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Friday, October 28, 2011

Vehicle to Grid (V2G)

“Plug-ins can earn money supporting the grid, so we call them cash-back cars” – Jon Wellinghoff, FERC Chairman

Plug-in hybrids may help balance out a smarter electricity grid capable of easily sending power back and forth between generators and consumers, much like we send and receive e-mails on the Internet today.

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1. Background
2. Acronyms/Definitions
3. Business Case
4. Benefits
5. Risks/Issues
6. Success Factors
7. Companies
8. Next Steps
9. Links

  • Vehicle-to-grid (V2G) describes a system in which power can be sold to the electrical power grid by an electric-drive motor of a hybrid vehicle that is connected to the grid when it is not in use for transportation. Alternatively, when the car batteries need to be fully charged, the flow can be reversed and electricity can be drawn from the electrical power grid to charge the battery.
  • There has been considerable discussion of the merits of using EVs and PHEVs as a distributed source connected to the grid. It is envisaged that this could provide help load leveling at times of high demand and provide storage of energy from renewable sources.
  • Electric Storage is a new and emerging technology that has been identified by FERC as a functionality of smart grid. Due to the infancy of this technology, few standards exist that capture how it should be utilized on the Smart Grid. For example, to-date there exist no guidance or standards to address large or small mobile storage such as PHEVs. Electric Storage is treated as a distributed energy resource in some standards, but there may be distinctions between electric storage and connected generation.
  • When the car is in the V2G setting, the battery’s charge goes up or down depending on the needs of the grid operator, which sometimes must store surplus power and other times requires extra power to respond to surges in usage. The ability of the V2G car’s battery to act like a sponge provides a solution for utilities, which pay millions to generating stations that help balance the grid.
  • Note: the conversion efficiency of the battery is 0.93 and 80% of its capacity is available.
Flow of electricity and communications in a Vehicle-to-Grid infrastructure.
Source: Kempton and Tomic 2005. Journal of Power Sources

2. Acronyms/Definitions
  1. ACE – Area Control Error – A measure of the quality of operation of the grid. ACE includes a frequency regulation component. ACE must be kept within grid operating requirements.
  2. Carbitrage - This is a fusion of 'car' and 'arbitrage'. When the electric utility would like to buy power from the V2G network, it holds an auction. The car owners are able to define the parameters under which they will sell energy from their battery pack. Many factors would be considered when setting minimum sale price including the cost of the secondary fuel in a PHEV and battery cycle wear. When this minimum price is satisfied, it is deemed as meeting carbitrage.
  3. DSM - Demand-Side Management- In the context of plug-in vehicles is simply the interruption or reduction of recharging when required to ease grid imbalances, and the resumption and completion of recharging at a later time.
  4. Dynamic Demand - A semi-passive technology for adjusting load demands on an electrical power grid. The concept is that by monitoring the frequency of the power grid, as well as their own control parameters, individual, intermittent loads would switch on or off at optimal moments to smoothen the overall system load, offsetting and reducing spikes in peak-load demand on the grid. As this switching would only advance or delay the appliance operating cycle by a few seconds, it would be unnoticeable to the end user.
  5. GIEV – Grid Integrated Electric Vehicles
  6. GVI - Grid Vehicle Integration - Term coined by Tom Gage, CEO of electric car tech maker AC Propulsion. Taken literally (flowing in one direction from the vehicle to the grid) V2G represents a misnomer for a comprehensive system for managing that spiky load to match supply and demand. He said "Maybe V2G isn’t the right term in the big picture. What we want to talk about is grid-vehicle integration, or GVI.” In otherwords a two-way flow."
  7. Regulation -The continuous adjustment of AC electricity frequency (60 Hz)
  8. Regulation Ancillary Service – The continuous matching of supply with demand in a control area. This would represent an economic opportunity for Vehicle to be available for short bursts of charge and discharge. Power plants provide regulation today, but they have slow response, low efficiency, energy and economic.
  9. V1G – Grid to Vehicle One Way Communication - Utilizing Electric Vehicles in demand response include providing proportional charge rate signals
  10. V2G –Vehicle to Grid - Letting the vehicle take and give power back to the grid. Electric utility may be willing to purchase energy from customer during periods of peak demand
  11. V2G "Lite" - Drawing power from a battery could shorten the battery’s life and cause warranty tangles -- but simply reducing the level of car charging can accomplish many of the same tasks that V2G is targeting.   Most plug-in cars don't require a full night’s worth of charging to refill their batteries.  In fact, research from Idaho National Laboratory on Nissan Leaf owners’ charging habits shows that most spend about two hours out of their typical 10- to 11-hour overnight plug-in status not charging at all. While turning chargers completely off might not be a welcome use of that window of opportunity, slightly reducing the level of charging when it’s needed -- say, from full charge to 80 percent -- could help balance grid frequency fluctuations.

