Xose Perez of Tinkerman has written an article detailing the build of his weather station.
The power system consists of a LiPo battery and a solar panel. The Arduino Fio is project platform. It’s a ATmega328P (the same micro as the UNO), has a connection for a LiPo battery, a charge circuit based on the MAX1555 (with an USB connector) and a socket for an XBee radio module. So I just really had to wire things up and work on the code to reduce the power consumption to its minimum.
There are still some thing left to do, Xose said:
It would be interesting to add some sort of power monitoring to the solar panel. Right now I only get voltage readings but most of the time the panel is in nearly open circuit mode. Being able of actually get readings for the power it is providing to the charging circuit (in mW) will provide a more accurate view of the and maybe increase the performance or under-scale the solution (maybe a smaller battery or solar panel would do the job).