Plane of Array

What is Plane of Array irradiance

Plane of Array (POA) irradiance, also called Global Tilted Irradiance (GTI), is the solar radiation hitting the actual tilted surface of PV modules. Unlike GHI which measures irradiance on horizontal, POA accounts for the panel’s specific tilt angle and azimuth orientation. POA is the direct input to PV power calculation.

POA combines three components:

1. Direct beam: DNI projected onto the tilted plane
2. Diffuse: DHI on tilted plane (calculated through sky models)
3. Ground-reflected: GHI multiplied by albedo and view factor from the array to the ground

For Indian solar installations at latitude-equivalent tilt, POA typically exceeds horizontal GHI by 8-12 percent on annual basis. South-facing tilted panels capture significantly more energy than horizontal because they better match the sun’s path.

Why POA matters

Yield prediction. POA directly drives PV power output; see Solar Yield in India, kWh-per-kW Benchmarks by State for state-level yield outcomes built on POA-based modelling.

PR calculation. Performance Ratio normalises actual generation against POA-derived expectation.

Bifacial analysis. Rear-side POA is critical for bifacial gain.

Plant design. Tilt and azimuth optimisation maximises POA.

Performance benchmarking. POA-based PR is more accurate than GHI-based.

POA equation

Where:

• θ is the angle of incidence between sun and panel normal
• f_diffuse is the sky diffuse view factor
• f_ground is the ground view factor

Technical deep dive

Sky models for diffuse component

Perez model accounts for circumsolar and horizon brightening effects.

POA gain over GHI by tilt

For Delhi (28° latitude), south-facing:

Bifacial POA

For bifacial modules:

• Front POA: standard calculation
• Rear POA: complex calculation involving ground albedo, view factors, inter-row shading
• Total POA = Front POA + Rear POA × bifaciality factor

Bifacial POA gain: 5-25 percent depending on albedo and clearance.

Tracker POA

Single-axis trackers continuously adjust tilt and azimuth to track the sun:

• Tracker POA: 1.25-1.35× horizontal GHI
• Fixed POA at latitude: 1.10-1.15× horizontal GHI
• Tracker yield gain: ~15-25%

Real-world applications

Solar yield prediction software inputs, combined with module efficiency to derive expected AC output.

Plant performance monitoring.

PR calculation.

Bifacial analysis.

Tracker yield prediction.

Row-spacing and shading analysis, since inter-row shade directly subtracts from POA at low sun angles — dedicated tools such as SurgePV’s shadow analysis module model this at the individual-cell level.

Comparison: GHI vs POA

Best practices

Use POA for PR calculation, not GHI.

Install in-plane pyranometers on utility plants.

Use Perez sky model for highest accuracy, the default in bankable software covered in PV Yield Simulation Software: 2026 Bankable Guide.

Apply realistic albedo for ground reflection.

Document tilt and azimuth assumptions in yield reports.

Indian market context

Indian utility plants typically install in-plane pyranometers for accurate PR.

PVsyst, SAM and PVGIS provide POA calculation.

Bifacial yield models include detailed rear-side POA.

NIWE and Solargis provide tilt-specific POA estimates; for the state-wise GHI and peak sun hour benchmarks feeding these calculations, see Solar Irradiance Data India, State-Wise Peak Sun Hours.

Standards and certifications

Key takeaways

POA (Plane of Array) irradiance is the solar radiation hitting the actual tilted PV surface, calculated from GHI, DNI, DHI and ground-reflected components. POA is 8-12 percent higher than GHI for Indian latitude tilt. POA-based PR provides accurate plant quality assessment. Bifacial modules require additional rear-side POA calculation. Standard for PV yield modelling in PVsyst, SAM and bankable yield reports.

Further reading

For how Plane of Array plays out in real projects, these guides go deeper:

• Solar Irradiance Data India, Peak Sun Hours
• Inverter MPPT: 8 Critical Selection Factors (2026)

Sources

• IEC 61724, Performance monitoring.
• Perez R., et al., Modelling daylight availability, Solar Energy 1990.
• ISO 9060, Pyranometer classification.
• PVsyst software documentation.
• NREL System Advisor Model (SAM).
• NIWE Solar Resource Atlas.
• Solargis Solar Resource Database.
• IEA PVPS Task 16 publications.
• Duffie J. A., Beckman W. A., Solar Engineering of Thermal Processes, Wiley.