Is Embodied Energy a Better Starting Point for Solving Energy Security Issues?—Based on an Overview of Embodied Energy-Related Research

Abstract

Embodied energy is termed as the total (direct and indirect) energy required to produce economic or environmental goods and services. It is different from the direct energy measurement of energy consumption. Due to the importance of energy security, it has attracted increasing attention. In order to explore whether and to what extent embodied energy can provide a more innovative approach and competitive perspective to energy security issues, 2608 relevant pieces of literature from the Web of Science core collection are analyzed in this study. Results show that embodied energy has been taken seriously. Moreover, by reviewing the typical literature, this paper first summarizes the embodied energy calculation methods and models, then investigates how embodied energy provides a new perspective to energy issues, and lastly analyzes how to show value in energy security issues in its application of guiding policy-making and energy security studies. In summary, there is no doubt that embodied energy can provide a more integrated perspective on energy consumption and demand and provide a more scientific reference for policy-making to enhance energy security. However, because of data and application scope limitations, establishing a comprehensive energy security research and application system with embodied energy measurements needs hard work.

1. Introduction

Human survival and development cannot exist without energy. Energy is the lifeblood of economic development and modern society. An appropriate approach to addressing energy security has become a part of the development strategies of various countries, regions, as well as the whole world [1,2]. It also occupies an essential position in the policy agenda of many nations. In contemporary economic developments, energy tends to become a significant political, social, and economic objective [3]. In the meantime, global economic growth means that the demand for energy is increasing year by year. According to The World Energy Outlook 2018, based on current and scheduled policies, energy demand is expected to grow by more than 25% by 2040, requiring an annual investment of $2 trillion in new energy supplies [4]. However, the increase in proven energy reserves is far behind the rise in energy consumption. According to the BP Statistical Review of World Energy in 2018, the remaining recoverable reserves of coal in the world were 1,035,012 million tons by the end of 2017, with a reserve–production ratio of 134, but only 79 in the Asia-Pacific region, and the reserves–production ratios of natural gas and oil were only 54.1 and 52.5, respectively [5]. Besides, global climate change and pollution caused by energy consumption also need to be considered by energy policymakers [6,7]. Additionally, because of the unbalanced distribution of resources, the energy security of a country is also affected by its import and export target areas. For example, in 2017, China’s dependence on foreign oil reached 67% [8]. Therefore, it is a serious challenge for all countries to ensure energy supply and demand balance through effective energy management, and then to achieve sustainable development of the economy and environment, especially for large energy-consuming countries like China, the United States, and the United Kingdom. In order to ensure the long-term stability of energy supply and demand, improve energy efficiency, and reduce environmental impact, it is necessary to formulate effective energy security policies. To this end, many indicators such as energy intensity, net–import dependency, and energy per capita for measuring energy (primary) security were proposed in many articles, and many scholars and practitioners use these indicators to evaluate the safety status of industries or regions [9,10,11,12,13]. However, these indicators are based on direct energy use, which cannot fully describe energy consumption. Therefore, integrating indirect energy in the energy measurement system may provide a new perspective for understanding regional energy security issues and ultimately lead to a more intelligent discussion of energy security issues [2]. As early as the 1980s, Costanza [14] put forward that a critical aspect of energy analysis is to determine the total energy demanded to produce economic or environmental products and services. This total energy is called embodied energy. Compared with the analysis based on direct energy supply and demand, embodied energy can provide a more comprehensive perspective on economic and social energy-related issues, which may help to provide an empirical reference in the ecological and economic system [14,15]. At present, scholars have made many attempts to apply embodied energy to analyze energy issues in the industry or regional and international trade, such as evaluating energy policies for guiding policy-making. For example, through the embodied energy analysis in the import and export trade of the UK, Tang et al. concluded that the problem of energy security in the UK is more serious than conventional understanding [16]. By studying the role of embodied energy in the European manufacturing industry, Popescu et al. [3] found that the burden of carbon tax within Europe on domestic countries and industries is unequal. Embodied energy can incorporate indirect energy consumption into conventional energy security indicators and can also change perceptions of regional energy security performance and performance compared with other regions [2]. However, although embodied energy is widely used, a comprehensive review of how embodied energy is used in different areas such as in measuring energy consumption or flow paths in industrial or regional economic systems is lacking.

Therefore, the aim of this paper is to form a comprehensive understanding of embodied energy and investigate its application, and especially to explore whether it can provide a more innovative and competitive perspective on the research of energy security issues and depict its value. This paper illustrates the development of related research and reviews some typical research to summarize and identify how embodied energy measurement benefits energy issues, and especially how embodied energy can benefit energy security enhancement. In particular, this paper offers the following contributions:

(1)

A comprehensive understanding of embodied energy and development of relevant research;

(2)

An analysis of why and how embodied energy can benefit energy security issues;

(3)

Future improvement and research directions.

To do so, we have organized the paper as follows. Section 2 provides a historical and overall understanding of related research by elaborating on the definition of embodied energy and its characteristics and presenting development trends, research fields, and research trends of related research on it. Section 3 summarizes the embodied energy calculation methods and models, how embodied energy provides a new perspective to energy issues, and how to show its worth in energy security issues through guiding policy-making and energy security studies. Section 4 highlights some key insights for the application of embodied energy in energy security issues and raises some questions which cannot be completely answered here. Section 5 concludes the paper.

2. Background and Development

2.1. Definition and Characteristics of Embodied Energy

2.1.1. Definition of Embodied Energy

The definition of embodied energy is not controversial. It is derived from systems ecology [14,17], and its formal appearance in public was proposed by the International Federation of Advanced Research Institutions (IFIAS) in 1974 at a conference, which was being used for measuring the total energy required for the production of economic or environmental goods and services. It includes the energy consumed directly and indirectly in every stage of the process. In 1980, embodied energy appeared in an academic paper for the first time. Costanza [14] responded to some scholars’ queries about embodied energy and demonstrated how to calculate embodied energy in the economic system through the input–output method in his article “Embodied Energy and Economic Valuation” in 1980.

