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Solar shading loss calculator

Shade is one of solar's biggest hidden enemies — and a small shadow can cost far more than it looks. Estimate how much energy your array loses to shading, see your effective output, and understand why series wiring makes partial shade so costly.

Your array's output with no shade — in whatever unit you like; the result matches it.
How much of the array falls under shade at the shaded time.
Share of daily sun hours affected (e.g. a tree shading only the morning).
How much partial shade is amplified by wiring.
0% estimated energy lost
0 effective output (same unit)
0 output lost to shade
— shade impact factor

This is an estimate. Base loss = area% × time%. The wiring factor multiplies partial-shade impact, because series-wired panels drag each other down. Real losses depend on exact layout and shadow position.

How the shading loss calculator works The shaded area fraction multiplied by the fraction of the day shaded gives a base loss, which is amplified by a wiring factor to give the estimated energy lost and the effective output. What you enter Area shaded % of array Time shaded % of day Base loss × wiring factor series wiring amplifies it Energy lost + effective output what you actually keep
How the calculator estimates shading loss and your remaining output.

How loss grows with shaded area

This curve updates with your inputs above. It shows how estimated energy loss climbs as more of the array is shaded — and how much steeper that climb is on series-wired strings compared with module-level electronics.

Energy loss rises with shaded area, steeper on series strings.

Shade seems simple — cover part of a panel, lose part of the power. But solar shading is sneakier than that. Depending on how your panels are wired, a shadow falling on just one corner of one panel can cut the output of an entire string. This calculator gives you a realistic estimate of the loss, and explains why the "how it's wired" question matters so much.

The simple part: area and time

At the most basic level, if shade covers part of your array for part of the day, the energy lost is roughly the shaded fraction multiplied by the fraction of the day it lasts. A shadow over 20% of the array for 25% of the day is a base loss of about 5%. That's the starting point — but it's only the start.

The hidden part: series wiring

Here's the catch. Panels wired in a series string all carry the same current, so the most-shaded panel sets the limit for the whole string — like the narrowest point in a pipe throttling the flow. Shade one cell, and you can throttle every panel wired in series with it. This is why a small shadow often costs far more than its area suggests. The calculator's "wiring" setting applies a factor to reflect this: module-level electronics (microinverters or optimisers) limit the damage to the shaded panel, while a plain series string spreads it, and a string with failed bypass diodes is worst of all.

Why the mitigation choice matters

This is the single biggest lever you have over shading loss. With microinverters or DC optimisers, each panel works independently, so a shaded panel only loses its own share. On a traditional string inverter, one shaded panel can drag its neighbours down. If you know part of your array will be shaded at times, module-level electronics often pay for themselves in recovered energy.

How to reduce shading loss

The best fix is avoiding shade at the design stage — keep panels clear of chimneys, vents, trees, and nearby rooflines, especially around midday when the sun is strongest. Where some shade is unavoidable, group shaded panels onto their own string, use module-level electronics, and make sure bypass diodes work. Don't forget soiling — dust and dirt act like soft shade, which is why regular cleaning matters.

Related tools

To see your unshaded baseline, use the energy production calculator, and to plan a well-oriented, low-shade layout, the panel tilt calculator helps you point the array correctly. For series strings, the string sizing calculator sets how panels are grouped.

Frequently asked questions

How much does shading reduce solar output?

Roughly the shaded area fraction times the shaded time fraction — but on series strings the loss can be much bigger, because one shaded panel limits the whole string.

Why does a little shade cause a big loss?

Series-wired panels share the same current, so the most-shaded panel throttles the whole string. Shading one cell can cut current for every panel in series with it.

How do I reduce shading losses?

Avoid shade in design, use microinverters or optimisers so a shaded panel doesn't drag down others, group shaded panels together, keep bypass diodes working, and clean regularly.