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The Plug-In and BEV Adoption Wild Card: Vehicle-to-Grid


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.

  • 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
Cars on-line
% households
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.




Seems to be a better option that the Hydrogen economy.


V2G is particularly nice when you can run SOFCs on renewable fuels like SNG, methanol or ethanol. They can run continuously at lower output levels and supply the grid when not supplying energy for transportation.


You would need a messaging service to keep car owners informed of what was going on. That could be combined with a household controller that turns down appliances when needed. Since the 30 kwh batteries would be expensive ($10,000?)regardless of car model some kind of offset financing might be needed. It's like the Jetsons but with physical reality.


At current battery prices, this will never work. Suppose the price of a LiIon battery is $500/kWh. Suppose that the battery has a lifespan of 1000 cycles. Then each kWh will cost the car owner 50 cents in battery write-off.

The economics however differ for short-term and long-term regulations as shallow discharges do not affect battery life as much as deep discharges.

Harvey D.

Both wind and sun power need some sort of standby power sources. Hydro plants, with their huge reservoirs, can best play this role, where it is available.

Relying on PHEVs and BEVs to regulate grid power availability will only make sense when the on-board ESD (Energy Storage Device) reaches 50+ KWh in a compact low cost unit such as the EEStor unit.

Secondly, improved centralized power supply controls and metering are needed to manage such systems. Of course, PHEVs/BEVs owners should be able to charge their ESD at low cost (5 cents/KWh)during off-peak hours and sell power at a much higher price (15+ cents/KWh) during peak hours. This could generate enough profit for ESD owners to offset a major part of the intial cost on a 5 year time frame.

No other subsidies (from the power companies) should be required.

Rafael Seidl

Ok, let's think about this in practical terms. Fast forward a few years and pretend that you own a PHEV or BEV featuring fancy new battery technology. It takes 8 hours for it to fully charge off a standard but dedicated 110V 15A household circuit. Your an operating range - assuming a light touch on the gas pedal - of 50 miles. On weekdays, your commute to and from work plus various errands average 25 miles. Ergo, you normally only need to charge the vehicle for about four hours each night, though it is actually connected for about eight hours. In principle, that means your battery pack could support grid load leveling tasks for at least four hours each night. There is just one snag: there is not much call for peak shaving at night.

Moreover, your vehicle would need to be part of a (wireless) data network used to manage when and where V2G transactions are required. This would involve non-repudiable electronic authentication and authorization in both directions plus the inevitable client-side software upgrades and patches, all of which is a can of worms in its own right (though feasible).

Ok, so what if you could connect the vehicle to the grid while it is parked at your place of work during the day? This assumes the facility features the neccessary all-weather grid connection ports in the parking lot plus the trunk lines into the grid. The utility would need to pay your employer for the availability and actual use of this rather expensive infrastructure. Inevitably, that reduces the cut available to the vehicle owners.

The business end of such a grid connection port would consist of several feet of cabling on a self-winding drum and, a suitable plug. You don't want to lug that around in the vehicle. The port could support higher power levels than an ordinary household circuit. However, the 20kW number mentioned in the article implies a whopping 50 amps at 400 volts effective, far greater than anything Joe Schmoe is used to dealing with today. Short circuits and arcing due to moisture and/or soiled contacts are very real dangers that could lead to serious damage, even an electrical fire.

For safety, such an outlet would need to feature low-power handshaking circuitry plus connectivity to bespoke data network to control the port's main circuit breaker. The outlet must not be live until and unless a qualified vehicle has been hooked up correctly.

You would need to set a minimum battery charge level (expressed as remaining operating range) below which your vehicle automatically opts out of the V2G arrangement, even though it remains connected. This safeguard ensures you will be able to get home (in a PHEV, the on-board computer could set the threshold based on how full your fuel tank is).

Last not least, your battery pack would have to support far more frequent and possibly deep charge/discharge cycles while connected to the grid. Even with adequate cooling, this tends to shorten the life expectancy of your battery pack. Since the utility could not afford to pay you enough to cover a replacement pack during the vehicle's lifetime, this is a critical issue. Along with vehicle cost, weight and packaging issues, battery pack life expectancy is a major reason why no carmaker is yet offering PHEVs or BEVs.


So, from the above, I gather that the key drawback here is battery discharge which leads to battery failure which obviously is probably prohibitively expensive for the BEV or PHEV owner providing power to the grid.

Based on that, this program would need to be scaled way back to just provide power under extreme energy usage spikes or the degree of discharge would need to be severely limited (as in the Prius) to extend battery life. Alternatively, we would need to some sort of breakthrough in storage to include capacitor technology.

