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Solar Panel Shading Calculator

Estimate annual kWh and feed-in tariff revenue lost to partial shading on your Australian solar array. Free calculator with topology-specific models.

Solar Panel Shading Calculator

Annual baseline output
8,456 kWh
Annual kWh lost
238 kWh
Annual revenue lost
$81
Array output reduction
2.8%
Recommendation
Optimize string layout to isolate shaded panels.

How to use this calculator

Enter eight values and the calculator returns annual baseline kWh, annual kWh lost to shading, annual revenue lost in AUD, and an inverter-topology recommendation.

  1. System size (kW) — total nameplate. 6.6 kW (oversized to a 5 kW inverter) is the dominant Australian residential configuration.
  2. Peak sun hours per day — Brisbane 4.8, Sydney 4.2, Melbourne 3.8, Perth 5.0, Adelaide 4.5, Hobart 3.5. The Bureau of Meteorology and APVI provide finer-grained values.
  3. System efficiency (%) — 78% is a sensible CEC-compatible derate.
  4. Electricity rate (A$/kWh) — AER quarterly residential averages around 32–38c/kWh in NSW and VIC, 28c in QLD, 32c in SA, 36c in WA in 2026.
  5. Total panels in array — count from your CEC system design.
  6. Panels affected by shading — count of panels under shadow at any point in the day.
  7. Hours shaded per day — annual average across summer and winter.
  8. Shading severity (%) — gum trees 45–55%, palms 60–70%, walls and chimneys 80–95%, vent stacks and antennas 70–90%.
  9. Inverter topology — microinverter/optimiser, modern string with bypass, or pre-2005 system.

How shading really affects Australian solar output

Solar panels are wired in series strings. Current is limited by the lowest-current cell. When a cell is shaded, it restricts current for the entire string. Without protection, a single shaded cell could cripple a 10-panel string.

Bypass diodes solve this — typically 3 per panel, one per cell group of 20–24 cells. When light on a cell group falls below roughly 20% of full irradiance, that group’s diode shunts current around it. The string loses one-third of one panel’s output, not the whole string’s output. Every CEC-listed panel sold in Australia has bypass diodes.

Optimisers (SolarEdge, Tigo) and microinverters (Enphase IQ8) add per-module MPPT tracking. A shaded panel only affects itself. They contain shading loss to the affected panel.

The shading-loss math

For a modern string with bypass diodes:

loss_fraction ≈ (shaded_panels / total_panels)
              × (hours_shaded / productive_hours_per_day)
              × (severity / 100)

productive_hours_per_day ≈ 8 (Australian PV-productive window)

For an older string with no bypass:

loss_fraction ≈ (hours_shaded / 8) × (severity / 100)

Worked example for a 6.6 kW system, 4.5 PSH, 78% derate, A$0.34/kWh, 2 of 16 panels shaded 3 h/day at 60% severity, modern string inverter:

  • Baseline annual kWh = 6.6 × 1000 × 4.5 × 0.78 × 365 / 1000 = 8,460 kWh
  • Loss fraction = (2/16) × (3/8) × 0.60 = 0.028
  • Annual kWh lost = 8,460 × 0.028 = 237 kWh
  • Annual revenue lost (retail value) ≈ A$81

Typical Australian shading scenarios

ScenarioSeverityHours/dayAnnual loss (modern string)
Solar hot water tank shadow on 1 panel90%1.51.0%
Antenna or vent stack on 1 panel80%10.6%
Neighbour’s two-storey wall on 3 panels90%24.2%
Gum tree, sparse, on 4 panels50%46.3%
Palm tree fronds across 2 panels70%33.3%
Bird dropping season on whole array10%810%
Bushfire smoke (3-month season, peak)25%8~6% over the year

Bushfire smoke is an underappreciated cause of seasonal loss in eastern Australia. The 2019–2020 Black Summer cost Sydney rooftop systems an estimated 30% of summer output. Recovery is automatic once smoke clears — no cleaning required.

