Amateur doing a 10kw system, can someone tell me if I missed anything

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  • WhittakerJ
    WhittakerJ Solar Expert Posts: 67 ✭✭
    #32
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    solar_dave wrote: »
    Central inverter in backyard and micro inverters on the roof, It may require a AC combiner to make a single connection the load center, it is a question for the AHJ as to what is acceptable.

    I just ran the Emphase compatibility check for my Trina TSM-275PA14 and they are not compatible...
    This being said what would you guys recommend since I can no longer do micro-inverters? Should I purchase a second central inverter? Is it worth the cost? Or just simply tie it into the Fronius one in a manner which will not be optimal?
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #33
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    WhittakerJ wrote: »
    Thanks Dave, so then my AC run would be about 108' from the inverter to the AC box. That would not be a problem?
    Lilkewise I would installer a combiner box on my air conditioner for the 6 micro-inverters and then run one 240v line down to a breaker/combiner box about 80 ft total to the electric box. Is this going to be ok?

    Couple of other questions. I live in Mesa, AZ. I'm not sure who my AHJ is. Does anyone know what:
    Breaker sizes would need to be for the two AC runs?
    Cable gauge?
    Length to bury 240v run from rear of house?
    Acceptable conduit?

    Mesa I heard was like no permit required for solar, call the building department.
    Not so lucky up in Glendale. They also required a AC disconnect accessible to the street. APS required a separate meter to measure the solar output, asking for a reading once a year.
    APS or SRP for the interconnect?
    I didn't bury any conduit, just ran it down the side of the house, but mine was pretty close.

    I have 2 central inverters that join the AC output in the combiner pictured. Each has to 30 amp breaker with the box connected to a 60 amp in the main panel. What is the rating on your main panel? You are in derate main breaker territory with that much solar on a 200 amp load-center.

    Cable gauge is dictated by the attached device(s) ratings as are the breaker ratings.

    edit
    I am betting that connecting to the AC circuit won't fly.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #34
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything

    The "on roof" array is very small for a central GTI of its own. SMA makes a 2kW unit @ about $2,000. Do you think it's worth it? http://www.solar-electric.com/smasuboy2020.html

    Perhaps in companion to an 8kW SMA for the main array: http://www.solar-electric.com/smasuboy8080.html

    You can't just guess at wiring sizes and fuses/breakers. You need to know what the actually configuration of the array will be in terms of Voltage and current. If the 'main array' is, for example, thirty-two 250 Watt panels and each has a Vmp of 30 and Imp of 8 you can make it up in several different ways. The first thing you'd look at is the right Voltage to supply whatever GTI is chosen. It could be strings of eight in series, but that would be 240 Vmp; would the inverter run at that?

    More likely it would require ten in series for 300 Volts, and that would mean three strings in parallel - and two panels that don't fit in. The inverter might accept two parallel strings of 16 (480 Volts), but the Voc would then likely exceed input maximum.

    You have to try some different configurations and see which work with which inverter's input range. Write them all down, use a V-drop calculator to determine what wire size would be needed and what losses would be incurred, and check the cost on the calculation.

    This is not going to be an easy design.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #35
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything

    I am with coot on this, not easy, one thing to make it a bit simpler would be to take the main array and the roof array and run the wiring thru your attic, it would save a lot of trenching. The micro-inverter circuit is pretty simple, a 15amp AC setup should suffice. If there was a place to locate the central inverter close to the array then the 240 AC run is a single line.
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  • WhittakerJ
    WhittakerJ Solar Expert Posts: 67 ✭✭
    #36
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    solar_dave wrote: »
    I am with coot on this, not easy, one thing to make it a bit simpler would be to take the main array and the roof array and run the wiring thru your attic, it would save a lot of trenching. The micro-inverter circuit is pretty simple, a 15amp AC setup should suffice. If there was a place to locate the central inverter close to the array then the 240 AC run is a single line.

