Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: The Physics Behind the Spanish Blackout
Date: Thu, 12 Jun 2025 17:47:24 -0700
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On 6/12/2025 4:55 PM, KevinJ93 wrote:
> On 6/11/25 6:06 PM, Don Y wrote:
>  >> My solar PV system has battery storage and I subscribe to Tesla's
>  >> Virtual Power Plant. When the grid is under stress I allow up to 50%
>  >> of the storage to be used by the grid for which I get paid $2 per kWh.
>  >
>  > Not bad when you consider they charge $0.15/KWHr to sell that electricity
>  > to you in the first place!  You're just letting someone take your car
>  > (house)
> 
> My batteries only get charged from solar (My account with PG&E does not permit 
> charging from the  grid as that as that would allow arbitrage).

Yes, my point was that they charge you much less for energy delivered than
they are willing to pay for energy stored.  (of course, you had to make the
investment in much the same way THEY had to invest in the distribution
network).

>  > for a drive -- without any mechanical wear-and-tear on a vehicle, any
>  > risk of an "accident", theft, etc. -- and are being reimbursed for that
>  > "generosity".  Much more generous than many "friends" would be in
>  > reimbursing you for their convenience!
> 
> I calculated the cost of the wear and tear on the battery is (very) 
> approximately $0.25/kWh.

So, if you have a surplus, it makes sense to make it available (even though
whether or not you have a buyer may be uncertain on any given day)

>  > What sort of capacity do you have and how easily do you "top it off"
>  > purely from solar?
> 
> I only have 27kWh of storage (2 Tesla Powerwall units). In the summer I average 
> 20-35kWh per day of surplus generated by solar. So if the battery has 
> discharged to 25% (own use plus any exported) in the evening it can be fully 
> recharged the next day.

We use about 25KWHr/day (it's not "hot" yet).  So, would need to generate
about 50KWHr daily to meet that sort of storage ability.  Without resorting to
a tracking collector, I think we're limited to about 6.5 usable solar hours
daily.  So, would need ~8KW from an array to "bank" that much.

>  >> I usually get a few hours notice through the App on my phone and I can
>  >> opt-out for any event. This is in California although Tesla operates
>  >> similar programs throughout the country.
>  >
>  > So, they have good enough models to *predict* when there will be a need?
>  > Or, is there *always* a need and they just "spread the wealth"?
> 
> The models are usually pretty accurate (https://www.caiso.com/todays-outlook/). 
> Among other things the next day's predicted consumption is based on historical 
> data and weather predictions (air conditioner use is a large component of the 
> power demand).

But, presumably, they have *generation* capability to meet those needs?
Are they relying on your storage IN LIEU OF more expensive peak generation?

> A couple of times there have been emergencies where there has only been minutes 
> of warning.

So, you could have a "standing offer" that they could avail themselves of?
The rate of compensation doesn't vary with the severity of their *need*?

>  >> Tesla vehicles do not (yet) support Vehicle to Grid (V2G) operation
>  >> although the extra hardware required is minimal as the conversion from
>  >> AC to DC in the car is already pretty much bidirectional to achieve
>  >> high-efficiency. (Just using Diodes is too inefficient)
>  >>
>  >>> <...>
>  >
>