Why gross battery energy, usable capacity and inverter settings matter for residential sodium-ion storage.

Recent media coverage has brought attention to AuroraCell’s residential sodium-ion energy storage system, RESS. Readers may have noticed two capacity figures: 9.7 kWh in early reporting and 9.3 kWh in our current product specifications.

These figures describe different energy boundaries. Here, we explain the distinction—and why the inverter also matters when determining how much battery energy your system can access.

Why Did Media Coverage Report 9.7 kWh?

Early coverage, including pv magazine’s launch article, referenced approximately 9.7 kWh.

This figure represents gross nominal cell-level energy. It should be distinguished from the usable energy specified for the complete battery system.

AuroraCell specifies 9.3 kWh of usable battery-system energy at 100% depth of discharge under reference operating conditions. This is the figure to use when evaluating the RESS battery’s specified usable capacity.

Neither figure should be interpreted as a guarantee of the AC energy delivered to household appliances.

What Does 100% Depth of Discharge Mean?

Depth of discharge, or DoD, describes how much of the specified battery capacity can be discharged within its permitted operating limits.

For RESS, 100% DoD means that all of the specified 9.3 kWh usable battery capacity can be accessed under the reference operating conditions, with a compatible, correctly configured inverter.

It does not mean discharging the cells to zero volts or operating beyond the battery management system’s protection limits.

Why the Inverter’s Lower Voltage Limit Matters

A “48 V” inverter designation alone does not establish compatibility with the battery’s full operating range.

To access the full specified usable capacity, the inverter must support discharge down to the RESS lower operating limit of 32 V, with the correct battery settings and communication.

An inverter that stops discharging at a higher voltage may leave part of the available battery energy unused.

For illustration, our battery-side reference values are:

For example, a 40 V cut-off may make approximately 1.2 kWh less energy accessible than operation down to 32 V under the same reference conditions.

These are approximate battery-side values. Actual delivered energy depends on temperature, discharge current, wiring losses, BMS settings and inverter efficiency. AC energy supplied to the home will be lower due to conversion losses.

This is why selecting and correctly configuring the inverter is particularly important for sodium-ion battery systems.

A Matched Inverter Solution

AuroraCell offers a matched 12 kW three-phase hybrid inverter supporting a 30–60 V battery voltage range, as described on our RESS product page.

This range accommodates the intended RESS voltage window and enables access to the battery’s full specified operating range when correctly configured. The inverter’s 30 V capability does not change the battery’s specified 32 V lower operating limit.

Other low-voltage hybrid inverters can also be suitable, provided their operating voltage range, communication protocol and battery settings are compatible.

Our Commitment to Technical Transparency

The key figures are:

• 9.7 kWh: Gross nominal cell-level energy referenced in early reporting.
• 9.3 kWh: Specified usable battery-system energy at 100% DoD under reference conditions.
• 32 V: Required lower battery operating voltage for accessing the full specified usable capacity with a correctly configured inverter.

The important consideration is how much energy the complete battery-and-inverter system can make available under its actual operating conditions.

At AuroraCell, we believe transparent technical specifications help installers, system integrators and homeowners make informed decisions about sodium-ion energy storage.

Explore the AuroraCell RESS product page or contact our team at info@aurora-cell.com for technical information and inverter compatibility guidance.