Abstract
Studying the grid integration of renewable energy power generation is crucial for achieving the goal of carbon neutrality since it may have a significant influence on the secure and reliable functioning of the power system. In order to solve the problem of deviation impact caused by renewable energy fluctuations and the optimal scheduling of VPP (Virtual Power Plant), the study divides the internal aggregation unit of the virtual power plant into two parts to model. One part is the source equipment, including wind power generation equipment, gas turbine, gas boiler and waste heat boiler. And the other part is the generalized Energy storage, including electric vehicles, air conditioners and alternative response loads. Ultimately, a generalized energy storage-based virtual power plant operation optimization model is developed under multi-market coordination of electricity-gas-heat-carbon. According to the study’s findings, adding more power-to-gas technology boosts revenue in the carbon trading market by 25.24 percent. The energy market’s revenue is equal to that in the absence of a carbon trading market, and the income of the natural gas market increases by $ 32.96. The income of the carbon trading market is $ 181.51, and the final operating cost is reduced by $ 180.80, a drop of 7.81%. To sum up, the suggested approach may more effectively achieve the best distribution of different energy sources, increase the dependability of VPP operation, and make it more low-carbon.
Keywords
Introduction
In today’s society, the whole world is vigorously promoting the industrialization, resulting in increasingly bad ecological environment and shortage of traditional fossil energy. The world is in a critical transition period of replacing traditional fossil energy with renewable energy. Low pollution, sustainability, and environmental friendliness are benefits of renewable energy sources like solar and wind energy. Additionally, nations all around the world are aggressively supporting renewable energy producing technologies like photovoltaics and wind power [1]. In the past, the old power system used a large-scale power distribution method, which resulted in significant expense and power loss during transmission [2]. Since the development of distributed generation of renewable energy, it is utilized extensively in power grids and has the qualities of minimal pollution, cost savings, and excellent transmission efficiency. The electrical grid’s ability to operate steadily and safely will be jeopardized by operational irregularities [3]. The Virtual Power Plant (VPP) can make better use of the power market to increase the flexibility and cost-effectiveness of energy dispatching on the demand side. And it can coordinate and interact between the supply and demand sides of the power system. In addition, large-scale renewable energy integration into the grid has been facilitated by the advancement of energy storage technologies. Among them, a generalized energy storage system can quantify the flexible load response capability, which makes the generalized energy storage operation optimization strategy more rapid [4]. The research aims to ensure the reliability and stability of power grid operation, suppress the functional deviation of VPP caused by the uncertainty of wind and rain, reduce the optimal operation cost of VPP. And the operation fluctuation caused by industrial energy transformation and renewable energy can be solved. Therefore, the research comprehensively considers the synergy of virtual energy storage and electric energy storage, and uses electric to gas equipment to build the VPP operation optimization model under the coordination of electricity, heat, gas and carbon multi-market. Finally it arranges the VPP model based on generalized energy storage to ensure low carbon and high income in multi-market transactions.
Related work
In today’s society, countries around the world apply VPP projects to ensure the reliable grid connection of uncertain and strong renewable energy. And by aggregating different distributed equipment, the external stable and reliable power supply is realized. So it can realize the direct participation of renewable energy in the power market [5]. In addition, energy storage in a broad sense refers to all equipment and measures that can change the spatiotemporal characteristics of electric energy and play a buffer role in electricity’s supply and demand. And energy storage can further deal with the unpredictability of renewable sources of energy like sunlight and wind [6]. Many scholars have conducted in-depth discussions on VPP in generalized energy storage. To more effectively regulate the distributed generating system’s indirectness, Alahyari et al. [7] designed a VPP quotation strategy method including flexible demand, energy storage, and wind power production, and the success rate of the plan was verified by experiments. In order to assess the potential of VPP urban development, Wang et al. [8] proposed the concept of VPP to offer the flexibility that the renewable energy system requires and to choose the appropriate grid services. Finally a multi-market collaborative optimization model based on VPP was proposed. Experimental results show that the model takes full advantage of the flexibility of DER and provides results that can serve as a blueprint for more VPP applications. To support the presence of small-scale renewable energy producers in the market, Chang et al. [9] introduced the concept of VPP to apply energy storage system together with microturbine-based generators to reduce the variability of output. In order to ensure that the generation of VPP keeps the market contract value steady, VPP adopts a new centralized feeder flow control (FFC) method. Comparing it with the traditional method, the research results verified the effectiveness of the