There's a 40 mile (64 km) model in rural Maine (Route 1 in Aroostook County). The webpage claims it is the largest in the world (obviously not true, at least not as of today). The webpage is also delightfully early-90s-esque. http://pages.umpi.edu/nmms/solar/

Edit: There's a youtube video where some guys made a revolving (but temporary) to-scale model in the desert. https://www.youtube.com/watch?v=Kj4524AAZdE