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PG&E Demonstrates Vehicle-to-Grid Technology

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

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.




I don't trust that they will leave enough power to get me home. What happenes on those days that there is an accident and you spend 20 extra minutes doing 7 miles an hour.


Love the idea of V2G and I currently use my electric motorcycle to power critical parts of my household in a power failure. It's worth pursuing the idea but I don't think it will fly unless A) the customer has the ability to dynamically set parameters (don't want to go to my bike for a long trip and discover that it's been partially drained) and B) the cycle life of the batteries becomes virtually infinite. Cycles are way to valuable right now spend on V2G.


I like V2G if we have SOFCs that run on NG in our cars. This is a good form of distributed generation and there is no reason why my car can not be used for this when sitting in my garage. I would not use finite battery cycles for this however.

Harvey D.


It would be rather easy to pre-set disconnect based on battery discharge levels and time of day contribution to V2G.

However, I doubt that Energy Cos would buy back energy at a higher cost than they can produce it with their old dirty coal fired generation plants, unless they have to pay for the pollution created.


In terms of life-cycle and the economics of doing this those papers referenced above show that even taking into account battery degradation, a profit is to be made.


I don't trust that they will leave enough power to get me home. What happenes on those days that there is an accident and you spend 20 extra minutes doing 7 miles an hour.

With an EV, at 7mph, your energy efficiency will be far better than it would at 55-70mph. Unlike a gasoline vehicle, where efficiency drops as load drops, and where mileage stays about the same, or gets worse, when stuck in traffic. EVs have relatively proportional energy consumption compared to speed. What you should be worried about is them taking out the usual amount on a weekend, and you, seeing a wide open highway, average 80mph instead of 60mph. Then you may be in trouble. ;)


V2G really depends on the SOC of the pack and the cost of the additional (relatively small) cycle compared to the price paid for the electricity. This would be great if the cars were plugged in after the morning commute, and that excess was used during the peak in the early to late afternoon. No impact on range (compared to stock w/no charging) if the only thing taken out is what's put in.

Kit P.

I am in love with the idea of a utility providing reliable service.


This reminds me of the parallel processing project where idle PCs are used over the net to solve large problems. This was a concept that Al Gore tried to explain to a Congressman in Congressional testimony, before he got cut off by the Congressman to receive more insults from him.


Too much trouble...I may decide, midday, that I need to go to X destination after work outside of my normal commute and now I may not have enough power for it.

Was Gore talking about all of the projects already occuring (SETI, protein folding, etc)? You better hire a few PhD holders in Comp science to have a program worth a damn that can make efficient use of the parallel processing. Intel has a chip "capable" of doing nearly 300 trillion operations per second while consuming the power of your average desktop...too bad only the guys at the national laboratories would even know where to begin with the programming of that 80 core beast.


Too much trouble...I may decide, midday, that I need to go to X destination after work outside of my normal commute and now I may not have enough power for it.

Then you can buy back a couple of hours worth of charge at a much higher rate, so you'll have enough when you get off work. ;) Unless it's a completely spur of the moment thing, I don't think you'll have much trouble. The only problem would be if you were consistently at 5-10% SOC after a daily commute, but if that's the case, you may find yourself in as much trouble when speeding, as you would be putting on more miles at a reasonable rate of speed/driving style.


if it is to much truble don;t do it.
it is kind of buying stocks. you can earn money but i can lose to and in this case it would be flexibility.
i can imagine that i have web excess to my car and easaly can sell an amount of electric. like i see the electrisity price is high i because its a sunny day and all the aircose need powering. i sell all my electrisity and take my bike.
or i expect the next day to need a lot of driving so i don't sell any.
offcourse you can set a default schema like on wednesday's i'm free so sell. on monday's i do the shopping so don't sell.


No thanks, you are telling me that I should be FORCED to give my energy away at a low rate and then, if I need energy I have to pay MORE for it ? Did you really think this out before you posted it?

