Designing a Grid-Tie PV system. Help please

Hat man
Hat man Registered Users Posts: 6 ✭
in Solar Beginners Corner #1
Ok so I am getting close to installing a grid tied system on my house with the help of a great local electrician. I am in central Virginia lat 38 degrees. I am looking at installing the PV panels on my 5/12 pitch 23deg. Light colored 24ga standing seam roof. Luckily if faces due south with no shading after 9am.

For panels I am leaning toward installing 20 Kyocera KD210GX-LPU 210 watt
flat to the roof. The system will be grid tied with no battery backup.

Here are the questions:

1. Inverter Selection. For inverters I am looking at the Fronious IG 4000 using two strings of ten. The Min Vmp at Max Temp (Vdc) is 215 and the Max Voc at Min temp is 376 for each string.
It seems like a lot of folks on this board think that the Xantrex inverters are better. So I am wondering which one would be best for this size system and also allow for the easiest data monitoring.

2. Roof Mounting. I understand that ventilation under the panels is key to efficiency. I like the look of the SolarMount S5! Clamps but that would put the panels only 2” off the pans which does not seem like enough ventilation. I am thinking of using standard unirac rails attached to 5!u mini clamps with the L feet. I think that this would give me 5-6” of air gap. For maximum ventilation it makes since to mount the panels in portrait format (4 rows so 14’) with the rails going up and down the roof thus creating a stronger air current under the panels. Like this configuration in this article:
http://www.backwoodshome.com/articles2/yago94.html

But I am wondering about the strength of having the rails mounted on top of one seam rather than crossing many seams if they ran perpendicular to the pans. I have very heavy 24 gauge Fabral roofing with 1.5” tall seams.

3. Wiring. The Inverter is 30-35’ from the array. I am debating about running 4 wires from the two strings straight to the inverter vs. having a fused combiner box and just running 2 wires. Lightning is a moderate risk here so I want to put an arrester in. Would I need two with the first option?

Oh my that is a lot of questions. Sorry about that. But any advice would be greatly appreciated.
Thanks
Ryan
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Comments

  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #2
    Re: Designing a Grid-Tie PV system. Help please

    I would suggest a Xantrex GT4.0 , lower cost and more built in options, no external extra disconnect required as they are built in on the GT series

    On mounting, you don't have to use a pre-made solution. I prefer using 2x4 & 2x8 aluminum screen enclosure stock. Comes upto 30ft lengths and is great for making racks and about one quarter the cost. You might have to get a PE to sign off on your plans, but its worth the effort

    Going over a metal roof, you want to get as much distance as you can between the panels and the roof for air flow, the standing seam roofs can burn your hand or cook eggs in even cold weather, that's allot of IR to deal with.

    On your Panel choice, do some searching here on the Evergreen panels, best price per watt and better tolerance that the Kyocera ... you can probably say 3-4K just in this choice alone. The "B" grade are the best bang for the buck, I have a roof full of them and they are the best panels I've used yet ( I have had arrays with Kyocera, Photowatt and Solarex before the Evergreens )
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #3
    Re: Designing a Grid-Tie PV system. Help please

    Regarding inverter choice, I'd have a look at the efficiency ratings as this will directly affect the income from the array (Euro ratings):
    • Xantrex GT: 94.5%
    • Fronius: 93.5%
    • SMA Sunny Boy 95.5%
    • SMA Sunny Boy TL: 96% (only an option if transformless inverters are allowed in your country)

    Some inverters have cheaper monitoring options if you like to upload data to the web or export to spreadsheets etc. I believe the Xantrex's have a lot of this already integrated to a degree, whereas the SMA ancillaries are notoriously expensive.
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  • Hat man
    Hat man Registered Users Posts: 6 ✭
    #4
    Re: Designing a Grid-Tie PV system. Help please

    Thanks for the input Solar Guppy.
    I am not familiar with 2x4 & 2x8 aluminum screen enclosure stock. What does a 30' length typically cost and where does one normally procure such an item? I can see how an inspector might question them but I am all into saving some doah if it is as strong. How do you top mount panels on to them?

    It sounds like as far as the system goes you would recmomend something like 20 evergreen ES-A-210-fa2 in a string feeding a Xantrex GT4.0.
    In what way do the evergreen's have better tolerance that the Kyocera?

