Introduction #

How to use solar irradiance data for PV design: convert resource maps or site measurements into peak sun hours (PSH) or daily insolation (kWh/m²/day), then feed array sizing and production tools. Irradiance (W/m²) is instantaneous intensity; design usually needs energy over a day. Use the Peak Sun Hours Calculator to convert climate bands or W/m² × daylight hours into planning PSH.

Best for: engineers turning weather/resource files into sizing inputs.

Not ideal for: replacing TMY weather-year simulations (PVsyst/SAM) or satellite API products.

Irradiance vs insolation vs PSH #

Conclusion: W/m² is power density; kWh/m²/day and PSH are energy metrics for sizing.

Term Unit Use
Irradiance W/m² Instant intensity (sensor / clear-sky)
Insolation / irradiation kWh/m²/day Daily energy on a surface
Peak sun hours h/day Equivalent hours at 1,000 W/m²

At STC reference, 1 kWh/m²/day ≈ 1 PSH before site derate.

CTA: Convert average W/m² in the Peak Sun Hours Calculator (irradiance fields).

Simple conversion #

Conclusion: Daily insolation ≈ (average W/m² ÷ 1000) × daylight hours (when average is over daylight).

Example: 417 W/m² average over 12 h → 417/1000 × 12 = 5.0 kWh/m²/day → ~5.0 PSH before derate.

Prefer plane-of-array (POA) data when tilt is fixed; GHI-only data needs transposition for accuracy (out of scope here—use OEM/meteo tools).

How data enters CalcPanel tools #

  1. Get PSH → Peak Sun Hours
  2. Size array → Solar Panel Sizing / How to Size a Commercial Solar Array
  3. Annual kWh → PV Energy Production with losses from Solar System Losses & Derating

Tilt effects: Solar Panel Tilt Angle Explained · Panel Tilt Calculator.

Common mistakes #

  1. Treating daylight hours as PSH.
  2. Using GHI as POA on steep roofs without adjustment.
  3. Double-counting soiling in both resource and loss %.
  4. Summer-only irradiance for winter autonomy.

Next steps #

  1. Peak Sun Hours Calculator on the Solar calculator hub.
  2. Solar Panel Sizing · PV Energy Production.
  3. Losses guide for derate bands.

Assumptions and disclaimer #

Average W/m² conversions are planning screens. Bankable designs need measured or licensed weather datasets and transposition models.

FAQ #

How do I use solar irradiance data for PV design?

Convert irradiance into daily insolation or peak sun hours, then enter PSH into array sizing and production calculators. Example: 417 W/m² × 12 h → 5.0 PSH before derate.

What is the difference between irradiance and peak sun hours?

Irradiance is instantaneous W/m². Peak sun hours are equivalent full-sun hours at 1,000 W/m² matching daily energy.

Can I enter W/m² in CalcPanel?

Yes—the Peak Sun Hours Calculator accepts average irradiance and daylight hours to set insolation/PSH.

Do I still need system losses?

Yes. Resource (PSH) and equipment/soiling losses are separate—see Solar System Losses & Derating.