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| Energy storage is helping Zhejiang move towards the "future power grid" |
| Release time:2023-02-14 08:44:44| Viewed： |
The power system is undergoing a very painful transformation process in recent years, and the power grid needs to be "reshaped".
The amount of electricity consumption is often used to measure the level of local economic development. As one of the most dynamic provinces in China's economy, Zhejiang is worthy of the name of "a big province of electricity". However, most of the time, one-third of Zhejiang's electricity needs to be imported from other provinces.
Unlike centralized PV power stations, distributed PV is located on the user side, possibly on the roof of a factory. In the traditional sense, the boundary between power consumption side and power generation side becomes blurred. Distributed power generation is the development trend of new energy, but it will also bring challenges to the grid.
"Many ordinary people do not feel the difficulties faced by the power system. They think that there is no problem if they can light up the lights and use electrical appliances at home. In fact, the power system has been undergoing a very painful transformation process in recent years. The pressure to meet the peak in summer and winter is huge." A person from Zhejiang Power Grid said to the reporter of China News Weekly, Zhejiang power grid is facing the dual challenges of high proportion of foreign power and large-scale grid connection of new energy. The power grid needs to be "reshaped".
How to meet the new energy is not only a challenge faced by Zhejiang Power Grid, but also a problem to be solved by the central government in 2021 to build a new power system. In the middle of 2021, the State Grid Corporation of China issued the Action Plan for Building a New Power System with New Energy as the Main Body (2021-2030), selecting three provinces and three regions to "promote the construction of new power system demonstration areas", including Zhejiang, Qinghai and Fujian.
Compared with Qinghai, a traditional province of clean energy, and Fujian, a province of nuclear power and wind power, how can Zhejiang, a "power province", explore the potential of scattered new energy and ensure the smooth operation of the grid under the double uncertainty of foreign power and new energy? Zhejiang Power Grid hopes to give the answer to the question.
Distributed photovoltaic "start a prairie fire"
In the middle of September 2022, Gao Songjiu, Secretary of the Party Committee of the State Grid Ningbo Beilun District Power Supply Company, was worried about the typhoon that was about to cross the border. On the evening of September 14, the 12th typhoon "Meihua" of this year landed in Zhejiang. It is one of the strongest typhoons that have affected Beilun in Ningbo in the past 50 years.
What worries Gao Songjiu is whether many rooftop photovoltaic systems in Beilun District can survive the extreme weather. Fortunately, they have withstood the test of typhoon in the end.
In the past two years, rooftop PV has expanded rapidly in Beilun District. Tan Zhi is the head of Zhedian (Ningbo Beilun) Smart Energy Service Co., Ltd., a state-owned joint venture whose main businesses include clean energy and smart energy. He told China News Weekly that since 2021, the installed capacity of distributed photovoltaic has increased significantly. "The annual target for the increase in Beilun District is about 65 megawatts. By the beginning of October, the target for this year has been achieved".
"The industry generally believes that the 'high-quality roof' suitable for the development of distributed photovoltaic has several conditions: first, the property right of the roof is clear, second, the cement roof is better than the color steel tile roof, third, the roof is not covered, and in addition, the enterprise should have sufficient absorption capacity." Tan Zhi said frankly, in fact, the remaining "high-quality roof" in Beilun District this year is already rare.
Xusheng Automotive Technology Co., Ltd. is located in Lingfeng Industrial Community. Four of its nine factories have been built and put into production, and one factory is being installed. At present, photovoltaic power generation accounts for about 5% of the total power consumption of enterprises, and may reach about 10% in the next two years. Achieving this goal means that half of the power consumption of enterprises comes from photovoltaic during the period of sufficient sunlight. Gao Songjiu told reporters that this is also the goal of Lingfeng Industrial Community, that is, half of the electricity consumption comes from enterprise distributed photovoltaic and half comes from the large power grid during the peak period. The power consumption of Lingfeng Industrial Community is 500 million kilowatt-hours a year, including many "big energy users". The main direction of the community's construction of new park level power system is green transformation.