Specifically, in the research on energy issues in trade, embodied energy is the direct and indirect energy consumed in import and export goods and services in international trade, the direct and indirect energy consumed in the transfer of products and services from one region to another, and the direct and indirect energy consumed in the flow of products and services between industries or sectors [17,18,19,20,21,22]. Furthermore, in the relative micro-field, embodied energy refers to the energy consumed by all other products and services used in the manufacturing, maintenance, and processing of products. For example, in the related research of building and construction engineering, embodied energy refers to the energy embedded in all products and services used by a building from its design, initial construction, maintenance and replacement to its final demolition, which represents the energy consumed in the whole life cycle of the building [23,24]. Moreover, it is different from operation energy, and a concept can only reflect direct energy consumed in the construction phase.

In addition, based on embodied energy, to understand energy consumption and its environmental impact more deeply, concepts such as embodied coal, embodied oil, embodied solar energy, and embodied nuclear energy are extended from embodied energy. Like the definition of embodied energy, they represent a specific type of energy consumed directly and indirectly in products or services [25,26,27,28]. Moreover, the appearance of embodied CO2 and embodied emission can realize the linkage between energy consumption and environment issues [29,30].

2.1.2. Characteristics of Embodied Energy

Comprehensiveness

Compared with the traditional direct energy consumption measurement, the apparent advantage of embodied energy is that it calculates not only the direct energy consumption but also the indirect energy consumption. It calculates not only the energy consumption of a particular stage but also the energy consumption of the whole life cycle. Embodied energy analysis can integrate history and off-site energy consumption related to on-site production, which can provide a more systematic view of energy demand. Additionally, it can give us a more comprehensive perspective on evaluating all the energy demand for the development of a product or a country. [31,32].

Flowability

Because of the transaction characteristics of products and services, their transfer in different subjects makes embodied energy have the characteristics of flowability [33]. Especially in related research on energy issues in trade, the import and export of products and services between different regions, through embodied energy, can help explore the energy flow path and amount embedded in these trades; the flow of goods and services is the flow of energy.

Separability

In the previous discussion of the definition of embodied energy, it was stated that embodied energy is a comprehensive concept of energy. According to this, there are different types of energy, like coal, fossil oil, nature gas, hydro-energy, nuclear energy, and wind. Embodied energy can also be divided into different categories like embodied fossil oil, embodied coal, and embodied water. At present, more research is focused on the resources which occupy a relatively large proportion of the total energy consumption, such as embodied coal [25], embodied oil [26], and embodied water energy [34].

Scalability

The scalability of embodied energy is mainly reflected in two levels. First, it can extend from measuring all the energy consumed by a single product or service to measuring the energy consumption of the whole supply chain from upstream to downstream [35]. Second, in order to better reflect the impact of energy consumption on the environment, it can be gradually extended to the research field of emissions, and the terms “embodied carbon” [36,37], “embodied emissions”, and “embodied CO2” the authors in [38,39,40,41] have been using to measure the carbon dioxide emitted by a product or service in the whole production process.

2.2. Development of Relevant Embodied Energy Studies

2.2.1. Information on Relevant Embodied Energy Literature

Literature Selection Criteria and Procedure

The dataset of this study was built based on the search results from the Web of Science core collection. The Web of Science database is the most widely used for scientific literature, and it contains more than 6000 scientific and technological journals, more than 1700 social sciences journals, and more than 1100 art and humanities journals [42,43]. Moreover, it provides a statistical analysis of the search results and supports various retrieval methods such as terms, keywords, journals, and titles. In consideration of that, this study aimed to explore whether embodied energy could benefit energy security issues based on a comprehensive understanding of relevant embodied energy research; we first used “embodied energy” as a search term and found 4438 documents published in the journal up to 24 April 2019. Then, we filtered the initial dataset by using the following rules. First, we divided the dataset according to the type of literature; peer-reviewed journal articles, proceedings, and reviews were retained, while other types like abstracts, letters, case reports, and editorials were excluded. Second, we based our selection on research direction; we excluded those articles in totally irrelevant fields like PSYCHOLOGY, CELL BIOLOGY, SPORT SCIENCES, MICROBIOLOGY, ZOOLOG and others. Lastly, we excluded totally unrelated literature by skimming through the titles and abstracts. Then, we finally got 2608 documents for further analysis.

Annual Volume Analysis

Figure 1 is about the number of papers published in the past years. Research on embodied energy exhibited an ascending trend. In addition, during the development phase, the research was discrete before 1991, and the ascending trend became stable from 1991. This is due to the energy crisis caused by the Persian Gulf War in 1990, when many countries started to pay more attention to energy issues. Moreover, according to Price’s theory of the growth stage of scientific and technological literature, embodied energy-related research was in the embryonic stage before 1995. Then, it entered the stage of exponential growth in 1996, and this stage continued until 2015. After 2015, it showed a linear growth trend. In conclusion, although there was a slight decrease in 2018, the relevant studies of embodied energy are still in the stage of rapid development. Furthermore, it needs to be noted that the data are based on the search results of April, so the data of 2019 cannot reflect the number of papers throughout the year, but we believe more related articles would emerge until the end of the year.

Journal Distribution

Table 1. Journals with the most embodied energy publications.

