations, connected to a V2G aggregation server managed by Nuvve Corporation, were installed at a parking lot in Aichi Prefecture.