KB's Design

[max2k]

6000 gallon, running about 5000gph through the bio filter, and 3000-4000gph through the sand filters. FWIW, there is a kick-butt variable-speed pump that ponders love which is very efficient called "Flowfriend". The catch is that it's $2700 and - at least for my use - would literally take decades to pay off the price premium.

Static head is zero and dynamic head is around 5-8 ft.

the question is - is there biological reason for that much flow? At your current rate you're putting your entire pond through the filter every hour. My variable speed pump for the pool ran me down $800 and with $200 rebate from utility paid for itself in less than 8 months. May be you can buy that and plumb it in? It was relatively easy with PVC pipes / glue. It is very variable DC brushless motor with built in timer.

[kb58]

the question is - is there biological reason for that much flow? At your current rate you're putting your entire pond through the filter every hour. My variable speed pump for the pool ran me down $800 and with $200 rebate from utility paid for itself in less than 8 months. May be you can buy that and plumb it in? It was relatively easy with PVC pipes / glue. It is very variable DC brushless motor with built in timer.

Understood, I know all about the various pumps. Koi ponds and filtration systems are treated as "the more the better" as far as filtering goes. Koi fanatics insist on maximum flow for healthy fish. OTOH, the so-called rules change from year to year - 20 years ago when I built the pond the first time, cycling the volume once every 2 hours was "correct." Point being is that there's a wide spread of answers on what's considered the best filtration for koi. Might a smaller pump work fine? I'm sure it would, but the effects on water health are less certain beyond what water testing shows. That said, I have a backup pump which draws approximately 100 watts less and depending how the solar design goes, may or may not become the main pump.

[J.P.M.]

Partial bill offset is where things are probably headed, enough to get down to T1

What's T1 ? If you are referring to Tier 1, know that, like it or not:

1.) You will be on T.O.U. rates.
2.) Tiered rates are out the window for NEM 2.0 users.
3.) If you do nothing, once you get PV and are under NEM 2.0, you will default to schedule DR-SES. That's the T.O.U. rate I wrote about this A.M. There is another residential T.O.U. schedule that's a combination of T.O.U. with a tier rate laid over it, but DR - SES is usually a better deal for PV users.
4.)To be clear, there are no tiers associated with DR-SES.

It's a new ball game.

[kb58]

Of course you're correct, I know just enough terminology in this (new to me) field to be dangerous.

So I more accurately modeled my site in SAM with detailed shading and example equipment. I say "example" because I'm at the point that I have to determine how much power needs to be produced. From that I can then back-calculate final costs assuming TOU, NEM 2.0, and DR-SES in order to find the pay-down period and whether or not this is a wise investment.

I went through the SDGE bills and the monthly average is around 700 KWh. Earlier you (JPM) stressed how important it was to not under or overdo array size and I'm unsure how to do that. If I assume the SAM output is reasonable, is it not as simple as dividing the simulated yearly output by 12 and size the array to barely meet 681 KWh/month? I know there's degradation over time, but what else am I missing?

(The above aside, I'm currently walking my way through your very thorough response from yesterday.)

[kb58]

Stepping through your response yesterday:

SAM estimates that with shaded at our site, a 4-panel (250W each) array will produce 1497 kWh/yr, or around $344.

I estimate we use 8400 kWh/year, so:
8400 / 1497 = 5.6kW*

Following your example of off-peak-only usage, the annual bill would be about $1843. $1843 / 344 = 5.4 kW

Following your example of on-peak-only usage, the annual bill would be about $3862. $3862 / 344 = ~11.2 kW.

As you note, neither of the above is realistic and actual usage will be somewhere in between.

* Interestingly, the quote we received recommended a 5.6kW array, so the above isn't completely out of line (though that's array power, not AC power after losses).

[J.P.M.]

Of course you're correct, I know just enough terminology in this (new to me) field to be dangerous.

So I more accurately modeled my site in SAM with detailed shading and example equipment. I say "example" because I'm at the point that I have to determine how much power needs to be produced. From that I can then back-calculate final costs assuming TOU, NEM 2.0, and DR-SES in order to find the pay-down period and whether or not this is a wise investment.

I went through the SDGE bills and the monthly average is around 700 KWh. Earlier you (JPM) stressed how important it was to not under or overdo array size and I'm unsure how to do that. If I assume the SAM output is reasonable, is it not as simple as dividing the simulated yearly output by 12 and size the array to barely meet 681 KWh/month? I know there's degradation over time, but what else am I missing?

(The above aside, I'm currently walking my way through your very thorough response from yesterday.)

