Comparison of advantages and disadvantages of various energy storage systems

1, mechanical energy storage Mechanical energy storage mainly includes pumped storage, compressed air energy storage and flywheel energy storage.

(1) Pumped storage: when the grid trough the use of excess electricity as liquid energy media water from the low-lying reservoir to the high-lying reservoir, the grid peak load of high-lying reservoir water back to the lower reservoir to promote the turbine generator power generation, the efficiency is generally about 75%, commonly known as in 4 out 3, with daily adjustment capacity, for peak load and backup.

Shortcomings: difficult location, and its dependence on terrain; The investment cycle is large, and the loss is high, including the draining and storage loss + line loss; At this stage, it is also restricted by China's electricity price policy, and more than 80% of China's pumping and storage last year were in the sun.

(2) Compressed air energy storage (CAES) : compressed air energy storage is to use the remaining electricity of the power system when the load is low, driven by the motor to drive the air compressor, the air is pressed into the closed large-capacity underground cave as a gas storage chamber, when the system power generation is insufficient, the compressed air is mixed with oil or natural gas through the heat exchanger and combustion, into the gas turbine for power generation. There are more foreign studies, the technology is mature, and China began to be a little late, as if academician Lu Qiang has more research on this aspect, what is cold power cogeneration and so on.

Compressed air storage also has a peaking function, which is suitable for large-scale wind farms, because the mechanical work generated by wind energy can directly drive the compressor to rotate, reducing the intermediate conversion to electricity, thereby improving efficiency.

Disadvantages: One major drawback is low efficiency. The reason is that the temperature of the air increases when it is compressed, and the temperature decreases when the air is released and expanded. In the process of compressed air, some of the energy is lost as heat and must be reheated before expansion. Natural gas is usually used as a heat source to heat the air, which results in lower energy storage efficiency. Other conceivable disadvantages are the need for large gas storage units, certain geological conditions and reliance on burning fossil fuels.

(3) Flywheel energy storage: It is the use of high-speed rotating flywheel to store energy in the form of kinetic energy, and when energy is needed, the flywheel slows down and releases the stored energy. The single technology of flywheel energy storage is basically domestic (but the gap with foreign countries is more than 10 years), the difficulty is to develop new products with different functions according to different uses, so the flywheel energy storage power supply is a high-tech product but the original innovation is insufficient, which makes it more difficult to obtain the national scientific research funding support. The energy density is not high enough, the self-discharge rate is high, such as stopping charging, the energy will be exhausted within a few to dozens of hours. Only suitable for some market segments, such as high-quality uninterruptible power supplies.

2, electrical energy storage (1) Supercapacitor energy storage: The double electric layer structure composed of activated carbon porous electrode and electrolyte is used to obtain a large electrical capacity. Unlike batteries, which use chemical reactions, the charging and discharging process of supercapacitors is always a physical process. Short charging time, long service life, good temperature characteristics, energy saving and green environmental protection. Supercapacitors do not have too complicated things, that is, capacitor charging, and the rest is a matter of materials, and the current direction of research is whether the area is small and the capacitance is larger. The development of supercapacitors is still very fast, and the new supercapacitors based on graphene materials are very hot.

Disadvantages: Compared with batteries, their energy density leads to relatively low energy storage for the same weight, which directly leads to poor battery life and relies on the birth of new materials, such as graphene.

(2) Superconducting energy storage (SMES) : devices made of zero resistance of superconductors to store electrical energy. Superconducting energy storage system mainly includes superconducting diagram, low temperature system, power regulation system and monitoring system. Superconducting materials technology development is the top priority of superconducting energy storage technology, superconducting materials can be roughly divided into low temperature superconducting materials, high temperature superconducting materials and room temperature superconducting materials.

Disadvantages: The high cost of superconducting energy storage (materials and cryogenic refrigeration systems) makes its application very limited. Limited by reliability and economy, commercial application is still far away.

3. Electrochemical energy storage

(1) Lead-acid battery: It is a battery whose electrode is mainly made of lead and its oxide, and whose electrolyte is a sulfuric acid solution. At present, it is widely used in the world, the cycle life can reach about 1000 times, the efficiency can reach 80%-90%, the cost performance is high, and it is often used in the accident power supply or backup power supply of the power system.

