Low Carbon Scheduling Optimization of Flexible Integrated Energy System Considering CVaR and Energy Efficiency

Round 1

Reviewer 1 Report

The paper may be interesting as an example of analysis of multi-energy systems. The main contribution is in the aspects of modelling operational behavior and assess optimization issues.

Despite this may be of interest, the paper is very very poorely presented and all possible interesting contribution are compromised.

To be considered for further revision, there is need for a deep revision of the introduction with these main elements:

Clear definition of IES with motivations for its development Clear definition of IES main scope to be studied (i.e. the main issues to be analyzed for this new field) Literature on theoretical analyses Literature on lab test or practical examples Authors declaration of paper scope with clear motivations on the need to exactly focus on these aspects

 

Further elements in the following.

 

There is need of extensive writing revision: grammar, syntax, punctuation. At the moment it is very poor The issue of the operating mode is introduced in a trivial way. FTL is not the only one. Moreover It is not proper to go quickly to these control logic when it is not clear at all what is IES for the authors. A very vague definition that can go from microgrid, to distributed generation, to energy hub is given. Accordingly one cannot understand your specific issue (operating mode). Definition of IES should be moved in introduction rather than in later section. The literature review of the issue of flexibility is proposed in a very confused way with not particular reasoning and no clear discussing point. If you consider also my previous comment, you can imagine that the reader is totally lost … it is very hard to understand what you are really talking about, what’s your specific focus and points of investigation. Lines 113-121 cannot be considered as a clear way of presenting the scope of work: it is not clear what are “IES” since the definition is very wide and not particularly clear description is given, there are not motivations / justifications that what authors claim to be necessary to be investigated is a major concern for IES analyses. Authors do not provide any elements as regards typical configurations of IES (which technology, why, if any practical examples, etc.)

Author Response

First of all, I sincerely sorry for the way I expressed the content of this paper. I am so appreciate for your valuable comments. Thank you very much for your detailed and specific suggestions! I have made specific modifications to each of them.

Clear definition of IES with motivations for its development. Clear definition of IES main scope to be studied (i.e. the main issues to be analyzed for this new field). Literature on theoretical analyses. Literature on lab test or practical examples.

Response 1: IES definition: IES refers to the use of advanced physical information technology and innovative management mode in a certain region, integration of regional coal, oil, natural gas, electrical energy, thermal energy and other kinds of energy, to achieve a variety of heterogeneous energy subsystem coordination planning, optimization operation, collaborative management, interactive response and complementary. IES can meet people's demand for various energy sources (such as cold energy, thermal energy and electric energy), so it can also be called an energy hub.

Since this paper mainly studies the development of flexibility transformation of IES, the first part of the literature review reviews the flexibility of IES, which is carried out from the two aspects of energy supply side and demand side.

The issue of the operating mode is introduced in a trivial way. FTL is not the only one.

Response 2: FTL is an operating mode of gas turbine, not IES. This issue mentioned in the introduction is mainly to put forward that IES lacks some flexibility due to the operation mechanism of gas turbine, so as to continue the literature review below.

As for IES operating mode, this paper describes in detail in the second section and points out the differences and connections between FIES and TIES. The second section is mainly a detailed description of the problems studied, so the operation mode of FIES is elaborated here.

A very vague definition that can go from microgrid, to distributed generation, to energy hub is given.

Response 3: In the first question, specific definitions of IES are given. Actually, IES is the energy hub, in which a variety of energy conversion can be realized. At the same time, IES will also be distributed with many distributed power generation devices, such as wind power and photovoltaic units. Microgrid is actually related to IES, which is a small regional distribution network. The distribution network in IES can also be called microgrid, but IES has not only the grid but also the gas and heat networks. Therefore, the study of energy optimization of IES can be handled by referring to the basic model of microgrid optimization. That is to say, they have a very close relationship.

Accordingly one cannot understand your specific issue (operating mode).