    Thanks
    Ryan
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #5
    Re: Designing a Grid-Tie PV system. Help please

    The GT's are higher than 94.5%, not sure where you got that info

    http://www.global-download.schneider-electric.com/852575A6007E5FD3/all/1978D47275851DFE852576930030248C/$File/975-0334-01-01_rev-c.pdf

    Page A-5 is the GT4 is lised as 96% peak, 95.5% CEC rated for the current model

    for SMA http://www.sma.de/en_US/products/grid-tied-inverters/sunny-boy/sunny-boy-3000us-4000us.html

    Its 96.8% peak, 95.5% CEC for the 4000US

    Both are good inverters, the Xantrex is significantly less in price, longer warranty and has built in communications, having said that, either are fine inverters

    Fronius, I would stay away from as there have been issues, search this forum for one example of a dual string that had problems so bad, Fronius gave up and the user had to get inverters from another manufacture
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #6
    Re: Designing a Grid-Tie PV system. Help please

    Around here the aluminum is very common for pool cages and its very strong, light weight and easy to work with using a miter saw.

    I found a place in town that supplies all the contractors, its priced per foot, to mount 40 panels last year for everything, stock / screws / brackets ect was ~1200 dollars. I think I used 12 , 30ft 2x4's

    Its just one suggestion, I had a local PE ( professional engineer ) sign off on my plans for $250.00. The prefabbed stuff is very expensive
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #7
    Re: Designing a Grid-Tie PV system. Help please
    Solar Guppy wrote: »
    The GT's are higher than 94.5%, not sure where you got that info

    Got it from here: http://www.xantrex.com/web/id/178/p/1834/pt/5/product.asp
    As I mentioned all those I listed were the Euro efficiency rating.
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #8
    Re: Designing a Grid-Tie PV system. Help please
    stephendv wrote: »
    Got it from here: http://www.xantrex.com/web/id/178/p/1834/pt/5/product.asp
    As I mentioned all those I listed were the Euro efficiency rating.

    That's for the smallest GT2.8 ( scroll to the bottom ) , not the larger units from your link that have the performance I listed in the previous post
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #9
    Re: Designing a Grid-Tie PV system. Help please
    Solar Guppy wrote: »
    That's for the smallest GT2.8 ( scroll to the bottom ) , not the larger units from your link that have the performance I listed in the previous post

    Aha! my mistake. [18 characters]
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  • Hat man
    Hat man Registered Users Posts: 6 ✭
    #10
    Re: Designing a Grid-Tie PV system. Help please

    So Solar Guppy you have me thinking about switching over to installing Evergreen panels. I am thinking of 20 Evergreen 210 watt ES-A-210-fa(2or3)b panels wired in one string attached to a Xantrex GT4.0 or a SMA Sunnyboy 4000 inverter. Does anyone have any experience with the Evergreen blemished panels and is there any downside to them. They will be on a roof where looks don’t matter but performance and reliability does. I am curious if they will last as long and give as much juice as the first quality panels.

    Also I don't quite understand if I should use the fa2 or fa3 panels.

    I am also curious about the pros and cons of the two inverters.

    Is Evergreen really moving their operations to China?
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #11
    Re: Designing a Grid-Tie PV system. Help please

    hat man,
    the simple answer is a disappointing yes about evergreen having china operations.
    http://www.solarbuzz.com./news/NewsASMA247.htm
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #12
    Re: Designing a Grid-Tie PV system. Help please

    Best bang for the buck is the Evergreen seconds, outstanding performance, I have a roof full of them, its purely some very minor cosmetics, I'd say 95% of the panels I couldn't find even the smallest blemish on.

    Frankly I think its really just a ways for Evergreen to sell more product, very similar to what all manufactures do today, like "dented box" or "factory refurbished" which 99 out of 100 times is really the exact same new stock, just looking for ways to get rid of excess inventory but they can't undersell the normal sales channels, so the claim its off-spec is some way.

    The Evergreen String ribbon is the best cell on the market ( front contact ), I have 2.5 year old array, 5kw that has shown no signed of loss of performance. The ones your looking at are made in either Germany or Massachusetts and the fa2 vs fa3 is the frame color I believe.

