Press release
Energy Storage Inspection 2025: New efficiency records and first energy management test for home storage systems
22 home storage systems have been evaluated by the HTW Berlin, including new products from Fox ESS, Fronius, Kostal and SAX Power.
March 6, 2025
22 solar energy storage systems from a total of 17 manufacturers have been evaluated by the HTW Berlin University of Applied Sciences in this year’s Energy Storage Inspection. Eight of the systems were new to the test, including those from Fox ESS, Fronius, Kostal and SAX Power. Thanks to technological innovations, the Plenticore G3 hybrid inverter from Kostal and the Home Plus battery system from SAX Power set new efficiency records for charging and discharging operations.
HTW study confirms: RCT Power, Energy Depot, Fronius and KOSTAL shine with outstanding system efficiency
This year, 17 manufacturers with 22 electricity storage systems took part in the established comparison of energy efficiency. The Solar Storage Systems Research Group at HTW Berlin evaluated the energy efficiency of the devices in the two power classes: 5 kW and 10 kW. In the evaluation with the System Performance Index (SPI), the hybrid inverters from the manufacturers RCT Power, Energy Depot, Fronius and KOSTAL defended their top position. The researchers awarded 10 systems the highest efficiency class A. The results of the evaluation show the outstanding efficiency of European inverter manufacturers.
In addition to the European suppliers, only the Chinese manufacturers GoodWe and Fox ESS are represented among the best-placed devices this year. Fox ESS achieved a very good SPI (10 kW) of 94.8 % with the new H3-10.0-Smart hybrid inverter and the ECS2900-H6 battery. The new and powerful hybrid inverters PLENTICORE G3 M 10 from KOSTAL and Symo GEN24 12.0 Plus SC from Fronius performed even slightly better in combination with a BYD battery storage system. Both systems can charge and discharge the Battery-Box Premium HVS 12.8 with more than 10 kW. They are suitable for larger PV systems. The HTW researchers were surprised that two companies decided to take part in the study anonymously despite their product’s very good efficiency results.
Battery system with cutting-edge multilevel-technology achieves an average efficiency rating of more than 98 % in discharge mode for the first time
“Since 2018, we have evaluated over 90 photovoltaic battery systems as part of our Energy Storage Inspection. This is the first edition to include a battery system with multilevel-technology,“ says Dr. Johannes Weniger, initiator of the Energy Storage Inspection. The SAX Power Home Plus system is different from conventional inverters: A unqiue feature of the SAX Power Home Plus system is the incorporation of power electronics within each battery cell string. This feature allows the 24 battery cell strings within the device to be activated and deactivated with sub-second response times. At the point of output from the battery system, the voltages of the activated cell strings are combined into a sinusoidal alternating voltage. Compared to conventional inverters, the multilevel concept facilitates reduced conversion losses during both charging and discharging operations. The AC-coupled SAX Power Home Plus battery system achieved the highest efficiency levels ever recorded in all Energy Storage Inspections across the entire operating range.
New efficiency record of 98.2 % in charging mode: Kostal impresses with the new Plenticore G3 hybrid inverter
Unlike AC-coupled battery systems, DC-coupled systems combine all power electronic components in the hybrid inverter. One of the 18 hybrid inverters tested only achieved an average efficiency of 92 % in charging mode on the test bench. As a result, 8 % of the solar power is lost as heat in the hybrid inverter when charging the battery. With this less efficient device, the conversion losses are more than four times higher than with the front-runner PLENTICORE G3 M 10 from KOSTAL. “The IMS PCB technology enables us to better dissipate the heat from the silicon carbide power semiconductors on the PCB. This allowed us to achieve a higher power density in the same space. The advantage of this is the lower component temperatures of our high-performance battery connection which reduces the conversion losses in our new hybrid inverter,” explains Andreas Forck, Senior Manager R&D PV Electronics at KOSTAL.
One hybrid inverter in the test achieved only 54 % efficiency when delivering 100 watts
Although the Symo GEN24 12.0 Plus SC hybrid inverter from FRONIUS can provide a considerable output of more than 12 kW on the AC output side, it can still achieve an efficiency of 76 % at night even with a power output of 100 W. Only the Power Storage DC 10.0 and Power Battery 11.5 combo from RCT Power was able to surpass this value with an efficiency of 86 %. This means that the battery only needs to be discharged at 116 W so that the hybrid inverter from RCT Power can supply the electrical consumers in the house with 100 W. The inverter of an anonymous competitor only achieved an efficiency of 54 %, which means that the battery needs to be discharged at 186 W to supply the same load.
New energy management test by KIT and HTW Berlin demonstrates the advantages of forecast-based battery charging
FENECON, KOSTAL, Sonnen, RCT Power and two anonymous manufacturers participated in the new energy management test developed jointly by the Karlsruhe Institute of Technology (KIT) and HTW Berlin. The following chart compares the characteristics of the analyzed energy management systems. While 3 of the 6 energy managers tested require a web connection to receive the weather forecasts, the other 3 energy management systems create the forecasts based on data which is collected on site. Forecast-based energy management also differs in terms of how frequently the charging schedule is updated. Slower battery charging to extend battery life is only observed in the home storage system from FENECON and another anonymously participating manufacturer.
Forecast-based charging strategies extend the battery life
Most of the more than 1.7 million battery storage systems installed in Germany charge early in the morning when there is a surplus of solar power. The problem with this is that long durations at high charge levels shorten the lifetime of lithium-ion batteries. With their forecast-based energy management strategies, all six manufacturers were able to reduce the amount of time the battery spent fully charged. On sunny days, one of the solar power storage systems tested charges primarily in the late afternoon hours. This allowed the energy management system to reduce the amount of time the battery was fully charged by 8 hours. During the test period, this intelligent charging strategy halved the duration the battery storage system remained above a 90 % charge.
About the Energy Storage Inspection
In its annual Energy Storage Inspection, the Solar Storage Systems Research Group at HTW Berlin compares and evaluates the energy efficiency of PV-battery systems. Since 2018, 33 manufacturers with a total of 90 storage solutions have participated, including well-known companies such as BYD, Fenecon, Fronius, HagerEnergy, Kostal, SMA, Sonnen and Viessmann. In 2023, the researchers at HTW Berlin developed the Energy Storage Inspector, a tool to support private customers in their search for a suitable and efficient home storage system. The web app can be used to compare the most important efficiency characteristics of the analyzed storage systems. The Energy Storage Inspector is continuously being expanded to include new products. Interested manufacturers can contact the Solar Storage Systems Research Group at HTW Berlin directly.
