In short. An irrigation generator should be sized from the water requirement, not from pump horsepower or borewell depth. Flow and total head define the hydraulic power, pump and motor efficiencies convert it to electrical demand, and the motor starting method usually decides the generator kVA. Cable length to a submersible pump and high summer temperatures in Telangana then refine the choice. Getting the starting calculation right avoids the most common failure, a set that runs the pump but cannot start it.
Water first, then kVA
The farm needs water, the pump needs torque, the motor needs voltage and the generator must deliver all three at the right moment. That gives a clear engineering chain: water requirement, flow and head, pump, motor, starting method, cable, generator and finally the energy source, whether diesel, solar, battery or grid.
A common request is to match a borewell depth to a generator size. Bore depth alone does not establish generator size, because the pump’s duty depends on the dynamic water level, the delivery height and pipe friction, not the drilled depth.
Agricultural applications are not all the same
- Submersible borewell pumps, very common across Telangana, where long drop cables add voltage drop.
- Surface centrifugal pumps lifting from canals, tanks or open wells.
- Drip and sprinkler systems, which need steady pressure and often run filtration and fertigation equipment.
- Farm processing loads such as dryers, small mills, cold rooms and dairy chillers.
- Poultry and livestock sheds, where ventilation and lighting loss affects animal welfare within hours.
Each has a different load shape, and none should receive a generic HP-to-kVA recommendation.
From flow and head to electrical demand
Total head is the sum of the static lift from pumping water level to delivery point, plus friction losses in pipes and fittings, plus any pressure needed at the outlet. It is usually different from bore depth.
Pe = (ρ × g × Q × H) / (1000 × ηp × ηm)
Here Pe is the electrical input in kW, ρ is water density (about 1,000 kg/m³), g is 9.81 m/s², Q is flow in m³/s, H is total head in metres, and ηp and ηm are the pump and motor efficiencies from the pump curve and motor data.
Example (illustrative): a borewell pump delivers 10 litres per second (0.010 m³/s) against a total head of 60 m. Hydraulic power is 1,000 × 9.81 × 0.010 × 60 / 1000, or about 5.9 kW. With a pump efficiency of 0.60 and motor efficiency of 0.85, electrical input is about 11.5 kW. At a running power factor of 0.8 that is roughly 14.4 kVA. The starting demand, discussed below, will be several times larger.
Pump horsepower is an input, not the answer
When a customer says they have a 10 HP pump, that tells us the motor’s nominal output. We still need the voltage, whether the motor is single-phase or three-phase, full-load current, power factor, starting method, cable length and whether other loads run at the same time. A rule of thumb that multiplies HP by a fixed number ignores the factor that matters most, which is starting.
Motor starting usually governs
A pump motor draws far more current while accelerating than when running. Running kW is not starting kVA.
| Starting method | Typical starting current | Effect on generator size | Where it fits |
|---|---|---|---|
| Direct-on-line | About 6 to 8 times full-load current | Largest; often two to three times the running kVA requirement or more | Small motors, simple installations |
| Star-delta | About one third of DOL current | Reduced, but a transition surge occurs | Surface pumps that can start lightly loaded |
| Soft starter | Adjustable, commonly 2.5 to 4 times | Moderate | Larger pumps where a smaller set is wanted |
| Variable-speed drive | Close to full-load current | Smallest starting margin, but harmonics need review | Pressure-controlled drip and sprinkler systems |
Figures are typical ranges; the motor and starter data for the actual equipment govern. Starting current also depends on pump torque, acceleration time and the voltage dip the motor can tolerate. No universal multiplier should be applied without checking these.
Cable, voltage and site conditions
A submersible motor may sit 100 metres or more below the surface, and the drop cable plus the run from the generator adds resistance. Voltage drop during starting can be large enough that the motor fails to accelerate even when the generator is adequately sized. Our generator cable sizing page explains the calculation. Summer ambient temperatures in Telangana regularly exceed 40 °C, so generator output and cooling should be checked against derating data, and enclosures should be placed in shade with free airflow.
Choosing the energy source
Diesel generators suit intermittent irrigation, emergency backup when grid supply to agricultural feeders is restricted, and remote fields. Solar pumping suits daytime irrigation with low running cost, and a small generator can back it up during cloudy monsoon spells. Battery storage helps with sensitive loads such as dairy chillers and poultry ventilation. Where several pumps share a set, sequence their starts so only one motor accelerates at a time. Compare with water and wastewater power for larger pumping schemes, and see rental power for seasonal or short-term needs.
Common mistakes
- Sizing from borewell depth. The pump duty is set by water level and head, so the set may be badly undersized or oversized.
- Multiplying pump HP by a fixed factor. The starting method and cable are ignored, and the set stalls when the motor starts.
- Ignoring voltage drop in long drop cables. The motor overheats or fails to start, and windings burn out.
- Starting several pumps together. The combined inrush trips the generator.
- Running a single-phase pump from one phase of a lightly loaded three-phase set without checking imbalance. The set runs with unbalanced voltage that damages other loads.
What to send us
Send the pump nameplate photo, motor rating and voltage, starting method, flow required, pumping water level and delivery height, cable length and size, and any other loads that run at the same time. Site photos showing where the generator will stand help with cooling and access. Use the generator sales enquiry and we will check the starting case before recommending a size.
Questions engineers ask
What size generator do I need for a 10 HP borewell pump?
It depends mainly on the starting method and cable length. A 10 HP motor on direct-on-line starting usually needs a generator well above its running requirement, while a soft starter or drive reduces that. Send the motor data and we will calculate it rather than guess.
Why does my generator run the pump but fail to start it?
Starting current is several times running current, and the voltage dip during starting may stall the motor. Long cables and undersized sets make it worse. A larger set, a reduced-voltage starter or a heavier cable usually solves it.
Is borewell depth the same as pump head?
No. Head is measured from the pumping water level to the delivery point plus friction losses, and the water level is often far above the bottom of the bore. Use the pump curve and actual water level for sizing.
Can a generator back up a solar pump?
Yes, if the solar pump controller accepts an AC input or a changeover arrangement is provided. Size the generator for the pump motor and controller starting characteristics. Check the controller manufacturer’s guidance first.
How does summer heat affect an irrigation generator?
High ambient temperature reduces available output and stresses cooling. Check the derating data for the set, keep it shaded and well ventilated, and keep the radiator clean during dusty harvest periods.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.