The development level of renewable energy determines the success or failure of the construction of the Energy Internet. As countries pay more attention to the R&D and application of energy storage technology, significant progress has been made in related core supporting technologies.

　　Polaris Smart Grid Online News: The development level of renewable energy determines the success or failure of the construction of the Energy Internet. As countries pay more attention to the R&D and application of energy storage technology, significant progress has been made in related core supporting technologies. Compressed air energy storage technology, flow batteries, lithium-sulfur batteries and other technologies have moved toward industrialization or close to industrialization; hydrogen fuel cells, as the mainstream direction of fuel cells, have gradually expanded their application scale; heat storage technology has developed rapidly, and the market needs to pay more attention to it. Driven by the rapid development of the renewable energy industry, the electric vehicle industry, and the energy Internet industry, the energy storage industry is expected to show explosive growth; as the cost of renewable energy power storage continues to decrease, the scale of energy storage system application and technology costs will enter A new stage of virtuous cycle development; electric vehicle battery technology is expected to usher in a major breakthrough, and the market prospect is broad.

　　In recent years, the problem of climate change has become increasingly prominent, and it has risen from a simple environmental protection problem to a problem of human survival and development. The main cause of climate and environmental degradation is the carbon emissions of fossil energy consumption. It has become an important global consensus to promote the transformation of the energy consumption structure to a low-carbon and clean direction. Large-scale development of renewable energy is the key to the energy transition. To this end, 173 countries have formulated renewable energy development goals, and 146 countries have introduced supporting policies. In the past two years, despite being adversely affected by the global decline in fossil fuel prices, investment in the renewable energy industry has not been disrupted by this, and reached a new high in 2015.

　　In order to reduce dependence on fossil energy and promote global energy security, President Xi Jinping put forward an initiative at the United Nations Development Summit on September 26, 2015: to build a global energy Internet and promote a clean and green way to meet global energy demand. Energy Internet is mainly through the interconnection of large-scale power grids, which frees energy development from resource, time and space and environmental constraints, and promotes renewable energy such as solar, wind, and hydropower to gradually become dominant energy sources. Energy Internet has gained recognition and positive responses from more and more countries.

　　The key to the energy transition and the global energy Internet lies in the large-scale development of renewable energy, and the global renewable energy resources are very abundant, especially solar and wind energy. Authoritative data show that if one can obtain one-sixth of the energy radiated by the sun or one-fifth of the energy of wind energy, it can meet the energy needed by the current global economy.

　　1 The status and role of energy storage technology in the energy transition and energy Internet

　　Despite the huge development potential of renewable energy, its instability has restricted large-scale development, and this has led to a wave of abandonment of wind and light. Energy storage is a necessary condition for effectively adjusting the grid voltage, frequency and phase changes caused by renewable energy power generation, and promoting large-scale power generation of renewable energy sources and integrating them into the conventional power grid.

　　The essence of the Global Energy Internet is "smart grid + UHV grid + clean energy". Smart grid is the foundation, UHV grid is the key, clean energy is the foundation, and large-scale energy storage system is a key part of the construction of smart grid. To some extent, the degree of application of energy storage technology not only determines the level of renewable energy development, but also determines the success or failure of the energy Internet. Western countries have begun to attach importance to the R&D and industrialization of energy storage technology 10 years ago. The U.S. government uses its Advanced Research Projects Agency (DARPA) as a model to establish the Advanced Research Projects Agency-Energy (ARPA-E) to gather the nation’s best scientists, engineers, and entrepreneurs on renewable energy technologies. Research, and energy storage technology is its top priority. Germany's energy transition has attracted the attention of the world. The proportion of renewable energy in Germany's electricity sources has increased from 6% in 2000 to 30% in 2015, and this proportion will even reach 70% to 90% in some periods. The country’s energy transition attaches great importance to energy storage technology. In addition to funding related technology research and development, the government establishes a 50 million euro subsidy every year to help residents purchase energy storage systems. 1/3 of the German photovoltaic power generation comes from residents.

　　my country's energy storage industry has just started, and the relevant state departments have recently announced a series of documents supporting the energy storage industry. The National Development and Reform Commission and the Energy Administration issued the "Energy Technology Revolution and Innovation Action Plan (2016-2030)" in March 2016, which clearly pointed out in the "Advanced Energy Storage Technology Innovation" one of the 15 key tasks of the document: Renewable energy grid-connected, distributed and micro-grid, electric vehicle energy storage technology, master the key core technologies of each link of energy storage technology, complete demonstration and verification, and the overall technology has reached the international leading level, leading the development of energy storage technology and industry.

