Solar Battery Storage Calculator
Battery Capacity Sizing
Calculate required battery capacity for your solar system
Solar + Battery ROI
Calculate return on investment for solar battery storage
Formula
Battery Capacity = (Daily Usage x Backup Days) / DoD / Inverter Efficiency | Annual Savings = Daily Energy x (Peak Rate - Off-Peak Rate) x 365
Frequently Asked Questions
How much battery storage do I need for my home?
The average US home uses 30 kWh/day. For evening-only backup, 10-15 kWh is sufficient (one Tesla Powerwall 3). For full-day backup, 30-40 kWh. For multi-day outage protection, multiply daily usage by desired backup days and add 20% for losses.
What is depth of discharge (DoD)?
DoD is how much of the battery capacity you can actually use. Lithium iron phosphate (LFP) batteries allow 90-100% DoD. NMC lithium batteries allow 80-90%. Lead-acid only 50%. A 10 kWh battery at 90% DoD provides 9 kWh of usable energy.
Is a solar battery worth the investment?
It depends on your electricity rates, rate structure (time-of-use vs flat), and how much you value backup power. Batteries pay for themselves fastest with high peak rates ($0.30+/kWh) and low off-peak rates. The 30% federal tax credit significantly improves ROI.
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