Solar Power System Calculator
Size your off-grid solar system and estimate your payback period. Enter your daily energy usage and location details below.
US average is 4.5 peak sun hours. See sidebar table for your area.
48V is recommended for larger systems. 12V suits small RV setups.
How many days should batteries last without sun?
Common residential panels: 300-450W.
US average: $0.14/kWh. Check your utility bill.
Off-grid systems average $2.50/W installed. Grid-tied: ~$1.50/W.
How It Works
This calculator sizes a complete off-grid solar power system based on your daily energy consumption and local sun conditions. It accounts for real-world losses and battery chemistry.
Derating Factor (0.75)
The 0.75 derating factor accounts for real-world system losses: inverter efficiency (~90%), wiring losses (~2%), panel degradation, temperature losses, and dust/shading. A system rated at 100W typically produces about 75W in practice.
Depth of Discharge (DoD)
Lead-acid batteries should only be discharged to 50% to avoid damage and extend life. LiFePO4 (lithium iron phosphate) batteries can safely discharge to 80-90%, giving you more usable capacity per dollar invested.
Peak Sun Hours
Peak sun hours are not the same as daylight hours. They represent the equivalent number of hours with full 1,000 W/m² solar irradiance. A location with 6 daylight hours and partly cloudy skies may only have 4 peak sun hours. Use the sidebar table to find your area's value.