energy storage system

Energy storage technologies – exploring the different features and challenges

Energy storage technologies - exploring the different features and challenges
Based on the actual development of the industry, this article analyzes the main energy storage technologies, market application, problems and challenges.
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    Driven by the renewable energy power generation, electric vehicles and global energy storage industries, various types of energy storage technologies have made great progress in recent years.

    As of the end of 2018, the global installed capacity of battery energy storage technology was 6058.9 MW, of which China’s installed capacity was 1033.7 MW, and the United States, China and South Korea ranked the top three.

    Based on the actual development of the industry, this article analyzes the main energy storage technologies, market application, problems and challenges.

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    Typical battery energy storage technologies

    Battery energy storage technologies mainly include lead-acid batteries, lithium-ion batteries, flow batteries, sodium-based batteries and other types of battery energy storage technologies.

    Lead storage battery

    Lead-acid batteries used in energy storage projects include lead-acid batteries and lead-carbon batteries. The lead-carbon battery is a capacitive improvement of the negative electrode material on the basis of the traditional lead-acid battery, which significantly improves the cycle life of the battery.

    In recent years, the application of lead-acid batteries in the field of energy storage is mostly based on lead-carbon batteries with lower cost per kilowatt-hour, especially for Jiangsu, Guangdong, Beijing and other places where the industrial and commercial peak-valley electricity price difference is relatively high.

    Sodium-based battery

    Sodium-based batteries used in energy storage projects include high-temperature sodium-sulfur batteries, sodium-nickel batteries, and room-temperature aqueous sodium-ion batteries.

    Sodium-sulfur battery is a typical representative of sodium-based batteries, and is the most mature energy storage technology in high-temperature operating energy storage systems (350-400 °C).

    Industrial companies led by Japan’s NGK have implemented more than 430 MW of energy storage projects in Japan, the United States, the United Arab Emirates, Germany, Italy, France and other countries before 2015.

    Li-ion battery

    There are many kinds of lithium-ion batteries used in energy storage projects, including lithium polymer batteries, lithium manganese oxide batteries, and lithium titanate batteries, as well as lithium ion battery.

    From the perspective of one-time investment cost, cycle life, and safety, lithium iron phosphate is undoubtedly the lithium-ion battery energy storage system with the most comprehensive characteristics in the energy storage field, and is widely used in all aspects of power system transmission and distribution.

    Grevault C & I Energy Storage Battery
    Grevault C & I Energy Storage Battery

    Lithium iron phosphate battery has the advantages of high stability and long cycle life, and is a popular and most widely used lithium-ion battery technology for power energy storage systems.

    In recent years, affected by the cost reduction of lithium iron phosphate and the improvement of comprehensive performance, this technology has been widely used in all aspects of power system transmission and distribution.

    Technical characteristics of battery energy storage

    In terms of battery energy storage technology characteristics, due to the comprehensive influence of industrial scale, system cost, energy and power characteristics, service characteristics, and recyclability, lithium-ion batteries (lithium iron phosphate and ternary lithium batteries) currently have outstanding advantages.

    The lead-carbon batteries , all-vanadium redox flow battery and cascade utilization lithium battery are competitive in specific scenarios.

    The service life of lead-acid batteries is too short, the one-time investment cost of lithium titanate batteries is too high, the safety problems of sodium-sulfur batteries are prominent and technological progress is slow, and the energy cost of supercapacitors is too high. The latter types of technologies are currently insufficient in market competitiveness.

    (1) The scale of the industry determines the speed of upgrading the comprehensive technical parameters of energy storage.

    In terms of industrial scale, the order from large to small is: lithium-ion batteries, lead-carbon batteries, and all-vanadium redox flow batteries. The volume of consumer and transportation lithium-ion battery industries can well support the development of the lithium-ion battery energy storage market.

    This is the reason for the rapid progress of lithium iron phosphate and ternary lithium batteries in recent years; The high-temperature sodium-sulfur battery with a good development momentum has gradually faded out of the energy storage market due to the high technical threshold and insufficient participation of energy storage companies, resulting in slow technological progress.

    The number of suppliers of lithium-ion battery energy storage systems is far ahead of other battery energy storage technologies.

    (2) The system cost is related to the project investment return period and its profit margin.

    The energy storage system cost has two core parameters, namely the one-time investment cost and the whole life cycle cost of electricity. In an application scenario with a specific revenue model, the lower the one-time investment cost, the shorter the return on investment period, the lower the cost of electricity throughout the life cycle, and the greater the profit margin.Energy storage system cost

    The one-time investment cost refers to the total initial equipment investment. For battery energy storage systems, it includes energy storage converters, power management systems, energy storage batteries, fire-fighting equipment, and monitoring systems.

    In addition to lead-acid batteries, the one-time investment cost of lead-carbon batteries is 1,000 to 1,300 RMB/kWh, which is the lowest among various technologies. Driven by the electric vehicle industry, the cost of lithium iron phosphate and ternary lithium batteries has dropped extremely fast.

