Testing a solar powered railway

Just outside London, a test is underway to see if it’s possible to power commuter trains by solar power.
At a certain level, the railways are already using renewable supplies such as solar power, only they do so indirectly through supplies bought from the National Grid. Plugging solar panels into the railway may sound like an obvious and simple thing to do — which is exactly why it’s none of those at all.
There are some substantial advantages though, but only if they can overco