What are the energy storage technology in the smart grid?

Energy storage technology in many fields, including power system has a wide range of USES, within the scope of the power industry restructuring in the world in recent years for a variety of energy storage technology brings new opportunities for development, using these technologies can better realize energy management of electric power system, especially in the field of renewable energy and distributed generation, this effect is particularly obvious, in the traditional power generation and transmission and distribution networks, the new technology also can be used. Following a brief introduction to the basic principles of various energy storage technology and its development status.

1 pumped storage

Pumped storage power station in the upstream or downstream applications must be equipped with two reservoirs. In the off-peak load, pumping energy storage equipment working in motor state, will pump water to the downstream reservoir upstream reservoir preservation. At times of peak load, the pumping energy storage equipment in the state of the generator, using stored in the water in the upstream reservoir to generate electricity. Some high dam hydropower station has the water storage capacity, it can be used for electric power dispatching pumped storage power station. Using the mine or other cave underground pumping energy storage is technically feasible, sometimes also can use as a downstream reservoir, ocean in 1999, the Japanese built the first use of seawater pumped storage power station.

Pumping energy storage as early as the 1890 s has been applied in Italy and Switzerland, in 1933 the reversible units (including pump turbine and electric generator), there is a speed can be adjusted in order to improve the efficiency of energy unit. Pumped storage power station can be in any capacity building, the release of stored energy time could be from a few hours to a few days, its efficiency is between 70% and 85%.

Pumping energy storage is the most widely used in electric power system of a kind of energy storage technology, its main application fields including energy management, frequency control, and provide the spare capacity of the system. At present, all over the world, there are more than 90 GW of pumped storage units in operation, accounting for about 3% of the world's total installed capacity. Limit of pumped storage power station is more widely used an important restriction factor is a long construction period, large engineering investment.

2 advanced storage of the battery Energy storage

It is estimated that the global market demand for storage battery is about $15 billion a year, in terms of industrial battery, such as: used in UPS, power quality regulation, spare batteries, etc., the market volume of up to 5 billion dollars. In the United States, Europe and Asia, is to establish an enterprise in the production of energy storage power system with high performance battery. In the past 12 to 18 months, the existing production capacity of 300 mw battery production line put into operation a year.

Lead-acid batteries are the oldest, and most mature battery technology. It is a low-cost generic energy storage technology, can be used for power quality regulation and UPS etc. However, because the battery life is short, thus limiting its application in the field of energy management. ZnBr battery developed in the early 1970 s by Exxon, after years of research and development, has built a lot of capacity one KWH of ZnBr battery energy storage system, and through the test, the net efficiency of 75%.In the early 1980 s at the university of new south Wales, Australia led the way in, j of VRB battery, currently, in Japan has installed a 500 KW / 5 mw? H VRB energy storage system, the net efficiency is as high as 85%.

In recent years, all kinds of new type of battery were developed successively, and applied in the power system. The British REGENE sys Technologies are using PSB battery to build a 15 mw / 120 mw? H energy storage power station, the net efficiency of about 75%.NaS battery has high energy storage efficiency (about 89%), at the same time also has the ability of the output pulse power, the output pulse power can achieve continuous rated power values in the 30 s six times, this feature makes the NaS batteries can be used at the same time to peak of the power quality regulation and load regulation two purposes, so as to improve the economic benefit of the whole equipment. In Japan, the adoption of NaS battery technology demonstration projects of energy storage has more than 30, the total storage capacity of more than 20 mw, can be used for 8 h daily peak valley load regulation.

Compared with other battery, Lithium ion batteries The main advantage is high energy storage density

(300 ~ 400 KW? H/m3, 130 KW?H/t), energy storage efficiency (nearly 100%), and long service life (every discharge rechargeable 3000 times in less than 80% of the energy storage).Because of the advantages of lithium ion batteries to get fast development. But, although in a few years The lithium battery Already has a small mobile power supply 50% of the market, production of large capacity lithium ion battery there are still some challenging work to do, the main obstacle lies in its high cost, this is mainly because it needs special packing and equipped with necessary internal over charging protection circuit.

Of all the battery and the Metal - air cell is the most compact structure, and is expected to become the lowest cost of the battery, the battery is a kind of harmless to the environment. Its main drawback is that the battery charging is very difficult and low efficiency.

3 the flywheel energy storage

Most modern flywheel energy storage systems are passed by a cylindrical rotating mass and composed of magnetic suspension bearing support organizations. Is to eliminate the purpose of using magnetic levitation bearing friction loss, improve the life of the system. In order to ensure a high enough energy storage efficiency, flywheel system should be run in high vacuum environment, to reduce the wind resistance loss. The flywheel is connected to a motor or generator, through some form of power electronic devices, for adjusting the rotational speed of the flywheel, power exchange between energy storage devices and power grid.

