I do however have a 24/7 home server. I'm afraid to measure it.
Me too.
I should probably calculate the cost of leaving the HDDs spinning 24/7 vs letting them sleep or shutting the machine down at night and having to replace 1-2 drives a year.
I'm sure it must be cheaper to just keep them spinning though - at least at the rate that I've been replacing them due to requiring higher capacities anyway. (every 2-3 years)
It's the same thing with the server itself.
It's probably less expensive to keep what I have running until it dies, than the cost of buying something like a new NUC and a low-power NAS, for how much it will save me on the electricity bill.
When you work it out, it often ends up taking 10-20 years to recoup the cost of replacing functional but power-hungry hardware - by which point I would have replaced/upgraded the server anyway.
Honestly I'm more concerned about the cost of replacing hardware or buying these fancy sensing/networked power strips than I am about going green to "save the planet". Residential usage is such a small fraction of the problem and the majority of our power here is already provided by a wind farm.
I like minimizing my power consumption in theory, but unless the cost is minimal, it usually ends up not being worth it when you factor in how soon you are likely to replace the hardware anyway, and how much more efficient the new equivalent of that is.
However anything that can be done from a software point of view I am all in favor of because that has a direct impact on battery life when using portable devices. Things like not having to wake up the drive or accessing the network on every track change by storing the playlist in memory is sure to add up.
I got a "sensing" power socket with a 12v line that turns my amps off when the Media PC that drives it turns off. The only thing that remains on is the DAC because it has some issues being turned on and off all the time, and doesnt offer 12v triggers, unfortunately.
Now that is something I should probably look into.
My DAC does have a 12v trigger but I have no idea how to use it.
However there is a power strip that, when the DAC is switched off, none of those devices are required to have power.
At the same time, that's probably only going to save me 5W, and only for about 6-8 hours a day.