Regardless of the form of energy storage, the role of energy storage in the application of power grids (generating, transmission, distribution, and use) is basically the same, and it is an effective means to improve the reliability and resilience of power grids. The application of energy storage in the power grid first began in the early 20th century, and has a history of more than 100 years. The most traditional and the largest application of energy storage is pumped storage, which is currently developing towards the electrochemical distributed energy storage mode.
The role of energy storage devices in smart grid
Driven by related industries such as electric vehicles, the scale of the lithium battery industry has expanded rapidly and prices have fallen rapidly, and the application of lithium batteries as a distributed energy storage system has gradually increased. By the end of 2020, the cumulative scale of electrochemical energy storage projects in operation in China was 1,072.7MW, of which lithium battery energy storage projects accounted for about 60%.
Under the development background aiming at building a flexible smart grid, from the perspectives of improving grid resilience, adjustability, flexibility, intelligence, independence, and reducing coupling, energy storage is an effective means of any application. one. From the current energy storage components, lithium batteries are a more suitable choice, especially for user-side energy storage, the advantages of lithium batteries as energy storage components such as high energy density and long life are gradually emerging. However, the current growth of lithium battery energy storage applications on the user side is slow, and breakthroughs are still needed in terms of economy, safety, and applicability of the energy storage system itself.Also read：oem lifepo4 10kwh
- Can lithium batteries save money?
At present, the lithium battery energy storage on the user side does not have much other benefits except peak-shaving and valley-filling to earn the price difference between peaks and valleys, and there is a single way of economic return. The economy of peak-shaving and valley-filling is more dependent on the regional peak-valley electricity price, which shows the distribution area of the domestic peak-valley price difference. From the survey point of view, the peak-valley price difference in Beijing is the largest, exceeding 1 yuan, so the application of energy storage in peak-valley arbitrage is the most advantageous. Next are Tianjin, Shanghai, Jiangsu and Guangdong. In general, first-tier cities and coastal provinces are more active in implementing peak-valley electricity prices, so user-side energy storage will have better economics.
Shown is the peak-shaving and valley-filling yield of energy storage projects (the abscissa is the kWh investment cost, the ordinate is the full-life cycle yield, and the curves in different colors represent the change in the peak-valley price difference). The lithium battery model takes into account the charge-discharge efficiency, depth, and capacity decline. According to the number of 4500 cycles, plus the number of 1500-2000 echelon utilization cycles, 20% of the residual value is considered in the calculation. It can be seen from this that even with this ideal algorithm, the yield is not very impressive (only when the peak-to-valley price difference reaches 0.7 yuan, does the yield appear). In addition, the quality of lithium batteries in the energy storage industry is uneven, and it is difficult for owners and integrators to make an intuitive judgment on battery performance. The cycle times of lithium batteries on the market are in the range of 3,000 to 6,000 times (even if the manufacturer promises a higher cycle number, if it is only used for peak shaving and valley filling, the cycle life of the battery may not be reached, and the calendar life has already arrived. reduce battery usage efficiency), and there is still a big doubt about whether the actual operation is true. All of these increase investors' doubts about the economics of lithium battery energy storage projects, and increase the difficulty of lithium battery energy storage on the user side.
- Will lithium batteries be safer?
Lithium battery is an energy body, which is characterized by high energy density, so it has its own safety risks. The higher the energy density, the greater the safety risk. At present, the domestic lithium battery energy storage industry basically excludes ternary batteries, and it is also reasonable to think that lithium iron phosphate batteries are more suitable (the energy density of ternary batteries is higher than that of lithium iron phosphate batteries, and the safety risk of ternary batteries is also greater than that of lithium iron phosphate batteries) .Also read：Custom Lithium Ion Battery
It is necessary to improve the quality of lithium batteries and reduce the risk of battery runaway. At present, the safety of lithium battery energy storage is more concentrated on the lithium battery itself, but the energy storage system is not only lithium battery, but also other system equipment, protection equipment, etc., its safety issues are also worth noting. At present, more owners and integrators will mainly focus on the battery itself, but ignore the peripheral equipment and system integration design. For example, the investigation results of an energy storage accident in Shanxi show that the cause of the accident was the continuous discharge of the top of the fixing bolt to the casing, not the battery itself. South Korea summarizes the causes of 23 energy storage system accidents into four aspects: poor electric shock protection system, poor management of operation and operating environment, negligence in installation, and poor management of integrated control and protection system (see Polaris Energy Storage Network - battery is not the fault! For energy storage The cause of the power plant accident, South Korea proposed four major improvement measures). All of these show that, in addition to choosing high-quality lithium batteries, the safety of the energy storage system still has a certain probability of hidden dangers, which needs to be guaranteed by a more complete and systematic system integration design.
- Whether the lithium battery is applicable
First of all, from the perspective of attributes, the current application of energy storage systems in the power grid is more defined as a production unit. For user-side energy storage, its characteristics are closely related to user-side operation behavior, showing the characteristics of many points, wide area, large amount, and dispersion. It is a user-side device that can participate in adjustment. If it is only defined as a production unit, then its application constraints will be many.
At present, specifications for the construction, operation, and maintenance of lithium-ion battery energy storage systems have been established. For example, the national standard "GB51048-2014 Design Specifications for Electrochemical Energy Storage Power Stations" mainly defines energy storage as an independent production unit. At present, the design of user-side energy storage projects is difficult to meet the requirements of the specification. The national standard "GB/T36558-2020 General Technical Conditions for Electrochemical Energy Storage Systems for Power Systems" requires that the energy conversion efficiency of lithium-ion battery energy storage systems should not be lower than 92%, but in fact it is difficult for manufacturers to achieve them. The energy system efficiency is 88%, and the Tesla Powerpack energy storage system efficiency is 88% to 89%.Also read：Custom LiFePO4 Battery Cell
The application of lithium batteries in the user-side energy storage system, in addition to the reference specifications for lithium battery energy storage itself, is more related to the cooperation with the existing buildings and equipment on the user side, whether the relevant design codes match the existing building codes, and related protection. Whether the existing protection measures of the building can be used, etc., these parts lack reference in both design and practical application. The above work involves the integration of multidisciplinary knowledge, and it is necessary to strengthen communication and collaboration across professional fields.