In order to meet the requirements of European and American markets for the use of green power, the industrial enterprises in Lingfeng Industrial Community have a rigid demand for green power. At the end of 2020, the first point-to-point green power transaction in the country was initiated in Beilun District. In order to win more export quotas in the European and American markets, the clothing enterprise Shenzhou Group purchased 17 million kilowatt-hours of wind power from the state-owned wind energy to meet its green power demand. In 2021, Zhejiang's green power trading volume will be 300 million kilowatt-hours, of which 5000 kilowatt-hours will be traded in Ningbo.
Beilun District, which is densely populated with industrial enterprises, is the epitome of Zhejiang. Distributed PV installations are growing rapidly in Zhejiang, especially in its industrial parks. Zhejiang is implementing the "scenery doubling" project. During the "Fourteenth Five-Year Plan" period, the new offshore wind power and photovoltaic installed capacity in the province doubled, and the increment was guaranteed to reach 17 million kilowatts. Among them, the new photovoltaic installed capacity is more than 12.45 million kilowatts, striving to reach 15 million kilowatts.
"There are three characteristics of electricity consumption in Jianshan New Area: first, high load density, second, high penetration rate of new energy, many idle roofs of factories are used to develop distributed photovoltaic, and third, the high demand of power quality by high-end enterprises. This is the common feature of electricity consumption in some industrial parks in the future." Xiao Longhai, secretary of the Party Committee of Haining Power Supply Company of the State Grid, told China News Weekly. Jianshan New Area is an industrial park under the jurisdiction of Haining City, Jiaxing City. Standing at the commanding height of the park, you can see the solar panels on the roof of the plant and the fans on the riverside beach.
Xiao Longhai told reporters that the Haining Municipal Government has set up a special photovoltaic team to plan to "fully install" the idle roofs during the "14th Five-Year Plan", with an installed capacity of 1.8 million kilowatts. "Previously, some scholars calculated that to achieve the goal of 'double carbon', China's photovoltaic or other new energy installation needs to reach 1 kilowatt per capita. According to the registered residence population, Haining City has reached 1.11 kilowatts per capita this year, and Jianshan New Area has reached 9.87 kilowatts, more than 40 times the per capita level of Zhejiang."
At present, the installed capacity of Haining PV is 790000 kilowatts, and the annual power generation is about 650 million kilowatt-hours, accounting for about 5%~6% of the city's electricity consumption. The future goal is to reach one third, and Jianshan New Area has reached this goal.
The rapid increase of PV installed capacity is obviously inseparable from the proposal of the "double carbon" goal. Sun Ke, deputy director of the State Grid Zhejiang Electric Power Development Department, told China Newsweek that the essence of achieving the "double carbon" goal is to change the high dependence of mankind on fossil energy. Both globally and nationally, fossil energy still accounts for about 85%. It is not easy to reverse the energy use habits formed by human beings over the past 100 years. The path and means are to promote the use of new energy. Traditional energy such as coal and oil can also be used by burning, while wind and light must be converted into electricity to be used by human beings. The significance of electricity as a medium is self-evident.
However, with the increase of installed capacity of new energy such as scenery, the grid is facing unprecedented challenges.
As night fell, the State Grid Hangzhou Xiaoshan District Power Supply Company supported the Asian Games venues with 100% reliable green electricity to emit brilliant lights | provided by respondents
New energy+"big receiving end", how challenging is Zhejiang Power Grid?
Zhejiang power grid is a typical "big receiving end" power grid, with foreign power accounting for one-third of the total. The foreign power in peak load period is more than 30 million kilowatts, and in low load period is also 10 million kilowatts.
The largest source of power in the province is still coal power generation units. The total installed capacity of coal power generation units and "small thermal power" distributed in various places is about 48 million kilowatts. The installed capacity of natural gas units, nuclear power and hydropower is about 12.65 million kilowatts, 2.8 million kilowatts and 6 million kilowatts respectively.
In addition, it is a new energy based on photovoltaic. When the weather is good, the daily output of photovoltaic can reach 11 million to 12 million kilowatts. Wind power is more unstable, with daily output fluctuating between 4.5 million kilowatts and 2-3 million kilowatts.
