Is a 50% depth of discharge safe for lithium batteries?

Choosing the Right Number of Batteries

When designing an off-grid system, the number of batteries required is directly related to the desired days of autonomy and the depth of discharge. A 50% depth of discharge will result in a longer battery lifespan compared to a 80% depth of discharge. For example, a 10-day autonomy system with a 50% depth of discharge will require fewer batteries compared to the same system with an 80% depth of discharge.

Bank Sizing Considerations

To calculate the required bank size, consider the total system load in watt-hours (Wh) per day, the battery capacity in watt-hours (Wh), and the depth of discharge. For instance, a 5 kW system with an 8 kWh per day load will require a battery bank with a capacity of at least 40 kWh. With a 50% depth of discharge, this translates to a 80 kWh usable capacity.

Lithium Battery Depth of Discharge Considerations

Lithium batteries have a more complex depth of discharge profile compared to lead-acid batteries. Manufacturers often recommend avoiding depths of discharge below 20% to prevent capacity loss and extend the battery lifespan. However, a 50% depth of discharge can be safely used if the battery is properly sized and the system is designed to avoid frequent shallow discharges.