Shading: The Hidden Challenge for Solar Panels

The silent killer of solar performance

If your installer hasn't talked about shading, that's a red flag. Shading is the single biggest avoidable performance issue we see on solar systems — and most of the time, it can be designed out before the first panel goes on the roof.

Here's why it matters: solar panels work by passing current through a series of cells linked together. If even one cell is shaded, it acts like a bottleneck — pulling down the output of the entire string. A 10% shaded panel can lose 50% or more of its production. Multiply that across an array, and you've got a system that looks fine on paper but underperforms in real life.

What causes shading on UK roofs

Shading isn't just trees. In our 200+ installs across the North West, the most common culprits are:

• Chimney stacks — by far the biggest issue on Victorian and Edwardian terraces
• Dormer windows and roof projections — common on extended properties
• TV aerials and satellite dishes — easily moved or relocated as part of the install
• Neighbouring trees — especially in summer when they're in full leaf
• Adjacent buildings — terraced houses with taller neighbours, garages, outbuildings
• The roof itself — hip roofs, gables, and complex pitches that cast their own shadows

Why winter shading is worse than you think

The sun sits much lower in the sky in winter. At midday in December, it's only around 15 degrees above the horizon in Greater Manchester. That means even short obstacles cast very long shadows. A chimney stack that's clear in summer can throw a shadow halfway across your roof in January.

That doesn't mean winter solar doesn't work — a properly designed UK system still generates around 15-20% of its annual total during the winter months. But it does mean shade modelling needs to be done across all seasons, not just June.

How TJS Solar designs around shading

Before we quote any job, we run a proper shade analysis:

• Drone survey — we fly the roof and capture the surrounding obstacles in 3D
• Annual sun path modelling — we plot where shadows fall across every hour of every month
• Panel-level optimisation — where shading can't be avoided, we use Tigo optimisers or hybrid inverters with module-level MPPT to isolate the affected panels
• Half-cut cell panel selection — AIKO, Longi, and JA Solar all use half-cut cells, which significantly reduce shading losses compared with older full-cell designs
• Sigenergy SigenStor — for jobs where shading is a major factor, our preferred system has independent MPPT for every panel, completely eliminating string-level shading losses

Three questions to ask any solar installer

If you're getting solar quotes, here are three questions worth asking:

• "Have you done a shade analysis on my roof?" — if the answer is "we'll just put them on the south side", walk away
• "What's the expected annual generation per kWp?" — a proper installer will give you a real number (typically 850-950 kWh/kWp/year in the North West)
• "How are you handling [chimney/tree/dormer]?" — they should have a concrete answer

Shading isn't always a deal-breaker. With the right design, even partially shaded roofs can deliver excellent returns. But the only way to know is with a proper survey — not a Google Maps screenshot and a guess.

Need a proper shade analysis?

If you're in the North West and want a no-pressure assessment of your roof, including a full shading study, get in touch. We don't quote without seeing the site properly — and we won't install a system that we wouldn't put on our own house.