How to Size a Solar Submersible Pump for a Deep Well

Correct solar submersible pump sizing requires much more than matching a pump to the total depth of a well. A properly selected pump must deliver the required flow at the project’s actual total dynamic head while remaining compatible with the borehole diameter, sustainable well yield, delivery pipeline, controller and solar array.

For livestock watering, agricultural irrigation, remote farms and off-grid water supply, poor sizing can lead to low water delivery, excessive system cost, unnecessary solar capacity or unreliable operation. The correct approach is to size the hydraulic system first and the solar power system second.

This step-by-step guide explains how to size a solar submersible pump for a deep well using daily water demand, dynamic water level, total dynamic head, pump duty point, performance curves and solar conditions.

Quick Solar Submersible Pump Sizing Sequence

A practical deep-well sizing process follows this sequence:

Daily Water Demand → Required Flow → Dynamic Water Level → Total Dynamic Head → Pump Duty Point → Pump Curve → Well Yield → Borehole & Pipe System → Controller → Solar Array

The most important principle to remember is:

Well depth is not the same as pump head.

The pump should be selected according to the actual combination of flow and head required by the project.

What Information Do You Need Before Sizing a Deep Well Solar Pump?

Before selecting a pump, collect the following hydraulic, well and site information:

• Application: livestock, irrigation, domestic water, storage tank or another use
• Daily water demand
• Required flow rate
• Total well depth
• Static water level
• Dynamic water level
• Well or borehole diameter
• Tested well yield or recovery rate
• Delivery elevation
• Pipe length and internal diameter
• Required outlet pressure
• Water quality and sand content
• Local solar conditions
• Required backup power arrangement

A 150-meter borehole does not automatically require a pump capable of producing 150 meters of operating head. If the dynamic water level is 70 meters below ground, the hydraulic lift starts from approximately that pumping water level, then adds delivery elevation, required pressure and friction losses.

For a broader explanation of deep-well systems and applications, see our solar submersible pump guide for remote wells and boreholes.

Step 1: Calculate Daily Water Demand

The first step in solar submersible pump sizing is determining how much water the project actually requires each day.

Livestock Watering

For livestock applications, consider animal type, herd size, climate, seasonal temperature and peak daily consumption. Water demand can rise significantly during hot weather, so sizing only for mild-season consumption may result in shortages later.

Agricultural Irrigation

For irrigation, consider crop type, irrigated area, soil conditions, climate, irrigation method and irrigation schedule. Drip irrigation, sprinklers and open-field watering can have very different flow and pressure requirements.

Remote Farm Water Supply

Where the pump fills a storage tank, calculate the combined daily demand for livestock, irrigation, cleaning and other farm uses before selecting either the pump or the tank.

For additional planning guidance, see our daily water requirements guide for livestock and irrigation.

Step 2: Determine the Required Pumping Flow Rate

Once daily water demand is known, determine how much water must be pumped during the realistic daily pumping period.

A useful starting calculation is:

Required Average Flow = Daily Water Demand ÷ Available Pumping Hours

For example, suppose a remote farm requires 20,000 liters of water per day and the preliminary design assumes six effective pumping hours:

20,000 L ÷ 6 h ≈ 3,330 L/h

or approximately:

3.3 m³/h

The six-hour period in this example is not a universal solar pumping value. Actual available pumping time depends on location, season, solar irradiance, PV array size, controller characteristics and the selected pump.

The final design flow should also consider seasonal demand, water storage capacity and the sustainable yield of the well.

Step 3: Measure Static Water Level and Dynamic Water Level

Static and dynamic water levels are critical when sizing a deep well solar pump.

What Is Static Water Level?

The static water level is the distance from ground level to the water surface when the well has recovered and is not being pumped.

What Is Dynamic Water Level?

The dynamic water level is the water level while the well is being pumped at or near the expected operating flow.

What Is Drawdown?

When pumping begins, the water level normally falls. The difference between the static water level and the pumping water level is known as drawdown.

For pump sizing, the dynamic water level is generally more useful because it represents the hydraulic condition the pump experiences during operation.

Why Well Depth Is Not the Same as Pump Head

Consider a borehole that is 150 meters deep but has a dynamic water level 70 meters below ground. If water is delivered to a tank inlet 10 meters above ground, the basic vertical lift is approximately 80 meters before friction loss or additional pressure requirements are added.

Selecting a pump simply because the borehole is 150 meters deep could therefore lead to unnecessary oversizing.

Step 4: Calculate Total Dynamic Head

Total Dynamic Head (TDH) represents the total hydraulic head the pump must overcome while delivering the required flow.

