A solar water-pumping system can be a cost-effective, dependable method for serving your remote watering needs, whether it’s for irrigation, animal grazing, or potable use. For more details, see"Solar-Powered Water Pumping”.
A farmer in western New York plans to use solar-pumping to water 120 beef cattle. The water source is a drilled well located at the base of the hill, 1,800 feet from utility power. A surface-mounted 1,500-gallon polyethylene storage tank was installed at the top of the hill. The tank’s inlet is 71 feet above the ground level at the wellhead. To connect to the well, 340 feet of 11/4-inch poly pipe is needed (this common size tends to work well with most flow rates). A float switch is installed in the tank and is wired to the pump controller.
The storage tank will gravity-feed four 300-gallon stock tanks that are 25 to 40 feet lower. There are mechanical float valves in each stock tank to regulate the water level. This is a seasonal operation from April through October—no freeze-proofing is needed.
Additional Specifications
Well depth: 180 ft.
Static water level (SWL): 35 ft.
Recovery rate: 14 gpm
Anticipated drawdown: None, if pumping rate is kept below recovery rate
Water requirements: 120 beef cattle at 15 gpd each = 1,800 gpd
Avg. daily sun-hours (annual* average): 4.1 (246 daily sun-minutes) *A seasonal sun-hour average could be used, but could result in overestimating the gpd produced.
Estimated pump flow: 10 gpm
Total dynamic head (TDH):
- 35 ft. from SWL to ground level (pump is at 170 ft., but only the SWL counts)
- 71 vertical ft. from well ground level to the storage tank inlet
- Head loss from 170 ft. of 1 in. drop pipe in well: 2.93 per 100 ft. from table × 1.70 = 4.98 ft. (see table in “Solar-Powered Water Pumping,” this issue)
- Head loss from 340 ft. of 1.25 in. pipe to tank: (0.88 per 100 ft. from table × 3.4 = 2.99 ft.
Total TDH = 35 + 71 + 4.98 + 2.99 = 113.97 ft.
Pump sizing: A Grundfos sizing table or online calculator shows that the 11 SQF-2 pump will provide 10 gpm at 120 ft. and require 500 W. The calculator accounts for PV array losses, so there’s no need to upsize.
Output: 246 sun-minutes per day × 10 gpm = 2,460 gpd, which exceeds the water requirements.
Proposed Solar Water Pumping System
- Grundfos 11 SQF-2 pump
- Two 250 W modules in series (Vmp 62.2)
- Pole-mounted PV array
- CU200 pump controller with a Grundfos float switch in the storage tank
http://www.homepower.com/articles/solar-electricity/design-installation/methods-sizing-solar-water-pumping-system
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