Journals	Publications	Research Categories
Journal of Cleaner Production	211	Science & Technology—Other Topics; Engineering; Environmental Sciences & Ecology
Energy and Buildings	200	Construction & Building Technology; Energy & Fuels; Engineering
Energy Policy	118	Business & Economics; Energy & Fuels; Environmental Sciences & Ecology
Applied Energy	113	Energy & Fuels; Engineering
Building and Environment	95	Construction & Building Technology; Engineering
Renewable Sustainable Energy Reviews	87	Science & Technology—Other Topics Energy & Fuels
Environmental Science Technology	52	Engineering; Environmental Sciences & Ecology
Journal of Industrial Ecology	43	Science & Technology—Other Topics; Engineering; Environmental Sciences & Ecology
Resources Conservation and Recycling	41	Engineering; Environmental Sciences & Ecology
Building Research and Information	36	Construction & Building Technology

shows the top 10 journals with the most embodied energy publications. Among them, the Journal of Cleaner Production and Energy and Buildings rank as the champion and runner-up with 211 documents and 200 documents, respectively.

Moreover, these journals all belong to district 1 of JCR, which illustrates the importance of embodied energy-related research. Furthermore, based on the research area of these journals, it can be seen that the related research of embodied energy may be distributed in fields like Science and Technology—Other Topics, Engineering, Environmental Sciences and Ecology, Construction and Building Technology, and Energy and Fuels.

2.2.2. Research Field and Trend Analysis

Considering that this study aimed to explore the value of embodied energy on economic and environmental issues, and especially on energy security issues, this paper carried out a scientometric analysis by CitespaceV. Citespace is a java application for scientific literature analysis which was developed by Dr. Chen Chaomei from the School of Information Science and Technology, Redsell University and WISE Laboratory, jointly. Based on the algorithm and time, Citespace can identify the research frontier terminology in a specific knowledge field [44]. Specifically, this study used CiteSpace to conduct a co-occurrence analysis of terms and keywords.

Citespace’s co-occurrence analysis of keywords and terminology is an analysis of the keywords provided by authors in the dataset. Cluster analysis uses keywords with distinct characteristics such as the clustering object, so as to find popular words that have existed in the research field for many years, and which can depict the distribution of research fields. Figure 2 shows the largest network clustering map for the co-occurrence of keywords in embodied energy-related literature. The nodes represent the terms in the bibliography, the relationship between the nodes represents the co-occurrence relationship between them, and the label with “#” is the name of the term and keyword cluster. In Figure 5, the number of nodes is 226, the number of edges is 1780, the network density is 0.07, and the maximum network clustering spectrum accounts for 93% of the overall network, which is significantly representative. The module value (Modularity Q) is 0.3578, and the mean contour value (Mean Silhouette) is 0.5616, which means the divided cluster structure is obvious, and the clustering result is credible. As can be seen from the figure, the important and popular areas of embodied energy research are mainly distributed in areas of buildings, input–output analysis, ecological footprint accounting, and regional consumption activities.

In addition, in order to further understand the research focus of embodied energy, this paper exported the results to Excel and organized them.

Table 2. High-frequency keywords for embodied energy related research (Top 50).

No.	Keyword	Freq	No.	Keyword	Freq
1	embodied energy	761	26	climate change	104
2	life cycle assessment	454	27	carbon footprint	100
3	energy	378	28	embodied carbon	98
4	consumption	310	29	efficiency	93
5	co2 emission	281	30	input–output analysis	90
6	construction	236	31	energy efficiency	89
7	international trade	223	32	concrete	86
8	China	221	33	trade	81
9	sustainability	220	34	footprint	77
10	emission	215	35	sector	77
11	greenhouse gas emission	213	36	building material	76
12	system	211	37	life cycle energy	75
13	performance	201	38	house	72
14	building	197	39	optimization	70
15	impact	196	40	cost	58
16	LCA	167	41	energy use	56
17	environmental impact	165	42	technology	51
18	input–output analysis	164	43	office building	50
19	residential building	159	44	framework	49
20	model	151	45	simulation	46
21	design	131	46	inventory	45
22	energy consumption	130	47	policy	44
23	carbon	123	48	Embodied energy	41
24	life cycle	114	49	management	39
25	carbon emission	109	50	economy	38

shows the top 50 keywords in the frequency ranking. The 50 keywords show a total frequency of 7435 times, which accounts for 86.2% of the total keyword frequency, 8624.

From the research dimension reflected by the data, the high-frequency keywords can be divided into categories as follows: One is related to research methods, such as “life cycle assessment”, “input–output analysis”, and “simulation”; the other is related to research objects, such as “international trade”, “China”, “construction”, and “housing”; the third is related to research topics, such as “carbon dioxide emissions”, “greenhouse gas emissions”, “sustainability”, “energy efficiency”, “policy”, “cost”, “energy consumption”, and so on. It can be seen that since embodied energy has been used in academic research, issues related to China, trade, and construction have been holding a high level of attention, and “sustainability,” “energy performance,” and “emissions” are the central issues.

Furthermore, in order to investigate the latest research trend on embodied energy, this study also conducted a co-occurrence analysis of terms and keywords from 2016 to 2019.

Table 3. Results of keyword co-occurrence analysis for 2016–2019 (2019).

No.	Keywords	No.	Keywords	No.	Keywords
1	waste	9	operational energy	17	decomposition analysis
2	transfer	10	network	18	circular economy
3	supply chain	11	input–output model	19	cement
4	strength	12	input output	20	built environment
5	resource	13	flow	21	assessment lca
6	requirement	14	economic growth	22	air pollution
7	renewable energy	15	durability
8	power generation	16	driving force

shows the 2019 part of the 2016–2019 co-occurrence results. Twenty-two co-occurrence keywords emerged in these years, such as “waste”, “transfer”, “supply chain”, and “strength”. However, compared with the analysis results based on the whole documents, it is worth noting that there were new high-frequency keywords that emerged such as “network,” “flow,” “supply chain,” “driving force,” and “decomposition analysis,” which reflects the fact that embodied energy measurement has been applied in various fields of research and that some new research questions have emerged. At the same time, network and decomposition analysis have been applied in many articles.

Moreover, to explore the changes in the research highlights of embodied energy from the time span covered by the dataset and to determine the frontier trends, this paper also used Citespace to detect burst words. Burst words refer to words that appear more frequently or frequently in a certain period and can effectively portray the evolution of a research field according to the trend of word frequency and its time cover situation. Therefore, they are a supplement to the co-occurrence analysis of keywords and can help researchers explore the emerging frontier trend of relevant research.

