Energy is measured in many units, even within single measurement systems, and hence it is not surprising that, particularly for non-quantitative types, people often get confused when trying to understand the basics of energy efficiency and energy management. In my home country of South Africa we employ the metric system, and hence when we measure the energy content of fuels, we typically do so using the Joule, and its multiples, such as Kilojoules, Megajoules etc. We don’t use this unit of energy for everything though. Our most commonly used unit of electrical energy is the kilowatt-hour, but since all units of energy are interchangeable, electrical energy could just as easily be expressed in Joules. What I’d like to explain in this post is why I find the kilowatt-hour to be such a neat unit of energy.
When we see the units of energy consumption expressed as kWh on our electricity bills, few of us pause to think about the fact that the clues for reducing our bills lie within this unit and what it represents. From basic physics, Energy = Work, and Work = Power x Time. The kWh is a unit of energy that makes that simple equation explicit. So what’s so great about that you ask? Well, this unit of energy lights the path to energy conservation in the most simple fashion possible. It shows that there are only two strategies available to reduce the amount of energy consumed. The first is to reduce the kW (or power) used by a process, without compromising its performance. Here I refer to the average power required over a given period. This is the preserve of the high-efficiency motor, the lighting solutions that use less power to produce the same lumen output, the variable speed drive compressor and the like. It also includes energy efficiency strategies such as heat recovery, which are becoming a vitally important (and often very cost-effective) alternative to reducing input power. The second energy conservation strategy highlighted by the kWh is that of reducing the time for which an energy-consuming device operates. This is about switching off the lights and air conditioners when not required, employing daylight harvesting to reduce the need for electrically-powered lighting during daylight hours, eliminating unnecessary idling of machines, improving plant uptime, removing process bottlenecks and other measures designed to reduce operating time.
In summary, if an approach purports to be capable of reducing your energy consumption, ask yourself: does it reduce kilowatts, reduce hours or even better, do both? The humble kilowatt-hour gives us energy-saving clues that anyone can understand. And for those who say this is self-evident, ask yourself if you are truly employing these simple strategies in your quest to reduce energy consumption and emissions.
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