# How to figure energy needs for stock tank?



## Ohiogal (Mar 15, 2007)

Hi there, I have a stock tank that I heat using a stock tank heater. I want to switch to a solar array to generate the power. How do I go about figuring how big an array for that energy need? I have a garage roof with the perfect south facing angle and I'd like to install them on there.


----------



## Windy in Kansas (Jun 16, 2002)

Is your current stock tank heater electric, propane, or ??

If it is electric it should have a label on it showing how many amps it is rated at. Amps times voltage equals watts. One thousand watts used for one hour is called a kilowatt hour or KWH. 

For simple math--if your heater is a one thousand watt heater and it runs twenty-four hours each day then it would draw twenty-four KWH per day or if you prefer 24,000 watts per day.

I believe the folk on here tell that PV panels will generate for about 4-6 hours daily during the winter. So if you divide 24,000 by 6 hours you will get 4,000 watts of PV panels needed. If by 4 hours you would need 6,000 watts of PV panels.

You can buy a lot of electricity for what the panels and installation would cost to be blunt.

As an alternative have you considered installing a propane stock tank heater? I'm not sure if any commercially produced wood burning stock tank are still being produced but that might be another alternative.

As yet another alternative to keeping an open drinking hole in a stock tank is something I've only heard told about. A culvert is buried in the ground in an upright position with the stock tank placed over it. The warmer air from within the ground supplies just enough heating for a properly sized tank to keep a portion of it ice free.

You may also wish to view this former thread on stock tanks. http://foxyurl.com/sbn


----------



## SolarGary (Sep 8, 2005)

Hi,
You might want to consider a solar thermal approach rather than solar electric.
This is one I built for our neighbor:
http://www.builditsolar.com/Projects/WaterHeating/SolarHorseTank/SolarHorseTank.htm

And, some others -- some built by people on this forum:
http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm#Animals

I think that doing it with solar electric would likely be prohibitively expensive. If you have a 1500 watt stock tank, and it runs (say) 6 hours a day average in mid winter, that 9 KWH a day or 270KWH a month. 
The PVWatts calculator says that in our area it would take 4000 watt PV rig to average 270 KWH in mid winter. If you went with a conventional PV arrangement with batteries to store energy to run the heater at night, that's about a $40,000 rig. 
That's a lot compared to $200 solar thermal approach above 

Gary


----------



## TnAndy (Sep 15, 2005)

You be LOTS of dollars ahead to just use an insulated type stock tank with a small, thermostat controlled, electric backup for REALLY cold weather.

PV type solar should almost never even be considered for any type of electric heating.


----------



## wy_white_wolf (Oct 14, 2004)

If your tank heater is a 12VDC 50 watt model you will need about 900 watts in panels to run them 24 hours a day. Even putting it on a thermostat to have it run only when air temp is below freezing doesn't change that as you will have days in a row with freezing temps. 

(50 watts * 24 Hours *1.5 system effeciency / 2 hours winter insolation)

You would also need about 750AH of battery for this unless you wish to buy new batteries every year.


----------