Table 4. Top 34 keywords with the strongest citation bursts.

Keywords	Year	Strength	Begin	End	1980–2019
sustainability	1980	5.1744	1996	2007	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂▂
embodied energy	1980	16.9196	1997	2005	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂▂▂▂▂▂
import	1980	8.6156	1998	2010	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▃▃▃▃▃▃▂▂▂▂▂▂▂▂▂
united states	1980	10.8901	2001	2013	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▃▃▃▃▃▃▂▂▂▂▂▂
sustainable development	1980	6.7481	2004	2013	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▃▃▃▂▂▂▂▂▂
exergy	1980	8.1758	2006	2013	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▃▂▂▂▂▂▂
index	1980	4.5023	2007	2012	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▂▂▂▂▂▂▂
input–output approach	1980	5.9576	2007	2010	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂▂▂▂▂▂
emergy	1980	5.6802	2007	2013	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▂▂▂▂▂▂
responsibility	1980	5.1164	2007	2015	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▃▃▂▂▂▂
ecological footprint	1980	9.1417	2007	2014	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▃▂▂▂▂▂
emergy analysis	1980	5.2424	2007	2013	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▃▂▂▂▂▂▂
wood	1980	8.1945	2008	2013	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▃▂▂▂▂▂▂
biomas	1980	4.253	2009	2012	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂▂▂▂
energy analysis	1980	4.253	2009	2012	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂▂▂▂
energy use	1980	7.9758	2010	2012	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▂▂▂▂▂▂▂
methodology	1980	5.9936	2010	2013	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂▂▂
resources use	1980	4.1693	2011	2014	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂▂
oil	1980	3.745	2011	2013	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▂▂▂▂▂▂
environmental assessment	1980	5.3527	2011	2013	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▂▂▂▂▂▂
environment	1980	5.4648	2012	2014	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▂▂▂▂▂
greenhouse gas	1980	4.0218	2012	2013	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▂▂▂▂▂▂
cost	1980	4.8938	2012	2015	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂
dwelling	1980	5.2936	2012	2015	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▂▂▂▂
environmental performance	1980	5.3633	2012	2016	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▂▂▂
climate	1980	4.0194	2012	2016	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃▂▂▂
renewable energy	1980	6.2598	2013	2015	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▂▂▂▂
requirement	1980	3.9291	2013	2014	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▂▂▂▂▂
need	1980	6.1473	2013	2014	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▂▂▂▂▂
greenhouse gas	1980	4.4685	2013	2014	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▂▂▂▂▂
aggregation	1980	3.9093	2013	2014	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▂▂▂▂▂
embodied emission	1980	4.4425	2015	2019	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃▃▃
perspective	1980	5.2075	2016	2017	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▂▂
structural decomposition analysis	1980	7.881	2017	2019	▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▃▃▃

shows the results of the analysis. It can be seen that most frontier burst words were about sustainability and the environment, such as sustainability and sustainable development which were the main research frontiers between 1996–2007 and 2004–2013, respectively. Moreover, embodied emissions and structural decomposition analysis were the latest research highlights and trends.

3. Review Results

3.1. Calculation Methods of Embodied Energy

The input–output model is the basic method of calculating embodied energy [45]. It was founded by Wassily Leontief. According to the authors in [16,46], in the input–output model, the total output of an economy, $X$ can be expressed as the sum of intermediate consumption, $AX$, and final consumption, $Y$, where $X$ is the total output vector, $Y$ is the final consumption vector, and A is the direct input coefficients matrix that is shown in Equation (2). In this matrix, $\alpha$ is the technical coefficient. It describes the relationship between all sectors of the economy.

$$X=AX+Y={\left(I-A\right)}^{-1}Y$$

(1)

$$A=\left[\begin{array}{cccccc}{\alpha }_{11}& {\alpha }_{12}& \cdots & {\alpha }_{1j}& \cdots & {\alpha }_{1n}\\ {\alpha }_{21}& {\alpha }_{22}& \cdots & {\alpha }_{2j}& \cdots & {\alpha }_{2n}\\ \cdots & \cdots & \cdots & \cdots & \cdots & \cdots \\ {\alpha }_{i1}& {\alpha }_{i2}& \cdots & {\alpha }_{ij}& \cdots & {\alpha }_{in}\\ \cdots & \cdots & \cdots & \cdots & \cdots & \cdots \\ {\alpha }_{n1}& {\alpha }_{n2}& \cdots & {\alpha }_{nj}& \cdots & {\alpha }_{nn}\end{array}\right]$$

(2)

In addition, in Equation (1), $I$ is the identity matrix, and the matrix ${\left(I-A\right)}^{-1}$ is the Leontief inverse matrix.

$AX$ denotes the intermediate input vector which can be obtained by multiplying the direct input coefficient matrix by the total output vector. Turning to embodied energy, such as the embodied energy flow in global trade. For example, besides the technical coefficient $\alpha$, a complete consumption coefficient is also widely used in input-output modeling. Its matrix can be expressed as follows:

$$B=\left[\begin{array}{cccccc}{b}_{11}& b_{12}& \cdots & b_{1j}& \cdots & b_{1n}\\ b_{21}& b_{22}& \cdots & b_{2j}& \cdots & b_{2n}\\ \cdots & \cdots & \cdots & \cdots & \cdots & \cdots \\ b_{i1}& b_{i2}& \cdots & b_{ij}& \cdots & b_{in}\\ \cdots & \cdots & \cdots & \cdots & \cdots & \cdots \\ b_{n1}& b_{n2}& \cdots & b_{nj}& \cdots & b_{nn}\end{array}\right].$$

(3)

B is the complete consumption coefficient matrix and can be calculated as follows:

$$B={\left(I-A\right)}^{-1}-I$$

(4)

In matrix $B$, the parameter $b_{\mathrm{ij}}$ measures how much direct and indirect output from sector $i$ will be used given each output increase in sector $j$. Then embodied energy in international trade can be calculated as follows:

$$E=\frac{C}{Y+Y^I-Y^E}{{\displaystyle \sum }}_{j=1}^n{M}_j\times b_{ij}.$$

(5)

In Equation (5), E denotes embodied energy; $C$ denotes the energy consumption of a country or a region; $Y$ denotes the output of the energy sector; $Y^I$ denotes the energy sector’s imports from other countries; $Y^E$ denotes the energy sector’s exports to other countries; $M_j$ denotes exports in sector $j$.