method. The VPP bidding strategy used in the Spanish power market was optimized by using a multi-stage stochastic programming technique by this technique. This technique was created by Wozabal and Rameseder [10] to address the issue of variable wind energy output and stochastic electricity price. Extensive sample comparisons were carried out to confirm that the stochastic program obtained the best Optimal strategies are significantly better than deterministic programming. In order to solve the economic problems of fluctuations in electricity prices and rapid rises, Naval et al. [11] developed a new VPP design that incorporates every full-scale distributed renewable energy production technology currently on the market. The experimental findings of the VPP model showed the significance of technical and economic management of all production facilities to minimize grid reliance and cost when the model was applied to real data of an irrigation system. For addressing the issue of collective user day-ahead energy management with intermittent renewable energy generation and unknown market pricing, Yin et al. [12] created a two-stage robust Stackelberg game model. It was engaged in day-ahead and real-time market transactions, and ran as a VPP. The simulation findings supported the model’s logicalness and efficacy. The energy management service market’s VPP bidding technique was examined by Nguyen-Duc and Nguyen-Hong [13]. They also created a two-stage robust optimization model and used it to optimize tiny VPPs. The outcomes confirmed the technique’s efficacy and increased VPPs’ earnings. In order to explore the basic quantization properties related to charge transport and storage, Bueno and Davis [14] used a method that spans nanoelectronics, electrochemistry and derived nanosensing to connect. During this time, they analyzed and verified of the electrochemical characteristics of dry and wet electrons in the connection of charge electrokinetics. This was consistent with the generalized energy storage theoretical framework for electron transfer rates.
Based on the above-mentioned analysis of research on VPP and generalized energy storage, relatively mature results had been achieved in their respective fields. But there were few research contents that comprehensively considered the combination of distributed energy and generalized energy storage as well as the operation optimization in multiple markets. Most studies rarely designed carbon trading markets. The aforementioned issues are resolved by a VPP model based on generalized energy storage and its operation optimization under the multi-market coordination of electricity-heat-gas-carbon are studied and constructed. The innovation of the research lies in the comprehensive consideration of the system function of virtual energy storage and electric energy storage. So the two can work together under the generalized energy storage framework. In addition, the stabilizing effect of the generalized energy storage on the uncertainty of renewable energy such as the peak-shaving and valley filling effect on load fluctuation were fully considered. And the processing strategies of the virtual energy storage and electric energy storage in the generalized energy storage were fully studied in the case of separate access and simultaneous access.
Building a virtual power plant operation optimization model based on universal energy storage
Construction of the virtual power plant’s source layer equipment model
Due to the expansion of globalization, environmental pollution and energy shortages are becoming more and more serious, and countries around the world urgently need to use renewable energy to survive the critical transition period. VPP can use digital technology to achieve rapid transformation. It is a distributed power plant based on cloud technology. Through high-level software architecture, digital communication, control and other technologies can be used to realize the limited aggregation of various distributed equipment. For example, it includes methods for allocating energy and energy storage, realizing energy exchange, and sharing and optimizing configuration [15]. Its overall structure operates as shown in Fig. 1.
Virtual power plant operation structure.
At present, China is vigorously developing wind power generation. Models for wind power generation most frequently employ the Doubly Fed Induction Generator (DFIG) [16]. The wind turbine begins to produce energy when the wind speed exceeds the cut-in wind speed, allowing it to attain the rated power, which is the rated wind speed. And if the wind speed does not satisfy the parameters, it is the cut-out wind speed. See Eq. (1) for the relationship between wind turbine forecast output
In Eq. (1),
In Eq. (2),
In Eq. (3),
In Eq. (4),
In Eq. (5),
Gas fired boiler structure.
The principle of the gas boiler is as follows. First, natural gas is input from the gas port, fully burned in the combustion chamber, and water is input from the water inlet to the boiler. The burned natural gas heats the water, then it is sent into the pipeline through the water pump into the room for heat dissipation. After the heat dissipation is completed, the temperature of the water body drops. Finally the above steps are repeated. The relationship between the output thermal power and the volume of natural gas consumed in the gas boiler model is shown in Eq. (6).
In Eq. (6),
In Eq. (7),
VPP energy storage equipment model includes a battery model and a heat storage tank model. The battery model only studies the fixed energy storage composed of batteries, and uses a circuit model that can effectively reflect the electrical characteristics of the battery port. The battery model expression is Eq. (8).
In Eq. (8),
In Eq. (9),
In Eq. (10),
In Eq. (11),
In Eq. (12),
Structure of the first order ETP model of air conditioning building system.
