Before architectural drawings begin, four plot-design choices dominate your future solar PV performance: roof orientation, roof pitch, shading from neighbouring trees and buildings, and the form factor of the dwelling itself. This page walks through each.
Roof orientation
South-facing is optimal — a roof pitched at 30–40° facing due south delivers 100% of the regional generation potential. South-east and south-west deliver around 92–95%. East and west drop to ~78%. North-facing roofs only viable at low pitches (<15°) and even then deliver 45–50%. On a tight plot with no south-facing potential, consider dual-orientation arrays on a hipped roof.
Roof pitch
30–40° is the sweet spot for UK latitude. Higher pitches (50°+) generate slightly less in summer but more in winter, smoothing seasonal variation. Lower pitches (15–25°) generate slightly more annually but cause more cleaning maintenance from dust accumulation. In-roof solar is achievable at any pitch from 15° upward; flat roofs require a tilted frame and waterproof membrane upgrade.
Shading from neighbours
A single tall tree or neighbouring two-storey building to the south can cut annual generation by 20–40%. Conduct a winter solstice shading study (low sun angle 14° at noon, 21 December) to understand worst-case shadows. Microinverters or DC optimisers minimise the impact of partial shading by isolating affected panels.
Form factor
HEM rewards compact forms (form factor below 3 — surface area to floor area ratio). Long, thin or articulated forms have higher heat loss and more difficult roof geometry for PV. A simple rectangular or L-shape footprint with a generous south-facing roof slope is the FHS-optimal form.
Conservation Areas and listed-curtilage plots
For Conservation Area plots and infill within listed-building curtilages, in-roof PV is usually acceptable but BIPV (solar tiles) may be required to match adjoining heritage roofs. Pre-application planning advice is essential before architectural design completes.