Introduction to solar submersible borehole pumps

A solar submersible borehole pump is designed to lift underground water using electrical energy generated by solar panels. The pump is installed below the water level in a borehole, where it pushes water through a rising main pipe to a storage tank, irrigation network, livestock trough, or building water supply.

Choosing the right pump requires more than knowing the borehole depth or the motor's horsepower. A successful installation depends on the required water flow, pumping water level, delivery height, pipe friction, borehole yield, motor specifications, solar power availability, and the pump controller.

Pro-Logic Technologies Limited works with Hydrosol Drilling Solution on borehole-related enquiries and water pumping requirements. Property owners, farmers, institutions, and businesses should establish their water requirements and borehole characteristics before purchasing a solar submersible pump.

What is a solar submersible pump?

A submersible pump operates while immersed in water. Its motor drives an impeller or other pumping mechanism that moves water into the discharge pipe. Unlike a surface pump, it does not normally need to draw water through a long suction pipe from the ground.

Borehole submersible pumps are commonly selected for deep water sources where a surface pump would be unsuitable or unable to provide the required lift. The pump must be compatible with the borehole diameter and installed with the submergence, cooling, and operating conditions specified by its manufacturer.

Solar-powered submersible pumps can use dedicated DC motors or compatible AC motors supplied through suitable power-conversion equipment. The pump, motor, controller, and solar array must be selected as a compatible system.

Types of solar submersible pumps

DC solar submersible pumps

DC solar pumps operate using direct-current electrical power. Depending on the model, the controller may regulate the supply and optimise operation as solar power changes during the day.

These pumps can be suitable for smaller water supply systems, farms, remote properties, and installations where a dedicated solar pumping package meets the required hydraulic duty.

Before purchasing a DC pump, verify its operating voltage, current, controller requirements, rated flow, maximum head, water quality limits, and permitted operating range.

AC submersible pumps with solar inverters

Some borehole pumps use AC motors supplied by a compatible solar inverter or variable-frequency drive. The drive converts the available electrical power into the form required by the motor and may regulate its operating speed.

The inverter must be specifically suitable for the motor and the intended solar application. A general-purpose inverter should not be assumed to operate a borehole pump correctly without checking its ratings and control requirements.

AC systems can be appropriate for larger pumping applications, but the design must account for motor starting, drive compatibility, protective functions, and the available solar power.

Solar pumping systems with battery storage

A solar borehole system can be designed with batteries when stored electrical energy is necessary for the intended operating schedule. However, many agricultural and residential water systems can use a water storage tank instead of storing electricity.

Storing water can be simpler where the main objective is to have water available after the sun sets. Battery storage may be justified when pumping must continue outside normal solar production hours or when the wider installation requires electrical backup.

The decision should compare the daily water demand, pump power, required operating hours, storage options, battery cost, maintenance, and backup requirements.

Understanding pump performance curves

A pump performance curve shows how a pump behaves at different operating heads and flow rates. It is one of the most important tools for selecting a suitable borehole pump.

A pump may deliver a relatively high flow at a low head but substantially less water at a greater head. The advertised maximum flow is therefore not necessarily the flow the pump will provide in the installed system.

Selection should identify the required operating point and verify that the pump can meet the flow requirement at the calculated total dynamic head. The designer should also check efficiency, motor loading, allowable operating range, and manufacturer restrictions.

A pump that operates far outside its intended range may perform poorly, consume unnecessary energy, or experience premature wear.

Calculating the required pumping flow rate

The required flow rate is calculated from the volume of water needed and the effective pumping time.

Required flow rate = daily water demand ÷ effective pumping hours.

For example, a property requiring 6,000 litres per day and expecting eight effective pumping hours needs an average delivery rate of:

6,000 litres ÷ 8 hours = 750 litres per hour.

That is 12.5 litres per minute.

This calculation establishes a preliminary target. It does not prove that a particular pump is suitable. The selected pump must deliver the required volume at the actual total dynamic head, and the borehole must be able to sustain the pumping rate.

Solar pumping hours also vary with weather, panel orientation, shading, temperature, and equipment efficiency. The design should use realistic site conditions rather than assuming that the pump will run at full output throughout every daylight hour.

Determining total dynamic head

Total dynamic head is the combined head that the pump must overcome to move water through the system. It includes the lift from the pumping water level to the delivery point, friction losses in pipes and fittings, and any required delivery pressure expressed as equivalent water head.

