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**J.P.M.** · 03-23-2019, 12:40 PM

Since you ask:

Before you do what's often the least cost effective way to reduce an electric bill, start by doing want's usually the most cost effective way to reduce a bill : Reduce consumption. In your case that'll be easier. Start with an analysis of what a new pool pump and new A/C will cost vs. what they'll save. If by chance the annual savings divided by the cost are > you est. PV system payback, then, to the extent your estimates are reasonable and accurate, using PV to offset the current pumpA/C/whatever inefficiencies will be more cost effective than getting conservation improvements.

If conservation measures are more cost effective (and my guess is they will be), the conservatiopn savings will also compound when you realize the PV system you get can be reduced in size ~ in proportion to the load reduction the conservation improvements make.

If you are using the 14 % default value for system losses PVWatts uses, if you haven't done so, I'd suggest rerun w/10% system losses. Also know that for reasons that make perfect sense from the vendor's point of view (and not so good for the customer) vendors usually pad (under report) estimated system output by about 10 % or so. Go with your own numbers. You'll get a more realistic number. Then, if you choose to oversize, you'll at least be less from using a less inflated number to begin with.

Without talking about optimizing cost effective PV system sizes, figuring the $120/yr. min. against usage is pretty standard. Not a big deal, but divide $120 by what you believe is, or will be your ave. cost/kWh after PV and deduct that quotient from what you initially want the system to offset and make that the new system offset goal, and reduce system size accordingly.

On which panels: Today, panels are a commodity. Most all 5 kW systems in the same locatiopn, orientation and duty will produce about the same annual output for as long as you're likely to own one of them +/- a small amount of a couple % or so. Panels don't fail much except for infant mortality, and even that's pretty rare, making superior warranty claims less important. Also, panels all pretty much deteriorate at about the same rate. Even if performance rolloff is different, as a practical matter, you or any other consumer will never be able to measure it, much less verify it for a warranty claim. Believe it.

On vendors, place more priority on what your gut and what your gathered information tells you about vendor quality. Vendor integrity and work quality and professionalism is MUCH more important than the hype about superior panel quality. Just know and remember that a lot of the hype and B.S. cust. reviews are written by folks who are probably and absolutely clueless about what they bought, except maybe what they thought about the salesperson and how much (s)he smiled at them. Take such unverifiable information FWIW. Do your homework and trust your gut.

On price: Semper Solaris seems high, especially given that the other vendor is coming in ~ 25% higher for essentially the same product. I'd go with whatever system size you come up with from the rev. PVWatts modeling you do, putting as much of the system on the south roof as possible. Then, I'd call both vendors and tell them you're prepared to pay $2.50/STC W (or whatever price you want) TODAY, installed for your size choice and see what happens.

What will happen is the negotiating begins. Do not reveal other vendors prices. Doing so and you'll be giving away one of your negotiating tools. Firm competitor's prices is one thing all peddlers want. Price matching is a fool's errand. I used it a lot when I used to be a peddler. That's exactly what vendors want. Do it and you'll never pay lower if/when you do buy and besides, you have nothing to gain by revealing prices. Look at it from the vendor's side. Keeping prices to yourself is an advantage to you.

Lastly, get your roof inspected and serviced. A PV system will last a long time. Give the roof under it the highest probability of lasting as long. Cheap insurance you will not regret.

Welcome to the neighborhood and the forum of few(er) illusions.

Take what you want of the above. Scrap the rest.

**shadow1180** · 03-24-2019, 01:05 AM

Thank you for such detailed answer, now I have more questions:

If by chance the annual savings divided by the cost are > you est. PV system payback

I believe you meant: cost divided by annual savings = number of years to break even.
Unfortunately, replacing pump is not cost effective.
Current pump consumes ~2000 kWh, $480 annually.
Suppose new pump will be twice more effective, so we have $1000 kWh and $240, but pump replacing project is ~$4000 (pump, control panel, labor). Even if I shop for $3000, offsetting 1000 kWh with solar would cost around ~ $2000.
(Also cost will be even less, if I run pump in nights with TOU)

If you are using the 14 % default value for system losses PVWatts uses, if you haven't done so, I'd suggest rerun w/10% system losses.

I was running it with 13% losses.
Why should I use 10%? Modern components are so effective + no shading, makes less losses? So real number 10%?

