Just trying to figure out the economics, thanks in advance

[dsss]

I would appreciate any advice here as well. The math and usage is a bit confusing.

I have a less than ideal roof for solar on an older Victorian home (lots of varied sections, not a ton of eastern exposure, etc..). Private solar installers I have spoken with think at most I should put 24 panels up for about 7-8kw of use but Tesla came back with a design that was able to fit and use all 36 for the full 12kw system.

My annual consumption is around 17k kWH (EV, Hot Tub, AC, etc...)

Complicating matters, I live in the city of Alameda which has their own Power Utility (AMP) and has sunset their primary Net Metering program and now offers a watered down replacement plan. In this plan, I would be paying .26/kWh for everything coming in but only getting back .07kWh for what I send back. There is no TOU system in place but they have been debating one that would be (at least initially opt-in).

So, with all that in mind, i'm trying to decide between the "medium" (24 panels) and "large" (36 panels) system for my home, alongside 2 PowerWalls. The quoted price from Tesla (pre-tax credit) is $38k vs $30.5, so a difference of $7,500 (or $5,570 post tax incentive) Another factor is the last 12 panels added would certainly be far and away the least efficient so it does make me question the value of going with the large system?

Any and all help from the experts here would be appreciated. Thanks!

 

[BrettS]

What I would do is compare the annual production numbers for the two systems. You say that your annual consumption is about 17,000kWh and since you don’t get much back for then you will want something that produces less than that amount, but I believe that both systems will do so.

The fact that you have no TOU rate actually makes the math a lot easier since you only pay one price per kWh. In that case, just multiply the annual production rate of the solar system by the $.26 you’re paying per kWh. Say the 8kW system has an annual production rate of 9000kWh (use the numbers from your quotes though... that’s just a guess), so you would multiply 9000 by .26 and wind up with an annual savings of $2340. If the cost of that system is $22570 after the tax credit then it would pay for itself after about 9.6 years. Since you are getting powerwalls you should be able to consume all of the power that you produce so you won’t need to send anything back to the utility at the low rate.

Do the same thing with the larger system and see what that payback period would be. It may be more since you probably won’t be able to produce as much power from the extra panels due to their location.

 

[miimura]

This article suggests that those of us who live in Tier 2 & 3 fire risk areas can potentially get the full cost of the system reimbursed (up to 14k)?

The diff between winter ($100/month) to peak summer is drastic for me ($500/month). However, I still have a hard time wrapping my head around how this works. Let me explain what I *think* is happening and maybe you can tell me what I'm missing:

* solar generates electricity shoves it into SCE's grid. It doesnt matter what time this electricity is generated, it generates "credits" per kW
* your house continually uses electricity straight from the grid, despite generating electricity from solar
* even though you generate electricity credits, these credits aren't 1-to-1? Meaning a credit of kW generated doesn't equal to 1kW used during peak summer months?
* by pulling from batteries during those peak TOU hours, you can get the trading rate of kW credits to real consumed kW closer to 1-to-1?

