The answer
Must panels face south?
Panels do not have to face south. An east-west layout can generate more of its electricity in the morning and later afternoon, which may suit the building's demand even if annual output is lower than a comparable south-facing array.
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What do you gain and lose versus south-facing panels?
An unshaded south-facing roof is a strong choice when the aim is maximum annual generation. Energy Saving Trust's broad guide says east- or west-facing panels may produce around 15–20% less annual energy than equivalent panels facing directly south. That figure is not a prediction for your own house; slope, location and shade can change the comparison.
East-facing panels tend to produce more earlier in the day, west-facing panels later. An east-west system can spread output across more hours. That can suit a home with morning and early-evening activity or a business with a long operating day. But it only improves your economics if the extra power at those hours is actually used or exported on useful terms.
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Compare the real roof faces, not an ideal diagram
A partly shaded south roof may be a worse place for panels than a clear east-west pair. Chimneys and trees can shade one face at a particular time; dormers, vents and edge clearances affect usable space. Ask the installer to show the array on each roof plane, monthly generation for each plane and which hours the shading model expects losses.
Different orientations should be reflected in the electrical design. The installer may use separate inverter inputs or an appropriate module-level arrangement where useful. Do not assume optimisers are automatically needed: Energy Saving Trust says they can help with shading, not make an unshaded array generate more simply by being added.
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Which layout is better for your bill?
Compare the expected annual kWh, when it is produced, how much you would use directly and how much you would export. A south array might make more power overall, while an east-west option could put a greater proportion into your own demand hours. Both claims need a load pattern and a sensible import and export price assumption to be convincing.
If a battery is part of the proposal, repeat the comparison with and without it. Storage may change the value of midday surplus, but adds cost and losses. The useful outcome of a roof survey is a side-by-side choice grounded in your roof and bills, not a blanket rule that every Scottish roof must face south.
Where this guidance comes from
Check the original guidance.
These primary sources support the technical or scheme points above. Rules can change; follow the current source before making a commitment.
Apply this to your property
Check both sides of your roof.
A free solar survey can test the actual roof geometry and your daily electricity pattern before settling on an array layout.