Long term energy storage current situation and development

1. Pumped storage
2. Compressed air energy storage
3. Lithium ion battery
4. Liquid current energy storage
5. Molten salt thermal storage
6. Conclusion

In the process of accelerating the grid connection of new energy sources, the unstable power output has put higher requirements on the grid’s capacity to consume. In order to better cope with inter-day fluctuations and balance the energy gap between quarters, the construction of long term energy storage is urgent.

There are many methods of long term energy storage, each with its own unique advantages and disadvantages, and the choice of which route to take is determined by geography, economics and other factors.

Pumped storage

Pumped storage is a type of mechanical energy storage. The principle is to use pumped storage power plants to transport water from low reservoirs to high reservoirs and store it when the power grid is under low load, using the remaining power to start the pumps.

When the grid is at high load or in urgent need of power, the water in the high reservoir is released and the reverse water flow is used to drive the turbine to generate electricity.

The advantages of pumped storage include low cost, long life, and large storage capacity. The energy conversion rate of pumped storage is as high as 75% – 83%, and without considering the charging cost and discount rate of 0, the cost of pumped storage electricity is only 0.207RMB/kWh, which is the lowest cost of electricity among various storage technologies.

Pumped storage power plants have a very long life span, with mechanical and electrical equipment lasting more than 50 years and dams lasting 100 years, which is incomparable to other storage methods.

Pumped storage has a large capacity, usually up to the GW level, a long duration of discharge, and a wide range of regulation. Therefore, by using pumped storage power plants, the stability of the power system can be effectively improved and the ability to consume renewable energy generation can be enhanced. Disadvantages of pumped storage include obvious geographical constraints, high initial cost, and long development time.

Pumped storage has high geographical requirements and can only be built in places where mountains and hills exist. Moreover, the upper and lower reservoirs must be located within a relatively close distance and there must be a high height difference.

In conditions where the height difference is not significant, the energy density that can be achieved by pumped storage power plants is relatively limited.

Compressed air energy storage

Compressed air energy storage technology, is a kind of technology that uses compressed air to store energy. At present, compressed air technology, after pumped storage, is the second most suitable technology for GW-level large-scale power storage.

The working principle of compressed air energy storage is: in the low hours of electricity consumption, the air is compressed to high pressure and stored in a pressure vessel using electrical energy, so that the electrical energy is converted into the internal energy of the air and stored.

During peak hours, the high pressure air is released from the storage chamber and enters the expander to do work and drive the turbine to generate electricity. The advantages of compressed air include the lack of terrain constraints and the huge scope for future cost reduction.

Disadvantages of compressed air include high investment costs, low operating efficiency, etc. It, as wll as water storage similar, is heavy assets of energy storage, the expected operating cycle of up to 40 years, the return on investment is often more than 25 years, a longer payback period to a certain extent reduces the enthusiasm for investment.

Compressed air efficiency is still at a relatively low level. The current efficiency of projects involving the operation of between 50%-70%, compared to the mature pumped storage of 76% or so there is a gap, which to a certain extent affects the economy of the whole project. The industry chain of compressed air energy storage equipment mainly involves compressors, heat exchangers and expanders.

The compressor is a machine that compresses air to increase gas pressure, and is one of the most core components of the system, its performance has a decisive impact on the whole system, Chinese manufacturers mainly include Shaangu Power, Shengu Group, etc.

At present, the 100MV class compressor can basically be localized, but it is difficult to manufacture a single 300MW compressor.

Lithium ion battery

The advantages of lithium-ion battery include mature technology and large installed scale. Because of the early emergence of lithium-ion batteries and sufficient technical reserves, they have become the first choice for energy storage. There is an advanced odm best lithium battery manufacturer, TYCORUN Energy. It has over 15 years professional lithium battery manufacturing expericence.

According to Zhongguancun energy storage data, in 2021, lithium-ion batteries account for 89.7% of the installed capacity of new storage in China, which is the most representative new storage technology and the electrochemical technology with the largest installed capacity at present.