    By taking a similar process, but in reverse, utilities could allow plug-ins to charge at 80 percent most of the time, then use that extra charging capacity to absorb temporary spikes in intermittent wind or solar power that would otherwise threaten to destabilize the grid.

    Both these approaches could avoid the problems associated with the concept of vehicle-to-grid (V2G) systems that directly tap car batteries to serve the grid.
  12. V2H - Vehicle to Home – Linking the car to house rather than the grid. This potentially provides three benefits: it obviates the issue of exporting energy back to the grid; can reduce demands on the grid as a supplementary supply to the house; and could also provide emergency backup in the event of power outages.
  13. V2L - Vehicle to Load - Use of the PEV storage to provide power to a remote site or load that does not otherwise have electrical service. Examples include construction sites or camp sites.
  14. V2V – Vehicle to Vehicle - Use of the PEV storage to transfer electrical energy to another PEV

Regulation vs. Economic Dispatch

3. Business Case
  • PHEVs can potentially be used to store electrical energy in their onboard batteries for peak-shaving or power-quality applications, offering potentially powerful synergies to complement the electric power grid. With parallel advances in smart vehicles and the Smart Grid, PHEVs may become an integral part of the distribution system itself, providing storage, emergency supply, and grid stability.
  • Aggregation to provide 1 MW of power in order to enter the frequency regulation market. Vehicles provide 19 kW of power at home and 16 kW in commercial locations—given a high-power plug connection—but, due to driving requirements, not every vehicle will be available for V2G at the same time so about 200 vehicles would be needed to provide 1 MW of frequency regulation on demand.
  • Smart metering would also need to encompass dynamic pricing to make export of electricity to the grid more attractive during periods when wholesale prices are high.
  • GIEVs will be aggregated together as one electric power resource so that grid operators don’t have to interact with thousands of vehicles. An aggregator will monitor different energy markets and bid into those markets according to their aggregated vehicles’ available capacity and market price. The Smart Grid is key to the aggregation of devices to provide regulatory services.
  • In the new world of plugs-ins, your car should be able to sell energy you don't need back to the grid during times of peak power demand, such as in late summer afternoons, when both office buildings and homes are running air conditioning. Today, that peak demand is served by older, usually dirtier and less-efficient "peaker" generators that utilities fire up when needed. A national fleet of a million or more EVs, most sitting idle roughly 90 percent of the time, could serve as a massive national storage device that can be tapped as needed to meet peak demand. But you, the driver, will call the shots, determining how much power, if any, you'd be willing to sell to the grid on a given day. (Of course, your electric utility could call the shots, too, telling you what time of day you can, and can't, recharge your vehicle, at least without paying premium rates.) All this affects battery architecture, smart metering systems, communications protocols, a standard user interface, and common (and simple) messaging terminology — "bi-direction power flow management," in the argot of utilities.
  • A way 

4. Benefits
  • Peak Load Leveling - 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).
  • Regulation Services - Keeping voltage and frequency stable. Since demand can be measured locally by a simple frequency measurement, dynamic load leveling can be provided as needed. Consumer Financial Benefits for Participating in Regulation
    • Plugged In 12 hours each day (6 pm–6 am) 365 days * 12 hours = 4380 hours/year
    • Average historic price paid for regulation = $35/MWh
    • Average Regulation price during valley load periods = $28/MWh
    • Per Vehicle: 4380 hrs * $28 * .015 MW = $1800 annually
  • Spinning Reserves - Meet sudden demands for power
  • Renewable Integration - 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.
  • Protection During Power Outage - V2G could also be used as a buffer during power outages. As the New York Times explains: “After a power outage, a Florida man plugged his Toyota Prius into the backup uninterruptible power supply unit in his house and soon the refrigerator was humming and the lights were back on. “It was running everything in the house except the central air-conditioning” ... As long as it has fuel, the Prius can produce at least three kilowatts of continuous power, which is adequate to maintain a home’s basic functions.”

