The structure of household Energy Storage system includes batteries, inverters and other equipment. At present, products in the industry are independent of each other, which is easy to cause a variety of problems on final using, mainly including: complex system installation, difficult operation and maintenance, and battery’s low using efficiency and low protection levels.
- Integrated system cause complex installation :
- Most users hope to use it as “Household Appliances”, which puts forward higher requirements for system installation. At present, the complex and time-consuming on-site installation of residential energy storage has become the biggest problem for some users.There are two kinds of energy storage system for household use in the market: low-voltage system and high-voltage system.
- Low-voltage Energy Storage system is with 40~60V battery, which is connected to the inverter after several batteries are connected in parallel. Through the isolated DC-DC inside the inverter, it is coupled with the DC output of photovoltaic MPPT at the BUS, and finally the energy is converted into alternating current through the inverter output and connected to the grid. Some inverters have backup output function.
- Low-voltage system have the following main problems to cause long time installation and high cost: ①The inverter and battery are independently dispersed and very heavy, which is difficult on installation; ②The connection wire between inverter and battery connection is not standardized and need the on-site processing.
- High-voltage Energy Storage system adopts a two-stage architecture, in which several battery modules are output in series through the high-voltage control box, and the voltage range is generally 85~600V. The output of the battery cluster is connected to the inverter, and the DC-DC unit inside the inverter is coupled with the DC output of the photovoltaic MPPT at the BUS, and finally converted into alternating current through the inverter output and connected to the grid. Some inverters are equipped with backup output function.
- What is the main problen with the high-voltage system?One side,in order to avoid the direct series use of different batches of battery modules, it is necessary to do a good job in the production, shipment, warehouse, installation of strict batch management, which requires the investment of a lot of manpower and material resources, and the process will be very complicated, but also bring trouble to the customer stock. On the other hand,the difference between modules will be widened due to the self-consumption and capacity attenuation of the battery. Generally, the system needs to be checked before installation. If the difference between modules is large, manual power supplement is required, which is time-consuming and labor-consuming.
- The loss of system battery’s capacity because of module differences.Due to differences in cells,some batteries cannot be fully charged/discharged for a long time, resulting in partial capacity loss of the battery system.
- High technology requirement and high maintenance cost.In order to ensure the reliable and safe operation of household energy storage system, doing a good job in operation and maintenance is one of the effective measures.However, due to the relatively complex architecture of household high-voltage energy storage system, it requires high professional level of operation and maintenance personnel. In the actual use process, there are often problems of difficult maintenance, time-consuming and labor consumption, mainly for the following two reasons:
- Regular maintenance need to carry out SOC calibration, capacity calibration or main loop inspection for the battery pack.
- When the battery module is abnormal, the conventional lithium battery does not have the automatic balancing function, so maintenance personnel need to manually replenish the power on site, which cannot quickly respond to customer needs.
- Mixed use of old and new batteries accelerate the aging and capacity’s mismatch of new batteries.
- For the household low-voltage energy storage system lithium battery mix old and new, the battery internal resistance difference is large, easy to cause circulation, battery temperature rise, will accelerate the aging of new batteries.
- In the household high-voltage energy storage system, the old and new battery modules are mixed in series. Due to the barrel effect, the new battery module can only be used with the capacity of the old battery module, and the battery cluster will have serious capacity mismatch.
- For example, the available capacity of the new module is 100Ah, and the available capacity of the old module is 90Ah. If they are mixed, the battery cluster can only use 90Ah. To sum up, it is generally not recommended to use new and old lithium batteries directly in series or parallel.
- Low battery protection rating.