Field Tests of a Wind-Electric Controller for Parallel Stock Water Pumping and Heating

Many of the improvements in wind-electric stock water pumping systems are attributable to advanced controller strategies and hardware that maximize performance over a range of wind speeds. The cost of the early and more complex controllers was of the order of one quarter of the whole system. Sophisticated yet inexpensive-programmable micro-controllers are now being introduced that enhance both performance and reliability. This study utilized a micro-programmable logic controller (PLC) to place a variable auxiliary load in the form of a stock water heater in parallel with the pump motor. This improves the system’s economic viability on the Northern High Plains by mitigating stock tank freezing to help extend the grazing season. For the variable auxiliary load, the PLC uses long period pulse width modulation to drive a 3-phase solid-state relay. This continuously variable load strategy was designed to both increase the power factor when the pump is operating, and to extract resistive heating power in wind regimes not suitable for operating the pump. This paper reports on the preliminary but encouraging field studies directed toward optimizing the low wind speed water heating performance of this multi-tasking controller when the pump motor is inoperable.