1. The Important Characteristics of Energy Internet and the Important Role of Energy Storage
At the same time, energy-related companies are also actively exploring the energy transformation path (Examples of the State Grid Corporation's Global Energy Internet). Although the future energy visions put forward by different agencies are different in spirit, even the interpretation of the same concept will be different (see “Energy Internet Concepts, Key Technologies, and Exploration of Development Models”), but in fact the spirit embodied therein is It is similar in nature and similar to the energy transformation measures in countries such as the United States, Japan, and Germany. The summary of refining includes the following aspects:
In the above six representatives, energy storage technology has its unique role and role. It can be said that energy storage is a pillar technology for the development of the energy Internet. Mainly reflected in the following aspects:
(1) Increasing the proportion of renewable energy can promote sustainable development and reduce the use and pollution of fossil energy. Renewable energy output has a gap, which will produce fluctuations in output over time on different time scales. Energy storage technology can stabilize fluctuations in a short period of time and help the friendly access of renewable energy to the power grid, so as to effectively increase the utilization rate of renewable energy sources, reduce the abandonment of wind, and reduce the use of fossil energy. In the past few years, the environmental pollution is serious, and the discard of renewable energy has received significant attention. Under such circumstances, the effective consumption of renewable energy will gradually become a task that the country pays more attention to. The future of energy storage in this area Will be more.
(2) Increase the proportion of distributed energy sources and change the fully vertical dominating structure of traditional grids. China's traditional power and oil and gas energy systems reflect a completely top-down governance structure with a low share of distributed energy. Under the new situation, such an energy structure is facing obvious problems: the system is more rigid and cannot meet the ever-changing needs of various energy consumers for flexible and even energy production. Duplicated power stations often come from administrative The planning, while the transmission capacity of the power grid is limited, does not adequately consider the system's energy consumption capacity.
Distributed energy construction will be the direction of vigorous development in the next few years. One of the core considerations lies in the fact that the construction of distributed energy sources is often close to the load and can be consumed nearby, with little difficulty in resolving and reducing the long distance of the power grid. Demand for power transmission expansion. In addition, distributed energy can also be constructed according to local conditions, and comprehensive utilization of local natural, architectural and other conditions to achieve optimal allocation of resources (such as roof photovoltaic, etc.), so it is currently the focus of development.
The large-scale access of distributed energy to the power grid involves a number of technological and institutional changes, and energy storage controls the volatility of distributed energy sources and supports distributed energy to form local micro-grids to achieve local self-sufficient autonomy (even within regions. Energy trading, which in turn improves the stability of the entire energy system is very useful. In this regard, a centralized energy storage power station can provide support for the access of distributed energy within the region, and distributed energy storage configured near the user's terminal can also improve the utilization of distributed energy on the spot.
(3) Increase the use of multiple complementary energy sources and increase energy efficiency through the comprehensive utilization and mutual transformation of multiple energy sources. At present, many cities and parks have the comprehensive energy demand for cold-heat-electricity. Many parks' air-conditioning cooling load can account for 30-40% of the total load in summer peak hours. Refrigeration demand creates a great burden for the power grid; and At the same time, many renewable energy output and energy demand can not be completely matched, and often can only be discarded (discarded water in several provinces in the southwest, abandoned in the northwest provinces). If we vigorously develop multi-energy complementary technologies, we can convert various types of energy into each other, integrate multiple energy networks, improve the system's operational stability and comprehensive energy efficiency, and reduce peak loads and waste. For example, the hydrogen production technology can reduce the waste of abandoned wind and light, and the cold storage and heat storage technology can store cold in advance to reduce the peak cooling power load. During this process, energy storage technology can become a hub for the conversion and storage of multiple energy sources. Long-term, high-capacity, low-cost cold storage and heat storage technologies, and the preparation, storage, and efficient use of hydrogen energy are many technologies. The key support technology on the material side in complementary fields.
(4) Increase energy system flexibility. Traditional power grids require that the transmission and distribution power be balanced at the moment and the energy must be available immediately and cannot be stored. This characteristic obviously cannot effectively respond to the future energy transformation trend represented by the energy internet. Therefore, the flexibility of the system needs to be improved. In order to cope with the new characteristics and needs of energy system development in the new situation.
There are many supporting technologies to improve the flexibility of energy systems: for example, the flexibility of coal-fired power plants, the addition of gas turbine flexible units, the development of flexible DC power transmission technologies that support flexible bi-directional flow, and the deployment of energy storage. Many energy storage technologies have a series of advantages such as fast response and accurate output, which can provide the system with two-way adjustment of positive and negative power, and have a good prospect in increasing the flexibility of the power system. Therefore, the role of energy storage in the power system is not limited to cutting peaks and fill valleys. Providing various comprehensive ancillary services for the system can better leverage its strengths, and it is easier to obtain economic benefits. The US PJM market and the European electricity auxiliary service market have There are considerable examples of energy storage providing comprehensive ancillary services, demonstrating the technical and commercial feasibility of energy storage in providing ancillary services and increasing the flexibility of energy systems.
