DIY grid-tie roof mount in Tucson . . . some first-order questions

[TucsonMCM]

I'm in the planning stages for a ~ 4kW system on my roof in NE Tucson. I've got a few initial questions, and I'm sure I'll have more as things progress.

Personal background: I have an MSEE, have done a small 12V/230Ah solar system on a Sprinter, have a decent amount of experience w/ mechanical work (competent TIG welder, woodworker, bike mechanic, etc). Worked in hardware stores in high school, worked at a nuclear plant in college, and have dealt w/ modest electrical work during remodels, so am not naive about electric power, but much of the detail of a grid-tie install will be new to me. Comfortable w/ DIY and lean toward professional approaches versus hacks. Early retired, so view this work as productive stimulation, the $$ saviings is nice, but not the dominant motivation.

System: pretty modest ~4kW scale system, so 12 or so panels, intend to use Enphase microinverters and Ironridge racking, REC315 is tentative module choice but still shopping, roof is low-slope (~ 1:12) and will likely use tilt legs. Coincidentally, its also time to re-coat the white elastomeric on my roof, so I'd like to get the bases/feet figured out pretty soon, so I can install them before doing the re-coat.

Power company is TEP and they have an annual revision to the export price on residential solar. That occurs Oct. 1 and will almost certainly drop 10%. The rate at the time of your application is locked in for 10 years. My point here is that I need to get my application into TEP asap, which requires system line drawings and other details. Ideally in the next 15-30 days, so I can avoid any last-minute details delaying my application and forcing me into a lower export rate.

Blah, blah, blah . . . my immediate questions:

1) Design service recommendations. Given the urgency of my TPE application, I think that a design service would be worth the money. I've seen various companies online that will provide the drawings, stickers, etc needed for permits and utility applications; you input the components and site info. $250-300 seems the lowest from reputable providers for this largely hands-off, low/no support approach. Even better would be a local design service that could provide marginally more service: feedback on the initial system specs, guidance about regional gotchas, etc.
Can anyone recommend an AZ based design service? Ideally Tucson, or at least aware of TEP reqs if not in Tucson.
Any first-person experiences w/ other (non-AZ) providers of this type of service?

2) Material suppliers. Can anyone recommend low cost vendors for primary components? I want to get the panels and racking in AZ, so I can avoid freight costs. I get to PHX and Flagstaff periodically, and can easily fit panels and rails in my Sprinter. I'm considering Northern Arizona Wind/Solar, pricing seems OK. CEDGreentech in PHX quoted me better pricing on the Ironridge products, and about the same on Enphase. Where else should I be looking at? Happy to go further afield for the smaller components (Enphase, etc) since shipping $$ is modest.

3) Regional guidance. Anyone local that wants of offer tips, please do so. Familiarity w/ the TEP applications, Pima County permitting, system trade-offs at our latitude, things you would have done different . . . everything is welcome.

[nwdiver]

I'm in the planning stages for a ~ 4kW system on my roof in NE Tucson. I've got a few initial questions, and I'm sure I'll have more as things progress.

Personal background: I have an MSEE, have done a small 12V/230Ah solar system on a Sprinter, have a decent amount of experience w/ mechanical work (competent TIG welder, woodworker, bike mechanic, etc). Worked in hardware stores in high school, worked at a nuclear plant in college, and have dealt w/ modest electrical work during remodels, so am not naive about electric power, but much of the detail of a grid-tie install will be new to me. Comfortable w/ DIY and lean toward professional approaches versus hacks. Early retired, so view this work as productive stimulation, the $$ saviings is nice, but not the dominant motivation.

System: pretty modest ~4kW scale system, so 12 or so panels, intend to use Enphase microinverters and Ironridge racking, REC315 is tentative module choice but still shopping, roof is low-slope (~ 1:12) and will likely use tilt legs. Coincidentally, its also time to re-coat the white elastomeric on my roof, so I'd like to get the bases/feet figured out pretty soon, so I can install them before doing the re-coat.

Power company is TEP and they have an annual revision to the export price on residential solar. That occurs Oct. 1 and will almost certainly drop 10%. The rate at the time of your application is locked in for 10 years. My point here is that I need to get my application into TEP asap, which requires system line drawings and other details. Ideally in the next 15-30 days, so I can avoid any last-minute details delaying my application and forcing me into a lower export rate.

