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How to Size a Solar Panel Array

Sizing a solar panel array correctly ensures your system produces enough electricity every day without overspending on excess capacity. The three core variables are daily energy consumption (kWh), peak sun hours at your location, and the wattage rating of each panel.

Step-by-Step Sizing Guide

1. Measure Your Daily Usage: Check your electricity bill for monthly kWh and divide by 30. Add 15–20% buffer if you plan to add appliances later.
2. Find Your Peak Sun Hours: Look up your location's solar resource data. The default of 4.5 hours is a safe conservative estimate for most temperate regions.
3. Choose a Panel Wattage: Modern residential panels range from 300W to 450W. Higher-wattage panels reduce the number of panels needed for the same output.
4. Apply the Loss Factor: Multiply your raw requirement by 1.25. Real-world systems consistently produce less than their rated capacity due to heat, shading, and conversion losses.
5. Round Up the Count: Always round the panel count up to the next whole number to guarantee you meet your energy target.

Common Sizing Mistakes to Avoid

• Ignoring seasonal variation: Size for your worst month (typically December for northern climates), not the annual average.
• Skipping the loss factor: A 1:1 system will under-produce on hot days, cloudy periods, and as panels age.
• Using nameplate wattage alone: Panel output degrades 0.5–0.8% per year. Build in headroom for long-term performance.