For a larger greenhouse a mix of clear non solar and solar pv pannels optimised for different plants could be the way to go. The polycarbonate clear pannels are actualy cheap and likely strong enough that I am considering mounting solar pv directly to them. So: scratch building a greenhouse frame, that will support all the loads, and attaching the panels, and run the wires right through the polycarb, standard solar pannels, install@40" width and that works out to 3 per 12', 12 pannels for 40', for a neat eve to eve install.