What are solar tilt and azimuth?

Solar tilt is a panel's angle above horizontal; azimuth is the direction it faces. A UK network research report identifies south-facing panels tilted 30–40 degrees as a general optimum [S2]. Your roof needs a location-specific comparison because shading, mounting and daily demand change the design decision. PVGIS can compare alternative angles [S1]. Checked October 2026.

Last checked 19 October 2026

What do solar tilt and azimuth mean for your site?

Solar tilt is the angle of a panel above horizontal; azimuth describes its compass direction. PVGIS uses a south-centred azimuth convention [S1]. For your site, these inputs help explain why equally sized arrays can have different generation forecasts. Check them against the proposed roof drawing before accepting a quotation.

For UK annual output, a network research report gives a general optimum of south-facing panels at 30–40 degrees [S2]. Treat that as context, rather than a prescribed mounting angle for every commercial building. Read regional solar yield for location and weather considerations.

How much output is lost away from the optimum?

Energy Saving Trust gives around 15–20% lower energy for east- or west-facing roofs compared with south [S3]. That general comparison does not establish the penalty for your particular shallow commercial roof.

Use PVGIS to compare the actual slope and direction with its optimised arrangement. Keep location, panel capacity, technology and other loss assumptions unchanged [S1]. Calculate the percentage difference as:

• Loss = (optimised annual energy − proposed annual energy) ÷ optimised annual energy × 100.

For illustration only, assume outputs of 50,000 and 45,000 kilowatt-hours (kWh), a unit of energy. The difference is (50,000 − 45,000) ÷ 50,000 × 100 = 10%. These are assumed inputs, not PVGIS results for a named site.

Why consider an east-west flat-roof layout?

Ask for separate east- and west-facing model runs, then add their energy outputs. Compare monthly generation with your opening hours, rather than choosing solely by annual yield [S1]. Request row-shading and structural checks through the commercial flat-roof guide.

What should you do next?

Take the roof plan to the site check and get matched with an installer that covers your area.

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