Peak Sun Hours Calculator
Estimate peak sun hours from climate band or daily insolation for commercial PV sizing—planning values, not a full weather-year map.
Quick answer
PSH ≈ Daily insolation (kWh/m²/day) at STC reference, or use climate-band / state reference defaults. Example: 5.0 kWh/m²/day → 5.0 peak sun hours. Not a ZIP API—confirm with NREL PVWatts. Next: solar panel calculator or solar production calculator. Hub: Solar calculator.
Quick Peak Sun Hours Calculator
Pick a climate band (defaults shown).
Planning default for good-sun commercial sites.
Advanced Peak Sun Hours Calculator
Peak Sun Hours Results
Engineering disclaimer
Climate-band defaults are planning aids—not zip-code weather maps. Confirm with site irradiance data or PVWatts/OEM tools before procurement.
Climate band reference
| Band | Typical PSH |
|---|
People also ask
- What are peak sun hours? Equivalent full-sun hours at 1,000 W/m².
- Same as daylight hours? No—daylight is longer than PSH.
- How to use PSH? Feed into panel sizing and production tools.
Planning guidance
Peak sun hours (PSH) convert site irradiance into a single planning number for array sizing and yield screens. This page is a resource input step—not a weather-year map.
- Sizing: Use PSH in the solar panel sizing calculator (array kW from daily load).
- Yield: Reuse the same PSH in PV energy production for kWh estimates.
- Irradiance data: Walkthrough in how to use solar irradiance data.
- Off-grid: Pair with off-grid load sizing when autonomy drives array size.
- Hub: Solar calculator.
Last updated: 2026-08-07. Climate-band and state-zone defaults are planning aids—confirm with site data before procurement.
Typical scenarios
- Northern industrial roof: Often 3.5–4.5 PSH planning band; winter months may drop to ~2.0 PSH.
- Sunbelt commercial: 5.0–6.0 PSH common for annual yield screens.
- Shaded or dusty site: Apply 0.90–0.95 derate before locking array kW.
- Off-grid cabin: Size on worst-month PSH (~3.0–3.5) even if annual average is higher.
Peak sun hours vs daylight hours
Daylight hours measure how long the sun is above the horizon (often 10–14 h at mid-latitudes). Peak sun hours measure how much energy arrives, expressed as equivalent hours at the STC reference irradiance of 1,000 W/m².
A sunny 12-hour day might deliver only 5.0 PSH because irradiance is low at dawn and dusk. PV calculators use PSH—not daylight length—because panel output scales with irradiance, not clock time.
- Example: 12 h daylight with average 417 W/m² → (417 ÷ 1000) × 12 ≈ 5.0 kWh/m²/day ≈ 5.0 PSH.
- Planning rule: Never substitute daylight hours for PSH in sizing formulas.
Typical PSH by climate band
Use these bands when site insolation is unknown. Values are plane-of-array planning averages—not zip-code precision.
| Climate band | Typical PSH (h/day) | Example regions |
|---|---|---|
| Low sun | 3.0–3.5 | Northern Europe, Pacific NW, high-latitude industrial sites |
| Moderate | 4.0–4.5 | Mid-latitude rooftops, UK, northern US |
| Good | 4.8–5.2 | Central US, Mediterranean, many commercial roofs |
| High sun | 5.5–6.5 | Sunbelt US, desert Southwest, high-irradiance industrial parks |
After choosing a band, apply site derate (shading, soiling, tilt) before feeding PSH into panel sizing.
