Solar Battery Calculator: Size Your Storage System Right
Battery storage shifts your solar production from peak production hours to evening usage. Use this calculator to size a battery for either critical-load backup, daily cycling against time-of-use rates, or full off-grid independence.
Sizing assumes 60% backup of average daily usage. The federal residential credit is $0 for a 2026 expenditure. Increase capacity for whole-home backup or off-grid use.
Three Reasons to Buy a Battery
Keep critical loads (refrigerator, lights, internet) running during outages. 10-15 kWh covers a typical home for 1-2 days of essentials.
In states with time-of-use rates (California, Massachusetts, Arizona), batteries discharge at peak evening rates that can be 3x off-peak rates. ROI in 6-9 years.
For full grid independence, plan for 2-3 days of autonomy. Most homes need 30-60 kWh of usable storage plus an oversized solar array.
Battery Pricing in 2026
Residential lithium-iron-phosphate (LFP) batteries cost roughly $1,000 per kWh of usable capacity installed in 2026. A typical 13.5 kWh system (Tesla Powerwall, Enphase IQ Battery 10) lands at $13,500-$18,000 installed before incentives.
The federal residential credit does not reduce that price for a battery expenditure made after December 31, 2025. This calculator leaves the federal line at $0. State or utility battery incentives, if any, are not invented here — confirm them locally.
Solar Battery Calculator FAQ
See if a battery pays off where you live
Battery economics hinge on your state's net metering and time-of-use rates. Run the full calculator to see your solar + storage payback with local incentives applied.