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Solar Shading Analysis Calculator

Estimate production losses from shading on your solar array.

About this calculator

This calculator separates two different production figures: Unshaded Production is a simple estimate (System Size x Annual Sun Hours) of what the array would generate with no shade at all, and Production Loss (%) is a separate factor describing how much of that ideal figure shading actually takes away. Production Loss (%) is built from two ratios rather than a single "shade percentage": Shading Hours/Day divided by Peak Sun Hours/Day gives the FRACTION of the productive daylight window affected by shade, and that fraction is then multiplied by Shading Severity, the average percentage of panel output lost DURING those shaded hours (partial shade from a nearby tree branch might cut output 30-50%, while a building casting a hard shadow can cut it close to 100%). Neither System Size nor Annual Sun Hours affects Production Loss (%) at all -- shading severity is a property of the site's obstructions and the panels' daily sun exposure window, not the system's rated capacity or its location's overall sun resource.

Raising Peak Sun Hours/Day (a longer productive daylight window relative to the same shaded hours) LOWERS Production Loss (%), since the same shaded hours make up a smaller fraction of a longer day. Energy Lost and Actual Production both apply Production Loss (%) to Unshaded Production, so the same site-shading assumptions determine both regardless of how large the system is.

Inputs

kW
hrs
%
hrs
hrs

Results

Production Loss

12%

Actual Production

12,672 kWh/yr

Energy Lost1,728 kWh/yr
Unshaded Production14,400 kWh/yr
How to Use This Calculator
  1. Enter your system size in kilowatts and the annual peak sun hours for your location.
  2. Set the shading severity — the percentage of panel output lost during shaded periods.
  3. Input the average shading hours per day and your average peak sun hours per day.
  4. Review the production loss percentage and energy lost in kWh per year.
  5. Compare actual production against unshaded production to see the full annual impact of shading.

How the result changes with Peak Sun Hours/Day

Peak Sun Hours/DayProduction LossActual Production
2.524%10,944 kWh/yr
3.7516%12,096 kWh/yr
7.58%13,248 kWh/yr
106%13,536 kWh/yr

What each input means

System Size
Rated system size in kilowatts.
Annual Sun Hours
Total annual peak sun hours for your location.
Shading Severity
Percentage of panel output lost during shaded periods.
Shading Hours/Day
Average hours per day panels are affected by shade.
Peak Sun Hours/Day
Average daily peak sun hours.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    5 parameters
    System Size = 8, Annual Sun Hours = 1800, Shading Severity = 30, Shading Hours/Day = 2, Peak Sun Hours/Day = 5 = 5 input(s) provided
  2. Calculate Production Loss
    Production Loss
    12 = 12
  3. Calculate Actual Production
    Actual Production
    12672 = 12672
  4. Calculate Energy Lost
    Energy Lost
    1728 = 1728
  5. Calculate Unshaded Production
    Unshaded Production
    14400 = 14400

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

Why doesn't System Size affect Production Loss (%)?

Production Loss (%) describes how much of a system's output shading removes as a PERCENTAGE, which depends only on how much of the day is shaded (Shading Hours/Day versus Peak Sun Hours/Day) and how severe that shade is (Shading Severity) -- properties of the site's obstructions and sun exposure, not the system's rated capacity. A larger system loses proportionally more ENERGY (kWh) to the same shading, but the same PERCENTAGE of its output.

Why does a longer Peak Sun Hours/Day window reduce Production Loss (%)?

Production Loss (%) starts from the fraction of the productive day that's shaded -- Shading Hours/Day divided by Peak Sun Hours/Day. Holding Shading Hours/Day fixed, a longer Peak Sun Hours/Day window means those same shaded hours make up a smaller share of the day, so the same physical obstruction produces a smaller percentage loss on a site with more total daily sun exposure.

What's the difference between Shading Severity and Production Loss (%)?

Shading Severity is the percentage of PANEL OUTPUT lost only DURING the shaded hours -- a property of how dark the shade is. Production Loss (%) is the ANNUAL AVERAGE loss across the whole day, which is Shading Severity scaled down by the fraction of the day that's actually shaded, so a site with severe but brief shading can have a lower Production Loss (%) than a site with mild but nearly all-day shading.

How should I estimate Shading Severity for my situation?

Hard shade from a solid obstruction like a chimney or a neighboring building can approach 100% loss during the shaded period, since it blocks direct sunlight almost entirely; softer, partial shade from tree branches or foliage that still lets diffuse light through typically runs lower, often estimated in the 30-50% range. Site-specific shade analysis tools (a Solar Pathfinder or a smartphone shading app) give a much more precise figure than a rough visual estimate.

Does this calculator account for shading that moves throughout the year with the sun's position?

No -- Shading Hours/Day and Shading Severity are both single flat numbers you supply, meant to represent a typical or average day rather than season-by-season variation. Real shading from trees or nearby structures often changes with the sun's seasonal path, so a single annual estimate here is a simplification of what a full shading analysis across the year would show.

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