Solar Panel Size & Payback Estimator
Estimate the size of the residential solar system needed to offset your monthly electric bill and calculate the system's net financial payback.
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Current Monthly Electric Bill$180 / month
Daily Peak Sunlight Hours4.5 Hours
Varies by geography: Southwest US averages 5.5+ hours, Northeast averages ~4.0 hours.Estimated Solar Investment
System Capacity Required10.42 kW
Gross Installation Cost$31,250
Federal Tax Credit (30% ITC)-$9,375
Net System Cost$21,875
System Payback Period10.1 Years
Payback model factors 30% federal clean energy credit.
Solar Sizing and Payback Calculations
To estimate the size and cost effectiveness of a rooftop solar array, our calculator runs the following equations:
• Daily Generation Target (kWh): (Monthly kWh draw ÷ 30) × target offset %.
• System Size (kW): Target kWh ÷ Peak Sunlight Hours ÷ System Efficiency Factor (modeled at 80% to account for inverter and wiring losses).
• Federal Clean Energy Tax Credit (ITC): 30% discount off gross installer invoice cost.
• Net Financial Payback: Net investment cost ÷ annual utility savings.
• System Size (kW): Target kWh ÷ Peak Sunlight Hours ÷ System Efficiency Factor (modeled at 80% to account for inverter and wiring losses).
• Federal Clean Energy Tax Credit (ITC): 30% discount off gross installer invoice cost.
• Net Financial Payback: Net investment cost ÷ annual utility savings.
Typically, solar panels have an operating warranty of 25 to 30 years. After recovering the initial installation investment (usually between 6 and 9 years depending on state-level solar sunlight and utility pricing), the system provides essentially free electricity for the remaining decades of panel life.