Take a deep breath. FWIW, I think you're doin' fine - at least a lot better than I'd probably be doing if the situation were reversed. Besides, this ain't a race. Even if possible import tariffs raise prices, my guess is it won't be a draconian increase and anyway, slow, easy and deliberate always wins. Keep moving but don't get stampeded.

If/As you get more familiar w/SAM, the SDG & E tariff schemes, and PV in general, you may find some things are not as you might have thought, say, last week. Happens to me all the time, just less than before, (usually). Also, as I'm sure you know, SAM's a model and a bit better than a dart throw, but sometimes not much better. Trust the model, but trust your gut too. Just keep GIGO in mind.

On array sizing, use monthly totals as best as you can estimate summed over a year for the annual load.

Under NEM 2.0, SDG & E will carry your monthly balance, or use, or excess, forward until "trueup", which happens with the billing period that includes your startup ("Permission to Operate == PTO) date. You will then get an accounting of uses, credits and other stuff. If you owe SDG & E as a result of what you used, that's when you pay. If you were an excess generator (but you won't be because your a sharp PV person) by choice, and your credits cover the $120/yr. min., you'll either get credit against future use, or call them and tell them you want the money, which currently amounts to a paultry ~ $0.027/excess kWh, and another reason why oversizing without serious consideration and awareness is a waste of money and resources. No action by you with respect to surplus generation defaults to a credit against future use. That is how it works for me, but I'm not sure that is still how NEM 2.0 is working.

As for system annual performance degradation, SAM will take that into account as you input it. See the performance adjustment screen and the box near the top. Use the annual degradation from the data sheet for the panels you choose.

For max. cost effectiveness, any array sizing needs realistic (as best as can be realistically done when predicting the future anyway) estimates of what future needs will be, and (more crap shooting) of what POCO (SDG & E's) rates will look like in the future. FWIW, those rates, in spite of what you, I or anyone may think, do not always go up. Also, everyone wants an EV and everyone says so. I'd bet some of that is wishful thinking. Point is, when evaluating future needs, do as you wish, but be realistic. Choose wisely and be honest with yourself, not wishful.

As for most cost effectiveness as f(size), if I was in your shoes, and at your current PV knowledge level, I'd use SAM carefully after figuring out annual system revenue per STC kW using SDG & E soon to be DR-SES rates and times rather than SAM's prices, and after spreadsheeting DR- SES rates per hr. for all 8,760 hrs. in a yr. (I know, sounds daunting, but it's mostly a copy job that took me ~ 15 minutes once I got the tariff figured out, and I'm mostly a Luddite). I'd then get SAM's hourly output for a 1 STC kW array on the same spreadsheet and multiply the $/kWh rate by the hourly output to get a value for hourly revenue per STC kW. Then, sum all 8,760 hrs. in that column for annual revenue. Do that for several orientations that also account for shading and you'll quickly (?) zero in on an orientation that maximizes annual revenue under DR - SES. What you may find, and somewhat dependant on how much and where the shading occurs, is that annual revenue as f(orientation) is somewhat insensitive to orientation and does not change that much for what may seem like rather large orientation changes. With Miramar weather data and PVWatts and published SDG & E "possible" rates under the new DR-SES schedule, every STC kW will produce something like ~~ $390/yr. at a 30 deg. tilt and an azimuth between 200 and 225 deg. SAM's output estimates, together with SDG & E prices in the same manner as just described will perhaps produce something similar, but will not be identical with the PVWatts and no shade numbers. BTW, for San Marcos, I'd use Miramar NAS for SAM's weather source, same as mine.

More future uncertainty,(and there's not much to be done about this aspect of the future uncertainty even more than general predictions about the future): Optimum array orientation for revenue as bill offset will change every time SDG & E changes rates and times on DR-SES.

I suggested one way to size an array when being billed under DR - SES and gave a couple of examples to show the effects of time shifting of loads. That method will work, as you may have, or will yet read, when annual usage exceeds generation, and, while a bit unusual, I believe a valid way to size a PV system when the billing method is such that the per kWh rate charged, or credited, is not dependent on how much use occurred during any billing period. However, even though the method is sound, I haven't seen it elsewhere - yet - so most vendors may not be aware of it. I only mention that because, being probably unknown, you'll probably get strange looks from folks. Just sayin', and just so you know.


