Skip to main content

How long does a salt battery last?

The life of a battery of any type depends on various parameters, such as temperature (lead, lithium), depth of discharge (all batteries), charging and discharging currents (all batteries), length of storage before use (lithium, lead), etc.

An important parameter is the charging and discharging power (current intensity of charging and discharging). If a battery is very heavily loaded, such as in an e-vehicle, then the battery will not live as long as if it is only rarely discharged, as is the case with a UPS system.

The cycle depth also plays a role. For the salt battery, this can be seen in the following diagram. It should be noted that this curve is a "synthetic" curve derived from accelerated cell tests in the laboratory. After all, you can't wait 20 years for the tests to be completed. The diagram shows a life expectancy, i.e. an average life span for a standard cycle.

What is the charging behaviour of a salt battery?

The salt-nickel battery is a "cosy" battery. It charges slowly. The battery itself - without taking the battery inverter power into account - can absorb about 2 kW of power at maximum and only for a short time (1 hour) when the battery is almost empty. The salt battery is therefore not suitable for absorbing large and short-term PV production peaks.

If larger PV production peaks are to be utilised in order to reduce the return delivery to the electricity grid, a combination of battery and thermal storage is recommended. The battery storage then takes over the basic supply of the house with its own electricity and the thermal storage (heating rod or heat pump) stores additional surplus in the form of hot water.

How long does it take to fully charge a salt battery?

The duration until the salt battery is 100 % charged depends on the initial state of charge. It takes approx. 11 hours to completely charge a completely empty battery. 

The diagram gives insight into the loading times. Click on the image to see an enlarged version. 

What is the discharge behaviour of a salt battery?

Typically, a salt battery can be discharged faster than it can be charged. A 9 kWh salt storage can be discharged with a maximum of 6 kVA continuous power.

Due to the internal resistance of the battery, the internal temperature of the salt battery increases with large discharge currents. The battery can be operated with an internal temperature between 265° Celsius and 350° Celsius. This means that this battery has the widest operating temperature range of all known batteries.

The diagram shows the energy content of the battery at different discharge rates.

How much energy is needed to bring a 9 kWh salt battery to operating temperature (250° C)?

To bring a 9 kWh salt battery to operating temperature requires 9 kWh and takes about 6-8, maximum 12 hours. If the salt battery is heated up via normal mains electricity, the costs are only about 2 CHF in Switzerland – in Germany it costs about 3 EUR. Of course, the battery can also be heated up via your own photovoltaic system.

How much power is needed to keep the 9 kWh salt battery at operating temperature?

On average, 120 watts are required for self-preservation of the operating temperature per 9 kWh salt battery. The battery has an efficiency of 90 % with a standard cycle of C/5. This means that the battery requires approx. 10 % to maintain the temperature of 250° C.

With what maximum power can the batteries be discharged?

Each type of battery heats up during discharge because a battery has an "internal resistance". The internal resistance of the salt battery is greater than that of a lithium-ion battery (LIB). Thus, the salt battery heats up faster than a LIB. To prevent the saline battery from overheating during rapid discharging (internal temperature > 330° Celsius), innovenergy has limited this discharging power to 100 A per battery, which corresponds approximately to a discharging power of 5 kW.

The salidomo© ECO is a single-phase system with a single battery inverter with a capacity of 2.4 kW (or 3 kVA). The inverter can draw 2.4 kW of power from the battery.

The salidomo© 9 is a three-phase system with a rated power of 7.2 kW (or 9 kVA). The three battery inverters could draw about 7 kW from a single saline battery. However, due to the battery, only a maximum of 5 kW can be extracted. With the salidomo© 18, on the other hand, the entire inverter power of 7.2 kW can be taken from the two salt batteries.

The salidomo© EXT 27/36 is also a three-phase system with a nominal battery inverter power of 12 kW (or 15 kVA). The three batteries of the salidomo© EXT 27 can deliver a maximum of 15 kW; the four batteries of the salidomo© EXT 36 the whole 20 kW. The three battery inverters, however, can extract a maximum of 12 kW of power from the salidomo© batteries.

This discharge power applies at an operating temperature of 25° Celsius. If the temperature rises, the inverter power drops – this is called "derating".

See also technical data sheet of the inverters: