3-phase pressurized water system for off-grid home

At my Mt Best residence I collect and store rainwater at the top of a hill some 30m above my house and garden and this enables me to avoid using pumps.

For my friends and neighbors, who do not have a suitable hill nearby, I designed an efficient water pumping solution that utilizes a 3-phase motor, efficient multistage pump and a large (300L-450L) pressurized water tank. An example of my installation is depicted below.

Features of the 3-phase pump + large pressure tank solution are:

  • Daily energy consumption 0.1 kWh (negligible in daily solar energy budget)
  • Large pressure tank (300-450 litres) reduces number of daily pump starts to one and makes few hundred litres of pressurized water available even when power is turned off or unavailable
  • QUIET. The system does not turn the pump on every time you open the tap
  • 1-to-3-phase frequency inverter provides gradual motor start with high torque and no power spike
  • Efficient multi-stage stainless steel pump (Grundfos)
  • Adjustable pumping speed (3-phase power at 45-60Hz)
  • Adjustable power used for pumping (from 250 – 600 Watts for a 550W 3-phase motor)
  • Spare pump capacity (pressure and flow) in emergency such as fire

3 phase motors are cheaper, more efficient than 1-phase motors and can be started without a power hike. Given limited off-grid power supply, 3-phase inverter soft-start solution allows using more powerful motors and better pumps than a single-phase solution.

Single phase to 3 phase inverter is used to power 3-phase motor. Inverter is programmable and allows pump speed control. Above photo shows request to supply 3-phase motor with 55Hz.


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