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Vehicle-to-grid (V2G) describes a system in which plug-in electric vehicles, such as battery electric vehicles (BEV), plug-in hybrids (PHEV) or hydrogen fuel cell electric vehicles (FCEV), communicate with the power grid to sell demand response services by either returning electricity to the grid or by throttling their charging rate. 
Vehicle-to-grid can be used with gridable vehicles, that is, plug-in electric vehicles (BEV and PHEV), with grid capacity. Since at any given time 95 percent of cars are parked, the batteries in electric vehicles could be used to let electricity flow from the car to the electric distribution network and back. This represents an estimated value to the utilities of up to $4,000 per year per car.
Batteries have a finite number of charging cycles, as well as a shelf-life, therefore using vehicles as grid storage can impact battery longevity. Studies that cycle batteries two or more times per day have shown large decreases in capacity and greatly shortened life. However, battery capacity is a complex function of factors such as battery chemistry, charging and discharging rate, temperature, state of charge and age. Most studies with slower discharge rates show only a few percent of additional degradation while one study has suggested that improved longevity relative to vehicles that were not used for grid storage may be possible.
Sometimes the modulation of charging of a fleet of electric vehicles by an aggregator to offer services to the grid but without actual electrical flow from the vehicles to the grid is called unidirectional V2G, as opposed to the bidirectional V2G that is generally discussed in this article. The company AC Propulsion coined the term V2G for vehicle-to-grid.
- 1 Applications
- 2 Efficiency
- 3 Implementation by country
- 4 Research
- 5 Skepticism
- 6 Vehicles
- 7 See also
- 8 References
- 9 Further reading
- 10 External links
Peak load leveling
The concept allows V2G vehicles to provide power to help balance loads by "valley filling" (charging at night when demand is low) and "peak shaving" (sending power back to the grid when demand is high, see duck curve). Peak load leveling can enable utilities new ways to provide regulation services (keeping voltage and frequency stable) and provide spinning reserves (meet sudden demands for power). In future development, it has been proposed that such use of electric vehicles could buffer renewable power sources such as wind power, for example, by storing excess energy produced during windy periods and providing it back to the grid during high load periods, thus effectively stabilizing the intermittency of wind power. Some see this application of vehicle-to-grid technology as a renewable energy approach that can penetrate the baseline electric market.
It has been proposed that public utilities would not have to build as many natural gas or coal-fired power plants to meet peak demand or as an insurance policy against blackouts. Since demand can be measured locally by a simple frequency measurement, dynamic load leveling can be provided as needed. Carbitrage, a portmanteau of 'car' and 'arbitrage', is sometimes used to refer to the minimum price of electricity at which a vehicle would discharge its battery.
Modern electric vehicles can generally store in their batteries more than an average home's daily energy demand. Even without a PHEV's gas generation capabilities such a vehicle could be used for emergency power for several days (for example, lighting, home appliances, etc.). This would be an example of Vehicle-to-home transmission (V2H). As such they may be seen as a complementary technology for intermittent renewable power resources such as wind or solar electric. Hydrogen FCEVs with tanks containing up to 5.6 kg of hydrogen can deliver more than 90 kWh of electricity.
Any energy conversion has losses due to the laws of thermodynamics. Lower losses mean higher Energy conversion efficiency. Most modern battery electric vehicles use lithium-ion cells that can achieve round-trip efficiency greater than 90%. The efficiency of the battery depends on factors like charge rate, charge state, battery state of health, and temperature.
The majority of losses, however, are in system components other than the battery. Power electronics, such as inverters, typically dominate overall losses. A study found overall round-trip efficiency for V2G system in the range of 53% to 62%'. Another study reports an efficiency of about 70%. The overall efficiency however depends on several factors and can vary widely.
Implementation by country
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A study conducted in 2012 by the Idaho National Laboratory[dead link] revealed the following estimations and future plans for V2G in various countries. It is important to note that this is difficult to quantify because the technology is still in its nascent stage, and is therefore difficult to reliably predict adoption of the technology around the world. The following list is not intended to be exhaustive, but rather to give an idea of the scope of development and progress in these areas around the world.