Mitigation strategies, ranked by cost-effectiveness

  1. Trim or remove trees — A$300–A$1,500 per tree. If you’re recovering 8% on a 6.6 kW system at 34c/kWh, that’s A$230/yr — payback under 5 years for most jobs. Check council requirements; many Australian councils require permits for trees over a certain height.
  2. String layout optimisation — wire unshaded panels in one string, shaded panels in another. Free at install. CEC-accredited installers should do this by default.
  3. DC optimisers (SolarEdge, Tigo) — adds A$0.12–A$0.18/W. Best for partial shading and mixed-orientation hipped roofs.
  4. Microinverters (Enphase IQ8) — adds A$0.18–A$0.25/W. Best for complex roofs, heavy shading, or systems being designed for future battery integration.
  5. Move the array — if the chosen face has 15%+ shading and another face is shade-free, the extra cable run usually pays for itself within the first year.

Common mistakes

  • Forgetting that east/west splits double exposure to morning and afternoon shade. Hipped roofs in Australian suburbs often have 3–4 orientations — model each separately.
  • Underestimating bushfire smoke. If you’re in NSW or VIC, build in a 5–8% seasonal smoke buffer in projections.
  • Ignoring the FiT vs retail gap. A shaded kWh at home (self-consumed) is worth 34c; the same kWh exported is worth 4–8c. Self-consumption shifts the economics.
  • Trimming trees that fall under a council Tree Preservation Order. Always check with your local council before pruning anything over 3 m.

Sources

Frequently asked questions

How much shading is too much for an Australian rooftop system?
On a modern Clean Energy Council–certified array with bypass diodes (default on every panel since 2005), shading 2 of 16 panels for 3 hours at 60% blockage costs roughly 2.8% of annual output. On a 6.6 kW system producing 9,800 kWh/yr, that's 274 kWh worth about A$93 at the typical 34c/kWh import rate, or A$22 at a 8c export rate if exported. Once projected losses exceed 5% on a string inverter, you should be quoting optimisers (SolarEdge, Tigo) or microinverters (Enphase) — that's also where AS/NZS 5033 best-practice guidance lands.
Does shading affect my feed-in tariff?
Yes — directly. Most Australian feed-in tariffs in 2026 are between 4c and 12c per exported kWh, well below the 30–40c retail rate you pay. So a shaded kWh you would have self-consumed is worth far more than a shaded kWh you would have exported. The calculator values lost kWh at your retail import rate by default — if you're heavily export-dominant, multiply the result by your FiT-to-retail ratio for a true revenue figure. Solar Bonus and old 60c tariffs are mostly closed; the Victorian default minimum FiT is 4.9c/kWh from July 2026.
Should I get microinverters in Australia?
On Australian roofs with multiple orientations (common on hipped tile roofs in Melbourne and Sydney), or with significant gum-tree shading, microinverters typically pay back the A$1,500–A$2,500 premium in 6–8 years. On a simple north-facing colorbond roof with no obstructions, a quality string inverter (Sungrow, Fronius, Goodwe) is the right call. If the calculator shows projected loss above 5%, get an Enphase IQ8 quote alongside the string-inverter quote.
Where can I check shading on my Australian roof?
SunWiz's free tools and APVI's solar map show your suburb's annual GHI. For roof-specific analysis: Solcast (free residential tier) and the CSIRO's solar mapping service. Aurora Solar is used by most Australian installers — ask for the shade-analysis PDF as part of your quote. For DIY, take phone photos at 9 AM, midday, and 3 PM in mid-June (winter solstice, worst case) — that shows your worst-case shadow profile. CEC-accredited installers must perform shade analysis as part of standard design.
Do gum trees and palm trees count as the same kind of shading?
No. Eucalyptus tree shade is sparse and high — leaves are vertical and shed light irregularly, giving 40–60% diffuse shade. Palm tree fronds give 50–70% denser shade. Native callistemons and grevilleas often grow tall enough to cast hard shadow on rooftops within 5–8 years of planting. The calculator's severity input lets you model the difference: model gum trees at 45–55%, palms at 60–70%, dense hedges and bottlebrush at 70–85%.

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