How do the depth of the well and the amount of water affect the size of the solar submersible pump system?

Last updated: October 25, 2026

The depth of the well itself does not determine the size of the solar submersible pump system; rather, two factors determine it: the total lift (from the water level during pumping to the discharge point, including pipe losses) and the daily water requirement. The greater the lift or the greater the water volume, the greater the pump's power, and consequently, the greater the power of the solar panels and inverter, by approximately the same proportion.

What is the difference between well depth, water level, and total lift?

Many farmers say, "My well is 300 meters deep," and base their calculations on this figure, which often results in an overestimated system. The total depth is the length of the drilling, while the pump doesn't lift water from the bottom of the well but from the water level inside it. Therefore, we differentiate between four figures:

• Well depth: The length of the excavation is from the surface of the earth to the bottom.
• The static ratio: The water level in the well is when pumping has stopped.
• Moving (dynamic) level: The water level during pumping is deeper than at rest because the water sinks around the pump. The difference between the two is called the drop.
• Pump installation depth: It should be below the moving level by a safe distance so that the pump remains submerged at all times.

The total lift that the pump operates on is equal to the moving level, plus the height of the discharge point above ground level (overhead tank or pond), plus friction losses in pipes, elbows and valves, and any pressure required at the end of the line if pumping directly into a drip network.

How does the amount of water required affect the size of the system?

Solar energy operates only during the day, and its performance varies with the intensity of the radiation. Therefore, we convert the daily requirement into a design capacity by dividing it by the equivalent operating hours at full speed, which in most regions of the Kingdom are close to peak solar hours, approximately 5 to 7 hours depending on the season and the size of the panels.

For example, if the farm requires 150 m³ per day, assuming 6 equivalent hours, the design output is approximately 25 m³/hour. If you want the system to be sufficient even in winter when sunlight hours are lower, calculate based on winter hours, not summer. Details regarding seasonal operating hours are explained in the article "How Many Hours Does a Solar Submersible Pump Operate in Summer and Winter?".

Remember that the required water quantity isn't just what you want, but what the well can deliver. If the well's output is less than the pump's capacity, the water level will drop rapidly, and the pump will shut down due to dry-run protection. Therefore, determine your well's productivity before selecting a pump, either through pumping tests or from your previous pumping experience.

How do you calculate a diver's lifting and handling capacity?

The basic equation is simple: Hydraulic power in kilowatts = Discharge in cubic meters per hour × Total lift in meters ÷ 367. This is the power that actually reaches the water. However, the pump, motor, and cable have losses, so we divide by the overall efficiency, which ranges approximately between 50 and 651 TP3T for most submersible pumps, to get the required electrical power from the motor.

Illustrative example: From the well to the system

The figures are approximate and for illustrative purposes only:

1. Moving elevation: 120 meters. Tank height above ground: 5 meters. Estimated friction losses: 6 meters. Therefore, total lift is approximately 131 meters.
2. Design flow rate: 25 m³/hour (150 m³ per day over 6 hours).
3. Hydraulic power: 25 × 131 ÷ 367 ≈ 8.9 kW.
4. Total efficiency of 60%: 8.9 ÷ 0.6 ≈ 14.9 kW.
5. The closest standard 15 kW (20 hp) motor is at the limit, so the pump curve is reviewed, and 18.5 kW (25 hp) is often chosen for a safety margin.
6. Panel power at a factor of 1.3–1.5: approximately 24 to 28 kW peak for an 18.5 kW motor.

Therefore, one can start from Solar power system to operate a 25 hp submersible pump As a reference, then confirm the selection with the actual pump curve and well data.

Table: How does the system size change with lifting?

The table assumes a flow rate of 20 m³/hr and varies the total lift, assuming a total efficiency of 60% and a panel modulus of 1.4. All figures are estimates for illustrative purposes.

Observe the pattern: every 50-meter increase in lift at the same flow rate adds approximately the same amount of power. Conversely, if the lift is constant and the water flow is doubled, the power approximately doubles. This makes knowing the exact flow rate the most important figure in the design.

Quick comparison: Same quantity, two different wells

Let's assume two farms, each requiring 120 m³ per day, or approximately 20 m³/hour over 6 equivalent hours. The first farm has a rising elevation of about 45 meters, resulting in a total lift of approximately 50 meters. The second farm has a rising elevation of approximately 190 meters, resulting in a lift of approximately 200 meters. According to the table, the first farm requires a 5.5 kW motor and panels with a peak power of around 8 kW, while the second farm needs a motor with approximately 18.5 kW and panels with a peak power of around 26 kW—more than three times the power required for the same quantity of water. Therefore, it's incorrect to compare two submersible pump systems based solely on the number of panels without knowing the lift for which each system was designed, nor to simply transfer your neighbor's system design to your well just because the cultivated area is similar.

Things that change the account that many people don't notice

• The water level has decreased over the years: In some areas the well level drops gradually, so leave a margin for lifting, or choose a pump whose curve covers a deeper range.
• Pipe diameter: A narrow pipe significantly increases friction losses with increased flow rate, and sometimes increasing the pipe diameter is more economical than increasing the size of the pump and plates.
• Direct pumping for irrigation: If the pump feeds directly into a drip irrigation system, add the system's required pressure to the boost pressure. Pumping to a reservoir first simplifies the design and makes irrigation independent of sunlight, as explained in the article. Water tanks and irrigation network with submersible pump system.
• Plunger cable length: The deeper the pump, the longer the cable and the greater the voltage drop, thus requiring a larger cross-section.
• Pump efficiency at the point of operation: The pump operates efficiently within a specific range of its curve, and choosing a pump far from your work point wastes part of the plates.

For more information on reading pump specifications before purchasing, see Choosing a plunger pump: capacity, lift, and disposition.

Frequently Asked Questions