A racking system that requires no ballast or holes to be drilled into an almost-flat roof, and that still won’t take off in a high wind, sounds like magic. “It is a bit magical,” says Powerak managing director Ross Woodfield of the firm’s T-Rack ‘Air Series’ system, announced in mid-October.
The company has developed the product with the US market in mind, Woodfield says, where enormous “big box” warehouse retail centres are common.
Concrete ballast is common in the US, he says, and installers use a lot of it to mitigate the lift effect of wind on arrays. “Quite often these guys have got to put tonnes and tonnes of ballast on a roof.”
Massive warehouse retail centres, however, are simply not designed to take the weight.
“A lot of those buildings that are prime opportunity to retrofit with solar can’t be retrofitted.”
It’s a lost opportunity, because such roofs are a “perfect application” for power purchase agreements.
The T-Rack ‘Air Series’ technology is designed for roofs up to 10 metres high and does not need to be weighed down or fixed to the roof, so long as panels are not placed too close to the edge (solar modules can’t be closer than half the building’s height near the edge, so a system on a 10-metre-tall building must stop at least five metres form the roof edge). A perimeter fixing provides seismic integrity to the installation.
The system was tested at the MEL Consultants wind tunnel in Melbourne. In windy conditions lifting pressure is not uniformly distributed across rooftops, so the job for the engineers was to design a system that levelled out high areas of lift.
The two forces Powerak’s system relies on are gravity, or the downward force of the array, and lift, which changes with wind speed and direction.
Woodfield says the same solution to lift that was used on the roof of the National Tennis Centre in Melbourne was applied by the Powerak team, where deficit lift force is engineered back into the structure.
“That force vector has been put back into the structure,” he says.
Powerak’s patented design has engineered out lift in zones where the force builds under high-velocity wind conditions. The racking — made of injection molded HDPE structured foam and rolled form coated sheet metal — distributes the lift force away from peak zones into the adjacent regions.
“Wind engineering is very difficult. There is nothing linear about it,” says Woodfield, whose business partner George Cap is a physicist.
It’s because of the logarithmic mathematics of wind dynamics that the T-Rack system will not work on a roof much taller than 10 metres off the ground.
Fortunately, 10-metre-tall warehouses are the retail norm, especially in California.