[nkingsy]

This makes much more sense with large lifepo4 chemistry batteries that are expected to outlive the car by a wide margin.

Lifepo4 batteries > 50kwh should easily handle 500,000 miles.

Higher performance lithium ion will degrade at a rate faster than any expected return from a scheme like this.

At least in Northern California it’s now cheaper for me to run solar+battery off grid than to pay pge. Lifepo4 pushes it over the edge into profitability.

If off-grid is competitive, selling at peak prices is a no brainer.

[toomuchtodo]

I have 100k miles on my 2018 Model S having Supercharged it the majority of the time the last four years. It has only 6% battery degradation of the 100kw pack. Tesla warranties their powerwalls for 15 years when configured as part of their aggregated virtual power plants. The batteries are demonstrated to be durable.

New LFP chemistries that are heavier but more stable are ideal for stationary storage and high cycle counts, but the evidence shows in general that these packs are built for longevity (with very occasional early failures). You could probably do well buying a salvage Tesla and shucking the pack for working modules and coming out ahead economically (safety warning, do at your own risk, etc) if you don’t want or can’t get dedicated stationary storage (although it comes with generous federal, state, and utility subsidies in California).

[danans]

> if you don’t want or can’t get dedicated stationary storage (although it comes with generous federal, state, and utility subsidies in California).

I installed stationary LFP batteries (from Enphase) on my house in CA 1.5 years ago, but I then discovered that the state and utility subsidies [1] only apply if you are in a very low income (for CA) bracket, have a health condition that requires backup power, or live in a high fire risk zone.

I don't qualify for the first 2 categories, and my luck is that the high fire risk zone starts about a mile away from my house, so good from the fire risk perspective, but not for the subsidy. Still got the 26% federal tax credit (with IRA, it's now back up to 30%).

1. SGIP: https://www.cpuc.ca.gov/industries-and-topics/electrical-ene...

[mercutio2]

How do you like your Enphase batteries? I was pondering buying them, already have Enphase solar.

I'm particularly interested in whether you're doing any load-shifting with them, and if so, how easy it is to do with the software. I'm paying $.90/kWh at summer peak, so while I'm still on net-metering, I'm somewhat interested in going ahead and fully arbitraging during peak.

[danans]

> How do you like your Enphase batteries?

I'm mostly happy with them. The batteries are pretty much set-and-forget, but I change the reserve level by season (90% in winter, 30% in summer). The system automatically decides how to do load shifting to optimize for your particular rate structure. I will say the monitoring software can be janky at times. It's gotten better, but sometimes it is very slow to connect to the system.

> I'm paying $.90/kWh at summer peak

Whoa, where is that? That's 2x more expensive than California or Hawaii. You must be on a wholesale rate plan with very low off-peak rates if you are considering arbitrage. It's also good that you waited until this year, because before the IRA, the residential battery tax credit was only available if you charged it with on-site renewables, not from the grid.

I don't do any grid arbitrage in the sense of buying low and selling back to the grid from my batteries when rates are high. That's not possible for homeowners in CA, is it in your area? However, several places in Southern California already have home-battery based virtual-power-plants that you can participate in, and I think it integrates with Enphase batteries. In those programs, the arbitrage is managed by a 3rd party company which then compensates the homeowner.

However, my evening loads during the peak rate hours do draw on my battery until it hits its reserve level, so what I do is more like peak-rate avoidance than arbitrage.

My batteries also don't charge from the grid, just from my PV array. With subsidized net-metering 2.0, the difference between peak and off peak for me is only $.07/kWh, so there's really not a ton of economic value there, maybe like $70-80/year at most.

[mercutio2]

I live in Berkeley. PG&E’s peak EV-A rate for generation plus distribution was $.92 this summer. It doubled in a year or two.

My off peak rate for charging the car went from net $.15/kWh to $.36 during the summer.

It’s news to me that load shifting (if you’ve got batteries and solar) isn’t allowed by the CPUC, that does take the wind out of my sails a bit. But the peak rates are so high that just zeroing out my peak consumption is still probably worth it.

Does the system come with a “disconnect from the grid during emergencies” shunt?

