Before the architectural drawings begin, four plot-design choices decide most of your future solar PV performance: roof orientation, roof pitch, shading from neighbouring trees and buildings, and the form of the dwelling itself.
Roof orientation
A south-facing roof gives the most generation. South-east and south-west lose only a small share. East and west lose more, roughly a fifth. North-facing slopes are rarely worth using except at low pitch. On a plot with no south-facing roof, an east-west split across a dual-pitch roof is a common answer.
Roof pitch
Around 30–40° is close to the optimum for UK latitudes. Shallower and steeper pitches each give up a few per cent of annual output; steeper roofs favour winter generation. In-roof systems have a minimum pitch set by the manufacturer, and flat roofs need a tilted frame.
Shading from neighbours
A tall tree or a neighbouring two-storey building to the south can cut generation substantially. A winter shading study is worth doing: the midday sun on 21 December is only about 12–15° above the horizon across England. Microinverters or DC optimisers limit the effect of partial shading by isolating the affected panels.
Form
Compact forms lose less heat and give simpler roofs for PV. Long, thin or heavily articulated plans have more heat loss and more awkward roof geometry. A simple rectangular or L-shaped footprint with a generous south-facing slope suits both the energy calculation and the array.
Conservation areas and listed-curtilage plots
For conservation area plots and infill within the curtilage of a listed building, in-roof PV is often acceptable, but tile or slate systems may be needed to match neighbouring roofs. The guide to choosing a BIPV solar roof or in-roof panels covers the trade-offs. Get pre-application planning advice before the design is fixed.