Energies 2019 , 12 , 247
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As energy management is an important means by which to improve energy efficiency, the use of specific energy consumption (SEC) to identify potential improvements in energy efficiency is seen as an important instrument of energy management. Frequently, in both literature and international standards, SEC is used as an energy performance indicator to evaluate or measure the performance of energy efficiency. For example, Peng et al. [5] used SEC to evaluate changes in energy efficiency in the Chinese pulp and paper industry (PPI) over the period between 1985 and 2010, and Lawrence et al. [6] used SEC to investigate the possible effects of firm characteristics on energy efficiency in the PPI in Sweden. Furthermore, Fleiter et al. [7] used SEC to study energy efficiency in the German PPI and to assess the potential for energy savings, while Farla et al. [8] used SEC to portray changes in energy efficiency in the PPI. SEC is also used for benchmarking, although some concerns about SEC usage in benchmarking have been raised. Although the European standard on energy efficiency benchmarking (16231:2012) [9] provides the methodology needed for collecting and analysing energy data for energy efficiency benchmarking, the standard barely problematizes the challenges involved in using SEC for this purpose. For instance, Farla et al. [8] pointed out that “using the SECs from one country in a cross-country analysis may lead to distortions if the SECs for some of the products are relatively high (due to inefficient processes)” ([8], p. 748). Another example is found in Laurijssen et al. [10], where the authors used SEC to benchmark energy use at process unit level in the paper industry. Additionally, SEC can be used indirectly as in e.g., a study by Phylipsen et al. [11], where SEC was used to calculate an energy efficiency index (EEI), i.e., the ratio between the actual SEC and the reference SEC to explore the impact when the best available technologies (BATs) are used. Despite the widespread use of SEC as an indicator for energy efficiency, critical scientific papers on SEC seem—in the authors’ opinion—to be almost lacking. Three exceptions are an in-depth review on energy efficiency including SEC written by Patterson [12] and methodologies for international comparisons of energy efficiency by Phylipsen et al. [13], both published more than two decades ago, and a recent study addressing industrial energy benchmarking in the PPI by Rogers et al. [14]. In summary, although several research studies have adopted SEC as an indicator for the progress of improved energy efficiency, publications on critical assessments when using SEC are scarce. But at the same time, the international standard on energy management systems (ISO 50006:2017) [15] provides general principles and guidance on how a company can establish energy performance indicators and energy baselines for measuring its energy performance. Given the increasing importance of monitoring improved industrial energy efficiency and the rising popularity of SEC as an energy key performance indicator (e-KPI), an in-depth analysis and problematization of the pros and cons of using SEC would appear to be needed. The aim of this article is to critically analyse SEC in relation to industrial energy efficiency. 2. Background The variable characterizing energy use per produced product and expressed as a ratio of thermodynamic units per physical unit is often referred to in literature as specific energy consumption (e.g., [8,12,16]). The meaning of SEC is to portray how much energy is used for producing a unit of product. SEC is perhaps used due its convenience, i.e., the amount of energy can be directly reported per amount of product. Generally, SEC is calculated by dividing the amount of energy used with the amount of products. However, both, products and energy carriers are often chosen arbitrarily depending on the intended purpose of using SEC. For example, SEC can be calculated for the total amount of products or for individual products from the product mix. Similarly, SEC can be calculated for the total primary energy used or for specific energy carriers, e.g., how much electricity and heat separately has been used for producing a unit of product. SEC in international standards, such as e.g., ISO 50006:2017 [17], is recommended for being used as an energy performance indicator, since SEC allows measurement of the energy performance and thus the performance of benchmarking. Benchmarking of energy use in industry is the process of comparing and evaluating energy performance, where SEC can be used for benchmarking at various levels: process, site, national
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