A prominent advantage of flywheel energy storage is almost don't need to run maintenance and long life of equipment (20 years or tens of thousands of times depth charge) energy release process and no adverse effects on the environment. Of recycle of flywheel has good tracking performance and load, it can be used for those in terms of time and capacity between short-term energy storage application and storage for a long time.

Can be used in the realization of the flywheel energy storage devices, solid steel flywheel, also can use composite flywheel, specific what flywheel needs economic and technical comparison, the system cost, weight, size and material performance indicators such as a tradeoff. Using high density steel material, its edge linear velocity can reach 200 ~ 200 m/s, and USES the lighter weight, higher strength of composite material, its edge linear velocity can reach 600 ~ 1000 m/s. The flywheel is actual output energy depends on the speed range, it can't be in a very low speed under rated power output.

At present, has developed the high-power flywheel energy storage system, and applied to the field ofspecial and UPS. Beacon Power as leading level of the research institute is committed to the optimum design of flywheel energy storage, in order to use it for the long process of energy storage services (up to several hours), and reduce the cost. There are 2 KW/ 6 KW? H of the flywheel energy storage system used in communications equipment, power supply adopts fly wheel can realize the output power of megawatt, lasts a few minutes or several hours of energy storage device.

4 superconducting magnetic energy storage

Although the superconductivity was discovered as early as 1911 people, but until the 1970 s, just someone for the first time put forward the superconducting magnetic energy storage as a energy storage technology is applied in power system. Superconducting magnetic energy storage because of the fast electromagnetic response characteristics and high efficiency of energy storage (charge/discharge efficiency more than 95%), and soon attracted the attention of the power industry and the military. SMES in the application of power system include: load balancing, dynamic stability, transient stability, voltage stability, frequency adjustment and transmission capacity and improve power quality, etc.

SMES unit consists of a superconducting coil under low temperature environment, the low temperature is provided by containing liquid nitrogen or liquid helium containers of cryogenic equipment. Power change/adjustment system will SMES unit connected to ac power system, and can according to the need of the power system to charge and discharge energy storage coils. Usually use two kinds of power conversion system storage coils are connected to the ac power system, a kind of type is a current source converter; Another type is a voltage source inverter.

Compared with other energy storage technology, the SMES still expensive, in addition to the cost of the superconductor itself, to maintain the cost of low temperature is also quite considerable .If, however, the SMES coil with the existing combination of flexible ac transmission unit (FACTS) can reduce the cost of converter unit, this part of the cost in the lion's share in the cost of SMES. The existing research results show that the application of transmission and distribution, the micro (< 0.1 MW?H) and medium (0.1 ~ 100 mw? H) SMES system may be more economic. Using high temperature superconductors can drop energy storage system for low temperature and cooling conditions, so that further reduce the cost of SMES. Many SMES worldwide at present, the engineering is on or in the stage of development.

5 super capacitor energy storage

Capacitor is a device widely used in the power system. Compared with conventional capacitors, super capacitors have a higher dielectric constant, larger surface area or higher compression capacity. Ceramics, for example, the super capacitor has the quite high pressure level (about 1 KV) and dielectric strength, making them good candidates for future energy storage applications.

At present, super capacitors are used for peak power, low capacity of the occasion. Because the can work normally in a state of floating charge more than a decade, so the super capacitor can be in voltage drop and raise the level of power supply during the transient disturbance. Super capacitor installation is simple, small volume, and can run in various environment (hot, cold and wet), is now available for the application of low power level business services.

6 compressed air energy storage

Compressed air energy storage is not as simple as energy storage battery energy storage system, it is a kind of peak shaving with gas turbine power plants, for the same power output, it consumed 40% less gas than conventional gas turbine. This is because, when conventional gas turbine power generation is about two-thirds of the fuel consumption input for air compression, while CAES available cheap electricity power grid load is low compressed air in advance, and then according to the need to release the stored energy plus some gas to generate electricity. Compressed air is often stored in a suitable underground or under the lava cave. Through the lava was needed to build such a cave about 1 year and a half to two years.

The first put into commercial operation for CAES is built in Germany in 1978 Hundorf a 290 mw unit. The United States in 1991 in Alabama McIntosh, built the second commercial CAES, power of 110 mw unit, the construction of 30 months, at a cost of $65 million, which units to interconnection within 14 min. The third CAES of commercial operation, is currently the world's largest capacity CAES, to be built in Ohio state Norton, the whole plant installed capacity of 2700 mw, a total of 9 units, compressed air is stored in an existing 2200 ft deep underground limestone mine.

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