This idea sounds great ... until you need to hop in your car and drive somewhere midday and learn that the battery is mostly drained because it's a hot day and everyone's turned their A/C on full blast.
I'm sure the engineers have thought about that scenario and maybe only allow 20% of the battery to be used for the purpose of grid maintenance, but I imagine it will be difficult to sell the average car owner on the idea, because people are always thinking about worst cases.
I mean, think of it in terms of a conventional car. How would you like to never know with certainty whether you have a full tank or not when you get in your car?
A coal power plant might take several days to reach a "set point" and to generate a certain amount of power.
A natural gas plant might take as little as 5 minutes or as long as an hour to get operational.
A diesel generator might turn on and make power in as little as 30 seconds.
A hydro plant might be able to go from 0% to 100% in just a few seconds.
Given that the utility companies can't KNOW for sure EXACTLY how much power people will demand in the future they've always got excess capacity ready and waiting. But these idling plants aren't free and that drives the price of electricity up.
The idea behind V2G is that the utility companies can get some of their demand power from the cars whilst they fire up diesel generators or natural gas plants or whatever, thus saving them from having to keep those plants idling until they're definitely needed.
EDIT: The idea isn't that you constantly charge/discharge car batteries it's that you charge them in the morning after the drive to work so they're full by noon. Then as the day heats up you can pull small amounts of power from large amounts of cars until the demand is high enough that you fire up a peaker plant. Use that to charge the cars back up and provide the afternoon A/C electricity and shut it down as everyone starts to go home.
Instead of having the peaker plant be at ~20% capacity from 12-2, ~60% capacity from 2-5 and ~30% capacity from 5-7 you get to run 0% from 12-2, 80-100% from 2-5 and 30% from 5-7. Two hours of runtime saved per day is 600 hours per year. Turbine rebuilds aren't cheap; a buddy of mine is a private jet pilot and they have to put away between $500 and $2500 per hour that engines are running for overhaul at either 1000 or 2000 hour intervals. And that's for the kind of small engines in a 6-12 seater business jet. I'd wager that 20MW (~20,000 HP) natural gas turbines are substantially more.
More concerning is battery wear (in my mind).
While true self-driving cars should be cheaper than taxis and also allow for longer distances, I don't think this will be sufficient to change the dynamic significantly.
I've got my doubts over the viability of EV-based grid storage, and a lot of the viability depends on technologies. If we see a period of rapid charging carbon nanotube or graphene batteries which can literally be fully charged in seconds to minutes, and have a tremendous number of charge cycles, it starts looking more viable. Even a Tesla Supercharger situation is pretty good in terms of time -- few commuters will be inconvenienced if their vehicle only receives a net charge for the last 30 minutes of its idle cycle, which during a daytime commute scenario typically lasts 8-9 hours.
Presently the alternatives are ... few. Pumped hydro works but is very limited by available siting. There simply aren't that many places where you can run a pump/turbine between two large bodies of water with a significant grade separation, and far fewer in Kansas (or Illinois, or Florida for that matter). One of the more reactive alternatives is kinetic storage through flywheels, which offer tremendous charge/discharge rates, but are also very pricey: about $10,000 per kWh capacity
http://physics.ucsd.edu/do-the-math/2011/09/got-storage-how-...
I suspect idle EVs will be at best a small part of the total solution, but even a few-percent solution could be meaningful.
That said, my uncertainty about vehicle use isn't as bad upon return to home, at which time I'd be more amenable to allow discharge -- and this is right when my local leg of the grid needs a bump in supply: I'm about to switch on lights, TV, microwave, heat or A/C; things I'd leave off whilst at work.
For a consumer though, a single KW (3.6MJ) of power would be generated by moving 10m^3 (i.e. 10KL) of water 36m (approximating gravity at 10ms^-2). You can tweak those numbers but you end up needing two sizable water tanks quite far apart. Great if you have loads of land but not much use for consumer storage.
Feel free to correct any flaws in the calculations, I'd be much happier if I were off by an order of 10 or more.
https://en.wikipedia.org/wiki/Raccoon_Mountain_Pumped-Storag...
https://en.wikipedia.org/wiki/Bath_County_Pumped_Storage_Sta...
https://en.wikipedia.org/wiki/Ludington_Pumped_Storage_Power...
How long would 1 KW last for the average household, and, if 1 KW is not enough, how many cubic meters of water would the average household have to store?
They're already quite stingy about approving customer-owned DGs (because there is little or no financial benefit to the utility) - I can only imagine how they'll feel about people connecting a generator they don't control, at locations and times they can't predict, with the ability to disconnect them arbitrarily and drive away.
In order for V2G to become a reality, utilities will need far more advanced software and metering infrastructure to perform real-time load-flow analysis of their systems and determine if/how to dispatch connected EVs. At present few utilities even have the metering infrastructure to enable that kind of intelligent control, let alone the supervisory control software.
...and as I take it from other discussion, re-design, -engineering and replacement of some distribution station equipment and software to allow net power flow upstream when a substation's downstream DG exceeds downstream load, presently taken to be a fault condition.
A DG participation fee payable to the utility for infrastructure development and upgrades seems reasonable to me in light of these considerations.
It's noted that using one's car to contribute to grid stability may void current battery warranties, about which the article notes:
"Innovators in the field are gradually convincing car manufacturers of the potential to create a "value proposition for the car owner" and thus boost sales, Gage said. Ultimately, however, carmakers may be put at ease by experiments being conducted by the military."
Well, this story seems to point to the solution: put batteries in all the things! If its going to cost more to feed power back to the grid, then why not just make everything in your home store its own local power supply ..
To some extent, I'm already doing this - pretty much every electronic device in my house uses rechargeable batteries. So maybe the campaign by the utilities against feeding power to the grid is going to have the effect of pushing everyone to localise their power needs even further, and instead of pushing excess to an ageing, antiquated monopoly, us alternative-energy freaks are instead going to foster the creation of a heftier market for battery-protected devices. (I'd be quite happy to run my TV on battery power, if it only had one in it, like my laptops and cell phones and toothbrushes do ..)