　　International oil companies have begun to deploy in the field of energy storage. For example, Total has acquired battery manufacturer SAFT at a high price, ExxonMobil and FuelCellEnergy are cooperating to develop fuel cell technology, and Statoil will invest in offshore wind farms and related energy storage technologies. .

　　2 Overview and progress of energy storage technology application

　　Energy storage technology includes three major categories: physical energy storage, electrochemical energy storage, and battery energy storage, as well as five major application fields: power generation and auxiliary services, renewable energy grid connection, user side, power transmission and distribution, and electric vehicles.　　 As of the end of 2015, there were 327 energy storage projects (excluding pumped storage, compressed air and heat storage) in operation worldwide, the installed capacity increased from 50MW in 2005 to 950MW in 2015, and 180 projects were planned and under construction.

　　From the perspective of the distribution of various technologies, lithium-ion batteries have been applied in various fields. Sodium-sulfur batteries have the largest application ratio in power transmission and distribution and renewable energy grid-connected. Flywheel energy storage is used in auxiliary services (frequency modulation). Certain application advantages, flow batteries are mainly used in the field of renewable energy (renewable energy grid-connected, distributed micro-grid), and lead-acid batteries have a relatively large application in distributed micro-grids. The current application of energy storage technology is as follows.

　　2.1 Compressed air energy storage technology is moving towards industrialization

　　As the current energy storage technology with the largest capacity and the most mature technology in addition to pumped water storage, compressed air energy storage technology has attracted the attention of the industry. Internationally, a breakthrough has been made in near-isothermal compressed air energy storage technology, and small air compression vehicles are in a small-scale trial stage. . The Institute of Engineering Thermophysics of the Academy has successfully developed the first domestic 1.5MW supercritical compressed air energy storage system with independent intellectual property rights, which is more than 10% more efficient than traditional compressed air energy storage systems. It is a grid-level energy storage application in my country. Opened up room for development.

　　2.2 Significant progress has been made in flow battery technology

　　All vanadium redox flow batteries have made significant progress in key materials, stacks, battery system design and integration, and the industrial chain has been gradually improved. The overall industry has entered the initial stage of marketization, and it has been gradually developed in Japan, Canada, the United States, Australia and other countries. Start to replace lead-acid batteries. In addition, the flow battery technology has been expanded from all vanadium and zinc bromide systems to organic systems and water-soluble systems with lower cost and higher energy density. The research has demonstrated for the first time a new type of lithium iodide-sulfur (carbon) semi-solid-liquid two-phase composite. The feasibility of flow batteries can greatly improve battery capacity, safety and service life. Harvard University Brian Huskinson has developed a metal-free flow battery based on an organic molecule-benzoquinone, and has completed 100 charge and discharge cycles of the p-quinone-based battery. The cost can be reduced to 27 US dollars/(kW˙h), almost It is 1/3 of vanadium batteries, showing good economic and commercial prospects. The flow battery concept car has come out, with a maximum speed of over 300km/h and a cruising range of over 800km.

　　2.3 Lithium-ion batteries are still a hot research topic in the current energy storage field

　　Electric vehicles have become an important factor driving the research and development of lithium-ion battery technology. Currently, for lithium batteries, positive electrode materials lithium iron phosphate and nickel cobalt manganese ternary materials are the research focus, negative electrode materials nano-silicon and graphene are research hotspots, and there are more and more types of positive and negative materials, and the application range is wider and wider. As the current mainstream battery for electric vehicles, lithium-ion batteries have yet to improve their energy density. At present, the maximum energy density of electric vehicle batteries is about 170W˙h/kg, and the cruising range can reach up to 400km. Household lithium battery energy storage systems have been commercialized.