For a deep well system, TDH can include:

• Vertical lift from the dynamic water level to the delivery point
• Elevation above the wellhead
• Required pressure at the outlet
• Pipe friction losses
• Losses through valves, fittings, filters and irrigation equipment

A practical expression is:

TDH = Vertical Lift + Required Pressure Head + Friction Losses

Deep Well TDH Example

Assume a project has:

• Dynamic water level: 70 m below ground
• Storage tank inlet: 10 m above ground
• Estimated pipe and fitting losses: 8 m
• No additional pressurized irrigation requirement

The approximate TDH is:

70 m + 10 m + 8 m = 88 m TDH

The pump should therefore be evaluated at approximately 88 meters of operating head rather than at the full 150-meter borehole depth.

Step 5: Determine the Required Pump Duty Point

After determining the required flow and TDH, combine them into the project’s pump duty point.

The duty point describes the actual hydraulic condition the pump must satisfy:

Duty Point = Required Flow at Required Head

Using the example above:

• Required average flow: approximately 3.3 m³/h
• Total dynamic head: approximately 88 m

The target duty point is therefore approximately:

3.3 m³/h at 88 m TDH

This is one of the most important numbers in the entire sizing process. It is much more useful than choosing a pump by horsepower, maximum head or maximum flow alone.

Step 6: Select the Pump Using the Performance Curve

The next step is to compare the required duty point with the manufacturer’s pump performance curve.

Do not select a pump based only on:

• Maximum head
• Maximum flow
• Motor horsepower

Maximum head normally occurs at very low flow, while maximum flow occurs at much lower head. These two maximum values do not occur simultaneously.

The selected pump should deliver the required flow at the calculated TDH while operating within an appropriate region of its performance curve.

Step 7: Check Well Yield and Recovery Rate

The selected pump should not continuously withdraw water faster than the borehole can sustainably supply.

Useful well-test information includes:

• Tested well yield
• Dynamic water level at the tested pumping rate
• Drawdown
• Recovery rate after pumping

A higher-flow pump is not automatically better. If the pump exceeds the sustainable yield of the well, the water level can continue to fall, increasing the risk of unstable delivery or low-water shutdowns.

Where reliable pumping-test data is available, the selected operating flow should be consistent with the borehole’s sustainable production capacity.

Step 8: Check Borehole Diameter and Pump Installation

A hydraulically suitable pump must also physically fit the borehole and operate correctly in the installation.

Check:

• Borehole inside diameter
• Pump outside diameter
• Pump setting depth
• Discharge pipe dimensions
• Power cable clearance
• Well casing condition
• Cooling requirements specified for the selected pump

Do not assume that a pump with the correct head and flow can automatically be installed in every borehole.

Step 9: Check Pipe Diameter and Friction Loss

Pipe friction can add substantial head to a deep well system, especially where water must travel a long horizontal distance after reaching the wellhead.

Friction losses generally increase when:

• Pipe diameter becomes smaller
• Flow rate increases
• Pipeline length increases
• The system contains many bends, valves or fittings

A larger pipe diameter can reduce friction in some installations, although pipe cost, flow velocity and system layout must also be considered.

For long-distance farm water systems, pipe sizing should be evaluated together with pump selection rather than after the pump has already been chosen.

Step 10: Match the Solar Pump Controller and PV Array

Only after the hydraulic pump requirement is established should the controller and solar array be finalized.

Important electrical parameters include:

• Pump rated power
• Pump operating voltage
• Controller input voltage range
• Controller maximum input voltage
• PV module Vmp
• PV module Voc
• Temperature effects on PV voltage
• Local solar irradiance
• Expected electrical and system losses

There is no universal number of solar panels for every deep well pump. Panel quantity and series/parallel configuration depend on the specific pump, controller, PV module specifications, local temperature and solar resource.

Consider the Worst Solar Period, Not Only the Best Month

Where year-round water supply is required, system planning should consider the lower-solar periods of the year rather than sizing only around peak summer irradiance. Seasonal solar conditions can affect daily pumping time and total water production.

Step 11: Decide Between Water Storage, Batteries and AC/DC Backup

Many agricultural solar well pump systems can operate without batteries by storing water rather than electrical energy.

A common arrangement is:

Solar Power → Pump During Available Sunlight → Store Water → Use Water as Needed

Water Storage

For livestock and irrigation projects, a correctly sized storage tank can supply water outside the main solar pumping period without introducing battery cost and complexity.

Battery Storage

Batteries may be considered when the pump itself must operate during periods of insufficient solar input and water storage cannot meet the application requirement.

AC/DC Hybrid Operation

Depending on the pump and controller configuration, an AC/DC hybrid system may allow solar energy to serve as the primary power source while grid power or a generator provides backup when required.

Step 12: Consider Water Quality and Sand Content

Deep wells and boreholes may contain sand, sediment, minerals or chemically aggressive water that can affect pump service life.

