The writeup says Rv, street lights, water pumping, and navigation lights so I'm assuming boats somewhere however I looked at the premade kits and the panels in the marine kit is a kyocera so I don't know. Most Nav lights IMHO they refer to are marina beacons and the like in a marine environment but not subjected to the riggers of being on a sailboat.
All over eBay as low as $100. Of course, these will be no-name Chinese panels but there is a worldwide glut pushing prices to unheard-of levels.
I bought a 30 watt no-name last year for $60... To my layman's eyes, it seems well-made and sturdy. Even if it only lasts 5 years... then I'll be keeping my battery topped-up for $12 / year. That's tough to beat.
Provides power to change batteries from the sun when cruising or any time you are away from shore power. Other than the cost of the panels and charge controller its free power and no pollution or noise