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Solar Water Pumps

A solar water pump is simply any water pump that uses solar energy for its power source.  Solar water pumps are specially designed to utilize DC electric power from photovoltaic panels. They must work during low light conditions at reduced power, without stalling or overheating. Solar water pumps have one significant advantage over other types of pumps, they do not require the presence of an electric line in order to operate.  This makes them extremely useful in rural locations such as ranches and farms, or in the developing world where electricity is often not available.   In many parts of the world the cost of running traditional water piping or an electric line for a pump is cost prohibitive. A solar water pump is a perfect solution to this problem. Because of this they have been used extensively in places like India, Africa and Asia both for pulling water from wells, providing water to livestock, and for irrigation.

Solar pumps have plenty of application in the U.S. as well.  They have become extremely popular for rural and agricultural well pumping and are starting to replace many pumps that were originally operated by wind mills. Many homes in the U.S. rely on well water and solar pumps can be a convenient approach for keeping their water tanks full.  Solar pumps are also being used extensively in landscaping. Because they do not require any type of wiring they allow landscapers tremendous freedom in where to place water features such as fountains, streams and waterfalls. 

Solar pumps are friendlier to the environment and cheaper to operate than conventional AC pumps.  By harnessing the energy of the sun they eliminate the need to use traditional fuel sources such as oil or coal to generate the electricity they need to operate. This saves money as well, particularly in developing countries where electricity is both scare and expensive.  Also, because they eliminate the need for digging ditches for electric lines or putting up power line poles, they are less disruptive to the natural environment.   Another advantage of solar water pumps is that they are not dependent upon the grid for electricity. That means you can pump water even when the electricity goes out! For those homeowners who rely on well water this can be a big advantage.

Types of Pumps

Solar panels generate DC current and so the vast majority of solar pumps use direct current rather than alternating current so no current inverter is needed.  Most of the pumps are packaged without batteries so they really only run while the sun is shining.  However, for most typical uses this is perfectly acceptable and it has the advantage of being a very simple setup that requires little maintenance.  There are different kinds of pumps depending upon what you are trying to do:

  • Circulating Pumps: These types of pumps are often used in solar water heating applications. They can be used to move either water or a thermal transfer fluid such as antifreeze (glycol) through a home hot water heating system.  These same pumps can also be used for a pool heating system. They are also frequently used in landscaping applications for waterfalls or fountains.  Most circulating pumps are relatively small and many have the option to run on AC or DC power.

  • Submersible Pumps: Submersible solar pumps are generally used for pumping from wells, and are designed to fit inside the well casing in a drilled hole. The most common casing size is 6", but 5" and 4" are also common. Some older wells drilled for windmills are less than 4", and most solar submersible pumps will not fit - for that the best thing is to replace the windmill with an ERA jack pump. Submersible pumps can lift up to 650 feet and are used when the water supply is more than 20 feet from the surface. The well may be anywhere from a few feet to 1800 feet deep - but the deeper the well, the more expensive the system. Depths over 400 feet will generally cost quite a bit more. Solar powered well pumps are seldom suited for large amounts of water, such as irrigating larger fields if you have AC power available. The largest pumps generally available are 1/4 to 2 HP.

  • Surface Pumps: These types of pumps use a suctioning approach and are good for applications with shallow wells, ponds, streams or storage tanks. They work best if the water supply is 20 feet or less from the surface.   Whenever you should try to minimize the suction lift to just a few feet. The maximum possible suction for any pump is about 20 feet but if you push them to lift more than a few feet they will become noisy and come under more strain. As with other solar pumps the solar panels for the pump can be remote from the pump itself which allows a great deal of flexibility in placement. In some landscaping systems designed for pools and ponds the whole system floats with the solar panels lying just below the surface of the water.

  • Delivery pumps:
  • These pumps are used to move water from one place to another. Some are capable of high pressure while others are intended mainly for moving large volumes at low pressure (such as moving water from a cistern to a stock watering tank). Flows can be small (1/2 gallon per minute) up to 30-40 gpm.

