Solar Pump Sizing & Array, Panels & Pump HP
Sizes the array
Enter your daily water need, total head and sun hours to get the solar array in watt-peak, the panel count, the pump HP and the operating flow for your borewell or field.
Enter your duty
Next: install about 2,555 Wp (8 panels) with a matched 2.74 HP pump; oversize slightly for cloudy days, and reduce head with wider pipe to cut the array you need.
Sizing uses ρgQH with a wire-to-water efficiency and a derate for heat/dust; confirm with the pump's published duty curve.
Solar pump sizing — key facts
- Operating flow Q
- daily water ÷ (sun hrs × 3600)
- Hydraulic power
- ρ·g·Q·H (ρ=1000, g=9.81)
- Input power
- hydraulic ÷ efficiency
- Wire-to-water
- ≈ 35–45% for solar pumps
- Array Wp
- input power ÷ 0.8 derate
- Panels
- array Wp ÷ panel Wp
- Cut the array
- lower the head (wider pipe)
- Privacy
- Runs in your browser; nothing uploaded
From water need to a panel count, in one chain
A solar pump is sized backwards from the job, not the panel. Decide how much water you must move each day and the head it has to lift against; that fixes the hydraulic power, since the pump only runs through the sun hours and must squeeze the whole day's volume into them. Divide hydraulic power by the pump's wire-to-water efficiency — about 35–45% — to get the electrical input, then add a derate for heat and dust to land on the real array in watt-peak. Divide by your panel rating and you have the number of panels and the mounting you need.
This tool reports the array watt-peak, panel count, pump HP, operating flow in L/s and m³/hr, and the daily energy in kWh. Use it to compare designs: a wider delivery pipe trims the head and shrinks the array, while a small oversize buys resilience on cloudy days. Pair it with the Irrigation Pump Power and Solar Pump ROI tools to size the system and check it pays back.
Right-size the array
Watt-peak matched to your real water job.
Cut head, cut cost
A wider pipe lowers the array you must buy.
Plan for clouds
Oversize a little so dull days still deliver.
Know the flow & HP
Operating flow and pump HP for the borewell.
Frequently Asked Questions
How do I size a solar water pump?+
Start from the water you need each day and the total head it must lift against, work out the hydraulic power that demands, divide by the pump's wire-to-water efficiency to get input power, then add a derate for heat and dust to fix the solar array in watt-peak. Finally divide by your panel rating to get the panel count. This tool runs the whole chain for you.
What is the operating flow and how is it found?+
The pump only runs while the sun shines, so the flow it must deliver is the daily water need spread over the usable sun hours. Operating flow Q = daily water (m³) ÷ (sun hours × 3600), which gives litres per second. For example 30 m³/day over 7 sun hours is about 1.19 L/s, or roughly 4.3 m³/hr.
How is hydraulic power calculated?+
Hydraulic power is the useful work of lifting water: P = ρ · g · Q · H, with water density ρ = 1000 kg/m³, gravity g = 9.81 m/s², Q the operating flow in m³/s and H the total head in metres. It is the power the water actually carries; the pump and panels must supply more to cover losses.
What is wire-to-water efficiency?+
Wire-to-water efficiency is the share of electrical power that ends up as useful hydraulic power, after motor, pump and controller losses. Solar pumps typically sit around 35–45%, so input power = hydraulic power ÷ system efficiency. A lower efficiency means a bigger array for the same job, which is why pump quality matters.
Why is the array bigger than the input power?+
Panels rarely deliver their rated watt-peak in the field. Heat, dust, wiring losses and off-perpendicular sun cut real output, so the array is oversized by a derate factor — here array Wp = input power ÷ 0.8. The 0.8 derate (a 20% margin) keeps the pump fed through normal field conditions rather than only at lab test conditions.
How many panels will I need?+
Divide the required array watt-peak by the rating of one panel: panels = array Wp ÷ panel Wp, rounded up. Larger modern panels (550–600 Wp) cut the count versus older 330 Wp panels. The tool reports the array size and the panel count for the rating you enter so you can plan the mounting structure.
How can I reduce the array I need?+
Cutting the head is the most effective lever. Use a wider delivery pipe to lower friction loss, site the tank closer or lower, and avoid unnecessary lift — every metre of head removed shrinks the hydraulic power and therefore the array. Improving pump efficiency and spreading the draw over more sun hours also help.
Should I oversize for cloudy days?+
A modest oversize is wise. On overcast days output falls and the daily volume drops, so adding 10–20% array or a little storage buffers the crop through dull spells and early-morning or late-afternoon low light. Avoid gross oversizing, though — it wastes money and can over-pump a weak borewell.
Does it account for total dynamic head?+
You should enter the total head — the static lift from water level to discharge plus friction losses in the pipe and any pressure needed at the outlet. Using only the static lift understates the work and undersizes the array. If you know the friction loss, add it to the static head before entering it.
Are the results exact?+
They are sound design figures for planning an installation. Real performance varies with the specific pump curve, panel temperature, borewell drawdown, pipe sizing and local solar resource. Treat the array Wp, panel count and pump HP as a well-grounded starting point and confirm against the pump manufacturer's curve and a site survey.