Blah, blah, blah . . . my immediate questions:

1) Design service recommendations. Given the urgency of my TPE application, I think that a design service would be worth the money. I've seen various companies online that will provide the drawings, stickers, etc needed for permits and utility applications; you input the components and site info. $250-300 seems the lowest from reputable providers for this largely hands-off, low/no support approach. Even better would be a local design service that could provide marginally more service: feedback on the initial system specs, guidance about regional gotchas, etc.
Can anyone recommend an AZ based design service? Ideally Tucson, or at least aware of TEP reqs if not in Tucson.
Any first-person experiences w/ other (non-AZ) providers of this type of service?

2) Material suppliers. Can anyone recommend low cost vendors for primary components? I want to get the panels and racking in AZ, so I can avoid freight costs. I get to PHX and Flagstaff periodically, and can easily fit panels and rails in my Sprinter. I'm considering Northern Arizona Wind/Solar, pricing seems OK. CEDGreentech in PHX quoted me better pricing on the Ironridge products, and about the same on Enphase. Where else should I be looking at? Happy to go further afield for the smaller components (Enphase, etc) since shipping $$ is modest.

3) Regional guidance. Anyone local that wants of offer tips, please do so. Familiarity w/ the TEP applications, City of Tucson permitting, system trade-offs at our latitude, things you would have done different . . . everything is welcome.

Arizona wind and sun is in Flagstaff; Why the preference for Enphase if you want a cost effective system? With SMA you can get 10% more energy for ~15% less cost.

[Mike90250]

1: if you need rapid shutdown, there are alternatives to enphase
2: will you need an engineer to survey your roof for load bearing requirements? (does city require it)
3: Main electrical panel, will it work as is, or do you need an upgrade or line taps ?

[TucsonMCM]

1: if you need rapid shutdown, there are alternatives to enphase
2: will you need an engineer to survey your roof for load bearing requirements? (does city require it)
3: Main electrical panel, will it work as is, or do you need an upgrade or line taps ?

1) details like this (rapid shutdown) are where I can use some guidance. I can't find a coherent, centralized description of the requirements. UL-1703 for the panels and UL-1741 for the inverters are mentioned. Disconnect requiremenets are described but I don't see "rapid" anywhere. I'm not even clear (yet) on what rev of NEC applies. Is the applicable NEC the determining document for rapid shutdown?
2) I believe I'm OK here. My rafter size and spacing is pretty standard. Pima County waives structural calculations if you meet a prescriptive requirement (generally, min one connection per 10sf of equip, and min seperation between connections based on lbs of point load). The size and mass and racking of my array are all well within that prescription.
3) I think I'm good to go here. I have a 200A main panel, which was an upgrade circa ~2005 when a new AC unit was installed. Its conveniently placed under a large overhang, near one edge of the intended array placement. There are a total of 140A of load breakers on the 200A service. I had one installer give me a quote before I settled on DIY, and they acted "happy" w/ the main panel and didn't include any upgrades or mods in their quote. If I understand the 120% rule, then an array of my size will clearly fit. All that said, I would welcome more guidance on details of the grid-tie connection. TEP (my power co) provides a meter/socket for residential solr customers and they have several example interconnect schematics.

[TucsonMCM]

Arizona wind and sun is in Flagstaff; Why the preference for Enphase if you want a cost effective system? With SMA you can get 10% more energy for ~15% less cost.

I've been looking at AW&S, and may well buy my panels there. But their prices are high on Ironridge rails, and they don't stock the size/color I prefer or the flat roof mount (= ridiculous "broken case" fees). So am leaning to CEDGreentech in Phoenix for the Ironridge materials (although, bizzarely, they want to apply sales tax. When I mentioned the AZ exemption for retail sale of solar equipment they literally said "that's not true").

By "SMA" I assume you mean a string inverter, (my perception is SMA killed their microinverter product line)? Why would a string inverter yield 10% more energy? I understand the cost trade-offs, but w/o optimizers I would expect a string inverter to yield less, and with optimizers to yield approx the same as microinverters, no?