5. Risks/Issues
  • Battery Life - Concerns exist that the increased cycling of the batteries in this application will adversely affect the life of the battery. Current Li-ion batteries have a cycle life of 1,000 cycles irrespective of whether they are used for transport or static needs. The following calculation illustrates the additional cost of using the vehicle’s battery as a storage device for V2G applications based on today’s costs.
    • Currently a Li-ion battery with 35kWh storage capacity costs around $35,000 to manufacture.
    • With its life being 1,000 cycles, that equates to a cost per cycle of $35.
    • Assuming the charging efficiency is 92% and the battery is charged from 80% depletion at an overnight tariff of $0.10/kWh, then the cost for a charge is $3.01
    • Add this to the cycle cost and the cost to the owner is $38.01.
    • Therefore the price that the electricity would need to be bought back from the consumer to break even is $38 / (35 x 80%) = $0.86
    This is ten times the cost that the consumer paid for the electricity in the first instance. This breakeven sell back rate will reduce over time as battery costs reduce. The requirement for electricity from vehicles into the grid is only likely to happen at times of peak demand, because of the costs associated. In addition to the above costs to the consumer is the cost of installing the replacement power pack. On the other hand, the extra cycling for V2G are supposed to be shallow cycles that create less wear on the battery. It is the deep cycles that really hurt battery life.
  • Equipment Life - Transformers are designed to have a load and then cool off. There may be an impact on life expectancy if they are run constantly.
  • Capital Cost - Vehicle based bi-directional power interfaces can be expensive and require adding an onboard inverter so that the vehicle can send power upstream since most vehicles were designed only to take power from the grid. Nuvve claims that there are 5 vehicles either on or coming to market that won’t require additional hardware, but neither the Nissan Leaf nor Chevrolet Volt are in this category.
  • Battery Exchange - Batteries can be readily changed in vehicles with a simple architecture, but vehicles with integrated power packs to improve vehicle dynamics will not be so amenable to a swap and this operation may prove to be very costly. The extent of this cost is not known and not easily estimated without a known architecture.
  • Modeling - The implication of integrating information from individual customers, widespread sensors, and large numbers of PEVs with the real time operation of the grid needs study and modeling.
  • Complexity - We need a system that reduces the cost of vehicle fuel without any user interaction.
  • Fragmented Market - Utilities would have to get comfortable with the idea of buying power from millions of car batteries that will be plugged in and out by individual drivers at random times. Traditional demand response is far simpler. Several megawatts' worth of car batteries would likely have to become available before a utility would be convinced that a statistically stable asset for storing (and drawing) electricity exists at any given time in cars, and even then an excess buffer would have to exist -- and that would likely require hundreds of thousands of cars at a minimum. Utilities might even require a power provider to aggregate the electricity from cars into some sort of central substation before delivering it to a utility, which could upend the economics for the power provider.
  • Limited Life of Cars - We think of cars as long lasting machines, but really, they only last a limited number of hours: 100,000 miles at an average of 40 miles an hour is only 2,500 running hours. So maybe you can rely on the new car to last 2,500 to 5000 hours. You know there’s over 8,000 hours in a year, and the reason we put up with such short lifetimes for cars is that they spend almost all of their time parked. A bathroom fan is 50,000 hours. A kitchen refrigerator is 100,000 hours. From an economic standpoint, it doesn’t make any sense because it wears out the most expensive and life-limited part of an already life-limited product very fast.
  • Power Electronics Cost - If you decide to make a car able to be both charged and to sell electricity back to the grid, it increases the cost of the power electronics in the car. Now the battery charger, which originally only had to take current from the wall socket and use it to charge the battery, now has to be a bi-directional device and therefore much more expensive, more than twice as expensive than if it was just the charger. So you end up adding additional cost to the electrical part of a car.

6. Success Criteria
  • The energy providers will need to be fully confident of the availability and consistent reliability of the V2G energy.
  • Vehicle users will want to be confident of having a fully charged battery when they need it.
  • A controller that allows the vehicle owner to limit the amount of battery discharge to ensure they can meet the range needed for their next driving event.

7. Companies
  • Magic Consortium Mid-Atlantic Grid Interactive Cars Consortium - Created to further develop, test, and demonstrate Vehicle-to-Grid technology. The Consortium includes core partners from academia and the electric, automotive, and communications industries.
  • Nuvve, El Cajon, CA - Vehicle to grid technology (V2G) is approaching the commercialization stage thanks in part to the work of Professor Willet Kempton of the University of Delaware, who is now the CTO at startup Nuvve. Nuvve recently found its first customer in Denmark, where 30 vehicles will be used to support the grid.
    V2G Schematic - Source: Nuvve
       V2G requires aggregating the power potential from hundreds to thousands of vehicles into a sizeable power market that would be useful to utilities and grid operators. That is Nuvve’s added value – a server that can track the availability of the vehicles and send signals and data back and forth with the grid.

      The Nuvve solution has been tried in a field trial with PJM in USA for 2 years with 9 EVs participating in the trial. PJM is the largest RTO - Regional Transmission Organization - and serves 51 million people in the Eastern part of USA. They have a peak power demand of 144 GW and are a very large, advanced and experienced customer. During this trial it was determined that each car in average could "earn" $2,500 per year by participating in Nuvve's V2G solution. Assuming an 8 year lifetime of the EV (battery) and taking into account the cost of Nuvve’s operation, it corresponds to, discounted to today $ to around $10,000 per car over the lifetime of the car (battery) The actual amount the EV owner can expect earn will be determined in pilot trials about to start in 2011.

