By Mike Morris, NCAT Agricultural Specialist and Vicki Lynne, NCAT Energy Specialist; Updated by By Chris Lent, NCAT Agricultural Specialist
IntroductionCostSolar Pumping Technology—What You Need to KnowDesigning and Installing SystemsFrost-Free System DesignProject DescriptionsFurther Resources
Because of falling prices, long life, and low maintenance requirements, solar is rapidly becoming the first choice for pumping water in remote locations. This publication gives an introduction to solar-powered livestock-watering systems, including discussions of cost, components, and terminology, as well as some suggestions for designing and installing these systems. The strengths and weaknesses of solar pumping are compared to the main options for pumping in remote locations: mechanical windmills, wind turbines, and portable generators powered by gas, propane, or diesel fuel. Design considerations for freeze protection in water-pumping systems are also discussed. Descriptions of four successful projects and a brief resource list are included.
Remote or off-grid power sources—including solar panels, mechanical windmills, wind turbines, and portable generators—can pump water for livestock in locations where electricity from power lines is unavailable. By encouraging animals to move away from ponds and streams, these systems give livestock greater access to forage. They also reduce livestock pressure on stream banks, preventing nutrient loading, damage to streamside vegetation, erosion, and pollution.
Solar pumping works anywhere the sun shines, and most parts of the United States have plenty of sunlight to run these systems. Solar pumping is a natural match for summer grazing applications, since it produces the greatest volumes of water in sunny weather and during long summer days—exactly when animals need water the most. With proper precautions, solar pumping systems can be used during the winter months too, even though shorter daylight hours will cause reduced water output.
Why should you consider installing a solar-powered livestock watering system on your farm or ranch? These factors may affect your decision:
In 2012, the typical cost for a small to medium-sized solar pumping system suitable for stock watering is $2,000 to $6,000. This does not include installation costs or well drilling. Retail prices for solar panels have dropped dramatically, falling by around two- thirds between 2008 and 2012.
More good news for consumers is that solar pumping systems are eligible for a 30% federal Business Energy Investment Tax Credit. There is no maximum credit amount, and a similar 30% tax credit is available to homeowners. These incentives have been in place since 2005 and are scheduled to last until December 31, 2016. Agricultural producers are also eligible to apply for grants or loans from the competitive Rural Energy for America Program (REAP), administered by USDA Rural Development. Grants are up to 25% of eligible project costs. For more information, visit or contact your state USDA Rural Development office.
Note that conditions and exclusions apply to both the Business Energy Investment Tax Credit and the REAP program. The information above is accurate as of 2012, but rules may change for both of these programs. For current incentives, check with your solar dealer or visit the Database of State Incentives for Renewable Energy (DSIRE).
Even with big price decreases and readily available financial incentives, solar panels are by no means a cheap way to generate electricity. After all, consider the fact that a 100-watt solar panel costing hundreds of dollars generates only enough power to light a 100-watt light bulb. Solar pumping systems are designed to run on low power, usually just a fraction of a horsepower. The four solar pumping systems described at the end of this publication range from 128 to 420 watts, or 0.2 to 0.6 horsepower. If you are familiar with irrigation pumps ranging from several to 100 horsepower or more, you''ll need to scale down your expectations.
Many solar panels on the market today (in 2012) cost under $2.00 per watt, and a set of panels for a small to medium-sized system should cost well under $1,000. However, keep in mind that prices for pumps, racking, wire, controllers, and other components have not dropped. In the case of pumps (discussed at length below), quality has arguably improved, but so have prices.
Solar pumping is well-suited to low-head and low-volume situations. Where large volumes and deep wells are involved, solar pumping becomes prohibitively expensive because it requires specialized, expensive pumps and extremely large solar arrays. Likewise, most pressurized irrigation systems require far too much power to be run economically with solar panels, although solar pumping can be an excellent choice for small drip-irrigation systems.
Although solar electricity is not cheap, there are many situations where solar-powered pumping systems can be justified based on economic reasons alone. When you factor in installation, fuel, and maintenance costs over the life of the project, you may find that solar is the most attractive option.
If power lines are readily available, they will generally provide the cheapest source of electricity. For many who decide to install a solar pumping system, a major consideration is the cost of utility-line extensions. Line extensions commonly cost $10,000 to $50,000 or more per mile. One very rough rule of thumb is that remote pumping (whether solar-, wind-, or generator-powered) is worth considering whenever the distance from the utility grid exceeds about one-half mile.
How do you choose between solar power, a mechanical windmill, a wind-electric system, and a gas-, propane-, or diesel-powered generator? No two pumping situations are alike, but here are a few guidelines:
Solar-powered systems have a relatively high initial cost compared to low–quality, generator-powered systems, but they are long-lasting and require little maintenance. Solar watering systems have few moving parts, and the components in these systems have proven to be very reliable when installed properly. Warranties on solar panels are usually 20 years or more.
Gas- or propane-powered generators sometimes have a lower initial cost than solar power, although the cost of fuel must also be included. Low-end gas-powered generators require frequent maintenance and have a design life of only about 1,500 hours, making them a costly and labor-intensive option in the long run. On the other hand, better-quality generators have many strong points. A high-quality, self-starting propane-powered generator operates unattended, runs day and night, is easy to install, should last many years, and is especially well-suited to situations involving deep wells and high volumes of water. Warranties are typically two to three years.
