You shouldn't need to drill the panel frames.
However, with my Solar Trackers I used this arrangement, as the panels get a lot of stress, and the metal frame is an integral part of the overall structure. But drilling through the side of these Sharpe seconds the frame is double laminated so silicone is required in the bolt hole.
The previous photos were not so good clamps, these are how things should be.
Here is a couple of 250W panels and you can see how the clamps should work with the correct size of clamp to match the panel frame height. There are mid way clamps and end clamps.
Photo of bits on the floor are for the GRASOL PV rail system. Brackets bolts etc are either Stainless steel or aluminium. I will not buy the PV panel frame clamps until I have the PV panels themselves, then I know the real thickness of the frames. I look out for good deals on PV panels.
Just re-roofing at present on a south facing, installing those GRASOL brackets and PV rails for a 5kW installation. But will do 2off SMA SB2500 GTI's on this roof.
Most PV retail companies will sell you the PV clamps, but they do need to know the rail manufacturer.
I used to get clamps from these guys, but do not mention my name.!!!!
http://www.navitron.org.uk/store/solar-panels/pv-roof-mounting I think they post.....
I trust this helps?