And they asked us under what wiring regulations and standards that the panels does not meet the standards?

It's going to difficult to prove a defect that way I think. BS 7671 isn't a "thou shall do exactly this to comply" sort of document - rather it talks in general terms of things needing to be adequate for the circumstances. I can see the PV installers (if they were still about) taking the view that if the roof itself had been correctly built, there wouldn't have been any standing water and so both the connectors and the cables would be perfectly adequate, at least from a water ingress point of view. Routing and/or trip hazard is even more vague in BS 7671 - laying cables unclipped on a suitable surface where they're unlikely to be disturbed is certainly recognised as OK - whether your roof classes as "unlikely to be disturbed" is probably a matter of engineering judgement and the exact circumstances. Best practice, adequate, just-about-comply aren't always the same thing. Costs always come into play too - many customers given a choice between a state of the art cable management system or a sign on the access door that says no unauthorized access and a work policy that says all other trades when on the roof need to stay clear of the PV installation, will pick the less costly option. Ideally designers/installers should discuss all these sort of details with the end customer, but I suspect that most of the time they'll just assume that what they did on the previous jobs will likely be acceptable.

   - Andy.

Thank you Andy for sharing your perspective. I appreciate that BS 7671 allows for some flexibility in interpretation, we are currently facing a -45% performance shortfall, which suggests a significant issue that goes beyond just compliance considerations.

1. Limited Roof Access – The flat roofs in question are only accessible via skylight AOVs, meaning they are not routinely accessed or disturbed. This makes it unlikely that external factors have contributed to the current state of the installation.

2. Lack of Verification – Unfortunately, no one had the opportunity to review the finished installation to confirm its condition or functionality at the time of completion. As a result, there is uncertainty about whether the system was installed to an adequate standard and performing as expected from the outset.

3. Compliance Obligations – This system was a compulsory requirement to meet the council’s emissions targets. Given the current shortfall, the responsibility now falls on the management company to rectify the issue, which is a considerable concern.

Rather than just assessing whether the original installation met the minimum technical requirements, the key question is whether it was fit for purpose and capable of delivering the required performance. Our priority is to understand the cause of the shortfall—whether due to design, installation, or another factor—and explore a resolution that ensures compliance without placing undue burden on the management company.

I would greatly appreciate your thoughts on how best to move forward in addressing this issue.

Lack of Verification – Unfortunately, no one had the opportunity to review the finished installation to confirm its condition or functionality at the time of completion. As a result, there is uncertainty about whether the system was installed to an adequate standard and performing as expected from the outset.

Do you have any historical meter readings? Ideally PV generator meter which should tell you directly what the output was - so that could be compared with other systems for the same periods to compensate for weather variations (but I'm not sure they're always installed in these post-feed-in-tariff days), failing that ordinary import/export readings might provide some clues - e.g. did consumption drop noticeably when the PV system was commissioned? and/or do the import/export figures vary more than can be accounted for by the seasons?

   - Andy.

Yes I do. We are reaching almost 8 years. According to MCS data, annually we should be generating approx just over 31K Kwh. We have cumulatively only achieved 125K in all these years. Our FIT was never setup nor registered too. And we have only exported less than1000 Kwh..

So what do you think about performance? Thanks Andy.

“And if that is the case, the over-voltage trip level is something that within limits can be adjusted by the installer, as a software parameter.”

Yes in theory. Except that in most cases on this scale the OV protection is pre-set for G59/G99. Technically changeable in many (but not all) cases but only with DNO’s permission which would likely mean an additional relay closer to the point of supply. 

KIRAN.M said:

-45% performance shortfall

Is this against the installer’s estimate (which method did they use?) or a simplified building performance / EPC calculation (eg SAP)? You describe a flat roof with multiple orientations on a single inverter with considerable shading… if the calculation doesn’t take the detail into account (eg PVSyst or PVSol or similar modelling) it could be that the performance has been oversold rather than the system underperforming.

Although with the shutdowns you mention it could be both!

KIRAN.M said:

Lack of Verification – Unfortunately, no one had the opportunity to review the finished installation to confirm its condition or functionality at the time of completion. As a result, there is uncertainty about whether the system was installed to an adequate standard and performing as expected from the outset.

Are you saying the no test certification was issued (iaw. BS EN 62446) by the contractor? That would be a real red flag especially with the errors reported.

What documentation /was/ issued?

Hi Jam, This is the MCS certificate estimates. 
My apologies for not clarifying. 
Got 4 inverters / 4 different installations/ 4 blocks.  

Council requirement was to meet 10% Co2 emissions against the SAP figures. And it has to be in perpetuity. The issues all came to light as our Grid electric usage has risen and with unit prices changing its impacting the residents who purchased their properties as it has to be charged back via service charges. 

National developer was in charge of delivering as per the planning permission. I hope i am making sense. 

There was no documentation issued to the leaseholders upon exchanging of the contracts. Apart from the contractor who installed and notified the DNO (G83/2) there is no other documentation. The contractor has closed their business down. 

When I approached, national developer they told me they do not have any liability as so many years have passed. And there was no warranty certificates with installations either. Since the contractor has closed down the business and not MCS certified, MCS cannot help either. 

Our only recourse is NHBC. And that is why I have approached here for some knowledge and insights. And the MCS certificates was only issued to 3/4 blocks after 7.5 years. 

The cables and connectors supplied with PV modules are suitable for outdoor use, if of reputable manufacture. They should not be immersed in water, but in the rain is fine.

As to the other problems, we need a lot more detail to be able to advise.