Too bad the article is not explaining why SNCF is interested in this project. I can guess that electricity is one of the job of SNCF, they are using a lot of it, they have the skills and network to manage and distribute electricity. They could buy less electricity. Since rails are a well equiped infrastructure, it's cheaper to put PV in place and everything is available for cables and it's an electricity network by itself

I found some articles (in french). They already tested a solution to rapidly deploy PV on unused tracks : https://www.groupe-sncf.com/fr/innovation/solveig-prototype-ferrovoltaique

An another article is about this project and gives a bit more details : https://lenergeek.com/2026/02/06/une-startup-suisse-ose-limpensable-produire-de-lelectricite-directement-sur-les-rails-de-train/ It is an experimental project to find if PV panels could survive in such condition and if it is possible to manage both rail and energy operations on the same network.