How to Size Solar Water Pump Systems

Sizing Solar Water Pump Systems – Step 1

Determine which pump is better, a submersible pump or surface pump. This is based on the nature of the water source. Submersible pumps are sometimes suitable for either deep or surface water sources. Surface pumps can draw water from only 20-25 ft (7-8 m) below ground level but can push it far uphill.

Sizing Solar Water Pump Systems – Step 2

Determine your daily water requirements for your application using the table below:

ConsumerDaily RequirementsDaily Requirements
Each person, for all purposes75 gallons285 liters
Each milking cow30-35 gallons113-133 liters
Each cow/calf pair20 gallons76 liters
Each horse, dry cow, or beef animal15-20 gallons57-76 liters
Each sheep2 gallons7.6 liters
Each hog4 gallons15.2 liters
Each 100 chickens4 gallons15.2 liters
Gallons per hour = Gallons per day divided by “peak sun hours per day.”
Gallons per minute = Gallons per hour divided by 60

Peak sun hours (also known as solar insolation) refer to the average equivalent hours of total sun energy received per day. It varies depending on the geographic location and season.

Calculation Example
Let’s say you need to get a solar water pumping system to water Fifty cow/calf pairs. Looking at the above table, we see that each pair requires 20 gallons per day. Multiply your daily requirements by the number of pairs to get a total daily of 1,000 gallons. Now, divide the 1,000 gallons by the number of peak sun hours, which in this example we’ll say is five sun peak hours, to get 200 gallons per hour required daily. Lastly, divide that number by 60 (minutes) to arrive at 3.33 gallons per minute.

This means you will need a solar water pumping system capable of pumping at least 3.33 gallons per minute to sustain the daily watering requirements. Due to variations in peak sun hours from summer to winter, it is best to use this amount as your absolute minimum. From this example, a 4 GPM (gallon per minute) system would yield extra water in the summer months and still meet the requirements in the winter months.

Sizing Solar Water Pump Systems – Step 3

The most critical question you need to answer is whether or not your water source will produce enough water to supply the application and pump system. You may determine you need 8 GPM, but if your water source only recovers at 3 GPM, you will be unable to sustain your daily water requirements. If the water source is a well or a stream and the flow rate or recovery rate is unknown, a pump test can be performed to calculate this rate.

Sizing Solar Water Pump Systems – Step 4

Determine other key measures crucial in accurately designing a solar water pumping system:
A. If the application is a well, measure the well depth. Total Depth (TD) = _______ ft
B. Water Levels: Distance from the casing top to the dynamic water level during pump testing = _______ ft
Dynamic Water Level = _______ft
Static Water Level = _______ft
Water Source Recovery Rate = _______ GPM
Surface Pump Applications: Suction Lift = _______ft, Pressure Lift = _______ft
The suction lift is the distance from the water surface to the pump inlet port for surface pump systems. The pressure lift from the pump outlet to the delivery point is required.
C. If the water delivery point is far from the water source, refer to the pipe sizing charts to determine which pipe size is required for the application flow rate. Also, determine the elevation difference to the total lift requirement.
D. What is the inside diameter of the well casing pipe? _______ inches

Sizing Solar Water Pump Systems – Step 5

Contact our professionals for Coulee Pump datasheets for the pump/controller combinations to locate which configuration will work best for your application. Please note that the listed depths are the depth limits for each configuration. If the pumping results are at the low end of your requirements, look to increase your solar panel configuration or visit the next rated pump for better performance.

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