A practical sizing guide for EPCs, distributors, pump dealers, and irrigation buyers who need a reliable deep well model check before ordering.
To size a solar pump inverter for a deep well pump, start with the pump nameplate, rated voltage, phase, current, total dynamic head, target flow, cable distance, and PV array voltage. For many 380V three-phase deep well pumps, Solarseeker SP4 is the first path to check, but the pump curve must confirm the duty point.
Sizing Starts With Water Duty, Not Only kW
A deep well pump inverter is not selected by motor power alone. Two pumps with the same kW rating can behave very differently when one works in a shallow tank system and the other lifts water from a deep borehole.
The real job is to match four things at the same time: the pump motor, the water duty point, the inverter output, and the PV array. Missing one part can create weak water output, late morning starts, over-current trips, or a quote that looks cheap but fails on site.
This is why a message like “I need an inverter for a 7.5 kW well pump” is not enough. The supplier still needs to know whether the motor is 220V or 380V, single phase or three phase, how much current it draws, and how much head the system must overcome.
Deep Well Pump Inverter Sizing Checklist
Use this table before asking for a model recommendation. It gives the supplier enough data to check the electrical match, hydraulic duty point, PV voltage window, and installation risk.
| Data to check | Why it matters | What buyers should send |
|---|---|---|
| Pump nameplate | Shows rated power, voltage, phase, current, and frequency. | Clear photo of the full pump nameplate. |
| Rated voltage and phase | Decides the inverter output path before price. | 220V or 380V, single phase or three phase. |
| Rated current | Helps confirm overload margin and motor protection settings. | Nameplate current in A, plus service factor if available. |
| Total dynamic head | Shows the real lift and pressure the pump must handle. | Static water level, drawdown, outlet height, pipe route, and pressure target. |
| Target flow | Confirms whether the pump can meet the water demand at that head. | Required m3/h, L/min, or daily water volume. |
| Pump curve | Proves whether head and flow sit inside the pump’s working range. | Pump curve sheet, model datasheet, or catalog page. |
| Cable distance | Long cable runs increase voltage drop, heat, and service risk. | Distance from inverter to pump and cable size if known. |
| PV panel data | Checks whether the array can wake and feed the inverter correctly. | Panel wattage, Voc, Vmp, quantity, and planned series/parallel layout. |
| Site and water use | Helps judge operating hours, protection needs, and irrigation schedule. | Deep well, irrigation, tank filling, livestock water, or mixed use. |
| Photos | Reduce guessing when the pump, cabinet, or cable details are unclear. | Well head, old control box, pump cable, PV area, and installation environment. |
For a broader product overview, the Solarseeker solar pumping system page explains how the inverter connects PV input, motor control, and pump protection in one system path.
Build Total Dynamic Head Before Choosing the Inverter
Well depth is not the same as total dynamic head. A 100 m borehole does not always mean the pump works against 100 m of head. The water level, drawdown, outlet elevation, pipe length, pipe diameter, fittings, and pressure requirement all change the duty point.
A simple way to think about it is:
Total dynamic head = static lift + drawdown allowance + outlet elevation + pipe and fitting loss + pressure requirement.
This number does not size the inverter by itself. It tells you whether the selected pump can deliver the required flow at the real site condition. Once the pump duty point is confirmed, the inverter sizing becomes much cleaner.
For buyers who are still building the full system plan, Solarseeker’s system design workflow is a useful next check. If the project is specifically for wells, the well application guide can help organize head, flow, and application details before the inquiry.
Check Voltage, Phase, and Current Before Model Selection
The motor nameplate decides the safe output type. A 380V three-phase pump should not be treated like a 220V single-phase pump, even when the kW looks similar.
For larger 380V three-phase deep well and irrigation projects, the SP4 380V three-phase path is often the first Solarseeker product direction to review. It still needs the pump current, head, flow, PV plan, and cable distance before the final recommendation is made.
Current deserves special attention. Some buyers send only kW or HP, but rated current shows how hard the motor loads the inverter. It also supports overload protection, dry-run response, and commissioning checks after installation.
Phase is another common trap. A three-phase pump needs a matching three-phase output path. A single-phase pump may need a different product route. When the site power supply, pump motor, and solar inverter path do not match, the project should be checked before purchase.
