How to Choose a Solar Water Pump

Head first, flow second, then the model table. The method the manufacturer uses, written out.

A solar pump is chosen on two numbers. Get them right and the rest of the specification is a lookup. Get them wrong and the pump either never fills the tank or burns money on capacity nobody uses.

Step One: Calculate the Head

If there is a water tank, the head is the distance B plus C plus D divided by ten. If there is no tank, the head is simply distance B.

B is the vertical distance from the pump to ground level, which is the depth of the pump in the borehole.
C is the vertical rise from ground to the tank inlet.
D is the horizontal pipe run, which is divided by ten because friction in a horizontal run costs roughly a tenth of what the same distance costs vertically.

Step Two: Decide the Flow

How much water do you want per hour, or per day? A household water point and a two hectare irrigation plot are different questions with the same pump catalogue. Write down a daily volume and divide it by the hours of usable sun you get, not by 24.

Step Three: Read It Off the Model Table

The three Sinoware pumps cover this range:

Model	Flow	Head	Power	Voltage
SP-2D1.5-35-24-200, 2 inch	1500L	35 m	0.2HP	24V
SP-3DSC4-35-24-300, 3 inch	4000L	35 m	0.5HP	24V
SP-4DSC5.2-45-48-500, 4 inch	5200L	45 m	0.6HP	48V

Note that flow and head are both maximums, and they do not happen at the same time. A pump lifting near its maximum head delivers well below its maximum flow.

What Protects the Pump

Intelligent water shortage protection stops the pump automatically when the well runs dry, then restarts it 30 minutes later. That single feature is the difference between a borehole that recovers and a burnt out motor. The controllers also protect against high voltage, low voltage, over current and high temperature, and soft start avoids the impulse current that shortens motor life.

Why the Wetted Parts Matter

All three pumps use a 304 stainless steel shaft with an alloy mechanical seal. The four inch adds brass for the outlet, connector and oil cylinder, and NSK double bearings. In water with sand or salt in it, this is where a cheap pump fails first.

Why MPPT Is On the Controller

An MPPT controller keeps the array at its best operating point as the sun moves and the panel warms up. In pumping that shows up as more litres per day from the same panels, particularly in the first and last hours of usable light.