Battery Backup & Autonomy Calculator Estimate Solar Battery Needs Quickly calculate how much battery capacity you need to power your devices for 1–5 days without sunlight. Get the right solar panel size and battery bank in Wh and Ah instantly. Daily Energy Usage (Wh): Number of Backup Days: Depth of Discharge (% usable battery, default 80): System Voltage (V): 12V 24V 48V Peak Sun Hours per Day: Calculate