I had wanted to start a thread on renewable energy sources for powering locomotives, but here it is.
Most renewable energy sources are best adapted to generating electricity. That is true of the biggest long-used one, hydroelectricity, and also of the two big recently-developed ones, wind and solar energy. In fact, I'm rather surprised that photovoltaic cells have done as well as they have.
Though wind and solar energy are both rather obviously intermittent, renewable-energy supporters have stepped up to that challenge, like doing large-scale production of lithium-ion batteries and researching alternatives like flow batteries.
CleanTechnica and
Renewable Energy World are both enthusiast sites, but it's good to see what the enthusiasts are enthusing about.
The two sites have a rather interesting gap: coverage of synthetic fuels (synfuels). They do not have many articles on synfuel-related subjects like electrolysis, Fischer-Tropsch, power-to-gas, power-to-liquids, and ammonia.
But IMO, synfuels are necessary for extending the reach of synfuels into transport, because their usable-energy density is much higher than for batteries, even the best ones.
The most successfully electrified form of transport is rail transport, though it must be noted that rail-line electrification is only practical on lines with heavy traffic and relatively short lines, lines like urban-transit lines. For other lines, one will need batteries and synfuels.