Solar Irradiance Calculator (GHI / DNI / DHI → POA)

What this calculator does

Converts the three irradiance components — Global Horizontal (GHI), Direct Normal (DNI) and Diffuse Horizontal (DHI), in kWh/m²/day — into Plane-of-Array (POA) irradiance for any module tilt and azimuth at an Australian site. POA is the single most important input in every PV yield estimate; everything downstream (annual kWh, STC count, ROI, feed-in revenue) flows from it.

It also reports annual kWh/m², annual specific yield (kWh per kW installed), single-module daily and annual energy, and the value of one module per year at the local retail tariff. A consistency check flags inputs where GHI ≠ DNI · cos(zenith) + DHI — the most common manual-entry error when reading values out of a BoM grid file.

How to use it

1. Pull GHI, DNI and DHI for your site from the APVI Solar Mapping Service (pv-map.apvi.org.au) — type your postcode and download the location report. The BoM Solar Atlas is the underlying data source.
2. Enter your tilt (typical Australian roof pitch is 22°–30°) and azimuth (0° / 360° = true north — note Australia faces north; 90° = east, 270° = west).
3. Set albedo to 0.20 for typical Colorbond / tile roofing or 0.55 for fresh concrete. Roof colour barely matters for POA — what matters is what surrounds the array on the ground.
4. The calculator returns POA in kWh/m²/day plus annual specific yield and per-module economics in Australian dollars.

The math

The Liu–Jordan (1960) decomposition is the IEC 61724-1 reference and matches what CEC accredited designers use:

• Beam: POA_beam = DNI × cos(AOI) — what hits the panel directly.
• Sky diffuse: POA_diffuse = DHI × (1 + cos β) / 2 — scattered light from the sky dome.
• Ground reflected: POA_ground = GHI × ρ × (1 − cos β) / 2 — reflected off the ground.

Total POA × 365 gives annual kWh/m². Multiplied by module efficiency × PR × area, you get per-module annual energy.

Australian irradiance, BoM Solar Atlas + APVI

The BoM averages 35+ years of satellite-derived solar data on a 5 km grid; the APVI Solar Mapping Service combines this with rooftop tilt/azimuth/shading priors. Annual GHI varies 1.5× from coast to inland.

Source: BoM Solar Atlas / APVI Solar Mapping Service typical year, accessed 2024 Q4.

What POA tells you about Australian system sizing

Once annual POA is known, the CEC design chain is:

1. Annual specific yield = annual POA × PR. A north-facing 25° Sydney array with PR 0.78 gives ≈ 5.42 × 365 × 0.78 ≈ 1543 kWh/kW, which matches CEC and SunWiz field data within 2 %.
2. System size = annual_kWh / specific_yield. A 6500 kWh Sydney household needs ≈ 4.2 kW; a 9500 kWh Brisbane household ≈ 5.8 kW.
3. STC count for federal Small-scale Technology Certificates: CEC’s deeming formula uses your zone (NSW/QLD/SA = Zone 3, MEL/HBA = Zone 4, AS = Zone 1) and annual deeming kWh per kW, which is itself driven by the POA values above. The solar panel tax credit calculator handles the STC arithmetic.
4. Module count = kW / panel_kW. At 440 W panels (LONGi Hi-MO 6 / Trina Vertex S+ baseline 2026), a 6.6 kW system is 15 modules.

Australian-specific accuracy tips

• Use the APVI Solar Mapping Service for residential. It applies typical tilt/azimuth priors derived from satellite-detected installations in your postcode, so its output already approximates POA rather than raw GHI.
• Inland sites need higher soiling assumptions. The CEC Design Guidelines and SunWiz 2024 field data show inland NSW/QLD/SA/WA can lose 3–5 %/year to red dust between rains; PR of 0.74 is more realistic than 0.78. Coastal sites stay closer to 0.80. The solar panel soiling loss calculator lets you tune this per site.
• Cyclone-zone modules carry an irradiance-independent derate. AS/NZS 1170.2 cyclone Region C/D modules (FNQ, Pilbara, top half of WA/NT) typically use heavier glass with 0.5–1 % lower transmittance — knock the moduleEff input down by 0.2 percentage points if quoting a Tindo cyclone-rated panel.
• Cross-check against PVsyst or SAM for any commercial >100 kW project. The isotropic model used here is fine for residential but utility-scale projects with single-axis tracking need hour-by-hour Perez transposition.

How POA feeds the rest of your design

POA is the upstream variable for almost every other calculator on this site:

• The solar panel output calculator takes POA × PR as its core energy estimate.
• The solar system efficiency calculator inverts the relationship — given measured AC kWh and POA, it returns a real-world PR you can benchmark against the SunWiz / Solar Analytics 2024 fleet median (0.78).
• The solar panel tilt calculator and solar panel azimuth calculator feed directly into the AOI term of the beam component.
• The solar feed in tariff calculator splits POA-derived annual kWh between self-consumed (offset at AGL/Origin/Energy Australia retail rates ≈ A$0.30–0.38) and exported (paid at typical 5–10 c/kWh feed-in tariffs in 2026).

Authority sources

• BoM Solar Atlas — bom.gov.au/jsp/awap/solar — Bureau of Meteorology gridded irradiance, the underlying dataset for nearly every Australian PV design tool.
• APVI Solar Mapping Service — pv-map.apvi.org.au — Australian Photovoltaic Institute, applies typical tilt/azimuth priors to BoM data for postcode-level POA estimates.
• Clean Energy Council Design Guidelines for Grid-Connected Solar PV — design and PR conventions for STC accreditation.
• AS/NZS 5033:2021 — Installation and safety requirements for PV arrays — the wiring-side counterpart to the irradiance-side calculations.
• SunWiz / Solar Analytics 2024 PV Performance Index — fleet study of 4000+ residential systems giving the 0.78 PR median used as the default.