Robust Optimization Model for Energy Purchase and Sale of Electric–Gas Interconnection System in Multi-Energy Market
Round 1
Reviewer 1 Report
Dear Authors,
This is a very interesting study taking into account electric-gas interconnection system under multi-energy market. The aim of this study was to propose a robust optimization model of energy purchase and sale. The importance of this problem results from the internal coordination and optimization as well as the external flexible tendering problem in the multi-energy market and sale.
My questions are as follows:
What are the limitations of using this model?
Can this model be used in all conditions and in all economies?
How important can the application of this model be? Are only economic considerations relevant?
What is the significance of this model for sustainable energy management?
What is the environmental relevance of the model?
Author Response
Dear Reviewer:
Thank you very much for your reading and the comments concerning our manuscript entitled “Robust Optimization Model for Energy Purchase and Sale of Electric-Gas Interconnection System under Multi-Energy Market” (ID: applsci-658854). These comments have clearly pointed out the problems in the articles, and have important guiding significance for perfecting our research. Meanwhile, those comments are very helpful to recognize the deficiencies in our articles for us. After careful revising according to the comments, we reviewed the full text again, and hoped to get your approval. The revised parts have been marked in the text with the revision mode. The main corrections in the paper and the responds to your comments are as follows:
Responds to your comments:
Response to comment: (What are the limitations of using this model?)
Response: Thank you very much for your questions. First of all, the background of the model constructed in this paper is the day-ahead market bidding, which does not involve the bidding behavior of the in-day market. Secondly, considering the strong conservatism of the robust model, this paper determines the decisions under different conservativeness by adjusting the robust factors, which requires the system decision makers to have a clear understanding of their own risk bearing capacity and risk preference, that is, to determine the appropriate robust factors.
Response to comment: (Can this model be used in all conditions and in all economies?)
Response: Thank you for your question which is very meaningful. The model in this paper is suitable under the framework of Nordic power market. China's electricity market reform, including long-term electricity market and electricity spot market, follows the design of the mechanism of Nordic power market. Although the construction of electric power spot market is currently in the pilot phase, in the foreseeable future, China's electricity spot market will be more mature, and close to the Nordic power market, so this article will also apply to the future of China's electricity spot market. In terms of the decision-making body, the model in this paper is applicable to the economy providing comprehensive energy services, which uses a variety of energy sources to complement each other and realize multi-energy joint supply. Therefore, the decision-making body is unique, but the decision-making object is the day-ahead bidding declaration of a variety of energy sources and the output power of a variety of components.
Response to comment: (How important can the application of this model be? Are only economic considerations relevant?)
Response: Thank you very much for your questions. The model of this paper has great application value in practice. In the traditional integrated energy system decision-making, what experts thought most is the economic scheduling problem considering various output units and coupling units under the premise of multi-energy complementarity and user demand. But with the development of comprehensive energy service, participation in bidding multi-energy market will be increasingly important, because it will directly affect the level of profitability of comprehensive energy services units. China, from 2015, carried out the reform of incremental power distribution, opening up the incremental distribution market, so that the social capital could participate in the market competition of the increment distribution, and many placements electric company was founded. Among them, many mature allotment electric company, after a period of development, have expanded into the integrated energy services business, which provide a variety of energy supplies to their customers. In the future, the construction of China's energy market is increasingly perfect, rationing power companies that provide integrated energy will consider more of the strategies outlined in this paper for the purchase - sales strategies of multiple energy sources in different energy markets. Since this paper focuses on the purchasing and selling behavior of decision-makers of power-gas interconnection system in the multi-energy market, the economics of bidding decision is emphasized in the model objective function and related constraints.
Response to comment: (What is the significance of this model for sustainable energy management?)
Response: This paper considers the internal multi-energy coordinated operation management of the power-gas interconnection system, and multi-energy complementarity will improve the overall utilization efficiency of energy. Therefore, it is of great significance for sustainable energy management.
Response to comment: (What is the environmental relevance of the model?)
Response: Thank you for your questions. This paper focuses on the decision-making economy under bidding, regrettably there are few considerations on the environmental relevance. In the future study, we will further discuss the environmental benefits of the operation of the integrated energy system based on the power-gas interconnection system.
Sincerely thank you for your guidance on our article. Your evaluation is of great significance for improving the quality of the article. We have checked the whole article according to your suggestion. We sincerely hope to receive your approval.
Thank you and best regards.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This paper describes an optimization model for a coupled natural gas-electricity system with storage and a variety of demands and then applies the model to somewhat simplified actual price data (including considerations of uncertainty). The model is sophisticated enough, but I have some questions about its general applicability and the methods used.
