Running a Home Water Pump (Motor) on Solar

This guide covers the domestic motor that fills your overhead tank. It is not about farm tubewells, which use larger motors and a VFD solar drive; for those, see solar tubewell with VFD.

What a home pump draws

Pakistani homes usually use a 0.5 HP or 1 HP motor: a "donkey" (centrifugal or peripheral) pump at ground level, or a small submersible or jet pump where the water table is deeper. Typical figures, for planning only:

Generic, indicative figures. Check the rating plate on your own motor. Older or rewound motors often draw more.

A pump that fills a tank in 30 to 60 minutes uses well under 1 kWh a run. Example arithmetic only: a 1 HP pump drawing 900 W for 45 minutes uses 0.9 × 0.75 ≈ 0.7 kWh. On its own, that is a small load. Its impact is about power at the moment of starting, not energy over the day.

Diagram

Running a water pump on solar

Motor start

Surge is several times the running power

Inverter

Surge rating must cover the start

Timing

Run it in solar hours

Why starting current matters

A household pump motor is an induction motor. When it starts from standstill, it draws a burst of current well above its running current until it reaches speed. Engineering guidance for motors started directly on line puts the first instant at many times full-load current, falling as the motor speeds up. Single-phase pump motors with start capacitors soften this, but the surge is still real.

A solar inverter has two limits:

• Continuous rating: what it can supply for hours.
• Surge (peak) rating: what it can supply for a few seconds or less.

When the grid is present, many hybrid inverters can share or pass the load to the grid, depending on the model and its mode. During load-shedding, or on an off-grid system, the inverter and battery must deliver the whole spike alone. If the spike plus whatever else is running exceeds the surge rating, you may see:

• the inverter tripping on overload and the house going dark for a moment;
• the pump humming but not starting, then the inverter shutting it off;
• the battery voltage dipping and the inverter cutting out.

The classic trip is two motors starting together: the water pump and a fixed-speed AC compressor, or the pump and a fridge. Our guide to inverter vs non-inverter ACs explains the AC side.

How to size for a pump

1. List what runs at the same time as the pump. In summer that might be two ACs, fans, a fridge and lights.
2. Add their running power. Example arithmetic only: two inverter ACs at about 1.2 kW each, fans and lights at about 0.5 kW, fridge at about 0.2 kW gives roughly 3.1 kW.
3. Add the pump's running power. About 0.9 kW for a 1 HP pump brings the total to about 4 kW.
4. Check the surge headroom. The inverter's surge rating must cover the running total plus the pump's starting spike. A 6 kW class hybrid inverter usually gives more comfortable headroom for this kind of home than a small one.

This is one reason Solar Works Pakistan designs home systems from about 6 kW: a well-designed system of that class has room for ACs, fans and a water motor together. See inverter prices by size and the appliances guide for other loads.

How many panels for a 1 HP motor? You do not size panels for a domestic pump alone: it runs briefly and uses little energy. A home system sized for your ACs covers it easily in daylight; see solar for AC.

When to run the pump

Daytime, when the sun is strong, is best. Between late morning and mid-afternoon the panels usually have power to spare. Each unit the pump uses then is a unit you do not buy from the grid at your full tariff, and under net billing it is worth more used at home than exported. Read sizing under net billing for why self-use matters.

Practical tips:

• Fill the tank fully around midday so you rarely need to pump at night.
• Do not start the pump at the same moment as an AC after a power cut. Let the ACs settle first.
• Use a timer or float switch so the pump stops when the tank is full and does not run dry.
• Avoid pumping on battery at night unless you have sized for it.

Pumping on battery and during load-shedding

If you need water during evening load-shedding, the battery must supply both the surge and the energy.

• Energy: add the pump's run time to your night-time load. Example arithmetic only: 0.7 kWh per run, twice a night, adds about 1.4 kWh before losses. Our battery sizing guide shows how to include it.
• Power: the battery's maximum discharge current and the inverter's surge rating must both cover the start. A small battery can hold enough energy yet still struggle with a hard motor start.
• Inverter mode: in SBU mode the house runs on battery after sunset, so the pump draws from it. Our guide to SBU and SUB modes explains the settings.

Wiring and protection

• Give the pump its own circuit breaker sized to the motor, and an RCCB on the circuit where appropriate. See breakers and protection.
• Use cable of the right size for the motor current and the distance.
• Make sure the pump body and the system are properly earthed. Our earthing and surge protection guide covers this.
• If the pump trips often, have the motor and its capacitor checked before blaming the inverter.

Get today's price or a free site survey

Tell us your pump size, ACs and other main loads, and send your last 12 months of bills. Our engineers will size the inverter, panels and battery so the pump starts cleanly with everything else.

• WhatsApp or call: 0336 666 4321
• Email: info@solarworks.pk
• Head office: Main Boulevard, Sargodha Rd, Block F FDA City, Faisalabad
• Lahore branch: 2nd Floor, Jeff Heights, Gulberg, Lahore
• Hours: 9:00 AM to 6:00 PM, daily
• Service area: all of Punjab. See our Faisalabad and Lahore pages, the solar system price guide, or contact us.

Site surveys are normally free. Solar Works Pakistan was founded in 2021 and has served 300+ customers, including 50+ industrial clients.

Frequently asked questions

Can a 1 HP water motor run on a solar inverter?

Yes. A 1 HP domestic pump runs on a properly sized hybrid or on-grid inverter. The inverter must handle the motor's starting surge plus whatever else is running, especially during load-shedding when the grid cannot help.

Why does my inverter trip when the water pump starts?

The motor draws a short burst of current when starting. If that burst, plus your other running loads, exceeds the inverter's surge rating, it trips. Starting the pump when ACs are not starting, checking the motor and its capacitor, or using a larger inverter usually solves it.

How many solar panels do I need for a 1 HP motor?

A domestic pump does not need its own panels. It runs for a short time and uses little energy. A home system sized for your ACs and daytime loads covers the pump easily in daylight.

Can I run the water pump at night on battery?

Yes, if the battery has enough spare capacity and can deliver the starting current. Add the pump's run time to your night-time load when sizing the battery. Filling the tank at midday is cheaper and easier on the battery.

Is a submersible pump harder on the inverter than a donkey pump?

It can be. A submersible pump starts against the full column of water in the pipe, and its running current can be higher than a surface pump of the same HP. Check the rating plate and tell your designer which pump you have.

Does this apply to tubewells?

No. Farm tubewells use much bigger motors and are usually run through a VFD solar drive. See our solar tubewell guide.

Sources

1. Voltimum UK, "Q of the day: will a motor's starting current be six times full load?" (direct-on-line starting current): https://www.voltimum.co.uk/news/q-day-will-motors-starting-current-be-six