How much battery storage do I need for my off-grid system?
Battery storage requirements depend on your daily energy usage and desired backup days. Multiply your daily kWh usage by the number of backup days, then account for depth of discharge limits and system inefficiencies. See also our calculate Peukert's Law Discharge Time.
What's the difference between lead acid and lithium battery sizing?
Lead acid batteries should only be discharged to 50% capacity, requiring roughly double the capacity of lithium batteries which can safely discharge to 80%. Lithium also has higher efficiency and longer lifespan.
How do I calculate my daily energy usage?
List all your appliances with their power ratings in watts, estimate daily usage hours for each, then multiply watts × hours ÷ 1000 to get kWh per day. Add up all appliances for total daily usage.
What does depth of discharge (DoD) mean?
Depth of discharge is how much of the battery's capacity you use before recharging. Limiting DoD to 50% for lead acid and 80% for lithium significantly extends battery life and maintains performance.
How many days of autonomy should I plan for?
Most off-grid systems are designed for 3-5 days of autonomy to handle cloudy weather. Consider your local climate, backup generator availability, and critical vs non-critical loads when choosing autonomy days.
Should I choose 12V, 24V, or 48V for my battery bank?
Higher voltages are more efficient for larger systems. Use 12V for small systems (<1000W), 24V for medium systems (1000-3000W), and 48V for large systems (>3000W) to reduce current and wire losses.
What system efficiency should I use in calculations?
Typical system efficiency ranges from 80-90%, accounting for inverter losses, wiring losses, and battery inefficiencies. Use 85% as a conservative estimate, or 80% for systems with older equipment. You might also find our calculate Battery Discharge Rate Discharge Current useful.