Solar Panel Shading Calculator

How to use this calculator

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

1. System size (kW) — total nameplate. 6 kW is typical for Ontario and Quebec; 8–10 kW is common in Alberta where electricity is cheaper but homes use more power.
2. Peak sun hours per day — Toronto 3.8, Montreal 3.6, Vancouver 3.0, Calgary 4.0, Halifax 3.4. NRCan’s PV potential maps give finer values.
3. System efficiency (%) — 76% is a sensible Canadian derate factoring snow loss, cold-weather efficiency gains, and inverter losses.
4. Electricity rate (C$/kWh) — Ontario 15c (off-peak)–28c (peak), Quebec 8c, BC 11c, Alberta 16c. Use your average effective rate.
5. Total panels in array — from your system design.
6. Panels affected by shading — count of panels under shadow at any point.
7. Hours shaded per day — annual average; winter shadows are longest, so weight toward worst-case if shading varies.
8. Shading severity (%) — coniferous tree 70–85% (year-round), deciduous tree 50–70% summer (mostly clear winter), chimney 80–95%, snow patches on panels 90–100%.
9. Inverter topology — microinverter/optimizer (most common in Canada), modern string, or pre-2005 string.

How shading really affects Canadian solar output

Solar panels are wired in series strings. Current is limited by the lowest-current cell. A shaded cell becomes a bottleneck for the whole string. Without protection, even small obstructions could cause large losses.

Bypass diodes — 3 per panel, one per cell group of 20–24 cells — solve this. When light on a cell group falls below roughly 20% of full irradiance, the diode routes current around it. The string loses one-third of one panel’s output, not the whole string’s output. Every CSA-certified panel on the Canadian market has bypass diodes.

Microinverters (Enphase IQ8) and DC optimizers (SolarEdge, Tigo) add per-module MPPT tracking. A shaded panel only affects itself. Canadian installers heavily favour microinverters for their snow-shedding behaviour and simpler post-storm troubleshooting.

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 in summer, 5 in winter (Canadian average ~6.5)

For an older string with no bypass:

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

Worked example for a 6 kW Toronto system, 3.8 PSH, 76% derate, C$0.16/kWh, 2 of 14 panels shaded 3 h/day at 60% severity, modern string inverter:

• Baseline annual kWh = 6 × 1000 × 3.8 × 0.76 × 365 / 1000 = 6,323 kWh
• Loss fraction = (2/14) × (3/8) × 0.60 = 0.032
• Annual kWh lost = 6,323 × 0.032 = 202 kWh
• Annual revenue lost ≈ C$32

Typical Canadian shading scenarios

Deciduous trees are friends, not foes — leaves shade panels in summer when output is high, but bare branches barely affect winter sun. Coniferous trees (white pine, spruce, fir) keep needles year-round and impose constant shading.

Mitigation strategies, ranked by cost-effectiveness

1. Trim or remove trees — C$300–C$1,200 per tree in Canadian metros. If you recover 6% on a 6 kW system at 16c/kWh, that’s C$60/yr — payback 5–15 years depending on tree cost. Many municipalities require permits for tree removal; coniferous removal in BC is heavily regulated.
2. String layout optimization — wire unshaded panels in one string, shaded panels in another. Free at install.
3. Microinverters (Enphase IQ8) — adds C$0.12–C$0.18/W. Best for snow-shed shading, complex roofs, and any system going on a forested lot.
4. DC optimizers (SolarEdge) — adds C$0.10–C$0.15/W. Less common in Canada than microinverters but functionally similar.
5. Move the array — south-facing roof with 10%+ shade vs. east+west split: model both. Often the multi-orientation option produces more annual kWh.

Common mistakes

• Treating snow shading like permanent obstruction. Snow melts off panels rapidly — 24–72 hours typical. Don’t size systems pessimistically based on January worst case.
• Forgetting that winter sun is low. A 2 m tall fence south of your roof shades panels heavily December–February even if invisible in summer.
• Coniferous vs. deciduous confusion. A leaf-off oak in February shades very little; a Norway spruce shades the same.
• Ignoring TOU rates. Ontario off-peak vs. on-peak rates differ 3× — losing afternoon production (mid-peak) costs more than losing morning (off-peak).

Sources

• NRCan — PV Potential Maps — official Canadian solar resource data
• CanmetENERGY — federal energy research including PV reliability
• Canadian Renewable Energy Association (CanREA) — industry standards for installer practice
• Solar Alberta and Solar Nova Scotia — provincial advocacy and shade-analysis resources
• Google Project Sunroof — aerial-imagery shade estimator covering most Canadian metros