New Memeber and Starting New Project

[ItsFriz]

Figured I'd introduce myself, I'm a mechanical engineer looking to save money on some bills and tired of feeling bad for all the energy I burn...so figured I'd start by going solar. I bought a 12.5 kW system from a distributor for dirt cheap but could run into some issues with codes. So far I'm here primarily for the reason that I'm trying to figure out exactly what I need to be doing in between making calls to the building department asking them what direction I should be going in. Looking to learn as much as I can from you guys, thanks for having such a great place

[J.P.M.]

I'd respectfully suggest not buying or doing anything else until you get more informed.
Start with a copy of "Solar Power Your Home for Dummies" ~ $25 at bookstores/Amazon, or a slightly outdated free PDF download. I'd suggest reading the parts about energy conservation first.
So, part of what you need to be doing, as a first step, is to get the book and read it.
Then, get familiar w/your local jurisdictional requirements for residential PV, and more importantly the folks who administer and enforce local codes. The permitting people can be like Marines: your best friend or your worst enemy. Call them and tell them what your post here said.
If you're looking to save $$ and assuage your angst about burning energy, get your annual electrical loads in kWh/month/yr. and $ amounts and, even though it sounds like you've put the cart before the horse by buying equipment before knowing what the application is, if cost effectiveness is important to you, decide how much of your electric costs you want to offset w/PV. Think engineering economics of the kind you learned in M.E. school.
BTW, and FWIW only, know that unless you're already a real energy mizer, the best place to start reducing your electric bills is to reduce your usage before displacing some of the electrical load w/ PV. For most folks in the developed world and particularly in the U.S., conservation is a far more cost effective first step than PV and so almost always the first logical step in bill reduction.

Then, get familiar w/PVWatts, a residential PV model for preliminary design. Read all the help/info screens a couple of times, do a few runs and get preliminary sizing.

If, after you read the book and do the above stuff, you come back w/questions that address the gaps in your knowledge opened up by the read/self education and the other items mentioned above, your questions will have more meat on them and you'll get better answers you'll be able to understand. It'll save all of us some time and the knowledge exchange will be more efficient.

You'll find this to be a place with helpful folks, some of whom actually know what they're talking about. Just be a bit skeptical of the answers you get until you fully understand them.

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

[ItsFriz]

Thanks JPM , I really appreciate your suggestions and your willingness to help me out, I know I'm probably one of a thousand different stories like this. Ultimately, after going through all this, I really hope I'm able to serve as a resource for people in my area who want to do the install themselves but don't know what they need to know or how to navigate these unfamiliar waters. Part of the want to DIY this is I've met several installers who are glorified snake oil salesmen who want to sell you anything and everything and it's frustrating that they're still in business.

I did decide to reduce the power of the system to 11.6kW due to the tier 1/tier 2 requirements (in my area they allow a 10kW system is allowed to be oversized by 1.7x to make up for inefficiencies so 11.7 is the cutoff for tier 1/tier 2). The panels I'm using are 385w bifacial and may produce up to 410w with the reverse side gain. I suppose that might need to be considered when going through the electrical...

Have also been talking with the building department, the inspector who'll be in charge, and received a permit/all clear to start but still waiting on records to record the Notice of Commencement so the rough in inspection can be scheduled. I have installed flashing-style mounts but that's as far as I'll be going. One of my concerns is the permit was issued before the building department received any drawings or spec sheets of my components...but they know what they're doing and if anything comes up it's "Yes mister inspector sir, I'll fix it exactly like you said/get that to you right away sir." Like you said for a project like this they are the last person you want to make your enemy.

For the most part I'm pretty stubborn about having more solar than I need because I want some breathing room and intend to have a business out of my home eventually and want the extra electricity for a computer/server, but that's down the line.

Found a pdf copy of the book so I'll be going through that over the next few days. Thanks once again for all the suggestions and looking forward to being a part of all this and being able to help someone in my shoes in the future

[SunEagle]

To ItsFriz and sailnaked6842. You both posted exactly the same. Can you explain why?

[ItsFriz]

Yep, I created the sailnaked acct a few days ago (Tuesday I think?) and didn't see the registration email. Found it yesterday, it had expired, got another reactivation but still wasn't able to post...so made the second account wondering if the first had a problem. Both accts got approved yesterday and the sailnaked acct was still logged in so it posted from that acct. Reposted from Its Friz to eliminate confusion for the others since it would make no sense and tried to delete the first post, but no luck. Tried to send an email to let you know the sailnaked acct could be deleted but couldn't find an email for you or a way to PM. If you want to delete the account and the post that would be great

[J.P.M.]

