Help with picking anniversary month

[petesamprs]

I live in northern NJ and am finishing up the first year with my solar panels. This site has been invaluable along the way.

My array details are 46 panasonic panels (14.95kW) and 2 SE 7600H inverters w/ optimizers. More details here: https://www.solarpaneltalk.com/forum...ou-doublecheck

My PTO was on 2/6/20, and my utility set my default 'reset date' at the end of that billing cycle, so my solar bank was reset to 0 on 2/25/20. Below is the data on my solar production and usage since then. Production is calculated using solaredge's website data, and usage is calculated from my utility bills (by adding back my solar production). I don't have a consumption meter.

Capture2.JPG

Based on this, I finished my solar year on 2/25/21 with ~1,868 KWH in the bank that will be paid out at wholesale (ie, "wasted"). My overproduction for the year was 1,396 KWH, but that will likely be closer to 0 next year since we had some renovations going on at our house this past year, where portions of the house (including appliances) were not being used as regularly.

We generally produce more than we use in the fall, winter and spring (since heat is natural gas), and use more than we produce in the summer (3 AC zones, 30k gallon pool with heat pump).

Given this pattern, the online anniversary calculator is suggesting I should set my anniversary month to right after the summer like September, when I've burned through most/all of my bank. https://docs.google.com/spreadsheets...gid=1225290037

This seems to contradict the general advice to have a reset date in the early spring. Can you sanity check this for me? Since my utility only allows me to change this one time, I want to make sure I get it right

Any other suggestions also welcome.

thanks

[Ampster]

I think it is as much a personal preference that involves some risk management. There is no perfect date. One factor is the weather which will affect your generation and your loads over the season. You have no control over the weather. You do have some control over your loads and when you use them.

Some examples might be useful. I once had a home with electric resistance heat. The February True Up date was inconvenient one year because after a cold winter there was no time to build back reserve. I now live in a home with Air Condioning and a March True Up date. In this situation I enter Winter with some reserve which can easily be managed.

My goal has always been to acheive the lowest cost of energy so I do view having a both a dollar surplus and generation surplus as suboptimal. Most years I have been able through load shifting to consume more energy than my system produces but have a small dollar surplus at True Up. That surplus washes out against the net usage. I am able to do that because of very favorable TOU rates and some discretionary loads such as EVs.

[J.P.M.]

In general, but with plenty caveat for exceptions including but not limited to system size considerations, and for quirks and hooks in any particular utility tariff which are common to most POCO billing schedules, for PV system owners with systems that "on average" have a high probability of some overproduction in any 12 month period, and SRECs are not part of the deal, the trueup billing period that has, on average, the accumulated surplus, either + or -, that is closest to zero will likely be the most cost effective with respect to the impact of low surplus generation reimbursement rates.

If every year had identical billing period usage, generation and usage patterns, and daily system generation, would be a simple matter of choosing the billing period with the "bank" balance closest to zero as all 12 billing period totals would be the same year to year and stay invariant - that is, all Jan. POCO draw would be the same, year to year, as would all Feb. usage for all years, etc.

However, since monthly usage and irradiance patterns vary from year to year, that's not the reality, so we're stuck with a bit of a SWAG, but not necessarily a bad one.

Since PVWatts modeled values are probably +/- 10 % on an annual basis, I'd use PVWatts' daily output option, use it to get the modeled output for each of your particular billing periods (and so NOT by calendar month as your billing probably isn't first to last day of the month), and use those 12 month figures for your particular billing period production.

Then, for usage, I'd use your prior bills or whatever information you can get from your POCO, average each billing period for however many years you have data and use each billing period's average for the average annual use by billing period.

Finally, put all the data into columns as shown in your post, get the differences and pick the billing period with the difference that's closest to zero.

Anyway, that's what I did.

To reiterate, look out for particulars about your POCO's billing policies and quirks. Use kWh and not $$. As one example of many POCO games that can throw analysis off, my POCO changes billing period dates and number of days/billing cycle every year - not much, but they do, and the also play with # of days/billing cycle to be between 28 and 33 with a slight statistical preference for shorter billing periods in the warmer months which helps their revenue by deceasing baseline allowances when (higher) summer rates are in effect. Lots of quirky crap like that increases the uncertainty and leaves a bad taste. Your POCO probably has some of their own stuff.

[khanh dam]

I live in northern NJ and am finishing up the first year with my solar panels. This site has been invaluable along the way.

