Joining the ranks of already available free rendering engines for SketchUp (like Kerkythea and Indigo) is the free version of IDX Renditioner Express.
This is a full featured copy of the main product with the only limitations being a reduced image size (max. 600×480 versus 4096 x 4096 in the full version) and less lighting options.
Although the image size is very small in this free version, it may be worth to give the program a try based on user-friendliness: apparently it is pretty much a one-click renderer.