I have solar panels installed at the house in Guadalajara. They are from Sharp (Japan) but produced in US. According to the trade agreement there are is no custom itself.
I have represented and worked for a few months the association of Solar Panel distributors here in Guadalajara. As some of the companies import panels from China they have (had?) mayor customs problems and I have linked them to a specialist in customs. As it became a bit political (custom authorities asked high import fees under the rubric Electric Generator and not solar panels) we included a specialist from DF very close to the authorities (secretaria de economic). I have lost track something like a year ago as the association was disolved. In case you proceed being interested I can send you the information of the custom specialist I may highly recommend.
Let me know your e mail address.
By the way, Siegfried Schiffmacher, living as well in LM has sold or installed or knows about solar panels as well.