Roof orientation and pitch

How azimuth and inclination shape annual PV yield and its timing across the day.

Solar PV output depends on the direction modules face and their angle from horizontal. Orientation changes when sunlight reaches the array through the day. Pitch changes the angle at which that sunlight meets the module and affects seasonal production, drainage, soiling and mounting.

Neither should be reduced to “south good, everything else bad”. The useful design is the one that fits the roof safely and produces energy at valuable times with an honest yield estimate.

MCS definitions

MIS 3002 defines array orientation as azimuth relative to due south:

due south is 0 degrees
south-east and south-west are 45 degrees from south
east and west are 90 degrees from south

Inclination, or pitch, is measured from horizontal. A flat module is 0 degrees and a vertical module is 90 degrees.

As at 22 July 2026, MIS 3002 Issue 6.0 requires orientation to be rounded to the nearest 5 degrees and inclination to the nearest degree for its standard performance method. Those are calculation inputs, not construction tolerances.

Orientation changes the daily profile

A south-facing array tends to concentrate more output around the middle of the day. An east-facing array shifts production earlier, and a west-facing array shifts it later.

An east-west split can produce a broader, flatter curve than one south-facing plane. Its total annual yield per installed kWp may be lower in a simple comparison, but more of its output can coincide with morning and evening household demand. The flatter combined peak can also reduce inverter clipping for the same total DC capacity.

Assess each roof plane separately. Averaging east and west into “south” loses the timing and can misstate shading and inverter behaviour.

Pitch changes seasonal collection

A shallower angle tends to favour the higher summer sun, while a steeper angle can collect relatively more when the sun is lower. Local latitude, orientation and horizon all affect the annual balance.

There is no single optimum pitch that overrides the existing roof. Raising modules away from the roof plane adds structure, wind loading, row-to-row shade and planning or visual considerations. The small theoretical yield gain may not justify those consequences.

For a pitched roof, following the roof plane is usually the starting point, subject to structural and mounting design. For a flat roof, the designer chooses a mounting angle and spacing together rather than selecting tilt in isolation.

Flat-roof arrays

Flat-roof systems must deal with:

wind uplift and ballast or fixing loads
roof membrane compatibility and drainage
row spacing and self-shading
access for inspection and roof maintenance
edge zones and fire or access routes
dirt accumulation at low inclination

Packing rows more closely can install more kWp while increasing inter-row shade. The best option may produce more total annual energy from the roof even if each module has a less favourable angle. Model the complete layout, not one unshaded module.

Shade can outweigh aspect

A nominally favourable roof plane can perform worse than another plane if a chimney, dormer, tree or neighbouring building shades it. Shade is also electrical: its effect depends on string arrangement, bypass diodes and module-level electronics.

Measure orientation and pitch, then assess the real horizon and near objects. Do not apply a generic orientation percentage and a generic shade percentage independently if a proper model can represent their interaction.

Structural and roof condition come first

The highest-yield plane may not be the right installation surface. Roof condition, remaining life, structural capacity, fixings, wind loads, fire separation, access and waterproofing can rule out a layout or make pre-installation roof work sensible.

A reroof soon after PV installation adds removal and reinstatement cost and risk. The design survey should record the roof covering, defects and expected access route as well as the solar angles.

Comparing layout options

For each roof plane or mounting layout, compare:

installed module count and kWp
measured azimuth and inclination
annual AC yield using the same weather basis
monthly and hourly production shape
near and far shading
clipping and export curtailment
expected on-site use and export timing
structural and access consequences
cable route and string or tracker allocation

A claim that one orientation loses a fixed percentage everywhere is too crude for purchase decisions. Use the current MCS estimate for standard comparison and an interval model where timing or complex geometry materially affects the choice.

Applies to

Solar

Last reviewed

22 Jul 2026