Thanks JPM , I really appreciate your suggestions and your willingness to help me out, I know I'm probably one of a thousand different stories like this. Ultimately, after going through all this, I really hope I'm able to serve as a resource for people in my area who want to do the install themselves but don't know what they need to know or how to navigate these unfamiliar waters. Part of the want to DIY this is I've met several installers who are glorified snake oil salesmen who want to sell you anything and everything and it's frustrating that they're still in business.

I did decide to reduce the power of the system to 11.6kW due to the tier 1/tier 2 requirements (in my area they allow a 10kW system is allowed to be oversized by 1.7x to make up for inefficiencies so 11.7 is the cutoff for tier 1/tier 2). The panels I'm using are 385w bifacial and may produce up to 410w with the reverse side gain. I suppose that might need to be considered when going through the electrical...

Have also been talking with the building department, the inspector who'll be in charge, and received a permit/all clear to start but still waiting on records to record the Notice of Commencement so the rough in inspection can be scheduled. I have installed flashing-style mounts but that's as far as I'll be going. One of my concerns is the permit was issued before the building department received any drawings or spec sheets of my components...but they know what they're doing and if anything comes up it's "Yes mister inspector sir, I'll fix it exactly like you said/get that to you right away sir." Like you said for a project like this they are the last person you want to make your enemy.

For the most part I'm pretty stubborn about having more solar than I need because I want some breathing room and intend to have a business out of my home eventually and want the extra electricity for a computer/server, but that's down the line.

Found a pdf copy of the book so I'll be going through that over the next few days. Thanks once again for all the suggestions and looking forward to being a part of all this and being able to help someone in my shoes in the future

You're welcome.

Understood. One example of putting the knowledge cart before the horse and also maybe snake oil salespeople: If you are planning on a roof mount with the array(s) with an orientation parallel to the roof they're mounted on with something like a 15 cm. or so stand off from the roof deck, know that because the irradiance at most any time and also the daylong insolation reaching the backside of a panel will be close to zero, for a lot of reasons that's about what you can expect for a production contribution from the backside of a bifacial panel. Ground mounts fare a bit better in terms of backside contribution but because peddlers usually quote specious studies and use circular references and logic as well as using "up to" numbers for backside contribution, I wouldn't count on much from the backside of a panel. They might even hurt overall production a bit by lowering the overall panel's efficiency due to increased operating temps. as a result of a lower overall heat transfer coeff. from the panel to the surroundings.

[Mike90250]

Another DIY gotcha is the Roof Setback for isles for firefighters.
Specifically ask the building department what the setback requirements are (if any) and if you need Rapid Shutdown in your area. Rapid shutdown requirements may alter the electrical plan significantly.

[ItsFriz]

Good info to know, the distributor said close to the same thing, that the panels are better ground mounted due to the irradiance (roof gain would be roughly 5% rather than the 15~30 you could see ground mounted). But that leads me to a question, if any gain is to be had at all with roof mounting a bifacial will it be close to sunrise/sunset or is the panel itself is mildly transparent? But why would the operating temperature of the panel go up if the back side gain is zero? You'd think that relative to a standard panel they'd have the same production since the backside gain is zero? As the sun gets closer to sunset/sunrise I could see where this can become a bit of a differential equation where I certainly don't have enough info. Wanted to paint the roof white but figured that's just too much

[bcroe]

I have not seen any practical explanation of how the bifacial panels can be significantly beneficial. Too
bad because I might have a good ap. But even my original panels are somewhat bifacial, so what?
Bruce Roe

[ItsFriz]

Another DIY gotcha is the Roof Setback for isles for firefighters.
Specifically ask the building department what the setback requirements are (if any) and if you need Rapid Shutdown in your area. Rapid shutdown requirements may alter the electrical plan significantly.

Thanks Mike, according to the codes here it is not allowed to be mounted to an exterior wall or overhang the roof...I'll admit I didn't know about the setback until after I ordered the panels and drew up plans...that would have been a real problem

Rapid shutdown is another issue. I'm NEC 2017 compliant but I think someone has said they wanted an AC disconnect...but that needs to be clarified with the inspector since I believe my inverter shuts down the optimizers if grid voltage goes below a certain threshhold. It's on the list of questions I have for him but I always appreciate input

[J.P.M.]

Good info to know, the distributor said close to the same thing, that the panels are better ground mounted due to the irradiance (roof gain would be roughly 5% rather than the 15~30 you could see ground mounted). But that leads me to a question, if any gain is to be had at all with roof mounting a bifacial will it be close to sunrise/sunset or is the panel itself is mildly transparent? But why would the operating temperature of the panel go up if the back side gain is zero? You'd think that relative to a standard panel they'd have the same production since the backside gain is zero? As the sun gets closer to sunset/sunrise I could see where this can become a bit of a differential equation where I certainly don't have enough info. Wanted to paint the roof white but figured that's just too much

Good questions.