    I'm partial to Xantrex, SMA is a top notch brand as well, so which ever meets your needs and price point

    As to China and Solar panels, China will be king in less than 2-3 years, they are investing 100's of Billions, more than every other country combined.
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  • Hat man
    Hat man Registered Users Posts: 6 ✭
    #13
    Re: Designing a Grid-Tie PV system. Help please

    You are right it is the frame color and I was surprised that it seems to affect the ratings.
    the silver fa2 is rated 210 Watt, 11.23 Imp, 18.70 Vmp
    the black fa3 is rated 210 Watt 11.48 Imp, 18.30 Vmp

    If looks don't matter at all which is best for the performance of a string of 20 panels? More volts or more amps?

    Do you give any credit to the whispers that Evergreen might go bankrupt?
    That might affect the warranty a bit.

    Thanks
    Ryan
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #14
    Re: Designing a Grid-Tie PV system. Help please

    At those differences in Vmp/Imp--it does not really matter. The Pmp "Peak" is pretty rounded--so 2% percent difference shift in the exact Pmp=Imp*Vmp should not be even detectable when installed.

    It is probably just rounding error in testing. In theory, a black frame absorbs more heat so you could see a slight Vmp drop--however, you should not see an equal increase in Imp.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #15
    Re: Designing a Grid-Tie PV system. Help please

    There are no guarantees that ANY company will be around next month or next year, let alone 25 years from now, I don't think Evergreen is any worse than half a dozen other manufactures, but that's just an opinion and you have to decide for yourself.

    I owned photowatts that ending up having some issues interconnection failures and the company is gone, a soldering iron corrected the issues and all Si PV panels the only failure is bypass diodes or cell interconnection, both can be user fixed if the need would arise. I have 70 Evergreen on my roof, not a single issue and 30 are over 2.5 years old now, the other 40 I put up 9 months ago.

    The technology of string ribbon is the most efficient and lowest cost way to manufacture Silicon PV cells, so as long as there Si based PV, I don't see that technology disappearing
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  • Hat man
    Hat man Registered Users Posts: 6 ✭
    #16
    Re: Designing a Grid-Tie PV system. Help please

    Ok so we are nearing taking the plunge. Thanks to the good input on this forum the design has totally changed. We will be installing 20 Evergreen Evergreen ES-A-210-fa3b panels wired in one string with a SMA Sunny boy 4000US inverter. The question that I have now is about wiring as I am getting conflicting advice.

    Do I need a fused combiner box on the roof for a single string of panels?

    The panels will be wired in one long string and it is a 30 ft run through the attic to make it to the inverter which will be mounted on an outside wall on the opposite side of the house. Can I just use 10ga MC-4 cable run through matalic liquidtight conduit and plug the MC-4 ends into either end of the panel string on the roof? This seams much cleaner, cheaper and faster to install. My understanding is that the Sunnyboy 4000 has both a DC disconnect and fuses for the incoming DC wire.

    Thanks!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,631 admin
    #17
    Re: Designing a Grid-Tie PV system. Help please

    As far as I know--there is no regulatory or safety need to fuse/breaker your incoming strings as long as there is only one or two parallel connections.

    Three or more parallel connected strings--you need fusing/breaker for each string.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #18
    Re: Designing a Grid-Tie PV system. Help please

    The Xantrex GT4.0 has built-in disconnect as well. The run through the house needs to be emt
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  • a0128958
    a0128958 Solar Expert Posts: 316 ✭✭✭
    #19
    Re: Designing a Grid-Tie PV system. Help please
    Hat man wrote: »
    ...Can I just use 10ga MC-4 cable run through matalic liquidtight conduit and plug the MC-4 ends into either end of the panel string on the roof?...

    Is it OK (NEC) to run USE-2 through EMT inside a structure?

    Thanks.

    Best regards,

    Bill
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  • FreeWatts
    FreeWatts Registered Users Posts: 14 ✭
    #20
    Re: Designing a Grid-Tie PV system. Help please

    USE-2 is an outdoor wire and may need to be de-rated if used in EMT conduit.
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  • Hat man
    Hat man Registered Users Posts: 6 ✭
    #21
    Re: Designing a Grid-Tie PV system. Help please

    Does that mean that running 25' of USE-2 10ga wire through the attic in metalic conduit to the inverter will work? The attic max temp is about 120 degrees.

    Or should I use a roof mounted pass-through box and switch to THWN-2 wire? It would naturally be faster, easier and cheaper not to use the pass through box or a combiner box but to slip the wire into conduit and run it straight to the SMA 4000 inverter
    Ryan
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