ROI would take a lonnnnng time, in my view. It's the same idea as installing modules under asphalt roads or even above them. It's not really worth the O&M hassle whatsoever.

The same idea goes for installations like canals. They're linearly too so not the wisest use of modules. But the benefit of modules over water like that is lower rates of evaporation as the panels block the sun. Same is true for water department reservoirs that see lots of algae. The panels block the sun and choke out the algae.

But you're right about the shading. If these panels are installed in higher latitudes, then odds are they might never see the sun directly at certain times of the year. Usually solar designers only recommend flat horizontal mounting for modules in hurricane- or tropical storm-prone regions like near the tropics, or close to the Equator where the Sun shines directly overhead most of the year.

What I COULD see happening is if governments around the world start transitioning railroads to have H-frame structures that suspend feeder lines like what's used in electric trains with pantographs. If you set up those H-frames frequently enough, you have the underlying structure similar to carports and can install modules 4-10 modules wide. THEN you can utilize string inverters every 7-8 H-frames or so, converting the solar DC power into AC which can help feed the train loads as they pass or feed the grid.

Bonus of the above system is that over time, all trains including rail freighters become electric or at least hybrid to make use of the free power generated above them throughout the railway.

Lots of ideas!

I've always been an advocate of the canopies above train stations having solar panels to help power the local loads and maybe push power back to the grid.

Solar canopies are used in many other places like parking garages/lots and canals, so the technology is there.

I'm starting to wonder if it's the vibrations from the train that makes these installations risky. Those same vibrations would happen to in-track solar PV like what's shown in OP's article. It's certainly possible to design around, as the EU is showing!

By "in series", do you mean linearly? Depends on context.

For Commercial & Industrial (C&I) applications like rooftops, canopies, façades, canals, floating islands, and the like, panels can be strung in series linearly sure. But because C&I arrays also tend to be arranged in polygons and more often rectangles, this allows the solar designer to string in non-linear ways.

One way to string in these contexts is to prioritize loops where the start and finish of the string are 1 module apart. A lot of RF enthusiasts don't like it when modules are strung this way because conductors arranged in a loop act as an antenna that can send and receive EM waves.

Another way to string is the snake or zigzag method where strings are patterned like this: ,,,,|'''''''|,,,,|'''''''' in rows that are 2-modules wide. The snake method can also be applied to 3-mod, 4-mod, etc. wide rows depending on what stringing method ends up being feasible.

For ground-mount applications at the community-, Distributed Generation- (DG-), and utility-scales, solar stringing is usually done linearly or in loops due to the constraints of the racking, although snake/zigzag can apply in some instances. Ground-mounts can either take the form of fixed-tilt (FT) racking, single-axis trackers (SATs), or dual-axis trackers (DATs).

With FT, the usually racking setup is 2-in-Portrait (2P) where you have 2 rows of modules abutted next to each other facing South. These are usually designed in long rows along a property line, so it's easy to make strings completely linear or half-loops where you turn the string around at the halfway point of what would otherwise be a string line. FTs can also be arranged as 3- or 4-in-Landscape (3L or 4L) which allows for more loops and snakes/zigzags.

With SATs, you're always stringing things linearly.

For DATs, you get the same benefits as C&I, 3Ls, or 4Ls because each DAT is separated from the rest of the array so the mini-array can track the sun. Lines, loops, or snakes/zigzags work, with a preference for loops and snakes/zigzags because DATs are rarely sized large enough to accommodate the entire widths of strings (sometimes 15-30 modules in length).

With railroad-based solar, my bigger concern is that since the modules have to be in a single line that CAN'T repeat in rows to the North/South in a typical array, this means all those strings will need to run a long way before being collected at an inverter to turn into AC. That long length adds to voltage drop in the circuit, which is an energy loss on the system. You can get away with this by adding microinverters for every 1 or 2 modules. Microinverters like that add a lot more complexity in terms of Operations and Maintenance (O&M) purely because there are more parts to break down. With string inverters and even central inverters, you have less O&M breakage but the flip side is that those work better with more centralized/rectangular-like arrays.

Doesn't mean it can't be done, but it's certainly more expensive than any other implementation of solar.

One of the benefits I can actually see with using microinverters over string or central inverters is that you break up the "array" of modules so that shading from the trains affects less of the "array" than if everything was collected at the DC level. You can isolate the shade-affected parts better, and promote better energy reduction.

Idk I'm interested to see what comes from this! Definitely a wild idea haha

And if the railway track is electrified

We got 100% electrification rate in Switzerland!

But usually 15kV AC with 16.67 Hz, so probably not useful for connecting the panels to be honest.