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0 pointsmsandford12y ago0 comments

The car batteries are really only stop-gap measures to allow the utilities to better match their plants with demands. It's for synchronization only.

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.

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5 comments · 2 top-level

sliverstorm12y ago· 3 in thread

You wrote a very long post about the benefits. Thank you, but I already understand that. This really doesn't address my post in the slightest! Unless I'm just thick as a brick here.

jonmrodriguez12y ago

I think msandford is thinking that you think that this system would charge-cycle a car more than once per day, and if you do think this, he's addressing it by pointing out that the car would be charge-cycled only once per day, or less given that the system wouldn't need to utilize every car on a given day. So this extra <= 1 charge cycle per day shouldn't "murder" the battery longevity (or at least murder is way too strong of a word) compared to normal daily driving.

msandfordOP12y ago

Yes I was getting to that in a roundabout way. It wasn't very clear. You're going to have two charge cycles per day driving to and from work probably, and one or less for the V2G scenario. So it doesn't seem terribly murderful on battery life to me. Should have made that a lot more clear.

pyoung12y ago

Probably more like ~20-30 charge-cycles per year, as it would only be used on really hot days where AC usage is high and peaker plants are needed to meet that demand.

snowwindwaves12y ago

I think the electric car as dispatchable load holds the most promise. I don't know the physics of the batteries but I imagine that reducing the rate of charge of many car batteries would temporarily reduce demand without causing a charge / discharge cycle of the battery and would benefit the stability of the system in the short term if required

Edit: Also using car batteries as dispatchable load and not dispatchable generation simplifies the problem for utilities. They still have to deal with increased load but not drastic changes in power flows.

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