PJM Interconnection has envisioned using US Postal Service trucks, school buses and garbage trucks that remain unused overnight for grid connection. This could generate millions of dollars because these companies aid in storing and stabilizing some of the national grid's energy. The United States was projected to have one million electric vehicles on the road between 2015 and 2019. Studies indicate that 160 new power plants will need to be built by 2020 to compensate for electric vehicles if integration with the grid does not move forward.
In order to meet the 2030 target of 10 percent of Japan's energy being generated by renewable resources, a cost of $71.1 billion will be required for the upgrades of existing grid infrastructure. The Japanese charging infrastructure market is projected to grow from $118.6 million to $1.2 billion between 2015 and 2020. Starting in 2012, Nissan plans to bring to market a kit compatible with the LEAF EV that will be able to provide power back into a Japanese home. Currently, there is a prototype being tested in Japan. Average Japanese homes use 10 to 12 KWh/day, and with the LEAF's 24 KWh battery capacity, this kit could potentially provide up to two days of power. Production in additional markets will follow upon Nissan's ability to properly complete adaptations.
Denmark currently[when?] is a world leader in wind power generation. Initially, Denmark's goal is to replace 10% of all vehicles with PEVs, with an ultimate goal of a complete replacement to follow. The Edison Project implements a new set of goals that will allow enough turbines to be built to accommodate 50% of total power while using V2G to prevent negative impacts to the grid. Because of the unpredictability of wind, the Edison Project plans to use PEVs while they are plugged into the grid to store additional wind energy that the grid cannot handle. Then, during peak energy use hours, or when the wind is calm, the power stored in these PEVs will be fed back into the grid. To aid in the acceptance of EVs, policies have been enforced that create a tax differential between zero emission cars and traditional automobiles. The Danish PEV market value is expected to grow from $50 to $380 million between 2015 and 2020. PEV developmental progress and advancements pertaining to the use of renewable energy resources will make Denmark a market leader with respect to V2G innovation (ZigBee 2010).
Following the Edison project, the Nikola project was started which focused on demonstrating the V2G technology in a lab setting, located at the Risø Campus (DTU). DTU is a partner along with Nuvve and Nissan. The Nikola project is finishing in 2016, and lays the groundwork for Parker, which will use a fleet of EVs to demonstrate the technology in a real-life setting. this project is partnered by DTU, Insero, Nuvve, Nissan and Frederiksberg Forsyning (Danish DSO in Copenhagen). Besides demonstrating the technology the project also aims to clear the path for V2G-integration with other OEMs as well as calculating the business case for several types of V2G, such as Adaptive charging, overload protection, peak shaving, emergency backup and frequency balancing. the project starts in August 2016 and runs for 2 years. Other notable projects in Denmark are the SEEV4-City Interreg project which will demonstrate V2G in a car sharing fleet in the north harbour of Copenhagen and the ECOGrid 2.0, which will not include EVs but build the aggregator software to fully integrate it into the Danish electricity markets.
The V2G market in the UK will be stimulated by aggressive smart grid and PEV rollouts. Starting in January 2011, programs and strategies to assist in PEV have been implemented. The UK has begun devising strategies to increase the speed of adoption of EVs. This includes providing universal high-speed internet for use with smart grid meters, because most V2G-capable PEVs will not coordinate with the larger grid without it. The "Electric Delivery Plan for London" states that by 2015, there will be 500 on-road charging stations; 2,000 stations off-road in car parks; and 22,000 privately owned stations installed. Local grid substations will need to be upgraded for drivers who cannot park on their own property. By 2020 in the UK, every residential home will have been offered a smart meter, and about 1.7 million PEVs should be on the road. The UK's electric vehicle market value is projected to grow from $0.1 to $1.3 billion between 2015 and 2020 (ZigBee 2010).
