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 = equivalent hours at 1,000 W/m² matching daily energy (not clock daylight). Example: 5.0 kWh/m²/day → 5.0 peak sun hours. Pick a planning band from the US state / climate-zone table below—not a ZIP API; confirm with NREL PVWatts. Next: solar panel calculator or solar production calculator. Hub: Solar calculators hub.
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.
- By ZIP / location? Use the state / zone table for a first screen, then PVWatts—no ZIP calculator here.
- 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 calculators hub.
Last updated: 2026-08-07. Climate-band and state-zone defaults are planning aids—confirm with site data before procurement.
Typical scenarios
- Annual-yield screen: Use a long-term annual plane-of-array irradiation dataset with the proposed geometry.
- Season-critical system: Use the applicable monthly or design-period dataset rather than converting an annual average with a fixed percentage.
- Shaded or dusty site: Keep resource irradiation and modeled shading/soiling losses as separate, documented inputs.
- Off-grid recharge: Use the governing low-resource period and the project reliability criterion.
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 |
These illustrative bands are placeholders only. Replace them with plane-of-array irradiation for the project location, period, tilt and azimuth before design.
US state / climate-zone PSH reference (planning)
Illustrative annual-average planning bands only—not a location lookup and not suitable for deriving a winter value. Replace them with a project-specific monthly weather dataset from NREL PVWatts or an equivalent source.
| 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 |
| Mid-Atlantic (VA / MD / DE) | 4.2–4.9 | 2.8–3.6 |
| Upper Midwest / northern plains | 4.0–4.8 | 2.0–3.2 |
| HI (islands, planning band) | 5.0–5.8 | 4.2–5.0 |
| AK (southern coastal — verify locally) | 2.5–3.5 | 0.5–2.0 |
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
Resource PSH = daily plane-of-array irradiation (kWh/m²/day) ÷ 1 kW/m²
Effective equivalent hours = resource PSH × user-supplied downstream yield factor
Using the 1 kW/m² reference irradiance, 1 kWh/m²/day numerically equals 1 peak sun hour. Shading, soiling and conversion losses belong to a separate system-yield model. Deep-dive: how to use solar irradiance data.
Formula (quick reference)
Resource PSH = plane-of-array irradiation (kWh/m²/day) ÷ 1 kW/m². Keep shading, soiling and system-loss factors separate.
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?
If the value is a true time average over a known interval, daily irradiation is (average W/m² ÷ 1000) × represented hours. Divide that irradiation by 1 kW/m² to obtain resource PSH. Keep system losses separate.
What PSH should I use for panel sizing?
Match the plane-of-array irradiation period to the design objective: annual for annual yield, or the governing monthly/design period for seasonal recharge and reliability. Do not infer it from a universal seasonal percentage.
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?
Seasonal variation depends on location, array geometry and weather dataset. Use monthly plane-of-array irradiation for the governing period—see the 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
Daily plane-of-array irradiation in kWh/m²/day is numerically equal to resource peak sun hours when divided by the 1 kW/m² reference irradiance. Climate bands are illustrative assumptions, not location data.
Optional time-average irradiance with the hours represented converts to daily irradiation. The tool reports any downstream yield factor separately so losses are not mistaken for a change in solar resource.