Efficiency is one of the defining characteristics of sustainability. In the later chapters of this book, efficiency will be a key concept in the economic evaluation of technologies as sustainable or unsustainable. The efficiency of a technology is a measure of its output per unit of input. This calculation can also be derived as the rate of output production divided by the rate of input usage. Efficiency can therefore be measured only in relation to one input. When a technology has several inputs, each input will have its own efficiency measure.

This chapter addresses several important questions:

•  How do you measure the efficiency of a device?

•  What makes one device more efficient than another?

•  What is the ...

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