Editor's Note: Amy Gahran writes about mobile tech for CNN.com. She is a San Francisco Bay Area writer and media consultant whose blog, Contentious.com, explores how people communicate in the online age.
(CNN) -- Last week I offered some eco-friendly cell phone tips for people looking to save energy when they communicate.
So, today I'll add it's also worth noting that several manufacturers already offer solar cell phone chargers.
Solar cell phone chargers aren't just greener. They're also a handy piece of emergency equipment, especially if you get stranded (at least, during the daytime) with no access to a working electrical outlet. Or if you're spending time outdoors (at your kid's baseball game or doing yard work), you can keep your phone available and ready without running down the battery.
• iSun, which claims to be compatible (via adapter cables) with most feature phone and smartphone brands, as well as popular mobile gaming devices and media players. The company also offers a larger model for charging laptops.
• Solio Classic, a compact model featuring an attractive petal-like design and a long list of compatible mobile devices. (CNET review.)
• Solar iPhone glove, offered by GadgetTown.com.
• The Monaco mobile phone solar charger. See review at The Cell Phone Junkie.
Also, solar chargers are available for many cell phone accessories, such as speaker phones (for car use) or Bluetooth headsets.
The blog 12-volt Solar Panels recently explained how solar phone chargers work and reviewed a few models. They note that small two-watt solar chargers need about three hours of direct sunlight to fully charge a typical cell phone battery; 18-watt models can do the job in about 30 minutes.
Or: Why not charge your phone by bike? This year Nokia debuted a bike charger kit that works with Nokia phones. Inhabitat reports, "The first bike-powered chargers will be made available in Kenya for around €15 [$20 U.S.] and then go on sale later this year worldwide."
If you like building your own gadgets (or if you own a bike but not a Nokia phone), MAKE explains how to build your own bike-powered cell phone charger.
Whenever you buy a charger for your phone -- especially if you use a smartphone, which often have highly sensitive electronics -- check the manufacturer's charging specifications for your phone carefully to make sure that a third-party charger isn't likely to damage your phone. Also check whether using a different charger might void your warranty.
And of course, take a little time to research online product reviews, forum posts or other information from people with the same kind of phone as yours. What was their experience with the charger?
Remember that any nonstandard product combination is likely to yield some bad experiences. But a pattern of bad reviews (or no comments, which could indicate something doesn't work) is a red flag.