Like many people, I keep a server running at home 24/7. In my case, it’s an old but relatively quiet Compaq Evo D315 AMD Athlon XP2000 PC with 1GB of RAM, 750GB total disk space and running Solaris 10. It serves as my personal email server (Postfix and Dovecot), to run Temboz, and miscellaneous auxiliary services like DNS, SNMP or being a staging point for off-site backups via rsync. All in all, very light usage, less than 5% average CPU utilization.

I have a Kill-a-Watt power meter measuring the load on that shelf, and the server, along with other devices on standby power, consumes about 160W. At PG&E’s marginal rate of $0.13 per KWh, that comes to $180 a year, or half the cost of the machine itself. I am thinking of upgrading to a machine with 6 750GB or 1TB drives in a 4+2 redundant RAID-Z2 configuration for reliable backups (the current setup runs on ZFS for snapshots but has no provisions for drive failure). I will definitely look at power consumption more closely in my decision process

Update (2007-08-25):

I ended up getting a Sun Ultra 40 M2 dual-core AMD Opteron workstation with 6 additional Seagate 750GB drives. It is remarkably quiet and consumes only 160W, which is pretty good since it does have 7 drives spinning inside. ZFS benchmarks at 160MBps sustained disk I/O…