Before selecting a solar submersible pump, consider:

• Sand concentration
• Sediment load
• Water chemistry
• Corrosion risk
• Water temperature

Pump materials, impeller construction, bearings and sealing components should be suitable for the actual water conditions.

Complete Solar Submersible Pump Sizing Example

Consider a remote livestock farm with the following preliminary project data:

• Daily water demand: 20,000 L/day
• Assumed effective pumping period: 6 hours/day
• Dynamic water level: 70 m
• Storage tank inlet: 10 m above ground
• Estimated pipe and fitting losses: 8 m

1. Calculate Required Flow

20,000 L ÷ 6 h ≈ 3,330 L/h

or approximately:

3.3 m³/h

2. Calculate Total Dynamic Head

70 m + 10 m + 8 m = 88 m TDH

3. Define the Required Duty Point

Approximately 3.3 m³/h at 88 m TDH

4. Verify the Pump and Well

Next, compare this duty point with actual manufacturer performance curves and confirm that the borehole diameter and sustainable well yield are suitable for the selected flow.

5. Match the Electrical System

After the pump is selected hydraulically, confirm controller voltage limits and design the PV array according to the pump, controller, module specifications and local solar conditions.

This example is intended to demonstrate the sizing method. Final pump selection should use actual project data and the performance curve of the specific pump model.

Common Solar Submersible Pump Sizing Mistakes

Using Total Well Depth as Pump Head

Pump head should be based on actual hydraulic conditions, including dynamic water level, delivery elevation, required pressure and friction losses.

Selecting by Horsepower Alone

Two pumps with the same motor power can have very different head-flow characteristics.

Using Maximum Head and Maximum Flow Together

Maximum head and maximum flow normally occur at different operating points and should not be treated as simultaneous pump performance.

Ignoring Dynamic Water Level

Using only static water level can lead to incorrect sizing where significant drawdown occurs during pumping.

Ignoring Well Yield

A pump that delivers more water than the well can sustainably supply may cause excessive drawdown or unstable operation.

Ignoring Pipe Friction

Long pipelines, small pipe diameters and multiple fittings can significantly increase TDH.

Oversizing the Pump

A larger pump is not automatically better. Oversizing can increase equipment cost and solar power requirements without improving useful water delivery.

Sizing the Solar Array Before Selecting the Pump

The hydraulic requirement should be established first. Pump and controller selection then provide the basis for PV system sizing.

Solar Submersible Pump Sizing Checklist

Before requesting a pump sizing recommendation, prepare:

• Application
• Daily water demand
• Required flow rate
• Total well depth
• Static water level
• Dynamic water level
• Borehole diameter
• Well yield or pumping-test data
• Delivery elevation
• Pipe length and diameter
• Required outlet pressure
• Water quality
• Local solar conditions
• Backup power requirement

This information allows the system to be evaluated around the actual project duty point rather than relying only on horsepower, borehole depth or maximum pump ratings.

Frequently Asked Questions About Deep Well Solar Pump Sizing

How do I size a solar submersible pump for a deep well?

Start with daily water demand and required flow. Then determine dynamic water level and total dynamic head. The resulting flow and head form the pump duty point, which should be compared with the manufacturer’s performance curve.

Is well depth the same as pump head?

No. Pump head is determined by the actual hydraulic lift from the pumping water level to the delivery point, plus required pressure and friction losses. The physical bottom of the borehole does not automatically determine pump head.

Which is more important for sizing: static or dynamic water level?

Both are useful, but dynamic water level is normally more relevant because it represents the water level while the well is being pumped.

What is the duty point of a deep well pump?

The duty point is the required combination of flow and head that the pump must deliver under the project’s actual operating conditions.

How much flow does a deep well pump need?

Required flow depends on daily water demand, realistic pumping time, storage capacity and the sustainable yield of the well.

Can I size a deep well pump using horsepower?

No. Horsepower alone does not indicate whether a pump can deliver the required flow at the required head. The pump performance curve should be checked.

How many solar panels are needed for a deep well pump?

The number of panels depends on the selected pump, controller voltage requirements, PV module specifications, temperature conditions, solar irradiance and overall system design.

Can a solar submersible pump operate at night?

A direct solar pumping system depends on available solar input. Where water is needed outside the solar pumping period, the system may use water storage, batteries or AC/grid/generator backup depending on the application.

Can a solar submersible pump be used for livestock watering?

Yes. Deep well solar pumps are commonly used to transfer groundwater into storage tanks and livestock troughs on remote farms when flow, TDH, well yield and storage capacity are correctly matched.

What information should I send a pump supplier?

Provide total well depth, static and dynamic water levels, borehole diameter, tested well yield, required flow, delivery height, pipe length and diameter, daily water demand, application and available power conditions.