In California, I believe all the major utilities work the same way with respect to Net Metering. What I say here is definitely true for PG&E and I assume it's the same for SCE, LADWP, and SDG&E.
* For each TOU time period the net kWh is added up for the billing cycle. That kWh is converted to dollars at your retail tariff rate. Example:
Peak: -50kWh @ $0.54314 = -$27.16
Part-Peak: -200kWh @ $0.29903 = -$59.81
Off-Peak: 500kWh @ $0.14648 = $73.24
Total: -$13.73
That means that a credit of $13.73 would be added to your true-up for that hypothetical month even though you consumed 250kWh more than you generated. The total dollars in the 12 billing cycles is added to your payable bill after the minimum charges are deducted for any month that had a positive amount greater than the minimum charge added to the true-up.
* If your true-up total is dollar negative, they look at the total net kWh you consumed. If you were a net consumer of kWh during the whole true-up period, that TOU based credit balance is wiped out and your new true-up starts at $0. If you were a net generator of kWh during the true-up period, they will cut you a check for your net surplus kWh at a rate something like $0.03/kWh. This Net Surplus Compensation rate is calculated periodically according to a specific tariff and is based on the utility's wholesale electric costs.
* If you are on NEM 2.0 rules, there is an additional "Non-Bypassable Charge" for each kWh that you consume from the grid. I have not been able to figure out the exact calculation, but in my hypothetical example, you might consume 750kWh from the grid and feed in 500kWh. This would result in a NBC of something like $12 to $15 added to your minimum charges payable each month outside your true-up.
* Using batteries like Tesla Powerwalls will allow you to avoid paying for Peak consumption. It will increase your Peak credits and decrease your NEM credits during your generating hours. If your solar is so large that you are a net generator, the TOU differentials and time shifting really doesn't matter because your TOU credits are going to be wiped out anyway. In my case, I can pay PG&E significantly less with Powerwalls because my solar system is small and my true up always has a significant dollar amount owed.

 

[wjgjr]

What I would do is compare the annual production numbers for the two systems. You say that your annual consumption is about 17,000kWh and since you don’t get much back for then you will want something that produces less than that amount, but I believe that both systems will do so.

The fact that you have no TOU rate actually makes the math a lot easier since you only pay one price per kWh. In that case, just multiply the annual production rate of the solar system by the $.26 you’re paying per kWh. Say the 8kW system has an annual production rate of 9000kWh (use the numbers from your quotes though... that’s just a guess), so you would multiply 9000 by .26 and wind up with an annual savings of $2340. If the cost of that system is $22570 after the tax credit then it would pay for itself after about 9.6 years. Since you are getting powerwalls you should be able to consume all of the power that you produce so you won’t need to send anything back to the utility at the low rate.

Do the same thing with the larger system and see what that payback period would be. It may be more since you probably won’t be able to produce as much power from the extra panels due to their location.

I agree with this, and the only thing I would add for @dsss or somebody in a similar situation is to just make sure generation for a larger system wouldn't overwhelm the number of PWs you have. That is, if in the late spring/early summer you generate enough to cover your daytime usage and also fill the PWs you hopefully drained overnight, then you will be forced to send some power to the grid at the lower rate. This calculation should factor in your reserve plans as well - if you are concerned about outages and want to maintain 10kWh for reserve, as an example, that would also need to be considered.

Overall, the many different examples of utility rules just in this thread really illustrate why it would be so difficult for Tesla to provide payback estimates on a PW. Really, even their estimates of $ savings (as opposed to production estimates) on solar should be treated as an educated guess past a couple years as who knows how energy prices will change and how your local utility might change their rate structures. And I do think the complexity is an obstacle to wider adoption of solar.

 

[jjrandorin]

I apologize in advance if I sound dense but as a new solar owner, doesn’t all of this tou off peak on peak not come into play if your solar is sized to more than 100% of your usage?

The older agreements, that dont force time of use onto you and net meter on a 1:1 power in / power out basis (and dont have as many or any, non bypassable charges). I have net metering, with no TOU rates (regular tiered rate where the more power I use, the rates go up).


If you are not already on a time of use plan, you will be switched to one when you complete the PTO for your new solar system. The "peak / part peak etc does matter on a time of use plan, because the utility sets peak times in general to be when your solar is NOT producing, right now.

So, in your case, since you have SCE (if you are in temecula), You will pick between a 4-9PM peak and a 5-9PM peak with different non bybassable charges (montly charges that can not be offset by solar production). Your solar will go into the grid during off peak, and you will get a credit of say, 13 cents a kW for it, yet you will pull it out at 6pm when your home gets hot and you are running your AC at peak rates of 40+ cents a kW.

This is what people are talking about when they say the utility "devalued their solar". Since I am grandfathered in under an old plan, I dont have "peak / partial peak" etc. My solar just offsets my usage and goes in and comes out at the same rate as long as I stay in tier 1, which I sized my system such that I never really leave tier 1 (which means I dont use more than 200 ish kWh a month, net, from the utility.

