I rarely develop on Windows but recently I had to generate a Windows installer for a Node.js console application. I used Git on Windows to access the project's codebase.
I could not find any documentation where to put my SSH private key. The repository did not support username/password authentication. There seems to be some confusion over the key location. Besides, it seems to depend on which git implementation you use and how you use it. I used it directly from the CMD terminal. At the end I figured out that you can just put the key file
id_rsa or similar into the folder:
Account is your user name.
This approach worked on Windows 7 and Git version 2.9.0.windows.1.