Solar Installation: Technical Assessment & Compliance Review

The roof had been refurbished before the solar installation was carried out. It was therefore reasonable to expect the roof to remain weather-tight after the solar panels and mounting system were installed.

The evidence available suggests that the hook covers have not been incorporated into the slate covering in the way that would normally be expected from a properly designed roofing detail. Instead, pieces of flat plastic have been cut and pushed underneath the surrounding slates and then attached to the hook covers using adhesive or mastic.

This appears to be a makeshift arrangement rather than a proper, manufacturer-designed flashing detail. The concern is not simply how the installation looks. A roof needs to continue directing rainwater away from the structure after the mounting system has been installed.

Leaving parts of the hook covers exposed also creates an area where rain and wind-driven water can enter around the mounting point. Water can then find its way underneath the slates and onto the roof membrane or other parts of the roof construction.

This is particularly important because the purpose of the mounting system is not only to hold the solar panels in place. It must also be installed without compromising the existing weather protection of the roof.

The available information concerning MCS 012 also raises questions about the use of site-applied sealants as the main means of keeping mounting points weather-tight. A sealant should not be relied upon as a substitute for a properly designed and durable roofing detail.

The concern is therefore about the long-term performance of the roof, rather than whether the mastic currently appears to prevent visible leaks. Adhesive and sealant can deteriorate over time, particularly when exposed to movement, temperature changes and weather.

In my view, the roof should be treated as requiring proper inspection and repair rather than further reliance on the existing plastic and mastic arrangement.

The MCS Certificate identifies Renusol components as part of the installation. However, photographs of the installed system were subsequently provided to the manufacturers for identification.

Renusol identified the rail in the photograph as appearing to be a Fastensol product. Fastensol subsequently reviewed the available evidence and considered the roof hook to be consistent with its TH01 type.

This matters because Fastensol identifies the TH01 range as unsuitable for slate or composite slate roofs. If the installed hook is confirmed as a TH01, its suitability for the roof in question would therefore need to be established.

There is consequently a difference between what appears to have been installed and what is recorded in the certification documentation. This should be resolved before any further work is carried out.

Accurate records are important for more than just paperwork. They provide a record of what was actually installed and allow the suitability of the components, installation method and warranties to be checked.

If the components installed do not match the certified system, there is a reasonable question as to whether the installation was properly assessed and recorded when it was completed.

The first step should therefore be to establish exactly which roof hooks and rails were installed and whether those components were suitable for this particular roof.

Photographs and video evidence show movement of the solar panels and mounting system during periods of stronger wind. Some movement is expected in any structure exposed to wind, but excessive or repeated movement can place additional stress on rails, hooks, fixings and the points where the mounting system passes through the roof.

Over time, repeated movement can also affect the surrounding roofing materials. If the mounting points move, the weatherproofing around those points can deteriorate and allow water to enter the roof.

There is also visible deformation around one of the panels in the smaller array. Taken together with the movement shown in the video, this raises a concern that the mounting system may not be providing the level of restraint that should reasonably be expected.

Water entering a roof does not necessarily appear directly below the point where it entered. It can travel along the roofing felt, timber, battens, insulation and other surfaces before becoming visible inside the property.

This is why internal staining or dampness should not automatically be assumed to identify the exact point where water entered the roof.

Continued water entry can also have consequences for timber and other building materials. Repeated dampness may lead to deterioration of timber, corrosion of fixings, distortion and, in some circumstances, fungal decay.

The important point is that the structural, weatherproofing and water ingress concerns appear to be connected. Movement of the mounting system can affect the roof penetrations, and damage around those penetrations can then allow water into the roof.

In light of these concerns, continuing to modify the existing roof installation does not appear to provide a particularly satisfactory long-term solution. A more straightforward approach would be to remove the roof-mounted system, properly repair the roof and move the solar installation onto a suitable ground-mounted system.

The MCS Certificate gives an estimated annual generation of 2,785 kilowatt-hours. However, three years of recorded generation data show an average annual output of approximately 2,153.4 kilowatt-hours.

The difference is approximately 631.6 kilowatt-hours each year. In percentage terms, the recorded average is approximately 23% below the figure stated on the certificate. Put another way, the system would need to produce approximately 29% more electricity than its current average simply to reach the original 2,785 kilowatt-hour estimate.

The electrical arrangement may help explain some of this difference. The installation has panels on different roof orientations, with two east-facing panels connected in the same string as six panels facing approximately south.

East-facing panels receive their strongest sunlight earlier in the day, while south-facing panels generally perform best later. Putting differently orientated panels together in the same series string can therefore reduce the benefit that could otherwise be obtained from each group operating under its own conditions.