* solar generates electricity shoves it into SCE's grid. It doesnt matter what time this electricity is generated, it generates "credits" per kW
* your house continually uses electricity straight from the grid, despite generating electricity from solar
* even though you generate electricity credits, these credits aren't 1-to-1? Meaning a credit of kW generated doesn't equal to 1kW used during peak summer months?
* by pulling from batteries during those peak TOU hours, you can get the trading rate of kW credits to real consumed kW closer to 1-to-1?

* solar generates electricity shoves it into SCE's grid. It doesnt matter what time this electricity is generated, it generates "credits" per kW

Nope, it matters what rate is in effect when your solar is generated. What rate is in effect, when you are generating more than your home uses, is the rate they credit you at. Thats how they credit you (at least where you and I are in SCE territory, and in CA. No idea about other utilites around the country.

* your house continually uses electricity straight from the grid, despite generating electricity from solar

Nope, solar powers your home when it is up, and any Left over electricity goes into the grid. The excess electricity goes into the grid, not all of it. If you have solar only, and grid is down, however, you have no electricity at all. If you have regular grid connection, your solar first powers your home loads, and any you dont need at that second of generation is pushed to the grid, running your meter backwards. If you use more than your solar generates, you pull from the grid to supplement.

* even though you generate electricity credits, these credits aren't 1-to-1? Meaning a credit of kW generated doesn't equal to 1kW used during peak summer months?

As above, this depends on what plan you are on, and why the utilities changed peak and off peak times. Peak USED To be from 12-6, but that ment they were paying you peak rates for your solar, (when, pre covid, you likely were not home) then when you came home and turned everything on, you pulled out at off peak rates, which ment you got more than 1:1 energy. Now, with peak and off peak rates, they swapped that (again the devaulation of solar). Off peak rates are now peak solar generation, so they pay you off peak rates when you push into the grid, but when you come home and turn everything on, they will charge you peak rates so its flipped and a LOT less advantageous for anyone on these rates... unless...

You have batteries, which means that you can store some of your excess energy during peak generation, and then use it when the peak rates are in effect, bypassing using peak charged energy from the grid.


Also, The SGIP equity and resilliency plans are not in effect for us here in temecula I am fairly sure... and even if it were, the program was over subscribed within 12 days of being effective, so anyone interested will need to wait to see if there is more money put into it.

 

[njhtran]

The older agreements, that dont force time of use onto you and net meter on a 1:1 power in / power out basis (and dont have as many or any, non bypassable charges). I have net metering, with no TOU rates (regular tiered rate where the more power I use, the rates go up).


If you are not already on a time of use plan, you will be switched to one when you complete the PTO for your new solar system. The "peak / part peak etc does matter on a time of use plan, because the utility sets peak times in general to be when your solar is NOT producing, right now.

So, in your case, since you have SCE (if you are in temecula), You will pick between a 4-9PM peak and a 5-9PM peak with different non bybassable charges (montly charges that can not be offset by solar production). Your solar will go into the grid during off peak, and you will get a credit of say, 13 cents a kW for it, yet you will pull it out at 6pm when your home gets hot and you are running your AC at peak rates of 40+ cents a kW.

This is what people are talking about when they say the utility "devalued their solar". Since I am grandfathered in under an old plan, I dont have "peak / partial peak" etc. My solar just offsets my usage and goes in and comes out at the same rate as long as I stay in tier 1, which I sized my system such that I never really leave tier 1 (which means I dont use more than 200 ish kWh a month, net, from the utility.



* solar generates electricity shoves it into SCE's grid. It doesnt matter what time this electricity is generated, it generates "credits" per kW

Nope, it matters what rate is in effect when your solar is generated. What rate is in effect, when you are generating more than your home uses, is the rate they credit you at. Thats how they credit you (at least where you and I are in SCE territory, and in CA. No idea about other utilites around the country.

