Executive summary

A residential energy storage system from GoodWe has received a Level 3 rating for State of Charge performance from TÜV Rheinland. The rating follows testing against the 2 PfG 3165/12.25 specification and marks the highest SOC estimation level the standard defines. Engineers recorded a maximum deviation of 1.23% between reported and actual charge levels during repeated cycling. The system also balanced a 39.6% gap between two battery clusters down to zero under test conditions.

Established in 2010, GoodWe manufactures solar inverters and energy storage systems for residential, commercial, and utility-scale markets. The company has surpassed 100 GW of cumulative installations across more than 100 countries and employs around 6,000 people, with over 1,000 working in research and development.  

Its ESA Series falls under the residential category, an all-in-one system combining a hybrid inverter, stackable battery modules, and backup switching in a single pre-wired unit. TÜV Rheinland has now assessed the system against the 2 PfG 3165/12.25 specification for State of Charge performance, and it achieved Level 3, the top tier the specification allows. 

State of Charge tells a system how much usable energy is stored in its batteries at any given moment. Homeowners depend on this figure indirectly every time their system decides when to charge, discharge, or hold reserve for a backup event. If the estimate differs from reality, the system can misjudge how much power it actually has to work with. 

To test this, TÜV Rheinland ran the ESA system through repeated charge and discharge cycles and compared its reported SOC against a reference value obtained independently. The result showed a maximum deviation of just 1.23%, within the bounds required for Level 3. 

Testers also introduced a deliberate 10% SOC deviation to simulate a faulty initial reading. During subsequent operation, the system automatically recalibrated and brought its estimate back in line with the reference value. 

A separate test looked at how the system manages uneven battery clusters. Testers set up an initial SOC gap of 39.6% between two clusters within the same system. By adjusting the charging current sent to each cluster, ESA closed that gap to zero over the course of the test. This function matters in multi-module setups, where cells or modules show changes in alignment over time if left uncorrected. 

Combined, accurate SOC estimation, automatic recalibration, and cluster balancing give the system more reliable information about the energy available across its full battery pack. That supports firm control of self-consumption, backup reserves, and general energy use, while limiting the risk of a bad SOC reading or an unbalanced cluster affecting how the system runs afterward.