Multi portable fold panels into one SCC

MontyYoung
MontyYoung Registered Users Posts: 12 ✭✭
in Solar Beginners Corner #1
It's common to want to setup say three 18vmp folding panels each having 2-5 modules themselves & placing them at different spots like north, south, west. All going into a single MPPT.

I understand that with 2 or more modules one needs fusing in parallel, But how does one go about fusing multi folding panels that are themselves made of multi panels in parallel? I'm at a loss here on what to do. Furthermore, should these fold panels have fusing inside them since they have more then 3 modules? Again whats the go here?

Finally what about the power point tracking? I assume since the 5 panels in each folding panel are oriented same that the whole  behaves much like a single module. I should go mppt for each fold unit? What would be the cons/tradeoffs?

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Regarding fusing... The details is to look at the specifications of the panels and  see what their "series fuse" requirements are. And compare that to the Isc (short circuit current).

    For example, a typical panel is rated at 15 Amps series fuse, and perhaps 5.6 amps Imp and (approximately) 7 amps Isc (short circuit current) (for a 100 Watt Vmp~18 volt panel). So, three panels in series would each need a maximum of 15 amp series fuse.

    If the maximum series fuse rating for your folding panels is 10 amps, then 10 amp series fuse.

    It is possible that you will not find a series fuse rating for your panels... The suggested series fuse would be 1.25 x Isc or (1.25x7amps) 8.75 amps--Or 9-10 amps in this example.

    If you do not find a series fuse rating--It could be argued that the Mfg. never intended parallel operation and never went through the UL/NRTL testing required for LISTING of the panel. This is your decision to parallel or not these panels (using series fuses).

    Regarding a "virtual tracking array" (2 or more panels facing SE/South/SW, etc.)--This was the idea of "over paneling" an off grid system to provide "more hours of charging" like a tracking array would, without the cost/complexity of a mechanical tracker.

    The reason was that Lead Acid Batteries need a (roughly) 10-13%+ rate of charge for many hours per day--And the virtual tracker spreads out the current better over the day.

    If you are using (for example) Lithium Ion (LiFePO4 or similar) batteries--These batteries are much more efficient at charging and do not need a virtual array. The Li Ion batteries can take any and all charging current and apply 99% of the current to charging. Whether it is 4 hours in a day or 10 hours in a day. So doing a "virtual tracking array" is not really gaining you any advantages.

    As you suggest, placing 2-3 panels facing SE/S/SW is going to be somewhat less efficient when connected to a single MPPT type control. Ideally, you would want 2-3 separate MPPT controllers connected to each set of panels. However, you have the added costs of more controllers and having to pack the extra hardware--If this is for a recreational vehicle.

    But, because you are purposely "over paneling"--The losses for "one MPPT controller" may not matter that much unless you are trying for the "most harvest" you can... But again this assumes a Lead Acid battery (flooded cell, AGM, etc.) and needing "more hours of sun" for charging. If this is for a Li Ion battery, then as long as your maximum battery charging current is less that the Li Ion's max input current (can be upwards of 50% of the battery bank AmpHour capacity)--Then virtual tracking is not needed.

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