Solar & Battery Storage Sizing Calculator
Size your off-grid or grid-tie solar PV array, calculate required LiFePO4 battery storage (kWh & Ah), determine inverter continuous wattage, and view realistic balance-of-system cost estimates.
How These Calculations Work & Engineering Assumptions
Sizing an off-grid solar-plus-storage system requires matching peak generation capacity to the darkest, highest-demand periods of the year. Our calculator uses established National Renewable Energy Laboratory (NREL) and Institute of Electrical and Electronics Engineers (IEEE) methodologies:
1. Solar PV Array Sizing Formula
The solar array rating is calculated using the formula:
PV Array Size (kW) = Daily Consumption (kWh) ÷ (Peak Sun Hours × 0.80 Derate)
The 0.80 derate accounts for real-world environmental losses, including panel degradation over time, module temperature coefficients during peak summer heat, DC wiring voltage drop, and charge controller efficiency.
2. Battery Bank Usable Capacity & Depth of Discharge (DoD)
Battery bank sizing depends on the days of autonomy (how many days the home can run without solar sunlight) divided by the allowable Depth of Discharge (DoD).
- Lithium Iron Phosphate (LiFePO4): Operates safely at 80% to 90% DoD for 4,000–6,000 cycles without significant capacity degradation.
- Lead-Acid (AGM/Gel/Flooded): Should never be discharged below 50% DoD to prevent accelerated sulfation and premature cell failure.
3. Federal Tax Credit Incentives (US)
Under the Residential Clean Energy Credit (IRC Section 25D), qualified US taxpayers can claim a 30% federal tax credit on the full installed cost of both solar panels and battery storage systems with a minimum capacity of 3 kWh, regardless of whether the system is installed on-grid or completely off-grid.