Panels and New MX60

Hi have a friend who has the following Panels

Two are; Shell SP140-PC
140 watts 24 volt
SCC 4.7 amps
OCV 42.8V
Rated current 4.25 amps
Rated voltage 33.0


The other four are Sharp NT-R5E3E

175 watts 24 volt
SCC 5.40 A
OCV 44.4 V
Current 4.95 A
Voltage 35.4 V

He has a nominal 24v system, my take on wiring these up would be two strings consisting of 1 x Shell x 2 Sharp then parallel identical strings to MX or is therea better option, he lives in Spain so very rarely to we see temps below freezing and if so a few degrees over night. Or are the panels close enough spec to have 2 x Shell + 2 x Sharp + 2 x Sharp and have 3 Parallel Strings ? Which is best, or is there another option.

Thanks

Comments

  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Panels and New MX60

    Nigel,

    Option #1:
    “two strings consisting of 1 x Shell x 2 Sharp then parallel identical strings to MX”
    String STC Voc would be 42.8 V + (2 x 44.4 V) = 131.6 V
    String STC Vmp would be 33.0 V + (2 x 35.4 V) = 103.8 V
    String Imp would be ~lowest of individual modules in string, or ~4.25 A
    Estimated STC power for array would be 103.8 V x 4.25 A x 2 = ~882.3 W


    Option #2:
    “2 x Shell + 2 x Sharp + 2 x Sharp and have 3 Parallel Strings”
    Shell string STC Voc would be 2 x 42.8 V = 85.6 V
    Shell string STC Vmp would be 2 x 33.0 V = 66.0 V
    Shell string STC Imp = 4.25 A

    Each Sharp string STC Voc would be 2 x 44.4 V = 88.8 V
    Each Sharp string STC Vmp would be 2 x 35.4 V = 70.8 V
    Each Sharp string STC Imp = 4.95 A

    Array Vmp voltage would would be ~lowest of individual strings in array, or ~66.0 V
    Estimated STC power for the array would be 66.0 V x (4.25 A + 4.95 A + 4.95 A) = 933.9 W

    Analysis

    Option #1 advantages:
    • Only two strings, so individual string circuit breakers not required
    • Lower array current specs = lower power loss in wiring to controller
    Option #1 disadvantages:
    • Array Voc is fairly high. Applying the U.S. NEC temp correction factor of 110% for ambient temps down to 0 C (32 F) results in an array voltage of 131.6 V x 110% = 144.76 V. This is within the MX60’s overall limit of 150 V, but it exceeds the operational limit of ~141 V.
    • Option #1 configuration results in lower array power spec than Option #2
    • Option #1 configuration results in lower operating efficiency (~1% point) for MX60 due to higher input voltage
    Option #2 advantages:
    • Array Voc is relatively low (85.6 V), and will operate well within MX60 limits even with NEC TCF.
    • Option #2 configuration results in higher array power spec (~5.8%) than Option #1
    • Option #2 configuration results in higher operating efficiency (~1% point) for MX60 due to lower input voltage
    Option #2 disadvantages:
    • Three strings, so individual string circuit breakers are required
    • Higher array current specs = higher power loss in wiring to controller
    Recommendation

    I’d suck up the additional costs for circuit breakers and heavier gauge wire and go with Option #2 due to higher power and more conservative array Voc.

    HTH,
    Jim / crewzer
  • nigtomdaw
    nigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Panels and New MX60

    Jim I could just say thanks as normal, but I cut and pasted your detailed reply to my friend (customer who I sold the MX60 to, never met him lives about 30 minutes away)

    I gave the credit to you in others words I told him this was from my friend and expert in USA he emailed me this evening and it says it all

    Hi Nigel, just a quick email to say that I rewired my panels as to your instructions and, behold, I am now getting almost double the output! Thanks once again for your help and advice.

    Regards Chris


    Thats about as good as it gets, pour yourself a large one

    Regards Nigel Sunny Spain ps he took option 2
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Panels and New MX60

    Nigel,

    I'm glad that the suggestions worked out for you and your friend. As for pouring myself a large one, my plan is to put it on your "tab" and I will collect if I'm ever in your neighbourhood. ;)

    Regards,
    Jim / crewzer
  • nigtomdaw
    nigtomdaw Solar Expert Posts: 705 ✭✭
    Re: Panels and New MX60

    Im sure the tab will run long and deep in one direction only:cool:

    regards
    Nigel
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Panels and New MX60

    ;):D8)

    Jim / crewzer