The Importance of the Friction Coefficient for Ballasted Solar Systems

In addition to the force of the wind pulling upwards, ballasted solar mounting systems are also susceptible to the wind pulling and pushing against them in a sliding motion.

This is simply due to the solar mounting systems being designed to sit in place on the roof without the aid of being mechanically fixed.  It is therefore, vital that ballasted solutions are installed with the correct amount of weight to prevent them from both lifting off the roof and also sliding across the roof.

It is important to note that this is not a new requirement or regulation and that ballasting against the uplift and sliding forces have always existed.

The required amount of ballast is determined through a series of calculations that analyse and compute all of the possible forces acting upon the solar array, including the integral sliding forces.  This is ascertained from the friction coefficient, which measures the force of friction of a particular material.  This friction coefficient will be different depending on the type of material, since there are some materials which have a coarser surface than others.  For example, the friction coefficient will be higher for bitumen than for a PVC membrane.  In simplistic terms, the coarser the surface is, the greater resistance it will have.

Here at Sunfixings, we have always understood that there are time restraints for solar projects and that being asked to record the friction coefficients of roofing materials for every project is not only time consuming but also adds considerable cost to you.  So instead, we simply ask you to tell us what type of roofing material is present, whether it is PVC membrane, bitumen or concrete etc.  From this simple piece of information, we are able to determine the worst-case scenario value for the friction coefficient and enter this into our calculations.

A significant advantage that our ballasted calculations benefit from is the fact that we incorporate physically recorded results for both the sliding and uplift forces from our extensive wind tunnel testing procedures.  These results not only help us to understand how the system will behave but also allows us to determine a more realistic ballast requirement to prevent the solar array from lifting upwards or sliding across the roof.

We have always taken this approach in the information we ask from you and the way we calculate, simply because it removes the liability from you.  We pride ourselves in the fact that we can offer the reassurance of a 10 year system warranty, which not only includes the product itself but also the ballast calculations behind the system.

We do not rely on a simple “information in / information out” online calculation tool, instead we manually process all projects, which allows us to have several checkpoints throughout the entire design stage and can therefore, ensure correct information is being used and calculated at all times.  Our mantra is “whether 4kWp or 4MW, we calculate each project individually” with our highly qualified Technical Team to produce a design, ballast calculation / wind loading report, a detailed bill of materials and a clear plan of the solar array (which includes ballast requirements, location points and fixing points for non-ballasted projects).  This information in conjunction with our on-site technical support allows for quality PV installations to be undertaken and warranted with confidence.