Now that we understand most of the problems with this approach, is there anyone out there who can set forth possible solutions.

Is SMUD, for example, so naive, that they have not considered the battery problems outlined by the commenters above?

It also seems that the utility provider would need to compensate the vehicle owner for reduced battery life. Regardless, however, would the use of a battery powered vehicle be a good alternative to a generator in the case of a power outage? In this instance, the value of the BEV or PHEV would be enhanced as it would serve a dual use. As it is, I have a generator that just sits there as a form of insurance and serves no other purpose, at least for me.



That pretty much sums it up before this can be a reality. Add to that the fact that people don't like to think ahead. Having to think about how full you want the battery to be when you get back to your car, and at what time you will get back to your car will prove too much of a fuss for most people. I suspect that many people will not even bother to hook up their car at all.

However I do not agree with the data communication problems you envision. Networking over power lines is already available for some time. See:

Paul Dietz

I think the best you could do is have a way to turn off plug-in charging on demand, causing the vehicle to revert to HEV mode when you start it the next time. This would not increase battery cycling, but would make plug-in demand dispatchable.

My home air conditioner already has a wireless demand modifier. I get a $10/month discount from the local utility and allow them to remotely turn off the compressor up to three hours per day.


First, Rafael, the communications and data requirements you set out are trivial. Power exchange can also be handled inductively in the case of non-covered parking areas eliminating weather concerns and this also facilitates NFC (near field communications) which is quite reliable at 200kbits/sec comm speeds which easily handles highly encrypted data for a vehicle sitting all day with relatively limited bandwidth requirements. In fact a GSM transceiver's cost is so low that most vending machines now incorporate them for low bandwidth basic data transfer (they don't require EDGE, or CDMA-1/CDMA-2000 as all the data required could be done over CDPD and even the more mundane and earlier forms of comms which cost the cellular companies almost nothing). BTW- "quickpay" "smartpay", etc cards use NFC and there are no worries of RF since NFC uses magnetic fields at extremely low power (-110dBm would be at the high end).

Also what makes you think that everyone would be *forced* to buy into V2G just because they own an applicable vehicle?

Do you think twice before you process a credit card transaction? (other than identity theft) Those happen just fine unless there is a power outage or someone takes out the NOC and/or T-1 lines for the company. Same thing with authentication & hand shaking in this case. A simple HMAC protocol instituted into firmware ensures security in who can update your software as SHA-1 has only been cracked in theory on a piece of paper and will never happen over wireless unless you have the resources of a very large company at your disposal (we are talking about over the air interception here as the actual source connection is more vulnerable...if you have a super computer at your disposal).

Anne, Broadband over powerlines is a TERRIBLE idea that threatens our home security & public safety (plus Amateur radio operators) and the NTIA (govt version of FCC) and several non government organizations are moving to block this immediately. Broadband over powerlines (BPL) was put in place without meeting standard FCC requirements and the FCC turned a blind eye towards that but now HF radio communications are being destroyed by BPL since they don't mitigate their emissions properly(for example, the ONLY communications you had in New Orleans for long distance as all land lines were taken down (NOC, PSTNs were down), the TDMA & CDMA systems were down (cell phone companies), and VHF/UHF have limited range (repeater sites down and backbone/interconnects useless). BPL's data rates cause interference on their primary frequency (data rate), harmonics of that frequency (square waves have nasty near infinite bandwidth regardless of encoding schemes such as biphase manchester, et al), and the intermodulation products. Especially when you consider the amount of power they put behind this data transfer and how the unshielded (RF shielding not electrical) wiring acts as gigantic full wave antennas.


The cost of meeting renewable energy goals could encourage utilities to simply absorb some of the cost of v2g vehicles.This is money they would have to spend on a panoply of other tech anyhow.The owners would now become their customers rather than mobil oils.This is akin to giving away the phone in order to make money selling the phone services.Solving the aforementioned problems would be aggressively pursued by the utilities if a roadmap were laid out and governmental regs set.


I think that the use of a network to even out recharge times of BEVs and PHEVs is a great idea. There is no reason why all of them need to be recharged right at 7 when people get home and plug them in. Just program in a timer that says when you'll next need a full charge. But there's no way I want my expensive Li-ion batteries life used up to power sombody elses air-conditioning.

I also think that the fluctuations of wind power have been overblown (pardon). With enough wind generation in enough diverse locations I think you will find that your production will average out quite nicely; especially if you fly your wind generators at high enough altitudes.

