current is collected by the wiring in the panel. It is then supplied to a DC pump, the second component of the system. “Solar water pumps are designed to use solar power
effi ciently,” Buschermohle continues. “Conventional pumps require steady AC current that utility lines or generators supply. Solar pumps use DC current from batteries and/or PV panels. Also, they are designed to work effectively during low-light conditions, at reduced voltage, without stalling or overheating.” Eric Macias, chief operating offi cer of Lorentz, dis-
cussed solar powered water pumping systems during the March School of Successful Ranching, part of the 2015 Cattle Raisers Convention. Macias emphasized that the heart of any successful
rural water program is an effi cient, reliable and sustain- able pumping system driven by effi cient, whole system design; use of products with a long life; affordable maintenance; and the ability to monitor and measure system performance. “Good design starts with water consumption analy-
sis,” says Macias. “Compute the quantity of water re- quired by using the head of livestock that will be on the ranch and the amount needed by irrigated crops. Determine when water is required by documenting the use cycle throughout the day. Identify the source of the required water. Ground water from deep aquifers may be the better choice. If available well or surface water cannot meet demand, then water will need to be stored.”
Location of panels “Solar energy is very predictable, but the location
of the PV panels or modules is important,” Macias continues. “To understand how to best capture solar energy, we need a quick reminder of the relationship of the earth to the sun. “The earth is tilted and rotates on its tilted axis once
per day. Earth orbits the sun once per year facing it more in summer and less in winter. Due to the tilt of the earth the sun appears higher in the sky in the sum-
Good design starts with water consumption analysis.
62 The Cattleman May 2015
mer and the days are longer. As you near the equator, the smaller the summer/winter variance becomes.” Some of us need to relearn a small amount of ba-
sic physics to understand solar energy. We need to remember that radiation is a process whereby energy is radiated from a source. An example is solar energy radiated from the sun. Irradiation is the opposite of radiation; a process whereby radiated energy falls on a surface such as a PV panel. The amount of irradia- tion is the insolation level, which basically tells how much sunlight is shining down on us. By knowing the insolation levels of a particular
region we can determine the required size of the solar array. An array is a series of panels. Areas with poor insolation levels will need a larger
array than an area with high insolation levels. Once you know your region’s insolation level you can more accurately calculate array size and energy output. Insolation values are generally expressed in kilowatt hours per square meter per (kWh/m²/day). This is the amount of solar energy that strikes a square meter of the earth’s surface in a single day. Values are averaged to account for differences in the day lengths. “Irradiation level on the earth varies dramatically
depending on the atmospheric conditions, particularly with the amount of cloud cover,” Macias explains. “This variation becomes important when calculating solar generators, so accuracy is critical. If you want the solar pump system to perform in the winter months, you must oversize the array to account for low sunlight.
thecattlemanmagazine.com
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