The sun is the natural source of energy for an independent water supply. Solar water pumps and systems operate anywhere that the sun shines, and the longer it shines, the more water they pump. When its cloudy, they pump less water, but often you need less water when it is cloudy.
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 (AC) current from the utility grid or a generator. To use solar energy economically, the solar water pump system must utilize the long solar day, drawing a minimum of power. This means pumping more slowly than conventional pumps. Pumping at rates of less than 6 gpm requires different mechanisms from the conventional (centrifugal) pumps.
Small submersible solar water pumps are unique, both electrically and mechanically. The most efficient solar water pumps for wells are “positive displacement” pumps. They pump a certain amount of water with each rotation. If it is cloudy or early morning, the solar water pump will receive less energy and run more slowly. A positive displacement pump will pump approximately half as much water with half as much energy. Conventional AC pumps are usually centrifugal pumps that spin at a high speed to pump as many gallons per minute as possible. They also consume a large amount of power which can be illustrated by the size of the inverter required to power different sized AC pumps. If you run a centrifugal pump at half speed, it pumps one quarter the pressure. 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 water pump system that needs attention only once every 2 to 20 years depending on the model.
Solar powered water 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 water pump works slowly and efficiently all day. Often a solar water pump specifcally for wells will work fine in a well with a recovery rate too slow for a conventional AC pump.