Powerwall 2: SGIP/Incentives

[markb1]

That's kind of funny. Intentionally increasing load to qualify for a subsidy that encourages reducing load.

It's funny that it encourages that, but I was already planning to install my wall connector on a 100A breaker so I can charge faster when I need to. SGIP didn't figure into those plans.

 

[markb1]

How did Tesla plan to do the installation without any new panels (other than the Gateway)?

Looking at the site plan, I now think they do plan to install a subpanel. The diagram shows the addition of a "load center" in addition to the backup gateway.

 

[wwhitney]

Do you have to demonstrate more than peak demand of 15 kWs?

I believe the only criterion for the SGIP is that the peak historical (or forecast and subsequently verified) demand averaged over one metering interval (one hour) is at least the size of the inverters in the storage. So you'd have to maintain the 15 kW demand for 2 hours to be sure to have one metering interval with full 15 kW the entire interval.

But you can check yourself, see section 5.3 of the SGIP handbook, https://www.selfgenca.com/documents/handbook/2017

Now, it turns out that PG&E imposes an additional requirement if you have solar. If you don't have solar, then your interconnection is via a Non-Export Interconnection agreement, you are agreeing that you will just use the Powerwalls for load time-shifting, and that you'll never be a net exporter. If you do have solar, then the battery storage is typically categorized as "NEM Paired Storage". That means you can still export to the grid, but your total export to the grid for the year should not exceed what your solar produces. So you can use your battery storage for load time shifting, or solar production time shifting, or both, but not for direct rate arbitrage (charge from the grid at one time, push back to the grid at another).

The additional requirement for NEM Paired Storage is that if your battery storage is over 10 kW, it is limited to 150% of the size of your solar (for PG&E see the NEM tariff section 11e). So you could only add 15 kW of Powerwalls (3 units) as NEM Paired Storage if your solar system is at least 10 kW. If it is under 10 kW, then that doesn't work.

Now you would think that if you have solar that is less than 10 kW, it might be possible to add the 15 kW of storage via a non-export agreement for the storage, while keeping the solar on NEM. I don't know if that is allowed by PG&E or not. If it is, then that would work for the SGIP program.

As the above discussion is for PG&E, you'll need to check with your own power company to see if their tariffs differ.

Cheers, Wayne

 

[markb1]

I downloaded all my PGE data, which breaks it down into 15 minute intervals. I found there was a few instances in the summer where I consumed 5 kWh in 15 minutes, which means I was averaging roughly 20 kW during that period. Based on the wording from the handbook, that should qualify. The other thing for the large scale systems is that the system needs to be fully discharged 130 times a year. Debating if I would want to hook up the car charger to the system to help meet this requirement, although I should be able to do that without charging (roughly 5500 kWh)

Residential projects only require 52 discharges per year, regardless of system size. (Per my understanding, though that should probably go without saying when it comes to SGIP!)

 

[markb1]

I believe the only criterion for the SGIP is that the peak historical (or forecast and subsequently verified) demand averaged over one metering interval (one hour) is at least the size of the inverters in the storage. So you'd have to maintain the 15 kW demand for 2 hours to be sure to have one metering interval with full 15 kW the entire interval.

Doesn't the metering interval depend on the meter? I downloaded all my data from SDG&E, and it shows it in 15-minute intervals. Also, every interval starts at :00, :15, :30, and :45. So the interval start and end times are predictable. If the SGIP intent is really to estimate peak demand, the smallest interval available should be enough. The smaller the interval, the better the estimate, actually.

 

[wwhitney]

Doesn't the metering interval depend on the meter? I downloaded all my data from SDG&E, and it shows it in 15-minute intervals. Also, every interval starts at :00, :15, :30, and :45.

I'm unclear about that. Someone at PG&E's Solar Customer Service told me it was 15 minutes for commercial, 60 minutes for residential. I could imagine that the interval for regulatory purposes is different than the interval for data capture. So I don't know if it is 60 minutes or 15 minutes.

Cheers, Wayne

 

[Frankman60]

Section 4.2.5 in the SGIP handbook says that the smallest interval should be used, which would be 15 minutes. I posted that section of the handbook in my previous post. I downloaded my data from SDG&E for the past year and there are at least 10 instances where the 15 kW peek threshold is met, calculated using the formula in section 4.2.5 (kWhs used in 15 minute period times 4). I didn’t see any other requirements in the handbook for energy usage to qualify for a large installation unless I am missing something?

