programming and human factors
by Jeff Atwood
In When Hardware is
Free, Power is Expensive, I referenced a
Google whitepaper (pdf) that explained why typical PC power supplies
are not particularly efficient:
Most likely, the computer you're using wastes 30-40% of the electrical power it consumes because it is using an inefficient power supply. It's difficult to believe that something as basic as a power supply could be responsible for that amount of waste, but it's true. The problem with power supplies is that they generate heat, which saps away energy meant to power the computer. That happens when the power supply converts AC current into the DC current needed by computersGoogle's solution for their datacenter computers is a radical makeover-- switching wholesale to single-voltage 12 volt power supplies.
The net result of [the switch to a single-voltage 12v power supply] is a dramatic improvement in efficiency (including the power supply and the regulators) to about 85%, at virtually no cost. In other words, you won't have to pay more for a higher-efficiency PC, because the power supply is actually getting simpler, not more complicated. By spending another $20 or so extra, it is possible to use higher-quality components and achieve efficiencies well over 90%.Who knows when these hypothetical single-voltage systems will arrive on the market in the form of desktop PCs and laptops we can actually buy. In the meantime, it is possible to upgrade your computer with a high efficiency multiple-voltage power supply. Unfortunately, existing high efficiency power supplies aren't available "at virtually no cost"; they tend to be quite a bit more expensive than their less efficient cousins. I just upgraded my home PC to a high efficiency power supply:You won't be able to buy such computers for a while, and Google isn't planning on selling you any. But we're working with industry partners such as Intel to make this technology an open standard that everyone can use, and that all vendors hopefully will adopt. It's the right solution technically, and the right thing to do for the environment.
| Typical PSU | Efficient PSU | |||
| Computer off | 5 w | 5 w | ||
| Boot (peak) | 237 w | 215 w | -22 w | 9.3% |
| Idle at desktop | 205 w | 185 w | -20 w | 9.8% |
| 1 x Prime95 | 236 w | 217 w | -19 w | 8.1% |
| 2 x Prime95 | 257 w | 237 w | -20 w | 7.8% |
| DiRT demo peak | 270 w | 247 w | -23 w | 8.5% |
I was surprised to find that my PC uses 5 watts of power even when it's powered off. This is what's known as "standby" electricity loss, and at least one study showed it accounts for 6 to 16 percent of all energy use in homes, and another (pdf) estimates that standby power use is now responsible for 1% of total carbon emissions on earth. The only way to reduce your computer's power use to zero watts is to unplug it from the wall, or flip the power switch on the back of the power supply.
If you're interested in upgrading to a high-efficiency power supply, look for models tagged with the 80 PLUS designation, which are guaranteed 80% efficient at 20%, 50% and 100% of their rated load. Many vendors cut corners by stating their power supplies offer "up to" 80 percent efficiency, but what they don't tell you is that you'll only reach that level of efficiency under extreme power loads that are unrealistic for most desktops. Seasonic is a popular choice, as they have aggressively enforced the 80 PLUS certification on almost their entire product line. But fair warning: you will pay a premium.
That's a pretty sweet rig! You'll be able to play PONG like it's never been played before.
Haacked on May 26, 2007 2:15 AMFor ages I have been using computer hardware that runs with -48V DC (that is: "TELCO gear",) these days I am converting all my telematic gizmos to 13.8V DC ("12V" lead acid battery float charge) bus. Instant integrated UPS within the systems.
Nothing new in having some DC bus voltage inside the systems.
The new Sun/Fujitsu M9000 mainframe system has common intermediate 48V DC bus powering all modules, and all power supplies in system feed the same bus. Conversion efficiency optimization is very important when total power consumption is up to 45 kW per machine.
In commodity-hardware the +12V DC is definitely obvious choice.
For quite a while the CPU core supply switcher has been non-isolated DC-DC converter on system board next to the CPU. Efficiency has been 94-96% in most designs, and boosting it couple percent is in the realm of possibility (ever lower output voltages at high currents is difficult enough challenge.)
Still 5% of 120 Watts is 6 Watts, which is still hefty amount to blow away with the wind, but less difficult than the 120 Watts in the CPU...