A simplified expression is:

Total dynamic head = vertical pumping lift + friction losses + delivery-pressure head.

Suppose the pumping water level is 50 metres below the reference point, the water must rise another 10 metres to the tank inlet, and estimated friction losses are 6 metres. If the system discharges into an open tank without an additional pressure requirement, the approximate total dynamic head is 66 metres.

This example is illustrative. The actual calculation should account for the measured pumping water level, elevations, pipe route, fittings, flow rate, valves, and intended delivery conditions.

The pump should be selected from a curve that demonstrates the required flow at the calculated head.

Borehole diameter and pump dimensions

The pump's external diameter must be suitable for the borehole's internal diameter. Adequate clearance is required for installation, removal, and the manufacturer's specified operating conditions.

A pump that is too large may be impossible to install safely or may not have the required clearance. A pump that is unnecessarily small may limit the available flow or fail to meet the system's requirements.

The borehole completion details should be reviewed before ordering the pump. The installer should verify the casing diameter, any restrictions, the pump's dimensions, and the dimensions of the rising main and cable arrangement.

Pump selection should also consider the water quality and any manufacturer's limits concerning sand, suspended solids, or other contaminants.

Choosing the correct pump installation depth

Pump installation depth is not simply the same as total borehole depth. The pump must remain sufficiently submerged during operation, but it must also be installed in a position appropriate for the borehole construction and water-producing zones.

The static water level indicates the water level when pumping is stopped and the borehole has recovered. The pumping water level indicates the level while water is being withdrawn at a specified rate.

The difference between these levels is drawdown. The pump's position should be selected using reliable borehole records, water-level measurements, sustainable yield information, and manufacturer instructions.

The pump should not be placed directly on the borehole bottom. Sediment can accumulate there, and excessive proximity to sediment may increase the risk of drawing debris into the pump. The required clearance depends on the borehole construction and equipment specifications.

Borehole yield and pump capacity

The borehole's sustainable yield limits how much water can be withdrawn over time. Installing a high-capacity pump does not increase the natural water supply of the borehole.

If the pump removes water faster than the borehole replenishes it, the pumping water level may fall significantly. This can cause reduced output, dry-running events, or damage if adequate protection is not provided.

A pumping test or other suitable assessment may be needed to establish an appropriate operating rate. The pump's selected duty should reflect the available water supply and the property's daily demand.

Where the borehole cannot sustainably meet demand, options may include reducing the pumping rate, using a storage tank, adjusting the water-use schedule, or investigating the borehole's performance. Simply installing a larger pump is not a reliable solution.

Solar panel sizing for a submersible pump

The solar array must provide sufficient electrical power for the pump and controller under expected site conditions. Panel selection depends on the motor's electrical input, controller specifications, solar resource, temperature, shading, and expected daily pumping requirement.

The rated motor output is not necessarily the same as the electrical power required from the solar array. The system designer must account for the complete pump-and-controller arrangement and any conversion losses.

Series-connected panels increase voltage, while parallel-connected panels increase available current. The resulting configuration must remain within the controller's permitted operating voltage, maximum open-circuit voltage, current limits, and allowable array power.

The installer should also account for the effect of low solar irradiance. If the pump cannot maintain the required output during weaker sunlight, the system may need additional suitable array capacity, more storage, a different pump duty, or a revised operating schedule.

Solar controller compatibility

The controller is responsible for supplying and managing power to the pump. Some controllers include maximum power point tracking, overload protection, dry-run detection, thermal protection, fault indications, and speed control.

Not every feature is available on every model. The installation design should confirm the actual protective functions provided and determine whether additional sensors or protective devices are needed.

Controller selection must be compatible with the pump's motor type and electrical requirements. The controller should not be chosen solely because its advertised wattage appears similar to the pump's rated power.

Incorrect voltage, excessive current, incompatible motor control, or unsuitable wiring can result in faults and equipment damage. The manufacturer's documentation should be followed throughout the design and installation.

Electrical cable sizing

The cable supplying a submersible pump must be suitable for the operating current, voltage, cable length, installation environment, and temperature conditions.

Cable voltage drop is particularly important because the pump may be installed far below the surface and the cable route may be long. Excessive voltage drop can reduce performance and interfere with reliable motor operation.

