How do I calculate the solar submersible pump system based on horsepower and well depth?

Last updated: October 17, 2026

To calculate a solar-powered submersible pump system that starts with water, not panels: How many cubic meters per hour do you need, and from what depth will you lift it? From these two figures, calculate the hydraulic power, then the motor's horsepower, and then calculate the panels by multiplying the motor's power by 1.3 to 1.5. In this article, we will walk you through calculating a complete submersible pump system with numbers, step by step.

The data you need before any calculation

Most submersible pump design errors are caused by incomplete or estimated figures. Before calculating anything, add up the following:

• Required disposition: How many m³ per hour or per day do you need for irrigation, drinking water, and livestock?.
• Still water level: The water level in the well is at a point where pumping has stopped.
• Drop during pumping: How much does the water level drop when the submersible pump is operating? Their sum is the water level during pumping (dynamic level).
• High discharge: Height of the inlet opening in the tank or the highest point the water reaches above the ground surface.
• Pipe length and diameter: From the plunger to the tank, because it determines friction losses.

Note: The total depth of the well is not the same as the pumping depth. The well may be 200 meters deep, but the water level during pumping is 90 meters, and the pump lifts the water from that level, not from the bottom of the well.

Step 1: Calculate the total lift

Total head is the equivalent vertical distance that the pump must overcome, and it consists of three parts:

1. The dynamic level of water inside the well.
2. Height from ground surface to the discharge point in the tank.
3. Friction losses in pipes, elbows and valves are calculated from pipe tables according to diameter, length and discharge.

Example from a farm in Al-Ahsa: The static water level is 75 meters, and the drop during pumping is 15 meters, so the dynamic level is 75 + 15 = 90 meters. The tank is elevated, and the discharge point is at a height of 6 meters. We assume frictional losses in this example are 8 meters. Therefore:

Total lifting = 90 + 6 + 8 = 104 meters.

Step two: Calculating the required power

The well-known geometric relationship for calculating pump power is:

Power (kW) = Discharge (m³/h) × Total Head (m) ÷ 367 ÷ Pump Efficiency

The number 367 is a constant that combines water density, gravity, and the conversion from hours to seconds. The efficiency is taken from the pump's operating specifications; in this example, we will assume an efficiency of 60% (0.6) for both the pump and motor.

Continuing with the Al-Ahsa example, the required discharge is 12 m³ per hour:

1. 12 × 104 = 1248.
2. 1248 ÷ 367 = approximately 3.40 kilowatts, and this is the hydraulic power that actually reaches the water.
3. 3.40 ÷ 0.6 = approximately 5.67 kilowatts, and this is the power that the motor should draw.

Step three: Choosing the engine's horsepower

We convert kilowatts to horsepower: 5.67 ÷ 0.746 = approximately 7.6 horsepower.

Motors come in standard sizes such as 5, 7.5, 10, and 15 horsepower. A 7.5 horsepower motor produces approximately 7.5 x 0.746 = 5.6 kilowatts, which is slightly less than the required 5.67 kilowatts and therefore not sufficient for safe operation. Therefore, we choose a 10 horsepower motor. The general rule is: choose the next largest size and never run the motor at full power.

It is important to choose the pump so that the operating point (12 m³/hr at 104 meters) is close to the high efficiency zone in the pump curve, and not just that the horsepower is sufficient.

Step four: Calculating the panels and inverter

A 10 HP motor = 10 x 0.746 = 7.46 kW. Multiply by the panel's power factor:

• Minimum: 7.46 × 1.3 = approximately 9.7 kW.
• Upper limit: 7.46 × 1.5 = approximately 11.2 kilowatts.
• With 550 watt panels: 9.7 ÷ 0.55 ≈ 17.6 i.e. 18 panels, and 11.2 ÷ 0.55 ≈ 20.4 i.e. 20 to 21 panels.

For example, we would choose 20 panels (20 x 550 = 11 kW) if the inverter's voltage range allows for one or two series connections of that number. The inverter would be a variable frequency drive (VFD) with a capacity suitable for a motor of at least 10 hp, plus a margin as recommended by the manufacturer.

Area: At a rate of 5 to 6 m² per kilowatt, 11 kilowatts requires approximately 55 to 66 m² of exposed land.

The numbers in the table are approximate, and the final number is adjusted according to the method of connecting the series, the voltage range of the inverter, and the power of the chosen board.

How much water will the system pump daily?

The solar pump does not operate at full discharge throughout the day. Discharge is lower in the morning and afternoon, and near full discharge around midday. For a quick estimate, we assume the system provides approximately 5 to 6 hours of full discharge daily; however, this estimate varies depending on the season, region, and panel cleanliness.

In our example: 12 x 5 = 60 m³, and 12 x 6 = 72 m³. That's approximately 60 to 72 m³ per day. If your needs are higher, you can either increase the required flow and recalculate, or accept additional operation from another source.

Converse example: I have a 15 hp submersible pump, how many panels do I need?

Many farmers have working submersible pumps and want to convert them to solar power only. The calculation is straightforward:

1. 15 × 0.746 = 11.19 kilowatts.
2. 11.19 × 1.3 = 14.5 kW, and 11.19 × 1.5 = approximately 16.8 kW.
3. With 550W panels: approximately 27 to 31 panels.
4. Area: From 14.5 × 5 = 73 m² to 16.8 × 6 = 101 m² approximately.

But before proceeding, make sure the submersible pump is actually suitable for your well. If the hydraulic calculations say 10 horsepower is sufficient, you're paying for extra plates to run a motor that's too large.

Common errors in calculating the diving system

• Using the total well depth instead of the dynamic water level.
• Forgetting about the height of the tank and the losses from long pipes.
• The panels are designed to precisely match the motor's power, with no margin of 1.3 to 1.5.
• Installing panels in an incorrect orientation or angle. See Best orientation and tilt angle for panels For your city.
• Choosing panels without considering their voltage compatibility with the inverter. Read about Types of solar panels Before choosing.

If you want the complete picture of the components, tank, and maintenance, read on. The Complete Guide to Solar Energy for Agricultural Submersible PumpsLearn more about what we offer on our page. Agricultural submersible pump systems. For those who wish to delve deeper into design, there are Solar System Design Course Free.

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