Here's the thing. It's a pro machine and not really designed with an emphasis on power conservation.
You might be better off with a laptop or other power saving computer.
i know this isn't what you want to hear, but you could upgrade to the new Mac Pro. It uses very little to electricity.
Hmm, maybe some background about where I'm coming from with this. My SGI Onyx (which was a "REAL PROFESSIONAL" machine in the sense that any apple will never be, was also not designed for lots of power cycles or low power states. It wasn't really designed to be run outside of a dedicated server room with a staff of operators. But I ran it in my house anyways. It is also 20 years old now and was given to a collector of such vintage machines a few years ago.
CPU: You could replace the original CPU's with two 5150's having the latest "G0 stepping" (SLAGA), thus effectively cutting at least IDLE power consumption by 32W.
GPU: According to this source the 5770 is rated by AMD with 18W when idling (assuming PC flavour = MAC flavour). I seem to remember having read somewhere that someone was successfully running his Mac without any GPU at all, while only logging in remotely. Not sure whether it was a Cube or a MP and can't find it right now, unfortunately. But if true, it would be another 18W saved. Just make sure the system is running stable before pulling the GPU card.
RAM: If you have the two 4GB sticks lying around, you could give it a try. FB-DIMM's sport complex onboard electronics, which consumes quite a bit of power (around 5W per FB-DIMM stick according to this and this source). So a swap like hinted by you could net you another 20W or so.
I am platform agnostic and am open to using mac, linux, windows, whatever. I'd even go back to irix if SGI was still around. The power consumption of the apple is not unreasonable, however I have always been curious. Lots of people upgrade the 5150 to 5355 or 5365. Nobody ever mentions energy consumption or thermal load, except for the temperature of the chip itself. Which is IMO silly because the fans are thermostat controlled. I want to know, can I upgrade my machine while reducing the power consumption? Your hint about stepping answered this question with a big YES! and I think there could be some information gleaned here.
The usefulness of the information is of course limited. However, the largest component of my electric bill is the AC and computer, because I always charge my car at work and have no charging station at my apartment. The fridge and water heater are probably a distant 3rd. I live in a relatively warm part of the US, although we still get a few months of winter. The electric is cheap and reliable here, which reduces this to an academic exercise for me. If it wasn't cheap and reliable, I would have dumped the mac pro years ago. However, because I'm a nerd about such things, I find them interesting and don't mind experimenting. I think the L5335 will be an interesting upgrade. It is plenty fast at 2ghz, quad core (2 would be 8-core!), but has a TDP of 50W. Since it is newer, the idle consumption should be much lower as well.
Duly noted about the FBDIMMS as well. It's somewhat shocking that
each stick uses an additional ~5W on top of the actual RAM chips. 8 sticks is like having an extra incandescent lightbulb inside your desktop, and that's not even counting the actual memory! The nerd in me hates having empty slots, but sheesh!
I have not played with removing the gpu yet. Seems like a silly excuse but I don't really have a safe place to store it and my ESD equipment is at work right now.
There is of course one more big thing you could do (would apply to a mini as well, though): Unless your server is required to offer 24/7 service, you could have planned shutdowns and restarts (System settings --> Save energy --> Time plan [not sure about the real english names, as my OSX is non-english]) e.g. over night, which would bring the effective power consumption down to Zero and thus potentially drastically lower the power consumption (depending on the up-/downtimes).
And before someone crucifies me, here's the disclaimer: This would increase wear on the hardware, especially on mechanical drives (however, that should be negligible imo).
Ding Ding Ding! We have a winner here!
The mac pro has support for system sleep, and it works quite well. If apple had longevity concerns, we would have to hack it to get system sleep working. I have used and owned other workstations (The Octane that the MP replaced, and the Onyx before that) that state in their manuals that power cycles can reduce lifespan, and they are designed to be left running. The mac pro manual makes no such statments. Besides, it's nearly 10 years old and owes me nothing. However, I have not been using sleep since I updated to mavericks and especially yosemite (using the tiamo bootloader), because it takes what seems like an unreasonable amount of time to wake up again, 30 seconds or more. I think the newer OSX versions are optimized for SSDs, which my MP doesn't have (my mba and rmbp do of course, so I am aware of the benefits
)
Anyways, it took all of 10 minutes to sort out my 10.6 partition, make sure the configuration was correct and the system was up to date. Put machine to sleep, and connected my mba via vnc. The machine woke up within 3 seconds (according to my stopwatch. try that, yosemite!) and I was in in less than 10. So long as I keep the vpn server (nothing else is available outside my lan) up to date, I am comfortable with the security level of osx 10.6. I repeated the test, connecting my lumia to the VPN server. Same results. A little longer than with the machine already awake, but a lot less than I had always feared.
I have never used WOL features because they seemed unreliable to me, and seemed like an unnecessary extra variable. If I can't log in, is it the connection, is the machine still waking up, has the wake gotten stuck, etc. However, this would be the best way to reduce power consumption. I wonder how powerful applescript is here. If I could have the machine always stay up during working hours, but maybe go to sleep more quickly on nights and weekends, etc. Sleep instantly if the power goes out (my ups sucks otherwise).
The machine is used mainly as a vpn server both for my work and personal use. It also serves music. It is also an offsite backup storage for work (the MP is located at my home), our working directory is backed up to a separate disk in the mac pro and to a firewire external disk. There is yet another backup in a cloud server so what my mac pro does is not a critical service.
Moral of the story, all I really need to know about energy conservation, I learned in kindergarten. If you're not using something, turn it off. Or at least let it turn itself off
