Maximum depth of discharge for lead-acid batteries?

Understanding Depth of Discharge

Depth of discharge (DOD) is the percentage of the battery’s capacity that is used during a discharge cycle. For lead-acid batteries, a DOD of 50% means that 50% of the battery’s total capacity is used before the battery is recharged. A DOD of 100% would mean the battery is completely discharged, which can cause significant damage and reduce its lifespan.

Calculating Battery Capacity and Bank Sizing

When designing an off-grid system, it’s essential to calculate the total battery capacity and bank sizing to ensure the system can provide the required power for the desired number of days of autonomy. As a rule of thumb, a 200Ah battery can provide 8-10 hours of power at 20A. To calculate the total battery capacity, multiply the required daily power (in Wh) by the number of days of autonomy. For example, if the system requires 1000Wh per day and the desired autonomy is 5 days, the total capacity would be 5000Wh. To determine the required number of batteries, divide the total capacity by the capacity of a single battery.

Selecting the Right Battery Type

When selecting lead-acid batteries for an off-grid system, it’s essential to choose deep cycle batteries that are designed for frequent discharging and recharging. Look for batteries with a high cycle life (measured in cycles to 50% DOD) and a low self-discharge rate (measured in percentage per month). Some popular types of deep cycle batteries include AGM (Absorbed Glass Mat) and Gel batteries. Always follow the manufacturer’s guidelines for depth of discharge, charging, and maintenance to ensure the longest battery life.