Definition
Plane of Array (POA) irradiance is the total solar radiation received per unit area on a tilted PV module surface, computed as a transposition of GHI plus direct and diffuse contributions. The direct upstream input to PV energy yield.
POA Components
POA_total = POA_direct + POA_diffuse + POA_reflected
POA_direct = DNI × cos(incidence_angle)
POA_diffuse = DHI × transposition_factor_diffuse
POA_reflected = GHI × ρ_ground × (1 − cos(tilt)) / 2Where ρ_ground = albedo.
Transposition Models
| Model | Use | Accuracy |
|---|---|---|
| Isotropic (Liu-Jordan) | Simple | Lowest |
| Hay (1979) | PVsyst default | Moderate |
| Klucher | Better for diffuse | Good |
| Perez (1990) | Bankable standard | Best |
| Reindl | Variant | Good |
POA vs. GHI Examples
| Site | Annual GHI | Annual POA (tilt = latitude) | Transposition factor |
|---|---|---|---|
| Phoenix AZ | 2,100 | 2,350 | 1.12 |
| Bengaluru | 1,900 | 1,990 | 1.05 |
| Boston | 1,400 | 1,580 | 1.13 |
| Germany | 1,050 | 1,180 | 1.12 |
Key Takeaways
- POA = total solar radiation on tilted module surface.
- Direct + diffuse + reflected, transposed from GHI/DNI/DHI.
- Perez transposition is the bankable industry standard.
- POA = GHI × ~1.05–1.20 typically for optimal tilt.
- Bifacial designs compute POA_front and POA_rear separately.
Frequently Asked Questions
5 commonly searched questions about POA Irradiance (Plane of Array).
What is POA?
Plane of Array irradiance — solar radiation on the tilted module surface. Direct sum of: direct beam projected onto tilt, diffuse from sky, and reflected from ground.
How is POA calculated from GHI?
Via transposition models — Hay or Perez. POA = GHI × transposition factor (typically 1.05–1.20 for properly tilted arrays).
What model is best?
Perez (1990) is the bankable standard, especially for diffuse-dominated climates. Hay is simpler but less accurate. PVsyst defaults to Hay for residential, Perez recommended for utility.
Does POA include rear-side bifacial?
Standard POA refers to front-side. Bifacial designs use 'POA_front' + 'POA_rear' separately.
Why does POA matter?
Direct upstream input to module DC energy. Energy ≈ POA × module efficiency × area × PR.
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