A review of research on regional integrated energy system planning

1. Research background

According to geographical factors and the characteristics of energy generation/transmission/distribution/use, the integrated energy system can be divided into cross-regional level, regional level and user level. As an important link between the upper and lower levels, the regional integrated energy system covers multiple energy forms such as electricity/gas/heat/cold, and involves various links such as energy production, transmission, distribution, conversion, storage, and consumption. It is the key to realizing the construction of an integrated energy system. The planning of the district integrated energy system (DIES) needs to break the industry barriers and shift from the separate production and supply of various forms of energy and the independent planning mode to the joint planning of various forms of energy. It is necessary not only to achieve technological breakthroughs, but also to break the boundaries of policies and regions. This paper summarizes the current research work on DIES planning from the four aspects of multi-energy coupling theory, load forecasting method, technical and economic analysis, and planning optimization modeling and solution, and looks forward to the future research direction.

Figure 1 Full text architecture diagram

2. Main Difficulties

The main difficulties in DIES planning are as follows:

1) Multi-energy coupling modeling. The coupling between multiple energy sources in DIES is complex and widely exists in various links such as source, grid, load, and storage. Accurate and effective multi-energy coupling theory is the key to supporting IES planning, and it must meet multiple modeling requirements such as static, dynamic, and time delay characteristics.

2) Multi-element load forecasting method. DIES load forecasting needs to take into account electricity, gas, heat, cooling and other types of loads and their mutual coupling, and is affected by multiple factors such as economy, climate, building layout, population density, etc. Its forecasting difficulty is far greater than any single form of energy system forecasting.

3) Technical and economic evaluation. DIES is an organic whole composed of a variety of energy conversion equipment, energy storage equipment, energy supply pipelines and users, and the overall technical and economic feasibility of the system needs to be re-evaluated. For example, power-to-gas (P2G) technologies such as electrolysis hydrogen production do not have investment economics from the perspective of gas systems alone, but in DIES, they can generate added value by assisting the consumption of renewable energy. In addition, the diversification of DIES operating models will also make the technical and economic evaluation more complicated.

4) Planning optimization model and solution. DIES planning is a complex planning problem with multiple elements, multiple dimensions, multiple objectives, multiple levels, and nonlinearity. When modeling and solving it, it is necessary to consider the continuous, discontinuous, and time-varying characteristics, as well as the various uncertainties that are widely present in energy production, transmission, conversion, and consumption.

3. Examples and simulations

1) Theoretical research on various forms of energy coupling

The coupling mechanism of various forms of energy is the primary issue in realizing DIES planning. The earliest international research on the theory of multi-energy coupling model began with the Energy Hub theory proposed by ETH Zurich at the IEEE PES Conference & Exposition in 2005. This model completely constructs a DIES multi-energy coupling static linear model including sources, grids, loads, storage and other links, and analyzes the optimization potential in the coupling process.

The Energy Router concept was proposed by Alex Q. Huang of the FREEDM Center at North Carolina State University, USA, as a model for solving the information flow problem in the DIES energy coupling process. Energy Router focuses on the communication, control and management of DIES. Energy Router provides support to Energy Hub at the information level, which is conducive to promoting the further development of DIES in the future.

Other scholars have conducted research and exploration on the nonlinearity, dynamic characteristics, multiple time scales, uncertainty and other aspects of DIES, and have developed the Energy Hub model and Energy Router model. However, the overall model is still in the exploratory stage.

Figure 2 Multi-energy coupling modeling

2) Research on load forecasting methods

The energy demand of DIES is the sum of the energy demand of all energy consumers scattered in the region. Therefore, factors affecting a single user unit often have similar impacts on the energy consumption of the entire region, such as physical characteristics of buildings, lighting, user behavior, energy type, building density, layout, population density, etc. All factors that may affect DIES load can be summarized into five categories: indoor building conditions, building design characteristics, regional layout, local microclimate, and socio-economics.

The research results of DIES load forecasting methods are summarized and divided into macro-level forecasting methods (top-down methods) and micro-level forecasting methods (bottom-up methods). The two types of methods complement each other and have complementary advantages. Appropriate forecasting methods can be selected or combined according to specific planning objects.

Figure 3 Factors affecting DIES load forecasting

3) DIES technical and economic research

At present, the research hotspots on the technical and economic performance of DIES are mainly focused on the technical and economic performance evaluation of some typical equipment or small energy supply systems composed of two or more equipment. The focus of its technical evaluation is on the improvement of energy utilization efficiency and energy quality, and its analysis method is based on the first and second laws of thermodynamics. The focus of economic evaluation is on economic benefits and energy conservation and emission reduction, and it is generally evaluated by citing engineering economics theory.

In terms of technology, this paper focuses on summarizing the current status of research on energy efficiency, energy quality, pollutant emissions, etc. In terms of economy, it focuses on summarizing the latest research hotspots of DIES, such as CHP, CHP, P2G technology, and energy pipeline co-channel.

4) DIES planning optimization modeling and solution research

Due to the close coupling of multiple energies, DIES has a wide range of optimization space. It exists in various links such as source, network, load, and storage. Early explorations of DIES planning at home and abroad mainly focused on small energy supply systems with a typical coupling device (such as CHP and CCHP) as the core or a few certain devices, as well as the formulation of related operation strategies such as "heat determines electricity", without fully considering the optimization space of system equipment selection. Subsequent DIES planning is generally based on Energy Hub theory, and the coordinated optimization of equipment selection, site selection, capacity determination and operation scheduling scheme is achieved through hierarchical modeling and solution. At present, the planning work of DIES basically focuses on one point, such as energy station planning, energy network planning, energy storage planning or comprehensive demand side management, etc., and a relatively mature integrated planning of source, network, load, and storage has not yet been formed, and the coupling and complementary advantages between various links have not been fully explored. Based on the current research work, the complete DIES planning should be shown in the figure below.

Figure 4 DIES integrated planning of source, network, load and storage

4. Summary and Outlook

DIES planning is essentially a complex planning problem with multiple elements, multiple dimensions, multiple objectives, multiple levels, and nonlinearity. To break down industry barriers and transform the past model of separate production and supply and independent planning into joint planning of multi-energy systems, future research has a long way to go. Future research still needs to be further explored in the following aspects:

Dynamic characteristics, multi-time scale characteristics

Multiple uncertainty analysis and modeling

Multi-energy flow safety analysis and control

Market Mechanism and Transaction Structure

The original article was published in Automation of Electric Power Systems, Vol. 43, No. 7, 2019. Welcome to read it!