Battery energy storage is mainly through the oxidation-reduction reaction of the positive and negative electrodes of the battery for charging and discharging. The battery energy storage system (BESS) is composed of batteries, DC-AC inverters, control devices and auxiliary equipment (safety and environmental protection equipment), and is currently the most widely used in small distributed power generation systems. According to the different chemical substances used, batteries can be divided into lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, lithium-ion batteries, and so on.
Traditional battery energy storage has many problems such as high initial investment, short life span, and pollution to the environment. It is worth noting that the lithium-ion battery is a new type of high-energy secondary battery that has emerged in recent years. It was first introduced by Japan’s Sony in 1992. Because of its high working voltage, small size, high energy storage density (300~400kW·h/m3), no pollution, long cycle life (each discharge does not exceed 80% of the energy storage, it can be charged 3000 times), etc. People value and welcome. In addition, the charge-discharge conversion rate of lithium-ion batteries is as high as over 90%, which is higher than the conversion rate of pumped storage power stations, and also higher than the power generation rate (80%) of hydrogen fuel cells. At present, traditional lead-acid batteries are more commonly used in distributed power generation systems when using storage batteries. Various advantages make lithium-ion batteries play an increasingly important role in future distributed power generation and energy storage. Other new types of batteries developed in recent years include sodium-sulfur batteries and vanadium batteries.
In addition to being used in distributed power generation systems, battery energy storage is also used for peak regulation and frequency control in power systems. In order to improve the power grid’s ability to withstand power outages, the Alaska Power Grid has installed an online battery energy storage system that can provide peak power of 26.7MW. The system costs 30 million U.S. dollars and can reduce the possibility of a major power outage by more than 60%.
Table 1 and Table 2 respectively show the basic characteristics of common battery energy storage systems and the comparison of the performance indicators that the energy storage systems constituted by them have reached so far.
|Energy storage type||Typical rated power||Rated Capacity||Features||Application occasions|
|Lead-acid batteries||5kW~50MW||A few minutes ~ a few hours||Mature technology, low cost, short life span, environmental issues||Power quality adjustment, power station backup, black start|
|Flow battery||5kW~100MW||1~20h||Long life, deep release, suitable for combination, high efficiency and good environmental protection; but the energy density is slightly lower||Power quality adjustment, backup power supply, peak shaving and valley filling, energy management, renewable energy storage, EPS|
|Sodium Sulfur Battery||100kW~100MW||Hours||The specific energy and specific power are high. High temperature conditions and operational safety issues need to be improved||Power quality adjustment, backup power supply, peak shaving and valley filling, energy management, renewable energy storage, EPS|
|Lithium Ion Battery||100~170W||A few minutes ~ a few hours||Higher than energy. Group life and safety issues need to be improved||Power quality adjustment, backup power supply, UPS|
|Battery type||Power limit||Specific capacity (Wh/kg)||Specific power (Wh/kg)||Cycle life/time||Charge and discharge efficiency (%)||Self-discharge (%/month)|
|Lead-acid||Tens of megawatts||35~50||75~300||500~1500||0~80||2~5|
|NiMH||Dozens of megawatts||75||150~300||≥2500||0~70||5~20|
|Lithium Ion||Dozens of megawatts||150~200||200~315||≥ 2500||0~95||0~1|
|Sodium Sulfur||More than ten megawatts||150~240||90~230||≥ 4500||0~90||﹣|
|Vanadium flow||Hundreds of kilowatts||80~130||50~140||≥ 10000||0~80||﹣|
Phase change energy storage is carried out by taking advantage of the characteristics of phase change materials that absorb a large amount of latent heat and maintain a constant temperature during phase change. For example, at the valley value of the power grid, electric energy is converted into heat energy, stored in the phase change energy storage element, and used for heating water and heating at the peak of the power grid. It is mainly used for power peak shaving in power systems.