Heiwit obtains CEI 0-21 certification for its single-phase inverter for sodium-ion batteries

In the energy storage landscape, obtaining the CEI 0-21 certification for a grid-connected inverter paired with sodium-ion batteries is an important step. The result achieved by the Heiwit team represents not only a technological step forward, but also a system validation that opens up new opportunities for integrating renewables and decarbonising electricity grids.

Why certification of a grid-connected inverter is crucial

In the electrochemical storage sector, the certification of inverters for grid connection according to standards such as CEI 0-21 (low voltage) or CEI 0-16 (medium voltage) is an essential prerequisite for ensuring safety, reliability and full interoperability with grid operators.

Heiwit successfully completed this process, developing a solution that pairs latest-generation sodium-ion batteries with the Virgo single-phase hybrid inverter, optimised to manage the voltage and current characteristics typical of sodium.

The trials: testing and compliance

The route to certification involved extensive testing of:

• Electromagnetic compatibility (EMC)

• Response to network commands (e.g. anti-islanding, frequency/voltage adjustment)

• Electrical safety and energy efficiency

• BMS-inverter interfacing, with active sodium cell monitoring and management

One of the most challenging aspects was the calibration of voltage and current limits, as sodium ion batteries have different charge and discharge curves compared to lithium. This required firmware customisation on the inverter and the development of new balancing strategies, CAN communication and integrated protection algorithms.

The outlook for new markets

The potential is enormous: sodium-ion systems have good thermal stability and a reduced, though not zero, fire risk. They are sustainable (no lithium or cobalt) and use more abundant raw materials. With CEI 0-21 certification they can be connected to the Italian low-voltage grid.

Heiwit continues to invest in research and development to push the boundaries of innovation and deliver genuinely disruptive solutions in the storage sector.

Update: Heiwit holds CEI 0-21 certification for both the Lybra three-phase inverter and the Virgo single-phase inverter. For the Lybra with the battery, certification is issued by TÜV Rheinland: certificate no. A3 50741827 0001. For the Virgo with the 10 kWh battery, certification is issued by TÜV SÜD on the basis of the type tests: document no. D 132944 0003 of 17 October 2025. Compliance with CEI 0-21 applies to the combination of the inverter and the storage system, not to the individual component: in the Heiwit sodium-ion range You’ll find models designed to work in tandem with hybrid inverters.