I have first hand experience of the benefit this data centre has brought. I initially had a server when they were at the MTN data centre (Now used by Afrihost) and had frequent issues of power failure. Up until recently had an Afrihost VM which was unreliable because of power issues. Hetzner physically moved my server when they opened up their new data centre and I had no issue at all. Since then, I have not had a single instance of downtime (that I am aware of). Very impressed with Hetzner.
It's a relatively simple concept. When the outside temperature is cool enough (say below 20 deg) they turn off the aircons. They then pump fresh air in from the outside and let the hot air out at the top.