In the field of grid-scale energy storage applications and hybrid vehicles, batteries usually need to be circulated under high current density conditions, that is, high-rate charge and discharge operations, so that lead-acid batteries often fail due to sulphation of the anode, which greatly affects lead acid. Battery life. The lead carbon battery is based on the traditional lead-acid battery, which greatly increases the life of the lead-acid battery.
Lead carbon battery performance
The charging time of lead-carbon battery is one-eighth of that of lead-acid battery, and the cycle life is more than four times that of lead-acid battery. Compared with lithium battery, it also has the advantages of low temperature performance, low cost, mature production and recycling process, etc. The performance has also been greatly improved, and the industrial application of lead carbon batteries in the field of energy storage has begun to mature.
Yang Yusheng, an academician of the Chinese Academy of Sciences, believes that lead carbon batteries have been successfully applied to urban microgrids, wind energy storage power stations, wind circuit lights, etc. due to their significant advantages such as low cost, safety, easy availability of raw materials, reliability, and mature industrial technology. Providing kinetic energy for various electric vehicles is an energy storage battery that conforms to China's industrial layout and manufacturing level.
Composition of lead carbon battery
The lead carbon battery is a special capacitive lead-acid battery. The traditional lead-acid battery unit is composed of a lead dioxide positive plate and a sponge lead negative plate, while the asymmetric super capacitor is made of lead dioxide positive electrode. The plate and the carbon negative plate are composed. Since the two have a common positive plate, they can be combined in the same battery system, that is, a so-called lead carbon battery is formed. Figure 1 shows the evolution and changes in the structure from traditional lead-acid batteries to lead-carbon batteries.
As can be seen from Figure 1, the lead carbon battery incorporates a carbon material in the negative electrode compared to a conventional lead acid battery. The addition of carbon material accelerates the conversion of active materials during the conversion process. A new active center is formed on the surface of the activated carbon, which reduces the polarization during the charging process of the plate and inhibits the growth of lead sulfate particles, which is beneficial to the reduction of lead sulfate. Therefore, adding an appropriate amount of carbon to the lead-acid battery can effectively inhibit the accumulation of lead sulfate crystal on the surface of the negative electrode, slow down the trend of sulfation, and significantly increase the life of the battery cycle.
At the same time, in the high-rate charge and discharge process, the supercapacitor can quickly supply and absorb the charge, and play the role of a buffer. Therefore, the cooperation with the super capacitor increases the power of the battery and prolongs the cycle life of the battery.
Energy storage system
In the energy storage system, in addition to the application of the battery, a battery management system (BMS) and a process control system (PCS) are also involved. BMS is mainly used to estimate the state of charge of the power battery pack, that is, the remaining battery power; dynamic monitoring during battery charging and discharging is a key technology in the battery energy management system. Figure 2 shows a schematic diagram of an energy storage power plant operation management system.
When the energy storage power station cooperates with photovoltaic grid-connected power generation, the photovoltaic module first converts the light energy into electrical energy by using the photovoltaic effect of the solar panel, and then charges the battery pack, and converts the direct current into alternating current to supply the load through the inverter; BMS According to the change of sunshine intensity and load, the charge and discharge state of the battery pack is adjusted in real time, so that the whole system maintains continuity and stability.
The battery pack plays a major role in energy regulation and balancing the load throughout the energy storage system. It converts electrical energy into chemical energy when used in a low valley, so that it can be used when power is insufficient. The lead carbon battery itself has better charge and discharge receiving capacity (after 100% deep discharge, it is charged with 2.35V/unit constant voltage current limit 0.15C10(A) for 10 hours, and the charge is more than 98% of the discharged electricity); Self-discharge; and 70% DOD expected cycle life of 4,000 times, recyclable characteristics, making lead carbon batteries more advantageous than conventional energy-saving systems compared to traditional lead-acid batteries.
Lead carbon battery cost analysis
According to the analysis of the first part, the lead-carbon battery is a new type of lead-acid battery produced by the combination of the traditional lead-acid battery and the super-capacitor. In addition, in practice, the cost and price of the lead-carbon battery are affected by a series of factor prices. Including: activated carbon price and supply, lead price fluctuations, capacitor prices and other factors such as additives graphene.
As can be seen from Figure 4, in the second half of 2016, the price of activated carbon dropped first and then slowly recovered. The analysis in the previous report of this series can be known that the price of lead resources has generally been relatively stable in recent years, but the price has increased in the past six months. The specific trend is shown in Figure 5.
