Energy efficiency refers to using less energy to produce the same service or useful output. An engineer may define energy efficiency narrowly, for example with a focus on equipment output such as considering a car energy-efficient if it requires less energy to drive the exact same distance at exactly the same speed as another car. By contrast, an environmentalist or a politician may define an energy-efficient car more broadly including societal impacts, for example having a higher load factor when people carpool.
The difficulty in defining energy efficiency is relevant to its measurement. There is no definitive quantitative measurement of energy efficiency. We know how much energy has been consumed but we don’t know how much would have been consumed had we been more or less efficient. Instead, we must rely on a series of indicators to infer changes in energy efficiency. In its updated strategic plan for increasing philanthropy’s impact on the climate challenge, ClimateWorks Foundation (CWF) worked with Lawrence Berkeley National Laboratory (LBNL) to define a set of comprehensive indicators to track changes in energy efficiency progress, measure progress, and assess strategic opportunities.