But first, and believe what you want from someone with no skin in the game vs. a distributor, but with/for a roof mount w/common residential application and with ~ 15 cm or less clearance off the roof deck, you'll be lucky to be able to measure any increased production much less 5%.
That 15-30 % number is what he's read in the greenwash media or mfg. phony crap. It's a B.S. statement without the qualifiers that most people wearing rose colored glasses, or conmen leave out because they are either clueless about what they're spouting off about, or are trying to take advantage of the solar ignorance of the person they're trying to sell some something to, or repeating what they read/heard or otherwise acquired to make someone else think they know what they're talking about. Either or any way, it's all B.S. As I suggested in my first post to this thread, be skeptical. (That caveat, BTW, includes what follows below. It's all opinion.)

That distributor's comment might have been more accurate if he'd used 0% instead of 5% gain for a common roof mount. With a ground mount, unless you have a high tilt like > 30 deg. or more, which is usually unlikely in FL, and/or unless you're way off south for an azimuth with a high tilt, and/or you're array is high enough to drive under (like a carport or parking lot PV) and is located over a light colored/concrete surface with no adjoining shade and very light colored and reflective surroundings, you might get 10 % or so enhancement on a very sunny day, but lots less otherwise. A mostly south facing residential ground mount with an at latitude tilt a few feet (like 1m or less maybe) off a grass surface, which is probably a more realistic residential scenario, might get close to 5 % on a sunny day, but I'd kind of doubt it would be that much on an annual basis.

Then there's the consideration of how to mechanically support a bifacial panel using common racking. Common rooftop racking has 2 rails running across the back of a row or in any case rails that are great for support, but also real good at blocking sunlight. Up shot: You may run into some mounting situations and associated costs that may chew into the great deal you got on those panels.

Lots of studies on bifacials. Every one I've seen has dealt with the case of commercial installations or potential applications that use (usually single axis) tracking. None for residential. I'm not surprised. To anyone who has ever looked under an array up close under the midday sun it's a blinding flash of the obvious no brainer that there's hardly enough light under there to see anything at all much less generate power. Maybe that no light factoid has something to do with the dearth of studies for bifacial rooftop arrays. All the "studies" and White paper" stuff from outfits with skin in the came are, IMO only, pretty obviously self serving. The serious academic stuff in the journals and from outfits like NREL are all for commercial size installations and mostly single axis tracking arrays. Even a few (but by no means all) articles from the usually biased greenwash media and solar fanboy outfits say bifacials are great for commercial installs, but not ready for primetime residential at this time.

Can you provide a bit more about the panels you bought ? I'm not a fearmonger by nature but I wonder if you got a "deal" on what might be sloppy seconds or excess left over from some commercial installation. Not a dig at you, but if so, it wouldn't be the first time some peddler took advantage of someone's solar ignorance.

As for gains at sunrise/sunset:
Even with a panel oriented normal to the sun at such times, the irradiance is so low at those times, the times so short, and for short times of the year around the summer solstice for a total of a couple of months or so that it makes little, if any difference in annual output.
Bottom line: For a commonly oriented panel the gains at sunrise/sunset are about nil.
More reasons: For common orientations, the small amount of irradiance on the backside of a panel at such times is much less, that is, approx. as the cos(angle of incidence of beam radiation on the surface) which is usually > 70 deg. or so on the backside of a commonly oriented panel.
Common roof mounted array orientations don't see much of any direct backside irradiation except maybe around the summer solstice and then mostly in the higher latitudes. In FL, you will see even less.
Then there's the increase in reflection of glass as f(incidence angle). At, say 70 deg. A.O.I., even what's called non reflective glass will reflect ~ 40 % of the already small amount of radiation incident upon it, and even less yet as f(wavelength of light) in the shorter wavelengths of light useful for silicon devices such as solar panels.


The cell efficiency of a double sided panel will probably decrease because the operating temp. of the panel will increase.
Reason: Many if not most single face panels have a white backing that serves 2 purposes. First, it reflects some of the irradiance that made it through the cell back to the cell. Second, it serves as a reflector for the backside to help keep panel temps. lower than they otherwise would be for any (small) amount of incident albedo that may get to the backside of a panel.
Bi-facials have a dark back. But in a std. roof mount orientation, because the back side sees little to zero radiant energy from just about anywhere, direct, diffuse reflected, albedo, whatever, , that dark color isn't what causes the potential temp. increase in a bifacial vs. a monofacial panel. (But note that black backed mono panels generally have lower efficiencies than otherwise identical white backed panels).

In the end, what will increase temps. more for a bifacial is the glazing on the back side. It's glass and glass reflects infrared thermal radiation - that's why windows work as well as they do.

