Energies 2019 , 12 , 247
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and international benchmarking as in e.g., study by Andersson et al. [18]. Data for rough calculations of SEC is sometimes publicly available in larger companies’ annual sustainability reports. Despite the convenience of using SEC, several challenges have been pointed out in the literature (Table 1). Some solutions have also been presented. For example, Phylipsen et al. [11] use ratios between the actual SEC and the sector-specific reference SEC—the energy efficiency index.
Table 1. Examples of difficulties that have been cited in some of the references using specific energy consumption (SEC). DC—Developing countries.
Type of Difficulty
Difficulties in Citations
Reference Page
“Tracking of energy efficiency improvements in pulp and paper manufacturing is difficult, because publicly available data on production, capacity and energy use are limited. Additionally, some countries do not report biomass use for the pulp and paper sector, which makes it difficult to get an accurate picture of the sector’s energy needs.” “Difficulties in finding relevant data are related to difficulties in comparing production processes and end products.” “One difficulty of finding a set of SECs for the best available techniques is the fact that process steps in the pulp and paper industry are usually integrated. Therefore it is difficult to attribute part of the total energy consumption to any of the products.” “The measurement of energy efficiency in terms of physical-thermodynamic indicators is not as straightforward as it first appears because of the so-called joint production or partitioning problem. This refers to the difficulty in allocating one energy input to several outputs in an industry. [...] The problem arises when the energy input ( Δ H) has to be allocated to the different outputs (tonnes) in order to generate the desired indicators.” “ . . . what constitutes a useful energy output. The definition of useful implicitly requires some assignment of human values in order to define what is considered to be a useful output.” “In general, availability of plant data from DCs is limited. [ . . . ] Literature data is scattered and problematic.” “Comparing energy efficiency between countries is not straightforward because of differences in economic structure. Also within a country, the economic structure can change over time.”
Availability of information
[3]
42
Availability of information
[8]
755
Complexity of integrated processes
[8]
749
Partitioning of products
[12]
381
Assumptions, definition of final output, e.g., sold products or all produced products? Availability and quality of information Variation over time and among countries
[12]
383
[19]
6663
[11]
665
Additionally, there are general aspects affecting the SEC. The age of equipment and the plant itself are some of the aspects that can affect SEC. For example, although newer equipment tends to be more energy-efficient compared to older equipment, it can take a few years to optimize the new equipment after installing it [20]. The location of the plant can also have an effect on SEC, i.e., environmental conditions affect heat demand [20]. Additionally, the size of the plant, for example the width of the paper machine [20] and the production rate ([20,21]), are also variables that affect SEC. Some of the challenges regarding SEC are also faced by other energy use related fields, e.g., when calculating energy returned on energy invested (EROI) (e.g., [22–27]). Regarding benchmarking, different levels of analysis require different amounts of data. Generally, the more detailed benchmarking is, the more data is required [28]. SEC is one of the methods used for energy benchmarking at multi-national level, national/regional level, site level and process level, where SEC has been used most frequently in benchmarking studies at process level according to the results presented by Andersson et al. [18]. Further, the current average SEC is the preferred indicator for information about energy efficiency at regional or country level, provided that adequate data is available (according to [19]). 3. Data and Methods This article was inspired by the authors’ own experiences of using SEC to research industrial energy efficiency and can, therefore, be said to be explorative in nature. Specifically, this article was inspired by experiences while studying SEC to research industrial energy efficiency and factors tending to affect the energy efficiency as well as by research addressing energy management and
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