Given this pattern, the online anniversary calculator is suggesting I should set my anniversary month to right after the summer like September, when I've burned through most/all of my bank. https://docs.google.com/spreadsheets...gid=1225290037
This seems to contradict the general advice to have a reset date in the early spring.

HUH? who generally advises spring reset? after summer reset is best (edited to add if you use Air conditiioning and live in a hot climate)
by the way my utility DUKE screws me over by having spirng reset date.

[azdave]

My grid-tie agreement has an April 30th reset because that is the end of the POCO's fiscal year and there has never been an option the change it, not even once. Sucks for me because that is when I have the absolute most amount of credit built up and I get wholesale ($0.025 kWh) for the nearly 4000 kWh we saved up since September. Summer is our heaviest demand time in Phoenix of course and I would much rather use the credit than receive $100. Such is life.

[bcroe]

HUH? who generally advises spring reset? after summer reset is best
by the way my utility DUKE screws me over by having spirng reset date.

It depends on the individual situation. I am about breaking even on energy just now,
but will soon start on my highest production summer months, building up a reserve
for keeping warm in winter. Fall reset would be a disaster for me.

Seems like, if you use more energy than you generate, a good reset time is when
all reserve has been used up. For those who generate more than they use, best
might be about the time reserve stops dropping, begins rising. Bruce Roe

[khanh dam]

It depends on the individual situation. I am about breaking even on energy just now,
but will soon start on my highest production summer months, building up a reserve
for keeping warm in winter.

of course it varies. for people in the south that use air conditioning (almost everyone), spring reset is a disaster.

[foo1bar]

Unless you are altering how much power you consume based on how many kwh you have saved in reserve, it makes no difference when the reset/true-up occurs. Whether you have net production in the first months and net consumption in the last months or vice-versa doesn't actually matter because it still adds up to the same numbers for a 12 month period

*IF* you alter how much power you consume based on how many kwh you have saved in reserve, then it makes sense to have the true-up date be at the end of the time where you'd be consuming more to eat up the reserve.
Like if you're planning to run the AC more during summer because you have kwh in reserve, then set your date to be after the hotter part of summer.
If you're in a cold climate and plan to do balance your heating between propane/natural gas and banked kwh, based on how many kwh you have banked - then set your date near the end of the heating season.

If you're not going to alter your behavior much (I don't) - then it doesn't make a difference what date you choose.

[khanh dam]

Unless you are altering how much power you consume based on how many kwh you have saved in reserve, it makes no difference when the reset/true-up occurs.

this doesn't even pass the smell test. for example house without AC in the north, but uses electrical heat pump in winter will have high wintertime energy usage, but low production. In the summer exact opposite happens. A reset date in the fall will be a fianancial disaster if the utility gives them wholesale price or in DUKE's case gives you zero for your excess production.

only case where it does not make a difference is if the payout rate is the same as what you pay. which I've never heard of. Pretty sure the law lets them pay you less for over production.

[J.P.M.]

this doesn't even pass the smell test. for example house without AC in the north, but uses electrical heat pump in winter will have high wintertime energy usage, but low production. In the summer exact opposite happens. A reset date in the fall will be a fianancial disaster if the utility gives them wholesale price or in DUKE's case gives you zero for your excess production.

only case where it does not make a difference is if the payout rate is the same as what you pay. which I've never heard of. Pretty sure the law lets them pay you less for over production.

Regardless of what your nose may be misleading you to conclude, for a lot of NEM customers Foo1bar is pretty much correct, provided the PV system generates more than something like100 % of the household annual use.

Run any 12 months of billing and generation 12 times, advancing the true up billing period for each of the 12 trials by one billing period and see what the excess generation per billing period comes out to for each billing period, see that the excess generation per year does not change, and then go to an ENT quack and get your sniffer checked out.

Or, put 3 years of 12 months of gross usage and generation on a spreadsheet, 36 rows and starting with Dec. of the first year, sum the net usage for the that Dec. and the prior 11 months. Do that for the remaining months of the 2d and 3d years and see if the monthly net usage changes.

If you take the time to do that, and notwithstanding any (likely) particular quirks in a POCO's billing and NEM practices, you'll find the excess generation - and probably the compensation $ amount - will be the same for any chosen true up billing date.

Q.E.D.

If you have a choice of anniversary billing period with the closest to zero excess compensation, you will probably benefit maybe for the first year. But after 12 subsequent billing periods of that revised trueup billing year, the change things smooth out.

