Surprisingly, when people hear about pigments, they think it can't fade. Also, the finer-ground pigments cost more. There are other inkjet ink formulations that help the situation. For example, the Idanit inkjet printer and the Raster Graphics Arizona inkjet system use solvent-based pigmented inks which are far more durable in the sun. Because of that, these systems can use automotive-grade pigments, which offer outstanding durability.
Solvents have their own problems, however.
An obvious way to avoid the problems associated with inkjet fading is to use a machine other than an inkjet. Electrostatic printers use pigment-based toners and have long been the leaders in outdoors imaging. Electro-statics cost more than inkjets, and they take more expertise to run, but the results are very durable. And electrostatics are far faster than inkjets, making them the favorites of companies doing large runs of outdoor banners, signs, and posters. These systems use wax-like ribbons that transfer a thick, resiny protective coating to the top of the print while printing, giving the prints durability.