The disadvantages of lithium-ion battery energy storage include high expansion costs and insufficient lithium resources. Lithium-ion batteries provide power and storage energy devices are bound together, in the case of not enhancing the power, only enhance the capacity, the battery cost increases in equal proportion.

That is, the battery cost of a 4-hour energy storage system is four times that of a 1-hour energy storage system. And pumped storage, compressed air and other storage methods, if you want to simply increase the storage time, only an equal proportion of the configuration of the storage energy device can be.

Lithium-ion energy storage battery midstream equipment vendors are in a rapid development stage, and the market pattern is not yet determined. CATL, with its strong cost control ability and scale advantage, has come to the forefront, and now has established extensive cooperation with State Grid, five major power generation groups, Crestec, Nebula, Sunshine Power and other enterprises, temporarily ranking first.

BYD has been cultivating the European and American markets, with solid customer and channel advantages, and is temporarily ranked second in China. Penghui Energy is rapidly expanding in home energy storage with the help of overseas market, occupying the third place in China in terms of shipments.

Liquid current energy storage

Liquid current battery is a large-scale high-efficiency electrochemical energy storage device.

Different from other battery energy storage devices, liquid current battery stores the reaction active material in the electrolyte solution, which can realize the separation of electrochemical reaction and storage site, making the battery power and energy storage capacity design relatively independent, suitable for large-scale power storage and energy storage needs.

In long time energy storage, the biggest advantage of liquid flow battery is that output power and energy storage capacity can be designed separately. By increasing the number of single cells and electrode area, the power of liquid flow battery can be increased.

By increasing the volume of electrolyte or increasing the concentration of electrolyte, the power of liquid flow battery can be arbitrarily increased to more than 100 MWh.

The disadvantage of liquid flow battery is that the cost is too high. The fastest advancing liquid flow battery is the all-vanadium liquid flow battery, but it faces the problem of vanadium resource constraints, resulting in high costs and slow commercialization.

However, the expansion cost of all-vanadium batteries is low, and the larger the capacity, the lower the cost. With the emergence of industrial scale effect, vanadium liquid flow battery cost is expected to be reduced.

Molten salt thermal storage

The principle of molten salt thermal storage is to store and release thermal energy through temperature change, phase change or chemical reaction of the thermal storage medium.

The thermal storage medium absorbs electrical energy, radiant energy and other energy and saves it in the medium, and when the ambient temperature is lower than the medium temperature, the thermal storage medium can release the thermal energy storage.

Molten salt is a commonly used medium and high temperature sensible heat storage medium, with a wide range of liquid temperature, large thermal storage temperature difference, high thermal storage density, suitable for large-scale medium and high temperature thermal storage projects.

The advantages of molten salt heat storage are low cost and long heat storage time. Molten salt as a thermal storage medium has a low cost and stable working condition.

At the same time, the density of heat storage is very high and the storage time is long, which is suitable for large-scale medium and high temperature heat storage, and the storage capacity of 100MWh or more can be achieved by a single machine.

The disadvantage of molten salt heat storage is that it can only be applied to cogeneration scenarios. The molten salt is used to store energy by storing heat, and if the storage needs to be electrical energy, the whole process needs to complete the conversion of electrical energy – thermal energy – electrical energy, which is very inefficient.

Therefore, molten salt energy storage can only be applied in scenarios where thermal energy is used to generate electricity as a storage medium for energy, such as photothermal power generation, thermal power plant renovation, etc. Or it can be applied in scenarios where the end energy demand is thermal rather than electrical, such as clean heat supply.

The solar thermal power generation market promotes the maturation of the molten salt thermal storage industry chain. The main components of molten salt are sodium nitrate, potassium nitrate salt and other common chemical materials. At present, China’s molten salt supply and chemical salt services are more mature.

Conclusion

Adhering to the diversified technical route of storage still requires continued efforts.

Research and development of high safety, low cost, high reliability, long life, environmental protection of storage technology, construction of  facilities to fit the new power system, to help achieve the dual carbon goals is the ultimate goal of the development of energy storage.

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