[nwdiver]

By "SMA" I assume you mean a string inverter, (my perception is SMA killed their microinverter product line)? Why would a string inverter yield 10% more energy? I understand the cost trade-offs, but w/o optimizers I would expect a string inverter to yield less, and with optimizers to yield approx the same as microinverters, no?

~10% more kWh for ~15% less $. Instead of a 5kW system with micro inverters you can get a 5.5kW system with a string inverter 15% cheaper.

Micro Inverters are generally NOT more efficient. That's a myth perpetuated by Enphase. I've installed optimized systems and string inverters. There's ~no difference in annual production.

[TucsonMCM]

~10% more kWh for ~15% less $. Instead of a 5kW system with micro inverters you can get a 5.5kW system with a string inverter 15% cheaper.

Ah, OK, the +10% power is from ~ +10% in modules. So system economics not output efficiency per se.

I acknowledge this is the case, but doesn't this advantage diminish on lower power systems, since the inverter pricing ($/watt) is non-linear?
Also, my perception (correct me if I'm wrong) is a string inverter has a shorter lifetime than contemporary microinverters. Nominally one might expect a ~ 12 year life on a string inverter, while one might replace one or two of a dozen microinverters in 25 years? The warranties (10 year vs 25 year) sort of track this. So the total inverter cost over 25 years might be $1750 for micros (12x$125 original + 2x$125 replacement) versus $2200 for string ($1100 original + $1100 replacement). That ignores the possibility that the microinverter replacements are warranty/free.

I'm not necessarily an Enphase fanboy, and I'm open to alternatives. I admit there is an elegance to a microinverter approach which I do appreciate (and therefore value w/ $$). But def interested in calibrating my relatively newbie perceptions re: the trade-offs..

[nwdiver]

Ah, OK, the +10% power is from ~ +10% in modules. So system economics not output efficiency per se.

I acknowledge this is the case, but doesn't this advantage diminish on lower power systems, since the inverter pricing ($/watt) is non-linear?
Also, my perception (correct me if I'm wrong) is a string inverter has a shorter lifetime than contemporary microinverters. Nominally one might expect a ~ 12 year life on a string inverter, while one might replace one or two of a dozen microinverters in 25 years? The warranties (10 year vs 25 year) sort of track this. So the total inverter cost over 25 years might be $1750 for micros (12x$125 original + 2x$125 replacement) versus $2200 for string ($1100 original + $1100 replacement). That ignores the possibility that the microinverter replacements are warranty/free.

I'm not necessarily an Enphase fanboy, and I'm open to alternatives. I admit there is an elegance to a microinverter approach which I do appreciate (and therefore value w/ $$). But def interested in calibrating my relatively newbie perceptions re: the trade-offs..

The MTBF (mean time between failure) is unlikely to be significantly better for a micro inverter. Heat is the enemy of electronics... it's A LOT hotter under a solar panel than anywhere you install a string inverter. The 25 yr warranty is more a marketing requirement for Enphase. They wouldn't sell if you had to re-rack an array every ~10 years so the inverters really needed to match the panels.

You can also purchase an extended warranty out to 20 years for most string inverters if that's a concern. But given the progress of the technology and the time-value of $$$ I would just put the ~$300 it costs in an ETF and buy a new inverter when/if the old one fails in 15 years

[bcroe]

Just why you think micro inverters are more reliable, I do not understand. The wiring to
connect them will be considerably more expensive and failure prone. They do improve
on a situation of changing shade, perhaps the elegant thing about them is they are
no brain installation. For those with... Bruce Roe

[solarix]

I use CED greentech and SMA inverters with TIGO TS4-R-F modules to deal with the Rapid Shutdown b.s.

[TucsonMCM]

Not a lot of microinverter fans here, eh?

I've got some modest shade issues in my situation (neighbors trees) that may get marginally worse or better, depending on what they do w/ one off the trees. But for the sake of comparison, lets assume that I would use optimizers if I went w/ a string inverter. Its worth noting that a legit installer (Technicians for Sustainability here in Tucson) included optimizers on both their string inverter proposals.

Is the "microinverters cost more" mantra really true on smaller systems? The optimizers I've seen run $70-ish while an Enphase IQ7 is $125-ish. Assuming my system is 12 panels, that's a $660 delta in those components, I can't buy a 3000W inverter for $660. I'm ignoring lots of details in cabling, monitoring, etc which could add up. But on the primary components, it seems like micros can be competive.

