Combining Different Solar Sources

JRM
JRM Registered Users Posts: 31 ✭✭
in Off Grid Solar & Battery Systems #1
It's been a while since I last posted here.  I have a small solar set-up with 3 panels, a Classic 150SL controller, batteries and an inverter.  This is a test setup that runs a trailer and has worked fine.  Now I want to scale up to a house about 130 feet away from my "power shed".  Panels on the house and shed would face the same way (south), but the shed roof is steeper. The house would have 12 or 15 panels on the roof.  I thought I had planned ahead for upscaling, but (as usual for me anyway) I didn't think of everything.  I am planning to use the same panels on both the house and power shed (rated at 300 watts, 40 volts, and 7.5 amps each), and to wire them in series of three (for 120 volts and 7.5 amps) and, on the house, connect the strings of 3 in parallel.  My concern is how to integrate the existing panels on my shed.  At the shed I would be connecting a lead from the house that, at a maximum, could be carrying over 30 amps at a slightly lower voltage (from wire loss) to the single string from my power shed that has slightly higher voltage but a maximum of about 7.5 amps.  From my reading about parallel connections, I would end up with the lower voltage, but the current would be additive. So, this "combination" should work.  Is this thinking correct?  Or would it create problems that I I'm not aware of?  

John49
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Comments

  • Photowhit
    Photowhit Solar Expert Posts: 6,017 ✭✭✭✭✭
    #2
    Solar panels might have slightly different voltages, but not significantly different. 

    Adding the combined output shouldn't be an issue, perhaps some slightly more searching for maximum power point.

    Watch your output. The charge controllers are rated based on output. A classic can handle over paneling, but output will be limited to the limits Midnite suggests. The Classic has a bit of assorted amperage based on voltage and input.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • JRM
    JRM Registered Users Posts: 31 ✭✭
    #3
    Photowhit - Thank you for the reply.  It makes sense that parallel connection of different amp wires with similar voltage will simply add the current while using the lower voltage in the Classic for battery charging.  My maximum volts (about 120) and amps (less than 50) seem to be well within the capacity of the Classic 150SL.  My main worry was in creating unexpected problems.  So far, the Classic has withstood my learning by experience, but I don't want to create a problem that it can't cope with.  John49
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  • t00ls
    t00ls Solar Expert Posts: 263 ✭✭✭
    edited February 26 #4
    the reason for series connection is to get the maximum voltage out early in the morning, most MPPT charge controllers take high voltage low amperage DC converts it to a high frequency AC and inverts it to a low voltage high amperage DC ...basically a buck converter
    so the more voltage early in the morning means you charge your batteries longer....you cant have amperage without the voltage being enough to start charging

    I hope that made sense

    I have 2 strings of 6 panels in parallel with different voltages and different amperges...as long as the amps and volts in the different strings dont differ a lot, it is doable


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