General Comments:
While the writing is perfectly understandable, it also has a lot of minor grammar issues. The most common two seem to be missing articles (the, a, an) where they are needed and mismatch for singular/plural nouns. As an example, I’ve noted places in the first paragraph where changes are needed. Similar issues occur in the rest of the paper, but I believe they could be easily corrected by a native English speaker.
*An* integrated energy system deepens the coupling of *the* power system and other energy systems by utilizing energy conversion technology, thereby integrating multiple heterogeneous energy sources to achieve multi-energy complementarity and energy cascade utilization [1-3]. The participation of multiple energy sources makes *an* integrated energy system extremely flexible in participating in market transactions [4,5]. However, due to the differences in output power characteristic*s*, market structure, price mechanism and price volatility of heterogeneous energy source*s*, the decision-makers' bidding decisions should not only consider the internal influences of output power characteristic*s* and *the* coupling situation of multi-type heterogeneous energy sources, but also consider the external influence of *the* multi-dimensional market structure and multi-level price system, which will bring enormous challenge*s* for bidding decision-makers [6]. Therefore, it is urgent to carry out the research on bidding strategy of *the* integrated energy system in *a* multi-energy market, which will provide *a* scientific and reasonable decision-making basis for *both* the internal multi energy collaborative operation management and the external multi energy market bidding.
Why are there so many simplifications of the price data? Why can’t you use actual price data? Are there modeling limitations here?
Specific Comments:
Line 52-65: I’m not sure I understand what you have in mind here when you are talking about “Electric-gas interconnection systems”. You mention industrial parks, so I’m imagining that you mean some entity (probably a large factory) that buys NG and electricity, but also has the capability to produce electricity from NG. Is there more to this than that or does that capture the idea? This comes up again in line 121, where you say you are describing a “typical” system. But I’ve never heard of such a thing. Do any exist in the real world? Are any planned? A system that only converts between electricity and NG (and adds some storage) seems uneconomic to build, as we already have lots of other things that arbitrage between the NG and electricity markets (such as NG generators). If the analysis here is for a hypothetical system that is ok, but should be stated clearly.
Line 73: It seems like the sentence that starts around line 73 could use a lot of references.
Line 139: Again, a statement like “The energy hub model is widely used in the steady-state modeling of energy flow.” Calls for a few references. I think the broad statements like this need more support.
Line 441: This makes sense because electricity is usually a “higher-value” commodity.
Line 444: What does “optimal” mean in this paragraph. Renewable energy is uncertain and uncontrollable, and not something that is chosen. Hence, I don’t see what would be optimized – in my understanding, RES output should be an input to the model. Unless maybe you mean to describe he RES output that, if it happened to appear, would be the best. In that case, why wouldn’t you want maximum RES output all the time? You could sell all the excess and make more money. In the text, you explain that this is true in periods 8-9, but why isn’t it true all the time? Is there some limit on utilization of the RE that I missed?
Line 545: But would even higher vales of Gamma be appropriate? When expected and actual profit are so different, it seems like we would want to continue testing higher values of Gamma until they were the same. From a functional perspective, higher Gamma values are resulting in greater *actual* profit, which should be the actual objective of the decisionmaker. Or is there reason to believe that the uncertainty is overstated in this analysis, so lower Gamma values are acceptable?
Author Response
Dear Reviewer:
Thank you very much for your reading and the comments concerning our manuscript entitled “Robust Optimization Model for Energy Purchase and Sale of Electric-Gas Interconnection System under Multi-Energy Market” (ID: applsci-658854). These comments have clearly pointed out the problems in the articles, and have important guiding significance for perfecting our research. Meanwhile, those comments are very helpful to recognize the deficiencies in our articles for us. After careful revising according to the comments, we reviewed the full text again, corrected some grammatical mistakes and content errors in the text, and hoped to get your approval. The revised parts have been marked in the text with the revision mode. The main corrections in the paper and the responds to your comments are as follows:
Responds to your comments:
Response to comment: (While the writing is perfectly understandable, it also has a lot of minor grammar issues. The most common two seem to be missing articles (the, a, an) where they are needed and mismatch for singular/plural nouns. As an example, I’ve noted places in the first paragraph where changes are needed. Similar issues occur in the rest of the paper, but I believe they could be easily corrected by a native English speaker.)Response: Thank you very much for your suggestion. We have revised and polished the whole paper.
Response to comment: (Why are there so many simplifications of the price data? Why can’t you use actual price data? Are there modeling limitations here?)