    I could definitely take the main array and run it 20ft to my house then up the wall and into my attic. The problem with this is it adds about 40ft of extra wiring as I have to run up and down the walls. I don't think I necessarily have to trench the entire way. Once I reach my house I'm sure I can do conduit and tuck it where my concrete meets the bottom of my stucco.

    There is no permit required in the city of Mesa.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #37
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything

    Just saying, I guess you could do a DC combiner at the array and run a single set of DC lines to the Frontius. I see these mounted outside all the time, any reason for inside the garage?

    You will need to know your string combinations to determine the DC wire size and fusing required.
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  • WhittakerJ
    WhittakerJ Solar Expert Posts: 67 ✭✭
    #38
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    Cariboocoot wrote: »
    The "on roof" array is very small for a central GTI of its own. SMA makes a 2kW unit @ about $2,000. Do you think it's worth it? http://www.solar-electric.com/smasuboy2020.html

    Perhaps in companion to an 8kW SMA for the main array: http://www.solar-electric.com/smasuboy8080.html

    You can't just guess at wiring sizes and fuses/breakers. You need to know what the actually configuration of the array will be in terms of Voltage and current. If the 'main array' is, for example, thirty-two 250 Watt panels and each has a Vmp of 30 and Imp of 8 you can make it up in several different ways. The first thing you'd look at is the right Voltage to supply whatever GTI is chosen. It could be strings of eight in series, but that would be 240 Vmp; would the inverter run at that?

    More likely it would require ten in series for 300 Volts, and that would mean three strings in parallel - and two panels that don't fit in. The inverter might accept two parallel strings of 16 (480 Volts), but the Voc would then likely exceed input maximum.

    You have to try some different configurations and see which work with which inverter's input range. Write them all down, use a V-drop calculator to determine what wire size would be needed and what losses would be incurred, and check the cost on the calculation.

    This is not going to be an easy design.

    Yea doing 2 grid-tie inverters is pretty expensive. Although if you guys are indicating it is not good to tie in the 6 on the roof with the main array I'm not sure what other options I would have. I suppose I could try to fit 9 panels on the roof, change my ground mount to 27 panels, and then put this all on one central inverter. At least the roof at this point would be on its own string. I could move the inverter to the rear of my property. This would give me about 20' to the main array and about 20' to my 9 panels on my roof. Then from the rear run one AC 240v line to the electric box in the front. What are your thoughts on this?
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  • WhittakerJ
    WhittakerJ Solar Expert Posts: 67 ✭✭
    #39
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    solar_dave wrote: »
    Mesa I heard was like no permit required for solar, call the building department.
    Not so lucky up in Glendale. They also required a AC disconnect accessible to the street. APS required a separate meter to measure the solar output, asking for a reading once a year.
    APS or SRP for the interconnect?
    I didn't bury any conduit, just ran it down the side of the house, but mine was pretty close.

    I have 2 central inverters that join the AC output in the combiner pictured. Each has to 30 amp breaker with the box connected to a 60 amp in the main panel. What is the rating on your main panel? You are in derate main breaker territory with that much solar on a 200 amp load-center.

    Cable gauge is dictated by the attached device(s) ratings as are the breaker ratings.

    edit
    I am betting that connecting to the AC circuit won't fly.


    My main breaker is 200a. How do I calculate if I'm entering derate main breaker territory?

    Attachment not found.
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  • WhittakerJ
    WhittakerJ Solar Expert Posts: 67 ✭✭
    #40
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    solar_dave wrote: »
    Just saying, I guess you could do a DC combiner at the array and run a single set of DC lines to the Frontius. I see these mounted outside all the time, any reason for inside the garage?

    You will need to know your string combinations to determine the DC wire size and fusing required.

    No I just figured if I had to run towards the front of my house anyways why not put it in the comfort of my garage. I can definitely mount it on my house. It would just have to be in the rear because I would want it being my block wall as I would not want it just sitting on the side of my house facing the street given its cost.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #41
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    WhittakerJ wrote: »
    My main breaker is 200a. How do I calculate if I'm entering derate main breaker territory?

    Attachment not found.

