That's a good thread about adding solar panels, but it doesn't exactly address fasteners.
We have a 100 pound Motosat Datastorm (Satellite Internet) and a Motosat Executive TV dish (I installed the latter) on the roof and both are fastened with about #10 or #12 stainless steel sheet metal screws. What really provides the holding power is surface area of the aluminum bases and lots of Dicor between the mounting plate and the roof.
If your solar panel only has small mounting ears or tabs, you could add an aluminum plate to each mounting ear to provide more surface area for Dicor adhesion.
2005 Horizon 40AD, 2005 Jeep Liberty CRD