[Power] Power Digest, Vol 13, Issue 1

[Nicholas]

Quoting this:
When I first saw this post, I couldn't think of an application that I might
be directly involved in.  Since then I've learned that OLPC-au is actively
looking at XO-ARM as a school server.  Up until now, I've been thinking
that XS's need 100 watt panels. But I just measured
XS-ARM at 4 watts.  With an extra 2 watts for a USB 3G modem, a 30 watt
panel, and a 50 amp-hr deep cycle battery seem feasible.

End of quote
30w of solar probably will not be enough solar for an always-on application..
Damon has done quite a bit of work running his sheevaplug off-grid
solar complete with power logs. Here is his write-up
http://www.earth.org.uk/note-on-SheevaPlug-setup.html
He is also an admin at fieldlines.com
These are 5w Arm based servers.
But I seem to remember him posting on fieldlines.com that 120w and
40ah battery was not enough solar and storage to keep a 5w always-on
device running happily in winter. I know, the difference might be that
he is in London where the sun can be lost for weeks at a time. He did
do an upgrade to a 200w panel for 2009 Winter as per the article
linked above. This is a 24/7 application which can be a different
application to the one mentioned by the OP. The power logs should be
available somewhere and might be useful for your school server
project.

...Also on fieldlines.com there is a guy named ghurd, Glen Hurd who
makes and sells cheap rugged power regulator kits. They can be
configured several different ways, as wham-bang on off regulators as
well dump load converters as well Low Voltage Disconnect. They are
14.5US I think and shipped anywhere for 3. I've had a couple and they
are good robust converters with adjustable hysteresis. ghurd.info can
be used to order the converters. I have no connection with his
business other than having used the converters in my own small
systems. They were also a great learning device for when designing a
small micro-solar system..