Build a Solar Stock Tank

When winter rolls around, our reliable solar stock tank will save you money watering your animals and time and effort chopping ice.

| October/November 2010

  • solar stock tank inset
    Inset shows front corners from the top of the collector box.
    LEN CHURCHILL
  • solar stock tank
    This solar stock tank can save up to $3 per day in electricity costs.
    PHOTO: GARY REYSA
  • miniature greenhouse
    In spring and fall, you can use the collector box as a miniature greenhouse.
    STEVEN FAHEY
  • building stock tank
    The author built the insulated tank enclosure in a solar-heated shop.
    GARY REYSA
  • solar livestock water tank
    The author moves the tank into place before filling it with water.
    GARY REYSA

  • solar stock tank inset
  • solar stock tank
  • miniature greenhouse
  • building stock tank
  • solar livestock water tank

Typical stock tanks have a large, exposed water surface that loses heat. They also have highly conductive, single-wall sides and bottoms that are in direct contact with cold air or cold ground. If your goal is to design a tank to maximize heat loss, you couldn’t do much better than a typical galvanized or plastic stock tank. By using this easy-to-build solar stock tank, you probably won’t need an electric tank heater to keep your livestock waterer from freezing this winter.  It will provide ice-free water in all but the most extreme winter weather. We used it through two frigid Montana winters, and if it works here, it should work just about anywhere.

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, it’s also efficient.

  • It’s 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 “real” 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!



The solar-heated livestock waterer rarely requires an electric heater. If you get a little ice on the water overnight, it will usually melt later in the day.

A couple of times during winter — when we had several days of temperatures below 10 degrees and not much sun — we needed an electric tank heater to keep the water from freezing. Even in these extreme cases, though, the power used by the heater is greatly reduced, because it’s working less to maintain temperature.

Thighmaster
11/20/2018 4:16:32 PM

I built a similar box three years ago. Works reasonably well unless cloudy day precedes nights 0-20F. Works way better than without this box that's for sure. Still had to knock a hole in the ice on nights 0-20F. This year way better with propane stock tank heater, which I added with a new hole in the lid. Uses very little propane because of the box.


Thighmaster
11/20/2018 3:45:58 PM

I built a similar box three years ago. Works reasonably well unless cloudy day precedes nights 0-20F at 9,000' elevation. Works way better than without this box that's for sure. Still had to knock a hole in the ice on nights 0-20F. This year way better with propane stock tank heater, which I added with a new hole in the lid. Uses very little propane because of the box.


Thighmaster
11/20/2018 3:45:57 PM

I built a similar box three years ago. Works reasonably well unless cloudy day precedes nights 0-20F. Works way better than without this box that's for sure. Still had to knock a hole in the ice on nights 0-20F. This year way better with propane stock tank heater, which I added with a new hole in the lid. Uses very little propane because of the box.







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