A typical location within the U.S. gets an annual average of 5 full-sun-equivalent hours per day. This means that the 1000 W/mē solar flux reaching the ground when the sun is straight overhead is effectively available for 5 hours each day. Each square meter of panel is therefore exposed to 5 kWh of solar energy per day. At 15% efficiency, our square meter captures and delivers 0.75 kWh of energy, per day. - See more at:
http://physics.ucsd.edu/do-the-math/....PEa5WPfb.dpuf
That is based on average annual data, you can't count on that for any given day. Your device probably has no surface that is a square meter in size. 750w sounds like a lot, but that is for all day's collection. Lets say that you had 1/5th of a square meter of collection area, that would give you 150w per day (when/if you had 5 hours of full sun that day) Now to collect your solar power you need batteries, none of which are 100% efficient. Say - Li-ion at 80%, (which is one reason I believe that this scale of devices are one of the few examples where "Solar Power" makes any sense.) 80% at charging = 120w into the battery, then 80% at discharging = 96w per day, with it pointed directly at the sun, all day.
I couldn't find how much power the device consumes per hour of use/page turn, or such.
Luck;
Ken