Pump Sizing for Off-Grid Solar Water Systems?

Calculating Total Dynamic Head (TDH)

To calculate the TDH, you’ll need to determine the static head (SH), friction head (FH), and pressure head (PH). The static head is the depth of the well or storage tank, typically measured in feet or meters. For a shallow well, assume a static head of 20-50 feet (6-15 meters). The friction head depends on the pipe diameter, length, and water flow rate. Use a pipe friction loss chart or calculator to estimate the friction head, which can range from 0.1-10 feet (0.03-3 meters) of head loss per 100 feet (30 meters) of pipe. The pressure head is usually 0-10 feet (0-3 meters) depending on the system design.

Choosing the Right Pump

Use a pump sizing chart or software to find the suitable pump for your specific application. Consider the flow rate (GPM or LPM), static head, and total dynamic head. For example, a 1 HP (746 W) pump can deliver 5-10 GPM (19-38 LPM) of water at 20-50 feet (6-15 meters) of static head. A common solar water pump for a shallow well might have a flow rate of 5-10 GPM (19-38 LPM) and a power rating of 200-400 W. Ensure the pump is compatible with the solar panel array and system controller.

System Design Considerations

When designing an off-grid solar water system, consider the overall system efficiency, including the pump, panel array, and system controller. A well-designed system should aim to achieve at least 80% overall efficiency. Use a system design software to optimize the system performance and ensure it meets the daily water demand. For a shallow well, a 2 kW (2000 W) solar panel array can provide sufficient power to support a 1-2 HP (746-1500 W) pump, depending on the system losses and overall efficiency.