Compared with traditional thermal power, nuclear power and hydropower units, new energy such as scenery is more "uncontrollable". "For a complex system such as the power system, only 'controllable' can better manage its economy and security, and the power system also needs to be balanced in real time, that is, 'how much is generated and how much is used'. The biggest challenge brought by new energy power is' relying on the weather '," said Sun Ke.
It is crucial to predict the new energy output of "relying on the weather". Lou Xiansi, the dispatcher of Zhejiang Power Grid, told the reporter that taking photovoltaic as an example, the photovoltaic curve will be predicted every day, and then the start-up mode of thermal power units will be determined. In principle, Zhejiang will be able to access the Internet as much as the photovoltaic and wind power are generated, and will not abandon the light and wind.
Therefore, whether the thermal power unit is started, the starting time, the load rate, etc. shall be determined according to the prediction of the new energy output. The load rate of the coal-fired power unit after starting will be adjusted between 40% and 100%. Once the actual PV output deviates greatly from the forecast, the thermal power unit needs to be replaced urgently, otherwise, it can only purchase external power. However, it will be more difficult to purchase power in case of extreme conditions similar to this summer.
However, it is not easy to predict the PV output. Qian Jianguo, director of the Automation Division of State Grid Zhejiang Power Dispatch Control Center, told China Newsweek that whether and when a cloud appears will affect the photovoltaic output. "If a cloud appears at 8:00 or 9:00 when the PV output is still climbing, the impact will be limited. But if it appears at the peak of the output at noon, the impact will be large. The daily peak of PV output can reach 13 million kilowatts, but if it catches up with rainy days, it can be as low as one or two million kilowatts."
In the case of such large difference between peak and valley output of new energy represented by photovoltaic, the power grid is facing a double test. On the one hand, how to solve the problem of absorption without abandoning light and wind; On the other hand, the wind turbine cannot generate electricity on demand. How to ensure the power demand of users when there is no wind or light.
In a specific period of time, Zhejiang's new energy consumption has faced certain pressure. For example, before and after the Spring Festival, when the load is small and the photovoltaic output is large, it may be necessary to reduce the coal-fired power unit to the lower limit of technical output, or even be forced to shut down, but the adjustable space of the coal-fired power unit below the lower limit of output is very limited. On the same night, with the reduction of PV output, the load rate of coal-fired power units needs to be increased to more than 90%.
"Beilun District is both a big energy consumer and a big power producer. Because of its proximity to the port and convenient coal transportation, Beilun Power Plant was once the largest thermal power plant in China. But with more distributed photovoltaic grid connection, how to balance the relationship between traditional power generation methods and new energy utilization will bring a greater test to the improvement of the regulation capacity of the grid system," Gao Songjiu told reporters.
Even in summer, the daily duration of photovoltaic power generation is less than 8 hours, and the truly efficient duration is about 4 hours. After 16:00 every day, the PV output will drop significantly, but the residential power load will rise again in the evening. How can the resulting load gap be quickly filled? Qian Jianguo believes that in the face of the uncertainty brought by the new energy "relying on the weather" to the power supply side, "thermal power units still need to be 'guaranteed' at present. At present, Zhejiang is carrying out flexibility transformation on thermal power units."
In addition to the uncertainty brought by the new energy power supply, Zhejiang, as the "big receiving end" power grid, has a small adjustable range of external power, and has a large uncertainty when encountering such extreme weather in the summer of 2022. It is obvious that the hydropower in Sichuan, 2000 kilometers away, cannot fully meet the demand and supply of Zhejiang.
"The only uncontrollable factor in the traditional power system is the load. It is impossible to know the time and power consumption of users in advance. Now the power generation side is becoming increasingly uncontrollable. When there are more and more uncontrollable new energy sources, the power system needs to adapt to such uncertainty and complete the balance of the whole system." Sun Ke believes that this is the most critical problem to be solved by the new power system.
The flexibility transformation of thermal power units is to increase the adjustable capacity of the power supply side in the four sides of source, network, load and storage. To enhance the adjustability of the four sides is the goal of the State Grid Zhejiang Electric Power Co., Ltd. in 2020 to build a "diversified and integrated high elastic grid", which is also one of the goals of building a new power system. Now more emphasis is placed on the role of "digital traction", which includes demand-side management of "uncontrollable" loads through digital means.
