TOU for SCE in Southern California analysis

[sensij]

Thanks again for hunting this understanding down, it's amazing how complicated the TOU-D-T baseline calcs really are comparatively speaking!

Wow, it took you less than 2 hours to roll that in, while most of us Californians were sleeping. Really nice work. It looks good in a spot check, but it will take me longer than that to verify the result by my own calculations.

One interesting use of this is to see how small your array could have been and resulted in the same net bill, keeping the household consumption constant. Under the TOU-D-A, plan, it looks like it could be about 15% smaller before you have to start paying. Another way of looking at is it that if your usage stays the same, and the TOU structure and rate proportions stay the same (yeah, right), you could tolerate panel degradation of about 15% before you have an electric bill again. Of course, the difference between actuals and estimates will prevent that degree of sizing accuracy in a real system.

Actually, that sort of brings up another point... I think the fixed charges associated with each plan need to be paid, there is no way to credit them out by TOU accounting, so even though you are showing a negative number for your TOU-D-A result, there is still likely to be a bill to be paid at the end of the net metering year.

[J.P.M.]

Wow, my head has been rolling on this one. I followed your link to the Tesla forum and implemented the math the way miimura was suggesting as a starting point, but I had serious reservations about negative baseline percentages. Then when I returned here to status things, I see you've found more clarification and it makes more sense to me. I've adjusted the TOU-T to match the logic you last presented and it does make the TOU-T more appealing, but still not better than the TOU-D-A for me. I'm including a link if you want to see the TOU-D-T changes. The way the TOU-D-T requires month end data to calculate it's values (which are needed to arrive at month end values) seems almost circular, but if I just use the usage in kWh to calculate the month end data necessary to calculate % for baseline, then calculate the $'s I'm okay. I'll warn you that this new math does add a layer of complexity to the math in the spreadsheet to where it has noticeably slowed the calculation time down from near instant to a few seconds (depending on your hardware).

New TOU-D-T calcs:
Solar_TOU_Rev_M14_WIP.xlsm

Thanks again for hunting this understanding down, it's amazing how complicated the TOU-D-T baseline calcs really are comparatively speaking!

As said, welcome to POCO rate hell - be prepared for many iterations. You're doin' fine.

[insaneoctane]

Programming this into a spreadsheet will take more work, but at least we can see what the logic needs to be.

Edit:
Also note that the DWR charges and credits in that linked bill are based on the seasonal net kWh within the bill. That suggests that in a spreadsheet, the published bundled rates (inclusive of delivery, generation, DWR bond, DWR energy credit, etc) should be OK to use, even when energy is piecemealed into the different TOU's and tiers.

Wow, my head has been rolling on this one. I followed your link to the Tesla forum and implemented the math the way miimura was suggesting as a starting point, but I had serious reservations about negative baseline percentages. Then when I returned here to status things, I see you've found more clarification and it makes more sense to me. I've adjusted the TOU-T to match the logic you last presented and it does make the TOU-T more appealing, but still not better than the TOU-D-A for me. I'm including a link if you want to see the TOU-D-T changes. The way the TOU-D-T requires month end data to calculate it's values (which are needed to arrive at month end values) seems almost circular, but if I just use the usage in kWh to calculate the month end data necessary to calculate % for baseline, then calculate the $'s I'm okay. I'll warn you that this new math does add a layer of complexity to the math in the spreadsheet to where it has noticeably slowed the calculation time down from near instant to a few seconds (depending on your hardware).

New TOU-D-T calcs:
Solar_TOU_Rev_M14_WIP.xlsm

Thanks again for hunting this understanding down, it's amazing how complicated the TOU-D-T baseline calcs really are comparatively speaking!

[insaneoctane]

One more comment... in columns BL and BM, showing the charges in the standard tiered plan once you get into Tiers 2 and 3, you should also show credits for the hours of generation. Right now, you just show zero for those values. Those credits are calculated at the appropriate Tier 2 or 3 rate, in the same way that you put the net generation credits into column BK for Tier 1.

Edit: It looks like fixing that would knock another $30 off the annual bill for that plan, bring the total down to just under $230.

Senji,
Great catch. I certainly appreciate you looking into the spreadsheet in the detail necessary to catch that. I've fixed it now.

[sensij]

I should have known the answer would already be in the forum. In this post, an example TOU-D-T bill is provided. Since the bill is almost three years old, I verified that the language in the tariff applicable at that time that addressed the baseline and tier calculations is unchanged in today's tariff. From it, just looking at summertime since each season is handled separately when a billing period covers both, I can see the following:

Baseline allocation = 214.2 kWh (21 days of summer at 10.2 kWh / day)
Level 1 allocation (130% of baseline) = 278.4 kWh
Overall net consumption = -118 kWh
Peak: -367 kWh
Off-peak: 249 kWh

To calculate the % of the baseline that gets allocated to each TOU category, the minus sign is dropped.

