Water Pumping
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The sun is the natural source of energy for an independent water supply. Solar pumps operate anywhere that the sun shines, and the longer it shines, the more water they pump. When it's cloudy, they pump less water, but often you needless water when it is cloudy. Photovoltaic modules, the power source for solar pumping, have no moving parts, require no maintenance and last for decades. A properly designed solar pumping system will be efficient, simple and reliable.
Solar water pumping systems operate on direct current. The output of the solar power system varies throughout the day and with changes in weather conditions. The nature of variable electricity in the form of direct current (DC) is quite different from conventional, steady alternating current (AC)from the utility grid or a generator. To use solar energy economically, the pumping system must utilize the long solar day, drawing a minimum of power. This means pumping slower than conventional pumps. Pumping at rates of less than 6 gallons per minute (GPM) requires different mechanisms from the conventional (centrifugal) pumps.
Small solar pumps are unique, both electrically and mechanically. The most efficient pumps are “positive displacement pumps” which pump a certain amount of water with each rotation. If it is cloudy, or early morning, the pump will receive less energy and run slower. A “positive displacement” pump will pump approximately half as much water with half as much energy.
Conventional AC pumps are usually centrifugal pumps that turn at high speed to pump as many gallons per minute as possible. They also consume a large amount of power. If you run a centrifugal pump at 1/2 speed, it pumps 1/4 the water. Their efficiency is very low at low speeds and when pumping against high pressure.
If your water sources are remote from power lines, add up your long-term costs of fuel and repairs on generators, or the cost of utility line extensions. Now consider the savings with a solar pump that needs attention only once every 2 to 10 years.
Solar powered pumps can provide an equal volume of water per day without the high and inefficient energy demands of a large capacity AC pump. Instead of pumping a large volume of water in a short time and turning off, the solar pump works slowly and efficiently all day. Often a solar pump will work fine in a well with a recovery rate too slow for a conventional AC pump.
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Solar Submersible Pumps
If you are pumping from a well, we have solar pumps that can deliver from 1 gallon per minute (GPM) to over 20 GPM.
The smallest pump, the low power diaphragm pump from Shurflo operates from two 50 to 75 watt solar modules, depending on the head (vertical distance) it is pumping. It can pump 500 to 1000 gallons per day and lift water 200 feet. This pump requires service every 2 to 4 years.
If you have a higher lift, need more water or want a pump that does not require service for 5 to 10 years, the SunRise pump is a good choice. The SunRise can lift water 600 feet and can pump over 2000 gallons per day at lower lifts. It will require two to four 75 watt solar modules and a special SunPrimer controller. For greater water needs or deeper wells, any standard AC submersible pump (1/2 to 5 HP), can be solar powered when you use the Aerovironment AC Pump Controller. These controllers can also be used to retrofit an existing AC submersible pump to solar.
Surface Pumping
Surface pumps are less expensive than DC submersibles, where applicable. A surface pump is not submersible. It can draw water from a dug well, spring, pond, river or tank, and push it far uphill and through a long pipeline to fill a storage tank or to pressurize it for home use or for irrigation, livestock, etc. The pump may be placed at ground level, or suspended in a well in some cases.
All pumps are better at pushing than pulling. Surface
pumps must be placed no higher than 10 or 20 feet higher than the surface of the water source at sea
level (subtract one foot per 1000 feet elevation). Suction piping must be oversized a bit and not allow air entrapment (much like a drain line) and should be as short as possible. Pumps can push very long distances. The vertical lift and flow rates are the primary factors that determine power requirements.
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Pressurization
Many conventional AC powered water systems pump from a well or other water source into a pressure tank that stores water and stabilizes the pressure for household use. When you turn on water in the house, an airfilled bladder in the tank forces the water into the pipes. When the pressure drops, a pressure switch turns on the pump, refilling and repressurizing the tank. This works fine because of the ability of the AC pump to deliver a volume of water larger than the household uses. With a solar pump this will not work. First, the sun may not be shining when you need pressure. Second, many solar pumps deliver water too slowly to keep up with household use.
There are two ways to solve this problem. A non-pressurized water tank can be located high enough above the house for gravity to supply the water pressure. This can be on a hill or a tower. (Water pressure in PSI = head in feet times 0.433.) For reasonable pressure the tank needs to beat least 40 feet above the house. If this is not possible, a battery operated pressure booster pump can fill a pressure tank as needed from a storage tank that is filled by a solar pump in the daytime. The Flowlight Booster pump, as well as the Flojet and Shurflo pumps can be used for this purpose. You must use a pump that can deliver the maximum GPM required by the house, or have a pressure tank that is large enough to make up the difference between what the pressure pump can deliver and what is required, for the amount of time it is required. This is called the “drawdown volume” of the tank. Air filled pressure tanks can be obtained locally from a pump dealer.
CALCULATING SOLAR POWER NEEDS
With all solar powered pumps, the necessary solar array can be determined by looking at the watts required for the head and flow in your situation. Solar array watts should be at least 20% higher than the power required by the pump in your situation. If the pump runs on 24 volts, you will use pairs of solar modules wired in series. Two solar modules whose total wattage equals or exceeds the wattage required by the pump must be used. If the pump uses 48 volts, you will use groups of four solar modules wired in series whose total wattage exceeds the pump’s power requirement.
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