Solar Panel Output Calculator
Estimate the daily and annual energy output of a solar panel system based on panel wattage, quantity, peak sun hours, and system efficiency losses.
Rated power output of each panel (typically 250–600 W)
Total number of solar panels in the system
Average daily peak sun hours for your location (1–7 typical; use 4–5 for most of the US)
Overall system efficiency accounting for inverter, wiring, temperature, and soiling losses (typically 75–85%)
Your utility rate in cents per kWh — used to estimate annual savings
Formula
System DC Capacity (kW)
Psystem = (Panel Wattage × Number of Panels) ÷ 1,000
Daily AC Energy Output (kWh/day)
Edaily = Psystem × PSH × ηsystem
Annual Energy Output (kWh/year)
Eannual = Edaily × 365
Capacity Factor (%)
CF = Eannual ÷ (Psystem × 8,760) × 100
CO₂ Offset (metric tons/year)
CO₂ = Eannual × 0.386 kg/kWh ÷ 1,000
Where: PSH = Peak Sun Hours (equivalent full-sun hours per day); ηsystem = overall system efficiency (inverter + wiring + temperature + soiling losses).
Assumptions & References
- Peak Sun Hours (PSH) represent the number of hours per day when solar irradiance averages 1,000 W/m² (1 kW/m²). This is location-dependent and can be looked up via NREL PVWatts or the Global Solar Atlas.
- System efficiency (Performance Ratio) of 75–85% is typical for modern grid-tied systems, accounting for inverter losses (~4%), DC wiring losses (~2%), temperature derating (~5%), soiling (~2%), and mismatch losses (~2%). Source: NREL, 2014.
- CO₂ emission factor of 0.386 kg CO₂/kWh is the US average grid emission factor per the EPA eGRID 2022 national average.
- Annual output assumes uniform daily production (Edaily × 365). Actual output varies seasonally.
- This calculator does not account for shading, panel degradation (~0.5%/year), or local incentives.
- Electricity savings are calculated as: Annual kWh × (rate in $/kWh). Net metering policies vary by utility and state.