Max flow and max head never happen together
Almost every solar pump is sold on two numbers. A listing says 15 m³/h and 70 m, and the buyer reads it as a pump that moves 15 m³/h up 70 m. It does not. Those are the two ends of one curve, and the pump cannot be at both ends at once.
One point, not two numbers
Flow and head stated together, at the same moment. That single point is what an offer has to answer.
Power settles nothing
The same motor is sold in pumps built for flow and pumps built for head. Asking by horsepower leaves the choice to the seller.
Check the matched controller
Motor voltage is not an array voltage window. Check maximum Voc, MPPT range and current limits separately.
What the curve actually shows
A pump curve plots head on the vertical axis against flow on the horizontal. It slopes down from left to right, because the harder the pump has to push, the less it can move. Two points on that line have names, and both of them end up in catalogues.
Shut-off head
Where the line meets the vertical axis. The highest the pump can lift, with the discharge closed and no water moving. Catalogues call it maximum head.
Free delivery
Where the line meets the horizontal axis. The most the pump can move with nothing to push against. Catalogues call it maximum flow.
Neither point is useful on its own, and neither is where any real installation works. Both get printed because they are the two easiest numbers to measure and the two biggest numbers on the sheet.
Why power alone cannot select a pump
“I need a 1.5 HP solar pump” is the most common opening line in an enquiry, but it does not specify the required flow at head. Below are ten individual catalogue records grouped by rated power. These selected examples are not limits for an entire power class, and equal power does not mean identical motors or hydraulic designs.
| Power / type | Reference | Maximum flow (separate endpoint) | Maximum head (separate endpoint) |
|---|---|---|---|
| 750 W1 HP / DC; centrifugal / screw examples | CAT-0750-FCatalogue p. 13 | 10 m³/h | 50 m |
| 750 W1 HP / DC; centrifugal / screw examples | CAT-0750-HCatalogue p. 3 | 2 m³/h | 120 m |
| 1100 W1.5 HP / DC submersible examples | CAT-1100-FCatalogue p. 13 | 10 m³/h | 70 m |
| 1100 W1.5 HP / DC submersible examples | CAT-1100-HCatalogue p. 11 | 4.5 m³/h | 110 m |
| 1300 W1.75 HP / DC submersible examples | CAT-1300-FCatalogue p. 13 | 13 m³/h | 60 m |
| 1300 W1.75 HP / DC submersible examples | CAT-1300-HCatalogue p. 11 | 5.5 m³/h | 128 m |
| 1500 W2 HP / DC submersible examples | CAT-1500-FCatalogue p. 13 | 15 m³/h | 70 m |
| 1500 W2 HP / DC submersible examples | CAT-1500-HCatalogue p. 11 | 5 m³/h | 160 m |
| 2200 W3 HP / AC/DC hybrid submersible examples | CAT-2200-FCatalogue p. 26 | 22 m³/h | 62 m |
| 2200 W3 HP / AC/DC hybrid submersible examples | CAT-2200-HCatalogue p. 23 | 9 m³/h | 158 m |
Evidence register: OS-REF-PUMP-20260920. Transcriptions checked on . Reference IDs identify individual source records, not OmniSol product models. Request the model mapping and applicable documentation with your enquiry. Catalogue revision and test conditions are not confirmed; these are not independently tested results or a selection recommendation.
The 1500 W examples list maximum heads of 160 m and 70 m respectively, at separate endpoints from their maximum flows. The catalogue records demonstrate different hydraulic capabilities, not output at your site's duty point.
No curve means no verified output
Do not estimate a duty-point flow by drawing a straight line between catalogue maximum flow and maximum head. Ask for the exact model, hydraulic configuration, operating speed, curve document reference and revision, and the required point marked on that curve. A power class or an anonymous redrawn curve is not a substitute.
Updated . The previous endpoint-based calculation has been withdrawn.
The other number on the label
The array must match the controller as well as the pump. An unsuitable string may fail to meet the operating requirements or exceed an electrical input rating.
A motor voltage is not a PV input specification. DC and AC/DC hybrid controllers can have different limits even with the same motor rating. Use the exact controller part number and manual revision.
| Required controller evidence | Check separately |
|---|---|
| Maximum input Voc | Cold-corrected array open-circuit voltage must remain within the specified limit, including required design margins. |
| MPPT operating range | Check array operating voltage over the design temperature range; do not confuse Vmp with Voc. |
| Minimum input and start conditions | Confirm the documented start and operating requirements, including available power. |
| Current and power limits | Check parallel strings, module electrical data and the controller input ratings. |
| Motor and supply compatibility | Confirm approved motor type, rated voltage, controller configuration and any AC backup arrangement. |
Array-to-pump power ratios and panel counts are not universal installation rules. A qualified designer must check the selected equipment and site conditions; a catalogue wiring illustration is not a project wiring plan.
What a real answer looks like
Good answer
- The model number, and its curve, with your point marked on it
- The flow at your head, stated as one figure
- Motor voltage and the string arrangement that feeds it
- A test report if the duty point sits near the edge of the curve
Answer to push back on
- “Max flow 15 m³/h, max head 70 m” and nothing else
- A power rating offered as if it settled the question
- A curve for the series rather than the model
- A promise to confirm the flow after the order is placed
Three sentences you can paste into an email
- Please confirm the flow at my total dynamic head, not the maximum flow.
- Please send the flow-versus-head curve for the exact model offered, with that point marked.
- If you cannot mark that point on a curve, please send a test report taken at that duty point.
We answer all three in our own quotations without being asked.
Work out the head, then send it to us
The duty point means nothing until you have the head. Work it out, then send it over and we come back with a pump, its curve with your point on it, and a priced bill of materials.
Solar pump duty point FAQ
Can a solar pump deliver its maximum flow at its maximum head?
No. Those two figures are the opposite ends of one performance curve. Maximum head is measured with the discharge closed and no water moving; maximum flow is measured with almost nothing to push against. A pump listed as 15 m³/h and 70 m produces neither of those numbers at your site, because your site sits somewhere between the two.
What is a duty point on a solar pump?
The duty point is one flow at one total dynamic head, stated together. It is the only performance figure worth comparing offers on. Everything else on a catalogue page describes what the pump can do under conditions you do not have.
Does a 1.5 HP solar pump tell me how deep it can pump?
It does not. Two 1100 W catalogue examples list separate maxima of 10 m³/h and 70 m, and 4.5 m³/h and 110 m. Neither pair is a simultaneous operating point. Hydraulic design, configuration and operating conditions matter; power alone cannot select the pump.
How do I estimate flow at my head without a curve?
You cannot reliably infer flow from maximum flow and maximum head alone. Request the exact model curve, document revision and operating speed, with the required duty point marked. Two endpoints do not define the shape of the curve.
What should a supplier send to prove a pump meets my duty point?
A flow-versus-head curve for the exact model offered, with your duty point marked on it, or a test report taken at that point. A curve for the series rather than the specific model does not prove it, and neither does a promise to confirm the flow after the order is placed.
Why does the motor voltage of a DC solar pump matter?
Motor voltage helps identify a compatible controller, but does not determine its PV input limits. Check the exact controller manual for maximum open-circuit voltage, MPPT range, minimum input and start requirements, current limits and approved motor configuration.
Technical Guides
Products & Systems
Markets & Services
Need project-specific engineering support?
Free CAD layout, wind/snow load calculations, and BOM review included with project orders.