It's solar, of course the unit economics are going to pencil out positive in the majority of climates and energy markets. The real question is "why should we put them here instead of somewhere else."

I wonder if the benefits are legal/jurisdiction/political. The total amount of track they could install this on is huge, and it doesn't seem like something that will be disagreeable on the local level. It could just be the easiest place to put it to deal with property law and zoning etc.

Another political benefit is that it means work for a very large number of jurisdictions, as there are suitable tracks just about everywhere.

  Initially, he planned to remove dust from the surface of the photovoltaic cells using a cylindrical brush mounted on the rear of a train. “However, we realised that each time a train passes, it creates an airflow that sweeps away all the dust,” he said.