Also know that for reasons that make perfect sense from the vendor's point of view (and not so good for the customer) vendors usually pad (under report) estimated system output by about 10 % or so

That's what I didn't understand. They usually try to sell bigger system than you need. Why would they pad output? Could you please give an example?

$2.50/STC W

what is STC?

I wonder what is the real system price for vendor?
If they quote me: 16*330*2.91 = 15364

I could imagine breakdown like this(based on google prices):
Panels: $1/W: 16*330 = $5280
Optimizers: 16 *65 = $1040
Inverter: $1400
Labor + hardware + permits + fees, etc: $3200 (random number)
40% margin on top of it
== 15300

Considering they pay less for every component, their margin is even bigger. So, I believe shooting for $2.5/W, would be not far from fair project cost. Btw, I negotiate before site inspection, right?

One more question about upgrading main panel: are they talking only about installing a larger box? I believe they are not going to pull new wires to make it 200A?

Welcome to the neighborhood and the forum of few(er) illusions.

Thank you!

**J.P.M.** · 03-24-2019, 07:37 PM

Originally posted by shadow1180

Thank you for such detailed answer, now I have more questions:

I believe you meant: cost divided by annual savings = number of years to break even.
Unfortunately, replacing pump is not cost effective.
Current pump consumes ~2000 kWh, $480 annually.
Suppose new pump will be twice more effective, so we have $1000 kWh and $240, but pump replacing project is ~$4000 (pump, control panel, labor). Even if I shop for $3000, offsetting 1000 kWh with solar would cost around ~ $2000.
(Also cost will be even less, if I run pump in nights with TOU)

I was running it with 13% losses.
Why should I use 10%? Modern components are so effective + no shading, makes less losses? So real number 10%?

That's what I didn't understand. They usually try to sell bigger system than you need. Why would they pad output? Could you please give an example?

what is STC?

I wonder what is the real system price for vendor?
If they quote me: 16*330*2.91 = 15364

I could imagine breakdown like this(based on google prices):
Panels: $1/W: 16*330 = $5280
Optimizers: 16 *65 = $1040
Inverter: $1400
Labor + hardware + permits + fees, etc: $3200 (random number)
40% margin on top of it
== 15300

Considering they pay less for every component, their margin is even bigger. So, I believe shooting for $2.5/W, would be not far from fair project cost. Btw, I negotiate before site inspection, right?

One more question about upgrading main panel: are they talking only about installing a larger box? I believe they are not going to pull new wires to make it 200A?

Thank you!

In some order:

- You're welcome.

- You are correct, My error. My apologies. The statement should have been replacement cost/annual savings. I'll correct the post. Thank you for catching the brain fart.

- Read the PVWatts help screens for a description of system losses. It's a big fudge factor that rolls in a lot of things other, more involved models get involved in.
Bottom line: Using 10% system losses w/PVWatts is what seems to give a closer approx. to what users report from such things as PVOutlet and ther sources. It also usually gives a better match between PVWatts model output to those other more sophisticated models such as SAM or TRNSYS (two other models I use) or perhaps others. 10% also seems to give pretty close agreement with some software I wrote in the year 2000 and have been tweaking ever since. One thought: What's reported is likely from users with fairly new PV systems and so may be greater than annusl system output , say, 10 years from now. But after looking at systems I monitor in my HOA 9-10 yrs. and my own system for 5+ years, that 10 % seems to be holding up pretty good. Also, and to repeat, it seems to give a better match w/PVOutlet.
Further, if I use ~ 9.8 % system losses on my system, PVWatts seems to match my actual running 31 day average output since 11/01/2013 reasonably well (actual 31 day running ave. /PVWatts 31 day running ave. = 0.9924, pop. std. dev. = 0.099, n 1,952).
So, the "real" # is whatever seems to match reality as best as one can make it work. There is nothing special about 10%. It just seems to give a PVWatts model output that matches other models' output fairly well, and also what seems to be generally reported from users. Your results may and will probably vary. Use what you want. Just be informed.

