How to plan a solar array layout

Real roofs have several faces, chimneys and vents. Planning around them is where the achievable number comes from.

The realistic panel count comes from laying panels out around what is actually on the roof, not from dividing areas.

Step-by-step

1. Enter each roof plane with its dimensions, orientation and tilt.
2. Place the obstacles — chimneys, vents, skylights.
3. Try portrait and landscape on each plane.
4. Read the achievable count and the expected output of each plane.

Planes with different orientations

An east and a west plane produce at opposite ends of the day. Combining them gives a flatter curve than a single south array of the same size — less total, better matched to how households consume.

Panels on differently oriented planes generally need separate strings or optimisers, since their output profiles differ throughout the day. Wiring them together in one string wastes a good deal.

Obstacles shade more than they cover

A chimney occupies a square metre and casts a shadow across several, moving through the day and lengthening in winter. Clearance has to account for the shadow, not the object.

A useful check: the winter midday shadow is roughly two to three times the object's height in mid-latitudes. A two-metre chimney can shade five metres of roof at the season when you can least afford it.

Access and maintenance

Leave room to reach panels. A layout that packs the roof completely makes cleaning and any future repair need scaffolding across the whole array rather than access to one corner.

Frequently asked questions

Can I mix orientations in one system?

Yes, but planes facing different directions should be on separate strings or use optimisers. Wiring differently oriented panels in one string means the weakest limits the rest through much of the day.

How much clearance does a chimney need?

Enough for its winter shadow rather than its footprint. In mid-latitudes the midday winter shadow runs roughly two to three times the object's height.

Is an east-west array worth doing?

Often. It produces less in total than south-facing but spreads output across the day, which raises self-consumption — and that is what determines the financial return.