Denmark's Edison project, an abbreviation for 'Electric vehicles in a Distributed and Integrated market using Sustainable energy and Open Networks' was a partially state funded research project on the island of Bornholm in Eastern Denmark. The consortium of IBM, Siemens the hardware and software developer EURISCO, Denmark's largest energy company Ørsted A/S (formerly DONG Energy), the regional energy company Østkraft, the Technical University of Denmark and the Danish Energy Association, explored how to balance the unpredictable electricity loads generated by Denmark's many wind farms, currently generating approximately 20 percent of the country's total electricity production, by using electric vehicles (EV) and their accumulators. The aim of the project is to develop infrastructure that enables EVs to intelligently communicate with the grid to determine when charging, and ultimately discharging, can take place. At least one rebuild V2G capable Toyota Scion will be used in the project. The project is key in Denmark's ambitions to expand its wind-power generation to 50% by 2020. According to a source of British newspaper The Guardian 'It's never been tried at this scale' previously. The project concluded in 2013.
Southwest Research Institute
In 2014, Southwest Research Institute (SwRI) developed the first vehicle-to-grid aggregation system qualified by the Electric Reliability Council of Texas (ERCOT). The system allows for owners of electric delivery truck fleets to make money by assisting in managing the grid frequency. When the electric grid frequency drops below 60 Hertz, the system suspends vehicle charging which removes the load on the grid thus allowing the frequency to rise to a normal level. The system is the first of its kind because it operates autonomously.
The system was originally developed as part of the Smart Power Infrastructure Demonstration for Energy Reliability and Security (SPIDERS) Phase II program, led by Burns and McDonnell Engineering Company, Inc. The goals of the SPIDERS program are to increase energy security in the event of power loss from a physical or cyber disruption, provide emergency power, and manage the grid more efficiently. In November 2012, SwRI was awarded a $7 million contract from the U.S. Army Corps of Engineers to demonstrate the integration of vehicle-to-grid technologies as a source for emergency power at Fort Carson, Colorado. In 2013, SwRI researchers tested five DC fast-charge stations at the army post. The system passed integration and acceptance testing in August 2013.
Delft University of Technology
Prof. Dr. Ad van Wijk, Vincent Oldenbroek and Dr. Carla Robledo, researchers at Delft University of Technology, in 2016 conducted research on V2G technology with hydrogen FCEVs. Both experimental work with V2G FCEVs and techno-economic scenario studies for 100% renewable integrated energy and transport systems are done, using only hydrogen and electricity as energy carriers. They modified a Hyundai ix35 FCEV together with Hyundai R&D so it can deliver up to 10 kW DC Power while maintaining road access permit. They developed together with the company Accenda b.v. a V2G unit converting the DC power of the FCEV into 3-phase AC power and injecting it into the Dutch national electricity grid. The Future Energy Systems Group also recently did tests with their V2G FCEVs whether it could offer frequency reserves. Based on the positive outcome of the tests an MSc thesis was published looking into the technical and economic feasibility assessment of a hydrogen and FCEV based Car Park as Power Plant offering frequency reserves.
University of Delaware
Dr. Willett Kempton, Dr. Suresh Advani, and Dr. Ajay Prasad are the researchers at the US University of Delaware who are currently conducting research on the V2G technology, with Dr. Kempton being the lead on the project. Dr. Kempton has published a number of articles on the technology and the concept, many of which can be found on the V2G project page. The group is involved in researching the technology itself as well as its performance when used on the grid. In addition to the technical research, the team has worked with Dr. Meryl Gardner, a Marketing professor in the Alfred Lerner College of Business and Economic at the University of Delaware, to develop marketing strategies for both consumer and corporate fleet adoption. A 2006 Toyota Scion xB car was modified for testing in 2007.
Lawrence Berkeley National Laboratory
At Lawrence Berkeley National Laboratory, Dr. Samveg Saxena currently serves as the project lead for Vehicle-to-Grid Simulator (V2G-Sim). V2G-Sim is a simulation platform tool used to model spatial and temporal driving and charging behavior of individual plug-in electric vehicles on the electric grid. Its models are used to investigate the challenges and opportunities of V2G services, such as modulation of charging time and charging rate for peak demand response and utility frequency regulation. V2G-Sim has also been used to research the potential of plug-in electric vehicles for renewable energy integration. Preliminary findings using V2G-Sim have shown controlled V2G service can provide peak-shaving and valley-filling services to balance daily electric load and mitigate the duck curve. On the contrary, uncontrolled vehicle charging was shown to exacerbate the duck curve. The study also found that even at 20 percent fade in capacity, EV batteries still met the needs of 85 percent of drivers.
