Definition
Direct Normal Irradiance (DNI) is the solar radiation received per unit area perpendicular to the sun's direct beam, excluding diffuse and reflected components. Critical for solar tracker and concentrated solar power (CSP) yield modeling.
DNI vs. GHI Relationship
GHI = DNI × cos(solar zenith angle) + DHIA high DNI/GHI ratio indicates clear skies; a low ratio indicates cloudy or hazy conditions.
Use in Solar Design
- Trackers: yield gain over fixed ∝ DNI/GHI ratio.
- Fixed tilt: less sensitive; uses POA = GHI × transposition.
- CSP (concentrated solar power): requires high DNI (>2,000 kWh/m²/yr).
Data Sources
NREL NSRDB, Solargis, Meteonorm 8, NASA POWER, site-measured pyrheliometers.
Key Takeaways
- DNI = solar radiation perpendicular to the sun’s direct beam.
- Critical for tracker plant yield modeling.
- GHI = DNI × cos(zenith) + DHI.
- Desert sites have DNI 2,400–2,800 kWh/m²/yr; cloudy sites 700–1,000.
- Measured by pyrheliometer; modeled by Meteonorm/Solargis.
Frequently Asked Questions
5 commonly searched questions about DNI (Direct Normal Irradiance).
What is DNI?
Direct Normal Irradiance — solar radiation per unit area perpendicular to the sun's direct beam. Measured by pyrheliometer (sun-tracking sensor).
Why does DNI matter for trackers?
Trackers aim modules perpendicular to the sun to maximize direct beam capture. Higher DNI/GHI ratio = bigger tracker advantage.
What's the relationship: GHI = DNI × cos(zenith) + DHI?
Yes. GHI on horizontal = DNI projected onto horizontal + DHI from sky scattering.
Typical DNI values?
Desert sites: 2,400–2,800 kWh/m²/yr. Tropical hazy: 1,400–1,700. Cloudy temperate: 700–1,000. Coastal: variable.
What measures DNI?
Pyrheliometer — a sun-tracking sensor with a small acceptance angle (typically 5°). Reports W/m² of direct beam.
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