    Your back-feed breaker is limited to the main breaker + 20% of the main breaker total max (it is actually the buss bar rating but you need any thing different in writing from the manufacturer). This is the amount of incoming power a typical 200 amp panel can take. So you max back-feed breaker without derate is 40 amps, add some for the NEC safety factor and 10K watts of panels puts you over the 40 amps. You can change the main breaker to a smaller size, like 175 amps if the amount of loads are OK with that. Then it is 40 amps + 25 amps, for a 65 amp total back-feed.

    Edit what is the max AC out on the Frontius?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #42
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything

    The problem with having the array divided into two locations (providing Voltages can be met from both) is that you would have 10kW total array, but it would not all produce at peak at the same time. In an extreme case you'd have a 10kW inverter putting out 8kW sometimes and 2kW other times, depending on which array was getting best insolation. Kind of a waste of a 10kW inverter.

    You can also run some checks with PV Watts and see what sort of output to expect from each. It may not be worthwhile to have the 2kW on the roof at all if it's going to be too much trouble to wire up.

    Shame about the panels not being suitable for the micro-inverters. It does sort of point out why it's a good idea to do a design before buying anything, and then select the components that best suit. Sometimes those bargains aren't such a bargain.
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  • WhittakerJ
    WhittakerJ Solar Expert Posts: 67 ✭✭
    #43
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    solar_dave wrote: »
    Your back-feed breaker is limited to the main breaker + 20% of the main breaker total max (it is actually the buss bar rating but you need any thing different in writing from the manufacturer). This is the amount of incoming power a typical 200 amp panel can take. So you max back-feed breaker without derate is 40 amps, add some for the NEC safety factor and 10K watts of panels puts you over the 40 amps. You can change the main breaker to a smaller size, like 175 amps if the amount of loads are OK with that. Then it is 40 amps + 25 amps, for a 65 amp total back-feed.

    Edit what is the max AC out on the Frontius?

    The Fronius specs are here - http://www.fronius.com/cps/rde/xchg/SID-44294943-657D3819/fronius_usa/hs.xsl/2714_1483.htm

    Fronius IG Plus V 10.0-1

    I'm honestly not sure which number you're asking for.

    I haven't bought the inverter yet. So if that is the issue I have no problem going with one that will work...
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #44
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything

    Max continuous output = 41.7 Amps. Yep over the limit for sure, for just the inverter you will need like a 50 amp back-feed breaker to meet code.

    Perhaps you should scale back a bit to a 8kW inverter, that would squeak under I bet. With 8250 watts of panels that should be OK. remember that will not account for the roof mounted panels.
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  • WhittakerJ
    WhittakerJ Solar Expert Posts: 67 ✭✭
    #45
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    solar_dave wrote: »
    Max continuous output = 41.7 Amps. Yep over the limit for sure, for just the inverter you will need like a 50 amp back-feed breaker to meet code.

    Perhaps you should scale back a bit to a 8kW inverter, that would squeak under I bet. With 8250 watts of panels that should be OK. remember that will not account for the roof mounted panels.


    So you're saying from looking at my electric box that a 60A breaker would not be supported? How do you figure out those numbers? I know you explained it before I'm just trying to comprehend it.
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  • WhittakerJ
    WhittakerJ Solar Expert Posts: 67 ✭✭
    #46
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    WhittakerJ wrote: »
    So you're saying from looking at my electric box that a 60A breaker would not be supported? How do you figure out those numbers? I know you explained it before I'm just trying to comprehend it.

    Also, if this is a limitation of my electric box. Could I potentially do 2 5kw inverters or a different configuration? What is the max amperage my electric box will support?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #47
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    WhittakerJ wrote: »
    So you're saying from looking at my electric box that a 60A breaker would not be supported? How do you figure out those numbers? I know you explained it before I'm just trying to comprehend it.

    It's based on the current rating of the bars in the service panels. The "120%" rule allows a 100 Amp service to be back-fed 20 Amps, 40 Amps on a 200 Amp service, et cetera. There are some 'adjustments' that can be made sometimes such as putting in a smaller main breaker, but that option is not always available.

