Solar Water Pumps in Ghana: How to Size a Reliable System

Define the water task first

Write down the required volume per day, when the water is needed, and the destination: a household tank, livestock trough, storage reservoir or irrigation network. Separate daily demand from the peak delivery rate. A system that fills a tank through the day can meet a short morning demand without running the pump at that same peak flow.

Identify the source and its seasonal behaviour. A borehole, dug well, river, pond and storage tank each present different lift, water-quality and protection requirements. Confirm sustainable yield and water level with the relevant professionals; pumping faster than the source can replenish it can cause dry running or damage.

Calculate total dynamic head

Total dynamic head (TDH) combines the vertical lift from the pumping water level to the discharge point, drawdown while pumping, elevation of the tank or field, and friction losses in pipes, valves and fittings. Use the water level while pumping, not only the static level measured before the pump starts.

Pump flow falls as head rises. Read the manufacturer’s pump curve to find the flow available at the calculated TDH, then verify that it meets the required daily volume during the expected solar pumping hours. Pipe diameter, length, bends and filters can materially affect friction losses, so include them in the design.

Choose the pump, controller and PV array together

The pump type must suit the source and lift. Submersible pumps are commonly used for boreholes; surface pumps need a suitable suction arrangement and have practical limits on suction lift. Confirm water chemistry, sand or sediment tolerance, motor type, cable length and protection requirements with the pump manufacturer.

A solar pump controller manages the motor using the available PV power. Check its supported motor type, DC input voltage range, maximum current, MPPT range and dry-run protections. The PV string voltage must remain within the controller’s limits across site temperatures, while the array must provide adequate power for the expected operating window. Do not size the panels from the pump’s nominal motor rating alone.

Use water storage to smooth out solar supply

When practical, pump into a raised or ground-level tank and draw water from storage when needed. Water storage can be simpler and less costly than adding a large battery bank solely to keep the pump running after sunset. The tank volume should cover the intended demand and the site’s cloudy-day plan; a tank does not solve a source-yield problem.

If an electrical battery is required, include battery energy, discharge current, inverter or controller compatibility and protection in the design. A pump motor can have a substantial starting demand, so confirm starting capability and not just steady running power.

Protect water supply and equipment

Include dry-run or low-water protection, tank float switches or level sensors, appropriate non-return valves, intake screening, secure pump suspension and correctly rated electrical isolation. A borehole installation should prevent the pump from resting on sediment and should use a cable and splice system rated for the environment.

Inspect the array for dust and shading, check pipe joints and filters, test float switches, and watch for changes in flow, noise or water quality. Keep a record of the measured water level, operating hours and daily volume. FAO’s sourcebook covers design, operation, inspection and troubleshooting for solar PV pumping systems; use it alongside the exact equipment manuals.

Information to provide when requesting a quote

• Source type, static and pumping water level, seasonal changes and estimated sustainable yield.
• Required daily water volume, discharge point elevation, pipe route and intended pumping hours.
• Water quality, sediment conditions, intended uses and irrigation method if applicable.
• Pump curve at the proposed TDH, controller limits, array design and protection details.
• Storage capacity, low-water controls, installation scope and maintenance plan.

Further technical reading

The Food and Agriculture Organization’s solar irrigation sourcebook provides a detailed reference for the design and operation of PV pumping systems.