[Olpc-open] charging via solar power

[Sameer Verma]

Hi,
I purchased a solar panel that is capable of 4 watts. These are commonly
used by Volkswagen to trickle-charge their car batteries when cars are
shipped across. (http://search.ebay.com/vw-solar-panel_W0QQsojsZ1)

The panel is compact and easy to carry. Here are some observations that
I'd like to share:

I drained the battery as much as I could (loaded the USB port with a USB
light attachment) so that it was near zero. Then, I plugged in the solar
panel. The panel starts of at about 9.5 Volts in the morning with
indirect sunlight (8am) and will start pushing 13.9 volts by 10:30am, or
so. The panel does have a diode to prevent reverse flow. In the
beginning, the laptop keeps showing a red LED light that will blink
every few seconds.

The laptop also emits a high pitched sound from around the power plug
area. This sound will change its pitch as I move the panel from a
horizontal to a vertical position, in the direction of the Sun. Pitch
increases as light increases.

At around 11am, the sound goes away and the charging LED turns to
yellow. If I leave the panel in my car's rear window at an angle (so
that it catches the sunlight from around 10am to 4pm) I get a total of
16% battery charge.

I'll repeat these setups to see if I get stable results. Of course,
suggestions are welcome.

Questions:

Is the high-pitched sound indicative of damage to the power electronics
in the XO?
Is the sound emitting because the panel does not spit out a full 12 volts?
Will I get a better charge profile if I start with the battery charged
part way (LED shows yellow instead of red)?
Is the "official" solar panel much better because its a 5 watt panel
(will 1 watt make such a difference)?

Sameer

-- 
Dr. Sameer Verma, Ph.D.
Associate Professor of Information Systems
San Francisco State University
San Francisco CA 94132 USA
http://verma.sfsu.edu/
http://opensource.sfsu.edu/