Solar Panels on North-Facing and Shaded Roofs

Starting with the honest answer

Some roofs should not have solar panels on them. A due north-facing pitched slope on a domestic house is usually one of them, and a roof under heavy shade for most of the day is often another.

We would rather say that at survey than sell a system that disappoints. This page is about how we assess those situations and what the alternatives are, because there almost always are some.

Why north is different

A north-facing slope at a conventional domestic pitch is tilted away from the sun for most of the year. It catches direct sun only early and late on long summer days, and in winter — when household demand peaks and daylight is scarce — it receives very little.

Pitch is the variable that matters. The shallower the roof, the smaller the penalty, because a nearly flat plane approaches the performance of a horizontal surface regardless of aspect. A steep north slope is close to pointless. A very shallow one is a different conversation, particularly on a large single-storey or commercial roof where area is not the constraint.

Remember too that a north-facing slope usually has a south-facing one on the other side of the ridge. Even if that side is smaller or broken up, a small array in the right place beats a larger one in the wrong place.

Assessing shade properly

Shade is not a yes or no. It has a shape, a time and a season, and it needs measuring across the year rather than judged from a bright afternoon in June.

Three distinctions matter:

Hard versus soft. A chimney, an aerial, a flue or a dormer casts a sharply defined shadow that blocks a panel’s cells almost completely. A tree canopy casts dappled, moving shade that reduces output without eliminating it. Hard shade is far more damaging per square metre.

Position on the array. Because cells are wired in series through bypass diodes, a narrow shadow across the bottom of several panels can cost more than a larger shadow confined to one. Layout changes the loss.

Season. The sun sits low in winter, so a boundary that clears the array in summer may cross it entirely in December — and that is the worst kind, landing on the months when you can least afford the loss.

What per-panel electronics do and do not do

In a plain string, panels are wired in series and operate at a common current. A shaded panel restricts that current and every other panel in the string is dragged toward it. This is why one badly placed obstruction can affect a whole array.

Optimisers and microinverters break that link, letting each panel operate independently, so the unshaded ones keep working at full output. On a partially shaded roof that is a worthwhile recovery.

What they cannot do is make electricity from a panel in shadow. It produces what the light falling on it allows and no more. Where much of the array is shaded for much of the day, per-panel electronics recover the unaffected panels and nothing else — and you have paid extra for the hardware.

There is a durability point too. A cell repeatedly shaded while its neighbours are lit dissipates energy as heat, and hot spot cycling contributes to premature degradation.

Alternatives worth exploring

Another slope on the same house, even a smaller one. A garage, workshop, outbuilding or carport roof clear of the shading. A ground-mounted array, positioned and angled without compromise and kept clear of trees — needing more cable, a trench and a planning check, but often producing more than a compromised roof would.

And where nothing on the site works, storage alone on a time-of-use tariff can reduce a bill without any generation at all. It is not what you came for, but it may be the honest recommendation.