Defining ‘Efficiency’


Like “power” and “energy”, efficiency is a term that you’ll hear used often, but in a variety of contexts. So one use of the term, isn’t necessarily the same as another.

I’ve also heard it used as a proxy for something else, most commonly through phrases such as “wind power is inefficient; it only works 30% of the time” – where what the person is really talking about is capacity factor. (We’ll connect these two in the next lesson).

While in any context high efficiency is a good thing, used in different contexts it can be expressed in ways that might not be directly comparable. So it’s important to be clear about what we mean by it and consistent in how we use the term.

The following video does just that, distinguishing between efficiency at the point of power generation from efficiency at the point of consumption. When considering the former, it introduces another important term, one of great economic significance for electricity generating sources which use fuel: “primary energy“.

Having dealt with some definitions in this lesson, we’ll then focus in on its relevance to power generation in the next one. We’ll also revisit some of the impacts of efficiency on various economic issues such as land use and project costs in later lessons.