In Fig. 3, the ETP model regards the building heat capacity as the equivalent heat capacity, sets the equivalent thermal resistance as the resistance. And the indoor and outdoor node temperature are regarded as the voltage source of different two points in the circuit. The differential equation of the first order ETP model can be obtained by converting the first order ETP model of the air-conditioning building system into an equivalent circuit and solving it with Kirchhoff theorem. Once the air conditioner’s interior temperature is set and is at the recommended comfortable level, the electric power of the air conditioner
In Eq. (13),
In Eq. (14),
When examining VPP’s operational optimization technique, it is necessary to effectively link the electricity-heat-gas-carbon multi-market with different generalized energy storage equipment. And an operation optimization strategy based on the generalized energy storage VPP model under multi-market coordination is proposed. The research adds power-to-gas coupling equipment to the VPP model, so that the power-heat-gas-carbon multi-coordination market can be included in the participation in the power day-ahead dispatch and intraday balance markets. To make the computation of the chemical reaction efficiency of hydrogen generation by electrolysis of water and hydrogen methanation in the power-to-gas conversion simpler, the model of electrolyzer and methane reactor is established as shown in Eq. (15).
In Eq. (15),
VPP framework based on generalized energy storage.
Figure 4 shows that the research expands the electricity market into the energy market of the electric heating market. At each moment, VPP sells the excess electricity and thermal power produced to the market for profit. The marketers can be transformed into producers and sellers who can actively participate in the market to realize the synergistic coupling between the markets for electricity and natural gas. In addition, research will benefit from selling the heat generated in the reaction of power-to-gas equipment through the heat pipe network. Increase the revenue of virtual power plant in the carbon trading market and provide power-to-gas equipment more access to VPP Later gravitational capacity, according to the carbon trading market’s trading process. Finally, through multi-energy coupling equipment such as gas turbines, the coordinated energy, natural gas, and carbon emission markets enable the optimization of VPP’s operational processes. To address the energy supply changes brought on by the unpredictability of wind and solar power output, the research used the C&CG column constraint approach. The objective function is the strategy utilizing the multi-coordinated market’s virtual power plant’s lowest operational cost, jointly with its calculation is shown in Eq. (3.3).
In Eq. (3.3),
In Eq. (17),
In Eq. (18),
In Eq. (19),
Process based on column constraint generation algorithm.
In Fig. 5, the initialization operation is required first, and then the auxiliary variables are introduced. In the first iteration, the virtual energy storage output of the initialization wind and air conditioning is used for deterministic optimization. In the subsequent iteration, all the worst risk scenarios found in the
Analysis of VPP scheduling optimization results in the electricity-heat-gas-carbon multi-market
The scheduling optimization results are analyzed in order to confirm the accuracy of the generalized energy storage virtual power plant operation optimization model put forth in the study. Due to the capacity limitation of VPP itself, the study assumes that VPP is a price taker in each market. And it only needs to optimize the scheduling strategy of VPP in the market according to the anticipated output of wind energy and market transaction price. According to the predicted values of wind power and photovoltaic power and the predicted values of electricity purchase and sale prices and multi-energy loads, the VPP system parameters can be obtained as follows. The heat trading market price is 36.75 $/MWh, and the stationary energy consumption of the power-to-gas equipment is 0.18 MW. The price of carbon on the market for trading is 21.62 $/t, and the operating cost coefficient is 17.00$/MWh. The gas turbine’s carbon emissions the resistance is 0.065 t/GJ, and its quota coefficient is 0.102 t/GJ. The carbon emission quota for gas-fired boilers is 0.0623 t/GT, and the carbon emission intensity for burning natural gas is 2.01 kg/10
Dispatching results of virtual market in electric heating market.
Figure 6 shows the results of VPP scheduling in the electric heating market. Figure 6-(a) shows that when transaction price fluctuations in various markets are compared, all equipment works in accordance with the principles of economy and low-carbon environmental protection. Electric vehicles, energy storage and alternative loads Charging or converting other types of loads into electric loads when electricity prices are low. It needs discharge when the electricity price is high is consistent with converting the electrical load to other sources. Thereby the operating cost of the VPP and saving energy is reduced. The power of the power-to-gas equipment shows that the power-to-gas operation is performed during the 0–7 and 23–24 periods. At this time, VPP receives the least advantage from selling power to the grid, jointly with the gas turbine processing is maintained at the lowest level, which improves the operating economy of the system. Figure 6-(b) shows that it has not yet joined the heat market to sell excess heat energy, and the overall heating cost is low due to the large residual heat power of gas turbine. Therefore, the electricity-heat alternative load shows that the thermal load replaces the electric energy at most times to reduce the cost of electricity. The power of gas-fired boiler fluctuates with the change of natural gas and electricity market prices. On the basis of meeting the heat load, the excess heat is stored by the heat storage tank when the heating cost is low. When the heating cost is high, the heat storage tank releases heat to reduce the boiler heating to reduce the gas consumption cost. In addition, it can effectively reduce the carbon emissions caused by the combustion of natural gas in the boiler.
