Portable speaker systems are portable, of course, because they draw power usually by not being plugged in to a wall outlet. Typically they use rechargeable or disposable batteries. The Devotec Solar Sound Bluetooth Speakers make use of a portable battery, but in a creative twist this internal battery can be powered by solar rays.
The Devotec speakers sport a large solar panel for charging the built-in lithium battery. Charging time is longer via solar power – 12 to 24 hours – compared to charging via AC or a USB port, but you can probably run this speaker without worry if it outdoors and a sunny day. Playback is otherwise eight hours at normal volume operation and the speak includes wireless Bluetooth support, meaning you can wirelessly playback audio from Bluetooth enabled mobile phones and MP3 players.