    It is looking like the most practical solution is to down-size a bit and use just the one large array and a smaller inverter.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #48
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything

    I just looked at the Fronius site and you can run a 7.5 with up to 8600 watts of panels and it would meet the requirement for a 40 amp back-feed, max continuous output of 31.3 amps @ 240 Volts.

    http://www.fronius.com/cps/rde/xchg/SID-62EF19B6-7444C1AC/fronius_usa/hs.xsl/2714_1481.htm
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  • WhittakerJ
    WhittakerJ Solar Expert Posts: 67 ✭✭
    #49
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    Cariboocoot wrote: »
    It's based on the current rating of the bars in the service panels. The "120%" rule allows a 100 Amp service to be back-fed 20 Amps, 40 Amps on a 200 Amp service, et cetera. There are some 'adjustments' that can be made sometimes such as putting in a smaller main breaker, but that option is not always available.

    It is looking like the most practical solution is to down-size a bit and use just the one large array and a smaller inverter.

    Ah, ok I think I got it. Basically no breaker can be larger than 20% of the main breaker's size. Which puts me at 40a so if I understand correctly I could, technically, use two smaller inverters given that neither one exceeds the necessity of a 40a breaker, correct? This or sell some of the panels off and just find an inverter that only requires a 40a breaker. Which I'm assuming is why Dave recommended the 8kw.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #50
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    WhittakerJ wrote: »
    Ah, ok I think I got it. Basically no breaker can be larger than 20% of the main breaker's size. Which puts me at 40a so if I understand correctly I could, technically, use two smaller inverters given that neither one exceeds the necessity of a 40a breaker, correct? This or sell some of the panels off and just find an inverter that only requires a 40a breaker. Which I'm assuming is why Dave recommended the 8kw.

    Remember that is total back-feed of 40 amps minus the NEC required "buffer" on the breaker, the 7.5 fronius fits the bill exactly.
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  • SkiDoo55
    SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    #51
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    solar_dave wrote: »
    Max continuous output = 41.7 Amps. Yep over the limit for sure, for just the inverter you will need like a 50 amp back-feed breaker to meet code.

    Perhaps you should scale back a bit to a 8kW inverter, that would squeak under I bet. With 8250 watts of panels that should be OK. remember that will not account for the roof mounted panels.

    Wouldn't he need a 60 amp breaker? 41.7A x 125%. = 52.125 amp next available = 60A.
    Unless he is allowed to derate his Main Breaker this would exceed the 120% rule for backfeed.
    7680 inverted watts output is max on a 40 amp breaker. Inverter output is determining factor.
    He is going to have to look at inverter or combinations of inverters and also, if he would be allowed to. Downsize his main to get a larger backfeed breaker in. Would need a AC-Combiner box before main to bring multiple inverters together to feed a single main backfeed breaker.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
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  • WhittakerJ
    WhittakerJ Solar Expert Posts: 67 ✭✭
    #52
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    solar_dave wrote: »
    Remember that is total back-feed of 40 amps minus the NEC required "buffer" on the breaker, the 7.5 fronius fits the bill exactly.



    So that one, if I looked it up correctly, is 36.1a so it's under 40 and would work, right? Thanks for doing the leg work on that by the way, much appreciated!
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #53
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    SkiDoo55 wrote: »
    Wouldn't he need a 60 amp breaker? 41.7A x 125%. = 52.125 amp next available = 60A.
    Unless he is allowed to derate his Main Breaker this would exceed the 120% rule for backfeed.
    7680 inverted watts output is max on a 40 amp breaker. Inverter output is determining factor.
    He is going to have to look at inverter or combinations of inverters and also, if he would be allowed to. Downsize his main to get a larger backfeed breaker in. Would need a AC-Combiner box before main to bring multiple inverters together to feed a single main backfeed breaker.

