Mounting solar PV arrays on an existing roof is generally the first possibility to explore when considering an installation.
- The roof must be generally South facing, have a clear horizon and not be substantially over shadowed by trees or other structures throughout daylight hours.
- The roof must be in good condition with the roofing material, slates, tiles, corrugated sheets or similar, having an expected life of a further 25 years or more. Installing a new PV system over a roof which requires substantial maintenance within a few years can prove to be very expensive.
- The roof structure must be strong enough to support the additional weight of the array and fixings.
- The roof area available must be large enough to accommodate the number of panels required to achieve the desired output.
The pitch of the roof is not usually critical as the angle of the array can be optimised for maximum light using angled brackets in the mounting arrangements. Even flat roofs and vertical walls can be suitable and are frequently used. The available roof area on domestic houses can usually provide between 1 kWp and 4 kWp of output. This size of installation generally comes within "Permitted Development” and subject to some constraints requires no Local Planning Authority approvals. The installation of solar panels on farm buildings is also generally categorised as "Permitted Development"
Much larger roofs like cattle or sheep sheds, barns, chicken houses and grain stores can offer sufficient area for 20kWp up to 250kWp. For larger projects the capacity and rating of the local mains electricity connection is an essential part of the survey and subsequent planning of the project.