US state / climate-zone PSH reference (planning)
Illustrative annual-average plane-of-array planning bands for commercial screens—not ZIP-level accuracy. Winter critical loads often need 30–50% lower PSH. Confirm final design with NREL PVWatts.
| State / zone (examples) | Typical annual PSH | Winter-ish screen |
|---|---|---|
| AZ / NM / southern NV (Southwest desert) | 5.8–6.5 | 4.5–5.2 |
| CA inland / southern CA | 5.2–6.0 | 3.8–4.8 |
| TX / OK / southern plains | 5.0–5.8 | 3.5–4.5 |
| FL / Gulf Coast | 4.8–5.5 | 3.8–4.5 |
| CO / UT high desert & plateau | 5.0–5.8 | 3.2–4.2 |
| Midwest (IL / IN / OH / IA) | 4.2–4.8 | 2.5–3.5 |
| Northeast (NY / PA / New England) | 3.8–4.5 | 2.2–3.2 |
| Pacific NW (WA / OR western) | 3.2–4.0 | 1.5–2.8 |
| Southeast (GA / NC / SC inland) | 4.5–5.2 | 3.2–4.0 |
| Upper Midwest / northern plains | 4.0–4.8 | 2.0–3.2 |
Enter a chosen PSH above, then continue to panel sizing or production.
Irradiance → peak sun hours
When you have average plane-of-array irradiance (W/m²) and daylight hours, convert to insolation first, then PSH:
Insolation (kWh/m²/day) ≈ (avg W/m² ÷ 1000) × daylight hours
PSH ≈ Insolation × site derate
At STC reference, 1 kWh/m²/day numerically equals 1 peak sun hour before derate. Deep-dive: how to use solar irradiance data.
Formula (quick reference)
PSH ≈ Insolation (kWh/m²/day) × site derate (or use climate-band default).
From solar irradiance: Insolation (kWh/m²/day) ≈ (avg W/m² ÷ 1000) × daylight hours.
Formula and sources
Planning model only. Confirm PSH with measured or mapped site irradiance before procurement.
- NREL PVWatts — site-specific irradiance and PSH by location, tilt, and azimuth
- NREL System Advisor Model (SAM) — weather-year yield and loss modeling
- How to use solar irradiance data (CalcPanel)
Frequently Asked Questions
What are peak sun hours?
Peak sun hours are the equivalent number of hours at 1,000 W/m² that deliver the same daily energy as the actual irradiance profile. Example: 5.0 kWh/m²/day ≈ 5.0 PSH.
Peak sun hours vs daylight hours—what is the difference?
Daylight can be 10–14 h while PSH is often 3–6 h. PSH counts energy at STC reference, not clock time the sun is above the horizon. Never substitute daylight for PSH in sizing.
How do I convert solar irradiance (W/m²) to peak sun hours?
Estimate daily insolation as (average W/m² ÷ 1000) × daylight hours, then apply site derate. Example: 417 W/m² over 12 h → 5.0 kWh/m²/day → ~5.0 PSH before derate.
What PSH should I use for panel sizing?
Use site-average PSH for annual yield screens. For off-grid or winter-critical loads, use worst-month PSH (often 30–50% lower than summer). Enter the value in the solar panel sizing calculator.
Is this a zip-code map?
No—this is a planning calculator with climate bands, a US state/zone reference table, and insolation input. Use PVWatts or measured data for final design—we do not ship a ZIP API.
How do I find peak sun hours for my state?
Use the US state / climate-zone reference for a first screen (annual and winter-ish bands), then confirm with PVWatts for your city, tilt, and azimuth. Enter the planning PSH in the calculator above.
How do I use the result?
Enter PSH into solar panel sizing (array kW from daily load) and PV energy production (kWh from a known array).
What about seasonal variation?
Summer PSH can exceed winter by 30–50% at mid-latitudes. Size off-grid arrays on worst-month PSH when winters matter—see irradiance data guide.
What is the next step?
Carry PSH into panel sizing, then estimate annual kWh in the PV production calculator.
Is this a solar hours calculator?
Yes when people say “solar hours” they usually mean peak sun hours (PSH)—equivalent full-sun hours at 1,000 W/m²—not clock daylight. Use this calculator (and the state/zone table) for planning PSH, then enter the value in panel sizing or production tools.
How it works
For planning, daily plane-of-array insolation in kWh/m²/day is numerically equal to peak sun hours before site derate. Climate bands provide quick defaults when insolation is unknown.
Optional average irradiance (W/m²) with daylight hours converts to insolation so “solar irradiance” queries land on the same PSH workflow.