Roof Orientation and Solar: Direction Trade-Offs

Your roof's compass direction (orientation) has a significant impact on how much electricity your solar panels generate. South-facing is optimal in the UK, but east and west-facing roofs are far from useless. Here's what the numbers actually look like.

Output by Orientation

These figures show the percentage of maximum possible annual generation for a typical UK location (approximately 52°N latitude — the Midlands):

These percentages assume a standard 30–35° roof pitch. Steeper or shallower pitches shift the numbers somewhat.

Why South Is Best

The sun tracks across the southern sky in the UK. At solar noon (approximately 1pm BST), the sun is due south and at its highest point. Throughout the day, it rises in the east, arcs through the south, and sets in the west.

A south-facing roof catches the most direct sunlight for the longest period. At the optimal tilt of 30–35°, sunlight hits the panels at close to a perpendicular angle during peak hours, maximising energy capture.

Why East and West Are Still Good

An east or west-facing roof loses 15–20% compared to south, but:

The generation profile changes, not just the total. East-facing panels generate more in the morning and less in the afternoon. West-facing panels do the opposite. If you're home in the morning (east) or evening (west), the generation may actually match your consumption pattern better.

The payback period changes modestly. If a south-facing 4kW system pays back in 8 years, the same system facing east or west pays back in approximately 9–10 years. That's still an excellent return on investment.

You can install on both sides. If your roof ridge runs north-south, you have both east and west-facing slopes. Installing panels on both sides (a split system) can generate 85–90% of what a single south-facing array would, while giving you a longer generation window throughout the day.

Roof Tilt Angle

Tilt angle matters too, though less than orientation:

The sweet spot for south-facing panels in the UK is 30–35° — conveniently close to the pitch of most UK roofs (25–45°). For east/west-facing panels, flatter pitches perform relatively better because they catch more light from the wider sky.

What About North-Facing?

North-facing panels in the UK generate 50–60% of what south-facing panels produce. This is generally considered not worthwhile because:

• The payback period extends to 14–18+ years
• The cost per kWh generated is significantly higher
• Alternative approaches (ground mount, wall mount) usually produce more

However, there are edge cases where north-facing panels can make sense:

• As additional capacity when the south/east/west roof is already full
• On very shallow pitches (10–15°) where the orientation penalty is smaller
• In Scotland during summer, when the sun rises far to the northeast and sets far to the northwest

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Multi-Orientation Systems

Many UK homes have roof slopes facing different directions. A well-designed system can use multiple orientations:

Dual-Slope (East-West)

Panels on both the east and west slopes of a roof ridge. This requires an inverter with dual MPPT inputs (or separate string circuits) so that each orientation operates independently. Total generation is typically 85–90% of an equivalent south-facing system.

South + East or South + West

If you have a south-facing slope that's too small for all your panels, overflow panels can go on an adjacent east or west slope. Again, dual MPPT is important.

Avoiding the String Problem

When panels face different directions, they must be on separate MPPT circuits. Mixing orientations on a single string forces all panels to the lowest common denominator, losing far more output than the orientation difference alone.

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Real-World Generation by Orientation

For a 4kW system in the Midlands:

Savings depend on self-consumption rate — using more solar electricity directly saves more than exporting it.

Does Orientation Affect My Decision?

For south, southeast, southwest, east, or west orientations: install solar with confidence. The economics work well from any of these directions.

For north, northeast, or northwest: consider alternative mounting locations such as a flat roof with angled frames, ground mount, or a garden structure. If the north-facing roof is your only option and you still want solar, the maths is marginal — get a detailed generation estimate from your installer before committing.

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