Change of IP-addresses when VM is shut down

Hi,

I'm running an energycompany as from next week. Due to the nature of this, it is most important to have static IP-addresses for the VM's. This is mandatory by the government. Is there anyway I can fix the IP addresses for my virtual machines?

(I noticed this when Microsoft turned my VM's off due to a lack of credit in my trial account...). 

Is there anyone who know's how to fix this?

Thanks!