So I'm thinking that I might try this out next winter...a little late to mess with this year but could definitely save me some bucks on propane for the current tank heater.
Here is the excerpt from the article about it. The folks who came up with this used them through winters in Montana without them icing up at all, so I think they would be more than enough for here.
The Passive Solar Tank
The livestock waterer is built around a standard galvanized metal stock tank, which is surrounded by a well-insulated enclosure. The south wall of the enclosure is a double-glazed solar collector. Using two layers of corrugated plastic (double glazing) reduces overnight heat loss from the tank. The metal tank wall is just behind the collector glazing and acts as the collector absorber. The sun shines through the glazing onto the tank wall, which heats up the tank wall and the water. The tank wall is painted black to absorb heat from the sun efficiently. The waterer has a lid with an opening just large enough for animals to drink through, and this limits the heat loss from the water surface.
While this design is simple, itís also efficient.
Itís well-insulated. Heat loss is far less than from a bare metal or plastic tank.
The solar collector adds heat on sunny days, and the double glazing reduces heat loss from the collector.
Solar collectors are more efficient if they operate at a low temperature. The water only needs to be heated to just above 32 degrees Fahrenheit. This allows the absorber (tank wall) to run cool, which reduces heat loss out of the glazing. If the tank wall needed to be hot for the system to work, a lower percentage of the heat collected would be transferred to the water.
The water provides thermal mass so all of the available sun energy can be effectively stored.
The lid further reduces heat loss from the water surface.
We measured the energy consumption of an electric heater in the old tank (a bare, galvanized tank) at 8.5 kilowatt hours per full day during mild winter weather, with low night temperatures about 15 to 30 degrees and daytime highs about 25 to 40 degrees. We estimate the energy use for ďrealĒ winter weather is about 30 kilowatt hours per day, which would cost about $3 and result in about 50 pounds of carbon dioxide emissions per day!