Solar Water Pumping System – SS2 Solar Photovoltaic Installation & Maintenance Lesson Note (Second Term)

A solar water pump uses energy from the sun to lift water from a borehole or stream and push it to where it is needed. A basic solar pumping system often has no batteries. The pump works while the sun is out, and the water is stored in a high tank for later use.

Behavioural objectives

By the end of the lesson, students should be able to:

• explain what a solar water pump is and why many systems do not use batteries;
• name the four main parts of a solar water pumping system and state the job of each;
• explain Total Dynamic Head (TDH) and work out the vertical lift in a simple example;
• describe three uses of solar pumping in agriculture;
• list three maintenance and safety practices for a solar pump.

What is a solar water pump?

In many parts of Nigeria, farmers struggle to get water to their crops. Using a petrol generator is expensive because fuel prices keep rising. A solar water pump uses the sun’s energy to lift water from a borehole or a stream and push it to where it is needed.

A standard solar system uses batteries to store energy. In a basic solar pumping system, we often do not use batteries. Instead, we pump as much water as possible while the sun is out and store the water in a high tank.

Batteries are skipped because water tanks are cheaper and last longer than chemical batteries.

What are the main parts of the system?

To design a system, you need to know these four parts:

1. The solar array: These are the panels that catch the sun.
2. The controller (the brain): This sits between the panels and the pump. It makes sure the pump does not “struggle” when the sun is weak, such as in the early morning.
3. The pump: This is the motor that moves the water.
   • Submersible pump: Stays inside the borehole, underwater.
   • Surface pump: Sits on the ground near a river or well.
4. The storage tank: This acts like your “battery”. It holds the water for use at night or on cloudy days.

How do you design the system?

When designing, we do not just guess. We need to measure the Total Dynamic Head (TDH). This means “How hard does the pump have to push?”

To find the head, you add two things:

• Vertical lift: The distance from the water level in the ground to the top of the tank.
• Friction loss: The “resistance” the water feels as it rubs against the inside of the pipes. Long, thin pipes make the pump work harder.

Simple calculation step

If your borehole is 30 metres deep and your tank is 5 metres high, your vertical lift is 35 metres. You must choose a pump that is strong enough to “push” water that high, and you must also allow for friction loss in the pipes.

How is solar pumping used in agriculture?

In SS2 Agricultural Science, we learn about irrigation. Solar pumping makes irrigation automatic.

• Drip irrigation: The solar pump fills a tank, and the tank slowly “drips” water directly onto the roots of the plants. This saves water and energy.
• Livestock watering: Cattle and poultry need a constant supply of fresh water. Solar pumps keep the troughs full without the farmer having to be there to turn on a generator.
• Year-round farming: In the North or during the dry season, farmers can grow crops like tomatoes and onions even when there is no rain, simply by “harvesting” the sun.

How do you maintain a solar pump safely?

Solar pumps are “set and forget”, but they still need a little care to last 20 years.

1. Clean the panels: Dust and bird droppings act like a “blanket” over the panels. A quick wipe with water once a week can increase water flow by 20%.
2. Dry run protection: If the borehole goes dry, the pump can burn out. A good controller has a sensor that turns the pump off if there is no water.
3. The “vermin” problem: In a farm environment, rats love to chew on wires. All cables should be hidden in metal or thick plastic pipes (conduits).

Design checklist for the designer

• First, find out how much water the farm needs per day (in litres).
• Measure the depth of the water (the head).
• Size your panels to provide enough power even on “hazy” days.

Evaluation

1. Why do many basic solar pumping systems not use batteries?
2. Name the four main parts of a solar water pumping system.
3. State the difference between a submersible pump and a surface pump.
4. What two things are added to find the Total Dynamic Head?
5. Why is dry run protection important?

Assignment

1. Describe how a solar pump can be used for drip irrigation on a farm.
2. List the three maintenance and safety practices for a solar pump and say why each is needed.