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Net production efficiency (NPE) is the efficiency at which organisms assimilate energy into biomass for the next trophic level. Due to low metabolic rates and less energy spent on thermoregulatory processes, the NPE of ectotherms (cold-blooded animals) is 10 times higher than endotherms (warm-blooded animals).
Carnot Cycle and Efficiency01:26

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The Second Law of Thermodynamics asserts that it's impossible for any heat engine to achieve 100% efficiency. While contemplating the maximum possible efficiency, Nicolas Sadi Carnot conceptualized an ideal heat engine. This engine gets its energy from a high-temperature reservoir. It then performs some work and releases the remaining energy into a low-temperature reservoir.The Carnot cycle, named after Sadi Carnot, is fully reversible. The cycle consists of four distinct stages. In the first...
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Efficiency dilution: long-term exergy conversion trends in Japan.

Eric Williams1, Benjamin Warr, Robert U Ayres

  • 1Department of Civil and Environmental Engineering, School of Sustainability, Arizona State University, Tempe, Arizona, USA. ericwilliams@asu.edu

Environmental Science & Technology
|August 6, 2008
PubMed
Summary

Japan

Area of Science:

  • Thermodynamics
  • Energy Systems Analysis
  • Economic History

Background:

  • Exergy efficiency quantifies energy conversion to useful work.
  • Aggregate efficiency considers diverse technologies within economic sectors.

Purpose of the Study:

  • To analyze century-scale exergy efficiency trends in Japan.
  • To investigate the drivers of aggregate efficiency changes over time.

Main Methods:

  • Analysis of century-scale data on exergy efficiency.
  • Sector-specific examination of electricity generation, transport, steel production, and residential heating.
  • Estimation of net efficiencies aggregating different technologies.

Main Results:

  • Aggregate exergy efficiency in Japan slightly declined from ~38% (1970s) to ~33% (1998).

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  • Individual technology improvements were offset by the adoption of less exergy-efficient systems.
  • Phenomenon termed 'efficiency dilution' observed, analogous to declining ore grades.

    • Conclusions:

    • Despite technological advancements, overall exergy efficiency decreased due to shifts towards less efficient energy conversion pathways.
    • Increasing demand for energy services necessitates utilizing lower-quality resources, impacting net efficiency.
    • Understanding efficiency dilution is crucial for sustainable energy policy and resource management.