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

What this calculator does

Converts GHI / DNI / DHI (kWh/m²/day) into Plane-of-Array (POA) irradiance for any module tilt and azimuth at a Canadian site. POA drives every downstream PV calculation — annual kWh, Greener Homes Grant payback, provincial rebate ROI, micro-FIT/feed-in revenue.

It also reports annual kWh/m², annual specific yield (kWh per kWp installed), per-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 from a NRCan or CanmetENERGY data file.

How to use it

1. Pull GHI, DNI and DHI for your site from NRCan PV Potential (natural-resources.canada.ca/maps-tools-and-publications/pv-potential-tool) or CanmetENERGY TMY. Defaults match Toronto.
2. Enter your tilt (typical Canadian roof pitch is 4/12 to 8/12 = 18° to 34°; latitude-equivalent 35–45° is more common for ground-mount) and azimuth (180° = true south; magnetic declination at Toronto is ~10° W, Calgary ~17° E, Vancouver ~16° E — adjust if reading off a magnetic compass).
3. Set albedo to 0.22 for typical asphalt-shingle / grass mix in summer or 0.55–0.85 for fresh winter snow cover.
4. The calculator returns POA in kWh/m²/day plus annual specific yield and per-module economics in Canadian dollars.

The math

The Liu–Jordan (1960) decomposition is the IEC 61724-1 reference and matches what CanmetENERGY uses for their public PV Potential maps:

• Beam: POA_beam = DNI × cos(AOI)
• Sky diffuse: POA_diffuse = DHI × (1 + cos β) / 2
• Ground reflected: POA_ground = GHI × ρ × (1 − cos β) / 2

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

Canadian irradiance, NRCan PV Potential

NRCan’s tool provides 30-year average irradiance (1961–1990 baseline updated with satellite reanalysis to 2020) on a 10 km grid. Annual GHI varies 1.5× from coast to prairie.

Source: NRCan PV Potential Tool, accessed 2024 Q4.

What POA tells you about Canadian system sizing

Once annual POA is known, the design chain is:

1. Annual specific yield = annual POA × PR. A south-facing 35° Toronto array with PR 0.78 gives ≈ 4.05 × 365 × 0.78 ≈ 1153 kWh/kWp, matching CanmetENERGY field data within 3 %.
2. System size = annual_kWh / specific_yield. A 9000 kWh Ontario household needs ≈ 7.8 kWp; a 12000 kWh Alberta household ≈ 9.0 kWp.
3. Greener Homes Grant funding (federal, $5000 max) treats systems above 1 kWp as eligible; the eligible kWh-per-kWp determines payback. The solar panel tax credit calculator handles the federal + provincial stack.
4. Module count = kWp / panel_kWp. At 425 W panels (Heliene / Silfab Canadian-manufactured baseline 2026), a 7.5 kWp system is 18 modules.

Canadian-specific accuracy tips

• Use a winter-aware albedo. Above 50°N (most of Canada) snow cover lasts 80–140 days/year. Bumping albedo to 0.55 for that period adds 5–10 % to annual POA on a steep tilt — captured automatically if you enter the annual-average albedo as 0.30 instead of 0.22.
• Steep tilts win in Canada. Latitude + 15° tilts (50°–60°) self-clear snow much faster than the more typical 30° pitched roof, and they capture the high-angle late-winter sun better. The solar panel tilt calculator quantifies the trade-off.
• CSA C22.1 §64 cold-Voc string sizing. A clear −30 °C morning at Edmonton can lift module Voc 18 % above STC; if your tilted POA is high (clear skies + snow albedo + steep tilt), the inverter MPPT window matters more than the irradiance number alone. Cross-check using the solar string sizing calculator.
• Provincial tariff variation. A 1153 kWh/kWp Toronto system × 4.0 ¢/kWh feed-in (Ontario non-grandfathered) is much less per kWh than the same yield × 13.5 ¢/kWh (Quebec retail) self-consumed. POA tells you the kWh number; the solar feed in tariff calculator tells you what each kWh is worth.

How POA feeds the rest of your Canadian design

• 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 CanREA 2024 fleet median.
• The solar panel tilt calculator and solar panel azimuth calculator feed directly into the AOI term of the beam component.
• The solar panel snow loss calculator is the loss-side counterpart to the albedo gain modelled here.

Authority sources

• NRCan PV Potential and Insolation Maps — natural-resources.canada.ca — Natural Resources Canada gridded irradiance, the reference dataset for Canadian PV design.
• CanmetENERGY — government research lab that maintains the underlying TMY datasets and publishes RETScreen Expert (free Canadian PV design software).
• CSA F383 Installation Code for Solar PV Systems — design and yield-calculation conventions for Canadian commissioning paperwork.
• Greener Homes Grant program — natural-resources.canada.ca/energy-efficiency/homes — federal $5000 grant + interest-free loan, eligible system sizing depends on POA-derived yield.
• CanREA Module Reliability and Performance Reports — annual fleet PR studies that inform the default 0.78 PR figure.