I think word count is not the best metric precisely because of what you mention. “Krankenversicherungskarte” is one word vs the three word “health insurance card”, but they convey the same information in roughly the same amount of characters.
Overall I don’t find German particularly verbose, only sometimes a small phrase is condensed into a single word.
Do subway trains have batteries for the purpose of moving themselves? I don’t know much about subway trains specifically, but in my imagination I can’t picture one working during a power outage.
If they don’t carry large batteries then it makes perfect sense to me to dump the energy back into the grid. Electrical losses should be fairly small.