I've had quite a headache trying to figure this out - mostly due to not knowing where stderr / stdout goes on windows (and hence not being able to debug failure for the service to start).
I've been able to install a node app in C:\AppName, but not C:\Program Files\AppName (it will start when run manually from PowerShell, but not automatically from NSSM or node-windows)
For those that are intending to do this, hopefully that helps.
For those that are expert, I'd appreciate it if you'd peek at my script and look for any obvious errors. Maybe a windows guy would know what I'm doing wrong.
If you care to patch the docs:
AJ ONeal