Solar panel shutdown

Jradke34Jradke34 Registered Users, Users Awaiting Email Confirmation Posts: 2
This is my first year using solar off grid. I have an off grid cabin in the Upper Peninsula of Michigan and plan to shut my system off when I leave for the fall.  My questions are, after I shut down my system, should I turn off the breaker in the combiner box, should I disconnect my my solar panel cables going to the combiner box, and should I cover my panels with a tarp since the system will not be in use for 5 to 6 month.

Comments

  • PhotowhitPhotowhit Solar Expert Posts: 5,976 ✭✭✭✭✭
    No need to 'tarp' your panels if they don't go anywhere. Switching off the breakers in the combiner box should ensure that even a hail storm or tree/ice/snow damage to panels won't allow the others to back feed and create a problem. Of course the breakers already do that, but they are there...

    Taking the batteries home to trickle charge or just leaving them there?
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • Jradke34Jradke34 Registered Users, Users Awaiting Email Confirmation Posts: 2
    Plan on leaving the batteries up here. Should have close to a full charge when we leave 
  • BB.BB. Super Moderators, Administrators Posts: 32,924 admin
    What kind of batteries do you have? Typically, if flooded cell lead acid, they need to be charged at least once per month (self discharge).

    Assuming that it is "cold" up there... There is a rule of thumb of for every 10C (18F) below room temperature, the self discharge rate falls by 1/2... i.e., 25C vs 0C or below:
    • 25C below room temperature / 10C = 2.5 factor
    • (1/2)^2.5 = 0.18 lower self discharge rate.
    • 1 month * 1/0.18 lower rate = 5.6 months between charge (basically keeping batteries above 75% state of charge to slow "sulfation")
    Keeping loads turned off (turn off DC breaker to inverter/other DC loads) and leaving array+charge controller "running" during winter is an option... Panels will not charge battery bank when covered with snow (how much does that happen at your cabin)....

    You can run into the issue that the charge controller's energy usage (running the internal computer/electronics) can discharge the battery bank without "sun")...

    An option around that is to have a (100 Watt or so, depending on battery bank size/voltage) panel mounted vertically (such as a south facing wall) and a simple PWM controller to trickle charge the bank until you get back to start everything up.

    Beside sulfation (storing for days/weeks/months below 75% State of Charge), Lead Acid batteries will freeze at warmer temperatures at lower states of charge--Flooded Cell battery cases will crack from the ice... AGM will typically not be damaged at "below electrolyte" freezing temperatures...

    I will stop here--Your questions/answers?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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