Solar Water Pumping in Agriculture

Solar energy has many potential uses in agriculture but water pumping is one of the most efficient. Many farmers now use low capacity water pumps for crop irrigation, and there are many prime grazing properties that now have reliable water by using  solar-powered systems.

Cattle operations have learned that with today’s highly efficient, low maintenance DC pumps, you can drill a well, install a submerged well pump and quickly have a totally reliable watering source. In the old days, ranchers used windmills to water stock. This age-old technology still works, but features many moving parts and is considered maintenance intensive. In recent years, farmers or ranchers are going with low maintenance solar systems.

Other cattle farmers install low volume pumps to pump water from streams into water tanks to keep stock out of streams, protecting fragile stream banks and preserving overall water quality in the stream.

In a direct tie water pumping system, there are only two main components: The solar array that produces DC electricity, and the solar pump that runs off of the DC power. When sufficient sunlight is hitting the array, water is pumped. During low light periods, and at night, the pump is idle.

One question that always comes up is the viability of adding batteries to allow pumping during low-light or at night. In most cases we recommend against batteries. Some of the reasons follow:

• Batteries lower the overall efficiency as compared to direct connect since a certain amount of power is required to charge and maintain batteries. This lowers the power available to the pump which, in turn, lowers pump production.
• Batteries add to the cost to the system as it costs money for the batteries themselves and you also need as charge controller, battery enclosure, and additional wiring.
• Batteries require care and maintenance that isn't always convenient in remote properties. If batteries are undercharged and subjected to freezing temperatures they could be damaged. If batteries are overcharged and subjected to high temperatures their lifetime will be shortened dramatically.

In most cases we recommend a direct connect solar pumping system that is designed to give you all the water you need during a typical day without needing batteries. The key is to store water in a properly sized tank. For a livestock watering, we recommend that you install a storage tank that can hold a minimum of 3 days of water requirement.

The second most common question is how to stop a pump when the storage tank is full. It is relatively easy to use a float switch that trips a controller that tells your pump to stop and start. (Think bathroom commode tank). Another, less elegant approach is to simply use an overflow pipe (if the terrain allows) and keep pumping as long as adequate power is being sent to the pump.