|Image: Viridian Solar Roof Integrated Clearline Fusion System|
That the implementation of MCS012 has been a challenging process must be obvious to any outside observer. The standard for assessing the performance of solar roof mounting kits for wind resistance, weather tightness and spread of flame performance was first published in 2012. Indeed, it was written into the 2013 Guide to the Installation of PV Systems as a mandatory requirement, and 130 different certificates have now been issued to roof mounting kits and components.
However, a first delay was made necessary when so many manufacturers had left things until the last minute that a log-jam was created at the test laboratories. MCS wrote out to installers to announce that the requirement would be suspended until further notice.
A subsequent hold up due to concerns raised about EU notification was followed by inconsistencies between certifying bodies in the treatment of ‘universal’ roof integration kits that needed to be ironed out.
After such a delay, it feels like old news that the use of mounting kits accredited to MCS012 will eventually become mandatory for MCS registered solar PV installations on pitched roofs from May 2nd 2016, but it brings some big changes for the industry.
Read more about what MCS012 means for installers here.
MCS012 mounting systems intended to mount the panels above a roof covering are tested only for wind resistance (where they can be shown not to affect the fire resistance and weather tightness of the roof covering beneath).
This test is important because the resistance of most roof hooks to pull-out forces is determined not by the strength of the roof hook itself, but by the strength of its fixing to the roof. In sound timber, this strength is determined by a combination of the size and number of the wood screws and the gauge of the timber into which they have been screwed.
Because of this, resistance values from tests where the hook is fixed to larger timbers than those used in the UK cannot be used as they would over-state the strength.
Some manufacturers have not tested at all, but instead used EN1995-1-1 (or similar) to calculate a resistance force for their fixings. Such calculated screw pull out forces only apply when the timber to which the screw is attached is wider than 12x the diameter of the screw. Unfortunately with slender UK roof trusses, this is usually not the case, making calculated resistances invalid.
A roof hook tested to MCS012 will have a certified, tested resistance in kN to uplift forces, creating a level playing field. Solar installers can use this resistance with confidence to calculate the number of hooks required for their installation that would have a combined resistance higher than the design wind pressure multiplied by the installed panel area.
Solar systems that replace the roof covering have more significant testing requirements under MCS012, including a deluge test for weather tightness, a pressure test for wind uplift resistance and a test of the spread of flame.
The spread of flame test is a requirement for all building materials used as a roof covering. Building regulations, e.g. Approved Document B in England, impose limitations (area and location limitations) on the use of materials that do not achieve a high enough performance rating. To comply with building regulations without a fire rating is impossible (which raises questions about how some roof integration systems were compliant before MCS012 forced those manufacturers that had not already done so to perform these tests).
Read more about building regulations for fire and roof integrated solar here.
It was this test of the spread of flame that has caused the most recent delay to MCS012 coming into force. The original version of the standard had not properly accounted for universal roof integrated mounting systems (those that can be used with pretty much any solar panel).
MCS012 was previously silent on how to interpret the fire performance test for universal roof integrated mounting systems when these relied on the presence of the solar panel to achieve the fire rating of the system as a whole. As a consequence, certifying bodies (CBs) were left to develop their own interpretation, which they duly did, but inconsistently. Some CBs issued an MCS012 certificate that limited the system to be used with only the module with which the system had been fire tested, others tested with only one panel but issued the MCS012 certificate to apply when the mounting kit was used with any module at all.
The first interpretation is incredibly limiting for systems that give the installer freedom to choose any solar panel, implying that manufacturers of such systems would need to repeat costly fire testing with every single type of panel that their customers might want to use. In theory, the second interpretation is dangerous to public safety as it extends the tested fire performance to an installation using solar panels made from plastic, wood or, for that matter, chocolate.
Solar panels had rarely been fire tested before MCS012 made it mandatory. Their design appears so undifferentiated that it seemed obvious that they would perform identically in such tests. However as tests proceeded, reports emerged that outwardly identical-looking products were performing very differently in the fire test.
At the same time, regulators in the US had found a similar issue with fire rating of solar panels and published standards (UL 1703) categorising panels into 15 families that could be considered to have the same fire performance for the US fire tests. An international precedent exists.
The MCS012 working group decided that the responsible reaction to this new information was to choose the most restrictive (and therefore most safe) option - that a certificate can only be issued for the roof integration system with the panel(s) with which it has actually been tested. This change was implemented in the latest version of the standard.
Roof integration systems that use a dedicated solar panel or solar tile are unaffected by this change, as they will have already been tested with the only panel type they use.
However, manufacturers of universal solar roof integration kits that work with many types of solar panels now have a number of options available to them for their products to remain in compliance with the requirements of the MCS scheme (and building regulations). They can either:
(1) Re-test the system without the solar panel in place to achieve a certified fire rating that is independent of the fire performance of the panel;
(2) Re-test with a range of panels to achieve a certified fire rating. Installers must then choose panels to pair with the mounting system from a more limited range; or
(3) Change installation instructions such that the system must be installed above a material that achieves an adequate fire rating in its own right (for example a fire board or fire-proof membrane).
Now this is sorted out, and the certification consistently applied, the standard has been made mandatory for PV installations. Work to understand which features of a solar panel's design affects its fire performance is planned, with the goal of creating a similar set of product families to those in use in the US, but based on UK fire testing standards. In future, this would allow a manufacturer of universal systems to be used with a much wider range of panels based on a much smaller number of tests.