* your house continually uses electricity straight from the grid, despite generating electricity from solar

Nope, solar powers your home when it is up, and any Left over electricity goes into the grid. The excess electricity goes into the grid, not all of it. If you have solar only, and grid is down, however, you have no electricity at all. If you have regular grid connection, your solar first powers your home loads, and any you dont need at that second of generation is pushed to the grid, running your meter backwards. If you use more than your solar generates, you pull from the grid to supplement.

* even though you generate electricity credits, these credits aren't 1-to-1? Meaning a credit of kW generated doesn't equal to 1kW used during peak summer months?

As above, this depends on what plan you are on, and why the utilities changed peak and off peak times. Peak USED To be from 12-6, but that ment they were paying you peak rates for your solar, (when, pre covid, you likely were not home) then when you came home and turned everything on, you pulled out at off peak rates, which ment you got more than 1:1 energy. Now, with peak and off peak rates, they swapped that (again the devaulation of solar). Off peak rates are now peak solar generation, so they pay you off peak rates when you push into the grid, but when you come home and turn everything on, they will charge you peak rates so its flipped and a LOT less advantageous for anyone on these rates... unless...

You have batteries, which means that you can store some of your excess energy during peak generation, and then use it when the peak rates are in effect, bypassing using peak charged energy from the grid.


Also, The SGIP equity and resilliency plans are not in effect for us here in temecula I am fairly sure... and even if it were, the program as over subscribed within 12 days of being effective, so anyone interested will need to wait to see if there is more money put into it.

Excellent writeup! Thanks!

 

[Southpasfan]

After some number crunching let me know if this is wrong.

1. With Time of use billing (not one flat rate) it’s not really like you “bank energy” —- without powerwalls when your system produces more then you use you get a credit for it. But that credit is going to be some fraction of what you use later in peak time - it has to be because peak time is at night.

2. So, if you have a solar system you are incentivized to use energy during non peak but sunny time - without power walls you would nevwr come out ahead selling solar at non peak and using at peak. This is because on a basic level if you have to run the laundry or charge the car you have to do it sometime - you are going to use the energy either way.

3. Powerwalls allow a bit of benefit if the system is large enough to charge them off peak and then use them during peak. But that’s not very cost effective.

I was hoping this would be more simple but there is no way around doing the calculations if you want to try to max out self sufficiency

 

[wjgjr]

After some number crunching let me know if this is wrong.

1. With Time of use billing (not one flat rate) it’s not really like you “bank energy” —- without powerwalls when your system produces more then you use you get a credit for it. But that credit is going to be some fraction of what you use later in peak time - it has to be because peak time is at night.

2. So, if you have a solar system you are incentivized to use energy during non peak but sunny time - without power walls you would nevwr come out ahead selling solar at non peak and using at peak. This is because on a basic level if you have to run the laundry or charge the car you have to do it sometime - you are going to use the energy either way.

3. Powerwalls allow a bit of benefit if the system is large enough to charge them off peak and then use them during peak. But that’s not very cost effective.

I was hoping this would be more simple but there is no way around doing the calculations if you want to try to max out self sufficiency

On point #2, you are just incentivized to use energy during off-peak time since you are still getting credit for solar you send to the grid (at the lower, off-peak rate.) It doesn't really make a difference if you do your laundry in the morning before the sun comes up, effectively "borrowing" energy from the grid and then paying it back with solar during the day or if you do laundry at noon diverting solar that would have gone to the grid instead to your home use.

On point #3, rather than saying that's not very cost effective, I would say the cost benefit is highly dependent on the specific TOU plan - including what the peak hours are and the rate differences between peak and off-peak.

 

[miimura]

After some number crunching let me know if this is wrong.

1. With Time of use billing (not one flat rate) it’s not really like you “bank energy” —- without powerwalls when your system produces more then you use you get a credit for it. But that credit is going to be some fraction of what you use later in peak time - it has to be because peak time is at night.

