How They Work
Solar water pumps are specially designed to utilize DC power from photovoltaic modules or wind turbines. The pumps work with variable amounts of power as the sun provides more or less energy during the course of the day. Low volume pumps use positive displacement mechanisms, which seal water in cavities and force it upwards. Lift capacity is maintained even while pumping slowly. These differ from a conventional centrifugal pump that needs to spin quickly to work efficiently, and cannot operate in low light conditions.
Our water pumps use a pump controller, which is an electronic device that acts like an automatic transmission, helping the pump to start and keeps it from stalling in weak sunlight or weak wind.
Because the sun doesn’t shine all of the time, most systems use water storage tanks as a simple and economical way to store excess water pumped during sunny days. A float switch should be added to the system to turn the pump off when the water tank fills.
A pumping system using a small solar array or wind turbine can be inexpensive and easy to install and maintain. The solar panels provide a consistent supply of water during sunny days and can be installed in valleys and wooded areas where wind exposure is poor. A wind turbine can generate power long after the sun sets. The specific installation location will determine which is more advantageous
What Solar Water Pumping Can Be Used For
- Domestic Water:
Solar pumps are used for private homes, villages, medical clinics, etc. A water pump can be powered by its own PV array, or by a main system that powers lights and appliances. An elevated storage tank may be used, or a second pump called a booster pump can provide necessary water pressure.
Cattle ranchers are enthusiastic users of solar pumps. Their water sources are scattered over vast rangeland where power lines are few and costs of transport and maintenance are high. Some ranchers use solar pumps to distribute water through several miles (over 5 km) of pipelines. Others use portable systems, and move them from one water source to another
Solar pumps are used on small farms, orchards, vineyards and gardens. It is most economical to power the pump directly from the PV array, store water in a tank, and then distribute it by gravity flow. Where pressurizing is required, storage batteries stabilize the voltage for consistent flow and distribution, and may eliminate the need for a storage tank. Batteries also introduce cost, complexity and additional maintenance into the system.
Designing a Solar Pumping Solution
For solar water pumps, first identify how much water you need per day and the vertical lift required. Next, determine whether a submersible pump or a surface pump is best. Submersible pumps are suited both to deep well and to surface water sources. Surface pumps can only draw water from about 20 feet below ground level, but they can push it far uphill.
To determine the flow rate required, use the following equation:
- Gallons per Hour = Gallons Per Day/ Available Peak Sun Hours per Day
Peak Sun Hours refer to the average equivalent hours of full sun energy received per day. It varies with the location and the season. Use the map below to find an estimate of the available peak sun hours per day where you live.
Deciding on a Pump
The decision of what type, make, and model of pump to use in a given situation is very critical to the overall success of a project, and should be given thorough consideration prior to purchase. The main considerations are:
Volume. How much water is required per day?
Location. What is the physical location of the project?
Water source. Is the source a well, a pond, a stream or cistern?
Depth. How deep is the well?
Water level. What is the “static” water level within the well?
Recovery Period. What is the “rate of recovery”? (At what rate in gallons per minute does the water re-enter the well while being pumped?)
Head. What is the TDH (Total Dynamic Head)? The vertical distance as measured from the surface of the standing water in the well to the point of delivery into tank, etc.
Pipe. What is the inside diameter of the delivery pipe and what is the total pipe length?
Water Temperature. Through special application, it is possible to pump water > 120 degrees F, and even higher.
Wire Length. What is the total proposed distance from the PV array to the pump?