Results of virtual power plant in the market for gas and carbon trading.
Figure 7 shows the VPP scheduling results in the market for trading gas and carbon. Figure 7-(a) shows that alternative gas loads can comprehensively compare the cost of gas and electricity, as well as increasing VPP revenue in different markets in different periods. During the period of low electricity price of electricity to gas equipment, it is necessary to convert the surplus electricity into natural gas to reduce the overall gas purchase cost of the system. By recovering its reaction waste heat, part of the working power of the gas-fired boiler is reduced and the gas consumption of the boiler is reduced. And the carbon emissions generated by natural gas combustion in the boiler is effectively reduced. For the increment of alternative gas load, considering the marginal effect, the electricity price and gas price are comprehensively compared, and the electricity load is converted into gas load at the time of high price. At the time of low electricity price, the gas load is converted to the electricity load to realize the space-time transfer between multi-energy loads. The income of VPP is increased in different markets at different time periods and the operation and dispatching costs is reduced. Figure 7-(b) shows that VPP benefits from the trading market by selling excess carbon allowances. Participating in the market for carbon trading, gas turbines and gas boilers will adjust their output through their own carbon trading quotas and actual carbon emission intensity. During the power-to-gas working period, the CO
Four scenarios for VPP construction
Four scenarios for VPP construction
Four distinct VPP operation scenarios have been researched and developed in order to confirm that the research aggregated VPPs have superior economies. And it can deliver more advantages by engaging in the multi collaborative market. For particular cases, see Table 1. The data of the study is from the VPP of the State Power Investment Corporation. Scenario 4 in Table 1 includes all contents of power-to-gas equipment, gas turbines, gas-fired boilers, generalized energy storage, energy market, natural gas market and carbon trading market. Scenario 2 eliminates the content of the power-to-gas equipment, scenario 3 removes the content of the carbon trading market. Scenario 1 removes the contents of power-to-gas equipment and carbon trading market. And scenario 1 is the VPP operation scenario of document [8], scenario 2 is the aggregated VPP operation scenario proposed by the study, scenario 3 is the VPP operation scenario of document [11], and scenario 4 is the VPP operation scenario of document [13].The research takes 24 h as the total electricity duration and 1 h as the step size to conduct experiments, and uses MATLAB for modeling and solution.
The corresponding costs in the four scenarios
MATLAB may be used to determine the optimization outcomes of VPP operation in the multi-collaborative market under four situations, as indicated in Table 2. Table 2 shows that in Scenario 1, the only way to achieve multi-energy time transfer and lower VPP operating costs is by managing electric vehicles and alternative loads in the power market. The advantages of the energy market will rise by $ 116.10 in comparison to Scenario 4. But the benefits of the natural gas market will decline by $296.88. And the overall operating expenses will rise by $ 199.24. In contrast to Scenario 4, Scenario 2 demonstrates that the revenue from the energy market rises by $ 216.18, the revenue from the natural gas market falls by $400.00, the revenue from the carbon trading market falls by $ 36.58, and the final operating cost rises by $ 56.39. The income from the energy market falls by $ 132.71 in Scenario 3 compared to Scenario 1, while the revenue from the natural gas market rises by $ 263.92. However, the total operating cost increased by $ 124.41 when compared to the three markets in Scenario II. The company obtained $ 181.51 in the carbon trading market through the polymerization of electricity to gas equipment. And the final operating cost decreased by $ 180.80, or 7.81%, compared to the three phases of scenario IV. The income of the energy market is the same. The income of the natural gas market increases from
Gas boiler, gas turbine, and carbon trading market allotment output power under various situations.
To confirm the impact of participation in the carbon trading market on the operation of VPP, the output power of gas turbines and gas boilers as well as the sales quotas in the carbon trading market were acquired, as shown in Fig. 8. Scenarios 1 and 2 were chosen for comparison. Figure 8-(a) shows that in Scenario 2, once VPP joins the carbon trading market, the income from carbon trading and the energy market is lower than the cost of gas turbine power generation, and the output of gas turbines stays steady. When power prices were very high, comparing the two scenarios of the gas turbine, the second scenario can obtain more benefits. Figure 8-(b) shows that the power change of the output equipment is consistent with the advantage of the second scenario in the carbon trading market, which is greater than that of the first scenario. The carbon trading quota is enhanced in the 14–20 timeframe.
