Solar Water Pumping
-- Sizing, Site Rules and the Diesel Comparison
Solar Water Pumping: Sizing, Site Rules and the Diesel Comparison
A solar water pump is a hydraulic problem wearing an electrical costume. The pump, not the sun, sets the power demand: flow rate against head. Get that number first and the array, controller, and storage follow. This page is the engineering version: how we size systems from 300 W portable units to 100 kW hybrid installations, what sites work, and the assumptions behind the zero-fuel-cost claim.
The sizing formula
Hydraulic power in kilowatts is flow (m³/h) × head (m) ÷ 367, before pump and motor losses. A worked example: moving 10 m³/h from a 50 m head needs about 1.4 kW at the water. With a realistic wire-to-water efficiency of roughly 50–70%, the array has to supply closer to 2–2.8 kW at the pump's input. That number is what the rest of the design hangs on.
Two consequences follow. First, head is expensive : doubling the head doubles the power for the same flow, which is why deep-well pumping is a different machine class from surface pumping. Second, most irrigation is a daytime load , so the default design is direct drive: the array powers the pump while the sun shines and the water goes into a storage tank for later use. Batteries are the exception, reserved for 24/7 water supply and emergency potable systems, where storage cost is justified by the availability requirement.
What the equipment range looks like
| Parameter | Range we build to |
|---|---|
| Head (total dynamic head) | Up to 200 m in submersible configurations |
| Flow rate | 1–300 m³/day across agricultural and livestock units; 50–200 m³/h for high-capacity flood-response pumps |
| Array | 300 W to 100 kW |
| Pump types | Submersible and surface |
| Drive | MPPT (Maximum Power Point Tracking) pump control, variable speed |
| Storage | Battery backup optional; tank storage is the default buffer |
| Hybrid | Grid or generator backup where water availability is critical |
Note the two flow figures describe different machine classes, not one continuous range: the 1–300 m³/day band is farm and livestock duty, while 50–200 m³/h is emergency flood response. The source page listed them side by side without that distinction, and the mix-up is the single most common error we see in pump enquiries. A 300 W unit is a garden or livestock pump; a 100 kW installation is a farm block or a municipal backup. Treat the table as an envelope, not a menu.
Site rules: what works and what doesn't
Solar pumping fits sites without reliable grid power where the alternative is a diesel pump or a long feeder trench: remote farms, wells, rivers and reservoirs as water sources, rotating crop fields that need mobile systems, and disaster zones where the infrastructure is gone. The site checklist is short: the water source and its drawdown rate, the head and the pipe run, because friction losses in long runs matter, the daily water demand in m³, and space for the array with unobstructed sun.
It is the wrong tool where the source cannot sustain the flow, because a well that cannot recharge will beat any pump. It is the wrong tool where head exceeds what the pump class handles. And, honestly, it is the wrong tool where cheap grid power already reaches the pump house: in that case the solar system is a sustainability project, not an economic one, and it should be budgeted as one.
The diesel comparison, stated with its assumptions
"Zero fuel cost" is true and incomplete. The honest comparison runs on three assumptions: diesel price per liter , which is the avoided cost; utilization , because an irrigation pump used four months a year displaces less fuel than a livestock pump running daily; and maintenance , because a diesel engine needs service and rebuilds while a solar pump's maintenance is mostly keeping the array clean. Under typical conditions, with diesel at regional prices and a pump running through a growing season, the fuel savings alone recover a comparable solar installation within a few seasons, before the generator's maintenance and the logistics of fueling a remote site are counted. Ask any vendor quoting you a payback to show these three assumptions. If they won't, the number is decoration.
Portable and automated systems
Trailer-mounted systems with quick-connect arrays deploy without foundations, which is why they dominate emergency response: roll in, connect pump and array, pump. Adjustable panel tilt and universal pump connections keep the unit flexible across sites. Automation matters more on unmanned sites than on staffed farms, because a pump that runs dry destroys itself quietly: remote monitoring, flow optimization, fault detection, and dry-run protection are not features we treat as optional on remote installs.
Scope: this page covers solar pumping for irrigation, livestock, and emergency water supply. It does not cover desalination, municipal water treatment, or pumped hydropower storage. For the DC bus side of these systems, the sizing logic in our controller sizing calculator applies, and our all-in-one solar street lights run on the same MPPT charge-control platform.