1. Introduction
At present, fossil fuel combustion is the world’s main mode of energy generation. The carbon dioxide generated from this process accounts for more than 70% of the total concentration of greenhouse gases emitted, causing serious problems in resources, the environment, and climate change. These problems have triggered global action towards energy conservation and emissions reduction. The Paris Climate Conference reached an agreement to keep the increase in global temperature below 2 °C [
1]. Most of China’s CO
2 emissions are related to energy consumption in its cities [
2]. In order to reach target CO
2 emissions by 2026, China needs to decrease energy and carbon intensity levels by 43% and 45%, respectively, from 2015 to 2030 [
3].
The energy internet, emerging under the trend of energy conservation and emissions reduction, is a new, integrated energy utilization system, including renewable energy, distributed generation, hydrogen storage technology, electric vehicles (EVs), and internet technology [
4]. It has the following characteristics: cross-complementation of multiple energy sources; deep coupling of multiple systems; support of multiple new technologies; and two-way interaction of energy flow and information flow [
5,
6]. The energy internets in different regions all have the above characteristics, but their coverage and emphases are different. The micro energy internet is a complex of microgrids and integrated energy centers, equivalent to an energy local area network (LAN) [
7,
8]. A microgrid is more focused on a small power distribution system. The global energy internet is composed of several micro energy internets connected by an ultra-high voltage (UHV) grid [
9]. Because the energy internet has such characteristics, it could play an important role in energy structure adjustment, energy conservation, and emissions reduction. First of all, the establishment of a carbon emissions reduction capacity assessment system could effectively make use of a significant contribution from the energy internet in this respect. Secondly, the energy internet needs a large amount of investment, covers a wide range of fields, and has a long construction period. Defining the effects it could have on low-carbon development is of great significance for guiding rational planning and scientific investment.
At present, there is much literature on the study of the energy internet, mainly on conceptual frameworks, key equipment, core technologies, and market operations. However, the specific research content and analysis angles are different. The more systematic research has focused on the following aspects:
From the perspective of grid acceptance, grid-connected coordination of distributed equipment and power electronics technology has been studied. The stability of a power system can be improved by coordinating the planning of distributed devices across a wide area, but attention should be paid to energy management, reactive power, and voltage control of the intelligent distribution network or microgrid [
10]. Shukla proposed a small-signal stability-constrained distribution system reconfiguration (DSR) methodology to deal with uncertainties associated with the load demand and the power output of renewable energy based distributed generation [
11]. Yao et al. used the “stratified optimization” strategy and the “distributed optimization” strategy as the main methods to model the coordinated optimization problem of large-scale distributed equipment [
12]. The optimization degree of distributed devices will affect the efficiency of resource utilization in the energy internet. The breakthrough of power electronics technology has provided a strong impetus for the development of smart grids and the energy internet. Huang et al. proposed a plug-and-play future distribution system architecture for distributed renewable energy and distributed energy storage devices [
13]. A solid-state transformer can support distributed power supply and energy storage equipment to access a distribution network through a high-frequency power electronic interface [
14]. UHV flexible direct current (DC) technology, which is being widely studied at present, is the backbone technology of the energy internet [
15]. The realization of these technologies has also become a link of system coupling in the energy internet, which provides a reference for the following research on the system coupling relationship.
From the perspective of energy dispatch and utilization, the optimal scheduling of low-carbon energy was studied. Li et al. proposed a zero-carbon emission micro energy internet (ZCE-MEI) architecture by introducing a non-supplementary fired compressed air energy storage (NSF-CAES) hub to achieve joint scheduling of clean power and thermal energy [
16]. Based on a software defined network (SDN), Hou et al. utilized a new heuristic approach to design effective decisions for energy transport and storage collaboration [
17]. As the background of economic dispatch (ED) in renewable integration systems, Tong et al. presented a new distributionally robust optimization (DRO) ED framework (DRED) [
18]. Zhou et al. used a three-stage Stackelberg game theory and big data to solve the problem of coordinated management of renewable energy and traditional energy [
19]. In this paper, the mechanisms used for energy saving and emission reduction on the power side of the energy internet were based on the aforementioned research on the clean scheduling of low-carbon energy.
From the perspective of the supporting role of information technology in the energy internet, internet technology and communication technology were studied. Xu et al. introduced the architecture and communication performance of energy routers that were used to regulate key devices in the energy internet [
20]. Tapscott and Wu introduced the principles and characteristics of blockchain technology and its application for the energy internet [
21,
22]. Pan et al. introduced the significant impact of the application for the Internet of Things on improving energy efficiency [
23]. Huang proposed the concept of the future renewable electric energy delivery and management (FREEDM) system and studied its framework and feasible technologies [
24]. In addition, there is also some literature from the perspective of energy data analysis to explore the market operation of the energy internet [
25]. These technologies and operation modes promote the coupling and energy trading among the transportation system, energy storage system, natural gas system, and power system on the user side, which are the basis of the mechanism analysis of energy saving and emissions reduction on the user side.