    The one-time investment cost of lithium iron phosphate is 1,600-2,000 RMB/kWh, and the ex-factory cost of most suppliers is about 1,800 RMB/kWh.

    (3) The energy and power characteristics determine the occupied space and its applicable scenarios.

    In terms of energy density, the order from large to small is: ternary lithium battery (180-240 Wh/kg), lithium iron phosphate battery (120-150 Wh/kg), lead-carbon battery (25-50 Wh/kg), full battery Vanadium redox flow battery (7~15 Wh/kg).

    For grid-side energy storage (generally occupying substation space) and user-side energy storage, which require a high space requirement, in addition to selecting the appropriate energy storage technology for the application scenario, the energy density is also crucial to the standard floor space.

    Based on the industry consensus, the 40-foot container is the standard, the energy of the ternary lithium battery system can reach up to 4 MWh, the lithium iron phosphate is 2-3 MWh, the lead-carbon battery is 1.0-1.5 MWh, and individual companies can also achieve about 2 MWh.

    Battery energy storage technology market

    As of the end of June 2019, the global battery energy storage installed capacity was 7 427.5 MW, accounting for 4.1% of the global energy storage market.

    The installed capacity of battery energy storage in China is 1 160.8 MW. Among them, the installed capacity of lithium-ion batteries is 872.0 MW, accounting for 75.1%; lead-acid batteries are 264.2 MW; flow batteries are 19.5 MW; other batteries are 5.1 MW.

    Among them, lead-acid batteries are mainly used in energy-based applications, especially the engineering projects with an hourly rate of 4-8 h. Both liquid flow batteries and sodium-based batteries are mainly used in energy-based applications, and the hourly rate of flow battery energy storage projects is above 4 hours.

    Lithium-ion battery energy storage systems have both energy and power applications. Regardless of the application of industrial and commercial energy storage systems or power batteries, lithium-ion batteries are used because of their excellent battery performance.

    Lithium iron phosphate and ternary lithium battery energy storage systems have a wide application coverage, and lithium titanate batteries are mainly used for power applications with an hourly rate of 0.5 h and below.

    In the past three years, the accumulative growth of battery energy storage projects has been rapid. Statistical analysis of the energy storage projects put into operation in the past three years by large categories of energy storage technologies, the results are shown in Figure 7.

    Figure 7 Installed capacity of battery energy storage projects in operation
    Figure 7 Installed capacity of battery energy storage projects in operation

    Flow batteries, sodium-based batteries, and other types of battery technologies are growing slowly, especially sodium-sulfur batteries with large installed volumes. Lead-acid batteries and lithium-ion batteries have grown rapidly, especially lithium-ion batteries. The chain growth rates in 2016, 2017 and 2018 were 87%, 79.2% and 77.5% respectively.

    Problems and Challenges

    Technical and economic constraints

    Besides pumped storage, other types of energy storage technologies are still relatively expensive. The high cost of non-pumped storage technology is a key factor restricting the large-scale development of the energy storage industry.

    The current investment power cost of the pumped storage power station is 1600-2100 yuan/kW, and the kWh cost is about 0.25 yuan/kWh. Among the electrochemical energy storage technologies, lead-carbon batteries and lithium iron phosphate batteries are more economical, and the cost per unit of electricity is 0.5-0.7 yuan/kWh and 0.6-0.8 yuan/kWh, respectively.

    In the future, low-cost and long-life energy storage batteries will be the mainstream of technology research and development and market application.

    Technical performance limitations

    There are short board effects in the performance of characteristic parameters of different types of energy storage technologies.

    The site selection of pumped storage is limited, the construction period is long, the start-up and response speed are slow, and the energy conversion efficiency is low; the electrochemical energy storage power level is low, the continuous discharge time is short, the service life is still short, and some technologies have environmental pollution risks.Technical performance limitations

    The new compressed air energy storage technology has low efficiency (generally 50%), short service life, high-pressure sealing requires high equipment quality, and high operation and maintenance costs.

    The flywheel energy storage discharge time is short, and it can only last for a few seconds to minutes. Self-discharge phenomenon, high-speed rotating bearings are heavily dependent on imports. Hydrogen storage and other new energy storage technologies are still in their infancy.

    Limitations of scenario adaptability

    Energy storage application scenarios are diverse, and there are few Ontology technology development layouts for specific application scenarios.

    Different application scenarios have different requirements for energy storage technology, and the shortcomings of various energy storage technologies determine their application limitations.

    Pumped storage is mainly suitable for peak load regulation and long-term frequency regulation of large power grids across regions; although electrochemical energy storage has greatly improved its comprehensive performance indicators in recent years.

    However, the performance of technical indicators such as cycle life and power level is still different from the requirements of long life and large capacity of power system components. Limited by the cost of electricity and power cost, it is not enough to make it widely used in applicable scenarios.

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