The K4 already has a lighted cover, but that one is designed to draw power from the K4. This cover has its own 1.5A battery, and it can even charge the Kindle.You'll need 8 hours of direct sunlight to fully charge the backup battery, and SolarFocus is boasting that it can provide up to 3 months runtime for the K4.
The cover weighs around 8 ounces, and it's available now. Retail is $80, and you can find it on Amazon, or in retail store including REI and LL Bean. SoloarFocus also has authorized resellers lined up for France, Canada and Holland.
I'm hoping to catch a glimpse of this at CES, but my schedule is getting a little crowded (yay!).
In any case, this is an $80 Kindle case. As shiny as it, I'm not sure that this is really worth the money. This case costs as much as the Kindle inside it, and it's never going to pay itself off. The K4 simply doesn't use that much power. At best this case is mainly valuable for the geek cred.
But if they gave me one to review, I would not turn it down.
P.S. SolarFocus also has a $60 case for the K4, only this one lacks the solar panel (but it does have the battery).