Response 4: IES operation mode is described in the second section. In the subsequent case analysis, the system operation structure diagram has been attached to help readers better understand the three different modes.

In order to better understand the above three operating modes, the IES structure diagram of three different modes is drawn below, which can intuitively see the differences of the three modes.

Figure 5. Three operating mode structure comparison ((a) Traditional operation mode; (b) TED operation mode; (c) CTED operation mode)

Definition of IES should be moved in introduction rather than in later section.

Response 5: The definition of IES has been added to the introduction as required.

The literature review of the issue of flexibility is proposed in a very confused way with not particular reasoning and no clear discussing point.

Response 6: The first part of the literature review summarizes the flexibility of IES, which is carried out from the two aspects of energy supply side and demand side. However, most literatures mainly focus more on the flexibility of one side (supply side or demand side), and do not use energy storage devices to improve the overall flexibility of the system, so this problem has certain significance.

It is very hard to understand what you are really talking about, what’s your specific focus and points of investigation. Lines 113-121 cannot be considered as a clear way of presenting the scope of work: it is not clear what are “IES” since the definition is very wide and not particularly clear description is given, there are not motivations / justifications that what authors claim to be necessary to be investigated is a major concern for IES analyses.

Response 7: I'm sorry that I didn't give an exact definition of IES, which confused you about the overall idea of this paper. So, I will give you an overview of the logic of the introduction to help you have a better understand of this paper.

First of all, the main purpose of the first part is to introduce our topic, namely the need to study the flexibility of IES. Then, literature review is conducted on the flexibility research of IES. After summary, it can be found that most of the flexibility research focuses on the supply side or the demand side, and the overall flexibility of the system is not considered from the perspective of the application of energy storage devices. What’s more, a review is made on the model methods for solving the optimal scheduling of IES, which can be concluded that many literatures adopted stochastic optimization method to solve the problem, but they did not pay enough attention to the control of system operation risk. Therefore, according to this motivation, a stochastic optimization model based on CVaR is proposed. Moreover, the scenario clustering method, as a key step in the process of stochastic optimization, is reviewed. Based on the shortcomings of conventional clustering methods, the FCM-CCQ method, which can conduct post-evaluation of clustering results, is proposed. Finally, the main research content of this paper is described.

Authors do not provide any elements as regards typical configurations of IES (which technology, why, if any practical examples, etc.)

Response 8: There are some basic elements mentioned in the introduction, such as gas turbine, distributed generator (wind power and photovoltaic), gas boiler, etc. This is explained in more detail in Section 2 of the paper.

Author Response File: Author Response.pdf

Reviewer 2 Report

General comment: This paper introduces the fuzzy c-mean -- clustering 25 comprehensive quality (FCM-CCQ) algorithm, which is a novel method superior to the general 26 clustering method, and performs cluster analysis on the output scenarios of wind power and 27 photovoltaic.

Introduction: The Introduction should be improve focusing on the aim of the paper, main methods, main results and few recommendations based on empirical results. The authors should explain their research novelty compared to previous studies from literature.
Methodology: Indicate limits and advantages of methods. Indicate alternative methods. Provide practical comments to introduce the methods.
Results: The interpretations are too superficial. More comments of the results are required and comparisons with similar studies from literature. More details on data are required.
Discussion: Interpretations of the results are provided, but a more critical position is required. The literature review should be extended.
Bibliography/References: The reference list is not up-to-date. Add recent references, especially those from journals indexed in international databases, WoS and Scopus.
Other remarks: -
Decision: Accept with major corrections or resubmit.

Comments for author File: Comments.pdf

Author Response

Thank you very much for your detailed remarks and suggestions! I have made specific modifications to each of them.

The abstract should be more concise. Only one sentence to introduce the issue is necessary.

Response 1: The abstract has been revised as required. The details are as follows:

However, with the extensive access of renewable energy, the uncertainty and intermittenness of renewable energy power generation will greatly reduce the utilization efficiency of renewable energy and the supply flexibility of IES so as to increase the operational risk of system operator.

