Solar Array voltage much lower than it should be?

Hello, I have 6 solar panels at 158w, 18.9Vmp, 8.47A Imp, hooked in series to create a Vmp of 113.4

My MPPT charge controller with a max input voltage of 150V says that my PV voltage is anywhere from 30V to 38V during the most illuminated part of the day.

In the morning it will correctly show that the PV voltage is 90v and then will climb to 110v over an hour or two. Then I'll check it in another hour or two and it will have a voltage between 30v and 40v.

I have it hooked up to 6 12v batteries connected at 24v.

I do live in a really hot desert. but I couldn't be losing that much voltage from heat losses could I?

I'm only getting about 15 amps max when it shows the 30v-40v range. My maximum should be around 25 amps.

Please help me figure this out, it's really irritating that I can't run the appliances I need to because of this.


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar Array voltage much lower than it should be?

    Welcome to the forum.

    Can you tell us which controller you have?

    First a little bit about array configuration on an MPPT controller: In short you really shouldn't be running that high of an array Vmp unless it is absolutely necessary.

    Second, input Voltage alone doesn't tell the whole story. You need to look at current as well as Voltage both on input and output: if the Watts in equals the Watts out (within reason) then the controller is probably functioning correctly.

    So then we're down to things like shading issues. With all the panels in series if one of them gets block it will pretty much 'knock out' the whole array. Voltages in the 30's indicates half the array isn't doing anything. Another possible killer is heat failure of a connection or even of a bypass diode.

    I hate to say it but you are probably going to have to disconnect all the panels in the array and then try them two (in series) at a time. If each pair shows good (Voltage around 36) then try them in sets of three. This will need to be done on separate days of course, so that you can trace the Voltage effect over time as you are experiencing now.

    Your maximum current is really about 30 Amps, but you'd only see that if the panels are all producing and there is the demand for it.
  • VicVic Solar Expert Posts: 3,003 ✭✭✭✭
    Re: Solar Array voltage much lower than it should be?

    Hi Jared ..

    In addition to what has been mentioned, if your MPPT Charge Controller (CC) can have its FirmWare updated in the field, you might look to see if there is more recent FW for it, and do the update, if it can accept it.

    Shading possibilities have been mentioned, and, then the PVs need to be oriented and elevated, such that the midday sun is close to right angles to the location of the sun. You are probably aware of this.

    FWIW. Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Solar Array voltage much lower than it should be?

    Are your batteries in Absorb or Float when this drop occurs? if so they are probably getting near full charge state.
    Are they FLAs? Have you checked them with a hydrometer? What is the SG?
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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