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Glass is more than half full... PV+ESS is the bomb.

jboy210

Supporting Member
Dec 2, 2016
5,157
3,207
Northern California
Yeah TOU-B and TOU-C wouldn't be so bad... assuming you were able to size your solar to cover your EV charging as well. Because then you could just use the NEM with TOU-B/C and you wouldn't need the "discounted" off-peak charging period under EV2-A.

But this EV2-A rate is just insane for all your other normal home consumption. I can't imagine how people live with this EV2-A thing. Solar generation is a fraction of what you'd see under TOU-C, but the costs during peak time are like 2x higher.
You have confirmed my estimates.

We stayed on TOU-B even though we have 2 Teslas because we have been working from home for 5+ years and will likely stay that way. So we only need to charge a car every other week.
 

holeydonut

Supporting Member
Jun 27, 2020
1,820
1,195
East Bay NorCal
My thought was that price polarization increased the value of the ESS. Currently on TOU-B the price differential even for summer doesn't seem to create enough value to do anything but minimize imports from the grid.

Last year my system underperformed production estimates by 3-4k kWh. This year we are trending very good, perhaps even above estimates due to drought conditions. I don't have an EV and my PV production vs home usage doesn't support getting one if break even was a requirement.

With 90% round trip efficiency, would it be wrong to assume parity with taking ~ 2 kWh from the grid at EV2-A off peak prices for every 1 kWh exported to the grid during peak rates?

IMO, PG&E makes all this super complicated on purpose haha. But to paraphrase what I think you're dealing with... your PV system broadly offsets your normal home annual consumption. So you're fine on E-TOU-B. As a result, your Powerwalls are primarily a resiliency thing because you aren't on EV2-A and your "TOU polarization" is minimal.

But if you are planning to get an EV, your solar won't be enough to offset your EV charging. So at that time, you should consider EV2-A (or whatever EV rate is available at that time). Edit: Or you can try to add a bunch more solar panels. For that future version of you, the Powerwalls could be super valuable to manage the TOU.

My rule of thumb is that peak EV2-A is 2.5x more than off-peak EV2-A. But with PG&E changing rates every year who knows what is "right" haha. I think we can all agree that TOU rate variations will never be in the homeowners favor, so the batteries are super nice since they make you agnostic to TOU.

One last thing... since you have batteries... I don't think you should view getting a EV as a break-even exercise with your PV. It makes more sense to consider the opportunity cost of paying Big-Oil for gasoline instead of paying Big-Monopoly for grid energy. Your grid energy cost will be lower on EV2-A vs E-TOU-B unless you can add a bunch more solar panels on your roof.
 
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h2ofun

Active Member
Aug 11, 2020
2,657
490
auburn, ca
Priorities got in the way of conducting this analysis but with 3 PW and a PV production curve shifted later in the day due to my mostly west facing panels, I wondered if it would be BETTER for me to be on EV2-A rather than TOU-B. I have high confidence in making it from 3 pm to midnight without touching grid power. (In the summer we will reach 100 kWh usage days.) If I could run my home off 18 cent power from 12a - 3 pm while the power walls fill up and then export 100% of PV production from 3:00 pm to sundown, I think i'd be in even better price arbitrage situation than I am currently. Am I crazy?

Maybe stupid questions, but does your Dishwasher and other appliances have a delay start features? I often load up my dishwasher after dinner, put in the soap and then hit 2 or 3 hr delay so it starts after 9:00 pm. It would not be any different to say 5 or 6 hour delay so it kicked off after midnight.
Thats great if you have gas heat. But try you analysis with electric heating like I have when one has basically no winter solar, so the batteries for a lot of time will either be dead, or I have to put them on backup only mode for a power outage. All because Tesla will not let me charge the batteries in the winter from the grid.
 

h2ofun

Active Member
Aug 11, 2020
2,657
490
auburn, ca
If you assumed the ESS solved your "TOU Peak vs Off Peak" problem, then the next question to ask if if your PV production and consumption are broadly neutral from a NEM standpoint. If you're expecting your TOU-B to break-even (ignoring TOU crap) then your opportunity cost is the same on both plans.

My situation is a bit stupid because my solar system is only sized to my normal home annual usage. A future EV cannot be covered by the generation of my solar panels. So I need the EV2-A since my house is a NEM net-deficit with the EV being the culprit. I can fit maybe 1 or 2 more solar panels that actually face South. I guess down the road if PG&E increases off-peak EV charging rates to $0.40 per kWh ... then North facing panels would still make economic sense for the NEM credit.
This is why I am trying to get a whole bunch of North facing solar panels.
 

holeydonut

Supporting Member
Jun 27, 2020
1,820
1,195
East Bay NorCal
I am only trying this now, since I assume with NEM3, if one were to add more panels, then it would force one off NEM1 or NEM2. So, its now or never to try.


