Solar Water Pumps for Wells, Irrigation and Stock Tanks

A solar water pump suits low-lift, modest-volume jobs: filling a stock tank, moving water from a shallow well, or feeding small drip irrigation. Use a submersible pump down a well and a surface pump to push water along a pipeline. For deep wells, choose a submersible displacement pump, and store water in a tank instead of buying batteries.

What a solar water pump does well

A solar pump runs straight from its panels, usually on direct current, and pumps whenever the sun is up. The National Center for Appropriate Technology (NCAT), a nonprofit that advises farmers and ranchers, says solar pumping is well suited to low-head, low-volume situations. “Head” is the height the water has to rise. Where wells are deep and volumes large, the pumps and panel arrays get specialized and costly.

NCAT also says DC pumps typically use one-third to one-half the power of AC pumps, which is why most solar systems use them. An AC pump needs an inverter, and NCAT puts inverter efficiency at about 93 percent at best, so the array has to be sized up to cover the loss.

Submersible or surface: matching the pump to the water source

Every pump is either submersible or surface, and either displacement or centrifugal. The table sums up where each kind fits, based on NCAT’s guide.

Most pressurized irrigation, such as sprinklers over a large lawn or field, needs far more power than solar panels can supply economically, according to NCAT. NCAT adds that helical rotor pumps can handle some particles in the water without damage.

How much water do you need?

Start with the daily total, because pump and panel size follow from it. NCAT says the size of the pump depends on how much water you need and how high and how far it has to travel, and the pump in turn sets the number of panels. Most water pumping systems need two to six panels.

For livestock, NDSU Extension says water needs vary with species, size, pregnancy, lactation, diet and temperature. Its tables put feeder lambs at 1.0 to 1.5 gallons per head per day, while its figures for cattle and horses run to several gallons a head and more, and every animal drinks more in hot weather. Plan for the hottest week of the year, not an average day.

Two ranches in NCAT’s guide give a sense of scale. One pumps from a 65-foot well with four 80-watt panels and a submersible piston pump, delivering up to 5.5 gallons per minute, enough for 100 cow and calf pairs. Another waters 36 pairs from a 10-foot well with two 64-watt panels and a diaphragm pump.

Tanks, float switches and backup for cloudy days

NCAT advises against batteries for most livestock systems, because they cut efficiency and add cost and upkeep. Its alternative is three to 10 days of water stored in tanks, and Mississippi State University Extension recommends a livestock tank that holds at least three days of average demand. A battery makes sense in three cases: the storage tank is not high enough to feed by gravity, there is too little storage and water is needed at night or in cloud, or water must keep flowing to stop it freezing.

Two small parts protect the system. A float switch turns the pump on and off as the stock tank fills, and low-water cutoff electrodes stop the pump if the well runs low. Both report to the pump controller, which Mississippi State calls the brain of the system. When a raised tank feeds troughs by gravity, check that it sits high enough, since NCAT notes some float valves need a minimum pressure to work.

Panels, kits and the rest of the setup

Place the array where it gets open sky for most of the day and keep it clean; see how to clean solar panels. For a pump far from any power line, read grid-tied vs off-grid solar for how stand-alone systems work. Kits that bundle a panel with a charge controller suit pumps that need a battery.

More solar gear for water, from solar pool covers to solar bird bath fountains, is in the pool and water section.