From the perspective of the impact of various raw materials, in theory, the price of lead carbon batteries is largely determined by the price of lead. The elasticity of demand for lead is small, and the fluctuation of lead price is likely to increase the cost of lead carbon batteries. On the other hand, the company usually has price linkages to downstream customers, and there is a time lag, so fluctuations in lead prices may also bring profits to both parties. As for the graphene with good conductivity and ductility, compared with activated carbon, due to its high price, the demand for graphene is more flexible for lead-carbon batteries, and it is more common in the process of processing. A certain amount of activated carbon is added to improve the performance of the conventional lead-acid battery.
Due to the use of lead-carbon technology, the performance of lead-carbon batteries is far superior to traditional lead-acid batteries, and at the same time has the low price advantage and mature industrial manufacturing base similar to traditional lead-acid batteries, and is extremely strong in various application fields. Competitive advantage.
In the current field of energy storage, chemical storage methods with a wide range of applications and concerns have lithium-ion batteries in addition to lead-carbon batteries. In addition, pumped storage is one of the most widely used and most mature physical energy storage methods in the world. Next, compare and analyze these three energy storage methods.
Lead carbon battery
Since the lead carbon battery is developed on the traditional lead-acid battery, it has many advantages: one is charging fast, increasing the charging speed by 8 times; the second is that the discharge power is increased by 3 times; the third is that the cycle life is increased to 6 times. The number of cycles of charging is up to 2000 times; the fourth is cost-effective, which is higher than the price of lead-acid batteries, but the life of recycling is greatly improved; the fifth is safe and stable, and can be widely used in various new energy and energy-saving fields. . As the output increases, the cost of lead-carbon batteries decreases further with the increase in scale effect, and the future application prospects are broader.
Lithium Ion Battery
Another chemical energy storage method corresponding to a lead carbon battery is a lithium ion battery. Lithium-ion batteries have the advantages of high energy density, long cycle life, low self-discharge rate and environmental protection, and are mainly used in today's notebook and mobile phone industries. Due to its own advantages, lithium-ion batteries are also an ideal choice for large-scale energy storage systems in the future.
In future applications, lithium-ion batteries still have problems in terms of safety, cycle life, cost, and operating temperature range. Unlike other rechargeable batteries, the capacity of a lithium-ion battery will slowly decline, depending on the number of uses and temperature. This phenomenon of decay can be expressed as a decrease in capacity or as an increase in internal resistance.
Despite the promotion of power battery applications, lithium battery technology and cost have been greatly improved, but the current cost of lithium batteries is still more than three times that of lead carbon batteries. In the field of energy storage, in addition to high-end data centers and usage scenarios where the weight of energy storage batteries is strictly limited, there are currently very few commercial projects using lithium batteries for energy storage.
Pumped energy storage
Pumped water storage is the most widely used and most mature energy storage method in the world today. It belongs to physical energy storage. Pumped storage energy is a form of storing electrical energy into gravitational potential energy when pumping water from the lower pool to the upper reservoir during the period of low power load. The overall efficiency is between 70% and 85%, and it is applied to the peak filling of the power system. Valley, FM, phase modulation, emergency backup, etc. However, the establishment of pumped storage energy depends to a large extent on the choice of geographical location, so it will be limited in further development and application in the future.
Energy storage management platform conception
A 12MWh energy storage power station is charged for 8 hours per day during the valley electricity period. The charge and discharge depth is calculated according to 80%, and the average daily charge is 9300kWh. The accumulated charge and discharge remains stable. During the peak electricity period, it was discharged for 8 hours, the average daily discharge was 8400 kWh, the charge and discharge efficiency reached 90.51%, and the financial calculation was based on 85%. The peak electricity price is 1.05 points, the valley electricity price is 0.31 yuan, and the daily income is 5938.03 yuan. According to 360 days, the annual income is 2,137,691 yuan.
The actual running data has reached the design data standard. At present, the storage battery has a discharge depth of 70%, but the battery can fully meet the 80% DOD operation. According to this calculation, the battery is charged for 8 hours per day, and the average daily charge is 10666.7kWh. During the peak electricity period, the battery was discharged for 8 hours, and the average daily discharge was 9600 kWh; the charge and discharge efficiency was 90%. Combined with the existing peak-to-valley electricity price difference, the average daily income is about 6773.33 yuan, which is 14% higher than 70% charge and discharge. According to the 360-day operation, the annual income is about 2,448,400 yuan, and the income is increased by 14%.
The expected increase in revenue is mainly due to the improvement of charging and discharging efficiency. The number of times of charging is currently 6,000 times, no significant attenuation, 70% of DOD has taken into account the possibility of attenuation, and has not reached the limit after shrinking in the future. 80% is end of life and meets international standards.