    8. Next Steps
    • ABB, the Swiss energy conglomerate, and GM have teamed up to study how Volt batteries perform during power outages or times of peak energy demand. The first phase of the experiment is nearly complete as the lithium ion cells are readied for interconnection with a utility power grid. Three power companies are expected to sign agreements in the coming months to test the batteries, said Pablo Rosenfeld, manager of ABB's distributed energy storage program.

      At N.C. State University's Centennial Campus, where ABB has its Corporate Research Center and North American headquarters for the Power Products and Power Systems Division, a Volt T-pack rests on a lab floor, wired to equipment and monitors. The battery is rapidly drained and charged, simulating how it would be called to duty in a neighborhood.

      Ultimately the ABB-GM study will determine whether the benefits of reusing Volt batteries are worth the cost when compared to other available options. Those could include buying power on the wholesale market, building power plants, or paying customers incentives to participate in energy conservation programs.

      ABB teamed up with GM in September and has spent several months creating a lab prototype of the battery pack to be tested in the field.

      More than 1,000 individual cells will be reconfigured into a boxy cabinet that will contain the equivalent of five T-packs, holding enough power to keep a half-dozen homes running for at least several hours.

      ABB is running final tests on the inverter and software that will link the batteries, which operate on direct current, to the power grid, which uses alternating current. The inverter will monitor the power supply and draw electricity as needed, functioning as a power management system.
      ABB has yet to determine how the batteries will be cooled in the summer and warmed in the winter, said Sandeep Bala, an ABB engineer in Raleigh. Lithium ion cells are prone to overheating, controlled in the Volt with liquid coolant.

    • Charlotte-based Duke Energy also is doing a pilot study in Indiana with Itochu, a Japanese company with energy and technology interests. It remains to be seen whether used batteries are preferable to new batteries, said Mike Rowand, Duke's director for technology development.
      "What is a given is energy storage," Rowand said. "Intuitively, a used battery is going to be cheaper than a new battery, but if 50 percent of the cost is taken up in repurposing it, then it may not be such a great deal."

    9. Links
    1. University of Delaware - Vehicle to Grid Technology
    2. BERR – UK Department for Business Enterprise and Regulatory Reform - Investigation into the Scope for the Transport Sector to Switch to Electric Vehicles and Plugin Hybrid Vehicles October 2008
    3. V2G - Green Car Congress
    4. Bucks for balancing: Can plug-in vehicles of the future extract cash – and carbon – from the power grid - a research collaboration between a team of engineers from Ricardo and National Grid, the operator of the high voltage electricity transmission system within Great Britain (GB).
      Key findings:
      • Using demand side management alone, the projected fleet of plug-in electric vehicles in 2020 would be able to provide an average of 6% of daily GB network balancing service requirements. This rises to a maximum of 10% in the evening and overnight.
      • Demand side management would provide a modest annual financial return to the individual vehicle owner of approximately £50 (US$82) for zero investment (effectively the equivalent of an 18% saving on recharging costs).
      • Vehicle-To-Grid (V2G) based grid balancing was shown to provide significantly greater revenue on an individual vehicle basis—ranging from approximately £600 (US$980) per year for a 3 kW system to in the region of £8,000 (US$13,000) per year for a 50 kW three phase installation. However, the very significant capital cost of a vehicle based bi-directional power interface and the balancing market size limitations that would restrict the value of the service if implemented fleet wide, would serve to render the fleet scale roll-out of the V2G balancing service uneconomic.
      • V2G operation may however be attractive for owners of captive vehicle fleets such as industrial or local delivery vehicles, battery exchange depots or aggregated batches of life expired vehicle batteries, where interface costs might be shared across multiple vehicles or battery packs.
      • With the increased requirement for grid balancing services arising from the changing dynamics of the generation mix, plug-in vehicles could be made to work in synergy with the electricity market to help balance supply and demand, so reducing the reliance on conventional generation for the provision of these services; hence this has the potential to reduce CO2 emissions.

    1 comment:

    1. Mark,

      Great article as usual. Glad you put in the section about battery life. I can't see why this Vehicle-to-Grid concept has gotten so much play, when we are very challenged to make a cost effective grid-scale storage battery in one 10MW/40MWh chunk, as opposed to hundreds or thousands of PHEV batteries. When all is said and done, Vehicle-to-Grid is a very complicated, difficult to manage way to build grid storage at $1Million/MWh and up.

      Vic Babbitt