Doesn't the metering interval depend on the meter? I downloaded all my data from SDG&E, and it shows it in 15-minute intervals. Also, every interval starts at :00, :15, :30, and :45. So the interval start and end times are predictable. If the SGIP intent is really to estimate peak demand, the smallest interval available should be enough. The smaller the interval, the better the estimate, actually.

 

[wwhitney]

Section 4.2.5 in the SGIP handbook says that the smallest interval should be used, which would be 15 minutes.

Yes, the SGIP handbook 4.2.5 is quite clear about using the 15 minute data (if available) for estimating peak demand. I was confusing this question with the question of what the interval is used in the power company tariffs, for things like billing NBCs.

Cheers, Wayne

 

[jandesailorman]

Wayne,
Per your discussion of NEM paired storage above, a customer with PV paired with storage could export as much as they would have if they didn't have storage; so you could charge from solar (or even from the grid, if you don't care about ITC) in morning and discharge to grid in evening as long as your annual or maybe monthly grid discharge is less than it would have been without storage, is that right?

But I think Tesla PWs are currently configured so that is impossible, is THAT right?

 

[dailo]

Thank you for all the informative posts! Do you think the Tesla reps are as informed? I'm still waiting for my call from them, but I was not aware of the NEM Paired storage requirement. I have a 9 kW system, so just short of the 150% requirement. May not be worth it to try to add more panels to make it to that requirement.

I believe the only criterion for the SGIP is that the peak historical (or forecast and subsequently verified) demand averaged over one metering interval (one hour) is at least the size of the inverters in the storage. So you'd have to maintain the 15 kW demand for 2 hours to be sure to have one metering interval with full 15 kW the entire interval.

But you can check yourself, see section 5.3 of the SGIP handbook, https://www.selfgenca.com/documents/handbook/2017

Now, it turns out that PG&E imposes an additional requirement if you have solar. If you don't have solar, then your interconnection is via a Non-Export Interconnection agreement, you are agreeing that you will just use the Powerwalls for load time-shifting, and that you'll never be a net exporter. If you do have solar, then the battery storage is typically categorized as "NEM Paired Storage". That means you can still export to the grid, but your total export to the grid for the year should not exceed what your solar produces. So you can use your battery storage for load time shifting, or solar production time shifting, or both, but not for direct rate arbitrage (charge from the grid at one time, push back to the grid at another).

The additional requirement for NEM Paired Storage is that if your battery storage is over 10 kW, it is limited to 150% of the size of your solar (for PG&E see the NEM tariff section 11e). So you could only add 15 kW of Powerwalls (3 units) as NEM Paired Storage if your solar system is at least 10 kW. If it is under 10 kW, then that doesn't work.

Now you would think that if you have solar that is less than 10 kW, it might be possible to add the 15 kW of storage via a non-export agreement for the storage, while keeping the solar on NEM. I don't know if that is allowed by PG&E or not. If it is, then that would work for the SGIP program.

As the above discussion is for PG&E, you'll need to check with your own power company to see if their tariffs differ.

Cheers, Wayne

 

[markb1]

SDG&E's NEM tariff has the same 150% rule. (I think it's a CPUC rule.) But it's sort of ambiguous about whether it's talking about the sum total of all the storage devices (which admittedly would make more sense) or just the individual storage devices.

The other thing is that to qualify as NEM Paired Storage, it must meet these two conditions:

(i) Integrated Storage: Integrated Energy Storage is defined as a method of storing energy from a renewable energy resource that is integrated into the renewable electrical generating facility as part of the generation process
For example, in order to be defined as integrated, a battery-
based storage device must be capable of storing energy from only the renewable electrical
generating facility


(ii). Directly Connected: Directly Connected Storage is defined as being both: (i) directly connected
to the renewable electrical generating facility via an internal power line (i.e., power may not be
transmitted from the renewable facility to the energy storage via an external distribution line) and
(ii) the storage device must be operated as part of the renewable electrical generating facility.

I don't think "integrated storage" applies to Powerwall.

