Earlier quoted context omitted.
It's also worth mentioning that, by his own admission, OP only managed to save less than 2 euro cents per day (60 / 3360). Maybe he has different ideas, and that's perfectly fine, but personally I value reliability and uptime far more than 2 cents. EDIT: I failed at math. See below comments. :V
Ok, the implementation wasn’t very fantastic cost wise. However I still think this could be a big area of improvement. How can we reduce energy usage of servers? There’s a lot of work with ARM lately, I’m curious if that could be used in server workloads like this.
The most effective way is to be able to dynamically distribute load across a large array of servers, turning some off at times of lower load. Anyone who runs a large datacenter probably already does this or something equivalent, either to save money or to service more customers with the same amount of hardware. It's more effective to optimize the hardware architecture, but it's worth noting that improvements in efficiency usually don't translate to reductions in power consumption. Instead, it causes induced demand and usage increases to fill available capacity.