And yes, they are easier to design with. Despite @bcroe's passive-aggressive insult to my intelligence, ease of design and install is a benefit regardless of your capabiities. I can TIG weld a bike frame reasonably well, but does that mean I'm stupid to buy a mass produced one that cost more than raw tubes?

[J.P.M.]

Not a lot of microinverter fans here, eh?

I've got some modest shade issues in my situation (neighbors trees) that may get marginally worse or better, depending on what they do w/ one off the trees. But for the sake of comparison, lets assume that I would use optimizers if I went w/ a string inverter. Its worth noting that a legit installer (Technicians for Sustainability here in Tucson) included optimizers on both their string inverter proposals.

Is the "microinverters cost more" mantra really true on smaller systems? The optimizers I've seen run $70-ish while an Enphase IQ7 is $125-ish. Assuming my system is 12 panels, that's a $660 delta in those components, I can't buy a 3000W inverter for $660. I'm ignoring lots of details in cabling, monitoring, etc which could add up. But on the primary components, it seems like micros can be competive.

And yes, they are easier to design with. Despite @bcroe's passive-aggressive insult to my intelligence, ease of design and install is a benefit regardless of your capabiities. I can TIG weld a bike frame reasonably well, but does that mean I'm stupid to buy a mass produced one that cost more than raw tubes?

The idea is that things with fewer points of failure will probably fail less and so have a statistically lower probability of failure. That's usually abbreviated to the KISS principle.

Additionally, string inverters can usually be located in cooler places, like a garage. that not only makes things better for the electronics but makes them easier to get at.

Being on a roof, attached to a dark colored colored object sitting in the sun is not the best environment to expect a long service life for stuff that doesn't usually like heat. Id expect that to be particularly true in Tucson.

BTW, be sure to leave room in the design layout or at least a way to get at all the micros if/when they begin to fail.

I can't speak for Bruce, but it looks (reads) to me like he wasn't insulting your intelligence as much as trying to reduce your ignorance and increase your awareness about some of the potential drawbacks of micros that a lot of the smart money and experience knows about and that the peddlers and advert hype seems to leave out.

Micros may seem easier to design with to you. I'd suggest they have some inherent limitations that make it more difficult to design a better and more fit for purpose system with them. About the only real advantage they seem to have is they handle shade better than string inverters. If I had an application with that much shade, I'd wonder about and research the economic viability of the project before I spent much time and money on it.

I used to design weldments and write welding WPS's and PQR's and before that I used to be qualified on various weld procedures, but I'm not sure that does much to influence my opinions about microinverters or other heat sensitive electronics in mostly hot and often inaccessible places and in unnecessary designed-in redundance.

You wrote that you wanted advice.

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

[nwdiver]

Not a lot of microinverter fans here, eh?

I've got some modest shade issues in my situation (neighbors trees) that may get marginally worse or better, depending on what they do w/ one off the trees. But for the sake of comparison, lets assume that I would use optimizers if I went w/ a string inverter. Its worth noting that a legit installer (Technicians for Sustainability here in Tucson) included optimizers on both their string inverter proposals.

Is the "microinverters cost more" mantra really true on smaller systems? The optimizers I've seen run $70-ish while an Enphase IQ7 is $125-ish. Assuming my system is 12 panels, that's a $660 delta in those components, I can't buy a 3000W inverter for $660. I'm ignoring lots of details in cabling, monitoring, etc which could add up. But on the primary components, it seems like micros can be competive.

And yes, they are easier to design with. Despite @bcroe's passive-aggressive insult to my intelligence, ease of design and install is a benefit regardless of your capabiities. I can TIG weld a bike frame reasonably well, but does that mean I'm stupid to buy a mass produced one that cost more than raw tubes?

Modern String inverters also handle shade for the most part just as well as micros or optimizers. You can get a 3kW string inverter for ~$900 that also includes wifi monitoring. 3kW of Enphase IQ7s might cost ~$1125-ish but then you need to buy the proprietary trunk cable at ~$25 per panel then if you want monitoring that's another ~$400. So you'll end up paying ~50% more for micro inverters vs a string inverter for ~no tangible benefit aside from the real estate saving on a wall somewhere.

