A while ago I heard of Kerkythea, a program that can generate very nice-looking images from 3D models. And, as an added bonus, it comes with a very helpful SketchUp plugin to send your model, complete with sun and lights (which can be added using a naming scheme defined by the plugin), to the Kerkythea rendering program.
Looking around the website, I was surprised to see that it’s completely free. I’d expect high-quality rendering software like it to charge a (fairly hefty) fee, but it says right on their terms and privacy page that it is indeed free, even for commercial purposes.
You do, however, have to provide a bunch of information to be given the download link. Doesn’t mean it has to be accurate, though.
And once you’ve done that, it’s fairly easy to use with SketchUp (the website gives instructions for installing the plugin). Just press the export button and open it up.
Keep in mind that you may have to change the rendering options for a nice image. Press the green “Start” button to begin rendering, then you should be able to choose a better option from there.