Solar Panel Output Calculator
Calculate electrical output per individual solar panel and total rooftop array, accounting for panel wattage, tilt orientation, soiling, and temperature loss.
Panel Specifications & Array Count
Panel & Array Output Formula
Daily Output per Panel (kWh) = [Panel Watts × Peak Sun Hours × Derate % × (1 - Temp Loss %)] ÷ 1,000- Panel Rated Wattage: STC (Standard Test Conditions) output rating of a single module (e.g. 400 Watts).
- Derate Factor: Inverter efficiency, dust/soiling, and angle mismatch losses (typically 80% to 85%).
- Temperature Derate: Thermal power loss on hot summer days (typically 0.35% to 0.40% loss per °C above 25°C).
Step-by-Step Worked Example
Calculation Steps:
How to Use This Calculator
Assumptions & Limitations
- Panels are unshaded and south or east/west oriented with typical roof slope (20° to 35°).
- Panel efficiency degradation is estimated at standard 0.5% per operating year.
Frequently Asked Questions
Why doesn't a 400W solar panel produce 400 Watts all day long?
Panels only hit their peak 400W nameplate rating under ideal noon conditions (1,000 W/m² irradiance at 25°C). In morning and late afternoon hours, lower sun angles reduce irradiance, producing less instantaneous wattage.
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