How about this. While you are at work today, I'll siphon about 5 gallons of gas out of your car and pay you $1.50 a gallon (I mean, heck, you aren't using all that gas and it just makes your car probably won't need that much gas on any given day). Decide that you need to go somewhere after work outside of your normal commute? I'll sell the gasoline back to you for $3/gallon.


V2G looks like a bridge too far to me. Overly complex but very politically correct.

In general the utilities have excess capacity. But they can be stressed when every AC is on in the summer. Even so, only in the worst hours of summers in a few areas do shortages develop. At night there is excess capacity.

It seems better to encourage the use of solar panels at the house/building to cut peak utility loads. The controls and technology is established although it is still not the norm.

Notice solar panels can also charge the car if it is at home. At night charge the car from the grid. The excess capacity is there and the chargers will not be very complex.

V2G will certainly work. It just doesn't seem to match load curves well. And I suspect encouraging solar will be a far better use of funds.


Wow. What a spectacularly bad idea.


Not a terrible idea but to hand over "control" of the process to the power utils is a trouble zone. The intelligence should be in the hands of the consumer such that they program the pack to make itself available on their selected schedule. The utils, like many big systems need to move outside the centralized formula which keeps them at the locus.

What V2G may do a good job of suggesting is that several auxiliary 40+KWh packs charging overnight and then providing mains power to a household during daytime - would decouple homes from the grid except for backup/supplemental use. In sun belts add PV charging, and home electrification over thirty years could be very cheap indeed.

Cautionary item here is the utils desire to centralize system resources when the grid concept should be emphasizing de-centralization for security and reliability reasons. The days of large geo-physical grid blackouts are still with us and will not resolve via more centralization.


Why bother involving cars in this concept at all?
Why not just hook-up a bunch of cheap lead-acid batteries so that they charge during off-peak and discharge during peak? Because it is a spectacularly bad idea, as Cervus wrote.


Those that don't want to participate don't have to. The others will make the money.


Why not buy a bunch of lead acid batteries? It only makes economic sense because the battery is bought primarily for transport reasons. V2G is an added benefit.


The power company in Maryland paid us to let them install a radio controlled device on our house air conditioner compressor. This allowed them to cycle our compressors so they didn't all come on at once and bring the whole grid down. Another thing power companies have done is to sell "interruptable" power at a lower rate, requiring 2 power meters. Either method would apply nicely to EV drivers. This vehicle to grid technology, however, seems like a bad idea for the guy who owns the battery. Don't additional cycles shorten battery life? If the EV is a rental, or owned by someone you don't care about, then of course v2g is a brilliant idea.


If the amount of money paid for the use of my battery is enough to cover depreciation and still let me earn a bit of money why wouldn't the power company simply buy their own batteries (or even better, buy used batteries that no longer have quite enough charge to be used in a car ... say 70% max left). They could also use more suitable battery technologies for stationary applications. (e.g. selenium flow?)


No thanks, you are telling me that I should be FORCED to give my energy away at a low rate and then, if I need energy I have to pay MORE for it ? Did you really think this out before you posted it?

No. I'm telling you that if your electric vehicle is V2G, which would probably be voluntary. And if you decide at around noon that you want to take a side trip after work, and have already had the needed energy pulled from the pack, then you can buy it back for an increased rate. You would be penalized for unusual behavior.

If you normally drive a set amount, and can make money, including the decrease in pack capacity via V2G, then you normally wouldn't get penalized. Of course, this is assuming you have very little spare capacity, so in that respect you've put yourself in a bit of a corner in the first place. Otoh, if your little side trip is hundreds of miles, it's not exactly little.

Or, you can probably drive ~10mph slower on the highway and have enough energy to make a small side trip. Your argument assumes the driver has next to no spare capacity thanks to V2G, which I find very unlikely, but I suppose it could happen if the driver was very aggressive w/ V2G or had a very small pack compared for the commute. I.e. that can't plan for you know what.