In the above model, the consumption coefficient B followed a simple extension of monetary input–output balance, ${\displaystyle \sum }_{i=1}{\epsilon }_i{X}_{ij}={\epsilon }_i{X}_i$, which has been criticized for it cannot reflect energy conversation conditions. Therefore, the authors in [31,33] proposed another model. In their study, the principle of input–output balance for Producer $i$ is shown in Figure 3.

It illustrates that the physical balance in terms of embodied energy flow for producer $i$ can be expressed as follows:

$$d_i+{{\displaystyle \sum }}_{j=1}^n{\epsilon }_j\times x_{ji}={\epsilon }_i\times \left({{\displaystyle \sum }}_{j=1}^n{x}_{ij}+f_i\right)\left(i=1,2,\cdots .n;j=1,2,\cdots ,n\right).$$

(6)

In this equation, $d_i$ denotes the direct energy input of sector $i$; ${\epsilon }_j$ denotes the indirect energy intensity of sector $j$; $x_{ij}$ denotes the intermediate input $j$ to produce product $i$; $f_i$ denotes the sum of final consumption. It can also be expressed as a matrix as follows:

$$D^T+X^T{Z}^T=Y{Z}^T.$$

(7)

In Equation (7), $D^T=\left(\begin{array}{c}{d}_1\\ d_2\\ ⋮\\ d_n\end{array}\right)$; $X^T=\left(\begin{array}{ccc}{x}_{11}& \cdots & x_{n1}\\ ⋮& \ddots & ⋮\\ x_{1n}& \cdots & x_{nn}\end{array}\right)$; $Z^T=\left(\begin{array}{c}{\epsilon }_1\\ {\epsilon }_2\\ ⋮\\ {\epsilon }_n\end{array}\right)$; and $Y=\left(\begin{array}{cccc}{\displaystyle \sum }_{j=1}^n{x}_{1j}+f_1& 0& \cdots & 0\\ 0& \ddots & 0& 0\\ ⋮& 0& \ddots & ⋮\\ 0& 0& \cdots & {\displaystyle \sum }_{j=1}^n{x}_{nj}+f_n\end{array}\right)$; $Z=D\times {\left(Y-X\right)}^{-1}$, and it is the embodied energy intensity vector. Thus, embodied energy $E$ can be calculated by the following equation:

$$E=Z\times X.$$

(8)

In addition, different input–output models have been developed to satisfy different research contexts. Specifically, the single-region input–output (SRIO) model is popular in academic research; it uses data from a region or a country to calculate the embodied energy in a system [47]. For example, Tang et al. (2013) used this method to calculate the embodied energy sources in British international trade [16]. Lin et al. (2017) [47] used this method to calculate the embodied energy consumption of China’s construction industry. It is also widely used in the calculation of implicit carbon emissions. Typically, Yan and Yang (2010), Xu et al. (2011), and Minx et al. (2011) [48,49,50] use a single regional input–output (SRIO) approach to evaluate China’s embodied emissions in different periods. However, the assumption of this approach is that the same technology is used to produce the same products in all countries and regions. The results may be biased as it does not distinguish between imports and domestic production, nor can it reflect the impact of different intermediate inputs [51]. Therefore, in order to more accurately reflect the relationship between energy consumption and flow in different regions, multi-region input–output models (MRIO) appeared. Generally, the Global Trade Analysis Project (GTAP) and OECD input–output databases are the two most prominent sources for MRIO models [41,45,52,53]. In this way, the input–output data of various countries are based on unified statistics, and more parties can better approve bilateral trade flow data. For example, Bortolamedi (2015) [2] used this method to calculate the embodied energy in trade and further integrated it into a new energy security index to better guide the assessment of regional security performance and the comparative analysis of the regional security situation. Zhang et al. (2016) [54] and Gao et al. (2018) [55] used this method to calculate the embodied energy for exploring how the embodied energy is transferred between regions through China’s domestic trade. However, MRIO is often criticized for its extensive data requirements [51]. At the same time, in order to better integrate energy issues with environmental impacts, the Environment Input–Output (EIO) method emerged. If the division of SRIO and RIO is based on the data foundation difference of the embodied energy measurement, EIO is based on the calculation ideology of embodied energy. It is an extension of the standard Leontief input–output (I-O) model and describes the total energy consumption (embodied energy) required by the economic output (goods or services) of a production unit driven by final demand. EIO can calculate the direct energy consumption of a sector’s final demand and all indirect energy consumption of other sectors in the supply chain [56]. It is also usually combined with Life Circle Analysis (LCA), called the EIO–LCA model. New and typical research like that of Tao et al. (2018) [57] used this method to calculate and decompose the embodied energy in manufacturing trade between China and the European Union (EU) from 1995 to 2011. Furthermore, because EIO–LCA can provide a life cycle perspective, this method is used in urban planning. It can provide a linkage between urban system activities and their lifecycle materials and energy input and can reveal the relationship between specific urban areas and supply areas. It then provides a foundation for further investigation of the ecological, social, and political impact of a series of activities in one place on another [58].

