1.Technological principle & features
The power storage device composed of power storage elements and the grid access device composed of power electronic devices become the two major parts of the power storage system. The power storage device mainly realizes the storage, release or fast power exchange of power. The power grid access device realizes the bidirectional transfer and conversion of power between the power storage device and the power grid, It also realizes functions such as power peak regulation, energy optimization, improving power supply reliability and power system stability.
The capacity range of the power storage system is relatively wide---from tens of kilowatts to hundreds of megawatts; the discharge time span is large---from milliseconds to hours; the application range is wide, running through the entire power generation, transmission, distribution, and power consumption systems; The research and application of large-scale electric energy storage technology has just started. It is a brand new topic and is also a hot field of research at home and abroad.
2.Commonly used power station storage methods
At present, power storage technologies mainly include physical energy storage (such as pumped hydro storage, compressed air power storage, flywheel power storage, etc.), chemical power storage (such as various types of batteries, renewable fuel power batteries, flow batteries, super-capacitors, etc.) and electromagnetic power storage (such as superconducting electromagnetic power storage, etc.), etc.
1) The most mature and widely used physical power storage is pumped storage, which is mainly used for peak regulation, valley filling, frequency regulation, phase regulation, and emergency backup of power systems. The release time of pumped storage can be from a few hours to a few days, and its energy conversion efficiency is from 70% to 85%. The construction period of pumped-storage power stations is long and limited by terrain. When the power station is far away from the electricity consumption area, the transmission loss is large. Compressed air power storage has been applied as early as 1978, but due to the constraints of terrain and geological conditions, it has not been widely promoted. The flywheel power storage uses the motor to drive the flywheel to rotate at a high speed, and then converts electrical energy into mechanical energy and stores it, that flywheel then drives the generator to generate electricity when needed. The characteristics of flywheel power storage are long life, no pollution, low maintenance, but low energy density, which can be used as a supplement to the battery system.
2) There are many types of chemical energy storage, and the technical development level and application prospects are also different:
(1) Battery power storage is the most mature and reliable power storage technology at present. According to the different chemical substances used, it can be divided into lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, lithium-ion batteries, sodium-sulfur batteries, etc. Lead-acid battery has the characteristics of mature technology, can be made into large-capacity storage system, low unit energy cost and system cost, safety, reliability and good re-usability. It is also the most practical power storage system at present, and has been used in small wind power generation, photovoltaic power generation. It has been widely used in small and medium-sized distributed power generation systems. But because lead is a source of heavy metal pollution, lead-acid batteries are not the future development trend. The cost of advanced batteries such as lithium-ion, sodium-sulfur, and nickel-metal hydride batteries is relatively high, and the large-capacity power storage technology is immature. The performance of the product cannot meet the requirements of energy storage, and its economy cannot achieve commercial operation.
(2) Large-scale renewable fuel power cells have the characteristics of large investment, high price and low cycle conversion efficiency.So it is not suitable for commercial power storage systems at present.
(3)(3) Flow power storage batteries have the advantages of high energy conversion efficiency, low operation and maintenance costs, etc., and are one of the technologies for high-efficiency, large-scale grid-connected power generation, energy storage, and regulation. Flow power storage technology has been exemplary applied in developed countries such as the United States, Germany, Japan and the United Kingdom, and our country is still in the research and development stage.