My distain for micro inverters is mostly due to the fact that they cost more for ~no return. Plus their existence is mostly due to electricians not wanting to put in the effort to learn about series-parallel DC circuits. Tiny AC inverters cost more but they were more comfortable with AC so that's what they bought....

[foo1bar]

1) details like this (rapid shutdown) are where I can use some guidance. I can't find a coherent, centralized description of the requirements. UL-1703 for the panels and UL-1741 for the inverters are mentioned. Disconnect requiremenets are described but I don't see "rapid" anywhere. I'm not even clear (yet) on what rev of NEC applies. Is the applicable NEC the determining document for rapid shutdown?

Rapid shutdown is described in 690.12 of 2017 NEC (Tucson I *believe* is using 2017 NEC - based on a very quick web search - do your own confirmation of that)

Each of the inverter manufacturers are going to have a thing about how their system is (or can be) rapid shutdown compliant.
ex:
https://www.sma-america.com/newsroom...lications.htmlhttps://www.sma-america.com/newsroom...lications.html
from searching "site:sma-america.com rapid shutdown"

Probably a supply house doing "kits" will help with supplying you the right equipment to do rapid shutdown.

I went with Solaredge system (partial shading, multiple orientations) and although I didn't need rapid shutdown (earlier NEC version) I know it does rapid shutdown because that was one of it's selling points.

3) I think I'm good to go here. I have a 200A main panel, which was an upgrade circa ~2005 when a new AC unit was installed. Its conveniently placed under a large overhang, near one edge of the intended array placement. There are a total of 140A of load breakers on the 200A service. I had one installer give me a quote before I settled on DIY, and they acted "happy" w/ the main panel and didn't include any upgrades or mods in their quote. If I understand the 120% rule, then an array of my size will clearly fit.

It really really depends on how your main panel is setup. IMO a few diagrams (and potentially some pictures) can communicate a lot more than words.
The 120% rule says that if you have a 200A main breaker and a 200A bus for that breaker you can put a 40A breaker at the far end (200A * 1.2 - 200A = 40A)
IF it's a 225A bus, then that equation is 225A * 1.2 - 200A = 70A.

You may not even need to look at the 120% rule though.
If it's a 200A main breaker and 200A bus - and 140A of load you can possibly add a 60A backfeed breaker... Under older NEC I think it was 705.12(D)(2)(3)(c) – Sum of inverter and load OCPDs.
I don't see that in 2017 NEC though.... Ah - I think it may now be NEC 705.12(B)(2)(3)(c) in 2017 NEC. (with a requirement for a warning label)
nfpa.org has free access to the 2017 NEC (and other versions)


Of course you also potentially could use 120% rule in that situation and downsize the main breaker - so 150A main with 200A bus = 200A * 1.2 - 150A = 90A max backfeed. Swapping out a main breaker is serious matter though.... I'd triple check that I'd torqued that thing correctly.

Really - a lot of possible options you have for the backfeed - but I'm making a LOT of guesses about what you have and my guesses are probably wrong.

[foo1bar]

Modern String inverters also handle shade for the most part just as well as micros or optimizers.

My guess is string inverters are likely to be a few percent worse in many partial shading situations. And probably just as good or maybe better in a few specific cases of partial shading.
I think the cost savings (probably) are more than that few percent.
Except when you add in rapid shutdown requirements, I think the cost savings isn't nearly as much.
But I haven't priced things out lately.

For OP's situation I don't know how things would price out between Enphase, Solaredge and SMA w/ rapid shutdown...
The cost of the propietary cable (and my desire for less electronics on the roof) pushed me to solaredge over enphase for my system, but prices change - and my system was bigger.

My distain for micro inverters is mostly due to the fact that they cost more for ~no return. Plus their existence is mostly due to electricians not wanting to put in the effort to learn about series-parallel DC circuits.

If I had wanted to do an SMA system, I believe I would have had less production due to 3+ orientations and shading. For me, enphase was the most expensive option. Solaredge was more expensive than SMA - but gave me per-panel information, and I believe handles multiple orientations and shading better.

Per-panel info is not a huge benefit at the end of the day. IMO it's not nearly as beneficial as the salesman will hype it up. But it is fun. And on a commercial (church) installation it helped me identify that the installers screwed up, not connecting 2 of the >100 panels