Collaborative Complementary Electricity Trading Mechanism Between new Energy and Coal-Fired Power Generation Enterprises in Power Grid Under the Dual Carbon Targets

. To promote the implementation of the national strategy of “carbon peaking and carbon neutrality” (the dual carbon targets), China is constructing a new power grid with renewable energy as its main component. This power grid presents new challenges regarding the reliability, security, and stability of power supply and economic operations. At the same time, there are also a series of key issues in the collaborative and complementary electricity trading between renewable energy and coal-fired power generation companies, especially how to strengthen the optimal allocation of resources between provinces. This article firstly identifies the changes in the new power system under the dual carbon targets. Then, it analyzes the key issues of the collaborative and complementary trading mechanism between renewable energy and coal-fired power generation companies from two perspectives: inter provincial and intra provincial market collaboration and the diversified transaction demand of multiple market entities. Finally, suggestions are put forward for the construction of this electricity trading mechanism.


Introduction
Since the beginning of the twenty-first century, the global climate problem caused by excessive carbon emissions has become increasingly serious, and the clean and lowcarbon energy transition and the active response to climate change have become the direction of global joint efforts [1]. The 2020 Central Economic Work Conference stated that China's carbon dioxide emissions will reach a peak by 2030 and achieve carbon neutrality by 2060. To achieve its carbon peak and neutrality targets, China will release implementation plans for peaking carbon dioxide emissions in key areas and sectors as well as a series of supporting measures. At present, carbon emissions from the energy industry account for more than 80% of the total national volumes, and the power industry is the largest single carbon emission industry in my country, accounting for about 51% of the total emissions of various industries [2]. In order to promote the dual carbon targets, China will build a power system with new energy as the main body, and further expand the installed scale of new energy. While the intermittence and volatility of clean energy power generation such as wind and light, the traditional sub-periods clearing model has been difficult to adapt to the physical characteristics, economic characteristics, and transaction needs of different market players. Thus, it is also difficult to meet the construction needs of the future power market. In systems involving high uncertainty, a simplistic deterministic clearing model will most likely result in an uneconomical outcome, and hard-to-meet construction needs of the future power market as well [3]. At the same time, the imbalance of renewable energy generation and utilization among regions in China has become increasingly serious. It has also become one of the key problems to be solved in how to strengthen the optimal allocation of resources among provinces in the construction of the power market. Therefore, it is necessary to study the changes between new energy and coal-fired power generation enterprises in the power grid under the carbon peaking and carbon neutrality goals. Then, find out the key problems, and establish a scientific, reasonable, and comprehensive power system based on the current multi-scenario trading mode of the power market. The coal-fired power generation enterprises should establish a cooperative and complementary trading mechanism, and build a new power market trading system with complete varieties, flexibility, and effectiveness.

2.Changes in the new power system under the dual carbon targets
As an important field to achieve the "double carbon" target, the power system's low-carbon development plays a vital role in the realization of this target. The large-scale access of wind power and photovoltaic will not only have an impact on the stable operation of the power grid, but also on the power grid morphology, operation characteristics and supply-demand relationship of the entire power system. The new energy with high penetration rate, which will become the main power source, will profoundly change the structure, characteristics, and mechanism of the traditional power system. In addition, the thermal power will further develop in the direction of clean and efficient, it will become a reserve to ensure the balance of power. The large-scale access of wind power and photovoltaic will not only have an impact on the stable operation of the power grid but also on the power grid morphology, operation characteristics, and supplydemand relationship of the entire power system. The new power system will present the characteristics of a high proportion of new energy and power electronics, which will bring new challenges to the reliability, security, and stability of power supply and economic operation. However, a series of key problems need to be solved in the new electric power market trading mechanism.

Analysis on key issues of inter provincial and intra provincial market synergy
Since the economic and social development of China is based on the province, the electric power industry has formed a supply pattern based on the province for a long time. At the same time, the unbalanced distribution of energy resources and the requirements for the development of renewable energy in China objectively determine the national unified power market system soon. This system should start with the "two-level operation" of inter provincial and intra provincial markets, and adopt the "two-level declaration and two-level clearing" mode.
Combined with the national unified electric power market planning, there are three key problems to be solved in the current inter provincial and intra provincial power market in China: inter provincial and intra provincial market positioning and convergence; the implementation plan between provinces and linkage within provinces; the responsibility and allocation of deviations between and within provinces under the background of the "double carbon" target and the construction of new power system, as shown in Figure 1.

