[citation][nom]oam_75[/nom]there are many solar panels smaller than a "netbooks" cover that can produce 1-1.5 Watts. With the processor consuming just 500mW, I am wondering if a solar or even a hybrid systems could result in netbooks with solar panels on the opposite side of the screen that could work for extended times (few days?) without the need to be recharged.[/citation]
Dc-dc converters aren't 100% efficient even at low power. In addition to that, assuming you'll be using the machine's battery as buffer, charging it using a small solar panel going in and out of threshold while you're drawing from it is also far from a 100% efficient transfer.
I think you're onto something really really interesting and good, though but you're really going to have to lower your expectations as technology is today. Realistically, the additional cost won't be worth the marginal increase in runtime, BUT embedding a solar charger on the cover of a small netbook would be a niche device for people away from an outlet for extended periods.
I'd buy one.