One small reason of several why most POCO's with NEM agreements only allow one trueup date adjustment, besides keeping the bookkeeping costs down, is so customers don't use trueup year shifting to game the system.

Took me a bit of effort to figure this out after I shifted my trueup billing period after the first yr. of array operation from an Oct. billing with high accumulated excess generation to a March billing with low accumulated excess generation.

That move gave me a few extra bucks in Oct. after the first year of array operation, but more to the point, by shifting the trueup date to March, I got the benefit of getting "credit" against future use at the higher retail use rates instead of what would have been excess generation at the end of the next 12 billing periods with that excess generation paid at the low excess generation rate.

BUT, that was only for the first year. After that, it doesn't matter what the trueup date is.

Assuming, for the sake of not confusing the issue at hand with non relevant details about varying weather and usage patterns, and perhaps oversimplifying things by defining any and all years to have the same weather and usage patterns, beyond the first year, changing the trueup date won't get or cost you anything.

[foo1bar]

this doesn't even pass the smell test. for example house without AC in the north, but uses electrical heat pump in winter will have high wintertime energy usage, but low production. In the summer exact opposite happens. A reset date in the fall will be a fianancial disaster if the utility gives them wholesale price or in DUKE's case gives you zero for your excess production.

only case where it does not make a difference is if the payout rate is the same as what you pay. which I've never heard of. Pretty sure the law lets them pay you less for over production.

No - only case where it makes a difference is when you change behavior based on your true-up date.

Let's do an example. To make it a little easier to follow I'll lump it into quarters instead of months.

PeriodA -100kwh
PeriodB +300kwh (highest net production)
PeriodC +100kwh
PeriodD -250kwh (highest net consumption)
(And following year there is same production/consumption pattern.)

If my true-up is after Period D, my net production is -100 + 300 +100 -250 = 50kwh net production
If my true-up is after Period C, my net production is -250 -100 + 300 +100 = 50kwh net production
If my true-up is after Period B, my net production is: +100 -250 -100 +300 = 50kwh net production
If my true-up is after Period A, my net production is + 300 +100 -250 -100 = 50kwh net production


In every case there's a 50kwh net production, which you get wholesale price (or maybe get nothing for)

When the true-up happens doesn't change things.
It has a small effect with the first N-months when you change the true-up date (because now it's not 12 months - it's some other number of months)
And the last N months - from the true-up date to when you close the account.

[khanh dam]

of course adding the same four numbers will always give you the same answer!!!!
that is NOT what the utility does. they take one month and make it ZERO (or pay you about 1/4 its value)
time to redo your homework
have a positive number go to zero, just like the utility math works.

[bcroe]

Forgot to mention, PoCo pays me ZERO for any surplus at true up, so to not
lose that value, I must pick a time it is minimum. Bruce Roe

[foo1bar]

of course adding the same four numbers will always give you the same answer!!!!
that is NOT what the utility does. they take one month and make it ZERO (or pay you about 1/4 its value)

How does your utility do the true-up?

Because most utilities I've dealt with or seen talked about do a calculation of what was the net amount for the past 12 months.
So if you've had a total net production of 50kwh for the past 12 months you get paid out at wholesale rates for that 50kwh (or get $0 for it)
And it doesn't matter then if your higher consumption months were in month 1 or month 12.

time to redo your homework
have a positive number go to zero, just like the utility math works.

Um - I thought it was obvious that is what happens in the example I gave - the net overproduction of 50kwh for the 12 months gets paid out at wholesale rates (or not paid out at all)
It doesn't really matter when the true-up date is - any time you take a twelve month period you have a 50kwh overproduction.

It's only if you start changing behavior so that you consume more and use up some of that over production that you wind up with a different result.

[J.P.M.]

of course adding the same four numbers will always give you the same answer!!!!
that is NOT what the utility does. they take one month and make it ZERO (or pay you about 1/4 its value)
time to redo your homework
have a positive number go to zero, just like the utility math works.

I'm calling B.S. on your posts to this thread.
You are ignorant of the concept and the particulars of how net metering works.
You are beyond your knowledge base and in way over your head.
You are spreading misinformation to others who may need accurate information and be misled by your blather.
You've had three people, all of whom have a lot of engineering training and experience as well as a lot of solar knowledge, two of whom are either working or retired P.E.'s trying to pound some sense into your skull and you persist in the misinformation and stubborn garbage that can lead people astray.

I call that rude and inconsiderate behavior and I call you out for it.

Knock off the B.S. You're doing harm to the cause of alternate energy and also misleading readers of this forum.