Battery Capacity Degradation Conditions

The usable battery capacity in kWh stated in the datasheet is issued based on a test conducted in a temperature and humidity controlled test environment using 0.25C charging power.

The usable battery capacity experienced by our customers can vary based on external conditions as well as usage of the battery over time. Here below we identify possible root causes for battery usable capacity degradation:

Low Ambient Temperature:

As it is common for other lithium-ion batteries (for example in electric vehicles) especially LFP based, the usable battery capacity will decrease for ambient temperatures lower than 25°C (rated temperature for internal testing). Some battery systems may include heating systems to compensate for this capacity loss but these affect the efficiency and conversion losses.

In our testing we predict that each 1°C decrease in ambient temperature below 25°C will correspond to around 1% usable capacity decrease in kWh. This decrease is fully reversible meaning that when the ambient temperature increases, the usable capacity will increase.

Battery Aging:

As for all other battery products, the usable capacity in kWh will decrease with usage of the battery. Sungrow provides a publicly available Warranty Document which explains the conditions in which the warranty applies and the way the usable capacity must be measured to submit a warranty claim.

In our testing we assume an everyday battery utilization with a 100% DOD (depth of discharging) cycles. The Warranty Document specifies a minimum throughput energy (MWh) for each SBR battery model for 60% of SOH remaining after 10 years of usage. We expect the cumulative 10-years capacity decrease typically by 30% in such scenario. In the Warranty Document, an additional warranty condition is specified with a different throughput energy (MWh) within the same 10-year period which will result in an expected remaining DOD of at least 80%.

This usable capacity decrease due to battery ageing is irreversible.

These two conditions are to be considered independent of each other. These conditions are not to be considered exhaustive as other conditions may affect the battery capacity for each battery system.