% allocated to peak = 367 / (367+249) = 59.58%
% allocated to off-peak = 249 / (367+249) = 40.42%

Therefore, the level 1 allocations are (not sure how the rounding works, but this is what is on the bill)
peak: .5958 * 278.4 = 166 kWh
offpeak: .4042 * 278.4 = 112 kWh

With that figured, the bill then breaks down to
peak, level 1 = -166 kWh
peak, level 2 = (-367--166) = -201 kWh
off-peak, level 1 = 112 kWh
off-peak, level 2 = (249-112) = 137 kWh

The same math works to explain the winter time portion of the bill, with the baseline allocation coming from 9 days * 9.2 kWh / day.

Programming this into a spreadsheet will take more work, but at least we can see what the logic needs to be.

Edit:
Also note that the DWR charges and credits in that linked bill are based on the seasonal net kWh within the bill. That suggests that in a spreadsheet, the published bundled rates (inclusive of delivery, generation, DWR bond, DWR energy credit, etc) should be OK to use, even when energy is piecemealed into the different TOU's and tiers.

[sensij]

One more comment... in columns BL and BM, showing the charges in the standard tiered plan once you get into Tiers 2 and 3, you should also show credits for the hours of generation. Right now, you just show zero for those values. Those credits are calculated at the appropriate Tier 2 or 3 rate, in the same way that you put the net generation credits into column BK for Tier 1.

Edit: It looks like fixing that would knock another $30 off the annual bill for that plan, bring the total down to just under $230.

[sensij]

Sensij, I'm glad the TOU-D-A appear to match.
As, for the TOU-D-T, I read the tariff sheet you referred to and that is most definitely, not the way I used to calculate baseline. I read the tariff sheet a few times but couldn't really "get" it. Your description is much easier to follow by itself, but can't confirm it matches what I read:



Sounds like I've got more work to see if TOU-D-T does anything for me still.....

There is a thread in a Tesla forum that is discussing this at the same level of detail you seek. This post in particular provides an explanation similar to mine, but nowhere do I see how to handle it if your net usage during a particular TOU period is negative, as it would be for you in Peak for most of the year. The thread suggests that if you sign up for the TOU-D-T plan, the calculation in the margin of your bill will explain it, but given the limitations on plan switching I'm not sure it really matters enough for you to try to find out. As you've shown, TOU-D-A is likely to leave you with a net metering credit at the annual true-up, which is the best possible outcome. Only once you have more loads that you plan to add will it be worth re-evaluating, but who knows what the rates will be at that time anyway.

[insaneoctane]

I've spent some more time with the TOU-D-A calculations and the spreadsheet produces the same result I would get. If it saves some time for others looking at it, of the 19 columns in the S to AK range for TOU-D-A, only three are really needed to get at the end result... T, AF, and AI, corresponding to basic TOU charges, the 0.10/kWh "credit", and the fixed monthly charge. The rest appear to be for data presentation in the charts.

I'm not sure the TOU-D-T calculations are correct. The baseline allocation in that plan needs to be divided among the different TOU categories (off-peak, on-peak) according to the monthly use in that category, and the tiers are calculated from there. For example, in a month with 400 kWh baseline allocation, with 60% off-peak and 40% on-peak usage, there would be 240 kWh of baseline allocation in off-peak and 160 kWh of allocation in on-peak before moving into the next tier. I haven't followed the spreadsheet's TOU-D-T calculations used closely enough to be 100% sure, but I don't see that accounted for. See Special condition 7 on page 12 of the tariff for more information.

Sensij, I'm glad the TOU-D-A appear to match.
As, for the TOU-D-T, I read the tariff sheet you referred to and that is most definitely, not the way I used to calculate baseline. I read the tariff sheet a few times but couldn't really "get" it. Your description is much easier to follow by itself, but can't confirm it matches what I read:

In order to determine the allocation of baseline kWh to each Time-of-Use (TOU) period, the customer’s baseline allowance for the billing period is first allocated to each TOU period based on the ratio of the metered seasonal kWh in the TOU period to the total metered seasonal kWhs in the billing cycle. TOU kWhs are then assigned to each tier by applying the existing tiering parameters. Baseline allowance for distribution to TOU periods is the minimum of the standard allocation as set forth in Preliminary Statement, Part H, or total metered kWh for the billing cycle

Sounds like I've got more work to see if TOU-D-T does anything for me still.....