This is a design issue rather than evidence that the individual panels themselves are defective.

More importantly, the current roof installation has already created concerns about weatherproofing, mounting components and structural movement. Continuing to invest in modifications to the roof would leave those concerns attached to the system.

A different approach is therefore to remove the existing roof-mounted panels and mounting equipment, repair and properly weather the roof, and install a new solar array using Renusol ground mounts.

The proposed alternative is a 12-panel array using 12 × 410 W modules. This gives a total installed capacity of 4.92 kilowatts.

Based on the EU PVGIS generation estimate provided for the proposed arrangement, the expected annual generation is approximately 4,737.64 kilowatt-hours.

Compared with the existing measured average of 2,153.4 kilowatt-hours, this represents approximately 2,584 additional kilowatt-hours of generation per year if the estimate is achieved.

The ground-mounted approach also has an important practical advantage: it removes the solar mounting system from the roof altogether. This means that future inspection, maintenance or replacement of the solar equipment would not require further penetration or disturbance of the roof.

The Renusol ground-mounted option should therefore be considered as a practical alternative to continuing to modify the existing roof installation. It separates the solar installation from the roof and allows the roof to be repaired as a roof, without having to accommodate solar mounting hardware at the same time.

The inverter's internet and Wi-Fi monitoring connection was not established as part of the original installation.

This is important because the manufacturer's warranty documentation states that an internet connection is required for monitoring and that where a system is not connected to the internet, the warranty period is reduced to three years.

The monitoring connection also provides a useful way of identifying problems with the system. A connected system can provide information about its performance and can help identify faults that might otherwise go unnoticed.

Without the monitoring connection, the owner has less information about how the system is performing and may only become aware of a problem when the generation figures fall noticeably or another fault becomes apparent.

The lack of commissioning therefore has both a practical and a warranty consequence. It is another indication that the original installation and commissioning process should be reviewed as part of the overall resolution.

If a replacement or new system is installed using the proposed Renusol ground-mounted arrangement, the inverter and monitoring system should be properly commissioned, connected and registered from the outset.

The first concern is the way the solar mounting hooks have been incorporated into the roof. The use of cut plastic pieces, adhesive and mastic does not give confidence in the long-term weatherproofing of the roof, particularly where the mounting system is also subject to movement.

The second concern is the uncertainty over the actual mounting components used. The available evidence suggests that the installed hooks may not correspond with the components recorded in the MCS documentation. There is also a question over whether the identified hook is suitable for the slate or composite slate roof.

The third concern is the physical movement of the array. Movement under wind loading places additional stress on the mounting system and the areas where it connects to the roof. When considered alongside the weatherproofing concerns, this provides a reasonable basis for investigating whether the roof has been compromised.

The fourth concern is the system's actual generation. The existing installation has averaged approximately 2,153.4 kilowatt-hours per year over the available three-year period, compared with the 2,785 kilowatt-hours stated on the MCS Certificate.

The different roof orientations within the existing electrical configuration provide a possible explanation for some of the underperformance. Two east-facing panels have been connected in the same string as six south-facing panels, meaning that panels receiving different amounts of sunlight are operating together rather than being configured to work independently.

The fifth concern is the failure to establish the inverter's internet monitoring connection. This has potential implications for both the manufacturer's warranty and the ability to identify problems with the system.

Taken together, these issues suggest that continuing to make isolated repairs to the existing roof-mounted installation may not be the most straightforward way of resolving the underlying concerns.

A more complete solution would be to remove the existing roof-mounted solar equipment, properly repair and weatherproof the roof, and install the replacement solar array using Renusol ground mounts.

The proposed ground-mounted system consists of 12 × 410 W panels, giving a total capacity of 4.92 kW. The available EU PVGIS estimate indicates potential annual generation of approximately 4,737.64 kilowatt-hours.

This approach has the advantage of separating the solar installation from the roof. Once the roof has been properly repaired, it would no longer have solar mounting hooks, rails or associated penetrations that need to be maintained as part of the solar system.

It would also provide a clearer basis for documenting the replacement installation. The mounting system, electrical configuration, inverter, commissioning records and certification could all relate to the new installation rather than continuing to rely on disputed or uncertain aspects of the existing roof-mounted system.

The purpose of the proposed solution is therefore not simply to increase solar generation. It is to separate two problems that have become connected: the need to restore the roof to a reliable, weather-tight condition and the need to provide a properly installed and documented solar system.

On that basis, the preferred course for consideration is to treat the roof repair and solar replacement as one coordinated project, with the existing roof-mounted system removed, the roof properly restored, and a new Renusol ground-mounted array installed and commissioned in accordance with the applicable requirements.