The most efficient integrated energy storage

June 2019

Very good efficiency rating for Junelight in the Energy Storage Inspection 2019.

At 89.4 percent, Siemens’ integrated energy storage system has been proven to be the most efficient of all test systems

Every year, renowned experts from the University of Applied Sciences “Hochschule für Technik und Wirtschaft (HTW) Berlin“ thoroughly test energy storage systems available in Germany – most recently with the Energy Storage Inspection 2019 (Stromspeicher-Inspektion 2019). Only a few manufacturers are confident enough to participate and permit the resulting data to be published. Although German consumers have a choice of more than 300 systems from 26 manufacturers, only seven manufacturers consented to being named.    

Highest efficiency with a “very good” rating

So it’s no wonder that all the named systems achieved an efficiency of over 88 percent and received a “very good” rating indicating that they were “highly efficient.” Of all the integrated systems tested, the Junelight Smart Battery 9.9 from Siemens received the highest rating of 89.4 percent, followed by the sonnenBatterie eco 8.0/6 at 88.6 percent. Other providers of integrated systems decided against participation or publication.

Highest battery efficiency of all the named systems

Efficiency affects the carbon footprint

The researchers emphasized that it is mainly the storage efficiency that has a negative or positive impact on the carbon footprint and makes a contribution to climate protection. For example, they took a highly efficient storage system and a less efficient storage system and compared their simulated carbon footprint based on grid supply and grid in-feed.


The result: Whereas highly efficient storage reduces annual CO₂ emissions by around 35 kg, the less efficient system increases the household climate footprint by as much as 92 kg per year. “If you consider high efficiency when purchasing storage, you will not only save money later on, but you will also be doing something good for the environment,” says Dr. Volker Quaschning, professor of renewable energy systems at HTW Berlin and co-author of the study.

Benefits of integrated systems

Integrated systems include the batteries as well as the inverter and control intelligence. All the components are systematically coordinated and optimized in combination with each other. This is especially relevant in terms of safety. In this regard, the Junelight Smart Battery has even been independently certified as a system by the VDE.

But integrated systems also offer significant advantages in terms of commissioning and service. You enjoy the benefits of a single contact as well as a warranty and service concept. If a problem occurs, troubleshooting is fast and efficient and you have only one point of contact for both the battery and inverter manufacturer.    

About the study

The Energy Storage Inspection – a scientific study by HTW Berlin funded by the German Federal Environmental Foundation (Deutsche Bundesstiftung Umwelt, or DBU) – was conducted for the second time in 2019. 


The Solar Storage Systems Research Group at HTW invited all suppliers currently active on the German market to participate and ultimately tested the efficiency of 16 battery systems for photovoltaic systems from eight participating companies. Seven companies consented to have the results published. The laboratory tests were performed by independent testing institutes. The first Energy Storage Inspection was conducted in 2018.

Released by Verena Koppe