MPPT.. 3 parallel strings of 2 or 3 parallel strings of 3??

ywhic
ywhic Solar Expert Posts: 621 ✭✭
in Off Grid Solar & Battery Systems #1
Okay..

I had decided to split my panels into 3 parallel strings of 2.. and use my 3 of my 6 breakers in the combiner box. This will leave room to grow for 3 more sets... or if I get real lucky 3 24V (36-37 VMP with matching IMP) panels..

Someone suggested going with 2 strings or 3 panels to get more volts into the MPPT circuit and maybe gain more AMPS in conversion.. though I don't think it will matter.. the Midnite site shows 60 amps max output into a 12v bank no matter how I string them..

There is no real wire loss issue as the panels volts is 24v (nominal) and 8 amps per string (max of 18 feet with 10 AWG). and there is no combiner box cost as I've aready got it wired up..

I've got 6 of these..

145W
18 VMP
8.05 IMP
21.6 VOC
8.95 ISC

I will driving initially a 12v battery bank and the 2 panels to make about 36 VMP made more eff sense then trying to convert 54v (from 3 panels in series) to 12v..

Controller is the Midnite Classic 150

I mean speaking of the MPPT portion..

Can I put a 24v (nominal) 36-37VMP panel on a breaker and match it to the 'stringed' panels that are in the box??

I found some 190w panels that are 36.75 VMP but only 5.17 IMP rated.. though I forget which drags down a parallel setup is it the volts or the amps?? most of the 240-250 watt panels I found are for on-grid and only have 28-30 VMP ratings though the IMP Amps is closer at 8 amps..

I can find 140w Kyoceras to double up and almost match the current pairs.. 17.7 VMP and 7.91 IMP..
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: MPPT.. 3 parallel strings of 2 or s parallel strings of 3??

    The Amps out would be the same regardless of panel configuration.
    The higher the array Voltage in comparison to the battery Voltage the harder the controller has to work to down-convert the Voltage; efficiency drops, and thus over-all power captured.
    For a 12 Volt system it is best to stay with a nominal 24 Volt array (Vmp around 35 to 36).

    When paralleling panels or strings of panels the Imp doesn't really matter; it is more important to have similar Vmp. The current will be cumulative. Your panels two in series are Vmp 36, so the 190 Watt panel would work fine in parallel and so would a string of two of the KD 140's. Both are within 2% of your existing array's Vmp. No worries.
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