Agro-Technology, Simple Efficiency Concepts in Irrigation

By Tony Lampard

Motors use three-fifths of the world’s electricity.  Their largest use, at least a fifth of their total output, is pumping.  A typical pumping system has so many compounding losses (pipe, throttle, pump, drive-train, motor, electricity transmission and distribution and the power plant itself) that a hundred units of fossil fuel at a typical power station will deliver only ten units of flow out of the pipe.

Using the paradigm shift introduced by renowned efficiency expert engineer Lock Lee in water reticulation designs and other efficiency concepts, a design review suggests the conventional Centre Pivot Irrigation systems are not well designed to optimize efficiency.    Most of the conventional pumping systems are also inefficient.   This is not to suggest the design engineers are incompetent; Lock Lee’s approach, although extremely simple, is a radical shift from the conventional approach to designing pumping systems.   

Before we move on to the Lock Lee principle there are two efficiency concepts worth mentioning: –

  1. Rail/road has a rule of thumb 12fold reduction in energy demand.   The tractor profile wheels typically found in centre pivots (as shown) are perhaps an even higher energy load than a wheel on tar; so, replacing these with rail wheels on tracks or gantries (overhead rail) may be worth considering. 
  2. Many years ago, American farmers developed a very simple system of electrodes in a gypsum plug for accurately determining the moisture level in the soil to optimise the irrigation where the conductivity could be translated into water sink.   With sophisticated SCADA systems that have developed more recently dosing the exact amount of water by reading sensors buried in the soil in front of the carriage and automatically adjusting water feed rates with variable frequency drives (vfd) should be reasonably practical. 

Big, Straight, Short.  Use big pipes and small pumps.   Friction falls as nearly the 5th power of the pipe diameter, so making the pipes 50% fatter reduces the friction by 86%.   Compounding losses of bends, valves etc. should be eliminated as much as possible.   This would need to be evaluated firstly in a detailed design review followed by pilot trials, but multiple water pipes fed by vfd (individually controlled to feed the water demand from each sink) is a concept that would seem to be the most appropriate. 

Additionally.  A typical conventional pumping system has so many compounding losses (pipe, throttle, pump, drive-train, motor, electricity transmission and distribution and power plant) that a hundred units of fossil fuel at a typical power station will deliver only ten units of flow out of the pipe.

Featured image by Süleyman Şahan from Pexels

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