Response: Thanks to your question and this is a very important. In effect, it is considered to can use the actual clearing price data of a certain period of time and directly calculate using the method of expectations. But this paper chooses to use the actual data, by fitting, sampling and clustering to generate price, the reason for this is:1) it can be used as a standardized method and has a wide range of applications. For example, in countries like China, where the power spot market is in the early stage of construction, the price data is not typical and the data volume is small. Direct use of actual price data will lead to inaccurate model optimization results.2) if the actual data is directly used, the larger the data volume, the more accurate the results will be, but the results will easily fall into dimension disaster and the time of model calculation is not controllable. On the premise of ensuring the accuracy of model optimization results, the method in this paper is used to make the calculation time of the model controllable
Response to comment: (Line 52-65: I’m not sure I understand what you have in mind here when you are talking about “Electric-gas interconnection systems”. You mention industrial parks, so I’m imagining that you mean some entity (probably a large factory) that buys NG and electricity, but also has the capability to produce electricity from NG. Is there more to this than that or does that capture the idea? This comes up again in line 121, where you say you are describing a “typical” system. But I’ve never heard of such a thing. Do any exist in the real world? Are any planned? A system that only converts between electricity and NG (and adds some storage) seems uneconomic to build, as we already have lots of other things that arbitrage between the NG and electricity markets (such as NG generators). If the analysis here is for a hypothetical system that is ok, but should be stated clearly.)Response: Thank you for your questions. The industrial park is actually an example, representing thatthe electrical and gas interconnected system is essentially a regional integrated energy system, and regional integrated energy system in the industrial park area has a better application. Since 2015, China has carried out the increment distribution reform, one important development direction is to carry out comprehensive energy services. Incremental power distribution pilot is mostly located in industrial parks or new campuses of universities, such as incremental power distribution pilot in Pinggu mafang industrial park, incremental power distribution pilot in Changping new campus of Beijing university of chemical technology, and incremental power distribution pilot in Caofeidian chemical park. expanded parkswhich have good environment for the development of new distribution network, the construction of multi-energy pipe network and the application of energy conversion equipment.
In this paper, the decision makers are not the factory of the industrial park, for example, the decision makers in industrial park’s electric-gas interconnection system is integrated energy service provider, it can be distribution companies, sell electricity companies, power grid companies, even gas companies, whose manage user(factory) participate in the market purchase and sale of energy transactions, thus to meet the user's demand for a variety of energy.
Among China's state-owned enterprises, State Grid Corporation is gradually transitioning to this role. It has set up a large number of integrated energy service companies in various cities and introduced social capital or local governments to jointly hold shares, which is also a highlight of China's incremental power distribution reform.
In China's private sector, Xiexin is a well developed comprehensive energy service provider, it has a "six-in-one" technology platform that comprehensively utilizes natural gas, LED, solar energy, wind energy, low thermal energy, energy storage. In addition, it also provides representative comprehensive energy solutions, such as the National Energy Administration multi-energy integrated optimization of energy system demonstration, new energy micro grid demonstration, "Internet +" wisdom energy (energy) Internet demonstration, China's largest user side li-ion battery energy storage demonstration projects, etc. Xiexin smart energy, a subsidiary of Xiexin company, has successfully won the bid for the pilot project of incremental power distribution in Jinzhai in Anhui province, Puyang in Henan province and Yangzhong inJiangsu province, among the first 106 incremental power distribution network demonstration projects in China.
Response to comment: (It seems like the sentence that starts around line 73 could use a lot of references.)Response: Thank you very much for your suggestions. We have added citations to the paper.
Response to comment: (Line 139: Again, a statement like “The energy hub model is widely used in the steady-state modeling of energy flow.” Calls for a few references. I think the broad statements like this need more support.)
Response: Thank you again for your valuable advices. In terms of references, we have made overall modifications in the paper.
Response to comment: (This makes sense because electricity is usually a “higher-value” commodity.)Response: Thank you for your affirmation, indeed, electricity, as a secondary energy, has a higher added value.
Response to comment: (Line 444: What does “optimal” mean in this paragraph. Renewable energy is uncertain and uncontrollable, and not something that is chosen. Hence, I don’t see what would be optimized – in my understanding, RES output should be an input to the model. Unless maybe you mean to describe he RES output that, if it happened to appear, would be the best. In that case, why wouldn’t you want maximum RES output all the time? You could sell all the excess and make more money. In the text, you explain that this is true in periods 8-9, but why isn’t it true all the time? Is there some limit on utilization of the RE that I missed?)Response: Thank you very much for your advices. Indeed, the description of the renewable energy output optimal value is not detailed enough. As a matter of fact, the system output is taken as the total value of bidding declaration, which is optimized to reduce the deviation between the output declaration and the actual declaration the next day to maximize the profit. The contribution of the power output in the system comes from the renewable energy units. After the power output of some renewable energy units is converted into other energy forms or supplies power to the coupling unit, the remaining part is the bidding value of the system power output. Therefore, the optimal value of renewable energy unit output is actually the renewable energy unit output under the optimal energy purchase and sale strategy of the system. Of course, it is not the actual output of renewable energy unit next day. However, to declare according to the purchasing and selling energy declaration strategy corresponding to the optimal output of renewable energy units described in the original text, the system output deviation will be minimized and the return will be maximized. Therefore, the "optimal value" of renewable energy in the original text can be understood as the "optimal declared value" to some extent. In view of this problem, we explain the optimal output of renewable energy units in this paper.
