The AgBot: Solar Powered Farm Machinery  

GoodCleanTech has a post on experiments in creating solar powered farm machinery - AgBot Multi-Function Robot Is Powered by the Sun.

Louisiana State University (LSU) developed a multi-function robot called AgBot that's powered by solar energy. As of current, AgBot's functionality are still limited - during daytime, it makes the perfect autonomous garden bot, while at night it's a security machine. AgBot reportedly has the capability to both fertilize soil and plant seeds. It uses its built-in GPS system to plot a map of the land, utilizing high-tech sensory identification system to mark structures so it won't bump into them later.

For its function as a security bot, it uses a night-vision camera mounted atop a 360 degree swivel, an advanced motion detector, and a frequency alarm system. Unfortunately, its four hour battery life span doesn't make it an ideal security device for now. Nevertheless, the current model is just a prototype and the designers expect the final product to have stronger motors, and perhaps, a longer running time. Ultimately, the goal is to have as many functions for the AgBot as possible, making the machine customizable "as if buying a computer and selecting the only desired components versus a package that includes unnecessary options."