Sid Hoffman

Didn't this very website have a story about one of the power companies in the UK which had wind generators all over the country? I believe their finding was that the wind is always blowing somewhere, and as long as you have turbines in prime locations all over the country (and correctify me if I'm wrong, the UK is comparable in size to California in terms of wind-potential square miles) that you always had a very predictable amount of wind generated power. A "floor" so to speak, that was virtually never broken and made planning easy once the installed base of wind turbines was large enough.


This is a very interesting idea. It appears that the necessary engineering is in place to provide:

1) Plug-in safety connections direct and inductive
2) Comms links and encryption via EVDO/EDGE cellular, etc.
3) Programmed levelling fetch/requests from grid source

The first application should be with fleets. Both the NYC and Sacramento fleets seem reasonable test beds. Sacramento might want to build out a PV bank that would utilize the cumulative BEV/PHEV storage as simply another storage system. Solving the deep discharge question is a matter of setting limits on battery discharge below certain levels - always leaving enough energy to meet the work day demand by the day start time.

The economics have a feasable model in place in the business/consumer renewable to grid formulas in use now. So the key seems to start with a fleet, wholly owned and operated under fixed charge station conditions. Sacramento can further justify the higher cost of BEV/PHEV vehicles by levelling and providing nighttime V2G flows from the PV banks. We could use a cost/kwH curve over 5,10 and 15 year battery evolution to better determine long term ROI.

The fleet implementation should help shake out the greater variables in a consumer model and better indicate the efficiencies of costs over time.


Is'nt this a little 'cart before horse'. Does'nt a major car company have to mass produce Plug-ins Before something like this is possible?

Rafael Seidl

Anne, Patrick -

you rightly point out that a number of solutions to the data communications and transaction protocols already exist elsewhere and could be adapted fairly easily. This is correct, I merely wanted to underscore that V2G requires more than just the power infrastructure.

Joseph -

no-one is going to build a PHEV or BEV production vehicle unless both the technology and the economics make sense. The V2G concept is intended to address the currently poor economics of large battery packs by putting them to good use even when the vehicle is parked. If creating that infrastructure what it takes to make the economics work for series production, then it absolutely legitimate to think the concept through because multiple industries would have to conduct parallel R&D.

Any time you have to install any new stationary infrastructure, there is the chicken-and-egg question of how soon the market it serves can achieve critical mass. Getting oil companies and their gas station franchisees to switch from one liquid fuel grade or type to another is relatively straightforward yet the inertia that must be overcome is substantial. V2G would require a far greater investment from the utilities, so the business risk would have to be acceptable to them as well as to carmakers.


A123systems batteries, as well as other similar chemistries, may solve the cycle life problem.


The "won't register for V2G" problem is easily solved:  have the car analyze its typical use-cycle and register and manage itself.  For PHEV's, this is easily done.

As for the "user won't plug in", people who don't want to get the discount from plugging in will be free to pay top dollar.

Willett Kempton

We appreciate the interest. Also we appreciate the excellent and accurate GCC summary of this complex topic. Apart from the communications bandwidth, which we have considered only briefly, all the above points are addressed in the two peer-reviewed articles cited above (Kempton & Tomic 2005). For example, we suggest 220/240 VAC not 115, ALL our cost equations factor in battery degradation, and we suggest only using V2G in electric markets for which revenue exceeds cost. Peak power is probably not one of them, given current battery technologies. As new battery technologies' cycle lives increase to exceed vehicle life, the battery wear term in the cost equations go to zero and many more electric markets become economic. We've been thinking about this for 10 years and it has been reviewed very thoroughly by all industries concerned, and all subsystems have been prototyped and tested. For those interested in more depth on this topic, we suggest the two Kempton and Tomic articles referenced above, but linked above only by DOIs--they are available (in proof) to those without library subscription at our website:

W. Kempton and J. Tomic


Thanks for stopping by!  It's great that you're actually reading comments by the hoi polloi.

Felix Kramer

For a general overview of the ZEV Technology Symposium (including links back to Green Car Congress posts on sub-topics), see my blog at

-- Felix Kramer, Founder,


I would not want to use any of my battery cycles for this, but an SOFC that wants to be run continuously would do just fine.

Gale Jarvis

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It's good to hear BP & GM talk about alternative fuels, but 50 years to implement is too long.

Perhaps this link will spark more attention:

It is GM's electric concept car the Chevy Volt. If more people begin to demand alternative fuel cars, we should be able to speed the rate at which the technology is developed.

We have started an Investor Forum where Investors can meet and discuss topics like this:

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