The House of Marley Roots Solar is a portable speaker that’s built for beach parties. Its features sound neat, but solar-charging is ineffective and audio quality isn’t the best.

[Jamie Matthews], for instance, built a loudspeaker that runs on solar power but can also work in the dark thanks to two supercapacitors. The speaker’s 3D-printed case has a 60 x 90 mm 2 solar ...