The advanced viewshed analysis plugin allows you to very quickly generate a binary viewshed (can I see it or not?) using a DEM and a set of points. In my quick demo below I used the OS Terrain50 dataset with just a couple of point representing wind turbines. I set the search radius to 50000 or 50km and adjusted the observer height to 125m, the height of the turbine tips. The plugin generates an output GeoTIFF for each input observation point (these can be merged using the cumulative check box).
Once the viewshed is generated the QthreeJS plugin lets you turn it into an interactive 3D object that you can play with in your browser.
Using this plugin you can build up a complex 3D object in just a few clicks. I set my DEM to the Terrain50 dataset and added the observation points and extruded them as cylinders to the height of the turbine tips, 125m. If I had a COLLADA model of a turbine I could use that.
Green areas are where you can see the turbines (highlighted orange). In all other areas they are hidden from view.
To view an interactive example of QthreeJS output, try this: Schiehallion