　　2.4 Lithium-sulfur battery is currently the closest industrialized high-energy density battery

　　The theoretical energy density of lithium-sulfur batteries exceeds 2700W˙h/kg, and the actual energy density can reach 400～600W˙h/kg. At present, the energy density of lithium-sulfur batteries that have reached the commercial level abroad has reached 300W˙h/kg. my country has developed a lithium-sulfur secondary battery with an energy density higher than 600W˙h/kg, which is at the international advanced level. High-energy density batteries such as lithium-air batteries, aluminum-air batteries, and magnesium batteries have become the focus of current research.

　　The application scale of 2.5 hydrogen fuel cells is gradually expanding

　　Hydrogen fuel cell is still the mainstream direction of fuel cell development. The related technology has basically reached the requirements of industrialization, and it has been applied to trains, passenger cars, bicycles, forklifts, small helicopters and other vehicles on a small scale. The passenger car has a cruising range of 500-700km, and the energy consumption of 100km is only equivalent to 3.3L of gasoline. At present, the cost of using fossil fuels to upgrade hydrogen production in some countries is roughly the same as that of gasoline. Renewable energy hydrogen production, biological hydrogen production and normal temperature and pressure land hydrogen transmission have become the research focus.

　　2.6 The heat storage market is receiving increasing attention

　　At present, heat storage technology is developing rapidly. Some thermal energy storage technologies are already very mature, especially sensible heat storage, but the market size is still small, mainly due to the high cost of thermal energy storage and the lack of sufficient attention to thermal energy storage by the society. It is estimated that the heat storage system can save 30% to 40% of the global energy. The industry is studying the use of heat storage batteries to absorb heat in the car or capture solar heat, convert heat energy into electricity, provide heating and cooling for the compartment, and reduce the cost of electric car batteries. It is expected to increase car battery life by more than 40%.

　　3 Energy storage industry and technology outlook

　　3.1 The installed capacity of solar and wind power generation is growing rapidly, and the cost of power generation continues to fall

　　According to statistics of the installed capacity of solar and wind energy in the past 20 years, the installed capacity of solar energy has doubled every two years, and the installed capacity of wind energy has doubled every 4 years. The global installed capacity of solar energy has increased from 5.1GW in 2005 to 227GW in 2015. Wind energy installed capacity From 59GW in 2005 to 433GW in 2015. It is estimated that the installed solar power capacity will reach 1500GW and 2400GW in 2025 and 2030 respectively, and the installed wind power capacity will reach 1200GW and 2000GW respectively in the same period. Energy storage technology, as a key technology to support the grid connection of renewable energy, has a huge market potential.

　　The price of crystalline silicon photovoltaic cells has continued to decrease, and the price has dropped sharply from US$76 in 1977 to US$0.3 in 2015. The cost of solar and wind power generation has dropped by 50% to 60% in the past five years. At present, solar photovoltaic power generation and onshore wind power have become competitive in some countries. According to current development trends, wind power and photovoltaic power generation are expected to become the cheapest power generation methods in many countries by 2025.

　　3.2 Household energy storage will show a rapid growth trend

　　In the past five years, household energy storage has developed rapidly in Germany, the United States, Australia, Japan and other countries. According to the latest data released by HIS and REN, the global installed capacity of household photovoltaic power generation battery energy storage is expected to reach 1,000MW in 2020. After 2020, Energy storage systems will become an indispensable part of power production and operation, while the growth rate of energy storage in industry, commerce, and especially residential households will be significantly higher than that of grid energy storage. The application of energy storage technology is expected to enter a period of large-scale development in 2025.

　　3.3 Battery technology is expected to make major breakthroughs in the next 10 years. At present, the energy density of electric vehicle batteries ranges from 80 to 180W˙h/kg. From the current battery R&D progress, industrial investment, and related support policies, battery technology is expected in the next 10 years. A major breakthrough has been made, and the energy density is expected to reach 300-350W˙h/kg, which will enable the electric vehicle's cruising range to reach 600-800km.