नहीं कोई गम, रेलवे से हैं हम - Aman

As far as I could search, I've found no mention of Solar -powered trains other than IR's trials with Solar powered coaches. The only thing I could find was a discussion on using Solar power to super heat water in fireless steam locomotives.
Usually our locomotives consume power on the order of Mega watts. I doubt if consistently meeting such power levels is possible with just the area available on the shell of a locomotive. And since, the output of the panels is affected by the surroundings and weather also, consistently meeting the power requirement of the locomotive will be very difficult, even more so on gradients etc. Even for using simultaneously with the OHE power,...
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the design will become extremely complicated as the OHE will be on AC power and Solar Panels always generate DC power. The additional equipment required for regulating the supply form the Solar panel will eat up a lot of space on the locomotive. And the most frustrating problem will be using the Solar power and the OHE power together as a lot of care has to be taken before connecting any power supply in parallel to a power grid.
However, on-board solar power might be a good option with battery operated shunting locomotives, which can haul a battery car fitted with solar panels to recharge the battery.
A more easy alternative is a fuel cell locomotive using hydrogen fuel cells to generate energy. These will generate very tiny amounts of Carbon dioxide as compared to diesels and the best part is that all the existing diesel locomotives can be retrofitted with fuel cells after removing the diesel engines, saving on the development cost and time. Some research has been conducted on this in IR ( No functional locos though). You can see a mention of it in this document : click here