Silhouette shots are a great art form and I really like them. I don’t have so much experience with it, but I’m still willing to learn more. I think it is impressive to see, that you can ad something when you take something away (color & details). You can get the effect if you shot against the (evening) sun. The following photo is a nice example.
But is also possible to generate such an effect by post processing. The original of the first picture was a boring street scene on an overcast winter day.
All what I did to the photo, was to tone map it to its extreme and “risk” to lose a lot of information in the shadows. More structure appeared in the clouds too. That was more coincidentally but I like the result.