Say you get that main-to-12V DC at 90% efficiency, multiply by 95% and total system efficiency is 86% If both converters are running at 95%, the net result is 90% total conversion efficiency.
(The result is the same when there are lot of output converters.)
Is it possible to make 95% efficient mains-AC-to-12VDC supply ? Most likely it is. A 300 Watt supply would still have 15 Watt waste power to blow away.
Engineers view on the issue is that yes, single optimized converter from mains-AC-to-intermediate-DC plus a number of non-isolated very high efficiency DC-DC converters does make very much sense.
The mains supply converter has required 2000 Volt isolation (which is an added difficulty with lots of output voltages), while final converters need not be isolated at all.
Stand-by power generation can be separate 10 Watt supply in the mains converter performing at 80% efficiency without being noteworthy.
For embedded uses there is already amazingly small "picoPSU" by mini-box.com. Various models drink up 12V DC or 6-26V or whatever, and the entire power converter fits on top of motherboard power connector. The lovely wonders of "mini-itx"...
Good to know. Anyway, many PCs spend hours off, so we should also disconnect completely our PC while it is supposed to be off (as you mention), as an extra way to save energy... for us and for the planet...
Nacho on May 26, 2007 3:09 AMDepending on where you live, who cares about efficiency?
In my area, I am paying to heat my house 9ish months of the year.
100% of the energy consumed by my PC is released as either heat, or light. The light is there for functionality, and the heat is where the "inefficiency" goes.
All of that energy "lost" by my PC is floating around my office in the form of heat, and comes directly off the portion of my energy bill devoted to heating my environment.
Now the situation is obviously different if you own and operate an air conditioner, or otherwise don't want the heat, but for the sizable portion of the world that needs that heat, the situation is far less grim.
Or am I missing something?
i just read google's paper. something odd strikes me: they remove the multiple voltage part of the power supply, only to place it on the motherboard.
i do understand that current motherboard already includes this part, so they are effectively removing one converting step. i also do understand that, when the voltage regulators are included on the motherboard, the manufacturer can size their regulator to draw the most efficiency out of them.
but then, do motherboard manufacturers care about efficiency ? do we have any study or any numbers on motherboard efficiency ?
rien on May 26, 2007 4:07 AMrektide: Um. Did you even read his post? The power draw COMING OUT OF THE PLUG AND INTO HIS COMPUTER was ~10% lower in its various uses. That'd suggest that the system is in fact more efficient.
Dave: As someone else stated, electrical heating is not very efficient compared to other methods. Also, the heat released by your computer isn't forced and doesn't radiate nearly as well as a device made for heating your home (ie your furnace), so that heat energy being thrown away by your computer is still very much a waste.
Nacho: I'd suggest using Jeff's second suggestion which is to just flip the rocker switch at the back of the PSU. Unplugging your computer is probably not worth it for the 5w power draw. @ 5w, assuming $.10/kWh, you'd have to leave the computer on for 3 months before it cost you a dime. It's probably not worth it at that point to be getting on your hands and knees to unplug the thing.
Another option is to plug it into a switched power strip/bar, and flip the switch on that after the computer's completed its shutdown sequence.
dnm on May 26, 2007 4:37 AMErm. 5w draw @ $.10/kWh would cost you $.40/mo or so. I got my numbers backwards.
*sulks into corner*
How much power does it use in standby low-power mode? That's the mode my PC is in the majority of the time and it would seem reducing the power in that mode is the best way to save energy.
David Avraamides on May 26, 2007 6:15 AMDave, even when all the heat is welcome, electricity is usually not the most economic way of heating.
Rien, on the efficiency thingy. There could be the possibility to design the onboard converterts more closely to the actual load, but then there are the PCI slots which consume unknown amounts. At least the bigger converters are more efficient, because higher voltage means less current and hence less losses.
Another thing for google may be to do away with the separate power supply for each PC and have a big one for each rack; bigger supplies are easier to get efficient. The telco people traditionally power their racks with some 48V dc because that makes it lot easier to run the stuff on battery.
Andreas Krey on May 26, 2007 6:21 AMdnm: untrue - heating your house with electricity is 100% efficient.
Harold on May 26, 2007 7:57 AMI bought a Seasonic 380w power supply about a year ago. On top of being more efficient, it's also less noisy, produces less heat and is ROHS compliant (less toxic metals in it).
