Backpacking and Biking Touring with Solar Energy

An early 21st century first world problem: how to keep our electronic devices charged while backpacking and/or bike touring. Is using a solar charger the solution? Maybe.

Several times while bike touring I have been asked if the 5 watt solar charger attached to my handlebar bag is propelling my bike.  This is a clear indication we are accustomed to energy on oil's terms.  Here is a quick reality check.  Burning oil does create carcinogenic, smog inducing, greenhouse gas emissions that may end up killing us all, but oil is an incredibly concentrated source of energy.  In a single gallon of gasoline there is about 114,000 BTU, or 33.41 kWh, or ~30,000 calories. That's the equivalent of 12 16oz jars of peanut butter!

Solar charging on the go in west Texas.  Who can name that mountain?
Of course the sun is an even greater and essentially limitless source of energy.  The trick is capturing and storing it efficiently. To get the same amount of energy out of that gallon of gasoline with today's commercially available solar photovoltaic (PV) technology you'd need roughly 300 square feet of solar panels sitting in the sun all day.  Fortunately, we don't need that much energy to run our phones, but creating electricity with solar PV requires time, direct sunlight, and a good amount of surface area.

I've used a solar charger for over 16,000 miles of bike touring and about 700 miles hiking on the Appalachian Trial with mixed success.  Below are important factors to consider.  I have only used the Suntactics sCharger-5, but these limitations aren't specific to this model and should be applicable to similar direct charge portable solar chargers.
  • What device are you trying to keep charged?  My Garmin Forerunner 410 GPS watch, which I use to log my routes and as an odometer while bike touring, has a 200 mAh battery and will charge even in variable overcast conditions.  My smart phone, which has a 2,000 mAh battery, needs direct uninterrupted sunlight as the screens light up to indicate charging.  If the screen is lighting up every time a cloud, tree, telephone pole, etc. creates a shadow on the solar charger, the battery can actually lose more juice than it gains. 
  • When are you planning to use the solar charger?  If you think you will be able to charge your smart phone while moving, re-read the above paragraph. Will you have significant down time during the daylight hours to charge?
  • Where are you planning to use the solar charger?  If you are in a remote desert location a solar charger can be very useful.  However, if you are traveling through forest and/or will have access to an outlet every few days, a solar charger is mostly extra weight.
What are the alternatives? First, don't use your device so much.  Keep your phone in airplane mode and turn it off at night.  Do without music, or save it for days when you are heading into town. Second, fully charge when you are in town for resupply.  Third, batteries.  A solar charger that works is going to weigh at least 8-16 oz, while a 6000 mAh battery bank  (good for 2-3 full smart phone charges) is less than 5 oz and a fraction of the size and cost.   Note that common pocket sized "solar chargers" such as this Inno Tech model have little solar charging functionality, and are really just a battery bank. 

Solar chargers provide independence, are useful in emergency situations, and work well with some devices (the Garmin GPS watch), which is why I'll continue to use mine while bike touring. On the other hand, while backpacking, where ultralight is priority number one, I'll go without it.  If I'm backpacking where resupply opportunities are regularly more than 4-5 days apart, then I'll consider a small battery bank before bringing my solar charger.  On the Appalachian Trail only the 100 Mile Wilderness will be a 4-5 day stretch without an outlet if you are hiking fast and light.

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