Can not find a working "String Sizing Tool"

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Can not find a working "String Sizing Tool"

Postby lonewolf on Thu Mar 14, 2019 10:53 am

My off-grid home (Outback PV systems) was totally destroyed in a forest fire last fall.
I am now planning to rebuild to the extend possible.
Cannot find a String Sizing tool that works

Have recently seen conflicting information on max wattage input to FM80's - formerly had 1200W of panels per FM80 @ 12V nom (2 strings of 600W per).
Now want to go to a 24V system.
Would like to have 8 each Canadian Solar CS6K 300MS Mono (300W)

Operating Voltage (Vmp)-32.7v (VOC)-39.9v
Operating Current (Imp)-9.33A (ISC)-9.91A

How can/should the strings be configured for use with a FM80 on a 24V system?
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Re: Can not find a working "String Sizing Tool"

Postby Kurt Lundquist on Thu Mar 14, 2019 12:09 pm

I'm sorry to hear about the loss of your home!

With 2 FM80s you should go with 2 modules in series x 2 parallel strings per FM80. If you had 9 modules you could go 3 in series with 2 parallel strings on one controller and the other 2 on the next one.

-Kurt
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Re: Can not find a working "String Sizing Tool"

Postby lonewolf on Thu Mar 14, 2019 2:57 pm

Thanks for the responses

As indicated (at my location with annual temp extremes from 105F to -30F) I had 2 parallel strings of 600W each into each FM80 on a 12V system without any incident for 12+ years. Worked great. Fully 'sold' on Outback's reliability.

Given that I am intending to migrate to a 24V system I 'figured' that a FM80 would accommodate twice the wattage - e.g. with 4 parallel strings of 600W
(from 8 panels of 300W each into 4 equal strings) OR 2 parallel strings of 1200W. But I do understand the with 4 per string the VOC will exceed specs.

So it would now appear that I should dial it back to 6 panels (2 strings of 900W with nominal VOC of +/- 120V). Cannot afford buying 2 FM80's at this time as I must replace EVERYTHING, just can't do it all at once ... not on a disabled vets pension anyway. BTW, there is no such thing as fire (or other home) insurance when off-grid - NTM WAY off-grid.

TMK, the Canadian Solar panels frames are stronger that all/most others - best for heavy snow loads (which is what happens here) - ntm high wind loads on my mountain. Also have a good price on them (IMO).
Last edited by lonewolf on Fri Mar 15, 2019 12:12 am, edited 1 time in total.
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Re: Can not find a working "String Sizing Tool"

Postby sodamo on Fri Mar 15, 2019 12:53 am

Have you considered going to a 48v system?
David
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