Thursday 2 May 2013

Is the Solar Keymark Fit for Purpose?

The Solar Keymark is held up as the "gold standard" for solar thermal accreditation, but is it still up to snuff?

So what happens when it rains?
Image courtesy: Viridian Solar
 They say that Nature abhors a vacuum. National test laboratories on the other hand love the stuff, and they've been falling over each other to fill the vacuum left by the current embodiment of the Solar Keymark with highly profitable testing requirements and a hotchpotch of local standards.

Ireland, France and now the UK have introduced additional requirements for solar thermal installations, and guess what? They're all ever so slightly different.

Solar thermal panel manufacturers are tearing their hair out. How has this come to pass?

The Keymark is intended to ensure the performance and durability of solar thermal collectors. A random sample of solar panels from the factory is selected and subjected to a battery of tests at one of a small number of accredited test laboratories.  In addition, the quality systems in use at the factory are regularly audited.

The tests are designed to answer the question "are the solar panels you're making this week any good", and the audit answers the question "is what you're going to be making next week anything like what we just tested?"

The tests are based on the European standard EN 12-975 parts 1 and 2. Part 1 determines the thermal performance of the panel, while part 2 assesses the durability of the solar panel. A series of tests attempt to break the panel, for example:

·         Leaving it to bake in the sun, then pumping cold water through it
·         Leaving it to bake in the sun, then throwing cold water over it
·         Dropping a ball-bearing onto the glass
·         Spraying the panel with water and seeing if any goes inside it
·         Trying to break the glass by pushing and pulling on it

It really is a very good test of the solar panel.

Unfortunately, it only considers the solar panel in isolation.

In most real life situations, a solar panel is attached to the roof of a building. People can be fussy about their roofs.  Most seem to prefer that the water stays outside when it rains and that the roof doesn’t end up in the garden after a windy night.  Building Regulations cover these two points, to which they add the requirement that if your neighbour’s house is on fire, your roof shouldn't go up in smoke at the first lick of a flame.

In theory a solar installer must be able to demonstrated to building control that the solar panel they have installed does not impair the weather tightness of the roof, is proof against the wind loads it may face, and is installed the correct distance from the boundary for the fire rating of the panel.

How does the Keymark help the installer with this?  

It doesn't.

Enter MCS012 (UK), CSTBat (France) and Irish Agrement (Ireland), none recognising the other.  (Read my article about MCS012 here)

The Keymark is no longer meeting the needs of the industry for a single, Europe-wide test to ensure free movement of goods and services.  It rapidly needs to mandate the following additional tests:

1. A wind uplift test with a defined substructure to which the panel is attached. The substructure should be representative of a worst-case timber width, as the strength of fixings to timber is affected by the ratio of timber width to the screw diameter.  The tests should also take into account that timber is a natural material, which is normally done by repeating the test and taking a worst case.  The current test limit of 1,000 Pa mandated by Keymark is completely inadequate for windy islands like the UK, especially once safety factors are applied.  Manufacturers should test their panels to failure and declare the limit.

2. A water penetration test for roof integrated systems, taking into account each family of roof coverings (tile, slate) with which the panel works.

3. A single fire test, which works across Europe.  Currently there are four different tests in the "harmonised" European fire standard, and different national governments require different tests.

CEN is currently developing a new version of EN12-975 with the aim of including optional tests for weather tightness and fire performance.  This cannot come soon enough for european solar manufacturers.

(Incidentally, everything written above applies to the EN61215 durability tests for solar PV modules. MCS 12 covers both solar thermal and solar PV, whereas the CSTBat only applies to solar thermal.  For once the UK has beaten France by getting its barriers to trade in first, perhaps not something to celebrate.)

This article first appeared in Solar Business Focus UK, Vol 7-2013, sister publication to