Considerations When Planning a PV Installation

Impact on heritage significance

For PV installations fixed directly to or within the setting of heritage assets such as historic buildings, the significance of the asset will need to be properly assessed and the impact of the installation on significance evaluated before applying for permission.

If the installation will harm significance, alternative options should be considered. Some heritage assets will not be suitable for PV installations, for instance listed buildings where the only practical location for panels is a prominent roof-slope. But there will be many listed buildings where panels can be fitted. Our Historic Environment Good Practice Advice in Planning Note 2 provides further advice on assessing the significance of heritage assets.

When planning an installation, you will need to think about the physical impact it could have on the building and whether it can be easily removed at the end of its operational life. The expected lifespan of a PV array and its associated equipment is typically much shorter than the roof covering, so it could have several PV installations installed over its life. It is important therefore to minimise any damage to the roof covering by carefully planning how the array is installed, maintained, and removed at the end of its useful life.

Deciding where to install the panels and managing their visual impact are important parts of the design process. All parts of the system that are visible should be considered carefully.

Impact on the building fabric

The type of building and the materials it is constructed from have implications for the design and impact. Where and how a PV array is installed will dictate the impact. If a PV array is ground-mounted next to the building, then the impact on the building may be significantly reduced.

Where panels are fixed over the existing roof covering, some tiles and slates might be broken during installation, so it’s a good idea to have some replacements available.

Many types of traditional roof covering, such as stone or hand-made tiles, can be difficult to find so it is important to make sure you can source replacement slates or tiles before you undertake any work.

Structural loading

With roof-mounted installations, you will need to check that the roof can support the additional wind, snow and static load imposed by the PV panels, and that it complies with Building Regulations Approved Document A: Structure. This must be done by a qualified structural engineer.

Ecological and environmental issues

All bat and wild bird roosts and nests are protected by law and if any proposed work will cause disturbance, then you should contact Natural England for advice about wildlife licences. Work to install a PV system could disturb bats even if they are inside the roof and you will need expert advice about when and how to carry out the work. Our Building Works and Bats web pages provide detailed guidance.

Pigeons and other birds can use solar panels to nest and seek shelter underneath which can cause issues with panels and the associated electrical cabling. The best method to prevent this from happening is to use bird guards around the panels at the time of installation to prevent birds from accessing the space beneath them. Our Bird Deterrents web pages provide more advice on deterrents on historic buildings.

System efficiency and sizing

PV installations should be designed to maximise their yield to provide the best return on investment. The aim is for the system to operate close to its theoretical maximum as much as possible and thus pay back faster. Environmental factors such as temperature, soiling and shading can affect this, as can the orientation and inclination of the panels, the latitude of the location, and losses in the electrical components of a system. The positioning of the PV installation should avoid principal roof slopes if they would be visible and would impact on the significance of the building.

The PV design should include how the array will be arranged and connected to inverters. Inverters need to be sized appropriately to make sure that the generated electricity is transformed efficiently into usable AC electricity. Under-sized inverters can lead to a reduction of the peak power generated from the PV array, which can impact the overall system efficiency.

PV cells degrade throughout their operational life and this means that the amount of electricity generated will decrease slightly each year. The best panels come with a 25-year product warranty, but after ten years, the productivity of a panel is likely to have dropped to 80%. The PV panel may continue to generate electricity beyond the manufacturer's warranty period, but it is important to understand the expected lifespan and how the energy yield will decline.

Shading

Shading from nearby buildings and trees, or objects further away such as hills, can also cause a significant drop in efficiency. When planning an installation, it is important to assess all near and far shading that may be cast on a PV array at different times of the day and at different times of the year. In winter the sun is much lower in the sky, and this may cause issues with far shading. Likewise, it is important to consider how the growth of vegetation or trees may result in shading over the lifespan of the installation as this can have a significant impact on how much electricity can be generated.

Parts of the building’s structure, such as chimneys or dormer windows, may cause shading. If arrays are configured in ‘strings’ so each panel is connected in series to the next in a line, if one part of the string is in shade, then the rest of the string will have its power production reduced. Using micro-inverters or solar optimisers can stop shading on one panel affecting performance on the others, but it is best to avoid any shading. 

The layout of an array itself can cause self-shading when the distance between free-standing panels has not been considered. This is where the rows of ground-mounted PV arrays cause shading of subsequent rows if the rows of tilted modules are too close to each other.