Just like in this question (npm global path prefix) all you need is to set proper npm prefix
.
UNIX:
$ npm config set prefix /usr/local
$ npm install -g bower
$ which bower
>> /usr/local/bin/bower
Windows ans NVM:
$ npm config set prefix /c/Users/xxxxxxx/AppData/Roaming/nvm/v8.9.2
$ npm install -g bower
Then bower
should be located just in your $PATH
.