(5) Promote the integration of energy and information, rely on the support of informatization to assist in the optimization of energy allocation. The transmission and distribution links of traditional energy systems show a high degree of centralized management and rigidity. Under the new situation, the interaction requirements of multiple services in the energy system can widely collect information from all parties involved in the system interaction, refer to the experience of “Internet Plus” reform in other fields, and rely on information to guide and assist in the optimal allocation of energy. In this regard, the energy-storage operation information data can access the energy information network to provide important energy-consumption information for the system. At the same time, the energy storage system can also accept the unified deployment of the cloud monitoring system of the next-generation energy network, and even more functions can be achieved based on the aggregation of distributed resources, such as virtual power plant (VPP) services.
(6) Promote the marketization of energy, restore its product attributes, rely on market forces to assist the optimal operation of the energy system, balance energy supply and demand, and stimulate the vitality of driving economic growth. Electricity can traditionally be stored out of the box, which greatly limits the types of available energy for energy trading in the electricity market. Adding energy storage can make electrical energy can be stored and used at a later time or even place. It will be of vital support to the diversification of electricity market services and commodities. In addition, the energy Internet involves the joint utilization and integration of multiple energy sources. Technologies based on the conversion and storage of different types of energy can also promote the optimal allocation of energy types and time periods, and reduce the waste of energy through conversion and storage. , And when the market needs it, participate in market interactions again to gain profits. In general, the energy internet requires various kinds of energy services, and the storage and conversion characteristics of energy storage can effectively support the provision of corresponding service types at the required time and place, which has a good application prospect.
2. Application Prospects of Several Key Energy Storage Technologies in the Energy Internet
There are many kinds of energy storage technologies. In this article, we will focus on technologies that already have a certain degree of maturity, and analyze their technological development direction and application prospects in the energy Internet. The author has summarized and summarized the core indicators that need attention in the application of several energy storage technologies in the field of energy internet, as shown in the following table, and will introduce each technology separately:
(1) Lithium-ion battery
Among the many energy storage technologies, the outstanding advantages of lithium-ion batteries are their relatively high energy density and power density, and their versatility in supporting the use of renewable energy and providing the flexibility required by the system. Lithium-ion batteries currently have examples of medium-to-large-scale (MW-level) power station applications, but in comparison, because of their high energy density and small footprint, they may have advantages in small- and medium-scale energy storage and distributed applications. . In addition, the strong power ramping characteristics of lithium-ion batteries make them have a good comprehensive effect in auxiliary services such as FM, and extensive participation in ancillary services is an important development direction, and it is very likely that they will be the first to implement business models and achieve a good economy. benefit.
In this regard, the urgent need for the development of lithium-ion batteries is to further reduce the cost and increase the lifespan so as to improve the economical efficiency of the technology. In addition, the decommissioning of a large number of upcoming power batteries will also bring opportunities and challenges for energy storage, improve battery quality, develop IoT technology to track battery usage history, develop standardized modules to reduce the difficulty of using ladders, and develop park-battery enterprises. - The model of quadrilateral cooperation for electric vehicles and energy service companies, development of fragmented energy management technologies, etc. may be the main solution to solve battery cascade utilization.
(2) Sodium-sulfur battery
The sodium-sulfur battery technology has a high proportion of installed capacity in the world, but its growth has been slightly weak in recent years. Part of the reason for this phenomenon is that the sodium-sulfur battery technology has a high degree of monopoly and is mainly controlled by the Japanese NGK. This technology is mainly suitable for MW-class energy storage. There are many examples of applications for grid connection in the renewable energy generation side. However, this technology occupies a large area, has a high operating temperature, and has a certain degree of danger. It is intrinsically not suitable for small-scale distribution. Power consumption and user-side requirements. Therefore, for the construction of medium-scale energy storage power stations, providing comprehensive service support for the energy system, this type of technology has a good application prospects.
(3) Lead-acid battery
Lead-acid batteries are veterans in the field of electrochemical energy storage. Their low cost and high cost have always been an important pillar of energy storage, but they have only been surpassed by lithium-ion batteries in recent years. Lead-acid batteries have a lower energy and bulk density than lithium-ion batteries, so the user-side end that places the most weight on space and load-bearing conditions is not as good as lithium-ion batteries, but in larger-scale applications (around MW) and conditional maintenance. Next, its price will be higher.
The main direction of the development of this type of technology is further based on the lead-carbon battery technology, to increase its life and available energy part (supporting deep discharge) to reduce the actual battery usage. In addition, further standardizing the recycling of lead-acid batteries and reducing the pollution brought about by the non-standard small workshops in the recycling process are of great significance to the whole society.
