I have this:
http://www.solio.com/charger/solio-charger-classic.html

I believe I had to order the mini nokia plug due to it's newness at the time (also bought the Gameboy adapter).

The solio has a battery. You run off the battery. However; so long as there is direct sunlight you can essentially run off the sun (even with a low battery in the solio) so even if the battery is low the solio is useful.

time to charge is always dependent upon sunlight. I can get 3/4 charge in a few hours in the summer (particularly around the summer solstice).

I have a 1800 mAH battery in my 800 so it can suck down most of the battery (if not all) when I charge from the battery but I'm not in the habit of running my battery down. Since the 900 has a smaller cap. battery you'll have power to spare if the Solio has to fully charge the battery.