Williams Eric, Warr Benjamin, Ayres Robert U
Department of Civil and Environmental Engineering, School of Sustainability, Arizona State University, Tempe, Arizona, USA.
Environ Sci Technol. 2008 Jul 1;42(13):4964-70. doi: 10.1021/es0716756.
This analysis characterizes century-scale trends in exergy efficiency in Japan. Exergy efficiency captures the degree to which energy inputs (such as coal) are converted into useful work (such as electricity or power to move a vehicle). This approach enables the estimation of net efficiencies which aggregate different technologies. Sectors specifically analyzed are electricity generation, transport, steel production, and residential space heating. One result is that the aggregate exergy efficiency of the Japanese economy declined slightly over the last half of the 20th century, reaching a high of around 38% in the late 1970s and falling to around 33% by 1998. The explanation for this is that while individual technologies improved dramatically over the century, less exergy-efficient ones were progressively adopted, yielding a net stabilization or decline. In the electricity sector, for instance, adoption of hydropower was followed by fossil-fired plants and then by nuclear power, each technology being successively less efficient from an exergy perspective. The underlying dynamic of this trend is analogous to declining ore grades in the mining sector. Increasing demand for exergy services requires expended utilization of resources from which it is more difficult to extract utility (e.g., falling water versus coal). We term this phenomenon efficiency dilution.
本分析描述了日本能值效率的百年尺度趋势。能值效率反映了能源输入（如煤炭）转化为有用功（如电力或驱动车辆的动力）的程度。这种方法能够估算综合不同技术的净效率。具体分析的部门包括发电、运输、钢铁生产和住宅空间供暖。一个结果是，日本经济的总能值效率在20世纪后半叶略有下降，在20世纪70年代末达到约38%的高位，到1998年降至约33%。对此的解释是，虽然各技术在整个世纪有显著改进，但能效较低的技术被逐渐采用，导致净稳定或下降。例如，在电力部门，先是采用了水力发电，然后是化石燃料发电厂，再是核能发电，从能值角度来看，每种技术的效率都依次降低。这一趋势的潜在动态类似于采矿业中矿石品位的下降。对能值服务需求的增加需要消耗更难提取效用的资源（例如，落差小的水流与煤炭）。我们将这种现象称为效率稀释。
