4 Difficulties & Challenges About Residential Solar Battery Storage

Residential solar battery storage system architecture is complex, involving batteries, inverters and other equipment. At present, the products in the industry are independent of each other, which may cause various problems in actual use, mainly including: complicated system installation, difficult operation and maintenance, inefficient utilization of residential solar battery, and low battery protection level.

System integration: complex installation

Residential solar battery storage is a complex system that combines multiple energy sources and is oriented to the general household, and most users want to use it as a "household appliance", which puts higher requirements on the system installation.

The complex and time-consuming installation of Residential Solar Battery Storage in the market has become the biggest problem for some users. Currently, there are two main types of residential solar battery system solutions on the market: low-voltage storage and high-voltage storage.

Low-voltage Residential Battery System (Inverter & Battery Decentralization)：

Residential low-voltage energy storage system is a solar battery system with a battery voltage range of 40~60V, which consists of several batteries connected in parallel to an inverter, which is cross-coupled with the DC output of PV MPPT at the bus by the internal isolated DC-DC of the inverter, and finally transformed into AC power through the inverter output and connected to the grid, and some inverters have a backup output function.

[Home 48V Solar System]

Low-voltage Home Solar Battery System Main problems:

① Inverter and battery are independently dispersed, heavy equipment and difficult to install.

② The connection lines of inverters and batteries cannot be standardized and need to be processed on site.

This leads to a long installation time for the whole system and increases the cost.

2. High Voltage Home Solar Battery System.

Residential High voltage battery sysem uses a two-stage architecture, which consists of several battery modules connected in series via a high-voltage control box output, the voltage range is generally 85~600V, the battery cluster output is connected to the inverter, through the DC-DC unit inside the inverter, and the DC output from the PV MPPT is cross-coupled at the bus bar, and finally The output of the battery cluster is connected to the inverter, and the DC-DC unit inside the inverter is cross-coupled with the DC output of the PV MPPT at the busbar, and finally converted into AC power through the inverter output and connected to the grid.

[Home High Voltage Solar System]

Main issues of High Voltage Home Solar Battery System:

In order to avoid using different batches of battery modules in series directly, strict batch management needs to be done in production, shipment, warehouse and installation, which requires a lot of human and material resources, and the process will be very tedious and complicated, and also brings troubles to customers' stock preparation.

In addition, the battery's self-consumption and capacity decay causes the difference between modules to be enlarged, and the general system needs to be checked before installation, and if the difference between modules is large, it also requires manual replenishment, which is time-consuming and labor-intensive.

Battery Capacity Mismatch: Capacity Loss Due to Differences in Battery Modules

1. Low-voltage Residential Battery System Parallel Mismatch

Traditional residential solar battery has a 48V/51.2V battery, which can be expanded by connecting multiple identical battery packs in parallel. Due to the differences in cells, modules and wiring harness, the charging/discharging current of batteries with high internal resistance is low, while the charging/discharging current of batteries with low internal resistance is high, and some batteries cannot be fully charged/discharged for a long time, which leads to partial capacity loss of residential battery system.

[Home 48V Solar System Parallel Mismatch Schematic]

2. High Voltage Residential Solar Battery Storage System Series Mismatch

The voltage range of high voltage battery systems for residential energy storage is generally from 85 to 600V, and the capacity expansion is achieved by connecting multiple battery modules in series. According to the characteristics of the series circuit, the charge/discharge current of each module is the same, but due to the difference of module capacity, the battery with smaller capacity is filled/discharged first, resulting in some battery modules cannot be filled/discharged for a long time and the battery clusters have partial capacity loss.

[Home High Voltage Solar Systems Parallel Mismatch Diagram]

Home Solar Battery System Maintenance: High Technical and Cost Threshold

In order to ensure the reliable and safe operation of residential solar battery storage system, good maintenance is one of the effective measures.

However, due to the relatively complex architecture of high-voltage residential battery system and the high professional level required for operation and maintenance personnel, maintenance is often difficult and time-consuming during the actual use of the system, mainly due to the following two reasons.

① Periodic maintenance, need to give the battery pack for SOC calibration, capacity calibration or main circuit inspection, etc.

② When the battery module is abnormal, the conventional lithium battery does not have automatic equalization function, which requires maintenance personnel to go to the site for manual replenishment and cannot quickly respond to customer needs.

③ For families living in remote areas, it will cost a lot of time to check and repair the battery when it is abnormal.

Mixed Use of Old & New Batteries: Accelerating the Aging of New Batteries & Capacity Mismatch

For the Home Solar Battery System, the old and new lithium batteries are mixed, and the difference in internal resistance of the batteries is large, which will easily cause circulation and increase the temperature of the batteries and accelerate the aging of the new batteries.

In the case of high-voltage battery system, the new and old battery modules are mixed in series, and 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 a serious capacity mismatch.

For example, the available capacity of the new module is 100Ah, the available capacity of the old module is 90Ah, if they are mixed, the battery cluster can only use the capacity of 90Ah. In summary, it is generally not recommended to use the old and new lithium batteries directly in series or in parallel.

In BSLBATT's past installation cases, we often encounter that consumers will first purchase some batteries for home energy storage system trial or initial testing of residential batteries, and when the quality of the batteries meet their expectations, they will choose to add more batteries to meet the actual application requirements and use the new batteries in direct parallel with the old ones, which will cause BSLBATT's battery abnormal performance in the work, such as the new battery is never fully charged and discharged, accelerating the battery aging! Therefore, we usually recommend customers to purchase residential battery storage system with sufficient number of batteries according to their actual power demand, so as to avoid mixing old and new batteries later.