Here's the deal: A single face panel usually has poly backing. That poly backing is a lousy insulator. That's good because the back of a panel is one of the two big surfaces (the other is the front side) that lose the heat the panel absorbs from sitting in the sun that doesn't get turned into electricity. Now, put glass over that (back) surface. The panel will now have a lower overall heat transfer coeff. because the added glass is a better insulator than monofacial panel's poly backing. Since the irradiation (solar energy input) is the same for either panel, mono or bifacial, the temp. of the panel with the lower heat trans. coeff. must go up to maintain the energy balance on the panel. Result: To a first approx., a heat/energy balance on the panels will show the bi facial panel will lose less heat per degree of temp. diff. between the surroundings and the panel. That means the bifacial panel/cell temp. must go up to maintain the energy balance on the panel. Higher cell temps. mean lower efficiency. How much ? Run an energy balance on two panels and find out.

Note: That's an approx. based on a heat balance and heat transfer characteristics. As a secondary consideration, if for no other reason that if the panel temp. goes up, the efficiency will drop, more irradiance will go into panel heat generation. That will raise the panel temps even more, but that's not a consideration for this discussion.

At this time I believe the powers that be have not standardized on a method to do an S.T.C. testing on bifacials. I suspect that process is complicated in that most to effectively all of the irradiance on the backside of a mostly equator facing panel will be :
1.) Diffuse
2.) Highly site dependent with respect to direction, intensity and wavelength.
3.) Highly dependent on panel orientation.

Those and other factors will make even meaningful definition of Standard Test Conditions a challenge.

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

[ItsFriz]

I see, that's a lot of information, I hadn't considered the effect the glass back would have. The loss due to temp. increase I suppose could happen but I imagine it's small to negligible.

The panels I bought were CSU-385-MB-AG, were about $170 a piece and came on the original Canadian Solar pallet. Could be commercial left overs, but my guess is they were intended for a residential ground mount system. Either way, the way I saw it is I'd be happy paying what I did for a 385w tier 1 panel - the manufacturer has a good reputation and they're not someone you'll have to worry about going out of business. The roof will be loaded up on panels and should do 11.6 kW so if there's no increase in production from the backside it's alright with me...if I do get some, even better.

[J.P.M.]

I see, that's a lot of information, I hadn't considered the effect the glass back would have. The loss due to temp. increase I suppose could happen but I imagine it's small to negligible.

The panels I bought were CSU-385-MB-AG, were about $170 a piece and came on the original Canadian Solar pallet. Could be commercial left overs, but my guess is they were intended for a residential ground mount system. Either way, the way I saw it is I'd be happy paying what I did for a 385w tier 1 panel - the manufacturer has a good reputation and they're not someone you'll have to worry about going out of business. The roof will be loaded up on panels and should do 11.6 kW so if there's no increase in production from the backside it's alright with me...if I do get some, even better.

Understood. Canadian solar is good stuff. More than a few in my HOA. No bifacials however.

Good luck.

[ItsFriz]

Thanks, I think you mentioned you're in Florida right? I'm installing near Tampa and just got a rough in scheduled for tomorrow and have been trying to figure out what's going to happen since so far it's seemed way too easy. I received an electrical permit (and provided an NOC), was given a clear to start and installed the mounting (they're products that are new to the U.S. market and don't have official PE stamped span tables). The county hasn't requested any documentation on the products I'm using or the 3 PE stamped drawing sets. Are those supposed to be turned in to receive the permit, or do they review them at rough in if you know? Just want to make sure that when the inspector comes he doesn't decide he's never going to let me pass, ya know?

[J.P.M.]

Thanks, I think you mentioned you're in Florida right? I'm installing near Tampa and just got a rough in scheduled for tomorrow and have been trying to figure out what's going to happen since so far it's seemed way too easy. I received an electrical permit (and provided an NOC), was given a clear to start and installed the mounting (they're products that are new to the U.S. market and don't have official PE stamped span tables). The county hasn't requested any documentation on the products I'm using or the 3 PE stamped drawing sets. Are those supposed to be turned in to receive the permit, or do they review them at rough in if you know? Just want to make sure that when the inspector comes he doesn't decide he's never going to let me pass, ya know?

No. I'm ~ 35 miles north of the San Diego airport.

I'm somewhat familiar w/ Tampa/St. Pete area w/ many good friends there (or no longer there), but I'm unfamiliar w/local practice/custom/requirements w/respect to doc. review/inspections.

Seems like you have nothing to lose and lots of potential gain w/ a phone call or 2. If it was me, I'd give them a buzz. Got nothing to lose and potentially a lot to gain.

Somewhat analogous to a deal that seems too good to be true, a project or portion of one that seems too easy probably has something missing that, like the big chunks in a cesspool, will eventually float to the top.