Lol, I think if my install went better, my wife would be open to it. But PG&E has beat us up so good for over a year ... we're not going to do anything for a while.
 

getakey

Active Member
Jan 28, 2020
1,309
428
95762
Thats great if you have gas heat. But try you analysis with electric heating like I have when one has basically no winter solar, so the batteries for a lot of time will either be dead, or I have to put them on backup only mode for a power outage. All because Tesla will not let me charge the batteries in the winter from the grid.
Didn't you get your PWs for free? And now you want to charge them from grid at off peak to off set your electric heat pulling from grid at Peak?
 

h2ofun

Active Member
Aug 11, 2020
2,657
490
auburn, ca
Didn't you get your PWs for free? And now you want to charge them from grid at off peak to off set your electric heat pulling from grid at Peak?
I have to cycle the batteries 52 times a year, for 5 years. So, if I cannot use the batteries in the winter, because solar cannot charge them when I am using 30 to 60 kwh per day for heating, I am screwed. AND, it is legal by both PGE's reports and SGIP's to charge from Grid. So yes, I would like Tesla to follow the law and allow be to meet the legal SGIP requirement I signed getting these batteries. Is this too much to ask. For folks, with is most, who have gas heating, you have no idea how big of a deal this is!
 

getakey

Active Member
Jan 28, 2020
1,309
428
95762
I have to cycle the batteries 52 times a year, for 5 years. So, if I cannot use the batteries in the winter, because solar cannot charge them when I am using 30 to 60 kwh per day for heating, I am screwed. AND, it is legal by both PGE's reports and SGIP's to charge from Grid. So yes, I would like Tesla to follow the law and allow be to meet the legal SGIP requirement I signed getting these batteries. Is this too much to ask. For folks, with is most, who have gas heating, you have no idea how big of a deal this is!
I looked at that cycle requirement and you be able to easily meet that. Didn't you make the choice to go to electric heat?
 

dareed1

Member
Jan 15, 2021
101
94
Belmont, CA
I have to cycle the batteries 52 times a year, for 5 years. So, if I cannot use the batteries in the winter, because solar cannot charge them when I am using 30 to 60 kwh per day for heating, I am screwed. AND, it is legal by both PGE's reports and SGIP's to charge from Grid. So yes, I would like Tesla to follow the law and allow be to meet the legal SGIP requirement I signed getting these batteries. Is this too much to ask. For folks, with is most, who have gas heating, you have no idea how big of a deal this is!
I really don't follow how you are "screwed". Over the course of a year you'll be generating more than you consume, even during TOU-C peak. Also, even in winter, there's a lot of solar generation. It appears that our 8kW system will average during November-January more than 15kWh per day.
Heat pumps do consume a lot of juice during the heating season, so with our 2 PW system, there's a number of days in which we can't even make it until 9PM on the PWs. Still, we're already in surplus generation for the year.

So why do you need to charge the PWs from the grid? I don't see a financial justification for it.
 

h2ofun

Active Member
Aug 11, 2020
2,657
490
auburn, ca
I looked at that cycle requirement and you be able to easily meet that. Didn't you make the choice to go to electric heat?
Yes but I had no ability after the remodel to go with ducted propane. Things would not have fit again. So yep, the electric heat matches the solar. What it does not match, IMO, is ev2-a rate plan.
 

h2ofun

Active Member
Aug 11, 2020
2,657
490
auburn, ca
I really don't follow how you are "screwed". Over the course of a year you'll be generating more than you consume, even during TOU-C peak. Also, even in winter, there's a lot of solar generation. It appears that our 8kW system will average during November-January more than 15kWh per day.
Heat pumps do consume a lot of juice during the heating season, so with our 2 PW system, there's a number of days in which we can't even make it until 9PM on the PWs. Still, we're already in surplus generation for the year.

So why do you need to charge the PWs from the grid? I don't see a financial justification for it.
I had plenty of 5kw total for solar during winter, and this winter was as mild as it gets w/o much rain.

I just have a different view from others, who are not in my shoes.
 

Southpasfan

Member
Jun 2, 2019
454
578
Pasadena
I have to cycle the batteries 52 times a year, for 5 years. So, if I cannot use the batteries in the winter, because solar cannot charge them when I am using 30 to 60 kwh per day for heating, I am screwed. AND, it is legal by both PGE's reports and SGIP's to charge from Grid. So yes, I would like Tesla to follow the law and allow be to meet the legal SGIP requirement I signed getting these batteries. Is this too much to ask. For folks, with is most, who have gas heating, you have no idea how big of a deal this is!
Maybe I am missing something, but isn't it pretty easy to cycle the batteries 52 times?

I think I've cycled them 52 times since February.
 

Southpasfan

Member
Jun 2, 2019
454
578
Pasadena
I have 5 to cycle. You and I just look at this differently.
Also, h2of, I didn't see whether you have an EV. I have three PWs and two EVs (a Model 3 and eGolf).

Since the car capacity is 100Kwh and the batteries are only 40, given some reasonable amount of driving I can cycle them easily.

Without EVs 65Kwh of PWs is not as easy to cycle.

You could also spend a couple thou on an electrically heated jacuzzi. That would solve it. :)

I have one of those as well. Ha!
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
9,488
10,670
Riverside Co. CA
I have 5 to cycle. You and I just look at this differently.
You wont have any issue cycling your batteries the required number of times, especially since you are enjoying being "off the electrical grid" since your install. That part of your complaint is really a non issue, but until you see it for yourself (after an entire year) you likely wont believe anyone else that says different.

Sort of similar to the different opinion it appears you have about powerwalls from when you started participating here till now, you will find that this is really not that much of an issue. You will set your reserves in winter to a higher number than they are now (or not, because you dont have to worry about "resiliency" because you have a generator), and you wont be in any way, shape or form screwed on anything.
 

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