Solar Water Pumping

Store water, not electricity

Most solar pumping systems have no battery. The pump runs while the sun shines and lifts water into a raised tank or pond, which then feeds by gravity whenever you need it. A tank costs far less than a battery and lasts much longer. And the dry season, when you need the most water, is also when the sun is strongest.

Two main types

A solar pump inverter is a VFD with built-in MPPT. It varies motor speed with the sunlight: slow in the morning, full speed at noon. The VFD's soft start avoids the inrush current of a direct-on-line start. Many models accept both DC from the panels and AC from the grid or a generator, so if you have a supply you can keep pumping on overcast days.

Sized from water and height, not horsepower

The two numbers that matter are water needed per day (m³) and total head: the water level in the well while pumping, plus tank height, plus pipe friction. For example, 30 m³/day at 40 m head needs about 3.3 kWh of hydraulic energy. Pump and motor together are roughly 45–55% efficient, so you need about 6–7 kWh of electricity a day and roughly 2–2.5 kWp of panels. We then choose a pump whose pump curve passes through that duty point, and arrange strings so the DC voltage sits in the drive's MPPT range.

Protecting the pump

• Dry-run protection: the drive watches motor current, or a level sensor sits in the well
• Float switch in the tank: the pump stops when it is full
• Surge and lightning protection on the DC side and the motor cable
• Correctly sized drop cable, because long runs lose a lot of voltage

Tell us how deep the well is, how many m³ per hour it yields, how high the tank sits and how many m³ a day you need. We will pick the pump and the array.