3.2. A New Perspective of Demand and Consumption of Energy

Generally, the greatest contribution of embodied energy is providing a new perspective for observing energy demand and consumption. Firstly, in related research on energy issues, one can get different research results through embodied energy measurement, which can be a meaningful comparison and compensation of results based on direct energy measurement. Therefore, it can enhance understanding of energy consumption of a region, country, or industry [36,56]. As Figure 4 shows, when considering indirect energy consumption, there are significant changes in sector energy consumption compositions [33].

Moreover, in the study of energy supply diversification, most studies are based on the perspective of energy sources or energy suppliers and only consider direct energy imports. Integrating embodied energy into relevant studies is an effective supplement for the vulnerability of conclusions drawn by considering direct energy supply only [59]. Moreover, through embodied energy measurement, Li et al. (2016) [60] found that energy embodied in domestic trade dominated Beijing’s energy consumption, while local direct energy accounted for less than 1/3 of Beijing’s total embodied energy consumption. Zhang et al. (2016) [54] found that the directions of energy flow between regions in China were different from the directions of direct energy flows. Similarly, in the research of energy imports and exports, because embodied energy covers both direct energy and indirect energy demand, energy relations between countries were different in comparison with relations only considering direct energy demand. For example, some indicators such as energy intensity, energy net import dependency, and primary energy carrier dependency all changed when considering embodied energy [2]. Cui et al. (2015) [61] found that the energy embodied in China’s global trade increased rapidly during 2001–2007 and faster than the total direct energy exported in the same period; China is shown as an energy exporter in terms of embodied energy. Tang et al. (2013) [16] found that alongside the more obvious direct energy imports, if net embodied fossil energy imports are considered, the gap between energy consumption and production in the UK is much larger than commonly perceived.

In addition, economic activities cannot be independent of energy supply limitations. However, it is easy to overlook this limitation when the analysis covers only a small part of the economic system, while embodied energy can help understand how the consumption of one activity shifts to another part of the system when analyzing economic activities from a system-wide perspective [14]. Furthermore, because embodied energy reflects not only the direct energy consumption of economic or environmental products but also the indirect energy consumption throughout their life cycle, it can effectively link the energy consumption relationships of different sectors. In particular, by applying complex network analysis techniques, scholars have a deeper understanding of the entire embodied energy flow network. For instance, Liu et al. (2010) [18] identified energy-intensive industries from an embodied energy perspective by measuring energy consumption in 29 industrial sectors with embodied energy in China and comparing the differences of production energy use. Furthermore, An et al. (2015) [15] depicted the embodied energy flow mode between industries in China and Shi et al. (2017) [22] revealed the energy flow pattern of global trade by embodied energy flow networks. A summary of related research can be seen in

Table 5. Typical research by using complex network analysis.

Author	Year	Study Target	Key Results
An et al. [15]	2015	Chinese Industries	The basic network features change little during the research period; industries that have most embodied energy flows change from oil-related industries to coal-related industries.
Shi et al. [22]	2017	global sectors	80% of flows are between different countries; the network is sensitive; The network presents an obvious clustering feature.
Chen et al. [17]	2018	Global	At the global level, small-world nature has been found; the economies are highly connected through embodied energy transfer.
Gao et al. [57]	2018	Interprovincial in China	Heterogeneity distribution of different types of energy flow.
Wang et al. [62]	2019	Global and China embodied rare earths	World embodied rare earths link network is clearly divided into two communities, and the network can reveal the small world nature characteristics; China, Germany, and the USA are the three most important economies.
Jiang et al. [63]	2018	The global embodied mineral flow between industrial sectors	There is significant small-world property in the global embodied mineral flow network; other Non-Metallic Mineral in China is the most important consumer of embodied minerals; the embodied mineral flows have strong directionality.
Tang et al. [64]	2019	Regional and sectoral energy network of China	Sectoral investigation indicates that infrastructure construction remained dominant in the current Chinese economy.
Sun et al. [33]	2016	Sectors in China	The small world nature identified key sectors of IEFNs (indirect energy flow networks;
Feng et al. [65]	2019	Internal and external industries of manufacturing in China	most of the embodied energy convergence and transmission is concentrated in a few industries; preferential selections is an important mechanism; the embodied energy flow patterns of the internal network of manufacturing mainly include two-focus and multi-focus convergence patterns.

.

Beyond using embodied energy to assess energy consumption in the macroeconomic system, embodied energy is also widely used in the microeconomic system, especially in energy-related research of building and construction projects [66,67]. For example, Held et al. (2012) [68] compared the total embodied energy of the water produced by eight interventions used in different areas to evaluate their energy efficiency and the role and status of people and materials in the process. The embodied energy of buildings has always been considered very important, and its combination with LCA links the energy consumption results of embodied energy with the environmental impact [69]. For example, the studies of Asdrubali et al. (2013) [70] and Basbagill et al. (2013) [71] on traditional building optimization and environmental impact optimization in the design stage used embodied energy as the measurement tool. Hashemi et al. (2015) [72] evaluated the current conditions of Ugandan low-income tropical housing by embodied energy with a focus on construction methods and materials in order to identify the key areas for improvement. Additionally, it can refer to relevant review articles such as Chastas’ s review article on embodied energy in residential buildings in 2016 [73].

3.3. Embodied Energy and Energy Security

Energy security is a critical issue for sustainable development [5]. The value of embodied energy measurement for energy security issues is reflected in two aspects at least. On the one hand, embodied energy can provide additional insights for appropriate energy policy to enhance energy security [17]. On the other hand, it can directly provide a helpful perspective for research on energy security issues.

Like the previous statement suggests, embodied energy can provide a new perspective to investigate energy consumption and energy flows in economic systems, which can be a basis for energy policymaking and implementation and help decision-makers make more appropriate policies [30,56,74,75]. For example, Shi et al. (2017) [22] studied the flow of global embodied energy between global sectors and believe that these results can provide new insight into the formulation of energy-related policies. Tang et al. (2019) [64] studied the embodied energy in China’s economy, which can help formulate fair and reasonable energy-saving policies for suppliers and consumers from regional and sectoral perspectives. Additionally, with the development of research, besides using embodied energy as a measurement tool to measure energy consumption and flow in trade to provide a meaningful perspective, scholars also use more methods to deeply explore energy-related issues on the basis of embodied energy measurement, which can be a clearer reference for policy-making.

