Speaking about Energy Efficiency with everybody, you may have noticed that almost everyone has her own definition of the topic. For some of us, Renewable Energies (REn) are part of Energy Efficiency such as solar panels or green district heating. For others, only actions on active systems or building’s envelops are eligible to this so-called appellation.
What’s the truth amongst all these potential definitions? Is there really a unique definition? Does it make sense to think in terms of an overall spectrum? What if there were several relevant definitions of Energy Efficiency, each one suitable for a given context?