auto start vm on login and shutdown on logout

I have been looking for this all day but can not find an answer anywhere. We have vmware 7 with vmware horizon 7.

We have over 100 vm's running all the time. For 40 of those the users are not assigned but 40 users are assigned to a pool of vm's. So when they login they get assigned a random vm.

I was wondering if there is a way to shut down the vm's, and let them auto start when a user logs into horizon. So we don't have those 40 running taking resources all the time and only be on when needed.

I know there is a way because i use shadow online pc myself, and those get shut down and boot when i login. I just cant find a way how to do this.

Thanks in advance.