Response to comment: (Line 545: But would even higher vales of Gamma be appropriate? When expected and actual profit are so different, it seems like we would want to continue testing higher values of Gamma until they were the same. From a functional perspective, higher Gamma values are resulting in greater *actual* profit, which should be the actual objective of the decisionmaker. Or is there reason to believe that the uncertainty is overstated in this analysis, so lower Gamma values are acceptable?)Response: Thank you for your question. The expected profit is under the probability distribution of each price sample, while the actual profit is the average profit obtained when a sample in the assumed price sample set actually occurs (this part is modified and supplemented in the article).The random sample is based on the transcendental hypothesis, but in fact, what will happen in the future can never be accurately predicted, the actual profit in the original text is more likely to be the approximate value of the actual profit obtained by simulation or test, rather than the actual profit in the full sense. The expected profit is the profit brought by the optimal strategy under the model input condition, which is more in line with the calculation concept of the model. In the actual situation, both the predicted profit and the actual profit in the original text are meaningful to the decision maker of the system. Therefore, from another perspective, whether the decision maker values the predicted profit or the actual profit determines the choice of Gamma values.
Sincerely thank you for your guidance on our article. Your evaluation is of great significance for improving the quality of the article. We have checked the whole article according to your suggestion. We sincerely hope to receive your approval.
Thank you and best regards.
Author Response File: Author Response.docx
Reviewer 3 Report
Due to large number of symbols and scattered equations nomenclature is necessity. I could not find which influencing factors are defined as a worst case scenario clearly defined. It seems as the difference between actual and forecasted(bided) value of generation serves as a uncertainty. Please address this in a concise way. I think authors should provide the Matlab code of the optimization problem? I think it would be very useful. Also results should be available in a digital form as a supplementary files on the mdpi server. Why is Nordpool used in the study, for us it would be more interesting to see results of one of Asian markets? Why didn't authors use some of the existing Asian markets?Author Response
Dear Reviewer:
Thank you very much for your reading and the comments concerning our manuscript entitled “Robust Optimization Model for Energy Purchase and Sale of Electric-Gas Interconnection System under Multi-Energy Market” (ID: applsci-658854). These comments have clearly pointed out the problems in the articles, and have important guiding significance for perfecting our research. Meanwhile, those comments are very helpful to recognize the deficiencies in our articles for us. After careful revising according to the comments, we reviewed the full text again, corrected some grammatical mistakes and content errors in the text, and hoped to get your approval. The revised parts have been marked in the text with the revision mode. The main corrections in the paper and the responds to your comments are as follows:
Responds to your comments:
Response to comment: (Due to large number of symbols and scattered equations nomenclature is necessity. I could not find which influencing factors are defined as a worst case scenario clearly defined. It seems as the difference between actual and forecasted(bided) value of generation serves as a uncertainty. Please address this in a concise way.)Response: We are very sorry for the unclear part of the article and thank you very much for your suggestions. We have revised the definition of decision variables and worst case in the paper according to your suggestions.
Response to comment: (I think authors should provide the Matlab code of the optimization problem? I think it would be very useful.)Response: Thank you for your advice. The Matlab code has been submitted in the attachment.
Response to comment: (Also results should be available in a digital form as a supplementary files on the mdpi server.)Response: Thank you for your advice. The key data has been submitted in the attachment. Thank you very much.
Response to comment: (Why is Nord pool used in the study, for us it would be more interesting to see results of one of Asian markets? Why didn't authors use some of the existing Asian markets?)Response: Thank you for your questions. During the research, we found that Nord pool is more mature than other markets. Taking China as an example, the construction of China's electric power spot market is in its infancy, and the price data is not typical. In addition, China's electric power trading center has not been separated from the State Grid Corporation of China. As the company's internal information, the trading data is not public. Even if it is public, the data is small and incomplete. The Nordic power market is relatively mature, and China's power market mechanism actually follows the design mechanism of Nordic power market. So, we choose Nord pool in the study.
Sincerely thank you for your guidance on our article. Your evaluation is of great significance for improving the quality of the article. We have checked the whole article according to your suggestion. We sincerely hope to receive your approval.
Thank you and best regards.
Author Response File: Author Response.docx
