While many people are familiar with the concept of first law efficiency, the notion of second law efficiency, suggested by Nakicenovic50 as an interesting, often more adequate definition of EE, is rather unknown. Here, we explain the concept of second law or entropy efficiency with a stylized example. The comparison of this concept to the notion of first law or energetic efficiency indicates that estimates about current efficiency improvement potentials depend heavily upon the efficiency concept employed.
Moreover, we explain why prevailing energy efficiencies are grossly overestimated when measured in terms of first law efficiencies. High figures that are commonly reported for the first law efficiencies of current technologies lead to the impression that efficiency improvement potentials are almost exhausted. These high figures represent negative signals and, therefore, serious barriers on the route to a sustainable economic development via the accomplishment of high efficiency standards.
In fact, the world-wide average of the second law efficiency of electricity consumption, for example, is estimated by Gilli et al. to be lower than 6 per cent.51 Thus, efficiency improvements appear to be promising52 and might be an important part of a broader strategy to restructure energy systems with respect to a sustainable economic development.
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