Help wiring 2 100w 16V panels to an MPPT CC.

Robw_z
Robw_z Registered Users Posts: 6
Hello,

I could probably figure this out myself but I figured I should ask to be safe. I am currently running a single 100W 16V(approx) panel into a Morningstar Sunsaver 15 amp MPPT which is charging an Optima yellow top.

It is not meeting my needs, I have a second 100w 16V panel, same one exactly, that I am going to add. Am I better off running them in a series or in parallel? All I have for now is 12 AWG wire, can I get away with this for now or double it up? Thanks for any input.

For clarity here are the panel specs: 98w, Vpm: 21.5V, Voc: 27V, Ipm: 4.5A, Isc: 4.8A

The ceiling on the CC is 200W and 15 amps.

-Rob

PS: series means I run the + of one panel into the - of the other right? Yeah I'm that new to this.

Comments

  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Help wiring 2 100w 16V panels to an MPPT CC.
    Robw_z wrote: »
    Am I better off running them in a series or in parallel? All I have for now is 12 AWG wire, can I get away with this for now or double it up? Thanks for any input.

    Panels in Parallel. With a Vmp of 21.5 going to a 12 volt battery, you would stand to gain quite a bit by using an MPPT controller. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Help wiring 2 100w 16V panels to an MPPT CC.

    i totally agree with vtmaps. go with paralleling.

    with the pwm controller the best you'll see is the 4.5a from each pv and using about 14.5v for the voltage (governed by the battery and not the pv) gives you 130.5w tops from those 2 100w pvs. an mppt cc would do wonders here.

    also to note that even though i don't know what your loads are that the extra loads may need to be drawn while the pvs are pumping the extra power into the batteries during the day as the batteries only hold so much amp hours in them. if the extra loads are during the night then you may need to expand upon the batteries as well.
  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    Re: Help wiring 2 100w 16V panels to an MPPT CC.

    If you are using the Sunsaver 15 MPPT, then put them in series, if using the non MPPT put them in parallel.
  • Robw_z
    Robw_z Registered Users Posts: 6
    Re: Help wiring 2 100w 16V panels to an MPPT CC.

    The load is a 12v 65 liter danfoss compressor(not thermoelectric) fridge which is very efficient as fridges go. It's running about half the time, theoretically more often during the heat of the day. Currently I can only read battery status via the 3 LED's on the Sunsaver MPPT, red yellow and green. Seems like the first night, starting from a full battery, it can stay in the green, but by the second morning it is yellow(approx half full), and then battery doesn't fully recover and it's all downhill from there. So if I can get the battery fully charged during the day I should be good.

    So far two votes for parallel, and then the moderator reverses the concencus with suggesting putting them in series. Hrmmmm.

    -Rob
  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    Re: Help wiring 2 100w 16V panels to an MPPT CC.

    Attachment not found.

    As noted above, max input voltage is 75V, so use series.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help wiring 2 100w 16V panels to an MPPT CC.

    Morningstar's info says that at 21.5 Vmp (panels in parallel) the efficiency will be approximately 95% @ 180 Watts output. At 43 Vmp (panels in series) it will be approximately 93%.
    Reference: http://lib.store.yahoo.net/lib/wind-sun/SSMPPT15-Owners.pdf chart on page 20
    Not much difference. It would come down to how far from the panels is the controller and would you need the extra Voltage to overcome resistance/use smaller wire?

    Now the real issue here: is there a current draw rating on that refrigerator? If so we could calculate a rough power consumption based on that and 50% duty cycle.
    There are different models of Optima yellow top batteries. Their capacities range from 41 to 55 Amp hours (20 hour rate).
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Help wiring 2 100w 16V panels to an MPPT CC.
    Now the real issue here: is there a current draw rating on that refrigerator? If so we could calculate a rough power consumption based on that and 50% duty cycle.

    Danfoss compressors have some sort of proportional (variable) current draw. At 12.5 volts it typically runs 4-5 amps. As battery voltage drops it draws a bit more. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help wiring 2 100w 16V panels to an MPPT CC.
    vtmaps wrote: »
    Danfoss compressors have some sort of proportional (variable) current draw. At 12.5 volts it typically runs 4-5 amps. As battery voltage drops it draws a bit more. --vtMaps

    Based on 5 Amps max and 50% duty cycle over 24 hours we get 60 Amp hours, and you can instantly see why a 55 Amp hour (max) battery could be in trouble.
  • Robw_z
    Robw_z Registered Users Posts: 6
    Re: Help wiring 2 100w 16V panels to an MPPT CC.

    The battery is 55 amp hours. This is the model of fridge: http://www.truckfridge.com/tf65.html

    It says nominal I put is 60 watts, average consumption is 24 watts an hour, and that's all it says about power consumption.

    I recognize the 55 amp hour Optima is not a prime choice, but I had one in good condition sitting around unused so it's what I'm going with for now unless it proves impossible for it to perform the task.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help wiring 2 100w 16V panels to an MPPT CC.
    Robw_z wrote: »
    The battery is 55 amp hours. This is the model of fridge: http://www.truckfridge.com/tf65.html

    It says nominal I put is 60 watts, average consumption is 24 watts an hour, and that's all it says about power consumption.

    I recognize the 55 amp hour Optima is not a prime choice, but I had one in good condition sitting around unused so it's what I'm going with for now unless it proves impossible for it to perform the task.

    24 Watts per hour average on a 12 Volt system is roughly 2 Amps per hour. At that rate the Optima would be 50% depleted in about 14 hours. Considering the typical short window of daily sunshine (4 to 5 hours), we may have pinpointed the problem: the battery can not store enough power to keep the 'frige going for the 20 hours when the sun is not there.