2. So, if you have a solar system you are incentivized to use energy during non peak but sunny time - without power walls you would nevwr come out ahead selling solar at non peak and using at peak. This is because on a basic level if you have to run the laundry or charge the car you have to do it sometime - you are going to use the energy either way.

3. Powerwalls allow a bit of benefit if the system is large enough to charge them off peak and then use them during peak. But that’s not very cost effective.

I was hoping this would be more simple but there is no way around doing the calculations if you want to try to max out self sufficiency

1. TOU billing banks kWh during each TOU period and converts it to dollars. If you generate during Off-Peak and consume during Peak, you will have to generate more Off-Peak kWh than Peak kWh consumption to compensate for the cost difference of those kWh.

2. The bottom line is that you should use energy Off-Peak as much as possible and minimize your Peak usage. There is a real chance that you will be left with significant net cost if most of your generation is during Off-Peak hours.

3. Powerwalls cannot be cost justified purely on time shifting power (TOU arbitration). You have to put a significant value on the backup power aspect of the system.

Years ago, Peak hours were much earlier, like noon to 6pm. It was easy to bank solar generation at high value and use it Off-Peak, especially with things like charging an EV overnight. However, now California has a lot of solar, so the Peak times are pushed later like 4-9pm. With those Peak hours, you're never going to generate more than you use during Peak without batteries. Not only that, but they've changed the Part-Peak so it starts at 3pm instead of 7am. That further devalues your solar generation. We used to say that people should size their solar for $0 annual bill. Now that they've changed the rules, you need a much larger system that can offset almost all of your kWh usage.

 

[Southpasfan]

This is a great thread for a beginner.

One would think, as I thought a week ago, that if you got a large enough system to where your "meter ran backwards" it would be pretty simple, and really simple if you were on either a tiered system or a flat rate system. If the meter "really ran backwards", in the morning of Day 1, you were at 200kwh for the month, and the sun comes up, and the system starts working, and no one is home with nothing on, and you produce, say 30kwh, you think you could come home at look at the meter and it would read 170kwh.

If that was ever the way it worked it does not work that way now. Or for sure it does not work that way with Southern Cal Edison or LA Department of Water and Power.

At best, in a flat rate system, at least in the example above your usage sits at 200kwh, and the excess 30kwh goes back into the grid, and then that 30kwy is converted to money at the end of the month (or maybe longer). That money never really nets out to the costs of using 30kwh on the same day later in the day after the sun is down, but it would have been close enough.

Anyway, that system does not exist with SCE or LADWP either.

So, since the "meter running backwards" does not exist, and the flat rate system does not exist, in a TOU system the problem is that without Powerwalls overproduction during daytime is not 1:1 credit (either in kwh or in dollars) with use during nightime.

That means to get the maximum benefit out of a system one has to dive deep into when the power is being produced, and try to schedule usage during that time.

Powerwalls have value for their backup function. Other than backup, PW's at best, can only minimize energy use from the grid during non-peak (non solar generating) time by discharging then. As a practical matter, by the way (and I have not done this experiment) if one tried to use powerwalls every day for this one has to use significantly less than PW capacity (probably not good to drain to zero) each evening and have a system large enough to generate extra kwh to recharge them the next day. Regardless, other than backup, the most you can get from a PW is the difference between off peak and peak multiplied by the hours of use. Depending on your utility, that might not be a whole lot, and make "paying" for the PW a super long term endeavor.

 

[jjrandorin]

After some number crunching let me know if this is wrong.

1. With Time of use billing (not one flat rate) it’s not really like you “bank energy” —- without powerwalls when your system produces more then you use you get a credit for it. But that credit is going to be some fraction of what you use later in peak time - it has to be because peak time is at night.

2. So, if you have a solar system you are incentivized to use energy during non peak but sunny time - without power walls you would nevwr come out ahead selling solar at non peak and using at peak. This is because on a basic level if you have to run the laundry or charge the car you have to do it sometime - you are going to use the energy either way.