Re-recognize "power grid digitalization"
Before and after the "National Day" holiday in 2022, Zhejiang ushered in several days of cool weather. But Qian Jianguo told reporters that the supply and demand of electricity are still tight. "This summer, faced with extreme high temperatures, Zhejiang's maximum daily load reached 110 million kilowatts. At the end of September, the maximum daily load dropped to about 70 million kilowatts. However, the thermal generator was operating at full load for a long time in the high temperature environment of 45 ℃ in summer, requiring maintenance to prepare for the peak winter, so the power supply capacity has been reduced in stages."
Extreme high temperature weather, coupled with the reduction of water and electricity transmission in Sichuan due to drought, makes the pressure of "peak shaving" of electricity consumption in Zhejiang this summer obvious.
Xiaoshan District of Hangzhou City is an important industrial town, with a relatively high proportion of energy-consuming enterprises, which can be regarded as the epitome of Zhejiang Province, a "province with a large load". This summer, when the situation of orderly power consumption was the most severe, the instantaneous maximum voltage drop load in a single day reached 1.19 million kilowatts, accounting for half of the total voltage drop limit in Hangzhou, but the daily load in Xiaoshan only accounted for 21% of that in Hangzhou. "In the 19-day period of orderly electricity use this summer, there were three days of such a significant load reduction, which required the participation of more than 4700 enterprises in the region." Xu Weifeng, Executive Director and Secretary of the Party Committee of the State Grid Hangzhou Xiaoshan District Power Supply Company, told China News Weekly.
During the orderly electricity use period, enterprises will be divided into four categories: ABCD, and the electricity demand of Class A enterprises with good benefits needs to be guaranteed. On the contrary, Class D enterprises belong to high energy-consuming enterprises and need to reduce the demand for electricity more significantly.
The relevant person in charge of State Grid Zhejiang Electric Power told the reporter that during peak shaving, the power grid paid more attention to the adjustable load of industrial enterprises. For example, 1000 factories reduced a certain load in a specific period of time, which can greatly relieve the pressure of the power grid at peak hours. The indicators of voltage drop load are generally decomposed layer by layer, from the provincial level to the county level.
For a long time, reducing the load of industrial enterprises during peak shaving mainly depends on the grass-roots staff to communicate in advance by telephone or door-to-door and share tasks with different enterprises based on experience. The person in charge explained, "For example, for a chemical plant, we need to communicate one day in advance, 'Can we shut down for one hour when the load pressure is high tomorrow at noon?' and then confirm when it needs to be shut down the next day. The labor investment is large, the communication cost is high, and the success rate can only be half."
A person from a local power supply company told the reporter, "We can't simply switch on and limit the power of the enterprise directly. When issuing the peak-shaving notice to the enterprise, it also needs to be 'justified and justified'. The enterprise will ask 'why others can use the power but I can't use it'. This actually puts forward high requirements for the accuracy of the peak-shaving scheme."
To realize this idea, based on the information collection of industrial enterprises in the early stage, such as knowing that a factory is not at the peak of production at about 1:00 p.m., such screening can greatly improve the success rate of communication.
Therefore, the digitalization of the power system not only transfers the original offline work to the online, but also includes the depth perception, accurate prediction and closed-loop control of all links of the power system's source network load storage. "From conventional generating units, new energy power stations, to transmission and distribution networks, to industrial enterprises, charging piles and energy storage facilities, it is necessary to continuously improve the monitoring ability, and combine the prediction results to carry out closed-loop control to achieve the dynamic optimization and balance of the power system." Chen Liyue told reporters that Zhejiang Power Grid has a strong perception ability to accurately collect more information at the minimum cost. "In the future, more data acquisition terminals will be installed in industrial enterprises, and even the effect of remote control during peak shaving will be achieved by signing agreements with enterprises."
"At present, the demand-side response of industrial enterprises has been accurate to the different equipment in the production workshop. Previously, we visited enterprises and communicated with them about the equipment that can be 'stopped' in the production process, such as welding, cutting and other production processes." Xu Weifeng told reporters that at present, 2500 industrial enterprises above the designated size in Xiaoshan have been connected to the real-time monitoring system.