One disadvantage of DC solar pumps which do not use batteries is that the energy they generate varies throughout the day based upon the available sunshine to the solar panels.  Therefore most DC solar pump kits include a device called a linear current booster (LCB), also called a pump controller, which acts like an automatic transmission, helping the pump to start and not to stall in weak sunlight. An LCB also allows the pump motor to run longer during the day by translating additional voltage to necessary current during periods of low sun.

Solar Panels for Pumps

Solar pumps get their power from solar panels. The type of solar panels you would use is no different than the kind that might be put on a roof in a residential solar electric system. Solar panels come in many different sizes.  Generally the larger they are the more watts of electricity they can generate. The number of watts you will need to generate, and therefore the number of solar panels you will need for your pump, depends upon the size of the pump and what you are going to use it for.  For example, when using solar panels with submersible well pumps the number of panels you will need depends greatly upon the depth of the well -- the deeper the well, the more power needed, and therefore the more solar panels needed. When using delivery pumps the number of panels you will need is a function of the volume of water you need to move (usually measured in gallons per minute) and the water pressure you must generate.

Most DC pumps are fairly small and only require a single solar panel. The solar pump kit manufacturer will have properly matched the solar panels output to the power requirements of the pump.  However, if you find your pump requires more energy you can usually add on another panel since most panels are designed to be connected in strings or modules.  The main thing is to be sure that you don't exceed the maximum voltage the pump can handle.  If you are not sure check with an electrician or the contractor that provided you the pump.

Low volume pumps use positive displacement (volumetric) mechanisms which seal water in cavities and force it upward. Lift capacity is maintained even while pumping slowly. These mechanisms include diaphragm, vane and piston pumps. These differ from a conventional centrifugal pump that needs to spin fast to work efficiently. Centrifugal pumps are used where higher volumes are required.

Most solar pumping systems use water storage rather than batteries, for simplicity and economy. A float switch can turn the pump off when the water tank fills, to prevent overflow. Compared with windmills, solar pumps are less expensive, and much easier to install and maintain. They provide a more consistent supply of water. They can be installed in valleys and wooded areas where wind exposure is poor. A PV array may be placed some distance away from the pump itself, even several hundred feet (100 m) away.

The smallest solar pumps require less than 150 watts, and can lift water from depths exceeding 200 Feet (65 m) at 1.5 gallons (5.7 liters) per minute. You may be surprised by the performance of such a small system. In a 10-hour sunny day a solar pump can lift 900 gallons (3400 liters). That's enough to supply several families, or 30 head of cattle, or 40 fruit trees! Slow solar pumping lets us utilize low-yield water sources. It also reduces the cost of long pipelines, since small-sized pipe may be used.

Determining the Type of Pump You Need

One of the first things you will need to do in most water pumping scenarios is determine whether a submersible pump or a surface pump is best. This is based on the nature of the water source. Submersible pumps are suited both to deep well and to surface water sources. Surface pumps can only draw water from about 20 feet (6m) below ground level, but they can push it far uphill. Where a surface pump is feasible, it is less expensive than a submersible, and a greater variety is available.

Once you have decided the type of pump you will need you will need to determine the flow rate required. Here is the equation, in the simplest terms: Gallons (Cubic Meters) per Hour = Gallons (Cubic Meters) Per Day / Available Peak Sun Hours per Day Peak Sun Hours refers to the average equivalent hours of full-sun energy received per day. It varies with the location and the season. For example, the arid central-western USA averages 7 peak hours in summer, and dips to 4.5 peak hours in mid-winter. In most cases, to be safe, you will want to talk to your well contractor or a local pump provider to ensure that you have correctly estimated your requirements but inevitably whoever you talk to is likely to ask one or more of the following questions, so be prepared:

  1. How deep is your well or alternative water source?
  2. What is the static water level in the well (the static level is that height in the well to which the water rises under it’s own pressure)?
  3. How many gallons per minute does your well produce?
  4. How many gallons per day do you need?
  5. Will you pump to a non-pressurized holding tank or to a pressure tank?
  6. How many feet above the well head is the tank located?
  7. If a pressure tank is used, how many pounds of pressure will you ask the pump to create?
  8. How many feet from the solar array to the well head?
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