My Solar Edge App and Expected Wh Readings

Recently had Titan Solar contractor add seven Silfab 410 HC+panels to the existing system of 18 Silfab 330 panels and inverter, also by Titan.  The seven panels are in direct sun yet never read uniform.  Per spec sheet, max power is 410, Voltage 38.99 max, current10.52.
The app reads in Wh.  When in direct sun, what would be the expected reading if they are producing near max power of 410?  Note the spec sheet has no units. 


  • BB.
    BB. Super Moderators, Administrators Posts: 33,404 admin
    Welcome to the forum Maranahome,

    I guess you are somewhere around Tucson Az--Nice sunny weather now (mostly)?

    Looking at your panel specs--They appear to be: (9x in series * 2) (7x in series)

    If you have Silfab 330 9x of them, 1x string , the Vmp of two strings of 9 (2x parallel strings):
    9 (330 Watt panels) in series * 34.72 Vmp per panel = 312.48 volts Vmp string (330 Watt panels)

    And the Silfab 410 Watt panels, 18x total, or 9x per string * 2 parallel strings:
    7 (410 Watt) Panels in series  * 38.99 Vmp = 272.93 Volts Vmp string (410 Watt panels)

    Now, I made a guess that you have 7+18 panel array with 3 strings (1x7 410 Watt series + 2x9 series 330 Watt)...

    Looking at the Vmp-array string voltages, if my guess is correct, is not a "great match"... Ideally, the two different panel strings should "match" Vmp-array per string, or miss-match by no more than 5-10%... Here, they miss-match by ~14%... That is a fairly large miss-match and you will be "pressed" to get an optimum output from this array configuration. To have a better match, it would be to make the 410 Watt array to have 8 panels in series--Them the Vmp-array per string would be a much better match...

    If you have some other configuration such as one MPPT solar charge controller connected to the 330 watt 9s*2p array; and a second MPPT controller connected to the 410 Watt * 7s*1p array... (similar would be 1x GT inverter to 330 Watt and a second GT inverter to the 410 Watt array).

    And to be clear--Watts are like Miles per Hour (a rate). And Watt*Hours is an "amount" (like miles driven). For example:

    200 Watts * 3 hours = 600 Watt*Hours

    The "optimum" (typical maximum array power on a cool/clear day with the GT Inverter and a correctly configured array would be:
    • (18 * 330 Watt) + (7 * 410 Watt) * 0.77 panel+GT inverter deratings = 8,810 Watts typical max output on a cool/clear day near solar noon...
    If the system is configured as one large array with 9*2 330 watt panels in series with 7s*1p 410 Watt array... Roughly the "worst case" best case harvest would be:
    • 272.93 Vmp-array (based on 410 strings) * 10.42 amps per one string = 2,844 Watts (410 string)
    • 272.93 Vmp-array (set by low voltage 410 string) * 9.51 Amps * 2 parallel strings = 5,191 Watts (330 Watt "degraded" Vmp-array voltage)
    • (2,884 Watts + 5,191 Watts) * 0.77 panel+controller deratings = 6,218 Watt "worst case" best case typical array output (cool/clear day)...
    So your "combo" array output would be somewhere between 6,218 and 8,810 Watts best case solar noon cool/clear day... Probably closer to 6,200 to 7,000 Watts or so...

    Again, this is based on your present combo array... If you added another 410 Watt panel, then you would have a much better Vmp-string matching voltage (almost perfect). And assuming your GT inverter is >9,210 Watts rated.

    If you have another configuration (another GT inverter, micro inverters, or something else)--Please let us know.

    Also, what do you mean exactly by "
    The seven panels are in direct sun yet never read uniform"... How are you measuring the 410 Watt panels to see they are not "uniform"? Do you have a (for example) micro GT inverter on each panel? For example, looking up Titan inverters:

    Needless to say--I am making guesses here based on what you have said so far...

    In general, if you have good solar panels, and good micro inverters+wiring, the typical reasons for variation in solar panel outputs are the results of shading--Where that is a chimney, vent stack, overhead electrical wires, trees, nearby buildings, etc.--ANY Shading on solar electric panel can dramatically reduce its output--By 50% or more is not unusual.

    Your thoughts and corrections to my guesses?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset