Energy storage technology value assessment highlights rigid expectations

For a long time, the power industry has always had a rigid expectation for energy storage technology. Humans have been exploring how to use energy storage technology to make the rigid power system with real-time balance of power generation, transmission, distribution and use more flexible, and ultimately change the basic form and function of the power system.

Large-capacity energy storage technology has taken off

For a long time in the past, the application technology of energy storage in power systems was mainly pumped storage, and its application areas were mainly in the peak-to-valley shifting and frequency regulation auxiliary services of power grids. In recent years, with the development of new energy power generation technology, the scale of access to the power grid of fluctuating power sources such as wind power and photovoltaic power generation has continued to expand, and the scale of distributed power sources in distribution networks has expanded, and the application technology and application areas of energy storage in power systems have undergone great changes. From the perspective of application technology, battery energy storage technology with an integrated power of megawatts suitable for power grids has emerged; from the perspective of application areas, the application of energy storage technology in power systems has expanded from the power grid to the power generation side and the user side, and from peak-to-valley shifting and frequency regulation auxiliary services to new energy grid connection, power transmission and distribution, distributed generation and microgrids.

There is no clear definition of advanced large-capacity energy storage technology suitable for power grids (since pumped storage technology is fully mature and has been maturely applied in power grids, it is not a research object). Considering the needs of the development of a high proportion of new energy power systems in the future, the needs of energy storage in the fields of new energy grid connection, peak shifting and valley filling, frequency regulation auxiliary services, delayed investment in transmission and distribution equipment, distributed generation and microgrids are considered from four dimensions: integrated power level, potential for technological progress, energy conversion efficiency, and power/energy cost. At present, compressed air energy storage, lead-acid batteries, lithium-ion batteries, flow batteries, flywheel energy storage, supercapacitors, and superconducting energy storage are in the demonstration or commercial application stage, with energy conversion efficiencies exceeding 60%, and have megawatt-level application conditions, which can be used as representatives of advanced large-capacity energy storage technologies.

According to statistics, by the end of 2016, the global total electrochemical energy storage capacity was 1.77 GW, of which lithium-ion batteries accounted for 65%; compressed air energy storage was about 1.5 GW. China's total electrochemical energy storage capacity was 243 MW, of which lithium-ion batteries accounted for 59%; compressed air energy storage was about 10 MW.

In 2016, in the international energy storage application market, grid-connected wind power and other new energy sources accounted for about 43%, frequency regulation and auxiliary services accounted for about 24%, power transmission and distribution accounted for 19%, and distributed generation and microgrids accounted for about 13%. In my country's energy storage application market, distributed generation and microgrids accounted for about 56%, grid-connected new energy applications accounted for about 35%, frequency regulation and auxiliary services accounted for about 2%, and others accounted for about 7%. The application of new energy grid-connected, distributed generation and microgrids accounts for about 90% of my country's energy storage application market share.

Energy storage application value assessment in three areas

(I) Grid side

Peak shifting and valley filling: Energy storage systems can store electricity as a load during low-consumption periods and release electricity as a power source during peak-consumption periods, thereby reducing the peak-to-valley difference in loads and improving system efficiency and the utilization of power transmission and distribution equipment. Peak shifting and valley filling requires relatively high energy and power from the energy storage system. Currently, except for pumped-storage power stations, other energy storage technologies do not have the ability to shift peaks and valleys.

Frequency regulation auxiliary services: Energy storage systems have fast power response and precise power control capabilities in seconds or even milliseconds, and have obvious advantages in grid frequency regulation applications. Especially for future power systems with a high proportion of new energy access, as the proportion of traditional power sources in the system decreases, the total rotational inertia of the system decreases, causing system frequency stability risks. Energy storage may have irreplaceable value in the field of grid frequency regulation. In a high-proportion new energy power system, the frequency regulation value of energy storage is mainly reflected in improving transient frequency characteristics and improving primary and secondary frequency regulation of the grid. Preliminary research by the State Grid Energy Research Institute shows that the frequency regulation value of energy storage can only be reflected when the proportion of fluctuating power sources such as wind power in the system exceeds 30%. The calculation results of a typical system show that the capacity ratio that needs to be configured with energy storage is about 0.2%.

Reduce investment in grid transformation and delay the construction of transmission and distribution networks: The energy storage system has the ability to regulate active power in both directions and reactive power in four quadrants, which can effectively alleviate the problems of node voltage increase and equipment overload after distributed photovoltaic access. When the voltage exceeds the limit or the current is overloaded, the energy storage system can store part of the distributed photovoltaic power, especially the power at the peak output time, to reduce the negative impact of the reverse flow of the distribution network on the increase of grid voltage and the risk of current overload, thereby reducing the demand for grid transformation and power restrictions caused by peak output. At the same time, in most cases, it is conducive to reducing the loss of distribution network. Energy storage access to the distribution network with high penetration of distributed power sources can effectively reduce the cost of grid transformation and power restriction losses. The calculation results of typical cases show that by optimizing the configuration of energy storage capacity, the cost of grid transformation and power restriction losses can be reduced by 20%.

(II) Power generation side

New energy grid connection: The application of energy storage in the grid connection of new energy such as wind power and photovoltaic power generation is mainly focused on increasing the output regulation capability of fluctuating power sources, tracking planned output, and smoothing wind power output. At present, energy storage battery technology is mainly used in the grid connection of new energy to improve the control characteristics of wind farms and photovoltaic power stations. There are more than 10 wind farm energy storage projects in operation around the world, with an installed capacity of more than 500,000 kilowatts.

Improve the frequency response characteristics of conventional power sources: Improve the frequency response characteristics of conventional power sources by operating in conjunction with existing power plants. The value of energy storage mainly includes: primary frequency regulation assessment income, AGC regulation assessment income, and AGC regulation compensation income. The 2MW lithium-ion battery energy storage system of the former Beijing Shijingshan Thermal Power Plant is the first megawatt-level energy storage system demonstration project in China with the main purpose of providing frequency regulation services. The "joint frequency regulation" operation mode of the project has economic benefits.

(III) User side

Distributed generation and microgrids: At present, the main application mode of energy storage system on the user side is the joint operation of distributed power supply and energy storage, or microgrid form. Energy storage is the key supporting technology for distributed generation and microgrids, and its value is mainly reflected in stabilizing system output, backup power supply, and achieving dispatchability.

Huge potential for future development and application

With the development of energy storage technology and the further improvement of its economic characteristics, energy storage has great potential for application in modern power grids with a high proportion of new energy access in the future. The application prospects of energy storage in power systems are predicted as follows:

2017-2020: During the 13th Five-Year Plan period, advanced large-capacity energy storage technology will be mainly applied in demonstration, and will move from demonstration to commercialization, exploring the establishment of a mature business model. The key application areas are distributed power generation and microgrids, frequency regulation auxiliary services, and new energy grid connection, and the application scenarios are mainly concentrated on the distribution network and power supply side. It is expected that the scale of my country's energy storage market will reach 15 GW in 2020, of which distributed power generation and microgrids, frequency regulation auxiliary services, and new energy grid connection will account for 50%, 20%, and 20% respectively.