What are peak sun hours and why do they matter for solar?

Peak sun hours (PSH) are the number of hours per day when sunlight intensity averages 1,000 W/m² — the standard test condition for solar panel ratings. A location with 5 PSH receives 5 hours of "full-strength" sun equivalent per day when accounting for the full daily solar curve. PSH directly determines how much energy your panels produce: a 5kW system at 5 PSH (×0.80 efficiency) generates 20 kWh/day. The same system at 4 PSH generates only 16 kWh/day — 20% less with no change in hardware.

What state has the most peak sun hours?

Arizona leads with 6.0–6.5 peak sun hours daily in most locations, followed by Nevada, New Mexico, and parts of California and Texas. The Southwest is the strongest solar region in the country. Hawaii averages 5.5–6.0 peak sun hours despite its tropical location.

How do I use peak sun hours to size a solar system?

Multiply your system size by peak sun hours and an efficiency factor: daily kWh = system kW × peak sun hours × 0.80. For example, a 6 kW system in Arizona (6 PSH) produces roughly 6 × 6 × 0.80 = 28.8 kWh per day. The 0.80 factor accounts for inverter loss, wiring, soiling, and temperature.

Quick Tools

Peak Sun Hours by State

Look up average peak sun hours for every US state — based on NREL solar radiation data for accurate solar system sizing.

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California

5.5

peak sun hours per day (annual average)

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All states — sorted by peak sun hours

How we calculate peak sun hours

Peak sun hours represent equivalent full-strength sun (1,000 W/m²) per day, derived from NREL satellite and ground measurements. This single value drives panel count, battery sizing, and payback calculations.

Daily kWh = System kW × PSH × 0.80

The 0.80 performance ratio accounts for inverter losses, temperature derating, soiling, and wiring losses typical in residential installations.

Frequently Asked Questions

What are peak sun hours and why do they matter for solar?: Peak sun hours (PSH) are the number of hours per day when sunlight intensity averages 1,000 W/m² — the standard test condition for solar panel ratings. A location with 5 PSH receives 5 hours of "full-strength" sun equivalent per day when accounting for the full daily solar curve. PSH directly determines how much energy your panels produce: a 5kW system at 5 PSH (×0.80 efficiency) generates 20 kWh/day. The same system at 4 PSH generates only 16 kWh/day — 20% less with no change in hardware.
What state has the most peak sun hours?: Arizona leads with 6.0–6.5 peak sun hours daily in most locations, followed by Nevada, New Mexico, and parts of California and Texas. The Southwest is the strongest solar region in the country. Hawaii averages 5.5–6.0 peak sun hours despite its tropical location.
How do I use peak sun hours to size a solar system?: Multiply your system size by peak sun hours and an efficiency factor: daily kWh = system kW × peak sun hours × 0.80. For example, a 6 kW system in Arizona (6 PSH) produces roughly 6 × 6 × 0.80 = 28.8 kWh per day. The 0.80 factor accounts for inverter loss, wiring, soiling, and temperature.

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Peak Sun Hours by State

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Reviewed April 2026

Methodology and source note

PowerSizing calculators use shared formulas, documented assumptions, and current planning inputs that are summarized on the methodology page. Use these tools for first-pass planning, comparison, and sanity checks, then confirm local code, pricing, utility tariff, and installer specifics before you buy equipment.