Selling power under different scenarios.
Changes in VPP carbon emissions and carbon trading under different scenarios.
The power sales outcomes of scenarios 2 and 4 are compared to produce the findings presented in Fig. 9. It serves as confirmation of the impact of integrated p2g devices on the performance of VPP in a multi-cooperative market. Figure 8 demonstrates that following the combination of equipment for power-to-gas, in the period of 1–7 and 23–24, VPP supplies the surplus power to the power-to-gas equipment in the day-ahead dispatch market. And it can obtain benefits in heat-gas-carbon, which is higher than that of the previous Revenue from grid electricity sales. As a result, at this time, Scenario 4’s electricity sold to the grid is less than Scenario 2’s. As a result, the energy market’s income declines.
Figure 10 shows the results of VPP carbon emissions and carbon trading changes in Scenario 2 and Scenario 9. Figure 10 shows that in the carbon trading market, power-to-gas equipment can effectively reduce the actual emissions of VPP through methanation and achieve a more low-carbon energy supply. And the carbon rights trading volume of VPP in the carbon trading market was increased, the income was increased by 25.24%, and the operating cost of VPP was reduced.
Efficiency of p2g operation and daily operating expense of VPP under various carbon trading prices.
The carbon trading price will fluctuate to support the policies of carbon neutrality and carbon peaking, which will have an impact on each VPP piece of equipment’s processing state. Figure 11 shows the changes in p2g operating efficiency and daily operating cost under different carbon trading prices. Figure 11-(a) demonstrates how the power-to-gas equipment will profit more from the carbon trading market as the price of carbon trading rises and how the working power will rise. The power-to-gas equipment’s daily operating pattern is unaffected when the carbon trading price is more than 64.85, and the quality of carbon absorbed remains stable. Figure 11-(b) shows that the trading quota for VPP in the carbon trading market will rise in line with the rise in carbon trading prices, and the power-to-gas machinery will also be upgraded. Therefore, the overall operating cost of VPP increases with the carbon trading price. Growth shows a downward trend. In the period of 1–7 and 23–24, VPP supplies the surplus power to the power-to-gas equipment in the day-ahead dispatching market. And it can obtain income from heat-gas-carbon, which is higher than the income from electricity sales to the grid.
In recent years, the policy of carbon neutrality and carbon peaking has been continuously promoted, and it is very important for industries to realize low-carbon strategies. VPP can effectively promote the synergy of energy sources on both sides of the source and load, and improve the economy and flexibility of energy dispatching. But it is very prone to problems such as unstable energy supply caused by random processing fluctuations of renewable energy. To address the issues mentioned above, research introduces virtual energy storage such as electric vehicles and alternative response loads. At the same time, it cooperates with gas turbines and gas boilers to form VPP, and constructs an operation optimization model based on generalized energy storage NPP under the electric-heat-gas-carbon multi-synergy market. The findings of the experiment demonstrate that when the equipment’s power to produce gas is running in the 0–7 and 23–24 periods. The benefit of VPP’s electricity sales to the grid is the smallest, and the gas turbine processing is maintained at the lowest level. When the market returns for Scenario 4 and Scenario 3 were compared, the returns on the energy market were unchanged, while the returns on the natural gas market increased by USD 32.96, from -USD 7436.60 to -USD 7403.64. Additionally, the company earned USD 181.51 from the carbon trading market by using equipment that converts electricity to gas, and its overall operating costs dropped by USD 180.80, or 7.81%. The power-to-gas technology boosts VPP’s carbon trading volume in the carbon trading market, and the income increases by 25.24% as a result. To sum up, the suggested generalized energy storage-based VPP operation optimization model can strengthen the connection between energy and the electricity-heat-gas-carbon market. The economics of VPP operation is improved effectively, thus achieving the objective of low-carbon environmental preservation. However, the research still needs to be done. The research is mainly based on the optimal overall scheduling, ignoring the distribution of benefits among different stakeholders. In the future, the problem of distribution of benefits among stakeholders under optimal scheduling can be added.
Footnotes
Funding
The work was financially supported by Science and Technology Projects from State Grid Corporation of China, (Research and Application of Key Technologies for Economic Operation of Virtual Power Plant Considering Real-time Carbon Flow, 5108-202218280A-2-383-XG).
