solar powered stock tank heater

We have had that question a few times over the years here... And, I don't think we ever had any good answers.

In winter, when there is just not a lot of sun, there is very little energy/heat available from the sun (worse the farther north you go).

http://www.solarelectricityhandbook.com/solar-irradiance.html

Great Falls
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 27° angle from vertical:
(Optimal winter settings)

Jan	Feb	Mar	Apr	May	Jun
2.31	3.40	4.06	4.44	4.50	4.60
Jul	Aug	Sep	Oct	Nov	Dec
5.08	5.01	4.61	3.69	2.67	2.14

Lets say you decide to use a 1,000 Watt stock tank heater:

http://stockyardsupply.com/index.php/watering-systems/stock-tank-de-icers-heaters/

Assume it is a 120 VAC 1,000 Watt heater and you want to use solar panels. Use 250 Watt @ Vmp~30 Volts, and 4 of those in series... Don't bother with batteries. They will be expensive and prone to failure. Just dump the heat into the tank and use the water itself for your energy storage.

• 1,000 Watts * 2.14 hours of sun * 0.77 derating for panels = 1,648 Watt*Hours per December day (really less because solar panels+sun+electrical IV curve from panels is not 100% panel->sun without using other stuff)
• 1,648 Watt*Hours => 5,623 BTU https://www.inchcalculator.com/convert/watt-hour-to-british-thermal-unit/

Guess that a propane heater is something like 50% efficient, that would be:

• 5,623 BTU per day / 91,500 BTU per Gallon (roughly) = 0.06 gallons of propane per day
• 20 gallon tank (roughly 80 lbs) / 0.06 gallon per day = 333 Days of "solar equivalent heat" (10 years of December)

Very little heat from 1,000 Watts of solar panels (ideally) connected to a 1,000 Watt solar heater... In the stock heater link above, they have a 12,470 BTU per Hour propane heater:

• 12,470 BTU per hour => 3,655 Watt*Hours per hour or ~3,655 Watt heater equivalent
• 12,470 BTU per hour / 91,500 BTU per gallon = 0.14 gallons of propane per hour
• 20 gallon (100 lb tank) / 0.14 gallons per hour = 144 hours of heating

How many hours of propane heating per day do you need? I don't even really have a guess. Size of tank, insulated or not, make up water per day or per week, temperature of makeup water, wind chill, exposure of tank to wind, etc.

If you can guess at how much ice per day is created in the tank, could work backwards from that. Say 20 lbs of ice per (bad) December day/24 hours:

• 20 lbs of water to ice * 144 BTU per lb of water/ice (latent heat of fusion) = 2,880 BTU per day

So, just guessing here with the 20 lbs of ice per day, but 1,000 Watts of solar panels may be able to prevent 20+ lbs of ice per day (very roughly 5,623 BTU per December day). And propane:

• 2,880 BTU per day of "anti icing" heat * 1/91.500 BTU per gallon (propane) * 1/0.50 efficiency (guess) = 0.06 gallons of propane per day
• 20 gallon tank propane (100 lbs) / 0.06 gallons of propane per 20 lbs of ice per day = 333 days of heating per 20 gallon propane tank (guessing at 20 lbs of ice per day)

Anyways, just some very quick math and, at least an idea, of how to figure how much heat per day if you can estimate/weight the amount of ice that that forms over 24 hours in your stock tanks. And for a "safety factor", I would use at least 2x (two times more energy estimated because of the very fuzzy guesses above).

Other than insulated tanks, under ground piping, etc... I am not sure what else to do/say:

https://duckduckgo.com/?q=insulated+stock+tank

I also guess you are trucking water or have a Wind powered water pump on site? No power? If wind pumping, can you simply let the wind pump overfill the tank during winter with "warm well water" to reduce/prevent icing?

-Bill