What are the implications of the results?

Response 2: The significance of the results has been added at the end of the abstract, the specific content is as follows:

The model is simulated in a numerical example, and the results demonstrate that the availability and applicability of the presented model are verified. In addition, the carbon dioxide emission of the traditional operation mode, thermoelectric decoupling operation mode and cooling, thermal and electricity decoupling operation mode of the IES decreases successively, the system flexibility is greatly enhanced, and the energy utilization rate of the system is improved as a whole. Finally, IES, after its flexible transformation, significantly achieve energy conservation, emission reduction and environmental protection.

It is better to have a separate section for literature review.

Response 3: The introduction has been reclassified into chapters and the literature review has been treated as an independent section.

Add recent references, especially those from journals indexed in international databases, WoS and Scopus.

Response 4: All the literatures you provided for reference have been added to the literature review. Thanks for the literature you provided to enrich the review content.

Describe more about figure 1.

Response 5: Some descriptions of figure 1 have been added.

Aiming at the above disadvantages, this paper has reformed the TIES and constructed a FIES whose structure is shown in Fig.1. The electrical load of the FIES is provided by distributed generators (solar, wind power), gas turbines and external network. The heat load is satisfied by two parts: one is the gas boiler which uses natural gas as fuel, and the other is the heat converter recovering the waste heat generated by the gas turbine. While the cooling load of the system is only provided by the electric chiller. The power, heating and cooling generated by the system are transmitted to the load end through the energy transmission network. Notably, the lines in yellow, red, blue and green represent different energy flow which are power, heating, cooling, and natural gas respectively. As for the concrete embodiment of system flexibility, apart from the storage battery, the FIES also adds heat storage and cold storage devices, namely, heat storage tank and ice storage tank.

More specifically, the addition of heat storage device can change the "FTL" mode in the TIES, that is, if the gas turbine has extra heat supply, excess heat energy can be stored in the thermal storage tank and released during the peak period of heat load, which can stabilize the fluctuation of thermal load of the system, reduce its influence on the power generation side, and ensure the efficient generation of gas turbine. What’s more, the cooling storage device can store part of the cold energy, so as to attain the cross-period application of cold energy. The system can generate electricity and refrigerate in the valley period of electricity price, and store the excess cold energy for users to use, greatly reducing the cooling cost of the system. Meanwhile, demand-side management is added to the system, which can transfer the load from peak period to valley period, so that enhances the economy and stable operation of the system.

The part of methodology is too technical. Insert comments to make link to your application.

Response 6: Some notes have been added to help you understand the application diagram of the specific methodology.

Describe more the data in your case study.

Response 7: More detailed data are presented in the appendix to the paper.

Table A1 IES basic component physical data

System element	Pmin（kw）	Pmax（kw）	Ramp rate (kw/h)	Maintenance cost(¥/kwh)	Energy conversion efficiency
Gas turbine	30	200	60	0.1685	0.8
Heat exchanger	0	600	—	0.08	0.85
Gas boiler	0	500	—	0.02	0.73
Wind power	0	150	—	0.11	0.95
Photovoltaic power	0	120	—	0.08	0.95
Electric chiller	0	13	—	0.03	4
Heating coil	0	10	—	0.06	0.88

Table A2 Physical data of energy storage device

Energy Storing Device	Initial  energy storage(kwh)	Rated energy capacity(kwh)	Discharge/charge efficiency	PCmax(kw)	PDmax(kw)	Self-discharge rate	Maintenance cost(¥/kwh)
Battery	5	20	0.95	5	10	0.05	0.02
Thermal storage tank	16	160	0.95	80	80	0.0.5	0.015
Cooling storage tank	10	100	0.95	80	80	0.0.5	0.015

 

More details on Figure 6 are necessary.