Although they cost about twice as much as comparable gas-powered generators, diesel-powered generators will often have a lower initial cost than wind- or solar-powered systems. In low-head and low-volume situations, a solar-powered system very often will produce cheaper water over the life of the system than a diesel-powered generator. On the other hand, where large volumes of water are required, a diesel-powered system may be the best available option. Warranties on diesel generators range from one to three years.
Mechanical windmills or windpumps—along-familiar sight in rural America—have a gearbox that converts the circular motion of the blades into up-and-down strokes of a pump cylinder. In a good location—one with average wind speeds above seven miles per hour—a wind-powered pump may produce cheaper water than a solar-powered pump. However, windmills often have a higher initial cost than comparable solar or generator-based pumping systems. A new windmill from Aermotor, a well-known company, will cost anywhere from $2,000 to $13,000, not including tower or installation costs. In general with windmills, you should expect much higher maintenance requirements than you would get with a solar-powered system. Warranties are typically five to seven years.
There is a night-and-day difference between the maintenance requirements of solar and wind-powered systems. Solar-powered systems typically operate nearly maintenance-free for years. On the other hand, wind turbines and windmills have somewhat demanding installation and maintenance requirements, and catastrophic failure is not uncommon. See the ATTRA publication Small-Scale Wind Energy on the Farm for more information.
The bottom line is that solar stacks up very well against the available alternatives, if you are looking to pump water in a remote location. If you are replacing a windmill, there is no question that you should seriously consider solar. In fact, solar-powered systems appear to be steadily replacing mechanical windmills and are well on their way to becoming the first choice for pumping water in remote locations.
All of these generalizations should be taken with a grain of salt. New equipment is coming on the market all the time, every option has its advantages, and it bears repeating that every pumping and stock-watering situation is site-specific.
Before talking to a dealer, it''s a good idea to know some basic terminology:
Solar Modules. Solar electric systems are sometimes called photovoltaic, or PV, systems. The word "photovoltaic" is often abbreviated "PV." Solar panels, or modules, generate direct current (DC) electricity. A group of modules is called an array. Modern solar panels are designed to withstand golf-ball-sized hail and usually come with 20-year (or longer) warranties. Most water-pumping systems will need two to six panels. The size and number of panels is determined by the voltage requirements of the pump. The size and type of pump, in turn, is determined by the amount of water needed and the height and distance the water needs to be pumped.
Mounting Structures. There are two ways to mount solar modules: on a fixed structure or on a tracking structure. Fixed mounts are less expensive than trackers and tolerate high winds better. They should ideally be oriented to face true south (not magnetic south), and the tilt angle also needs to be adjusted. The usual recommendation is to adjust the tilt angle to latitude minus 15 degrees for summer use, latitude plus 15 degrees for winter use, and equal to latitude for year-round operation. For example, if you were located at 40 degrees latitude, you would set the tilt angle at 25 degrees in the summer and 55 degrees in the winter, or else leave the tilt angle at 40 degrees year-round.
The effectiveness of a tracker is somewhat site-specific. Generally, the more sun hours available at a location, the more you''ll benefit from a tracking system. In a poor location receiving less than four hours of sun per day on average, a tracking system may not have much impact on the volume of water pumped. Also keep in mind that trackers add complexity to a system and make the system more susceptible to wind damage than a fixed array. Finally, it should also be pointed out that trackers have become less popular as solar panels have dropped in price. You may find that it''s easier and more cost-effective to simply add another panel or two, rather than install a tracker. An experienced dealer/installer can help you decide whether a tracker would be right at your location.
Pumps. Solar panels produce direct current (DC) power, and DC pumps typically use one-third to one-half the power of alternating current (AC) pumps. For this reasons, DC pumps are used far more often than AC pumps in solar-powered systems. However, the German companies Grundfos and Lorentz have both developed pumps that can run on either AC or DC power. This allows a backup AC generator to be used, without an AC-to-DC converter, when there are periods of little sun.
All pumps can be classed as either submersible or surface, and as either displacement or centrifugal.
Submersible pumps, placed down a well or sump, are very commonly used in small stock-watering applications. Among other advantages, they are not exposed to freezing temperatures, do not need special protection from the elements, and do not require priming. Surface pumps, located at or near the water surface, are used primarily for moving water through a pipeline. Some surface pumps can develop high heads and are suitable for moving water long distances or to high elevations.
Displacement pumps use diaphragms, vanes, or pistons to seal water in a chamber and force it through a discharge outlet—similar to the way your heart pumps blood. On the other hand, centrifugal pumps rely on centrifugal force. A spinning impeller adds energy to the water and pushes it into the discharge outlet, similar to the way water sprays off a spinning bicycle tire.
Displacement pumps operate at slower speeds than centrifugal pumps. They generally move less water but are more powerful—like driving a car in low gear—and are often used in deep well and high head situations. On the other hand, if there is a lot of water to move (high flow) without much increase in elevation (low head), usually a centrifugal pump is chosen for the job. Centrifugal pumps are generally high speed pumps that need to spin an impeller very quickly in order to produce any pressure at all. In partial sun, as the impeller slows down, a centrifugal pump often loses its ability to move water, while a displacement pump will keep pumping, albeit at a slower rate.
One type of submersible displacement pump, the helical rotary pump, has recently become popular on the solar water-pumping scene. The helical rotary pump uses screw-like rotors to pressurize and pump water. Helical rotor pumps are a good choice for a deep-well application, and they are well-suited for pumping low volumes of water at a high head. These pumps can also handle some particles in the water without being damaged. For this reason, some installers prefer helical rotor pumps for surface-water pumping from streams and ponds, where water clarity can be an issue.
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