Agriculture · Faisalabad, Lahore, Punjab
Solar Tubewell with VFD: Sizing by HP and Bore Depth
Short answer
A solar tubewell runs your pump motor on solar power through a VFD solar inverter, and the solar array is usually sized at roughly 1.2 to 1.5 times the motor's kW rating. A 10 HP (about 7.5 kW) tubewell motor typically needs around 9 to 11 kW of panels for good daytime pumping. Bore depth and water demand decide the motor size; the motor size then decides the array.
Solar Works Pakistan designs and installs solar tubewell systems for farms across Punjab. This guide explains how a solar water pump works, how to size it by horsepower and depth, what to check before converting a diesel or electric tubewell, and what to know about the Punjab tubewell solarisation scheme.
How a solar tubewell works
A solar tubewell from panels to field
- MORNINGLow sun: VFD runs the motor slowly, some water flows
- MIDDAYFull sun: motor at full speed, most of the day's water
- EVENING / CLOUDOutput falls: motor slows; grid or diesel backup if needed
The panels produce DC power and the VFD solar inverter converts it into three-phase AC to drive the motor. Most solar tubewells run without batteries; the "storage" is the water pumped into a channel, tank or field while the sun is up.
What does the VFD do?
VFD stands for variable frequency drive. Instead of switching the motor fully on or off, it changes the frequency of the supply so the motor's speed can rise and fall.
- It follows the sun. In the morning and evening the VFD runs the motor slower instead of tripping. Water still flows, just less of it.
- Soft start. The motor ramps up gently, avoiding the large direct-on-line starting current. Easier on the motor, pipes and panels.
- Built-in MPPT and protection. Solar pump VFDs track the panels' best operating point and protect the motor against dry running, overload and voltage problems (features vary by model).
A general-purpose industrial VFD is not the same as a solar pump VFD, which is designed to take a varying DC input straight from the panels.
We install solar pump VFDs from INVT, Invent and other established brands, matched to the motor's kW rating and the panel string voltage. The exact model is named in your quotation.
Sizing a solar tubewell by HP
One horsepower is about 0.746 kW. Because panels rarely give their full rating in Punjab heat and dust, and the motor should keep running through morning and afternoon, the array is normally larger than the motor. Indicative ranges for a first conversation, not a design:
| Motor size | Motor rating (approx.) | Indicative solar array | Approx. 615 W panels | VFD rating (indicative) |
|---|---|---|---|---|
| 5 HP | 3.7 kW | 4.5–5.5 kW | 8–9 | 4–5.5 kW |
| 7.5 HP | 5.5 kW | 6.5–8 kW | 11–13 | 5.5–7.5 kW |
| 10 HP | 7.5 kW | 9–11 kW | 15–18 | 7.5–11 kW |
| 15 HP | 11 kW | 13–16.5 kW | 22–27 | 11–15 kW |
| 20 HP | 15 kW | 18–22 kW | 30–36 | 15–18.5 kW |
| 25 HP | 18.5 kW | 22–28 kW | 36–46 | 18.5–22 kW |
Indicative only. The final size depends on the pump curve, bore depth, motor efficiency, daily water need, site conditions and the VFD's input voltage window. String voltage must fit the VFD's input range. Current panels: solar panel price in Pakistan.
How bore depth changes the size
- Total head: how high the water must be lifted. Roughly the water level depth in the bore (including drawdown while pumping), plus the height to the outlet, plus pipe friction.
- Flow: how much water you need, in litres per second or per hour.
Power rises with both: lifting the same water from twice the depth needs roughly twice the power. That is why a farm with a deep water table may need a 15 HP motor where a nearby farm with a shallow table manages with 7.5 HP.
Example arithmetic only: 10 litres per second from a total head of 40 metres is about 10 × 40 × 9.81 ≈ 3.9 kW of water power. With pump-and-motor efficiency of about 50–60%, the motor needs roughly 6.5–8 kW of input: a 10 HP motor and a 9–11 kW array. A real design uses the pump manufacturer's curve.
What to measure before you convert
- Static water level in the bore, and how far it drops while pumping (drawdown).
- Pump setting depth (for a submersible) and pipe size.
- Existing motor nameplate: HP or kW, voltage, phase and current.
- Water need: acres, crop and hours of pumping per day in the peak season.
- Space for the panel structure, with no shade from trees or buildings.
Converting an existing tubewell: diesel or electric
In many cases the existing three-phase motor can be kept and driven by a solar pump VFD, if it is in good condition and rated correctly. Old, rewound or badly worn motors may be better replaced, because a weak motor wastes solar power.
- Diesel tubewell to solar: the pump stays; the diesel engine is replaced by an electric motor (if it was belt- or shaft-driven) and the VFD. Some farms keep the engine as backup for cloudy spells.
- Electric (grid) tubewell to solar: the motor can often stay, running on solar by day and on the grid when needed through a suitable changeover.
