To calculate battery capacity for a solar system, divide your total daily watt-hours by depth of discharge and system voltage to get amp-hours needed. Use the formula: Total Wh ÷ DoD ÷ Voltage = Required. Your primary use case should drive capacity decisions, not maximum theoretical needs. Factor in 10-15% efficiency losses and plan for 20% capacity degradation over 10 years. Efficient battery capacity calculation is crucial for maximizing the benefits of a solar system. A typical solar battery stores about 10 kWh. To meet higher energy needs, you might require additional batteries. Installation costs are around $9,000. Whether you're powering a cabin, RV, tiny home, or just want backup energy, this tool gives you a solid starting point.