From the research directions mentioned above, the research on the energy internet mainly focused upon factors such as the conceptual framework, key equipment, core technology, and market operation. The literature on comprehensively studying the capacity of energy-saving and emissions reduction of the energy internet and its quantitative calculations does not yet exist. The research results of grid-connected coordination of distributed devices, optimized scheduling of low-carbon energy, and market operation in the energy internet have laid a good foundation for analyzing the energy-saving and emission reduction mechanisms of the energy internet in this paper.
The energy internet is an extension of the power system, and many scholars have conducted quantitative research on the low-carbon capabilities of the power system. Most of the existing research focuses on specific technologies and projects to calculate low carbon benefits by introducing some low carbon elements such as wind power [
26], carbon capture and storage (CCS) [
27], biomass power generation [
28], and photovoltaics [
29]. In the study of the analysis method and technical route, Zhou established a standardized assessment model for low-carbon benefits of the grid to achieve quantitative analysis of different transmission networks and different energy transmission modes [
30]. Based on the demand for a low carbon benefit assessment system of the smart grid in China, Jia et al. proposed another technical route from low carbon capacity assessment to low carbon efficiency [
31]. This is roughly consistent with the technical route of this paper. In the selection of low-carbon factors or capabilities, almost all existing literature has applied qualitative methods to decompose the comprehensive low-carbon capabilities of power systems. Cao et al. considered that the low-carbon factors of the power system included demand-side management, smart grid technology, low-carbon power generation technology, low-carbon energy utilization, and low-carbon power dispatch [
32]. Through the analysis of energy-saving and emissions reduction capabilities of the smart grid, Zhou et al. directly listed several low-carbon capabilities: power optimization comprehensive capacity, power grid efficiency comprehensive capacity, load shaping comprehensive capacity, and user energy-saving comprehensive capacity [
33]. Based on the above qualitative methods, this paper combined quantitative methods to separate the low-carbon capability of the energy internet. For the modeling method of comprehensive low-carbon benefits calculation of power system, Li et al. predicted the carbon emissions of power industry by linear smoothing method, and calculated the cost and benefits based on the carbon emission price [
34]. Ridge regression analysis is a commonly used modeling method for carbon emissions prediction in the power industry [
35]. In addition, some literature has quantitatively calculated the low-carbon benefits by using mathematical formulas. For example, Kang et al. deeply excavated and analyzed the coupling relation among the individual capabilities through the logical method, and proposed a comprehensive low-carbon capability evaluation model [
36]. Cai et al. elaborated the power load shaping ability which is caused by user interaction from three aspects of the electric vehicle, energy storage technology, and peak-load shifting, and then established the calculation model for load shaping ability [
37]. The mathematical formula method is a relatively simple and direct method used to calculate low-carbon capability. The low-carbon calculation method of power system provides a reference for the study in this paper.
In summary, the technical route, the selection of low-carbon factors, the quantitative calculation model of load-shaping ability, and the comprehensive evaluation model provide a good reference for in-depth study of carbon emissions reduction of the energy internet in this paper. At the same time, the comprehensive low-carbon estimation models of the power system in the research above noticed that the overlapping effect should be eliminated, but they were only the result of classification in theory. Moreover, there was no guarantee that the part of the overlap calculation was completely eliminated. However, some ideas from these results have given great inspiration to this paper. Therefore, this paper intended to study the calculation of carbon emissions reduction in the energy internet based on the research results above, and tried to solve the problem of overlap in the calculation model.
The regional energy internet is the basic unit and foundation of the global energy internet. There are many pilot projects focusing on the regional energy internet which have been constructed. Therefore, this paper took the regional energy internet as the research object, and used the combination of the power system, primary energy system (mainly the renewable energy system and natural gas system), transportation system, and thermal energy system to give the system boundary.
The paper aimed to solve the following problems: (1) To solve the problem of overlapping calculation, and divide the total low-carbon capacity into several single low-carbon capacities; (2) Based on the comprehensive analysis of the energy saving and emissions reduction generated by the coupling of various subsystems, establish a comprehensive calculation model of CO2 emissions reduction of the energy internet; (3) Analyze the contribution of each of the low-carbon capabilities to CO2 emissions reduction.