When talking to vendors, and as I mentioned and so repeat here, the new DR - SES times and rates are different than the old DR - SES rates and times. So much so in fact, while the average value of a kWh produced by the old DR - SES to offset a T.O.U. bill was about $0.31/kWh (~ $520/yr. per STC kW), the new DR - SES rates and times reduce that average value to offset a bill down to something like ~~ $0.22 - $0.23/kWh. (~ $390/yr. per STC kW). So, for you and others under DR - SES, vendors who tout PV savings using the old DR - SES, or the old tiered rates are misrepresenting savings by something like ($520-$390)/$250 = ~25 %, or reducing ROI or extending payback time by about the same amount. More things to think about for the go/nogo or size eval. case.

[J.P.M.]

It is worth pointing out that switching from DR to DR-SES will impact the *cost* side of the equation as well. For some, the same consumption would cost less under TOU than under the tiered plan, which implicitly adds to benefit of the PV system (imagine installing a 0 W system, just to get access to the tariff). For others, the opposite is true. Revenue calculations are very good at optimizing the orientation of the array, but are not enough of the story to deeply evaluate cost effectiveness.

Another point in favor of expediting the installation is that if you can get PTO before Dec 1, the new TOU hours won't apply for 5 years. Taking extra time to get the array size perfect and missing that deadline may not be the most cost effective plan.

Indeed. VERY worth noting.See my 09/22/17, 0933 hrs. post. Time shifting can easily be the second most cost effective way to lower an electric bill after thje first and ost cost effective way of reducing a bill: Not using the electricity in the first place.

[J.P.M.]

Stepping through your response yesterday:

SAM estimates that with shaded at our site, a 4-panel (250W each) array will produce 1497 kWh/yr, or around $344.

I estimate we use 8400 kWh/year, so:
8400 / 1497 = 5.6kW*

Following your example of off-peak-only usage, the annual bill would be about $1843. $1843 / 344 = 5.4 kW

Following your example of on-peak-only usage, the annual bill would be about $3862. $3862 / 344 = ~11.2 kW.

As you note, neither of the above is realistic and actual usage will be somewhere in between.

* Interestingly, the quote we received recommended a 5.6kW array, so the above isn't completely out of line (though that's array power, not AC power after losses).

Sounds and looks like you got that one down. Just know that a 100 % offset may not the most cost effective size. There's nothing sacred, mystical or even close to no brainer about a 100% or greater offset.

[kb58]

Where did you find SDG&E's DR-SES rates? Their site seems almost purposely obfuscated as far as locating future - let alone current - pricing. I'm talking about the expected hourly pricing throughout the day that you used for your spreadsheet calculations.

[J.P.M.]

Where did you find SDG&E's DR-SES rates? Their site seems almost purposely obfuscated as far as locating future - let alone current - pricing. I'm talking about the expected hourly pricing throughout the day that you used for your spreadsheet calculations.

Future "sort of/possible" rates are kind of obscure to get at/find. I believe they were part of something called a "rate case" from a few months ago. For current tariffs google "SDG & E + tariffs" and choose "current and effective tariffs" .

I'm kind of tied up just now. I'll scare out the source of the possible new/proposed rates for DR - SES later, or maybe Sensij can point in a direction sooner. I actually got the original from a posting he put up, but I've seen that SDG & E info a few times since.

You're finding out one way SDG & E makes not much effort to be helpful.

[sensij]

Current rates...

Google "sdge tariffs" -> Current and Effective Tariffs -> Residential

[kb58]

Got, thank you, sirs. http://regarchive.sdge.com/tm2/ssi/i...rates_res.html

[J.P.M.]

Got, thank you, sirs. http://regarchive.sdge.com/tm2/ssi/i...rates_res.html

Which will get you the current DR - SES rates, but not the proposed DR-SES rates using the new times. The current rates and newer, proposed rates are not the same. The proposed rates will probably be slightly different after final approval which I'd expect sometime around 12/01/2017 or maybe a bit sooner. The proposed rates are more of a suggestion by SDG & E.

[sensij]

Illustrative rates for the approved GRC. These were updated on 9/13 from what I've posted before.

http://docs.cpuc.ca.gov/PublishedDoc.../195586830.PDF

Those are based on Aug 2016 as a starting point, and don't include some of the "revenue requirement" increases that have occurred since then (if I am understanding correctly).

[kb58]

Yeah I know about peak summer hours shifting to 4-9pm - we recently had an in-company SDG&E presentation where they passed themselves off as our best friends...

For anyone else following this, attached is the pertinent info from the link above (noting the times will shift). I'm going to assume the following:
Summer peak: 4-9pm M/F
Summer semi-peak: 9-12pm and 6am - 4pm M/F
Summer off-peak: 12-6am

Winter I'll leave as-is

Ugh, I don't use Excel a whole lot but this'll be jumping in at the deep end!