Photovoltaic modules, the power source for solar water pump systems, have no moving parts, require no maintenance and last for decades. A properly designed solar water pumping system will be efficient, simple and reliable. Solar water pump systems operate on direct current, (the Shurflo 9300 solar water pump operates at 24v, the Grundfos SQflex solar water pump for wells operate as high as 300VDC).
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. 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.