Disadvantages: If the deep, fast high power discharge, the available capacity will decrease. It is characterized by low energy density and short life span. Lead-acid batteries have increased their cycle life a lot this year by adding super-active carbon materials to the negative plate of aluminate batteries.

(2) Lithium-ion battery: is a class of lithium metal or lithium alloy as a negative electrode material, the use of non-aqueous electrolyte solution of the battery. Mainly used in portable mobile devices, its efficiency can reach more than 95%, the discharge time can be up to a few hours, the number of cycles can be up to 5000 times or more, the response is fast, is the practical battery in the energy landscape, the most used at present. In recent years, technology has also been continuously upgraded, and positive and negative electrode materials have a variety of applications.

The mainstream power lithium batteries on the market are divided into three categories: lithium cobalt acid batteries, lithium manganese acid batteries and lithium iron phosphate batteries. The former has a high energy density, but the safety is slightly worse, the latter on the contrary, domestic electric vehicles such as BYD, most of which currently use lithium iron phosphate batteries. But it seems that foreigners are playing ternary lithium batteries and lithium iron phosphate batteries?

Lithium-sulfur batteries are also very hot, with sulfur as a positive electrode and lithium metal as a negative electrode, and the theoretical specific energy density can reach 2600wh/kg, and the actual energy density can reach 450wh/kg. However, how to greatly improve the battery charging and discharging cycle life, the use of safety is also a big problem.

Disadvantages: There are high prices (4 yuan /wh), overcharge leads to heating, burning and other safety problems, need to be charged protection.

(3) Sodium sulfur battery: It is a secondary battery with metal sodium as a negative electrode, sulfur as a positive electrode, and ceramic tube as an electrolyte diaphragm. The cycle can reach 4500 times, the discharge time is 6-7 hours, the cycle efficiency is 75%, the energy density is high, and the response time is fast. At present, more than 200 such energy storage power stations have been built in Japan, Germany, France, the United States and other places, which are mainly used for load leveling, peak shifting and improving power quality.

Disadvantages: Because of the use of liquid sodium, running at high temperatures, easy to burn. And if the grid goes out of power, it needs a diesel generator to help maintain the high temperature, or to help meet the conditions for cooling the battery.

(4) Flow battery: a high-performance battery that uses positive and negative electrolytes to separate and circulate respectively. The power and energy of the battery are not correlated, and the energy stored depends on the size of the storage tank, so it can store energy for up to a few hours to a few days, with a capacity of up to Mw. This battery has a number of systems, such as iron chromium system, zinc bromine system, sodium polysulfide bromine system and all vanadium system, of which vanadium battery is the most popular.

Disadvantages: the battery volume is too large; The battery has high requirements on ambient temperature. High prices (this may be a short-term phenomenon); The system is complex (it is a pump and a pipeline, which is not as simple as a non-flow battery such as lithium) battery energy storage has more or less environmental problems.



4, thermal energy storage: In the thermal energy storage system, the heat energy is stored in the medium of the insulated container, which can be converted back to electrical energy when needed, and can also be directly used and no longer converted back to electrical energy. Thermal energy storage can be divided into sensible heat storage and latent heat storage. The heat stored in thermal energy storage can be large, so it can be used in renewable energy generation.

Disadvantages: Thermal energy storage requires a variety of high temperature chemical thermal working medium, and the application occasions are relatively limited.

5, chemical energy storage Chemical energy storage: the use of hydrogen or synthetic natural gas as a secondary energy carrier, the use of excess electricity to produce hydrogen, you can directly use hydrogen as an energy carrier, you can also react with carbon dioxide into synthetic natural gas (methane), hydrogen or synthetic natural gas in addition to power generation, there are other ways to use such as transportation. Germany is keen to promote the technology and has demonstration projects in operation.

Disadvantages: The full cycle efficiency is low, the hydrogen production efficiency is only 40%, and the efficiency of synthetic natural gas is less than 35%.