Just a gotcha to consider.

Tom

The Truth is the Truth, even if no one believes it; and a lie is a lie even if everyone believes it

First off, a 100W incandescent bulb running 12-16 hours a day in the middle of winter is gonna use about all the energy that the 400W of panels is going to make. You go away and let the batteries get 60% discharged because of three cloudy, windless days, get a nice chunk of 10-below weather, and you'll have frozen batteries

Fully charged batteries will not freeze until the temperature drops to well below -50F, cold batteries lose some of their capacity, but are otherwise unharmed in cold temperatures, as long as you can keep the SG up over 1.250 or so. If you're not there and there are no loads, your solar and wind should have no problem keeping the batteries up.

100F during the day is not a real issue either. Your batteries have a bunch of mass and will stabilize at a temperature about midway between the high and low temperature of the day if you're not using them.

My batteries have been in an unheated shed, in an insulated box for three years now with no ill effects. We're charging and discharging them every day, but I have never seen the temperature in the box drop below 40F, and we have had days where it never gets above freezing and is 10 below when the sun comes up.

Is that enough holes in your theory? ;-)

Volvo Farmer

question:  how do the batteries keep themselves from freezing?  i understand that they heat up when being charged or discharged, but little of that would be happening when i'm not up there.  does the electrolite/water combo have a lower freezing temp than water alone?  

i would much rather NOT have to do all the things i talked of above!  i'm just worried and don't want my first set of batteries to have an early death due to cold.  i looked at the record lows for the area over the winter months, and the lowest i found was -21 F.  

so my batteries will be fine with temps this cold if they are in an insulated box?  

the fan before the diode idea is pretty smart.  do you think this is needed even if the "ceiling" of the box is a "gable" or "pent" with the vent hole centered on the peak?  

was also thinking of running both solar and wind through dump style controllers to keep things moving in the batteries during the cold.  does this sound like a good idea?  

thanks for all of your help!

Sulfuric acid does the same thing to water as ethylene glycol, salt, sugar, fertilizers, and many other solutes that act as "antifreeze":  Disrupts the crystal formation, thus lowering the freezing point.  In fully charged batteries virtually all of the sulphate ions are in the electrolyte, equivalent to a LOT of antifreeze.  In discharged batteries much of them are in the plates so the electrolyte is more dilute and freezes more easily.  But it's still good to well below the freezing point of unadulterated water.

Thus it's fine - better - to leave them unheated rather than discharge them keeping them warm.  If they get 'way cold their output voltage will be somewhat lower at first when you start using them after they've been sitting idle for many hours (i.e. morning load on a solar-only recharge system).  But they'll warm up with use.

alright i got it, don't worry about them freezing if they are full.

UGL-  you're explanations are very helpfuly to visulize whats happening within a cold bank.  

now i just need to get my butt in gear to finish my turbine!  my machinist called today and said the blade mounting hub is done, so soon i'll post how my motor works under 24 volt load and maybe even 12 volt jerry when i get a little time to crack the case and switch wiring stuff around.  

thanks so much for all of your help!