In addition to the production power demand of industrial enterprises, the air-conditioning load is another focus of the demand-side response in Zhejiang at present.
Xu Weifeng said that during the orderly electricity use period this summer, the daily air conditioning load of Xiaoshan District was 1.3 million kilowatts, accounting for more than 30%. If the air conditioning load can participate in the demand-side response through temperature control and switching period adjustment, part of the power demand can be compressed to a considerable extent. For example, if the air conditioning temperature in the shopping mall is raised by one degree, customers may not feel it. Another example is that the enterprise's air conditioning can be automatically turned on during the low period of power consumption, and actively adjust the temperature and reduce the load during the peak period of power consumption.
"This not only means energy saving, but also is crucial for power grid regulation." Qian Jianguo told reporters that optimizing the air conditioning load can alleviate the power consumption difficulties at the peak hours in the province to a considerable extent. Such optimization needs to be realized by digital means, such as accurately grasping the load data that can be lowered by increasing the air conditioning temperature by one degree, and finding out the capacity of the "reservoir" can better regulate the peak.
"The digital traction new power system is reflected in demand-side management, which can be understood as the reproduction of physical objects in the digital world, the use of digital twins and artificial intelligence for modeling and calculation, and then feedback to the physical power grid." Qian Jianguo said that digital means can optimize the combination of existing elements, "Compared with a pumped storage power station that may cost billions of yuan, digital means only need tens of millions of yuan to achieve the same peak shaving effect."
Zhejiang Haining Jianshan Industrial Park installed more than 370000 kilowatts of distributed photovoltaic and other new energy capacity, with an annual power generation of nearly 700 million kilowatt-hours | provided by respondents
Zhejiang Road Exploration Makes the Power Grid Smarter
In Sun Ke's view, the ability to build demand-side response by digital means makes the originally uncontrollable demand more orderly, thus enabling users to better participate in peak shaving. "To build a new type of power system, we need to find more adjustable capacities and resources on the four sides of source, network, load and storage, many of which have been neglected before."
The relevant person in charge of the State Grid Lishui Power Supply Company told China News Weekly for example that 80% of the hydropower stations in Lishui are runoff power stations without storage capacity, but usually there are one or several hydropower stations with better storage capacity regulation capacity in the upstream of its water system. When the storage power station is started, the downstream runoff power station can also use the water discharged from the power station to generate electricity. The kinetic energy of each cubic meter of water has been fully utilized in many hydropower stations in the same basin.
In the past, basin dispatching could not accurately grasp the time point of power generation and transmission of each power station. Now, by modeling a hydropower station in a basin, it can accurately grasp the water relationship between power stations, the time difference of power generation and the efficiency of water energy conversion of different units. Through precise calculation, the power generation output of the hydropower group in the basin can reach the goal of grid dispatching with the fastest speed or maximum efficiency at the required time point, It makes its support efficiency to the large power grid reach the highest during peak shaving.
Of course, among the four sides of source, network, load and storage, energy storage is the most intuitive resource and capacity for regulation. From the perspective of power grid, it is more important to coordinate the energy storage at the user side.
"We encourage the user side to invest and build energy storage. At present, the price of valley electricity is only 20 cents per kilowatt hour, while the price of peak electricity can reach 78 cents per kilowatt hour, and the difference between peak and valley electricity prices is enough to ensure the energy storage income. As long as the energy storage is' peak charging and discharging ', it is helping the large grid to adjust." Xiao Longhai said, at the same time, the energy storage built by the enterprise supporting distributed photovoltaic should also be used for grid adjustment, and the energy storage can operate independently when the grid is running smoothly. Once facing the power supply gap, the energy storage operation cannot go its own way, but needs to serve the power grid regulation.