Regarding "directly connected":

What does it mean that "the storage device must be operated as part of the renewable electrical generating facility"? Is there some way to setup a powerwall so it would not be considered that?

 

[miimura]

I think directly connected would apply to a hybrid inverter setup like an Outback Radian where the solar is connected via solar charge controllers directly charging the battery while the inverter is taking the DC from the battery to power loads. I don't see how a PowerWall 2 AC unit could be considered Directly Connected, so it must fall under Integrated Storage since it is programmed to charge only from solar. This would imply that TOU charging a PowerWall from the grid on a SDGE NEM account is not allowed if it is interconnected under the NEM Paired Storage rule.

 

[markb1]

More from SDG&E NEM-ST tariff (NEM is pretty much the same):

NEM Paired Storage is defined as an energy storage device paired with a renewable electrical generating facility...

Requirements for Large NEM Paired Storage (i.e.,all NEM Paired Storage except for devices that
are sized at 10 KW or smaller and paired with a solar renewable electrical generating facility)

Requirements for Small NEM Paired Storage (i.e., storage devices sized at 10 KW or less that are paired with a solar renewable electrical generating facility

It sure sounds like they are talking about individual devices.

 

[wwhitney]

I too found those definitions confusing, but after rereading I came to this understanding: "Integrated Storage" is DC-coupled to the solar panels. "Directly connected" is AC-coupled like the Powerwall. The only point of the "directly connected" definition, as I see it, is the "via an internal power line" portion. I.e. you can't have two services, with the solar on one service and the battery storage on another and rely on the power company's power lines to interconnect them.

Cheers, Wayne

 

[wwhitney]

It sure sounds like they are talking about individual devices.

That is not my reading. The party that first mentioned this to me was a solar contractor who ran into this limit with PG&E in the context of using multiple Powerwalls at a residence.

Cheers, Wayne

 

[Musterion]

More than 2 Powerwalls puts you in the large storage category. Whether or not you take the ITC is a separate issue; the large storage category has the feature that the SGIP rebate is reduced if you take the ITC.

So in the large storage category, if your project is cheap enough, you don't want to take the ITC, since the ITC is calculated on your cost after rebate. That is, when your cost after rebate is low enough, the ITC is low enough that it is below the amount of the rebate reduction on the SGIP, and you would lose money taking the ITC. Just something to check once you have a quote.


Not that I'm aware of for the rebate recipient, although I haven't closely read the handbook for large storage.


At the $0.40 per Watt rebate level, the rebate per Powerwall is $4,640. That's based on the labeled inverter size of 5 kW continuous, and the nameplate capacity of 13.2 kWh (which differs from the spec sheet of 13.5 kWh). The first 2 hours of capacity is rebated at $0.40 per Wh, or $4,000 for 10 kWh. The next 2 hours is rebated at half that rate, so $0.20 per watt hour for 3.2 kWh, or $640.

If you are in a different step with a lower rate, or taking the ITC for a lower rate, then just multiply $4,640 by the ratio of rates. For example, the Large Storage with ITC rate is $0.29 per Watt, so the the rebate on a Powerwall would be $3,364. Which means that the breakeven point for taking the ITC under Large Storage Step 2 (if charging 100% from solar) is $7,617 per Powerwall; at a project cost below that, you lose money taking the ITC.


Yes, they are very careful with the use of kW versus kWh. Remember that one of the goals of the SGIP is to reduce peak demand load on the grid, so the size of the inverter in kW is entirely relevant.

Cheers, Wayne

Wayne, thank you very much for pointing this out. Although I have read this entire thread (before it was split out), I am now faced with doing the actual calculations myself for my planned installation and find the SGIP rather inscrutable. So I have a few questions for you and anyone else who wants to chime in (like @miimura who is a wizard with spreadsheets, I have learned . Thank you also @Ulmo and @ohmman for your earlier planning help.

1) I cannot reproduce some of your numbers. For example, you mention a rebate of $3364 on powerwall "Large Storage with ITC" SGIP rate, I can’t reproduce. My understanding is this is based on a tiered rate per Wh of capacity. But which capacity is relevant? Spec sheet lists 14 kWh as total energy capacity, 13.5 as usually energy capacity. But even the stated SGIP step 2 rebate (and the one you quote, $4640), works out to 11.2 kWh — where does that number come from?