In another research initiative at Lawrence Berkeley Lab using V2G-Sim, V2G services were shown to have minor battery degradation impacts on electric vehicles as compared to cycling losses and calendar aging. In this study, three electric vehicles with different daily driving itineraries were modelled over a ten-year time horizon, with and without V2G services. Assuming daily V2G service from 7PM to 9PM at a charging rate of 1.440 kW, the capacity losses of the electric vehicles due to V2G over ten years were 2.68%, 2.66%, and 2.62%.
Nissan and Enel
In May 2016, Nissan and Enel power company announced a collaborative V2G trial project in the United Kingdom, the first of its kind in the country. The trial comprises 100 V2G charging units to be used by Nissan Leaf and e-NV200 electric van users. The project claims electric vehicle owners will be able to sell stored energy back to the grid at a profit.
One notable V2G project in the United States is at the University of Delaware, where a V2G team headed by Dr. Willett Kempton has been conducting on-going research. An early operational implementation in Europe was conducted via the German government-funded MeRegioMobil project at the "KIT Smart Energy Home" of Karlsruhe Institute of Technology in cooperation with Opel as vehicle partner and utility EnBW providing grid expertise. Their goals are to educate the public about the environmental and economic benefits of V2G and enhance the product market. Other investigators are the Pacific Gas and Electric Company, Xcel Energy, the National Renewable Energy Laboratory, and, in the United Kingdom, the University of Warwick.
University of Warwick
WMG and Jaguar Land Rover collaborated with the Energy and Electrical Systems group of the university. Dr Kotub Uddin analysed lithium ion batteries from commercially available EVs over a two year period. He created a model of battery degradation and discovered that some patterns of vehicle-to-grid storage were able to significantly increase the longevity of the vehicle's battery over conventional charging strategies, while permitting them to be driven in normal ways. 
There is some skepticism among experts about the feasibility of V2G. In 2007 an Environmental Defense representative stated: "It’s hard to take seriously the promises made for plug-in hybrids with 30 miles (48 km) all-electric range or any serious V2G application any time soon. It’s still in the science project stage." Most of skepticism comes from the cost of battery cycling and the dubious economics of V2G.
The more a battery is used the sooner it needs replacing. Replacement cost is approximately 1/3 the cost of the electric car. Over their lifespan, batteries degrade progressively with reduced capacity, cycle life, and safety due to chemical changes to the electrodes. Capacity loss/fade is expressed as a percentage of initial capacity after a number of cycles (e.g., 30% loss after 1,000 cycles). Cycling loss is due to usage and depends on both the maximum state of charge and the depth of discharge. JB Straubel, CTO of Tesla Inc., discounts V2G because battery wear outweighs economic benefit. He also prefers recycling over re-use for grid once batteries have reached the end of their useful car life. A 2017 study found decreasing capacity, and a 2012 hybrid-EV study found minor benefit.
Another common criticism is related to the overall efficiency of the process. Charging a battery system and returning that energy from the battery to the grid, which includes "inverting" the DC power back to AC inevitably incurs some losses. This needs to be factored against potential cost savings, along with increased emissions if the original source of power is fossil based. This cycle of energy efficiency may be compared with the 70–80% efficiency of large-scale pumped-storage hydroelectricity, which is however limited by geography.
There are several electric vehicles that have been modified or are design to be compatible with V2G. Hyundai ix35 FCEV from Delft University of Technology is modified with a 10 kW DC V2G output. Some vehicles that have V2G capability include the REV 300 ACX, the Boulder Electric Vehicle 500 series and 1000 series trucks, the ACPropulsion T-Zero, E-box and MINI-E, the Nissan Leaf and Nissan e-NV200. The Mitsubishi Outlander PHEV has a Vehicle To Home system in Japan that is also planned for roll out in Europe.
- Charge control
- Charging station
- Distributed generation
- Electric vehicle battery
- Electricity meter
- Energy demand management
- Feed-in tariff
- Grid energy storage
- Grid-tied electrical system
- Load profile
- Load balancing (electrical power)
- Operating reserve
- Peaking power plant
- Power outage
- Smart meter
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