[pct-l] solar chargers?

[James Vesely]

I have had the same experience when I had my solar panel hooked up
directly to a phone in that the phone doesn't like to have a variable or
on/off power source. 

Last year I hiked the JMT for 15 days with a combo solar/battery setup
from Bootstrap solar, http://www.bootstrapsolar.com  I used the panel
without the bamboo backing.  It had enough juice to charge my phone
(daily) and camera battery (every couple of days).  I used my phone and
camera pretty heavily my camera has a GPS function that I like to use
and I used my phone for listening to music and for my maps (Backcountry
Navigator)  The panel does not need the bamboo backing because the cells
are mounted on a PCB board and the board is very solid.  

What I found nice about the setup was that it worked even on clouding
days and it allowed me to charge my gear at night in the comfort of my
tent. The high capacity of the battery allowed me to get at least two
full charges of my phone with a fully charged backup battery. I found
that the battery capacity was a little large for most days as it never
got fully charged off the solar panel do to tree cover of clouds but if
you are in town you can charge it via USB.  

I am in the process of making a lighter version using a smaller battery
and charge components from Adafruit
http://www.adafruit.com/products/390  and the USB power supply from
Bootstrap (I like the 2amp multi port USB output charge capacity).  I am
planning on mounting everything on the back of the solar panel to make
it lighter and so I don't have to deal with the cable that needs to be
connected form the panel to the battery/charger. The calculated weight
with all components should weigh about 8 oz.  I also noticed that
Adafruit is now carrying a 5.6 watt 6 volt solar panel for under $50. 

Some thoughts on choosing a photovoltaic panel:  flex panels and any
amorphous processed cells have low efficiency stick with monocrystalline
cells witch can have up to 19% efficiency, don't believe the
manufacturers panel rating they are usually higher then in reality.  I
would like to get my hand on some multijunction cells (NASA cells) which
can have up to 40% efficiency but they cost 100's of dollars per watt.
If you plan on charging your phone directly connected to a solar panel
test it in less then ideal conditions example in and out of the sun, in
cloudy weather etc. most phones cannot handle that kind of power source.


Jim




Dennis, good point regarding the battery as back up and I plan on
carrying one once I get to Oregon next year on my thru- hike.  Hiking in
rainy conditions for several days in a row, which is common up there
won't keep a charge on the phone. 
I also have to say that the unit I have will still charge my phone in
lower light conditions such as late afternoon (even at sunset),
scattered cloud cover and walking in and out of tree shadow, albeit at a
slower rate.  When hiking under heavy tree cover I just simply unplug
the phone kept in the shoulder pouch  until I get back into better light
conditions without even slowing down to do it.