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Comment by mikelward | Hacker News Reader

What about batteries in the cars themselves? And residential batteries such as Tesla powerwall?

This keeps getting brought up but the power stored in your car battery is usually there so you can, ya know, drive. If grid uncertainty can deplete your car battery to smooth the grid out, then you have to accept that you could very likely not have your car on demand which is pretty unacceptable for most people. I mean can you imagine that on a particularly hot day, the car you took to the office and expected to charge at the charging station instead has a lower battery at the end of the day than when you arrived and now you can't drive home?

I had imagined they were talking not about depleting the battery into the grid, but rather choosing when to charge them. Right now Tesla is pretty primitive about when to charge, all you can do is give it a time to start charging.

But it is easy to imagine something much more advanced. Given some input like how long we've been plugged in, if we use the app to say "charge now", what utility we have (by selection or by GPS possibly), interact with the utility to adjust the charging rate.

At the moment I'm just set to charge starting at midnight. This is for 2 reasons: We recently switched to a 3x higher utility cost from 7pm-10pm, and also the car charging when I plugged it in made it hard to read my bill. We have these bills that say "You use X% more energy than your neighbors, can you think of anything you do from 5pm-7pm that you could cut back on?"

The moments where the electrical demand is the highest during the day, in addition to being at the time when solar production is starting/is winding down, is the time people are either leaving for their commute and so are expecting to have a full charge, commuting or finishing their commute with partially empty batteries in need of a reload.

Not that this would be and easy thing to do but I always read the demand curve as the best possible reason to have a lot of destination chargers (in addition to home chargers). People are out in the community with their cars during the day when solar production is highest. Start piping that production into those batteries when it isn't needed elsewhere.

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