By applying structural decomposition analysis (SDA), scholars can investigate not only energy consumption but also reasons for changes, which would benefit the specification of policy-making recommendations. Typical studies are combined with the structural deconstruction analysis method. Liu et al. (2018) [76] analyzed the reasons for the change of coal consumption in China based on embodied energy measurement. Their results indicated that coal consumption variations during 1997–2014 in China can be divided into four phases, and their reasons can be explained by four factors, including economic scale effect, industrial structure effect, energy intensity effect, and energy mix effect. Moreover, they identified the sectors’ roles in each factor based on SDA.

Other similar research includes Liu et al. (2010) [18], who identified the driving forces of embodied energy changes in exports through structural decomposition analysis (SDA); they suggested that the energy embodied in trade should receive special attention in energy policies and that environmental factors should be considered in policy-making, which can help harmonize the country’s economic development targets with its environmental priorities. Based on the decomposition analysis of the change trend of embodied energy flows in China and EU trade, Tao (2018) [57] analyzed the structural changes in the industrial sector, changes in energy structure, and changes in trade members. The author then pointed out that these results can help China better evaluate China–EU trade from a global and a clearer perspective and stated that it is significant for China to develop its own energy policy from a global perspective and to deal with subsequent trade and climate negotiations.

In addition, as described in the previous part, combined with complex network analysis, the related research of embodied energy can form a deeper understanding of energy issues from the perspective of the network, which can put forward more targeted recommendations based on network characteristics. For example, Gao et al. (2018) [55] used complex network technology to analyze the inter-provincial embodied energy transfer in China and explain in detail how the results of the analysis can be applied to policy development at all levels. Sun et al. (2016) [33] found that 20% of the energy flow edges carry approximately 80% of the total indirect energy flow volume based on the characteristics of embodied energy flow networks between China’s industrial sectors. Then, they stated that policy-making should consider not only key sectors but also key energy flow paths. Feng et al. (2019) [65] analyzed the embodied energy flow patterns in the internal and external industries of China’s manufacturing industry. They stated that China’s energy supply policy should consider the embodied energy convergence and transmission between internal and external industries of the manufacturing industry, energy-related industrial clusters, and key industries. Then, the transformation, upgrading, and sustainable development of China’s manufacturing industry and breaking energy and environmental constraints would enjoy the benefit. Meanwhile, similar research has been extended to a broader and subdivided field because of its separability and scalability. For instance, Wang et al. [62] (2019) identified different countries’ roles in the global rare earth resources flow network, and they suggested that China should develop policies based on its role in the rare earth flow network to enhance its influence in the global rare earth related industries.

In addition, in some literature, embodied energy can also be used to evaluate relevant policies. For example, Li et al. (2016) [59] found that in China’s 11th and 12th five-year plan, its energy policy cannot help reduce total energy consumption. Cui et al. (2015) [61] used embodied energy to analyze the impact of China’s export policy adjustment on China’s sustainable development. In summary, embodied energy-related research can provide a reference for more appropriate policy development and ultimately help enhance energy security.

Furthermore, the conventional energy security framework is usually confined in the context of direct energy commodity trade [77]. In contrast to direct energy input, embodied energy as a conception provides a complete perspective on energy analysis, and it can provide additional insights to energy security issues [17,78]. For instance, Tang (2013) [16] calculated the total amount of embodied fossil energy in the UK’s import and export, analyzed its industry and national distribution, and evaluated the amount of net embodied fossil energy import of the UK. From the results of those analyses, he argued that the energy security problem in the UK is more serious than the conclusion based on direct energy import and that the energy security policy should be reconsidered. Bortolamedi (2015) [2] argued that the incorporation of embodied energy into the energy security assessment system is a wise choice and can provide guidance for formulating better energy security policies. Chen et al. (2018) [17] argued that international organizations such as the International Energy Agency should extend their definition of energy security from an embodiment perspective. Moreau and Vuille (2018) [79] believe that although the traditional transfer of energy-intensive industries abroad can improve energy performance in the traditional sense, it might lead to energy use and security deterioration through embodied energy analysis. Therefore, they argued that energy security indicators should be adjusted in combination with embodied energy to avoid conflicts between energy intensity and energy trade security. Sato et al. (2017) [59] argued that when the diversity of direct energy imports is limited, the diversity of embodied energy imports helps to improve energy security.

In addition, although the application of embodied energy at the macro-level is still at a theoretical stage, its application at the relative micro-level to enhance energy security is more feasible. Typical studies include Uluer et al. (2016) [80], who integrated embodied energy into the performance evaluation system of energy reduction in the manufacturing process chain (E-MPC); as

Table 6. An evaluation system with embodied energy as an index [80].

Metrics/KPIs	Unit	Description
Power	kW	Instant power load
Energy	kWh, kJ	Energy consumed in a specific time period
Process energy	kWh, kJ	Total energy consumed by a process in a specific time period
Theoretical energy	kWh, kJ	Energy consumed only by manufacturing processes in a specific time period
Auxiliary energy	kWh, kJ	Energy consumed by subsystems of a machine tool in a specific time period
Indirect energy	kWh, kJ	Allocated energy consumed by services used to maintain the environment for production activities such as heating, lighting, etc.
Handling energy	kWh, kJ	Energy consumed by transportation equipment such as robots, conveyors, etc. Energy
Feature energy	kWh, kJ	Energy used to manufacture a feature
Embodied energy	kWh, kJ	Energy used to manufacture a part
Energy cost	Currency	The monetary cost of energy used for a specific time period
Value-added energy (VAE) per machine	%	Energy consumed by a machine during actual process activities as a percentage of all activities, including idling
Value-added energy (VAE) per part	%	Energy consumed by a part during all actual process activities as a percentage of all activities, including waiting, handling, and indirect shares

shows, embodied energy is one of the key performance indicators. Moreover, they gave an implementation program, as Figure 5 shows and conducted a pilot case study to prove its practicability and advantage. From the chart, we can see that embodied energy estimation and identification is an important process.

