What makes a good solar PV roof?

Written by: Phil Davis, Managing Director at Renewables First and specialist in hydropower, wind power and solar power system design.
Reviewed by the Renewables First engineering team for technical accuracy.

There are several factors which should be considered when assessing whether a roof will be good for solar PV installation. These factors apply to both commercial and residential PV developments. In summary, there are seven key characteristics necessary for a good solar roof:

1. Good roof orientation
   Ideally the roof would face directly south, to maximise the exposure to the sun and generate the most energy. However, east and west facing roofs still present a good opportunity for solar installations and offer good potential for energy generation, particularly if they can be designed to take advantage of morning or evening sunlight by using battery storage or matching self-consumption profiles. Shallow-pitched north-facing roofs can also be used (typically if the pitch is less than 10°).
2. Good roof pitch
   To maximise energy generation, the panel surface should be perpendicular to the sun’s rays. The optimum pitch angle on a south facing roof is around 40° to maximise energy generation and ensure consistency throughout the year. However, shallower or steeper pitches can also be effective, while flat roofs’ generation potential can be improved by using mounting systems which optimise the tilt angle.
3. Structurally sound
   The roof must be structurally sound to withstand the additional loading from the solar PV system. This may require a structural assessment, particularly for larger commercial buildings. In addition, the type of roof material will also affect the cost. Commercial roofs with asbestos can add complexities, often requiring replacement due to drilling through the sheets for fixings. Integrated systems are an option for tiled roofs, offering potential savings if the tiles are near end of life anyway.
4. Sufficient roof space
   There needs to be adequate roof space to install the desired array size while leaving the required setbacks from roof edges and ridges. This can be made more complicated if there are large amounts of roof furniture such as chimneys, dormers, or industrial equipment present.
5. Limited shading
   An ideal site will have no sources of shade over the installed panel area. Any sources of shade (mainly caused by trees or other structures) will reduce the generation potential. The use of optimisers will reduce the losses of the overall system but individual panel losses will still affect performance.
6. Limited environmental or heritage sensitivities
   Planning permission may be required for systems near listed buildings or in conservation areas. Larger systems over 50kW will also require approval.
7. Good grid connection
   You will need permission to export any surplus electricity, and for many sites this is a key constraint. The export capacity needs establishing early in the project because this can have a significant impact on the size of the system and the financial performance.

For answers to all of your solar power questions please visit our dedicated Commercial or Residential solar power pages. If you can’t find what you are looking for then send us your question and we’ll get an answer to you.

Do you own a site you think could benefit from a solar PV installation? Let us take a look, we can give you our initial thoughts on whether you would benefit from our solar feasibility service.

About the Author
Phil has worked in the renewables sector since 2001 and founded Hydro Generation, which became Renewables First in 2009.

A qualified mechanical engineer (BEng, MSc Renewable Energy Systems), Phil is a recognised expert in hydropower, wind and solar PV across all project stages.

View all posts by Phil