Solar
Solar Water Pumps for Boreholes and Farms: How to Size One
Short answer
A solar water pump runs on sunlight with little or no battery, and stores water in a tank instead. Size it from the water you need per day and the total head (vertical lift plus losses). Hydraulic power in watts is about 2.725 × flow (m³/h) × head (m), divided by pump efficiency, and the solar array is usually 1.3 to 1.5 times the pump power.
How solar pumping works
Panels feed a pump controller or drive that runs a DC or AC pump while the sun shines. Water is lifted into a storage tank for use at night and on cloudy days. This is usually cheaper than batteries and avoids diesel costs.
What you need to know first
- Daily water need (m³ per day) for people, animals or crops.
- Total dynamic head: depth to the pumping water level plus height to the tank plus pipe friction.
- Borehole yield and diameter from the drilling report.
- Peak sun hours: use about 5 for planning.
Worked example
You need 30 m³ per day. With about 6 effective pumping hours, flow is 5 m³/h. Total head is 40 m. Assuming overall pump efficiency of 45%:
Power ≈ 2.725 × 5 × 40 ÷ 0.45 ≈ 1,211 W, so choose a pump of about 1.5 kW. Allow 1.3 to 1.5 times that for the array, giving roughly 2 kWp of panels.
This is a planning estimate; the pump curve and borehole yield must confirm it.
Checks before you buy
- Borehole yield must exceed the pump flow, or the pump will run dry.
- Add dry-run and float-switch protection.
- Place the array in full sun, mounted securely against theft and wind.
- Size the storage tank for at least a day or two of use.
- Use pipework sized to keep friction losses low.
Get a design
Pump sizing depends on site data we measure with you. Ask about solar installation for farms, schools and estates.
Common questions
Do solar pumps need batteries?
Usually not. Most store water in a tank rather than electricity in batteries.
Can I run an existing AC pump on solar?
Often yes, through a solar pump inverter, but the pump must be suitable and the array sized for its start-up and running power.
What happens on cloudy days?
Output falls, so the pump delivers less water. Tank storage covers the gap.