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Using powerwalls for load shifting only

mikesm

Member
Apr 25, 2021
24
15
menlo park, CA
Hi... So we recently built a large house and have an EV, and currently on the PGE EV-A tariff. We have a lot of solar, but have a 400 Amp feed, and a generator for backup power. I understand generators are not supported with powerwalls, and Tesla doesn't have gateways for 400A feeds. We looked at Powerwalls for power backup in an outage, but felt the generator approach was a much better choice.

I'm now thinking about using powerwalls purely for load shifting, trying to figure out if the economics were to pan out. We have a 26 KW solar system, and generates more than 120 KWh a day (during the spring and summer). The primary goal would be to minimize any energy use during peak hour, and push any extra energy generated during the day back to the grid during peak pricing.

We have a 400A feed and a genset, so a traditional install will be problematic. If I just connected the gateway to the main panel ahead of the generator transfer switch, with nothing behind behind the gateway except the powerwalls, would this work for load shifting with the Tesla software configurations allowed?

thx
mike
 

arnolddeleon

Supporting Member
Supporting Member
Jul 21, 2012
909
984
SF Bay Area
Yes you can use just it for load shifting as you imagined. Peak rate - (rate during time the Powerwall is charging)*1.1 should give you much cost shifting you get per kWh. The 1.1 is trying to account for the 10% round trip losses. The amount that are you able to "win" is dependent on the amount of consumption you have during peak hours.

For most people numbers work roughly that the Powerwall will pay for itself, you don't really save much money. What you effectively get is "free" backup power capability. This will obviously not be case for you since you already solved your backup problem. Another benefit that load shifting/peak shaving does is remove to "guilt" with using energy during peak periods.

This is a long way of saying, don't be surprised that the numbers don't work for strict return on money if you give zero value to the other benefits.
 

h2ofun

Active Member
Aug 11, 2020
3,032
658
auburn, ca
Hi... So we recently built a large house and have an EV, and currently on the PGE EV-A tariff. We have a lot of solar, but have a 400 Amp feed, and a generator for backup power. I understand generators are not supported with powerwalls, and Tesla doesn't have gateways for 400A feeds. We looked at Powerwalls for power backup in an outage, but felt the generator approach was a much better choice.

I'm now thinking about using powerwalls purely for load shifting, trying to figure out if the economics were to pan out. We have a 26 KW solar system, and generates more than 120 KWh a day (during the spring and summer). The primary goal would be to minimize any energy use during peak hour, and push any extra energy generated during the day back to the grid during peak pricing.

We have a 400A feed and a genset, so a traditional install will be problematic. If I just connected the gateway to the main panel ahead of the generator transfer switch, with nothing behind behind the gateway except the powerwalls, would this work for load shifting with the Tesla software configurations allowed?

thx
mike
I have about 30KW of solar, 5 batteries, with a 400 amp service. Each 200 amp subpanel has its own gateway. 3 batteries on one, 2 batteries on other. Not sure the economics for lots of batteries makes sense, unless you have extra money to just spend, IMO I hit 180kwh output one day. I have lots of north facing panels and shade. With smoke now, I do about 125kwh per day
 

gravastar

VP of Snacks
Supporting Member
Aug 31, 2018
64
74
Dallas
I just started looking into it also. But without adding solar (nor do I presently have it). My time-of-use plan schedule is $0.158089 per kWh during the hours of 15:00-19:59 and $0.064705 per kWh any other time. Feb '21 was hard for many Texans. I would love to have that backup system. I wonder what my provider would think about this.
 

mikesm

Member
Apr 25, 2021
24
15
menlo park, CA
Yes you can use just it for load shifting as you imagined. Peak rate - (rate during time the Powerwall is charging)*1.1 should give you much cost shifting you get per kWh. The 1.1 is trying to account for the 10% round trip losses. The amount that are you able to "win" is dependent on the amount of consumption you have during peak hours.

