Solar Panels on East-West Facing Roofs

The common situation

A great many British houses have their ridge running north to south, which puts one roof slope facing east and the other west. There is no south slope to argue about, and the question is whether it is worth doing at all.

It usually is. East-west is a perfectly serviceable orientation, and in some households it produces a better practical outcome than south would. What it is not is the same design, and treating it as a south system pointed sideways gets both the sizing and the equipment wrong.

What changes: total versus shape

Two things move in opposite directions.

Annual total falls. A panel facing due east or due west at a typical domestic pitch generates appreciably less over a year than the same panel facing south. That is unavoidable geometry.

The daily shape improves. A south array produces a pronounced midday peak and little at either end of the day. An east-west array starts earlier, dips relative to south around noon, and keeps producing later into the evening. The curve is flatter and broader.

That matters because generation and consumption are valued differently. Electricity you use instead of importing is worth the full retail rate. Electricity you export is worth considerably less. A flatter curve overlaps household demand — morning routine, evening cooking, washing, vehicle charging — far better than a midday spike does, so a higher proportion of what the array makes is actually used in the house.

The compensating advantage: two slopes

An east-west house has two usable roof planes rather than one. Where a south-facing house fills its single slope and stops, an east-west house can populate both, so the resulting system is often larger in kWp on the same building.

More panels producing less each, spread over a longer day, with more of it self-consumed. Over a year that frequently lands in a similar place.

Design and electrical implications

The two slopes have to be treated as separate arrays electrically. They peak at different times, so a single string spanning both would force the whole array to track a compromise operating point and lose output from both sides.

The normal solution is two strings on two independent MPPT inputs — a feature of most modern string inverters — so each slope tracks its own maximum. Where slopes differ substantially in panel count, or a third orientation is involved, per-panel electronics or a further input becomes appropriate.

Inverter sizing also shifts. Because the two sides never peak together, the combined array can exceed the inverter’s rated output by more than a single-orientation design would allow without meaningful clipping. That is a design decision made deliberately, not an accident.

The combined system frequently exceeds 16A per phase — roughly 3.68kW single phase — which makes it a G99 application requiring network operator approval before installation rather than a G98 notification afterwards.

Storage and layout

East-west and storage suit each other. The array already matches demand better than south does; a battery absorbs the remaining midday surplus and releases it after dark. Where a household is out during the day, that combination is usually what makes the numbers work.

On layout, both slopes need assessing on their own terms. Morning and evening sun sits low in the sky, so obstructions that a high midday sun would clear — a neighbouring house, a tall hedge, a garage — cast long shadows onto an east or west array. Shading assessment on these roofs matters more, not less.

Honest limitations

Per panel, you will generate less than a south-facing installation. Winter output is weaker, because low winter sun favours a southerly aspect and short days cut the morning and evening advantage. And a due east or due west aspect with obstructions on that side may not be worth populating fully — sometimes the better answer is one slope, not two.