Given bright sunshine, a square metre of photovoltaic panel can generate half a killowatt, so each kilometre of track cold potentially supply ten megawatts – about five times the power requirement of even powerful fast electric locomotives.
It is, of course necessary to provide adequate separation between trains, and this is essentially what the existing signalling system does, preventing entry into a ‘block’ of track if there is already a train in it.
Whilst such a railway would only run in the daytime, the power would be absolutely free, and would exist precisely where it was needed and would not therefore have to be transported to the railway via long high tension lines. Moreover, being locally generated, high voltages would not be required. It might even be possible to run the system at a non-lethal voltage, as there is no requirement for the electricity to travel more than a few metres.
It is the cost of transporting power to the track over long distances that compels many railways in poorly populated parts of the world to not use electricity, but to run diesel powered locomotives.
Were diesel electric locomotives to be used, this could run on sunshine during the day, and switch to diesel at night.