Single-phase motors, very old motors and special pumps need checking case by case.
Structure, cable and protection
The panel structure for a tubewell is ground-mounted in open fields, facing wind, dust, livestock and sometimes flooding, so a raised design is common. See L2 vs L3 vs elevated solar structures. The DC cable run to the VFD and the cable down the bore to a submersible motor both need correct sizing to avoid voltage drop and overheating (see the solar cable size guide). DC breakers, surge protection and proper earthing protect the VFD against faults and lightning (see breakers and protection).
The Punjab government's tubewell solarisation scheme
The Punjab government runs a programme to convert agricultural tubewells to solar, the CM Solarization Program for Agricultural Tubewells. Based on official pages and news reports:
- The first phase targeted 8,000 tubewells running on diesel or grid electricity, with beneficiaries chosen by computerised ballot.
- A second phase of about 10,000 tubewells was reported for 2026, with a budget of roughly Rs 9.9 billion.
- Subsidies were reported in three tiers, about Rs 500,000, Rs 750,000 and Rs 1,000,000, linked to 10, 15 and 20 kW systems, with the farmer paying the rest.
- Reported eligibility: permanent Punjab residence, agricultural land in your name (at least 1 acre reported) and an existing diesel or electric tubewell.
Terms have changed between phases. Solar Works Pakistan is not part of the government and does not decide who qualifies. To apply or check status, use the Punjab Agriculture Department's official website (agriculture.punjab.gov.pk) or helpline. For a broader overview, see the Punjab solar power scheme guide.
A note on groundwater
Free daytime pumping can tempt farmers to pump more than the crop needs, and water specialists have raised concerns about falling water tables in parts of Punjab. A well-designed system pumps what the field needs; drip or sprinkler irrigation, where suitable, cuts the water and therefore the solar capacity required.
Solar tubewell and solar water pump price in Pakistan
| System (indicative) | What is included | Price |
|---|---|---|
| 5 HP solar tubewell | Panels, solar pump VFD, ground structure, cabling, protection, installation | WhatsApp for today's rate |
| 10 HP solar tubewell | Panels, solar pump VFD, ground structure, cabling, protection, installation | |
| 15 HP solar tubewell | Panels, solar pump VFD, ground structure, cabling, protection, installation | |
| 20 to 25 HP solar tubewell | Panels, solar pump VFD, ground structure, cabling, protection, installation | |
| VFD solar inverter only | Solar pump drive, by kW rating |
Prices change with the dollar rate, import costs and stock. They exclude the pump, motor and bore work unless stated in the quotation.
For farm processing or cold-storage loads beyond a pump, see industrial and commercial solar and the complete solar system price.
Get today's price or a free site survey
Send us a photo of your motor's nameplate, the bore depth and water level, and your location. Our engineers will suggest a system size and carry out a site survey at the farm.
- 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
We serve farms and businesses across Punjab. Contact us to book a site survey.
Frequently asked questions
How many solar panels are needed for a 10 HP tubewell?
A 10 HP motor is about 7.5 kW, and an array of roughly 9 to 11 kW is a common starting point: around 15 to 18 of today's 615 W panels. Bore depth, the pump curve and pumping hours decide the exact number.
What is a VFD solar inverter?
A variable frequency drive designed to take DC power directly from solar panels and run a three-phase pump motor. It adjusts motor speed to the sunlight, soft-starts the motor and protects it against faults.
Does a solar tubewell need batteries?
Usually not. The pump runs in sunlight hours and the water is stored in the field, a tank or a channel. Batteries large enough to run a tubewell motor at night are expensive and rarely worth it for irrigation.
Can I use my existing tubewell motor with solar?
Often yes, if it is a three-phase motor in good condition. Old, rewound or worn motors should be checked first, because a weak motor wastes solar power.
Will a solar tubewell work in winter and on cloudy days?
It will pump, but less water: shorter days, fog and low sun reduce output and the VFD slows the motor to match. Many farms keep a grid or diesel backup for long cloudy spells.
Does bore depth change the solar size?
Yes. The deeper the water, the more power is needed to lift the same amount. Depth and water demand set the motor size, and the motor size sets the array.
How do I apply for the Punjab solar tubewell subsidy?
Through the Punjab Agriculture Department, not through private installers. Check its official website or helpline for the current phase, eligibility and deadlines.
Sources
- Business Recorder, "Punjab launches solarization programme for tubewells" (12 Dec 2024).
- Dawn, "Solarisation plan — a silver lining for Punjab's farmers?" (6 Jan 2025).
- Punjab Information Technology Board, tubewell solarisation ballot (1 Feb 2025).
- Profit (Pakistan Today), "CM Punjab announces Rs1 million subsidy for 20 kW solar tube wells".
- Punjab Agriculture Department, agriculture.punjab.gov.pk (phase 2 notices, 2026).