Frequently Asked Questions (FAQ) – Solar Water Pumping

Normally, a storage tank is integrated in the design of a solar water pumping system. The storage tank acts as a “battery”. When the sun shines, the tank is filled up, when it is cloudy or dark, water can be used from the tank which is placed at a high point. It is also possible to include a backup generator in a solar water pumping system.

Generally not. If you can store the water you have pumped up, that will act as your battery for cloudy days. Only in case the yield of your borehole is limited and you have a high water consumption which requires you to also pump at night, you should consider integrating a battery.

A submersible pump is “submerged” under water, which means the pump itself always needs to be under the water to work. These are mostly used for pumping from boreholes and wells. Surface pumps need to stay above the water, a pipe is connected which “sucks” the water from a nearby water source, mostly a pond, lake or river.

DC-powered pumps run on direct current, which means the solar power (which is also direct current) does not need to be converted to AC-power. DC-powered pumps are generally 20-40% more efficient than AC-powered pumps. Due to the current low cost of solar panels, however, this difference in efficiency is not as important as it used to be. There are also pumps which can use both DC as well as AC power as their input.

As long as the solar panels are mounted with a pitch of 10-15 degrees, most of the dirt should be washed of by the rain. When the solar modules are particularly dirty, and no rain is expected due to a dry season, it can be smart to clean the solar panels though. Cleaning the solar panels should be done with a soft cloth (to protect the coating) and ideally demineralized water.

When you do not have a grid connection (or an unreliable one), it normally makes financial sense to install a solar water pump. The average payback period of such a system is 1-3 years in Tanzania. In case you have a reliable grid connection, it normally still makes sense to pump water using solar power, however, the payback period will be slightly longer (2-6 years).

The amount of water you need depends on many factors. These include:

• The size of the farm
• The crops you are growing
• The irrigation system you use (drip irrigation is most efficient)
• The soil type
• The climate

Together with the solar water pumping company you select, you can probably make a good calculation. Make sure to already think about future expansion of the farm!

This very much depends on the amount of people (and animals) dependent on the pump. Generally speaking, you can calculate with the following numbers in case of a central water pump:

• 20 – 50 liters / day per person
• 30 – 150 liters / day per cow (depends very much on whether they are producing milk or not)
• 5 – 10 liters / day per goat or sheep