If you don't have access to renewables, a personal solar panel like this is a really easy introduction to sustainable energy. It is an affordable and really effective step towards lightening your footprint and reducing your dependency on the grid.
This panel is so legit. It's the kind of gadget that you're immediately jealous of when you see someone else with one (if you're a bit of a child in that way, like I am). It'll set you back a Monash but it's a seriously good investment, considering it will eventually pay for itself with the energy you save.
My smartphone has a 2700mah battery and goes 0-100% in <2 hours in the middle of the day, every bit as fast as an A/C outlet. Even at low light dusk/dawn it's pretty efficient (particularly if you put your phone on flight mode). It charges my tablet too (7000mah battery) but obviously it takes longer and needs to be between 9am and 3pm.
My only criticism of this panel is when using both USB ports at once it can be tricky to get much juice unless you're directly under the sun at midday, however it would be unreasonable to expect otherwise from a 21W panel.
Overall its a SICK piece of kit and I highly recommend it, in or out of the city.
What: Anker 21W Solar Panel
Pros: lightweight, efficient, splashproof/weatherproof
Cons: Using both USB ports saps output considerably
Greatfor: everyday use, small-medium USB rechargeable devices (phones, lights, speakers, battery banks)
How Much: $100-$120