A solar pumping system is a chain of three parts: panels, controller, pump. Like every chain it is only as strong as its weakest link. Oversize the panels and money is wasted; undersize the pump and the field stays thirsty. This is the sizing logic our engineers use.
Step 1: Water per day
Everything starts with demand. Household supply might be 2–5 m³ a day; a small farm, 20–60. Write the number down, because it drives every later decision.
Step 2: Total dynamic head
Add the well's pumping water level (not the depth of the hole, but the depth the water actually sits at), the height to the storage tank, and pipe friction. Friction is the silent component: a long, narrow pipe can add 10–20 metres of effective head all by itself.
Step 3: Hydraulic power
Multiply flow by head to get the hydraulic power needed. A rough guide: lifting 1 m³ by 100 m takes about 0.27 kWh. Scale that by your daily volume and you have the energy the sun must supply each day.
Step 4: Array wattage
Divide the daily energy by your region's peak sun hours (typically 4.5 to 6), then add 25–30% for heat, dust, cable and conversion losses. That is the array's rated wattage; round up to a practical panel count.
Step 5: Controller and pump
The pump is chosen against head and flow from its curve (see our earlier guide to reading pump curves). The controller or inverter is matched to the array's voltage window and the motor's rated current, never by guesswork. An MPPT-capable controller recovers a meaningful share of your investment every day the light is less than perfect.
The two classic mistakes
- Sizing to the hole, not the water. A 60 m borehole with a static level at 20 m is a 20 m job.
- No cloudy-day margin. A system sized to perfect conditions under-delivers for a third of the year.