Thanks all, but seems my idea is a non-starter. I need 750kN pull-out resistance and the best bigHead will manage only 1/20 of that.

The requirement is to tie down Solar PV panels to a GRP 'flat' roof without compromising water resistance or membrane integrity. Normally you ballast the panels down but that needs ~300kg ballast per panel and the roof simply wont take the load. and finding a way to fix through the membrane and insulation to the underlying joists hasn't, despite my best googling, come up with a solution. Ideas?