A NEEA irrigation market characterization study estimates that roughly half of the wells used for irrigation on farms 100 acres or larger had pump heights (high lifts) of at least 100 feet (Navigant, 2013 Pg Figure 7).  NEEA further estimated that, in the three-state region, about 39% of all irrigation systems had a total dynamic head of 300 feet or more (Navigant, 2013 Pg Table 6). 

Some irrigation systems have high static head.  This is usually due to pumping from deeper wells but it can also from pumping up a steep hill.  Turbine pumps (also called “line shaft pumps”) are used in high head applications where the bulk of the energy expended is necessary to lift the water to a higher elevation.  Reducing the flow rate of these systems with variable speed drives (VSDs) reduces input power, but not the energy needed per volume of water pumped. 

In addition to the lack of improvement in energy intensity, VSDs have not been widely used in high static lift applications because on/off control can be very efficient and throttle valve flow control can be used with low energy losses. Also VSDs are much more expensive than on/off controls, although growers may prefer the convenience of VSDs.  Furthermore VSD cost is based on motor horsepower, which is greater for high-head applications so the cost-effectiveness of this application is further reduced. 

Finally, in a high static lift system, a small change in pump speed produces a large change in flow rate and the system curve can pass through many efficiency contour lines resulting in a decrease in pump efficiency (NRCS, 2010).  Energy savings are extremely application-specific and increase when pump curves are steeper and static lifts are small.  Therefore this technology is unlikely be appropriate for deemed measures. 

The irrigation application where energy savings can be achieved is where head varies due to either pumping from a well that draws down significantly over the course of the growing season or to a variety of areas that vary in elevation, as may be more typical of orchards in mountainous terrain.  In this case, the VSD can adjust the speed of the pump to deliver the pressure needed rather than the worst case scenario pressure (the well at the end of the season or the fields with highest elevation).  This application is described in ET #626, “Optimization of Variable-Speed Irrigation Pumping.”