Enter your monthly energy usage and sunlight conditions to instantly calculate how many solar panels you need, system size, annual energy production, savings, payback period, and CO2 reduction. Includes roof area estimate and visual layout.
📊 System Parameters
📈 Results
🏠 Roof Layout Preview
🔄 Sun Hours Comparison
| Sun Hours | Panels | System Size | Annual Energy | Payback |
|---|
📖 How to Use
- Enter your monthly energy usage in kWh (check your utility bill)
- Set your local peak sun hours — click a reference tag above for quick fill
- Choose panel wattage (common: 400W-550W) and installation cost per watt
- Enter your electricity rate to calculate savings and payback period
- Results update automatically, including panel count, annual energy, and CO₂ reduction
💡 System efficiency defaults to 80%, accounting for inverter losses, temperature effects, and wiring. Premium components may reach 85%; older systems might be 75%. Cost per watt includes installation — typically $2.50-$4.00/W in the US.
About the Solar Panel Calculator
The Solar Panel Calculator helps you quickly estimate how many solar panels you need, what system size to install, and how long it takes to recoup your investment. Simply enter your monthly energy consumption and local sun conditions to get a complete system design.
Calculations use industry-standard formulas: System size (kW) = Daily energy (kWh) ÷ (peak sun hours × system efficiency). Panel count = System size × 1000 ÷ panel wattage. Annual production = System size × peak sun hours × 365 × efficiency.
This tool also provides a roof area estimate (using a layout factor of 0.8 for maintenance access) and CO₂ reduction based on the grid average emission factor of 0.4 kg/kWh. Payback period = Total system cost ÷ Annual savings, helping you evaluate the financial viability of going solar.
All calculations run locally in your browser — your data never leaves your device. No registration required, completely free. Works on mobile and desktop.