    Exactly correct. I was just swagging the numbers.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #54
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    WhittakerJ wrote: »
    Ah, ok I think I got it. Basically no breaker can be larger than 20% of the main breaker's size. Which puts me at 40a so if I understand correctly I could, technically, use two smaller inverters given that neither one exceeds the necessity of a 40a breaker, correct? This or sell some of the panels off and just find an inverter that only requires a 40a breaker. Which I'm assuming is why Dave recommended the 8kw.

    It is in total.
    The "back feed" Amps from all sources are added to the "utility Amps" and the total can not exceed the breaker bus bars' rating, including the NEC derating (which is factored into the breaker sizing). This is why solar_dave recommended going down to the smaller inverter which would output only 32 Amps and would be connected through a 40 Amp breaker.
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  • WhittakerJ
    WhittakerJ Solar Expert Posts: 67 ✭✭
    #55
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    solar_dave wrote: »
    Exactly correct. I was just swagging the numbers.

    Now I'm confused, so it would work? Or will not?
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #56
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    WhittakerJ wrote: »
    So that one, if I looked it up correctly, is 36.1a so it's under 40 and would work, right? Thanks for doing the leg work on that by the way, much appreciated!


    Actually you need the 240V line of data.
    it states @ 240 V it will output max 31.3 that times the NEC required buffer of 1.25% gets you about 39.125, next size up is 40 amps.

    last column is the 7.5
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #57
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything

    We are talking about a 200 Amp main service, right?
    You should also check the current rating on the bus bars inside if at all possible. They may be higher than 200 Amps and if you have those numbers you're good to go.
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  • WhittakerJ
    WhittakerJ Solar Expert Posts: 67 ✭✭
    #58
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    solar_dave wrote: »
    Actually you need the 240V line of data.
    it states @ 240 V it will output max 31.3 that times the NEC required buffer of 1.25% gets you about 39.125, next size up is 40 amps.

    Sweet, thanks.

    So I have gone back to the Fronius tool. If I'm understanding you guys correctly I can use the 7.5-1 uni in combination with the fronius ig 2000. Use the 2000 to power my rooftop array and the 7.5-1 uni to power my main array in the backyard, correct?

    Attachment not found.

    Attachment not found.
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  • WhittakerJ
    WhittakerJ Solar Expert Posts: 67 ✭✭
    #59
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    WhittakerJ wrote: »
    Sweet, thanks.

    So I have gone back to the Fronius tool. If I'm understanding you guys correctly I can use the 7.5-1 uni in combination with the fronius ig 2000. Use the 2000 to power my rooftop array and the 7.5-1 uni to power my main array in the backyard, correct?

    Attachment not found.

    Attachment not found.


    I also have the room to add two more panels to the roof, right!?
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  • SkiDoo55
    SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    #60
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    WhittakerJ wrote: »
    Sweet, thanks.

    So I have gone back to the Fronius tool. If I'm understanding you guys correctly I can use the 7.5-1 uni in combination with the fronius ig 2000. Use the 2000 to power my rooftop array and the 7.5-1 uni to power my main array in the backyard, correct?

    Attachment not found.

    Attachment not found.

    Not without downsizing your main breaker if allowed.

    40 Amp is the MAX backfeed allowed on a 200 amp main panel

    The Fronius 75 would be at MAX allowed backfeed

    That is the Combined backfeed of all inverters.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #61
    Re: Amateur doing a 10kw system, can someone tell me if I missed anything
    WhittakerJ wrote: »
    Sweet, thanks.

    So I have gone back to the Fronius tool. If I'm understanding you guys correctly I can use the 7.5-1 uni in combination with the fronius ig 2000. Use the 2000 to power my rooftop array and the 7.5-1 uni to power my main array in the backyard, correct?

    Attachment not found.

    Attachment not found.


    NO your maximum back-feed on the current panel setup is the 7.5-1 uni only.
    If you want to add the 2000 you have to add a AC combiner and get the total for both into the main panel back-feed. That will put the total way over 40 amps.

    That is why I talked earlier about derating the main breaker and why coot was telling you to find out the Buss bar rating, it may be higher than the 200 amps.
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