For most people numbers work roughly that the Powerwall will pay for itself, you don't really save much money. What you effectively get is "free" backup power capability. This will obviously not be case for you since you already solved your backup problem. Another benefit that load shifting/peak shaving does is remove to "guilt" with using energy during peak periods.

This is a long way of saying, don't be surprised that the numbers don't work for strict return on money if you give zero value to the other benefits.

Got it. I would have liked to be able to use it as backup in combination with the generator, but with 400A feeds and the ATS wiring etc..., my installer thought it was too complicated to work properly. But we did run wiring and set things up for a future install.

Is SGIP something I should look at in my configuration to help? If I don't do SGIP, can I charge grid at offpeak if the solar in not generating enough due to weather or smoke?

If the numbers are just breakeven, we still might go for it. PG&E's rapacious prices are not headed down anytime soon, and with communities banning gas appliances and water heaters, and mandates for EV charging, PG&E's rates are probably going to skyrocket even more to try and push people out of the peak hour window because of lack of generation capacity. The regulators seem fine with squeezing high usage consumers aggressively, so I don't think folks like me are going to see any protection from even more usurious rates...
 

arnolddeleon

Supporting Member
Supporting Member
Jul 21, 2012
909
984
SF Bay Area
Got it. I would have liked to be able to use it as backup in combination with the generator, but with 400A feeds and the ATS wiring etc..., my installer thought it was too complicated to work properly. But we did run wiring and set things up for a future install.

Is SGIP something I should look at in my configuration to help? If I don't do SGIP, can I charge grid at offpeak if the solar in not generating enough due to weather or smoke?

If the numbers are just breakeven, we still might go for it. PG&E's rapacious prices are not headed down anytime soon, and with communities banning gas appliances and water heaters, and mandates for EV charging, PG&E's rates are probably going to skyrocket even more to try and push people out of the peak hour window because of lack of generation capacity. The regulators seem fine with squeezing high usage consumers aggressively, so I don't think folks like me are going to see any protection from even more usurious rates...
If you have solar Tesla won't configure your system for grid charging today. Who knows if that will change in the future.

I believe Tesla has stopped working with SGIP directly. 3rd parties do it but the price ends up being the same or higher. The big incentive that you get is the Federal Investment Tax Credit (ITC). That is believed to be the reason that Tesla doesn't let you charge from the grid if you have solar. If you charge "exclusively" from solar then it qualifies for the tax credit.

There is currently no topping off with grid power for systems with solar that I'm aware of.

Yes, one the benefits is some form on insurance from future rate increase.

I also have to add that I've found it quite satisfying and addictive to be self powered. Ever since I added more solar and battery I've found myself checking to see if made it through the night without using in significant grid power. I didn't realize how different the feeling is from my previous configuration where I was just focused on offsetting peak. I'm exporting/banking a little bit most days. I will likely need that for the winter since I use a heat pump for heating.
 

aesculus

Still Trying to Figure This All Out
May 31, 2015
4,530
2,599
Northern California
Hi... So we recently built a large house and have an EV, and currently on the PGE EV-A tariff.
Did you get a note from PG&E indicating how long you will remain on EVA? The best was 5 years and that was 18 months ago IIRC.

So you will need to look into that aspect as you plan the value of solar in the future. Unless PG&E starts letting us sell our solar power, other than the minute we generate it, the future for selling solar looks dim at best.
 
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mikesm

Member
Apr 25, 2021
24
15
menlo park, CA
If you have solar Tesla won't configure your system for grid charging today. Who knows if that will change in the future.

I believe Tesla has stopped working with SGIP directly. 3rd parties do it but the price ends up being the same or higher. The big incentive that you get is the Federal Investment Tax Credit (ITC). That is believed to be the reason that Tesla doesn't let you charge from the grid if you have solar. If you charge "exclusively" from solar then it qualifies for the tax credit.

There is currently no topping off with grid power for systems with solar that I'm aware of.

Yes, one the benefits is some form on insurance from future rate increase.

