Sodium-ion storage powers fully off-grid solar home in Germany

A homeowner in Augsburg, Germany, wanted to run their house without a connection to the public grid. The system needed to cover household demand day and night using only onsite solar and battery storage.

The basement installation made battery safety an important part of the choice. The homeowner had concerns about installing a large lithium-ion battery system indoors and asked SALZSTROM, BIWATT’s local distributor, about alternatives. SALZSTROM proposed a sodium-ion solution based on BIWATT R2 batteries and H3 hybrid inverter.

The installation pairs a 49 kWp PV array with 270 kWh of storage. It uses 60 BIWATT R2 sodium-ion battery units and four 12 kW BIWATT H3 inverters, providing 48 kW of inverter power.

Safety and environmental impact were key factors in the battery choice. BIWATT’s sodium-ion chemistry offers greater thermal stability and a lower risk of thermal runaway than LFP, addressing the homeowner’s concerns about a large indoor battery installation.

Lithium extraction can involve significant water use and land disturbance. BIWATT’s sodium-ion technology instead draws on abundant sodium resources and hard carbon derived from coconut shells, offering a lower-impact materials route that fits the homeowner’s goal of creating an all-green home energy system.

Cold-weather performance was especially important for a fully off-grid home. In winter, any energy used to heat the batteries would have to come from the home’s own solar-and-storage system. BIWATT rates the R2 for operation down to -30°C without an auxiliary heating system, keeping more stored energy available for household use.

The result is a home energy system powered entirely by onsite solar and storage, giving the homeowner a safe, fully green energy solution.

The 60 R2 units are linked through BIWATT’s dynamic balancing technology to form a single 270 kWh storage network. Solar power generated during the day is stored for use at night and when PV output is low.

The completed system is designed to supply the whole home continuously without a grid connection or the need to purchase grid electricity.

The homeowner described the result, saying, “You made a dream come true.”

BIWATT launched the world’s first sodium-ion all-in-one HESS in 2023. The indoor R2 followed in 2024, the outdoor R3 in 2025, and the stackable all-in-one R5 and I3 C&I storage system in 2026.

Contact BIWATT for more information.