Mixing Panels Questions

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verdigo
verdigo Solar Expert Posts: 428 ✭✭
in Solar Beginners Corner #1
I just purchased 4 Renogy 300 watt panels. I already have 4 Grape Solar 280 watt panels wired in two strings of two on my shed roof at a couple of degrees more than latitude. The 300 watt panels will be on a single axis tracking ground mount. I was wondering if it would be beneficial to put one of each in the strings rather than in like pairs. In other words would they average out? Grape panels are IMP 7.82a VMP 35.8v The Renogy panels are 8.01a and 37.46v. I have seen the grape panels at 9.4 amps with the system loaded before so I think they may be a little under rated.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
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    Re: Mixing Panels Questions

    With these panels, it probably does not matter.

    If you want to optimize, Measure the short circuit current of each panel and place panels with "matching" Imp/Isc in the same string (panels should be measured at close to the same time under the "same sun"--Current is proportional to the amount of sun light hitting the panel, and panel efficiency).

    It may be more trouble to measure the Isc/Imp than it is worth in power gain from matching panels (call it a 5% best case improvement--Is it worth it?).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
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    Re: Mixing Panels Questions

    Doesn't look like much difference either way.
    You've got less than 5% Vmp difference which is fine for parallel connection.
    You've got less than 3% Imp difference (by the ratings) which is fine for serial connections.

    Between the two differences, however, the Vmp will have the least power-loss effect. The controller is going to pick the V*I point anyway, and the series connection will limit the panel current to lowest Imp regardless. If the Grape panels really have an Imp around 9 then that is a much bigger current difference (about 12%; the Renogy panels if in series would limit the current to 8 Amps and you'd lose roughly 35 Watts per panel).
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  • verdigo
    verdigo Solar Expert Posts: 428 ✭✭
    #4
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    Re: Mixing Panels Questions

    I was just wondering for the most part. As Bill indicated it probably won't be worth the trouble, and as Mr Coot pointed out that the controller will find the max power point anyway. Still I may rig up one mixed string to see how it performs. I still have 4 more panels to buy to complete the project and with the grape panels being $400.00 each shipped, and the Renogy panels at $235.00 each it leaves little to think about in the way of choice. Thanks for your time guys.
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