I don't have any hands on experience with solar systems designed for winter use, however I have certainly pushed to the limits use of one of my regular solar pumping setups. More than once have chopped two inches of ice out of a trough well into December. That particular setup is two 700 gallon troughs hooked together and supplied by a floating 12v pump, but the supply line is setup so it completely drains back into the dugout each time pump kicks out, even all summer. Line between fence and troughs runs inside a length of 2 7/8 tubing to protect the 1 1/2 plastic. For use in extended cold temps, like Nov and Dec, first you rig your float power cable thru a switch so you control pump operation manually, usually you're feeding some by now, most often pumping during the time spent tearing a a few bales apart is sufficient for the day. I also tie a few straw bales together and lay them on the bank of dugout, covering the outlet hose right above the water line. This keeps the line from freezing at the ice level. The crossover line is buried under several inches of dirt between the two troughs, but eventually will freeze, and then I simply turn the outlet into each trough and fill it independently. You need to monitor the ice thickness on dugout as I found from experience, its easier to keep your pump halfassed chopped free to facilitate removal when its time to shut the system down for winter. Be sure your wires are secured to your water line. Oh and I forgot, once ice begins to set up on dugout, remove your tether line. I've pumped well into winter for upto 150 pair in this manner, not the greatest, but one can get by. I have often thought of putting a heater in the trough, then it could run automatic as the float wouldn't freeze, but just have never got there yet.
As for the proper systems, two are in the works, just haven't had time to complete them. One is going to be a gravity system as Dan is speaking of, and the other much like the first example in the attached link. I have seen both systems in operation and they are slick setups. I have my own hoe and such, so no biggie to take on such projects, cost isn't much of an issue that way, I just don't have time to get the dam things done is all. To hire stuff out, then it could get costly. And you can get double duty from your pumps if you use them in summer as well.
Anything that keeps them out of the dugout is good in my books. And while I have never had a wreck on ice myself, I've certainly heard of them, and no one needs that
Link on various systems