Cable sizing should account for the conductor material, cross-sectional area, route length, expected current, allowable voltage drop, insulation rating, and relevant electrical standards.

The cable must be suitable for submersible service where it is exposed to water. Any underwater joint must use an approved, appropriately rated method and materials designed for the application.

The pump should not be suspended solely by an ordinary electrical cable unless the manufacturer explicitly approves a cable designed for that purpose. Suitable mechanical support must be provided.

Electrical protection and safe isolation

A solar borehole pump installation requires protection appropriate to its DC and AC circuits. Depending on the equipment, this may include DC isolators, overcurrent protection, surge protection, earthing, motor protection, and suitable enclosures.

DC equipment must be rated for the circuit voltage and current because DC arcs can be hazardous and may not be extinguished by equipment intended only for AC service.

The solar array can produce voltage whenever it is illuminated. Electrical isolation and testing must follow the manufacturer's procedure and be performed by suitably qualified personnel using appropriately rated tools.

Protective devices must be selected for the equipment and installation conditions. Improvised connections, exposed conductors, unsuitable enclosures, and bypassed protection can create fire and electric-shock hazards.

Installing the rising main pipe

The rising main transports water from the submersible pump to the surface. It must be suitable for the expected flow, pressure, water quality, installation method, and operating environment.

Pipe diameter affects friction losses. A smaller pipe can increase friction and reduce the flow available at the delivery point, while a suitable larger pipe can reduce losses at additional material cost.

The design should account for pipe length, fittings, valves, flow rate, pressure rating, and the possible effects of pressure transients. Connections should be made according to the pipe and fitting manufacturer's instructions.

The pipe and pump assembly must be supported appropriately during installation. Poorly secured joints or unsuitable materials can lead to leaks, mechanical failure, or difficulty retrieving the pump for future maintenance.

Lowering the pump into the borehole

Pump lowering should be performed with appropriate lifting equipment and a safe installation procedure. The pump, rising main, electrical cable, and any support arrangements must be handled in a way that prevents mechanical damage.

The installer should avoid scraping the cable against sharp edges, crushing it between components, or allowing unsupported loads to stress electrical joints. The assembly must remain secure while it is lowered.

The final position should be checked against the borehole records and the pump manufacturer's instructions. Adequate submergence, cooling conditions, and clearance from the borehole bottom must be maintained.

The pump should not be installed at an arbitrary depth simply because the borehole is deep. Its position should be based on reliable measurements and the design requirements.

Installing a water-level sensor

A water-level sensor can help monitor the borehole and reduce the risk of operating the pump when water is insufficient. Some systems use dedicated probes or transducers, while others use controller-based dry-run detection.

The selected sensor must be compatible with the controller and suitable for the installation environment. Its location and settings should reflect the intended operating water level and the borehole's recovery characteristics.

Dry-run protection should not be assumed to be infallible. The installer should test the protection according to the manufacturer's procedure and ensure that the pump's operating rate remains appropriate for the borehole.

A sensor is a protective measure, not a substitute for assessing borehole yield and choosing the correct pump.

Tank-level controls and automatic operation

A tank-level switch or sensor can stop the pump when the storage tank reaches its designated upper level. This helps prevent overflow and unnecessary pumping.

The control arrangement must be compatible with the solar controller. Some controllers provide dedicated sensor terminals, while others require a suitable interface or relay arrangement.

The system may also use a low-water sensor in the borehole to prevent pumping when the water level falls below the permitted limit. The two functions serve different purposes: tank-level control manages storage, while borehole-level protection helps safeguard the pump.

Control wiring should be installed according to the manufacturer's instructions. A switch should not be connected directly to a motor circuit unless the equipment is explicitly designed for that arrangement.

Pump installation for elevated storage tanks

When water must be delivered to an elevated tank, the vertical lift and pipe friction contribute to the total dynamic head. The required pump flow must be evaluated at that head rather than at the pump's maximum advertised flow.

Tank height should be measured from the relevant reference level. The designer should also account for the route and elevation of the rising main, valves, bends, and the tank inlet.

If the tank supplies a building by gravity, the pressure available at each outlet depends on the vertical difference between the water surface and the outlet, as well as the losses in the distribution pipework.

A solar borehole pump that fills a tank may not be the same pump required for pressurising a multi-storey building. Where necessary, a separate booster pump can be selected for the building's pressure and flow requirements.