2) You quote using both 5kW continuous output spec and nameplate capacity (which itself is different from the 3 capacity numbers listed above). You only use these two numbers when calculating the time-based SGIP rebate amount. Why do you use different capacities here than the residential rebate (i.e. 13.2kWh vs 11.2kWh)?

3) Just to confirm, your breakeven number is the entire cost of project split per powerwall? (because it is substantially higher than equipment cost). If so, I guess that is your point.

4) Are you including tax liability (state/fed) of any SGIP rebate issued in your calculations?

To summarize I am trying to figure out best rebate scenario to use for a 4-Powerwall installation which is in the commercial category that Tesla will now file for me—SGIP with ITC or SGIP alone (without ITC). My current install costs are reasonable, $1900 plus $150 permitting.

 

[wwhitney]

1) I cannot reproduce some of your numbers. For example, you mention a rebate of $3364 on powerwall "Large Storage with ITC" SGIP rate, I can’t reproduce.

13.2 kWh is the name plate capacity (even though the spec sheet says 13.5 kWh), 5 kW is the spec sheet continuous power. Only the first two hours of reserve capacity at the rated power is fully incentivized; the additional capacity is incentivized at 50%. The calculation is

$0.29 * (2 * 5000 + 0.5 * 3200) = $3,364.

3) Just to confirm, your breakeven number is the entire cost of project split per powerwall? (because it is substantially higher than equipment cost). If so, I guess that is your point.

Yes.

4) Are you including tax liability (state/fed) of any SGIP rebate issued in your calculations?

The SGIP rebate is excluded from gross income per the US Code section I posted earlier in this thread.

My current install costs are reasonable, $1900 plus $150 permitting.

Assuming 9% sales tax (a guess), the above implies a total project cost of $26,800. That's a per Powerwall cost of $6,700. You are better off not taking the ITC and getting the higher SGIP rebate. Please double check my math.

Cheers, Wayne

 

[Musterion]

@wwhitney
Thank you so much for the clarifications and suggestions.

My sales tax rate is 8.5% (Santa Cruz County) and I'm on PG&E. Equipment cost would be 4 Powerwalls at retail price plus $700 backup gateway. Install costs as mentioned earlier, plus those taxes. About $26,680 if I've calculated correctly.

I have a followup question on your understanding of the "150% rule" and NEM Paired Storage classification. Does the 150% apply to the DC rating of the solar system or its CEC-AC rating? In my case with 15kW DC, 4 Powerwalls is 20kW and well less than 150%*15kW. But if based on CEC-AC rating, the two become much closer.

Finally, is there a another class besides "NEM Paired Storage" that such a Powerwall installation could meet or that might be preferable?

 

[markb1]

I have a followup question on your understanding of the "150% rule" and NEM Paired Storage classification. Does the 150% apply to the DC rating of the solar system or its CEC-AC rating? In my case with 15kW DC, 4 Powerwalls is 20kW and well less than 150%*15kW. But if based on CEC-AC rating, the two become much closer.

It’s definitely AC. That much is unambiguous. But I still think that a plain English interpretation is that the 150% rule doesn’t apply when each individual device is 10 kW or less. The utility company may interpret it differently, though, and I have no idea if the plain English interpretation would hold any weight in an argument with them.

 

[markb1]

Well, my SGIP developer application was just kicked back:

Your Developer Eligibility Application indicates you will be performing only a portion of the development activities.
Based on your indication of performing only 4 of the 13 development activities, you do not qualify for a SGIP Developer.

For the follow up question in section 2, “Do you plan to divide the project development activities with another entity…”, please indicate yes and identify who will be performing the other activities.

In general, if you have been working with a battery installer/developer, that entity is usually providing the substantial amount of the development activities.

Please revise your application and return to us.

I think they made some mistakes, here. The question they want me to answer yes to reads in full:

Do you plan to divide project development activities with another entity or entities, in different ways for different projects?

I would only have one project, at most, so of course the answer is no! And why do I have to know who will be performing the other development tasks at this stage?

Furthermore, this "substantial amount of the development activities" requirement does not apply to "individual homeowners applying for SGIP incentives for systems located on their own property" (according to the handbook).

Seems to me they are not following their own rules.