Other similar literature includes Mo et al. (2010) [81], who evaluated the embodied energy consumption in drinking water supply systems. Through the case study of a municipal water system, they proposed developing a more comprehensive understanding of embodied energy and drinking water and stated that water consumption could be affected by supply- and demand-side policies. Then, they proposed some practical recommendations like the actual water price being determined based on the energy price calculated by a more integrated system. Goe and Gaustad (2014) [82] argued that physical material constraints threaten energy security, but traditional approaches often lead to command-and-control policies and a broader definition of criticality that goes beyond physical scarcity to include sustainability indicators like embodied energy. Then, they took solar photovoltaic materials as an example and gave a targeted policy reference.

4. Discussion

Embodied energy is essentially an indicator of energy consumption in the econometric system relative to direct energy or operation energy. Because it reflects the direct and indirect energy consumption in the economic system, it can provide a new perspective for the study of energy-related issues. It enables us to analyze energy-related issues from the perspective of the whole supply chain and the whole energy flow network, instead of based on single energy supply or a single stage of energy consumption [14,74]. Moreover, due to the scalability of the concept of embodied energy and the application of more analytical methods like SDA and complex network analysis, embodied energy can be used in more fields and help us understand energy issues better. For example, it can be used to identify the linkage effects of policies and contribute to the entire industry and finally to solve energy security problems from the entire economic system. According to the literature, embodied energy is directly applied to the research of energy security issues in only a few studies. However, embodied energy can be used to evaluate the energy consumption of a building in its whole life cycle at the micro-level and help understand the energy flow between various regions or industries at the macro level. It can provide a systematic perspective rather than a separate approach for the improvement of energy security and energy sustainability issues.

At the same time, it is worth noting that although embodied energy can provide a more comprehensive perspective on energy consumption, its widespread application and revealing its real value in practice still face some challenges. As we proposed at the beginning of this study, to what extent embodied energy measurement can provide innovative ideas for energy security issues remains largely open.

4.1. How to Solve the Problem of Timeliness and Authority of Data?

At present, embodied energy calculation is based on input–output analysis and the data foundation are the input–output table. However, up to now, the newest input–output data can be found in the available databases like WIOD and Eora et al., which have lagged behind for at least three years. The limitation of data leads to a discussion on whether the conclusions based on these data can effectively reflect the current energy status, thus providing a valuable reference for energy policy development and other issues. For example, China’s input–output table has only been updated up to 2015, and it has been delayed for nearly four years. In 2017, China issued the “Several Opinions on Further Deepen the Reform of the Oil and Gas System,” which changed the energy management system and had a profound influence on energy supply and demand and the economy. Therefore, to what extent the research results based on data from 2015 can provide advisable and practical reference needs further discussion.

4.2. How to Develop More Practical Recommendations or Plans for Energy Policy-Making to Improve Energy Security?

Most of the existing research focuses on embodied energy analysis, such as the consumption of embodied energy, flow paths, and driving factors in different systems. Although some scholars proposed some recommendations for policy-making, most of them were just theoretical and gave directions. Hard work is still needed to transfer the suggestions to a feasibly specific policy or implementation plan. Moreover, from the research of policy evaluation to evaluate the value of embodied energy, because of the lack of sufficient research and uniform standards, further research is necessary.

4.3. To What Extent Can Help Solve Energy Security Issues?

We believe that the application of embodied energy allows us to have a different and more scientific understanding of existing energy security issues; For example, some studies mention that embodied energy should be integrated into energy security research systems [2,66]. However, building a complete set of energy research and practical systems based on embodied energy still requires hard work. For example, are existing energy security indicators also applicable to the embodied energy measurement framework? In the meantime, according to the definition of energy security issued by the International Energy Agency (IEA), the long-term energy security is the availability of a regular supply of energy at an affordable price [83], which means sufficient energy supply, stable price, and energy supply channel security. Embodied energy analysis cannot solve channel security. Moreover, with the increasing attention to environmental issues, the concept of energy security also extends to ecological security. In this context, whether embodied energy is better than other analyses such as embodied carbon emissions or emerge analysis needs further exploration.

5. Conclusions

This paper made a comprehensive description of the development and application of embodied energy in academia. Specifically, this paper firstly introduced the definition and characteristics of embodied energy and depicted the development of previous studies. Then, based on a review of the typical literature, this paper investigated how embodied energy can provide a meaningful reference for studies on energy, and especially on energy security.

Specifically, from the analysis of the literature, embodied energy has attracted enough attention, and it has been widely used in various fields. Among these fields, the investigation of embodied energy in trade and in buildings are two important fields. The input–output model is the calculation foundation of embodied energy, but it would be used in different models according to different contexts. Additionally, it can provide a new perspective on understanding energy consumption, which is useful to understanding energy demand and consumption based on direct energy consumption. At the same time, through a comprehensive understanding of energy consumption, it can be a useful and more explicit reference for policy-making to enhance energy security. Moreover, it is an advisable choice to integrate embodied energy into the study of energy security issues.

In summary, as an energy measurement tool, embodied energy can provide more comprehensive results of energy consumption, which contains all indirect and direct energy consumption. It can benefit the understanding of how to improve the energy efficiency and energy sustainability of the economic system, then provide recommendations and directions for policy-making to enhance energy security. Indeed, because of the limitations of the data foundation, research foundation, and methodology, we still face many challenges in exploring more of the value of embodied energy in the study and practice of energy security issues. Therefore, related topics are still worth developing in the future.