Solar Panel Energy Estimate

Estimate the daily kilowatt-hours your solar array can deliver using the panel wattage, the average peak sun hours at your location, and the number of identical panels in the string.

Use the STC (standard test condition) rating printed on the panel data sheet.
Find this value in local irradiance maps or PVWatts® data—most regions range between 3 and 6 hours.
Count panels wired in the same orientation and array; mixed panel types require separate calculations.

This estimate assumes panels operate at their STC wattage under clear-sky conditions. Local shading, inverter clipping, temperature, snow cover, and maintenance can significantly affect actual energy production—consult a licensed installer for system design.

Examples

  • 410 W panel × 5.2 sun hours × 12 panels ⇒ 25.6 kWh/day before PR adjustment
  • 370 W panel × 4.5 sun hours × 8 panels ⇒ 13.3 kWh/day (≈10.6 kWh/day at 80% PR)
  • 320 W panel × 3.8 sun hours × 16 panels ⇒ 19.5 kWh/day
  • 450 W panel × 6.0 sun hours × 4 panels ⇒ 10.8 kWh/day for a small rooftop array

FAQ

What exactly are peak sun hours?

They represent the total solar energy received per day expressed as an equivalent number of hours at 1,000 W/m². Multiply your panel wattage by this value to estimate ideal production.

Why divide the watt-hours by 1,000?

Panel wattage multiplied by hours yields watt-hours. Dividing by 1,000 converts watt-hours to kilowatt-hours (kWh), which is the unit utilities use for billing and most monitoring systems.

How do I include shading or temperature losses?

After the calculation, multiply by your system's performance ratio. If you anticipate 18% losses, use a PR of 0.82. Many installers provide a PR estimate in the proposal.

Can I model battery charging or seasonal variation?

Use monthly peak sun hour data to run the calculation for each month, then apply your battery round-trip efficiency or seasonal derate factors.

Additional Information

  • Daily energy (kWh) = Panel wattage × Peak sun hours × Panel count ÷ 1,000.
  • Peak sun hours compress the varying intensity of sunlight into an equivalent number of full-power hours, making comparisons across seasons easier.
  • To account for real-world losses, multiply the result by a performance ratio (PR). Typical PR values range from 0.75 to 0.85 after inverter, wiring, and temperature losses.

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