How to mount this?

[zolee]

Hi,

Soon I'll have to install a new roof on the garage, and on top of it goes a new set of 10x 550 Wp panels.
The roof is 0.6 mm ribbed steel sheet with 10 mm polyurethane insulation on the bottom side (see pics), 12 degree slope.
The solar shop sent me these short rails for mounting with the self tapping screws (see pics).

Now, the problem is that the rail is not wide enough to cover across two ridges (ridge center to center is 110 mm) if I try to mount in the preferred direction (along the ridges).
And if I install it across the ridges I can cover 3 of them and install 6 screws, but I lose a lot on positioning flexibility (basically I need to be mm accurate with the rails).

We don't have much wind here, but the summer storms are unpredictable, this year we had two with really strong winds that caused a lot of damage.

Can I install them in any direction? Or it's not enough "meat" to install along the ridge?
Should I use the supplied screws or get some pop rivets? How many of each per rail?

Thanks, Z

 

[rodrick]

running across three ribs I would think would have less rocking/twisting abilities resulting in lower chances of leaking roof

 

[zolee]

Update:

The panels are finally mounted. It was a tricky task to put the rails in the exact position. We started the first row with a string line, then put on the panels and aligned the rails. Then the second, third etc...row.
We didn't use the screws provided by the seller (it was only 3 per rail anyway) but I bought some designed specially for thin sheet solar mounts. On the first and fourth row we managed to hit the rafters, so there we installed long 100mm screws for extra hold.
The wiring is not finished yet, scheduled for this week.