Every drop of wisdom counts with solar pump systems

As we were reminded during the last three years of drought, a good water supply is critical for successful ranch operation. Cattle require an adequate amount of water for body growth, fetal growth and lactation, and to replace moisture lost in urine, feces, sweat or by evaporation from the lungs or skin.

Robert Fears

Freelance Writer

Robert Fears is a freelance writer based in Georgetown, Texas.

Adequate water is also needed for ranch households and for some of the chores done around the barn and corrals.

“Solar pumping systems provide a viable method to water livestock in locations where utility electricity is not available,” says Lori Marsh, Virginia Tech. “They can be used to provide pressurized water from wells or low-lying ponds or streams to locations at higher elevations.”

“A solar-powered water pumping system is made of two basic components – PV (photovoltaic) panels and a pump,” says Michael Buschermohle, University of Tennessee.

Amount of water demand determines required size and number of PV panels

“The PV panels are the power supply, with a solar cell being their smallest element. Each solar cell has two or more specially prepared layers of semiconductor material that produce direct current (DC) electricity when exposed to light. This DC current is collected by wiring in the panel. It is then supplied either to a DC pump or occasionally stored in batteries for future use by the pump.”

“The heart of any successful rural water program is an efficient, reliable and sustainable pumping system driven by efficient whole-system design,” emphasizes Eric Macias, chief operating officer of Lorentz. “The design should include use of products with a long life, affordable maintenance and ability to monitor and measure system performance.

“Good design starts with water consumption analysis,” Macias says. “Compute quantity of required water using the number of livestock that will be on the ranch and the amount needed by irrigated crops."

"Determine when water is needed by documenting the use cycle during the day. Identify the source of required water. Ground water from deep aquifers may be the better choice for reliability. If output of the well or surface-water source cannot meet water demand, then water will need to be stored.”

Location of panels

“Solar energy is very predictable, but location of the PV panels or modules is important,” Macias continues. “To understand how to best capture solar energy, we need a quick reminder on the relationship of earth to sun. The earth is tilted and makes a complete rotation on its axis once every 24 hours."

"Earth orbits the sun once per year, facing it more in summer and less in winter. Due to tilt of the earth, the sun appears higher in the sky in the summer, and days are longer. As you move closer to the equator, summer/winter variance becomes smaller.”

Some of us need to relearn a small amount of basic physics to understand solar energy. We need to remember that radiation is a process where energy is radiated from a source. An example is solar energy radiated from the sun.

Irradiation is the opposite of radiation and is a process where energy falls on a certain surface. More simply, radiation is a process where energy leaves a source and irradiation is the process by which a surface receives energy.

Solar insolation is the amount of electromagnetic energy (solar radiation) that falls on the earth’s surface. By knowing the insolation levels of a particular region, we can determine the required size of the solar array (set of PV panels) and energy output. An area with poor insolation levels will need a larger array than an area with high insolation levels.

Insolation values are generally expressed in kilowatt hours per square meter per day. This is the amount of solar energy (measured in kilowatt hours) that strikes a square meter of the earth’s surface in a single day. Values are averaged to account for differences in day lengths.

“Irradiation level on the earth varies dramatically depending on the atmospheric conditions, particularly the amount of cloud cover,” Macias explained. “This variation becomes important when calculating solar generators, so accuracy is critical."

“If the solar pump system is expected to perform during winter months, the array should be oversized to account for low sunlight. Peak irradiation is 1,000 watts per square meter. If we have a 740-watt solar array and our motor requires 600 watts to achieve the desired flow rate, double the array size to 1,480 watts. This will ensure maximum flow rate from the pump on days with irradiation of 500 watts per square meter."

“Consider the changing arc of the sun at different times of the year in the planning process,” continues Macias. “To maximize capture of sunlight modules, PV panels must be mounted tilting toward the sun, which means that solar modules must be installed facing south in the Northern Hemisphere and facing north in the Southern Hemisphere."

"Optimum tilt angle is determined by the location’s latitude. In summer, tilt should be the latitude minus 15 degrees, and in winter, it should be latitude plus 15 degrees. As a year-round compromise for pumping applications, tilt can equal the latitude."

“Consider shading when planning a solar-powered water system,” says Macias. “Shading caused by distant objects does not have a significant effect on output because diffused light, or light bouncing off of other surfaces, will contribute to module outputs."

"Shading from near objects will cause more severe drops in power and can easily stop the complete output from a module. Production levels of any modules connected in series to a shaded module is reduced to that of the shaded modules. Shading can reduce output from a module or a series of modules to zero.”

When choosing a location for solar power installation, make sure nearby trees will not provide a shading effect on the PV panels. Even though trees may not be a current problem, they will continue to grow and may cause reduced output in the future. Trees have leaves in the spring and summer, which increases their shading effect.

Tools and computer apps are available for viewing the solar path. Sunseeker, for example, provides a flat-view compass and an augmented reality 3-D camera showing the solar path, its hour intervals, its winter and summer solstice paths, rise and set times, and a map showing solar direction at each daylight hour.

Providing enough water

“Water storage is a key component of a reliable solar-powered pumping system,” says Macias. “A minimum of one day’s water consumption should be stored, and three days or more is better. Most USDA-NRCS solar pumping system designs require a minimum storage of seven days.

“Storage volume is based on number of water sources, number of animals to be watered and their daily water consumption in a given pasture. If you are trying to water 100 head of cattle at 25 gallons per day per head, and you are using a 1,000-gallon tank on a single well, you might have trouble keeping the storage tank full or even run out of water during really hot months. This can be alleviated by utilizing adequate water storage."

“Storing water requires almost no maintenance and is much more cost-effective than storing power in batteries or hauling a generator. The only reason a generator or batteries should be used in a livestock water supply system is when well production is low or water demand cannot be met by daytime pumping,” Macias continues. “If sized right, a solar pumping system should be independent of any other power source to meet water demand.”

The pump system controller is a very important component because it allows the pump to start and run at reduced output in low-sunlight hours. Through maximum power point tracking, a system is optimized to produce 10 to 15 percent more water in a day. The controller also protects the pump from running dry, stores system performance data and tells the pump to shut off when the tank is full.

Safety

“PV panels generate DC electricity, which should be respected,” says Macias. “Develop and follow a safety program based on local safety rules and codes of practice. Three 185-watt modules in a series generate 150 volts, whereas any amount greater than 42 volts of either DC or AC (alternating current) electricity is considered unsafe. Handle PV modules with care and respect.”

A switch to disconnect solar panels from the pump is a very important safety measure and is part of every professional installation. The disconnect switch is placed between the solar generator and controller and must be a DC type for high amperage. It must be connected as per manufacturer’s instructions. A disconnect switch is a national electrical code requirement in most countries.

“Although a disconnect switch is used to cut off power to the pump, PV modules produce power when they are in daylight and cannot be switched off,” Macias adds. “Before working on the equipment, cover PV modules with a sheet or cover of opaque material to stop power generation.”

Before purchase, it is important to look at the maintenance costs associated with various solar pumping systems. Some systems contain non-serviceable components, meaning that the entire pump, motor and control have to be replaced when only one of the parts malfunctions.

This considerably increases maintenance costs. In buying a solar water system, also compare gallon-per-day performance, component life expectancy and warranty coverage. Ensure that the vendor is reputable and is able to service what they sell.