One day I wondered if a Vendée-Globe race could be done with marine vehicles other than sailboats, like submarines... But recharging batteries requires running a diesel generator with a snorkel and fuel capacity aboard small private submarines would be limited. Then I remembered a photo of a military submarine plainly visible in clear shallow waters of the Caribbean Sea and imagined deploying solar panels at periscope depth.
Sunlight is partially absorbed by water, but it is possible to improve the output of a solar cell by putting a fluorescent layer on top and such layer can be made with household materials.