If you thought Regen's Renu solar-powered iPod dock was unbelievable, get a load of its big brother, the Reverb. It's 3-feet tall and capable of cranking out 60 watts of power off of the sun's rays.
My guess is that you will need all 3-feet of that space to generate enough electricity to play your music for 4.5 hours at full volume/12 hours at a normal volume. Of course, it takes 20 hours of outdoor sun exposure (or 40 hours indoor) to reach a full charge. If you are not patient enough to wait, the Reverb can be powered up via a regular electrical socket—although I would suggest spending your $2,229 elsewhere if you see yourself doing that frequently. Speaking of being patient, the Reverb won't be available in April of 2010. [Reverb via Gizmag via Inhabitat]