Research on Benefit Assessment of Multi-scenario Integrated Energy System

. With the rapid development of economy, China's energy is in the stage of rapid transformation, and the market demand for comprehensive energy service in the whole society is increasing. Therefore, China needs to vigorously promote the construction of a comprehensive energy system energy supply mode with new energy as the main body, so as to realize the reasonable allocation of resources and the high proportion of clean energy consumption. To effectively evaluate the quality of the system operating benefits, this paper with a variety of typical comprehensive energy system as the background, through the establishment of comprehensive energy system scenario operating benefit evaluation index system, build index based on hierarchical analysis method weight model and entropy method of fuzzy comprehensive evaluation model, evaluate the benefits of various types of comprehensive energy system.


Typical scenario of integrated energy system operation
The comprehensive energy system is mainly composed of electricity, heat and cold energy structure, including wind energy, photovoltaic, natural gas, oil, biomass energy and cold-combined thermal power system, gas-fired boiler, ground source heat pump, distributed energy storage and other multi-energy flow energy supply system coupled with other energy sources [1][2]. By promoting the coordination and integration of source, network, load and storage, energy utilization efficiency and renewable energy consumption rate are improved, system operation cost and carbon emissions are reduced to meet the users' demand for electricity, heat energy and refrigeration [9].
Compared with traditional energy systems, integrated energy systems have the following five advantages: -Environmental protection. The integrated energy system can provide cooling, heating and combined power supply to realize energy cascade utilization and improve energy utilization rate.
-Economical efficiency. The location layout of the comprehensive energy system is relatively centralized, similar to the end users, so as to meet the energy consumption of distributed clean energy, which not only reduces the transmission distance, but also reduces the energy loss in the transmission process.
-Safe reliability. The integrated energy system contains a variety of clean energy resources, which improves the reliability of energy use, provides electricity, cooling and heat energy to users, and prevents large-scale power failure accidents.
-Independent character. In remote areas, it is usually difficult to achieve centralized energy supply. According to the local resource endowment, new renewable energy can be connected to the grid, so as to independently realize distributed energy supply.
-Flexibility. The integrated energy system can adopt the operation mode of grid connection or isolated network. When the capacity of the self-generated network is insufficient, it can be input by the external large power grid. When the capacity is sufficient, it can output rich energy and store it in the internal storage units.
In this paper, the integrated energy system scenario is divided into "residential integrated energy system", "industrial integrated energy system", "agricultural integrated energy system" and "entertainment integrated energy system" [11,13] ."Residential comprehensive energy system" is mainly decentralized individual families, and common load types include electricity, heat and cold. The energy main body is relatively scattered and the total load is small, which is suitable for the supply load demand of small distributed units."Industrial integrated energy system" mainly focuses on centralized energy use, and there are obvious peak and valley periods. The common load types include electricity, heat, cold, gas and other loads, and the total load is large, suitable for the supply demand of large distributed units. Most of them are unified dispatching and supply by integrated energy system operators or power grid."Agricultural integrated energy system" is mainly agricultural production individuals or collective, and common load types include electricity and heat, such as biogas digester biogas residue recycling, and the supply units are determined according to different production scales. The "entertainment integrated energy system" is mainly in the entertainment or tourism industry, and the common load types include electricity, heat and cold, the energy is concentrated, and the total load is large, which is suitable for the system operators or the unified dispatching supply demand of the power grid, and suitable for the supply of large distributed units.As shown in Figure Figure 1.

Construction of comprehensive energy system evaluation index
According to the comprehensive energy system analysis results of multiple scenarios, combined with the current situation of industrial development and the characteristics of various types [9][10][11] , on the basis of the index system systematic, independence, comprehensive, scientific, operability construction principle, from the comprehensive energy system economy, operational, environmental protection and social four aspects to build evaluation index system, the regulators can fully evaluate the comprehensive energy system project or the comprehensive benefit and feasibility of [3][4] . The construction index system is shown in Table 1.

