How much does shading reduce solar output?

In string inverter systems, shading on one panel can reduce output for the entire string — far worse than the shaded area percentage suggests. With microinverters or DC optimizers, shading only affects the shaded panel directly.

What percentage shading is acceptable for solar?

Less than 10% weighted shading is generally acceptable. Sites with 15-25% loss can still be economical with microinverters. Above 30% shading loss, solar ROI is typically poor. Avoid any shading between 10am and 2pm — this is the critical peak production window.

Solar Shading Calculator

How much energy do trees or buildings cost you? Enter shading by time period — get your annual kWh loss.

System and shading

System size?

Peak sun hours?

hrs/day

Shading by time period

Morning shading (7am–11am)?

Midday shading (11am–3pm)?

Afternoon shading (3pm–7pm)?

Annual energy loss from shading

424 kWh/year

Production without shading11,300 kWh/yr

Production with shading10,877 kWh/yr

Overall shading loss3.8%

Daily average loss1.2 kWh/day

Loss breakdown by period

Period	Shading %	Annual loss (kWh)
Morning (7am–11am)	10%	283
Midday (11am–3pm)	0%	0
Afternoon (3pm–7pm)	5%	141

Link copied to clipboard

How to Use This Calculator

Enter system size and sun hours

Start with your system size in kW and your location's peak sun hours per day. These establish your baseline unshaded production. The calculator uses a standard 86% system efficiency to convert raw solar resource into expected output.

Estimate shading by time period

Think about what shades your roof throughout the day. A large oak tree to the east might shade morning production 30% while leaving midday and afternoon clear. A neighbor's roofline to the west might cast late afternoon shadows from October to February. Enter your best estimate for each of the three periods:

Morning (7am–11am) — East-facing obstructions, morning shadows from trees
Midday (11am–3pm) — Nearby tall buildings, chimneys, adjacent structures directly south
Afternoon (3pm–7pm) — West-facing trees, neighbor's garage, evening horizon obstructions

If you're not sure, walk your roof at different times or observe which areas stay in shadow during each period on a clear day.

Read the results

The calculator shows your unshaded vs. shaded annual production, the percentage of production lost to shading, and a breakdown of which time period causes the most loss. Midday shading is most damaging — it affects the peak production window when solar panels produce roughly 50% of their daily output.

The Formula

Unshaded annual kWh = System kW × PSH × 0.86 × 365 Weighted shading loss = (Morning shading × 0.25) + (Midday shading × 0.50) + (Afternoon shading × 0.25) Shaded annual kWh = Unshaded kWh × (1 − Weighted shading loss) Annual energy loss = Unshaded kWh − Shaded kWh

The production weights reflect the actual distribution of solar energy output throughout the day. Midday (11am-3pm) accounts for approximately 50% of daily production because the sun is highest in the sky and radiation intensity is greatest. Morning and afternoon each contribute about 25%, with production tapering off toward sunrise and sunset.

Important caveat: this model treats shading as a simple percentage loss. In real string-inverter systems, shading on one panel can reduce output for the entire string — making partial shading significantly worse than the math suggests. With microinverters or power optimizers, each panel operates independently, limiting shading impact to the shaded panel only.

Example

8 kW system with a large oak tree to the east

A homeowner in Nashville has an 8 kW system (4.5 peak sun hours). A large oak tree to the east shades the east-facing panels from sunrise until about 10am — roughly 50% of morning production affected. The tree doesn't affect midday or afternoon production.

System size8 kW

Peak sun hours4.5 hrs/day

Morning shading50%

Midday shading0%

Afternoon shading0%

Results

Unshaded production12,700 kWh/yr

Shaded production11,113 kWh/yr

Annual loss1,587 kWh/yr (12.5%)

At $0.14/kWh, this 1,587 kWh annual loss costs about $222/year. If the tree can be trimmed (not removed) to reduce morning shading to 20%, the loss drops to ~635 kWh/yr — saving $134/year more. Whether trimming the tree is worth the cost depends on the tree's value and trimming expense.

This example also illustrates a key decision: a string-inverter system would lose far more than shown if the shaded east-facing panels are wired in the same string as the unshaded south-facing panels. Proper system design separates east/west panels from south panels.

FAQ

How much does shading actually reduce solar output? ▼

For partial shading in a string inverter system, the impact is often worse than the shaded area percentage would suggest. When even one cell of one panel in a string is shaded, the panel's bypass diodes activate, reducing that panel's output by 30-60%. The shaded panel then becomes the "bottleneck" for the entire string. Modern systems with microinverters or DC optimizers isolate each panel, so shading only affects the shaded panel — roughly as this calculator estimates.

Should I trim trees or cut them down for solar? ▼

Usually, selective trimming rather than removal is the right answer. Use this calculator to estimate the annual kWh loss from current shading, multiply by your electricity rate to get the annual dollar cost, then compare that to the trimming cost. A professional arborist can trim branches that cast shade without harming the tree. If trees provide significant energy savings in summer cooling, removing them may cost more in AC bills than the solar gain is worth.

Do microinverters or power optimizers solve the shading problem? ▼

Yes — significantly. Enphase microinverters and SolarEdge power optimizers each allow a shaded panel to operate at its own maximum power point without dragging down neighboring panels. For roofs with known shading issues, the additional cost of microinverters ($150-200 per panel premium over string inverter systems) is often recovered within 3-5 years through better shaded production. If you have a roof with zero shading and never will, a string inverter is cheaper and equally effective.

What percentage shading is acceptable for a solar installation? ▼

Most solar installers consider shading of less than 10% on the primary production area acceptable. Sites with 15-25% weighted shading loss can still be economical if the economics otherwise work — especially with microinverters and in high-electricity-rate areas. Above 30% weighted shading loss, solar ROI is typically poor and alternative panel placement should be explored. Critical rule: avoid ANY shading between 10am and 2pm if at all possible — this is the peak production window.

How do I measure how much shade my roof gets? ▼

The most accurate method is a shade analysis tool like the Solmetric SunEye or the Solar Pathfinder, which professional installers use. DIY methods: take photos of your roof from each panel location pointing toward the sun at 9am, 12pm, and 3pm on a clear day — any obstructions visible in the upper arc of the sky represent shading. Google's Project Sunroof uses satellite data to estimate shade and production for US addresses. Your installer should provide a shade analysis report before system design.