PiJuice made a solar powered weather station. The key component  is their self-deisgned PiJuice solar module with integrated battery specially designed for use with a six volt solar panel.

A full linux machine like the Raspberry Pi is probably overkill for a weather station. The power requirements can be reduced by using a lower power ARM or AVR system, but this gets the job done and that’s what counts.

Spurred on by the completion of my two previous projects, the Compact Camera and Portable Games Console, I wanted to find a new challenge. The natural progression was an outdoor remote system…I wanted to build a Raspberry Pi weather station that was able to sustain itself off grid and send me the results through a wireless connection, from anywhere! This project really has had its challenges, but luckily powering the Raspberry Pi is one of the main challenges that has been made easy by using the PiJuice as a power supply with it’s added solar support.

Source: Electronics-Lab.com Blog » Raspberry Pi Solar Weather Station