I also have to add that I've found it quite satisfying and addictive to be self powered. Ever since I added more solar and battery I've found myself checking to see if made it through the night without using in significant grid power. I didn't realize how different the feeling is from my previous configuration where I was just focused on offsetting peak. I'm exporting/banking a little bit most days. I will likely need that for the winter since I use a heat pump for heating.

Well, Tesla didn't install my solar, and for load shifting alone, I don't think I need to have the inverters "behind" the powerwall. In fact, I don't think I need to have the gateway know about Solar at all. So in that case, why wouldn't Tesla let me charge from the Grid? In fact, how would it even know if Solar was being generated at all? Surely in that case it would let me charge from the grid because it can't tell if there is solar there or not.

This is my biggest issue with Tesla products' design - it's like a Mom who always keeps telling you to put your coat on before you go outside so you don't catch a cold, and make sure you eat a proper breakfast before you leave for school.. :) They don't integrate generator support, because after all, Powerwall's are the best way to do backup power (because you never lose power because of bad weather that might have a lot of cloud cover), or that no one would ever need a transfer switch of more than 200A, etc...

It looks like all the SGIP funds are gone, at least for PG&E customers, so that doesn't look like it's an option. Is there still federal credit for battery storage?

I'm not that big into self-powering, though I can see the appeal of it. It doesn't appear to be cost effective now, though at $0.51 a KWh, I think my diesel generator can beat that in terms of power generation cost . It's a large industrial Kohler unit I got off ebay (at a fraction of the list cost) that was supposed to go a cell site for backup, and is rated for prime power. I guess I could run it during peak power hours and disconnect from the grid completely, and flip back on when rates went to off peak, but why go to through the hassle and the emissions just to save a few cents. If PG&E keeps jack up prices I guess at some point everyone will be running natural gas or Diesel to go off grid because the economics will keep getting better.

PG&E has not told me I need to migrate off of EV-A as far as I can tell.. Do the E-TOU tariffs not support selling power back to PG&E at their own pricing? They don't mention that difference on their website in the little comparison model they show you...
 

aesculus

Still Trying to Figure This All Out
May 31, 2015
4,530
2,599
Northern California
PG&E has not told me I need to migrate off of EV-A as far as I can tell.. Do the E-TOU tariffs not support selling power back to PG&E at their own pricing? They don't mention that difference on their website in the little comparison model they show you...
It may only be a solar limitation (ie selling solar power back to them).
Existing EV-A customers seeking to commence service on NEM2.0 rate and
continue service on EV-A for up to 5 years must submit an interconnection application by
November 30, 2019
 

Zabe

Member
Jun 11, 2021
83
50
Placerville, CA
You can still sign up for EV2-A. You cannot sign up for EV-A it was discontinued for new customers. EV-A had a longer peak time during the week 2pm-9pm, partial peak 7am-2pm and 9pm to 11pm, and a short off peak time 11pm-7am. It had a super cheap (for PG&E) $0.14384/kWH during off peak hours, and a very high on-peak rate of $0.55885/kWH during the summer season.

EV-A Rate plan
EV2A Rate Plan
 

Zabe

Member
Jun 11, 2021
83
50
Placerville, CA
Based on what you want to do I would say you probably will want to wait and see what happens with Tesla and the VPP in California. It looks like there is at least somewhat of a push to change the tax credit to allow Powerwall's with solar to grid charge but still get the tax credit. I do not know who has to approve a change like this. For the time being what you want you cannot get.

How long do you think you would get away with running an industrial diesel generator for all of your on-peak power needs in Menlo Park?
 

BGbreeder

Member
Jun 19, 2020
430
255
Bay Area
Based on what you want to do I would say you probably will want to wait and see what happens with Tesla and the VPP in California. It looks like there is at least somewhat of a push to change the tax credit to allow Powerwall's with solar to grid charge but still get the tax credit. I do not know who has to approve a change like this. For the time being what you want you cannot get.

How long do you think you would get away with running an industrial diesel generator for all of your on-peak power needs in Menlo Park?
Yes, Menlo Park would seem to be a challenging area for routine generator use. There is the "small" issue of the CARB, and BAAQMD, and that according to BAAQMD diesel generators may only be run under certain conditions, which don't, at least at the moment, include routine or peak shaving uses. (Needs to be an "emergency event".)