The energy storage facilities on the user side can also serve the power grid regulation, which indicates that the boundary between power generation and consumption is more blurred in the new power system. In the traditional power system, the boundary between power generation and power consumption is clear, but now the boundary between the two is becoming more and more blurred. The load side that originally belongs to power consumption may become the power side because of the addition of distributed photovoltaic, and the trend of the integration of source, grid, load and storage is becoming increasingly obvious. Among the 100 new power system pilot projects built during the "14th Five-Year Plan" period in Zhejiang Province, the number of "integration of source, network, load and storage" projects reached 65.
In fact, on the load side, there are many resources that can be mined. Xiao Longhai gave an example to the reporter. For example, the charging pile originally belongs to the load side, but is currently promoting the V2G mode, that is, new energy vehicles can return power to the grid through the charging pile. "After work in the evening, there will be a large number of new energy vehicles in charge, which is just another peak of the load in the day. At this time, if the grid is facing a supply gap, the charging pile can change from the charging state to the discharging state. The new energy vehicles are equivalent to mobile energy storage devices, which can be guided to discharge at this time through the price mechanism to earn the difference."
With the integration of source, network, load and storage, the role of distribution network is also changed. Compared with the mode of centralized power generation in the traditional power system and transmission by different levels of power grid, the local and local consumption of distributed new energy is the future trend.
"At present, Lishui is usually the receiving end of the power grid in the daytime, and has the ability to transmit electricity when the water and light are strong in the afternoon or when the load is low in the evening of the flood season. In the future, it is hoped that local new energy can be absorbed more locally, otherwise the regional power grid may need to buy a large amount of electricity from the provincial power grid in one day, and also significantly reverse the transmission of electricity in the low load period. One in and one out will cause considerable power loss." The head of the State Grid Lishui Power Supply Company told reporters.
"In the future, the distribution network will gradually become an 'autonomous' unit, which will operate independently under normal conditions. If it encounters problems that cannot be solved, it will seek help from the large power grid. For example, the photovoltaic output in the distribution network is insufficient, and facing the power supply gap, it will need the large power grid to deliver power. On the contrary, if the large power grid needs peak shaving, the distribution network can also fully tap its own resources to assist the large power grid," Xiao Longhai said, The relationship between the distribution network and the large power grid in the future should be "solve your own problems and try not to cause trouble to the large power grid".
"The voltage levels of new energy power stations of different scales are different. If they are small, they will be connected to the distribution network. If they are large, they will be connected to the main power grid. For new energy power stations connected to the main power grid, it is more like throwing a stone into the sea, which will not have an impact. But for new energy power stations connected to the distribution network, it is like throwing a stone into the water basin, which will inevitably cause greater waves and face greater absorption pressure. Therefore, some distribution networks " Sun Ke explained.
A factory at the end of the distribution network can also form its own "microgrid". "If the installed capacity of distributed PV in a certain region is large, and the public grid is difficult to undertake, and the user's power consumption is large and sensitive to price, a micro-grid can be formed, that is, a micro-grid. The public grid and the internal distributed PV together constitute its power supply. When the internal power supply is insufficient, it can purchase power from the public grid, and vice versa, it can also sell power to the public grid," Sun Ke said, Balance is the first principle of power system, and so is microgrid, which requires an energy management system. "Building a micro-grid system also requires cost, and it needs to be economical, applicable and technically feasible. In the future, the public power grid cannot 'cover the whole world', and it may be difficult to meet some differentiated needs. Users can calculate whether it is more cost-effective to purchase power from the public power grid or to build a micro-grid system."
Microgrid can be composed of a factory, an industrial park, or a commercial complex. For example, if an enterprise has a high demand for electric energy and a high proportion of the cost, the construction of microgrid will be more dynamic.
Sun Ke told reporters that at present, micro-grid has appeared in Zhejiang, but the number is not large. In the future, it is necessary to prepare for the joint operation of micro-grid and public grid.
In Sun Ke's view, the network plays the most important role in the integration of source, network, load and storage. "The power system is probably the largest artificial system in the world, unlike the ecosystem, which can adjust itself. The power system depends on the regulation of 'brain' and 'neural network'. The power grid plays the role of 'brain' and 'neural network'. It used to meet the 'uncontrollable' load with the 'controllable' power source. Now it needs to adjust the supply and demand to make it better balanced, which undoubtedly requires the power grid to be more intelligent." |