Analysis on diversified transaction demands of multiple market entities
Under the new electric power system, the physical and economic characteristics such as load characteristics, cost characteristics, and operation constraints of multiple market players are different, and the transaction demand of participating in the power market is diversified. The trans regional and trans provincial power transmission agreement implements the national energy strategy and requires priority to ensure its implementation; New energy is required to be preferentially consumed and utilized, but it has high random volatility; Coal power has changed from the main power supply to the regulatory power supply; The supply of electricity for residents and agriculture should be given priority to maintaining the price stability; Energy storage has flexible two-way interaction characteristics, fast response speed, and strong regulation ability. Besides, the demand side of electricity is required to ensure the balance of supply and demand in the power system, and promote renewable energy consumption, energy conservation, and emission reduction [4]. At present, the demand side mainly participates in the power market in the form of demand response or auxiliary services, to regulate the load fluctuation of the power grid and improve the system efficiency [5]. The differentiated physical and economic characteristics and diversified transaction demands of the above multi-market players put forward higher technical requirements for the transaction clearing model of the new power market. Therefore, it is necessary to build a new power market, further improve the market mechanism and transaction clearing model, better adapt to the physical and economic characteristics and transaction needs of multiple

Inter provincial and intra provincial market positioning and convergence mechanism.
According to the inter provincial and intra provincial market positioning, the inter provincial and intra provincial market linkage mechanism should be improved from three aspects: firstly, improve the inter provincial and intra provincial market coordination operation mode. Secondly, improve the mechanism for provincial companies to participate in inter provincial transactions on behalf of users. Thirdly, improve the inter provincial settlement mechanism. It is necessary to clarify the settlement rules under the circumstances of different responsible parties, and make good connection with the provincial settlement rules. After the conditions are met, the "unified declaration and two-level clearing" will be gradually realized, that is, the unified market subject will be adopted in the inter provincial and intra provincial markets, and the inter provincial transaction results will be formed on the inter provincial platform first, and then the clearing will be carried out on the intra provincial platform,as shown in Fig.2.

The mechanism of implementation plan between provinces and linkage within provinces.
The inter provincial execution plan shall follow the principles of relevant transaction adjustment and reduction and recovery of transaction execution, and relate to the provincial market after adjustment. According to the changes of the power supply and demand situation, the parties to the transaction can adjust the trading volume and monthly arrangement not occurring in the transaction contract through contract transactions within the contract execution cycle in the transaction platform. When adjusting the transaction price, transaction period, and other contract elements in the transaction contract, the relevant adjustment and change agreement shall be signed to clarify the adjustment contents, which shall be implemented after the security check. The trans regional and trans provincial transaction plan shall be implemented according to the agreed curve in principle. When it is necessary to adjust and reduce due to grid security, clean energy consumption and other reasons, the dispatching agency shall adjust in accordance with the principle conducive to grid security and clean energy consumption.
Then, the dispatching agency shall provide the reasons for adjustment afterward and restore in reverse order according to the principle of transaction priority and transaction execution reduction.

Responsibility and sharing mechanism of inter provincial and intra provincial deviations.
The power settlement mechanism for responsibility deviation shall settle the deviation between the contract curve and the dispatching execution curve of trans regional and trans provincial transactions in the form of daily clearing and monthly settlement. In case of deviation in the execution of the contract electricity and power curve during the execution of the transaction, the responsibility for the execution deviation caused by the seller and the buyer shall be determined, and the Beijing Power Trading Center shall carry out the deviation settlement. As the inter provincial market is the boundary of the intra provincial market, the deviation of the inter provincial implementation plan needs to be adjusted and solved by the units in the province. The settlement cost of deviation across regions and provinces shall be shared by the market entities within each province in accordance with the principle of "one, who benefits from it, bears the responsibility."

Energy block trading mechanism with time scale considering supply and demand characteristics of inter provincial and intra provincial entities
According to the differentiated physical and economic characteristics of market players and diversified trading needs, four types of energy block trading varieties are designed: period block (PB), sustaining block (sb), curve block (CB), and variable block (VB). They are shown in the table below, as shown in Table 1. The declaration contents and clear rules of the four types of energy blocks are different. By selecting a single energy block or flexibly combining different energy blocks for trading quotation, it can adapt to and meet the diversified trading needs of multiple market entities for priority clearing, supply guarantee, continuous operation, flexible regulation, etc. It is conducive to promoting the standardization of the power market and making the market entities more convenient to participate in the power market, as shown in Table 2.

Conclusion
This article studies the changes in the new power system under the double carbon target and analyses some key problems existing in the new power market trading mechanism. It mainly focuses on the problem of inter provincial and intra provincial market synergy and the problem of diversified trading needs of multiple market players, and gives suggestions on the collaborative complementary trading mechanism between new energy and coal-fired power generation enterprises. Through the continuous improvement of the power market mechanism, operation mechanism, and price mechanism of new energy and coal-fired power generation enterprises, it is more reliable for China to play the decisive role of the market in allocating resources and the role of the government, and solve some of the key problems. Therefore, accelerate the construction of a unified, open, and orderly new power system that adapts to the rapid development of new energy and promotes the realization of the national strategy of "carbon peaking and carbon neutralization."