Response 8: The detailed description of figure 6 is as follows:

In Fig.6, the curves are roughly divided into two groups, and each group is composed of 10 curves. The group of curves on the left (lines in blue) is the 10 typical scenarios after the clustering of PV generation. Another set of curves on the right of the figure are 10 typical output scenarios after wind power clustering. The scheduling optimization of IES is calculated based on each typical wind power and photovoltaic scenario. As the principle of dispatching optimization is the same in each scenario, the following paper analyzes the dispatching optimization results under the operation of Case 3 by taking one typical scenario out of these 10 scenarios.

Present more details on figures 7-9.

Response 9: The detailed description of figures 7-9 is shown below:

After the program calculation, Figs.7-9 show the scheduling results of three different energy sources in the system at 24hours a day. In addition, the dashed lines in the three figures represent the load prediction curves of the three energy sources respectively. In detail, as we can see in Fig.7, wind power and photovoltaic, as base-load, have priority in power generation, and gas turbine, as the main system power supply unit, is in shutdown state between 0:00-4:00 PM because of its generating cost which is higher than power purchase cost from external grid, but at the peak load period basically at full output power since the electricity load is at its highest during the day. What’s more, to achieve balance between supply and demand at the same time, the peak load period between 18:00 to 22:00 also curtail part of the electricity, called demand side management. It can be basically seen that the part of power supply beyond the power load prediction curve is consumed in the energy storage charging, electric chiller and selling to the external power grid. Fig. 8 illustrates the scheduling results of thermal energy. It can be observed that the thermal storage tank stores the excess heat energy in the time periods from 8:00 to 9:00, 12:00, 15:00 to 16:00, 19:00 to 20:00, and releases thermal during 22:00 to 24:00, which realizes the decoupling of heat energy and electric energy and making energy utilization more reasonable. This measure avoids energy loss and resource waste caused by excessive heat production of gas turbine. Fig. 9 describes the dispatching result with satisfaction of cooling load. It can be seen clearly from the image that the ice storage machine uses electricity to store ice in the off-peak load period (6:00-7:00) of electricity price which can be observed that is lower than the price at peak-load (8:00-9:00) from the Fig,A2, and then releases cold energy at 8:00, so as to realize the division of the supply time of electric energy into cold energy, thus avoiding the high electricity price at peak load and saving the cost of electricity purchase.

Compare your results with expectations and with previous studies.

Response 10: The conclusion has been revised as required:

Finally, comparing with previous studies, the following conclusions differences are drawn through the analysis of simulation examples in this paper:

Apart from the operation mode of IES in other research, The the IES after the transformation is in good operation condition as a whole, and the cold, hot and electric loads are satisfied, which ensures the reliability of the energy supply of the system. At the same time, heat storage, electricity storage and cold storage equipment are charged/discharged at appropriate time, which further improves the flexibility of the overall operation of the system, and reflects the principle of economical, reliable and safe operation of IES. Meanwhile, the system is optimized from the perspective of carbon emission, and the environmental benefit of system operation can be improved after flexible transformation. Based on the analysis of carbon emission penalty price mechanism, the conclusion is that CO2 emission will decrease with the increase of penalty price coefficient, but when it reaches the critical value, it cannot be further reduced due to the constraint of energy supply demand. In terms of energy utilization efficiency of the system, compared with the original comprehensive energy systemIES in other research, the flexible comprehensive energy system can integrally improve the energy utilization efficiency and strengthen the rationality of the utilization of limited resources. Compared with the traditional clustering method, the FCM-CCQ algorithm presented in this paper can better explain the number selection of clustering centers, and the clustering analysis process is more scientific and logical. The stochastic optimization method considering CVaR is adopted to fully consider the risk existing in the system operation process, which previous studies didn’t take account into. Risk management selects the corresponding weighting factor λ according to the decision-maker's different degree of risk preference, so the corresponding scheduling optimization strategy is adopted pertinently.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Accept in present form