Solar PV Overview
A practical guide to how solar PV systems generate electricity, how roof orientation affects output, and what to consider before estimating system size.
How Solar Output Varies Across the Day and Year
Solar photovoltaic systems generate electricity from daylight, with output changing throughout the day and across the year. In the UK, expected generation is shaped by roof orientation, pitch, shading, usable roof area and wider site conditions.
For most sites, the aim is not simply to fit as many panels as possible, but to understand what the roof or ground area can realistically support and what level of generation that layout may deliver.
This page is intended as a high-level guide before using our solar calculator. It does not replace detailed design, structural review or electrical assessment, but it provides a useful early view of likely performance.
The Bell-Shaped Production Curve
On a clear day, solar generation typically follows a bell-shaped curve. Output rises through the morning, reaches its highest level around the middle of the day, and then falls away again into the evening.
This matters because peak output is only reached for a limited part of the day. The more useful measure is the total energy produced over the full day, month and year.
Cloud cover, seasonal sun angle, orientation and pitch all influence the exact shape of the curve, but the overall pattern remains broadly consistent.
Lower in Winter, Higher in Summer
In the UK, solar generation is much stronger in summer than in winter. Longer days, higher sun angles and better irradiance all combine to produce significantly more energy in the brighter months.
Winter generation can still be valuable, but it will usually be notably lower. This is particularly important when reviewing annual expectations, battery charging behaviour and the likely timing of exported energy.
A realistic solar estimate should always reflect this seasonal spread rather than assuming a flat level of production throughout the year.
South Facing Compared with East-West
South-facing roofs are usually associated with the highest annual yield because they receive the most direct sunlight across the main part of the day.
However, that does not automatically mean south-facing layouts are always the best commercial choice. East-west roofs can produce a broader generation profile, helping deliver output earlier in the morning and later into the afternoon.
For sites with demand spread across the working day, this can sometimes improve on-site energy use even where total annual generation is slightly lower than an equivalent south-facing array.
East-west layouts can also allow efficient use of larger roof spans and may suit buildings where midday peak output is less important than a longer generation window.
Roof Construction and Installation Approach
Solar PV can be installed on many roof types, including metal sheet, fibre cement, standing seam, tile and slate roofs. The mounting method varies depending on the roof covering and structural arrangement beneath it.
On commercial buildings, sheeted roofs are often well suited to larger arrays, but the roof condition, purlin spacing, fixing strategy and structural capacity all need to be considered properly.
On domestic roofs, tile and slate systems are common, with layouts often shaped by rooflights, chimneys, hips, valleys and access requirements.
In all cases, usable roof area is less than the total roof face. Obstructions, access margins and engineering setbacks reduce the space available for modules.
Posts, Trays and Open Site Layouts
Where roof space is limited or unsuitable, ground mounted systems can provide an alternative. These are commonly installed either on driven posts or on tray-based support systems depending on the ground conditions and project constraints.
Ground mount layouts offer more flexibility in orientation and tilt, and can be a strong option for commercial and agricultural sites with available land.
They also bring their own considerations, including row spacing, access, cable routes, ground conditions, planning context and visual impact.
Wind Loading and Distances from Roof Edges
Solar layouts are not defined by panel dimensions alone. Wind loading is an important design factor, especially around roof perimeters, corners and leading edges where uplift forces are usually higher.
For that reason, panels are often kept back from roof edges rather than being installed right to the full extent of the roof face. These margins help reduce exposure and support a safer, more robust design.
The required distances depend on the building, exposure, height, roof structure and mounting system. This is one of the reasons why a quick calculator can only ever provide an outline estimate rather than a final design.
Use the Solar Calculator
Our solar calculator asks for the key starting points: roof orientation, roof pitch, and the length and width of the roof area. Using these, it provides a high-level estimate of likely system size and indicative annual generation.
This is intended as an early-stage guide for commercial projects with relevance to domestic systems as well. It is a useful starting point before more detailed review of structure, electrical integration, export constraints and site-specific design.
Supporting Pages
Solar system planning is often linked to storage and early-stage generation review.
Need Help Reviewing a Solar PV Project?
SJ1 Renewables can support early-stage solar review, roof and ground mount assessment, and wider project development for commercial and domestic systems.