Economic indicators
-Internal rate of return. The internal rate of return is the discount rate when the present value of the investment capital inflow and the outflow value are equal and equal to 0. The higher the internal rate of return indicates that the higher the economy of the comprehensive energy system, the stronger its invest-ability. The calculation formula is shown in (1): Where: is the capital inflow, is the capital outflow, t is the number of project construction years, and 1 is the internal rate of return. -Payback period.
The investment payback period is the period in which the investment cost can be recovered under the condition of the guaranteed return on investment. The shorter the investment payback period indicates that the faster the recovery rate of the system, the better the economy of the investment. The calculation formula is shown in (2): Where: is the benchmark return rate, and T is the investment payback period.
-Net present value.
The net present value is used to evaluate the overall economic benefit of the project. The larger the value is, the better the income generating capacity of the system and the stronger the comprehensive economic capacity. The calculation formula is shown in (3): Where: I is the discount rate and F2 is the net present value.
-Profit rate. The profit margin is the profit margin of the evaluation project in the whole investment cycle. The higher the profit margin indicates that the stronger the investability of the comprehensive energy system. The calculation formula is shown in (4): 3 (4) Where: is the total annual profit of the comprehensive energy project, and S is the total investment of the comprehensive energy project.
-Energy consumption cost. Energy consumption cost refers to the unit energy consumption cost in the operation process of the integrated energy system, mainly covering the electricity cost, heat cost, cold cost and natural gas cost. The lower the energy consumption cost indicates that the smaller the amount of investment in the integrated energy system, and the less the necessary investment. The calculation formula is shown in (5): 4 Where: Fe, Fh, Fc and Fg are the annual energy consumption costs of electricity, heat, cold and gas of the integrated energy system respectively; Qe, Qh, Qc and Qg are the electricity consumption, heat consumption, cold consumption and total amount of natural gas in the integrated energy system.

Operational indicators
-System operation efficiency.
The operation efficiency of the system is the embodiment of the operation ability of the system within a certain time range. It is mainly obtained by comparing the input or output of the system. The greater the value of the system operation efficiency is, the greater the reliability of the system energy supply is.The calculation formula is shown in (6): Where: is the sum of the output energy of the annual system, and is the sum of the input energy of the annual system.
-Grid-connected electricity. Grid-connected power refers to the total amount of electricity integrated into the power grid. The greater the value, the more power involved in the operation of the system, the greater the transmission capacity of the system. The calculation formula is shown in (7): 6 (1 ) (7) Where: γ is the self-use proportion coefficient, set by the manager of the integrated energy system. is the total annual power generation capacity of the integrated energy power generation system.

Environmental indicators
-Renewable energy utilization rate.
The utilization rate of renewable energy is the ability of the comprehensive energy system to absorb renewable energy such as wind, solar or geothermal, which is mainly measured by the proportion of the installed capacity of renewable energy in the total installed capacity of the system. The larger the value indicates that the higher the utilization degree of the integrated energy system for renewable energy, and the higher the degree of energy saving. The calculation formula is shown in (8): 7 Where: is the annual installed capacity of renewable energy of the system, and is the annual installed capacity of the system. -Carbon emission.
Carbon emission refers to the total of annual carbon emission of the integrated energy system. The smaller the value, it indicates that the higher the ratio of renewable energy adopted in the system, the stronger the environmental performance of the system.

Social indicators.
-Drive the upstream and downstream industries.
The development of the comprehensive energy system enables the upstream and downstream industries to develop simultaneously, such as energy equipment suppliers, energy storage and other related industries. This index makes statistics on the number of upstream and downstream industries entering the market. The larger the index value indicates that the more upstream and downstream industries are driven, the faster the development rate of the industry is. -User satisfaction.
User satisfaction index Through random sampling survey of users participating in the energy system and scoring the specific satisfaction index, the corresponding results are obtained by weighted average method of the obtained samples. The higher the user satisfaction degree is, the higher the social awareness of the comprehensive energy system is, and the better the development prospect is.

Evaluation methodology
The traditional fuzzy comprehensive evaluation method is highly subjective, so it is necessary to introduce quantitative evaluation method to scientifically judge the feasibility of indicators. This paper introduces entropy weight method to evaluate the above index [5][6][7][8]12] .The technical road-map for the evaluation is shown in Figure  2.

The initial weights were calculated
-Construct a judgment matrix. Construct the judgment matrix S with 11 evaluation indexes according to the importance degree. The calculation formula is shown in (9) Where is the maximum eigenvalue of S, and r is the average random consistency index.

Entropy weight method calculation
The entropy weight method can determine the weight of the index by calculating the entropy value of the data, and the entropy value can be used to judge the validity of the data information. The entropy value and the index weight ratio can eliminate the subjectivity of the traditional fuzzy evaluation. The calculation process is performed as follows: -Construct the judgment matrix , where e is the number of items participating in the evaluation.
-The above judgment matrix is standardized, as shown in formula (14):

Conclusion
This paper analyzes multiple application scenarios for integrated energy system, and combined with the characteristics of the scene to build the comprehensive index evaluation system, mainly contains four primary indicators and eleven secondary indicators, dimension covers economy, operational, environmental protection and sociality, finally through the traditional fuzzy comprehensive evaluation method and the combination of index weight, so that the index system has realistic significance, provide useful reference for China's energy development.