Electrical energy has always been storable, including efficient storage in AC form. Even in the first half of the 20th century, AC power could be “stored” overnight or even longer using lead-acid/rectifier-converter sets, compressed air storage or pumped storage power plants. In the late 20th century, the three energy storage technologies have improved in terms of efficiency, performance, and price. However, in general, these energy storage methods do not perform well economically on a small-scale (distributed) basis. Due to the “concentration” effect and several natural physical reasons, pumped hydro power plants and compressed air energy storage have very considerable economies of scale, these technologies are more widely used in traditional systems, but almost all are used in central power plants. Even in the early 1990s, the technology for energy storage systems and other small energy storage devices such as flywheels had no positive business case for widespread adoption. The only exceptions are very small lead-acid and carbon-zinc batteries, which are based on uninterruptible power supplies and serve as backup for critical loads and energy demands. Such distributed systems exploded in the last quarter of the 20th century. Two key points to the success of these business cases are often the articulation of energy storage issues:
(1) Growth in the number of appliances and equipment that require absolutely continuous service, such as digital devices and robotic machinery. Overall, the value of service reliability and continuity is growing, as opposed to energy itself.
(2) General Uninterruptible power supply units in the case of full discharge, each group of working cycles is less than 10 times: the purpose of the unit is to provide available power backup, not regular power. This uninterruptible power supply will not “wear out” or drain from the daily charge/discharge process after hundreds of charge/discharge cycles, as is the case with lead-acid batteries.
During the last decade of the 20th century and into the 21st century, advances in chemistry and energy storage control technology have improved electrical storage (supercontainers), chemical (batteries and hybrid systems), and mechanical storage (flywheels) in nearly every important performance category. etc.) technology. Energy density has increased significantly, and batteries, and in some cases flywheels, have become light and compact enough to allow electric vehicles for personal and light industrial use. From a power system standpoint, when weight and size become secondary criteria, the most important advancement is the number of life cycles. In the late 20th century, lead-acid batteries could go through about 500 charge/discharge cycles before being “depleted”. Modern Li-ion batteries can reach 5-7 times that of lead-acid batteries, which makes a better business case for non-UPS applications. In addition, changes in storage control technology are also important. With the development of digitization and the electric vehicle industry, the size and control storage capacity of the power system energy storage unit has decreased rapidly enough to make it dispatchable quickly, and in many cases, the control is fast and accurate enough to be a stability resource of the system.