Trying to design winter battery storage system

rp3703

I finally updated my signature line so I wouldn’t have to keep describing my system every time I posted on here. That will save me a paragraph. Anyhow, in a previous thread https://forum.solar-electric.com/discussion/353337/storing-batteries-in-a-northern-ontario-winter/p1 it has been suggested that I leave my batteries on a separate, vertically mounted panel with small charge controller to keep them alive through the winter since the regular roof mounted panels could get covered in snow for 2-3 months straight. Bill (BB.) even did the math for the suggested panel size. A lot of the contributors suggested I just cut everything off and let them sit since the cold weather will slow their rate of discharge as long as they are at float when I leave but it was pointed out that there will still be 2-3 warm months after I leave and 1-2 warm months before I return that the batteries will be sitting. If the batteries would be fine sitting at float for 2-3 months of below freezing temps, would I not just be able to use one of my regular roof mounted panels (2˚ pitch roof) and just run it into a small charge controller to keep the batteries alive till the snow hits. Then the batteries would be sitting with no charge until the panel clears off 2-3 months later. I realize the concern was that the charge controller could pull enough power on it’s own to draw down the batteries but do they not make one that does not use power when no power is being produced by the panel?

Estragon

Mppt controllers, like the midnite classic, will tend to have higher idle consumption that a small, simple, pwm controller.

In the case of a classic, idle will be ~3-5w. Doesn't sound like much, but even at 3w, thats 3x24x30=2160w/month. A pwm controller would typically be much lower.

mcgivor

Shutting everything down means not much could go wrong, as long as the batteries were fully charged when leaving, cold is your friend in this case, basically  putting them to sleep, or hibernation if you like, this will minimize self discharge. Sometimes less is more.

mike95490

it all depends on the self-consumption of the charge controller.  A 20 MPPT from Morningstar consumes less than the Classic, and a PWM even less.