Tesla recommends placing the transfer switch between the essential load panel and the gateway/solar/Powerwalls. That configuration has the benefit of not exposing Powerwalls and solar to the vagaries of generator power that tends to be of significantly lower quality than grid power (THD, frequency, voltage regulation). There is also the concern that while Powerwalls raise the frequency as their charge level nears 100%, generators aren't required to respond to the changing frequency, and respond reasonably, and I am unaware of anyone who has coupled solar and batteries to a generator without a suitable charge controller. Given the costs involved (solar / Powerwall), it would seem to be an expensive experiment, don't you think?

All the best,

BG
 
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mikesm

Member
Apr 25, 2021
24
15
menlo park, CA
Based on what you want to do I would say you probably will want to wait and see what happens with Tesla and the VPP in California. It looks like there is at least somewhat of a push to change the tax credit to allow Powerwall's with solar to grid charge but still get the tax credit. I do not know who has to approve a change like this. For the time being what you want you cannot get.

How long do you think you would get away with running an industrial diesel generator for all of your on-peak power needs in Menlo Park?

What is VPP? I didn't think SGIP was open anymore in PG&E land, or are you talking about a Federal tax credit? Sorry, we looked into this 3 years ago when we were finalizing the build for the house, but it seems a lot of things have changed.

I wasn't really serious about using the diesel for peak power (at least not yet!, and we are on a 1 acre lot so it can run without neighbors complaining about noise). But even at 25% load (not the most efficient which is near 50% load), I calculated it would generate power at $0.55/KWh. If you use a Kohler RCL30 nat gas unit, again at 25% load, I calculate about $0.33/KWh at current pricing. Now, I don't think people should buy these things for peak load use, but if you are already getting one for backup power, if PG&E keeps jacking up rates, it is something that people will be looking at, particularly outside the Bay Area or urban areas.

My main point is how egregious PG&E peak hour pricing is. If I can generate power with nat gas at significantly les than PG&E's RETAIL price for peak hour, things are seriously broken.
 

mikesm

Member
Apr 25, 2021
24
15
menlo park, CA

It doesn't appear to indicate you get bill credit for this unless you are already in a NEM program. If you are already can sell energy back at retail prices, what good does being part of VPP do?
 

power.saver

Grid Specialist
Supporting Member
Mar 4, 2018
631
666
Arcadia, CA
It doesn't appear to indicate you get bill credit for this unless you are already in a NEM program. If you are already can sell energy back at retail prices, what good does being part of VPP do?
It let's you sell back more during the peak period than you otherwise could from just exporting solar.
 
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mikesm

Member
Apr 25, 2021
24
15
menlo park, CA
It let's you sell back more during the peak period than you otherwise could from just exporting solar.

Ah, so you mean this allows grid charging in addition to Solar? I doubt the economics would make sense to to store all the solar I typically generate (>100 KWh daily in the summer), but if the delta is big enough maybe it would, or be useful as a hedge on really cloudy days.
 

power.saver

Grid Specialist
Supporting Member
Mar 4, 2018
631
666
Arcadia, CA
Ah, so you mean this allows grid charging in addition to Solar? I doubt the economics would make sense to to store all the solar I typically generate (>100 KWh daily in the summer), but if the delta is big enough maybe it would, or be useful as a hedge on really cloudy days.
No, it doesn't allow grid charging. It only allows full export of your PW's stored energy during an event which is usually in the peak period.
 

mikesm

Member
Apr 25, 2021
24
15
menlo park, CA
No, it doesn't allow grid charging. It only allows full export of your PW's stored energy during an event which is usually in the peak period.

I'm sorry I am being slow. I really must be misunderstanding something. Let's say I have 4 PW's and charge them fully with solar during the day. Why can't I push all of that solar back to the grid during the peak hours, of course after powering whatever home is demanding during that window?
 

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