Panels and New MX60

nigtomdaw

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

crewzer

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

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

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

Re: Panels and New MX60

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

regards
Nigel

crewzer

Re: Panels and New MX60

:D8)

Jim / crewzer