- Vendors pad (that is, underestimate) output for a lot of reasons. The usual explanation that does have some validity is to cover uncertainties in actual or future conditions that might decrease output from what a model comes up with. OK, a few, MAYBE 10% excess surface makes some sense. Just be honest about it. Start w/ best est. from a reliable model or several, and then explain to the user what that means. The way the uncertainty cloak is used makes it more of a red herring that gains validity from consumer ignorance than may be useful and honest. Often too, uncertainties get stacked up by sellers and that, say, 10% extra desired output for uncertainties, that is 110% of desired output, gets multiplied by an added 4,000 kWh/yr. or so for a hoped for EV, then all that gets multiplied by another fudge factor for a "bigger" family or any other real or perceived or wished for future lifestyle adjustments. Pretty soon, there might be, say, 30% excess generation capacity and the owner winds up getting pennies/kWh or pretty much squat for what that 30% excess capacity pays from the POCO. The ignorant user is then happy when looking at a lower or even to zero bill, but in their ignorance don't understand they'd have almost the same low bill with a much smaller (read less expensive) system.
But the biggest reason that oversizing is so common is most likely because no salesperson ever got fired for selling too much product. Reality: Vendors make money putting their product on your property, not saving you money on your electric bill. That's your job, and PV can be one tool to accomplish that task - but know that it isn't the first thing done and it needs some education to do it in a way that doesn't wind up costing more in the end than if no PV was installed in the first place.

- STC == Standard Test Conditions. It's the conditions under which solar panels are rated or (electrically) sized. Example: If a panel is a "300 W" panel, that means under conditions of 25 C. amb. temp., no wind and 1,000 W/m^2 simulated irradiance normal to the panel, that panel put out 300 W. In most operating environments and conditions, it won't. Somewhat analogous to an internal combustion engine (an "ICE") that's rated for 300 HP but will rarely if ever operate at that output level. There are other rating methods. Those others, IMO only, are unnecessary and only add confusion for the ignorant. I attempt to be clear by using the (usually implied) "STC".

- The quoted prices are what a vendor proposes to charge you. They are the real prices to you. You have the option of finding the most bang for your buck. If that means DIY in your opinion, well, that's another option and for some, a viable one.

About maybe 3 or 4 times/yr. some poster shows up here and rags on about robber vendors and how they (vendors) get cheaper prices for materials, and find labor in the parking lot at big box, and do a $25K job in 2 days and how they're all (the vendors that is) getting over like fat rats in a cheese factory. Not to you, but to such posters I say, OK, even if all that is true - and I bet some of it is and some of it ain't - if you don't like way the game is run - do it yourself. At least you'll (hopefully) get educated or, pay for the business expense, warehousing trucks, insurance and labor (not all of which is illegal). Then, add the cost of service and warranty and all the other costs associated w/running a business.

Most PV buyers are clueless about what's required to design and put together a safe, reliable PV system and, it seems to me anyway, such opinions about robber vendors come from those who are also clueless about what it takes to start and the even tougher job of maintaining a successful business. To such folks I suggest: Try it.

- As for negotiating, you start the process with first contact and a written set of goals for all the vendors you contact for their use to help get you a first rough estimate. Then, using those and refined project goals going forward, that process more/less continues through to design refinement, bid evaluation/selection, contract signing, more design, permitting, construction, inspection and sign off by AHJ's and POCOS as required until the system has received PTO (permission to operate) and operates according to the design parameters set up. The negotiating process is about a lot more than just initial price. Done right, it's also a means of better communication about goals and a good tool to help avoid misunderstandings and resolve disagreements.

That $2.50/ STC W I used was a serving suggestion based on what I might think I know about pricing these days and what selling to the market by vendors might get in terms of what some vendor might live with and still not think they need to skimp too much in ways you'll never see, know about or understand. You may do better or not as good. I'll suggest this: If one vendor is 20 + % higher for the same product and you've convinced yourself they are both reputable and fit to work on your property, something ain't right. Either they are both good but one of them is dancing with your leg on price, or one is not up to the other's quality and the ill informed reviews written by the solar ignorant are again working their magic. Or something is wrong with your vendor selection methods. Or some combination of the above.

- A new panel involves more than just a new box. Not being there it's hard to speculate what's required. I'd suggest contacting some licensed electrical contractor independently from PV vendors and getting a quote from them. FWIW, that $1.5K - $2K seems high, but I'm not in the business of installing electrical panels.

Take what may want of the above. Scrap the rest.

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