In recent years, with the energy shortage and the accelerated demand for home energy storage, energy storage projects have become a hot spot in the market, and the installed capacity has increased rapidly. In the first half of this year, the number of large and medium-sized energy storage projects announced in China has approached 60GWh. The total installed capacity of energy storage in the United States in 2021 is about 6.8GWh, and it is expected to reach 12GWh by the end of 2022. By the end of 2021, the installed capacity of electrochemical energy storage in Europe will reach 3.3GWh, and it is expected to reach 4.7WGh this year.
With the rapid increase in the installed capacity of energy storage projects, the development trend is to increase the capacity of a single project. It is precisely because of this development trend that the safety of energy storage projects is particularly important. So from a technical point of view, how to ensure the safety of large-scale energy storage projects? Generally speaking, we can start from three aspects, that is, the safety of the battery cell itself, the performance of the inverter and the fire protection system.
1. The safety of the battery cell itself
Safety mainly comes from the battery cell itself. The quality and consistency of the cells are good, and the probability of failure is small or the durability is strong. Therefore, when selecting key equipment for large and medium-sized energy storage projects, we must use first-line brand cells. In terms of cell types, there are ternary lithium batteries and lithium iron phosphate batteries, but the proportion of lithium iron phosphate batteries is higher, accounting for more than 90%. According to industry sources, more manufacturers will use lithium iron phosphate batteries in the future, because the safety of lithium iron phosphate batteries is relatively higher.
In addition, the production capacity of lithium batteries is expanding very rapidly. In the future, lithium iron phosphate batteries may continue to grow to 95%, and the remaining 5% will be reserved for other types of batteries, such as flow batteries, sodium-ion batteries, and so on. From the perspective of energy storage battery cell manufacturers, the first echelon includes CATL and other manufacturers; the second echelon includes REPT, CALB and so on. Of course, lithium battery manufacturers in the world such as GOTION HIGH-TECH and BYD also have related products.
2. Influence of inverter performance on safety of energy storage projects
Generally speaking, the inverter will connect the energy management system (EMS) and the battery management system (BMS) in series to protect the battery. Among them, EMS is the decision-making link, the inverter is the execution link, and the BMS is the monitoring link. The inverter is centered in the energy storage system, communicates with the EMS upward, and manages the BMS downward to play a more protective role. For example, when the energy storage power station is connected to the external large power grid, if the large power grid has frequency or voltage fluctuations that are not conducive to the energy storage power station, the inverter will play the role of protecting the DC side battery pack.
Therefore, the inverter is also a particularly critical link in safety. In terms of difficulty, the inverter is the most difficult. Because there are only 30 or 40 kinds of materials that need to be managed in the production process of cells, and thousands of accessories that need to be dispatched in the production process of inverters, the complexity of inverter production is higher. In addition, the production of inverters includes power electronics, high-voltage electrical, control, chips and other fields, and the technical barriers are even higher.
At present, in the large-scale centralized energy storage inverter market, SINENG has the highest market share, SUNGROW is the second, and KELONG is the third. These three companies basically share the inverter market for energy storage projects of more than 100MWh, with a combined market share of up to 80%. Among them, SINENG has a market share of about 40% and has a great advantage. The main reason may be that SINENG does not carry out system integration business, while SUNGROW carries out integration business. The second difficulty is BMS. BMS covers hardware and software, and there will be more and more hardware-oriented levels in the future.
With the rise of the energy storage market, many Chinese chip manufacturers have begun to develop BMS-related chips in the past two years, and there may be fierce competition in the BMS IC market in the next few years. Relatively speaking, EMS is less difficult. Because EMS can be considered as a pure software system, the threshold is not very high, and it is only necessary to be familiar with the grid connection standards and operating characteristics. Some experts believe that companies capable of making industrial control software in the market can achieve breakthroughs in a few months.
3. Fire-fighting measures to ensure energy storage safety
Generally speaking, the materials required for the production of lithium ion batteries mainly include cathode materials, anode materials, electrolytes, separators and packaging materials. The battery pack mainly includes battery modules, cover plates, protective layers, cooling systems and battery trays. Due to the characteristics of the lithium-ion battery structure, if thermal runaway occurs, as the temperature rises, the separator will decompose at the earliest, and then the electrolyte, EC, etc. will undergo decomposition reactions, and the decomposition products of the electrolyte will also react with the positive and negative electrodes.
The cell separator will melt and decompose, and various reactions lead to the generation of a large amount of heat. The melting of the separator leads to an internal short circuit, and the release of electrical energy increases the generation of heat. This cumulative and mutually reinforcing destructive effect results in the rupture of the explosion-proof membrane of the cell, the ejection of electrolyte, and the occurrence of combustion and fire, or even explosion. In order to prevent fire or explosion accidents of energy storage projects, PACK level fire protection and advanced gas detection technology can be started.
Combined with monitoring of rare gases (such as carbon monoxide, methane, etc.), hidden situations can be discovered and early warning. There are also technologies that can monitor the number of particles in a fixed space. For example, when part of the connecting cables in the PACK are heated, the number of particles will rise sharply. This scheme of monitoring the number of particles can know the situation inside the battery earlier than the scheme of monitoring the rare gas that is heated and evaporated from the electrolyte, and can give an early warning 45 minutes in advance.
If this technology is combined with the PACK-level sprinkler fire protection technology, the problem of serious accidents or fires in the entire large-scale energy storage power station can be solved. Because if all fire sprinklers reach the PACK level, the PACK can be sprayed separately to cool down, and it can be completely cooled before an explosion occurs, preventing the spread of the accident. However, although the technology can be achieved at present, the cost is relatively high, and the future cost will be the difficulty of technology implementation. If fire protection can be done cheaply and efficiently, the safety of large-scale energy storage projects can be guaranteed, which is conducive to the promotion of GWh-level projects.
Energy storage projects are very popular now, but there are also many technical difficulties that require the joint efforts of enterprises and experts in the industry to solve them together.