I’ve heard conflicting reports about the availability and legality of those systems.

[danans]

> I live in Berkeley. PG&E’s peak EV-A rate for generation plus distribution was $.92 this summer

I live in the same service area. The peak EV2A rate (including both generation and distribution) is currently $0.55/kWh, and the off-peak is $0.24/kWh.

https://www.pge.com/en_US/residential/rate-plans/rate-plan-o...

Not sure where you are getting $0.92/kWh, but would be curious to learn.

> It’s news to me that load shifting (if you’ve got batteries and solar) isn’t allowed by the CPUC, that does take the wind out of my sails a bit. But the peak rates are so high that just zeroing out my peak consumption is still probably worth it.

Load shifting in the sense of shifting your load to different times to consume cleaner/cheaper electricity from the grid, is fine and even encouraged by the CPUC. There are all kinds of programs to encourage this. You can achieve this by simple behavioral changes, timed appliance runs, or by using battery storage.

What you can't do as an individual homeowner, AFAIK, is arbitrage power by buying low from the grid and selling back high to the grid later.

> Does the system come with a “disconnect from the grid during emergencies” shunt?

> I’ve heard conflicting reports about the availability and legality of those systems.

The only "emergency" that causes a disconnect is a power outage. That's no different than what solar inverters already do. The difference with the batteries is that when that happens, they form an isolated microgrid on your premises, thereby providing backup for that scenario.

What other sort of emergencies were you imagining? If you mean minimizing grid load during peak grid load events, then that's what the virtual peaker programs do, and those are completely legal, and active participants in the CAISO energy markets.

[nkingsy]

Good to hear about the S. I just got a used model X with free unlimited supercharging. Tesla doesn't recommend supercharging for around town use, which is strange considering it only goes over 1C for 5 minutes or so and only barely over, with active cooling.

The other strangeness for me is the recommendation to stay between 50 and 90 for daily use.

Studies of li-ion have shown 80-20 to be the optimal usage pattern for maximizing usable watts over the life of the battery.

[toomuchtodo]

Battery warranty is 8 years unlimited miles, so I don’t put much thought into pack health. Enjoy your spaceship.

[onlyrealcuzzo]

> If off-grid is competitive, selling at peak prices is a no brainer.

So why isn't the utility managing the storage directly then? Aren't they best suited to do this???

Or is this article just saying that EV car batteries could?

[Dylan16807]

> Aren't they best suited to do this???

They don't have a million EV batteries, purchased outside the scope of this program, sitting around idle and connected to the grid.

Their customers do.

[tuatoru]

Utilities don't yet have a million EV batteries laying around, but they (or specialist EoL battery companies) will soon.

From the abstract:-

> Participation rates fall below 10% if half of EV batteries at end-of-vehicle-life are used as stationary storage.

Half seems conservative to me. There are already lots of startups wanting your end-of-life EV battery.

[aurelwu]

end-of-life Battery usage will compete with recycling them and especially as material needed per kWh is going to keep going down it might be more economical to recycle them into a new battery - it also depends on costs of raw materials. I'd expect the share to be neither 0:100 nor 100:0 and to fluctuate quite a bit

[Dylan16807]

It makes sense to move a lot of load to older stationary batteries as those become more plentiful.

But more capacity is better, and getting things online sooner is better. And in 2030 almost all the capacity is going to be in non-retired packs in their original cars.

[fshbbdssbbgdd]

Utilities buy most of their power at wholesale rates, which are lower than the consumer rate they charge the end user. Net metering rules in some jurisdictions obligate the utilities to buy solar/battery power from users at consumer rates. That can be a good financial opportunity for homeowners and it’s driven a lot of the investment in home solar setups. But local policies can change. The rules are changing in California and it’s not going to be such a good deal anymore in the future.

[epistasis]

Utilities are, by and large, not economically rational actors. In addition to extreme bias in the C-suite towards old tech, they are highly constrained in decision making by public utility commissions, and decision making is often based on information that is 5-10 years old. It takes papers like this getting published, then publicized enough so that they PUC can't ignore it, before info can enter an IRP that plays out over 5-10 years.