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ARS Home » Plains Area » Bushland, Texas » Conservation and Production Research Laboratory » Livestock Nutrient Management Research » Research » Publications at this Location » Publication #133920


item Vick, Brian
item Clark, Ray

Submitted to: National Solar Conference
Publication Type: Proceedings
Publication Acceptance Date: 3/29/2002
Publication Date: 6/15/2002
Citation: Vick, B.D., Clark, R.N. 2002. Solar pv-water pumping with fixed and passive tracking panels. Solar Conference Proceedings. p.6.

Interpretive Summary: Livestock raised on pasture land in the Great Plains require a reliable water source, and usually the water is pumped from underground wells. Normally, utility supplied electricity is unavailable at these remote wells, so windmills or solar-powered pump systems are used to pump the water. In this paper, a DC solar water pumping system with fixed solar panels (e.g. solar panels that do not track the sun as the sun moves from east to west) was shown to water 35 head of cattle from a 100 foot well depth at a system cost of $2000 for a solar resource similar to Bushland, TX. The system cost of the DC solar water pumping system is based on: two 50 Watt solar panels, a solar panel mounting rack, a controller, 100 ft of polypipe, 300 ft of 14 gage electrical wire, and a diaphragm pump. Besides testing the fixed panel solar system, a passive tracking solar panel system was also tested. A passive tracking solar panel system tracks the sun from east to west using the sun's own energy. The passive tracking solar panel system was shown to be able to water an additional 5 cattle (40 head total) at an additional cost of $350 ($2350 total system cost) compared to using a standard fixed panel system. For comparison purposes, the smallest size windmill available (6-foot) with a 1 and 7/8 inch piston pump we estimate could water 80 cattle from a 100 foot well with a wind resource similar to Bushland, TX at a system cost of $5100. This windmill system cost is based on: a 6 ft windmill, 33 ft tower, 100 ft sucker rod, 30 ft pump rod, 100 ft (2 inch diameter) drop pipe, stuffing box, piston pump, leather cups. This paper on pricing and water pumped by the different solar panel systems (fixed and passive tracking) should help ranchers decide on which system will be best for their livestock operation.

Technical Abstract: A solar-PV (photovoltaic) water pumping study for pumping water for livestock was conducted over a 4-year period to determine the difference between using a passive one-axis tracking system compared to a fixed panel system. The passive tracking system provided 19% more power than the fixed panel system during the spring and summer, but only 15% more water was pumped. The reason the increase in the water pumped (15%) was lower than the increase in the power (19%) for passive tracking compared to the fixed panel system was due to the controller restricting the power going to the pump. The power increase was restricted to 19% for the passive tracking system compared to the 34% estimated power increase for a motorized tracking system because of the wind blowing the panels from the optimum position. During the winter and fall, the amount of time it took for the panels to point from west to east (early morning wake up) reduced the performance of the passive tracking system. The water pumped by either the fixed or the passive tracking system was essentially the same during late fall and winter. The passive tracking system could water 40 head of cattle at a cost of $2350 for a 100 foot well depth when the solar and wind resources were comparable to that of Bushland, TX. The fixed panel system could water 35 head of cattle at a cost of $2000 for the same well depth and solar/wind resource. Whether this additional increase in cattle to be watered with the passive tracking system is cost effective will depend on each rancher's livestock operation.