(4) Vanadium flow battery
The vanadium flow battery has a low volume energy density, and the energy conversion efficiency is about 70%. However, deep discharge is supported, safety is good, capacity and power can be separately designed, the cycle life is long, the battery recovery is relatively simple, and in recent years, The maturity of the industry chain is expected to be further explored. Domestically, excellent companies such as Dalian Finance and Beijing Puengeng have emerged. Therefore, this type of technology is applicable to medium and large-scale (MW-level) applications, whether as an independent power station or not. It is a good application prospect for the grid to provide comprehensive services, or to provide smooth and consumer services at large-scale new energy power stations.
The main development direction of this type of technology is to further improve the industrial chain, reduce costs, and improve system efficiency. In addition, the development of a new generation of flow battery technology (such as zinc bromide, organic systems, etc.) is also very meaningful for expanding the adaptation surface of this type of technology and improving the overall level of technology.
Flywheel energy storage technology has a fast response rate capability, compared with the battery energy storage technology to adapt to the instantaneous power fluctuations of the power system is more powerful, in the smooth instability output curve to provide a short-term frequency modulation in terms of its performance is very good competition force. However, the problem is that the energy density is very low and the degree of self-discharge is very high. Therefore, it cannot be adapted to any occasion where the energy volume is slightly larger. This type of technology is mainly suitable for coordinating with energy-based energy storage devices to suppress fluctuations, extend the life of their applications, or be used directly for power generation-side frequency modulation requirements and smooth output of renewable energy sources. The main development direction of this kind of technology lies in the development of high-performance composite materials to further improve the cost-effectiveness of such technologies.
The external characteristics of the supercapacitor are similar to those of the flywheel. They are mainly suitable for fast power response, but have low energy density and high self-discharge. Theoretically speaking, although the energy density of supercapacitor technology may be further increased, it is difficult to achieve the level of lithium-ion batteries, so it is still more suitable for short-term rapid charge and discharge occasions, so it can be used in conjunction with the battery, FM With respect to output power smoothness. In addition, with the development of the Internet of Energy, local mini-energy internet parks have to be built in many areas. In many cases, there are requirements for the instantaneous absorption and release of large amounts of energy. In this case, supercapacitors can be used to provide systems in a short time. Providing an energy cache (Cache) can effectively reduce the negative impact caused by large instantaneous loads and meet the requirements more than batteries.
(7) Compressed air
Compressed air energy storage technology has been continuously improving in recent years. The team of Tsinghua University and the Institute of Engineering Thermophysics of Chinese Academy of Sciences has made a lot of research and application progress in this area. The technology often needs to rely on geographical conditions (such as caves, etc.), and is more suitable for medium and large-scale applications. In order to obtain good overall energy efficiency, it needs to provide triple supply of cold, heat, and electricity. The main limitation of this technology is that if the triple energy efficiency is not carried out, and the response speed is slow, it is not suitable for drastic changes in power. Taking into account the above characteristics, this type of energy storage technology is particularly suitable for providing stable energy storage and supply services in geographically located areas where renewable energy supplies are abundant and where there is a demand for comprehensive applications of cold, heat, and electricity.
(8) Heat storage and cooling, heat and electricity triple supply technology
As the development of energy systems deepens, the boundaries of cold-hot-electric-gas networks will gradually open up and the various energy networks will merge. In fact, the energy demand for winter heating and summer cooling has always been outstanding in our country. The triple supply technology of cold, heat, and electricity can be used in conjunction with fuel cells and compressed air energy storage technologies, significantly increasing the overall energy efficiency of these types of technologies and ultimately improving Economic benefits. The use of heat storage technology to meet part of the demand for cooling and heating can significantly reduce the burden on the power grid and peak power consumption, and “release” the traditional operation of many power grids (such as the use of combined heat and power in the north for winter The large amount of wind generated due to the minimum power generated during heating provides a new solution to the optimal operation of the energy system. The outstanding advantages of heat storage technology are: 1) The cost of energy storage based on calorific value is much lower than that of electrochemical energy storage technology, 2) It is hopeful to support long-term (even cross-seasonal) energy storage, and thus in heat storage and multi-energy There will be great development in the future integration of complementary energy system architectures.
(9) Hydrogen Correlation and Fuel Cell Related Technologies
Hydrogen and fuel cell related technologies are hailed as a possible final solution for human energy, mainly because: 1) Fuel cell systems can achieve relatively high specific energy output, which can be achieved under the scenario of combined cooling, heating and power. High integrated energy efficiency and emission only water; 2) Hydrogen production from electrolyzed water can couple electricity and gas networks to provide a scheme for reserving power; 3) Fuel cell applications can be linked to transportation networks (fuel cell vehicles) , hot and cold network (triple supply), power grid and gas network (hydrogen surplus, battery power generation).
It can be seen that this type of technology can serve as a communication bridge between the several core energy use areas. Once the technology is mature, it can provide universal technical solutions. It is also a distributed technology (PEMFC) or a large-scale energy storage and application (SOFC).
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