[mchannon]

Funny. Contrary to everyone else worrying about the speakers and the PV's, I was thinking about the batteries failing fastest (assuming the thing keeps them to play at night).

Lead-acids would be garbage after 5 years, unless they were way oversized. After about 20 years, failure would be inevitable.

Ultracapacitors would probably last north of 50 years.

Whatever you encase the PV within needs to allow sunlight through. Diamond would probably not work for this. Silicon itself is freakin' hard (about 9 on the Mohs scale) so it would outperform even quartz in terms of abrasion resistance, and you could put its contacts on the back to keep them from eroding away. Silicon needs a different layer on the front to couple its high index of refraction to the incident light, and I'm not aware of any superior optically clear materials that could accomplish this.

Am not a speaker expert, but I'd be surprised if they didn't fail before the rest of the system. Apple's iPhone speakers will warble themselves dry after they're immersed in water, so I'm wondering if constant Toto will keep the sand out of the speakers.

An ultrasonic-interference sound generator based on piezoelectric elements might outperform a conventional speaker setup. Tinny > Short-lived.