2x KD135's with Sunsaver MPPT

Hi, I have been running a Sunsaver MPPT with two small 40 watt panels for some time with good results. I just upgraded my panels to two new KD135 panels. I know these panels are JUST slightly bigger than my controller is designed for.

I am going to be off-grid, cruising on my boat, spending much of this time in latitudes < 20 degrees. My question is how often will the controller be in overcurrent? I am up in seattle now, so have much more limited solar exposure. I know the controller isn't going to be damaged, but I really don't want to be wasting usable energy which could be going back into my batteries.

My gut feeling is that I need to buy one more controller, give each panel a dedicated controller so I don't loose anything, and I also gain some redundancy in case one controller goes wonky on me and I am in the middle of nowhere. If I go this way, other than a second temperature sensor, is there anything I need to do to keep these controllers working well together?

Also, I am most likely going to be getting a towed generator for passages, which is basically a wind generator but used water instead of wind to turn the generator. Is there anything to be aware of mixing this into the system?



  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
    Re: 2x KD135's with Sunsaver MPPT

    As long as you do not exceed the controller's maximum input voltage... And if you had 2-4x the amount of panels--you possibly would need a series protection fuse (prevent a short in the wiring being fed by the solar array)... But other than that--you will not cause any issues and break the controller.

    If you have more than 125% of the rated controller power--for example:
    • 15 amps * 14.5 volts * 1.25 = 272 watts
    Hot panels generate less Vmp--so generate less power through the MPPT controller. If your boat where ice bound instead of the tropics, you could see significantly better than 80% or so of "average maximum" collection from your panels:
    • 2*135 watts * 0.77 derating * 1/14.5 volts = 14.3 amps typical peak current in warm weather (my guess)
    If you had more than ~270-300 watts of panels, then a second controller would probably capture significantly more power... Otherwise, you are probably just losing a little bit during the middle of the day...

    Carrying / wiring a spare--your choice. Perhaps a small Honda eu1000i + AC Battery Charger (good for shore power to--if available) and a few extra gallons of gasoline would be a good "spare"--covers solar equipment failure and just plain cloudy weather.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: 2x KD135's with Sunsaver MPPT

    there's also the issue of shading of the pvs from the boat that will also rob some of the power of the pvs. it will be fine even if it does exceed the 15a limit once in awhile.