Solar water pumping is sized in the opposite direction to most solar systems. Instead of starting from an electrical load, you start from litres per day and total head, then find a pump whose curve delivers that duty at the voltage your array produces at midday. The array is matched to the pump, not to a battery.
Step 1: Daily water demand
| Use | Typical daily demand |
|---|---|
| Drip irrigation, vegetables | 3-6 mm/day over the wetted area |
| Orchard drip | 4-8 mm/day in peak season |
| Cattle watering | 30-60 litres per head per day |
| Village standpipe | 15-25 litres per person per day |
Convert to m³/day and add 10-15 percent for losses and cleaning. A one-hectare drip block at 5 mm/day needs about 50 m³, but it is applied over a few hours, so the pump must deliver a high flow for a short period rather than a trickle all day.
Step 2: Total head, not just depth
Total head is the sum of static lift, drawdown, discharge head, and friction losses in pipe and fittings. Friction is the part most often forgotten: a long, undersized delivery line can add more head than the borehole itself.
Total head (m) = static lift + drawdown + delivery height + friction loss
Once you have flow (m³/day over the pumping window) and total head, the hydraulic energy requirement follows directly:
Hydraulic kWh/day = (volume m³ x head m x 2.725) / 1000 — assuming roughly 50-60 percent wire-to-water efficiency, divide the hydraulic value by that efficiency to get electrical energy.
Step 3: Match the pump to the array
Solar pumps are specified by flow at a given head and input voltage. Two rules keep the system stable:
- Choose a pump whose best-efficiency point sits at the head you actually have, not at the maximum head on the datasheet
- Size the array so that at 700-800 W/m² the pump still runs, and at full sun it does not exceed the controller’s input
Because output varies with sun, most irrigation systems use a storage tank rather than a battery. The tank buffers the mismatch between pumping hours and irrigation hours, and it costs far less per litre than a battery bank.
Battery or tank?
| Requirement | Best choice |
|---|---|
| Irrigate whenever you want | Tank, elevated or pressurised |
| Pump at night or before dawn | Tank with night storage, or battery if no tank space |
| Livestock water points | Small tank plus float valve |
| Very low yield aquifer | Slow pumping into storage all day |
Practical notes from the field
- Run the pump dry-protection as a hardware float or electrode, not only as a software limit
- Keep the array within a few metres of the pump controller to limit DC voltage drop
- A variable-frequency drive lets the pump follow the sun instead of switching on and off
- In hard water, plan for scaling on the pump stages and check flow annually
FAQ
How many solar panels do I need to run a 1 HP pump?
Roughly 1.5-2 kWp for a 1 HP submersible at moderate head, but the correct answer depends on total head and required flow. Two sites with the same pump can need very different arrays.
Can a solar pump work without a battery?
Yes — most irrigation systems pump directly into a tank or reservoir, which removes the battery entirely. A battery is only needed if pumping must happen when the sun is not shining.
What happens on a cloudy day?
The pump slows or stops. Storage volume should cover one to two cloudy days, or the irrigation schedule should be planned around a lower daily volume in the shoulder season.
Send us your daily water volume and total head and we will match a pump and array. Request a sizing proposal or see solar power for agriculture.