Commissioning and performance testing

Commissioning confirms that the pump and associated equipment have been installed correctly and operate within their specified limits.

Checks should include the solar array configuration, electrical readings, controller settings, protective functions, pump operation, water flow, and the integrity of the pipework. Where relevant, delivery pressure and the performance of tank-level controls should also be verified.

The pumping water level should be monitored during testing to help determine whether the selected operating rate is suitable for the borehole. A decline in water level or flow may require investigation before normal service continues.

Commissioning records should include the conditions under which measurements were made. Solar output varies with sunlight, and pump flow varies with total dynamic head and water level. Recorded results should therefore be interpreted in context rather than treated as fixed performance under all conditions.

Common solar submersible pump faults

A pump that fails to start may have an electrical supply problem, a controller fault, a protective shutdown, damaged cables, or a motor fault. A pump that starts but produces little water may have a different cause.

Low flow can result from a falling borehole water level, worn pumping components, blocked pipes, leakage, a closed valve, excessive head, or insufficient electrical input.

Repeated controller resets without proper diagnosis may hide the cause and lead to further damage. A technician should review fault codes, electrical readings, water flow, water level, and pipework before deciding which component requires repair or replacement.

Where electrical measurements are necessary, testing should be performed safely by qualified personnel.

Maintenance of solar submersible pumps

Maintenance should include inspections of the solar array, cables, controller, protection equipment, pipework, storage tank, and level controls. Changes in pump output or operating behaviour should be recorded and investigated.

Solar panels should be checked for shading, damage, and dirt accumulation. The controller should be inspected for alarms and signs of overheating or moisture ingress.

A pump does not always need to be removed from the borehole for routine maintenance. The decision to retrieve it should be based on symptoms, operating records, and appropriate diagnostic findings.

If pump removal is necessary, suitable lifting equipment and safe procedures are essential. Reinstallation should include checking the cable, joints, pipe connections, pump position, and protective functions.

Selecting spare parts and replacement equipment

When a pump or controller requires replacement, the replacement should be selected using the actual system specifications. The equipment label, model number, rated voltage, current, power, flow requirements, and controller details should be checked.

A replacement pump should also match the borehole diameter, total dynamic head, sustainable yield, and required daily water volume. Physical fit alone does not establish hydraulic or electrical compatibility.

Replacing a pump with a higher-powered model without reviewing the system can create problems. The solar array may be insufficient, the controller may be incompatible, or the borehole may not support the increased pumping rate.

Keeping installation records and equipment manuals helps reduce errors during future repairs.

Choosing between repair and replacement

The decision to repair or replace a solar borehole pump depends on the fault, age and condition of the equipment, availability of compatible parts, repair cost, and reliability requirements.

A controller fault may be repairable or may require a compatible replacement. A worn pump may be suitable for repair depending on its construction and the availability of parts. Severe motor damage or repeated failures may make replacement more practical.

Before deciding, the technician should establish the cause of the failure. A pump can be damaged by a system problem such as dry running, excessive sand, electrical incompatibility, or operation outside its permitted range. If that underlying issue is not corrected, a replacement pump may fail in the same way.

Information to prepare before requesting a pump quotation

Property owners and farmers should prepare as much of the following information as possible:

• Borehole depth and internal diameter.
• Static and pumping water levels, if available.
• Sustainable borehole yield or pumping-test results.
• Required daily water volume.
• Height of the delivery point or storage tank.
• Approximate rising main length and diameter.
• Existing pump, motor, controller, or solar panel specifications.
• Whether the water will be stored, used for irrigation, or supplied under pressure.
• Any known faults, controller alarms, or changes in water output.

This information allows the installer to identify what is known, what still needs to be measured, and which equipment specifications must be verified.

Solar submersible pump installation enquiries

Pro-Logic Technologies Limited works with Hydrosol Drilling Solution on borehole-related enquiries and water pumping requirements. Before selecting a solar submersible pump, ensure that the pump, controller, solar array, cable, rising main, and protective equipment are designed as one compatible system.

Contact: 0723763173

Website: https://prologictecnologies.co.ke

Correct pump selection, safe installation, suitable electrical protection, and documented commissioning are essential to a dependable borehole water supply. A properly designed system should meet the required water demand while respecting the borehole's sustainable yield and the equipment manufacturer's operating limits.