3. Powerwalls allow a bit of benefit if the system is large enough to charge them off peak and then use them during peak. But that’s not very cost effective.

I was hoping this would be more simple but there is no way around doing the calculations if you want to try to max out self sufficiency

Like others said, it depends on what you mean by "come out ahead". Without some sort of storage, you will need to actively look at shifting your loads for discretionary electric usage (things like charging your car, which should be done at off peak rates over night, or the laundry / dishwasher, like you mentioned). Without storage, most effective would be to shift those loads to the middle of the day, as long as you sized your solar array to be able to cover both your home usage and those loads. Its more "effective" to use the loads yourself than put it in the grid to pull it out later. Putting it into the grid to pull out later works, of course, but you still need to be mindful of your usage, etc (and make sure to size your system appropriately.

While battery storage doesnt normally "pencil out" if you strictly do dollars and cents, one of the things it allows you to do, as I mentioned is store some of the energy you generated during the sunlight hours for usage during peak time, thereby ensuring you are not paying the 40-45 or even 50c a kilowatt peak charges that our CA utilities have. In fact, if you have battery storage, it can be setup such that, when peak starts (say at 4pm), the batteries start powering the home automatically, while any left over solar that you ARE generating at that time gets pushed to the grid.

That means that from the period of start of peak (say 4pm) to end of solar generation (sundown), your solar goes into the grid at peak rates, while you are not pulling energy FROM the grid, because your batteries are powering your home (with solar you generated earlier), thereby giving the value of that energy the value of peak to YOU, vs the off peak it would have been if you didnt have batteries and sold it to the grid.

Saying all that, saving enough money to actually pay for the batteries over the 10 year to 70% capacity warranty doesnt usually pencil out fully, unless you put some value on the fact that you ALSO have backup energy, and will basically not need to worry about a power outage, as long as there is some sun. I never would have bought a backup generator (too noisy, too much maintenance concerns for me, etc), but given the powerwall functions somewhat like backup power, in addition to letting you use solar during a power outage, AND prepares you for "time of use" plans the utility is forcing on everyone, it made it a good value for me, even if the dollars and cents didnt fully equal out.

Not sure that makes sense, but the TL ; DR is it gives you some savings when combined with time of use utility plans, as well as some power independence.... but if you are trying to whip out "the spreadsheet" and say "in month 68 this powerwall will pay for itself", unless you attach a dollar value to having backup power, its likely that wont work.

 

[3mp_kwh]

My understanding is the precise answer depends on your utility and its exact rules when you over-produce. Some will pay you the full amount while others may pay only a lower/wholesale amount or nothing at all.

Right. Almost all utilities still considered to be full-NEM, are at least revisiting not writing checks to solar owners but instead crediting them for the over-generation and letting them "bank" those watts for lower sun periods (like winter).

Personally, as a utility analyst, I don't think of "Net Metering" as the over-simplified full reimbursement for generation/trans&dist (your full KWh rate). Where lingo has gone to "export" home solar watts, "import" utility watts, you're ROI still benefits when they buy watts back. It helps "net" what you supply, against what you demand despite how the export-rate is falling, while the import-rate remains full.

I think of AZ's Salt River Project, when I think of how unfair things can get: a solar export tariff @.028/KWh, versus their simultaneous peak/off-peak tariff charging $.33/KWh. If I remember right, they not only abuse the value of clean energy (by equating it to wholesale grid pricing, or the lowest solar PPA they can find), but are also one of the few areas charging by power volumes (demand charges). At, like, 3KW, 7KW and 10KW (Yes, like simply plugging in the supplied Tesla L2 charger, for 15 minutes) your whole monthly bill becomes fixed into significantly higher amounts. This may sound off-topic, but the education of what utilities are attempting is important. In fairness, they have higher fixed costs than they are allowed to recover with fixed charges. The increase of things like these demand-charges, or higher ($20-30) base monthly fees, enables lower volumetric pricing to achieve the same, or higher, bill. That, in turn, enables lower compensation for solar. Lastly, you see the animus for solar when a given utility only applies these tactics to its solar rates, and not the rest of its rate base.

