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  • Grid-connected Solar PV System

Solar Water Pumping

Solar Water Pump is considered simple and clean alternative to fuel burning engines as well as generators for domestic water, irrigation, and livestock requirements. Solar water pumps come in two categories; AC Submersible Solar Water Pumps and surface solar pumps. These solar water pumps show effective results during sunny and dry seasons. They require very low maintenance and work without any fuel deliveries. The flow rate of solar water pump can be determined by the intensity of sun as photovoltaic panels power them.

Solar pumping systems can be applied to all forms of daily use, water pumping for drinking water supply for remote villages and farms without connection to the water grid, for agricultural use such as livestock watering,agricultural irrigation, forestry irrigation, pond management, desert control, and industrial use such as waste water treatment etc. In recent years, with the promotion of the utilization of renewable energy resources, solar pumping systems are more and more used in municipal engineering, city center squares, parks, tourist sites, resorts and hotels,and fountain systems in residential areas.

The system is composed of a PV module, a pump and asolar pump controller. Based on the design philosophy thatit is more efficient to store water rather than electricity,there is no energy storing device such as storage battery in the system. The system is prepared to be combined with an elevated water storage, e.g. water tower or an uphill tank installation.

The PV module, an aggregation of PV cells connected in series and in parallel, absorbs solar irradiation and converts it into electrical energy, providing power for the whole system. The pump controller controls and adjusts the system operation and converts the DC produced by the PV module into AC to drive the pump, and adjusts the output frequency in real-time according to the variation of sun light intensity to realize the maximum power point tracking(MPPT). The pump, driven by 3-phase AC motor, can draw water from deep wells, rivers and lakes and pour it into storage tanks or reservoirs, or be connected directly to the irrigation system, fountain system, etc. According to the actual system demand and installation condition, different types of pumps such as centrifugal pump, axial flow pump,mixed flow pump or deep well pump can be used.

Solar water pumping system in Dhoobley, Somalia
Solar water pumping system in Dhoobley, Somalia

Some of the benefits of using solar to pump water includes:
i. Solar water pumping eliminates the need for fuel and all the costs associated with fueling like transporting, fueling labour etc.
ii. Minimal maintenance of solar makes them have a huge advantage over generators.
iii. Reliable source of energy. As long as there is light the solar systems will pump.
iv. No noise associated with generators
v. The return on investment (ROI) for solar is usually two years or less depending
vi. Solar water pumping are environmentally friendly. No fears of oil spills or smoke emitted by the generators.

For solar water pumping it’s better to have enough storage facility so that during the day the solar pump can pump enough water to be used when there is no sunshine. This avoids the need for batteries which are not cost effective.

Operation and maintenance
Solar water pumping systems operate automatically aided by the control unit, which acts as a brain of the whole system. Intelligent protection control and management on the system, in terms of low voltage, over voltage, over load, short circuit, deficiency of water in well, excess of water in tank, etc.
The only maintenance of the solar water pumping system is the normal borehole servicing and cleaning of the solar panels after some time to clear the settled dust.

With MPPT technique (Maximum Power Point Tracking), the control unit efficiency is over 95%.
Water required vs water produced by the source
Determine if your borehole will produce enough water to supply the pump system. You may determine you need 50 litres per minute but if your water source only produces 20 litres per minute you will be unable to sustain your daily water requirement. If the water source is a well or stream and the flow rate is unknown you can have a pump test performed.

Designing solar water pumping
For a borehole that is not yet equipped a driller’s report would be vital. Generally the information needed to equip a borehole include:
i. Well casing size
ii. Distance from surface to dynamic water level during pump testing
iii. Dynamic water level
iv. Distance from the surface to the static water level
v. Static water level
vi. Vertical lift from well casing to delivery point
vii. For Surface pumps: Suction lift (vertical distance from water to pump), Pressure lift (vertical distance from pump to delivery point)

A typical solar powered pumping system consists of a solar panel array that powers AC or DC pump, which in turn powers a bore or surface pump. The water is often pumped from the ground or stream into a storage tank that provides a gravity feed, so energy storage is not needed for these systems.

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