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One string or two?

Discussion in 'Solar PV Forum' started by Colin33, Aug 9, 2018.

Discuss One string or two? in the Solar PV Forum area at ElectrciansForums.co.uk.

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  1. Colin33
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    Colin33 Regular EF Member

    Location:
    Cornwall
    I'm relocating a 16 panel system from a field onto a barn roof. Currently, there are 16 panels, wired as two strings into an isolator. From the isolator there is a two core 4mm SWA which goes underground (about 150m) to the inverter in the farmhouse where it's wired into one of the inverter's two inputs. I've relocated the panels onto a barn roof, and relocated the inverter from a hot loft into the barn instead. This does away with the need for 150m swa run. My question is, is there any reason to wire in two strings as before, as it is easier to wire them together in a single string taking just one pair of wires back to the inverter? Voc will be just under 600v, so well within cable capacity. It's a couple of years since I completed my PV course and have done very little in the way of pv since so just after some gentle reassurance please ;-)
     
  2. whinmoor
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    whinmoor Electrician's Arms

    Location:
    Wakefield/Leeds, West Yorkshire
    Business Name:
    Medoria Solar
    Look at the inverter's datasheet to find the voltage limits. Then consider the voltage in cold weather. You'll probably find that you're exceeding the limits so will need to go for two strings.

    What inverter and panels are you using?
     
  3. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Top Poster Of Month

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    i prefer a 12 string.more chance of getting a few in tune>

     
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  4. littlespark
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    littlespark Electrician's Arms

    Location:
    Scottish Borders
    I think most installations are 2 strings or more - so if you have one faulty panel, only one string goes out. You’re still generating something although half of what you should
     
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  5. Colin33
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    Colin33 Regular EF Member

    Location:
    Cornwall
    Although they were wired in two strings originally, they were connected in the isolator to a two core swa so in fact only wired back to the inverter as one. I think therefore there'll be no problems with the inverter taking the voltage.
     
  6. Colin33
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    Colin33 Regular EF Member

    Location:
    Cornwall
    Do you think it's better that way, or isn't it more obvious to the end user that a fault exists if there is no generation at all?
     
  7. littlespark
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    littlespark Electrician's Arms

    Location:
    Scottish Borders
    You would only notice either way if you watched the inverter output on a daily basis. Unless you have an app that can read it.

    Do you have to notify your FIT payee that you are altering the installation?
     
  8. Gary K
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    Gary K Regular EF Member

    Location:
    norwich
    Not really altering it,rather just moving it slightly.
    Personally,I wouldn't ask the question as you may not like the answer and you cannot really plead ignorance then!
    Bit late now anyway seeing as the panels have already been moved.
    I suspect they were originally located in the field to get them registered before the FITS cut
     
  9. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    Were they connected in series at the isolator, if they were in parallel then surely the voltage would have been half before?
     
  10. Colin33
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    Colin33 Regular EF Member

    Location:
    Cornwall
    Yes, you're right of course! I think the best solution then is to wire them exactly as before. Though it will be pointless using an isolator at the panel end because it's too high up on the inside of the roof to be of any use. I want to bring just one pair of cables down from the roof to inverter so what is the best method of connecting 2 into one? A junction box (or boxes) or mc4 Y splitter?
     

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