By Chen Yongchong, Feng Caimei, Liu Dandan and Liu Yong
The National Energy Administration and relevant departments recently issued Development Plan on New Energy Storage Technologies (2021-2025) and Energy Technology Innovation Plan (2021-2025) – propelling energy storage firms to research diversified technologies, make breakthroughs in core equipment and strengthen innovation ability – and guiding them on finding direction of technical innovation and achieving scale development of new energy storage technologies. A key support to future power system based on new energy resources, the new documents call for improving inadequacies and upgrading existing energy storage technologies, reducing related costs, etc.
Types of new energy storage technologies
Energy storage technologies are used mainly in power supply (e.g. centralized grid integration of renewables and AGC energy storage auxiliary frequency modulation system), power grid (e.g. power grid transmission/distribution and auxiliary services), households & industrial parks and distributed micro-grid. Different applications require diversified technologies. According to storage time, energy storage could be classified into:
1) capacity type (≥4 hours), which could be used in “peak cut” to shrink peak-valley difference to improve both power system efficiency and equipment utilization. Other application areas include off-grid energy storage, etc.
2) energy type (1-2 hours), generally applying to composite energy storage (e.g. independent energy storage power station or power grid), given its multiple functions of peak load and frequency regulation, emergency standby, etc.
3) power type (15-30 minutes), applying to AGC auxiliary frequency modulation or used to smooth intermittent power fluctuation, both requiring energy storage systems to provide power support rapidly via absorbing or releasing energy instantly
4) standby type (≥15 minutes), playing a role in the case of sudden power failure of power grid or voltage dip
The classification is helpful to develop application-oriented energy storage technologies, and meets requirements from renewable energy power generation on different energy storage time. However, only a handful of new energy power stations actively install energy storage systems, due to factors like relatively high use costs and single business model of energy storage technologies. Hence the need of guidance and support from electricity price policies. As for scale development, it will expand from standby-type and power-type energy storage technologies to energy-type and capacity-type techniques.
At present, new energy power stations generally install power-type or energy-type energy storage systems to smooth out power fluctuation, but their demand for capacity-type system is increasing, because of growth in both new energy generating capacity and proportion. In many places, e.g. Inner Mongolia and Xinjiang, local governments have issued policies to propel application of capacity-type energy storage system, which will gradually enter commercial application and satisfy demand of the power system for longer-term energy storage.
Technical innovation trends
Different application fields require diversified energy storage technologies.
* Capacity-type energy storage mainly involves new lithium ion batteries, lead carbon batteries, flow batteries, sodium ion batteries, compressed air, thermal and cool storage systems, hydrogen storage, etc. In spite of entering the stage of commercial promotion, lead carbon battery and thermal/cool storage systems need breakthroughs in capacity expansion, cost reduction, service life extension, green manufacturing and green recycling, etc. Most firms engaged in flow and sodium ion batteries, currently in the demonstration application stage, need to deal with problems like relatively high costs and improve key performance of products. New lithium ion battery producers are conducting pilot tests or trying to make new breakthroughs in key technologies. Further, they need to develop special batteries, safe, low-cost, easy to be recycled and used in capacity-type energy storage.
* Power-type energy storage technologies involve superconducting energy storage, flywheel energy storage, supercapacitor and various power-type batteries. Main problems include high prices of products, low reliability, high requirements on maintenance, etc. Producers need to strengthen innovation regarding key materials and high-power devices.
* Energy type – represented by 0.5C or 1C lithium iron phosphate batteries and in the stage of commercial application – is a main way of applying lithium ion batteries to power energy storage.
* Standby-type energy storage system (e.g. lead storage batteries, flywheel energy storage system, etc.) has low self-discharge rate, quick response, and stable performance.
Key energy storage technologies in urgent need of breakthroughs concentrate on service life, recycling and safety – e.g. cycle life prediction, test and evaluation technologies; green recycling and regeneration technologies; safety detection; early warning and protection technologies. Service life of energy storage systems could be extended by means of material optimization, innovative structure design, repair/regeneration technologies, etc. – a measure to reduce costs per kilowatt hour of the electricity, decrease waste of resources, etc.
Repair & regeneration, cascade utilization and material recycling are three main ways to dispose waste energy storage batteries. Repair & regeneration technologies could reduce recycling pressure, propel cyclic utilization of energy storage materials and devices and promote long-life design of batteries. To achieve scale application of cascade utilization in the area of energy storage, researchers should improve related performance evaluation and quality control techniques to ensure safety. With regard to material recycling, enterprises need to upgrade automatic battery dismantling and material sorting technologies, reduce energy consumption and carbon emissions during recycling process, raise recycling rate, etc.
Enterprises are required to make new breakthroughs in whole process safety technologies of energy storage – pertaining to battery safety control, safety warning of electrochemical energy storage system, efficient fire extinction, etc., as detailed in Development Plan on New Energy Storage Technologies (2021-2025).
Safe, low-cost and sustainable development
A common goal of energy storage technology enterprises – strong impetus to propel development of renewable energy sources, reduce renewable energy utilization costs, stabilize power grid operation, etc. – is to achieve safe, low-cost and sustainable development. Hence, they are wise to conduct a comprehensive evaluation (regarding safety, costs, ability to realize sustainable development, etc.), upgrade business model and establish a market-oriented green energy storage technology innovation system, which integrates advantages of enterprises, universities and research institutes.
