Solar Power for Irrigation Pumps
One line: Pumps are the hardest load in solar. The running watts are small; the starting surge is not. Get the surge margin wrong and the system trips every time the pump starts.
Why pumps are a special case
An irrigation pump's nameplate might read 1.5 kW. At start-up, before the motor reaches speed, it can draw 3 to 4.5 kW for a fraction of a second — and this happens every time the pressure switch or timer cycles the pump on.
High-frequency inverters have limited surge tolerance. A unit rated just above the running load will trip on start, alarm, restart, trip again — and the farmer concludes the inverter is faulty when the specification was wrong.
Two solutions:
- Size the inverter well above the running load — typically 2–3× the largest motor, so surge sits inside the rating.
- Choose a low-frequency unit, which steps through a large transformer and tolerates surge far better.
When low-frequency is the answer
The HE310-5000-F is built for exactly this class of load:
| Parameter | Value | Why it matters |
|---|---|---|
| Rated power | 5000 W / 6300 VA | The VA rating gives headroom for poor power factor |
| Load peak ratio | 3:1 | A 1.5 kW pump with a 4.5 kW surge sits inside the capability |
| Battery voltage | 48 VDC | High current capability for motor starting |
| Battery capacity | Up to 500 Ah | Sustained draw for long pump runs |
| Input voltage range | 154–264 VAC | Tolerates weak or unstable rural supply |
| No-load loss | Below half a same-power high-frequency unit | Matters on long idle periods |
| Noise | <45 dB | — |
| Efficiency | >98% | — |
The 3:1 peak ratio is the specification that matters. It is the difference between a system that starts the pump and one that does not.
When a hybrid unit is enough
For a small, intermittently-used pump — a transfer pump for topping up a tank, say — a high-frequency hybrid unit with generous headroom does the job at lower cost:
| Pump running load | Suggested hybrid model |
|---|---|
| Up to 750 W | HE200-3000-O-I5 — 2000 W, IP54 |
| 0.75–1.5 kW | HE200-4200-T — 3600 W, 24 V |
| 1.5–3 kW | HE200-7200-F — 6200 W, 48 V |
| 3–5 kW, or repeated hard starts | HE310-5000-F — low-frequency, 3:1 peak |
The dividing line is not the running load but the number and hardness of starts. A pump that starts twice a day on a light duty cycle tolerates a high-frequency unit. A pump that starts on a pressure switch every few minutes does not.
Sizing the array for water pumping
Pumping is energy-intensive, and irrigation demand often peaks in the middle of the day — which happens to coincide with peak generation. That is favourable: the pump can run directly from PV during the day with the battery covering only starts and any evening running.
Pump energy (kWh/day) = pump power (kW) × hours of runningA 1.5 kW pump running 4 hours uses 6 kWh. At 5 peak-sun hours, that is 1.2 kW of array before losses, or around 1.5–1.6 kWp after derating. But PV output must also cover the surge — the inverter draws the start-up current from PV and battery together, so the battery must be sized to supply the difference briefly.
Practical installation notes
- Battery voltage must match the inverter. A 24 V battery on a 48 V unit damages the unit.
- Use adequate battery cable. Motor starting draws high current; undersized cable causes voltage drop and nuisance trips. Use the installation guide cable table.
- Do not route the utility input through an RCD — the inverter's filtering can trip it.
- For lead-acid, charge at no more than 0.2C. Pumps often run on lead-acid banks; over-current charging shortens life.
Note on certification
The HE310-5000-F holds CE EMC certification (CKEYS251201016) and GB 4943.1-2022 safety coverage (BDL260706S002), but no FCC or RoHS file. Battery type for this model is AGM deep-cycle or GEL, not lithium. Confirm before specifying — see the certifications page.