[J.P.M.]

If it helps to have a non-google drive option, I moved it into my dropbox, and it can be accessed with this link.

Iso: Got it. Thanx. It may be a bit before I respond. PM on the way.

[sensij]

If it helps to have a non-google drive option, I moved it into my dropbox, and it can be accessed by request.

[sensij]

Yes as of about 30 sec. ago. I get screen shot of P.1 and a message that says :" Whoops ! There was a problem loading more pages." I cannot access the shown page either. Go Figure. My Luddite brain is stymied.

I ran into that problem too, when I tried to use the "Open With" function. When I used the "Download" function, it came through correctly.

[J.P.M.]

Thank you for your feedback.
1. Although I am not looking to use my system to make money, I didn't realize that the NSCR program was *so* one sided! (ie <$0.05/kWh surplus) . It definitely shows that I should find a good use for my over production besides selling it back to SCE, so thanks for that.

2. Gut reaction to your observation about two low usage periods would be that we were out of town for extended period during those dates. If we were to stay and have a higher July, I still believe that TOU-D-A is the clear winner.

3. Although I don't remember flipping the sign on my data, I certainly might have. That decision was many calculations ago! I also did zero out the inverter when it was very close to zero and I will check if that has any significant play on results.

Again, thanks for taking the time to review!

JPM- I am curious if you are still having issues reading the file?

Yes as of about 30 sec. ago. I get screen shot of P.1 and a message that says :" Whoops ! There was a problem loading more pages." I cannot access the shown page either. Go Figure. My Luddite brain is stymied.

[sensij]

I've spent some more time with the TOU-D-A calculations and the spreadsheet produces the same result I would get. If it saves some time for others looking at it, of the 19 columns in the S to AK range for TOU-D-A, only three are really needed to get at the end result... T, AF, and AI, corresponding to basic TOU charges, the 0.10/kWh "credit", and the fixed monthly charge. The rest appear to be for data presentation in the charts.

I'm not sure the TOU-D-T calculations are correct. The baseline allocation in that plan needs to be divided among the different TOU categories (off-peak, on-peak) according to the monthly use in that category, and the tiers are calculated from there. For example, in a month with 400 kWh baseline allocation, with 60% off-peak and 40% on-peak usage, there would be 240 kWh of baseline allocation in off-peak and 160 kWh of allocation in on-peak before moving into the next tier. I haven't followed the spreadsheet's TOU-D-T calculations used closely enough to be 100% sure, but I don't see that accounted for. See Special condition 7 on page 12 of the tariff for more information.

[insaneoctane]

Thank you for sharing your work. There are a couple things in it that catch my attention and I'm digging more deeply to understand. Some initial comments though:

Thank you for your feedback.
1. Although I am not looking to use my system to make money, I didn't realize that the NSCR program was *so* one sided! (ie <$0.05/kWh surplus) . It definitely shows that I should find a good use for my over production besides selling it back to SCE, so thanks for that.

2. Gut reaction to your observation about two low usage periods would be that we were out of town for extended period during those dates. If we were to stay and have a higher July, I still believe that TOU-D-A is the clear winner.

3. Although I don't remember flipping the sign on my data, I certainly might have. That decision was many calculations ago! I also did zero out the inverter when it was very close to zero and I will check if that has any significant play on results.

Again, thanks for taking the time to review!

JPM- I am curious if you are still having issues reading the file?

[sensij]

Thank you for sharing your work. There are a couple things in it that catch my attention and I'm digging more deeply to understand. Some initial comments though:

1) It is good that you see the difference between two plans with negative annual balances is only in the fact that additional energy could have been consumed at no charge. Just to be clear, the actual financial credit that would be available to you at the annual true-up (end of the "relevant period" as SCE calls it) is the same no matter what your negative balance appears to be. It is just the (kWh generated - kWh consumed) * the net suplus compensation rate (NCSR, shown here). The result is that if your usage is as you project, the money in your packet at the end of the year would be the same for either -D-A or -D-T.

2) Your usage shows some interesting patterns (see picture of daily usage, from Column E of the spreadsheet), with much lower kWh used in July and in November. You are showing >25% less usage in July than in either June or August, which seems atypical to me. The July pattern in particular contributes substantially to the benefit of TOU-A for you, as I would calculate it. Why is your usage so much lower in that month?

daily usage.JPG

3) The signs in Column C seem to have been changed from the PVWatts (or SAM ) output. The negative values in their output when the sun isn't shining are to account for the energy used by the inverter even when there is no power to invert, and should be positive values in the sign convention you adopted. You seem to have just zeroed these out in your adjusted column D... it might not make much difference, but wanted to point it out.