PV Array Rules for Deep Well Projects
The PV array must match the inverter input window and the pump load. Too little array power can make the pump start late, stop in weak sunlight, or deliver poor flow. Too much voltage can trigger DC over-voltage alarms or damage components.
| Pump system | PV array power starting rule | Useful Vmp target |
|---|---|---|
| 220V single-phase pump | PV Array Power >= Pump Rated Power x 2.0 | Around 320V DC Vmp |
| 380V three-phase pump | PV Array Power >= Pump Rated Power x 1.3 to 1.5 | Around 540V DC Vmp |
These are starting rules, not a final string design. The actual panel count still depends on module Voc, module Vmp, local temperature, inverter DC input range, and the site’s sunlight conditions.
For irrigation water planning, water demand should also come from the crop and site condition, not from pump power alone. The FAO’s irrigation water management resources are a neutral reference for why water demand changes by crop, soil, climate, and schedule.
Panel string design and electrical installation should follow local electrical codes. Use qualified electricians or trained technicians for wiring, protection, grounding, and commissioning work.
Buyer Scenario: A Fast Quote That Was Not Ready
A distributor receives a request for a deep well pump inverter and forwards only one line: “7.5 kW pump, 80 m well.” The buyer wants a price the same day, but the data is not ready.
That message misses the pump voltage, phase, rated current, target flow, real water level, cable distance, and PV panel information. The well depth also does not confirm total dynamic head. Because of this, the supplier can only give a rough direction.
After the distributor sends the pump nameplate and a pump curve, the selection becomes much clearer. A 380V three-phase pump may point toward SP4, while another pump may need a different Solarseeker path. The PV panel data then decides whether the array voltage and power can support stable daytime pumping.
This small delay is better than a wrong shipment. A clean model check can prevent field callbacks, extra freight, cabinet changes, and installer time under the sun.
Common Sizing Mistakes That Cause Callbacks
Do not size by kW alone. Motor current, voltage, phase, and pump curve can change the model recommendation.
Avoid using well depth as the only head value. Static water level, drawdown, outlet height, and pipe loss may change the real duty point.
Never ignore cable distance. Long cable runs can create voltage drop, heating, weak output, and nuisance trips.
Be careful with old AC pumps. A pump that worked on grid power may still need insulation, bearing, cable, and current checks before solar conversion.
Do not treat panel wattage as the whole PV design. Vmp, Voc, temperature, and string layout decide whether the inverter starts and runs safely.
Copy This RFQ Message
You can copy and edit this message when asking Solarseeker or your local distributor for a model check:
Hello, we need to size a solar pump inverter for a deep well pump. Pump power is [kW/HP], voltage is [220V/380V], phase is [single-phase/three-phase], rated current is [A], and frequency is [Hz]. Required head is [m], target flow is [m3/h], well depth is [m], static water level is [m if known], drawdown is [m if known], and cable distance from inverter to pump is [m]. PV panel data is [W], Voc [V], Vmp [V], quantity [pcs], with [series/parallel plan if known]. Attached are pump nameplate, pump curve, site photos, cabinet photos, and PV layout. Please recommend the suitable inverter model and PV connection range.
FAQ
Can I size a solar pump inverter only by pump kW?
No. Pump kW gives only the basic power range. A reliable selection also needs voltage, phase, rated current, total dynamic head, target flow, pump curve, cable distance, and PV panel data.
What data is needed before sizing a deep well pump inverter?
Send the pump nameplate, voltage, phase, current, head, flow, well depth, static water level if known, drawdown if known, cable distance, PV panel Voc and Vmp, panel quantity, and site photos.
Is SP4 always required for deep well pumps?
No. SP4 is usually the first product path to check for 380V three-phase deep well or larger irrigation pumps. The final choice still depends on the motor nameplate, current, duty point, PV array, and site layout.
How many solar panels are needed for a deep well pump?
There is no safe panel count without module data. The supplier needs panel wattage, Voc, Vmp, local temperature range, pump power, and inverter input range before confirming the series and parallel layout.
Why do head and flow matter when choosing the inverter?
Head and flow confirm whether the pump can meet the site’s water demand. If the pump duty point is wrong, changing the inverter will not create enough water from the same pump.
Before You Ask for a Final Model
A deep well project deserves a model check before ordering. Send the pump nameplate, voltage, phase, rated current, head, flow, well data, cable distance, PV panel Voc/Vmp, panel quantity, and site photos.
When the data is ready, send it through the Solarseeker engineering contact page. Our team can review the pump, PV array, and site condition, then recommend a safer solar pump inverter path for the deep well system.