To get an accurate picture of your daily energy needs, review your utility bills for the past year. These data provide insights into peak usage times and seasonal fluctuations. Once you have a clear idea of your average daily consumption, you can start calculating the necessary battery capacity. Multiply your average daily consumption by the number of days you want the battery to run without a charge.
Not all batteries should be fully discharged to avoid damage and extend their service life. Most lithium-ion batteries allow a discharge depth of up to 80-90%, while lead-acid batteries typically have a maximum discharge depth of about 50%. When determining the battery size, DoD is calculated by dividing the total energy requirement by the maximum safe discharge percentage.
Example: If your home consumes 30 KWH per day and you want backup power for two days, you will need at least a 90 KWH battery.
Let's look at an example calculation:
1. Determine the daily energy consumption: 30 KWH/day
2. Decide the spare time: 2 days →30kwh × 2 = 60kwh
3. Accounting for discharge depth (assuming 80%) : 60kwh ÷ 0.8 = 75kwh
4. Add buffer for future growth: +20%→75 kWh × 1.2 = 90 kWh
