Help me with my expansion

CVN-71
CVN-71 Solar Expert Posts: 54 ✭✭
in Solar Beginners Corner #1
Hi, I designed my system several years ago and planned on expanding when i could afford it, I think I'm ready and want to run my ideas off the experts to see if I'm thinking this correctly. I currently have 8 Evergreens 205/210w, wired at 4 strings of 2 panels at 24V. I want to add 4 more Evergreens. I found four 205w clones with same specs. My pan is to rewire the array with 3 strings of 4 panels each, except alter voltage to 48W. I have a FM80 that will downconvert the 48V input out of the controller to 24v which is what my inverter and battery bank is. I believe if I do it this way, I won't have to change any of the wiring, correct? My wiring from combiner is oversized to handle the additional panels. Question on the string breakers, right now they are 15A for the 2 panels at 24V, will these need to be changed? Here are the specs of my panels: Thanks.

Power (W) 205 Watts
Open Circuit Voltage (V) 22.70 Voc
Short Circuit Current (A) 11.93 Isc
Maximum Power Voltage (V) 18.20 Vmp
Maximum Power Current (A) 11.27 Imp
Dimensions (in)(LxWxD) 65" x 37 1/2" x 1 3/8"
Weight (lb) 41 lb
Connector MC-4
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Help me with my expansion

    Are you going to be mixing panel types in the string? It would be best not to. If you do the Imp of the string will be limited to that of whichever panel has the lowest current.

    Slightly different Vmp per string would be less of an issue.

    As you add panels in series the current doesn't go up, only the Voltage. As such the breaker for each string will remain the same. So whatever the "maximum series fuse" rating is for the panels will work.

    Right now you have four parallel strings (of two panels) at <12 Amps each so your wiring must be able to take 48 Amps. Changing to three parallel strings (but of four panels) would actually reduce the current by 1/4 while doubling the Voltage (approximately). The MPPT controller should have no trouble with this, and a nominal 48 Volt array is about ideal for a 24 Volt system in terms of efficiency.

    On the whole it sounds like you thought it out well. :D
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  • CVN-71
    CVN-71 Solar Expert Posts: 54 ✭✭
    #3
    Re: Help me with my expansion

    Thanks Coot, I knew you'd be one to have an answer! Yes, the new panels are exact clones of 6 of my panels, so specs are the same. The other 2 odd panels are Evergreen 210w's but they are very close to the 205's, so I don't mind them being limited oh so slightly. My wire is 4awg at only 22' for drop. I'd have to check my engineering plan but I'm sure it can handle over 65A no problem. I wish it wasn't years since I designed this, I forgot a lot since then. Will have to bone up again and rerun all the numbers. I wish panels were as cheap then as they are now so i could have done it all at once. Evergreen going Tango Uniform didn't help either as their panels are hard to find since Cap7. Thanks again.
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