Solar Battery Storage Calculator

Your battery storage needs depend on your daily energy usage and how many days of backup you want. Multiply your daily kWh consumption by the number of backup days, then divide by the battery's depth of discharge (50% for lead acid, 80% for lithium). Add a 20% efficiency buffer on top of that total.

Depth of discharge refers to how much of a battery's total capacity you can safely use before recharging. Lead acid batteries should only be discharged to 50% to preserve their lifespan, while lithium (LiFePO4) batteries can typically handle 80% DoD. This means lithium batteries deliver more usable energy per kWh of rated capacity.

Lithium batteries (especially LiFePO4) have a higher depth of discharge (80%), longer cycle life (2,000–6,000 cycles), faster charge rates, and are lighter than lead acid. Lead acid batteries are less expensive upfront but require more total capacity and more maintenance. For most new off-grid or backup systems, lithium is the preferred choice.

System voltage affects wire sizing, inverter selection, and efficiency. 12V systems suit small loads under 1,000W. 24V works for mid-range systems up to 3,000W. 48V is the standard for whole-home systems above 3kW — it allows thinner cables, lower current, and pairs with most modern inverters and battery banks.

Divide your total required capacity in watt-hours (Wh) by your system voltage. For example, if you need 24,000 Wh at a 48V system, that equals 500 amp hours (Ah). The calculator does this automatically once you enter your energy usage and select your system voltage.

Peak sun hours represent the number of hours per day when sunlight intensity averages 1,000 watts per square meter — the standard test condition for solar panels. This is different from daylight hours. Most locations in the US average 4–6 peak sun hours. You can find your location's value from NREL's solar maps or by searching '[your city] peak sun hours'.

Real-world solar and battery systems always lose some energy to inverter conversion, wiring resistance, temperature effects, and battery inefficiency. A 20% efficiency buffer (multiplying by 1.2) is the industry-standard safety margin to ensure your system doesn't fall short under real operating conditions.

Yes. For off-grid systems, focus on the total recommended battery bank size and days of autonomy. For grid-tied backup (e.g. protecting against outages), set your backup duration to the number of hours or days you'd need to ride out a power cut. The capacity calculation logic applies equally to both use cases.