Can a solar panel work underwater?

Yes, if light reaches the cell and its materials are protected from water, but ordinary rooftop panels are not designed to be submerged. Water absorbs red and infrared wavelengths quickly while blue-green light penetrates farther, so underwater cells need materials tuned to that spectrum and watertight packaging. For a hobby test, keep voltages low, use a sealed purpose-built module, and compare output at increasing depths—never place mains-powered equipment near water.