How about this. While you are at work today, I'll siphon about 5 gallons of gas out of your car and pay you $1.50 a gallon (I mean, heck, you aren't using all that gas and it just makes your car probably won't need that much gas on any given day). Decide that you need to go somewhere after work outside of your normal commute? I'll sell the gasoline back to you for $3/gallon.

Well, it depends. If gas price depends on the time of day, and if I pay $.75 a gallon at night, and 9 out of 10 days get the 15 gallons per day that I need at that price, sell 5 gallons at work for $1.50 a gallon, and once every two weeks need to buy back 5 gallons of gas during peak rates at $3 a gallon, then I'd have no problem with that.

I make $33.75 every two weeks, less that unpredictable event, where I loose $15. I'm still on top. And... Since the side trip costs so much, I might decide it's worthwhile to plan in advance, or get more gasoline capacity. ;)

What you're talking about has little to do w/ V2G, but a lot to do with poor planning. Why not use an example where you buy an EV with a 15 mile range for a 60 miles one way commute? You would need a tow every day! :p


Neil, I'll repeat myself. Its about using a product twice over. The prime use is in transportation, that's why you really buy the battery. Once you have it though now you can make extra money with V2G. The capital outlay for the utility is not worth it if the only use of the batteries for balancing utility power. V2G is a method by which power companies can make use of energy storage capacity "already out there" in cars, bought by the public for other reasons. That is why the utility is prepared to pay the car owner a premium for the service. Although the premium won't make up for the initial battery cost it will more than cover the cost of battery deterioration.


I think Mick is on to the right thing - a "smart" grid where non time critical tasks can be scheduled to avoid peak hours or operate when there is excess power.

We will be seeing a lot of wind power in future, but we really need to rethink how we use it as it is very intermittent.

A point was made (by Marcus) that you might not want to use precious PHEV battery cycles for grid buffering - perhaps other heavier, cheaper batteries could be used for this - leave the light batteries for EVs and use heavier ones for power timeshifting.

Warren Heath

It seems to me that V2G would be most useful for emergency peak demands on the utility like one or more of: a bad heat wave, large transmission line failures, natural disasters such as earthquakes, hurricanes or ice storms, large generating station failures, terrorist attack, etc. It is extremely expensive for utilities to install sufficient capacity for a once in a decade type anomaly, V2G could save lives, during the power emergency, by absorbing power at night and redistributing it at peak times of the day.

Otherwise, it makes more sense to me, once batteries become available & sufficiently long lived, that many homes could have a Plugin Hybrid sized battery or ultra-capacitor bank of about 10 kwh, and a Synchronizing Inverter of 1-2 kw connected to the utility and a regular Inverter of 25 to 50 kw (about 10% to 50% of the size of an EV or HEV’s PEM and simpler) connected to household power. This battery bank could then provide a quick recharge for PHEV’s and about a quick 25% (50 mile) recharge of BEV’s, but more importantly would revolutionize power production & distribution. Now the typical household average grid energy requirement is 1-2 kw (with no or little electric heat), that is 4 to 9 amps @ 240 vac. As such each home would only need a feeble #16 cable to tap into the utility, instead of a heavy 2/0 cable and a large 100-250 kva transformer tied to a 4,160 – 13,800 volt utility distribution feed. A similar, but larger installation could be done in buildings. Gone would be the days of major power blackouts, brownouts and fears of terrorist or environmental disaster caused power failures. This distributed energy system of course would inevitably lead to distributed energy production, in particular CHP (Combined Heat & Power). Home solar stations of modest size, or home or neighborhood windmills, and home natural gas fed microCHP furnace/hot water/power generators, which could be small 1.5 kw natural gas or methanol fed fuel cells (not like your 15-50 kw automotive hydrogen fed fuel cell) or stirling engines or even small diesel engines with heat exchangers (which can generate power with >80% effective efficiency and no distribution losses).

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