 

[dotbombjoe]

This article suggests that those of us who live in Tier 2 & 3 fire risk areas can potentially get the full cost of the system reimbursed (up to 14k)?

Interactive map to see if you are in a tier 2 or 3 area:

CPUC FireMap

FWIW, I think you can also qualify if you are experienced 2 or more power outages due to PSPSs (when the utility shuts down the grid due to risk of fire or whatever)...presumably those two things largely correlate but apparently some people are in the latter group and not the first and I believe they still meet this first criteria for rebate.

...but, as I hinted, that is just one factor to qualify for the rebate. There is a second criteria that must also be met, see:

https://www.cpuc.ca.gov/uploadedFil...ntial Equity and Equity Resiliency Matrix.pdf

...basically, you have to live in a low income housing, have a medical issue requirement specialized medical equipment, or have a house reliant upon electric pumps for well water.

The diff between winter ($100/month) to peak summer is drastic for me ($500/month). However, I still have a hard time wrapping my head around how this works. Let me explain what I *think* is happening and maybe you can tell me what I'm missing:

* solar generates electricity shoves it into SCE's grid. It doesnt matter what time this electricity is generated, it generates "credits" per kW
* your house continually uses electricity straight from the grid, despite generating electricity from solar
* even though you generate electricity credits, these credits aren't 1-to-1? Meaning a credit of kW generated doesn't equal to 1kW used during peak summer months?
* by pulling from batteries during those peak TOU hours, you can get the trading rate of kW credits to real consumed kW closer to 1-to-1?

So, my point is that you can generally ignore winter usage entirely re: the power wall ROI. The summer months are really the only meaningful opportunity for arbitrage ("buy low/sell high"). If you accept this statement, then the arbitrage is basically controlled by how much power you can shift from peak times to off-peak times in the summer that you couldn't otherwise do without power walls.

This number is not going to be anywhere near the breakeven point for the usable lifetime of the battery.

For me, peak -> off-peak shifting in summer nets in the $0.27 range...but my usage is pretty light during these times except when I run the AC which I typically only do for maybe 14 days each summer. You can get your usage data from your utility and do some rough calculations by multiplying your total peak usage during summer hours by your gap value (peak v off-peak summer rate) and see how much money power wall could theoretically save you...but again, I can virtually guarantee that is a waste of time because they will not come close to breaking even over their lifespan. Subsidy is the only way for power walls to currently be reasonably cost effective (from a pure financial perspective -- there are other benefits that may factor into your own ROI analysis).

For completeness, people have reported using 3rd party services that pay you not to consume electricity during certain hours to generate much higher ROI; however, to do so, you have to violate the whole point of batteries and the sorts of efforts the various rebate plans are there to support which is to reduce peak demand.

The way these 3rd party services generally operate, as I understand them, is to reward you for reducing your consumption during areas of high stress on the grid. If you are using your batteries as intended, you won't receive rewards because you should never be consuming energy from the grid during peak hours anyway...so you can't reduce your demand during these reward periods -- it's zero already.

But due to failures in the policies of these companies and poor pricing incentives, they created a situation that actually incentivized maximum usage during the peak periods in day-to-day usage specifically so that when the reward time came, you could reduce your demand to zero. The rewards consistently happen between 6-8pm for example, and at least in the past, were often several times higher than the cost of using the peak energy day-to-day...thus resulting in a perverse situation where some powerwall users were better off financially setting up their cars to charge during these peak times so when the rewards were activated, they stop charging and collect a max reward...

My understanding is that such loopholes are harder or largely impossible to achieve anymore and I'd expect they will continue to be closed going forward, so even if you were inclined to do so, I wouldn't recommend banking on these techniques to improve ROI of your power walls.

Anyway, yes, definitely look into whether you qualify for rebates...and keep an eye out on changes to rebate policy. Battery backup for your home is awesome.