INSTALLATIONROOF MOUNTED
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if you are contemplating putting up to 50kWp on a single roof (barn/small industrial) you can be adding well over 5 tonnes to the roof structure before factoring in the weight of the mounting kit. Even the smaller domestic size cannot be dismissed weight-wise – say a typical consumer installation is 2kWp – this is perhaps 300kg when including the mounting kit. Now that’s not so far short of half a tonne.
If a building’s roof loading is increased by more than 15% then a structural survey is strictly speaking necessary to determine whether this loading is within the design criteria of the roof. Ignoring this can be an easy way for an insurer to simply walk away leaving you with a hole both in the roof and in the pocket.
So having factored in the weight and confirmed the loadings are acceptable the next issue is how to mount it on the roof. The biggest questions is: Will the roof last maintenance-free for 25 years or more? With a 25 year FIT it would be foolish to put PV on a roof that is perhaps only going to last 10 or so years. However, it is not always in the interest of the installer to point that out; something customers must beware of.
Roofing requirements Putting PV on a roof is a marriage for life, and not for the faint-hearted. Worst still, mounting PV if done badly can simply take a serviceable roof with many years of life to a leaking disaster needing immediate repair or replacement. The challenge here is that in most cases the PV is put up in the summer (no rain) and many roof mounting issues only show up after some months with temperature changes and weathering. So all may look well when the installation is made but not so rosy six months later in the depths of winter.
Roof work is for roofers. As obvious a statement as this is, many potential PV adopters see the challenge of PV as the technology rather than the mechanics of fitting it. While PV is unquestionably clever stuff the technology is packaged “plug and play” and fitting it is not rocket science. Would you ask electrician to fit a roof tile? That is not to say that there are not many MCS (Microgeneration Certification Scheme – a requirement to get the FIT) installers who are experts in both roof and electrical work.
For domestic installations most roof mount systems are secured under the roof tiles/slates and
www.solar-pv-uk.com Issue III 2011
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