Great buy.
Michael Graham Richard on May 26, 2007 8:52 AMI'd also be interested in the power consumption in Sleep/Hybrid Sleep mode. Sleep appears to be working much better in Vista than it did in XP - my computer has never crashed coming out of it. Could be my new computer, of course.
I'm quite happy with my 80 PLUS power supply - the SilverStone ST50EF (500W). When I was deciding on it a couple months ago, the price difference for upgrading to an 80 PLUS model was about the same as switching from non-modular cabling to modular.
Krenn on May 26, 2007 9:10 AMGood to see that everyday energy handling is entering in our mind ! But I'am still frightened about the energy used for doing nothing visible. There is the AMULET microprocessor, a ARM9 microprocessor (a very well designed CPU, and a real pleasure to work with, GP2X my love) without clock, it is indeed asynchronous. With this design, the energy used is related to the amounh of computing you are performing. One or two more ideas like this, and maybe we will be able to code without less ecological consciousness problem ;)
Marmakoide on May 26, 2007 9:14 AMVia has been doing its part to help as well, example:
http://www.linuxdevices.com/news/NS8508116370.html
Somehow I think that if there were more of a collaboration between Via, Intel, AMD, etc. some amazing things could be done in terms of CPU, chipset, and memory "power" per watt.
Of course in such a world we might not even have the options we do now, since commercial competition truly can drive innovation. Hopefully more than it squelches innovation to appease the greedy shareholders. And yes I realize without greed there would be no shareholders. One could hope for a somewhat less "Ferengi" economy though.
Bob on May 26, 2007 9:47 AMHarold: That's true. Doesn't mean its good for the environment or your wallet though. (Unless your going for an electric heat pump).
Siegfried on May 26, 2007 10:10 AMHarold/Dave: Only the last step in electrical heating - the conversion of electricity to heat - is 100% efficient. The electricity is usually generated at a pretty disappointing level of efficiency - 35% to 40%. So every unit of heat you get in the house sends almost two more units up a smokestack somewhere, along with the attendant C02 and other pollutants. Unless your house uses electrical resistance heating, its heating system is likely to give you much better efficiency, and the waste heat from your appliances is truly waste.
Western Infidels on May 26, 2007 10:39 AMI have a Corair HX 620, it costs an arm and a leg at $120 but it is completely silent and it is the highest performance PSU on the consumer market [that I know of]. 5 year warranty is another reason; it will last as long as my computer does.
Cappy on May 26, 2007 10:45 AMthis seems falacious to me. most of the power demands of a reasonably energy efficient system are going to come from the cpu. a 12v supply motherboard is still going to have to convert the 12v into the ~1.3v required by the cpu. requiring huge frigging mosfets on the motherboard just seems like you are moving the problem from the power supply to the mobo. sure your power supply is now 85% efficient (which is already available, but is significantly more expensive with conventional dual rail ATX's), but now your mobos voltage regulators are tossing off gobbs of waste heat too.
the notion of cheaper high efficiency power supplies is very alluring, and i do hope to see it become a possibility. but please consider the complications involved.
rektide on May 26, 2007 12:11 PMnote: the Corsair HX 520W and Corsair HX 620W PSUs are also made by Seasonic.
power man on May 26, 2007 1:11 PMYou won't be able to buy such computers for a while,
Not exactly. Why not just get an EPIC and NANO board which already do this and have for some time? They are not Core Duo 2 but some models can use single volt 12v PSUs. I love that google pretends they invented though. Makes the server farm cowpokes feel special!
Danny on May 26, 2007 1:59 PMI find it amazing that we have abstracted the consumption of energy to just kwh and $$. Depending on whether you're using renewable (hydro/wind/solar) energy or not, the depletion of fossil fuels and global warming are way more important than the money. A 65 watt computer left running full time consumes a barrel of oil (equivalent) in a year. 5,500,000 btu/barrel / 10,000 btu/kwh / 8760 hrs/year = 63 watts. How many hours a day do you run your SUV PC, Jeff?
I know you need high performance for games but for normal info-appliance usage, 237 or 215 watts is way overkill. So go get yourself a laptop or a Mac Mini. My mini uses about 20 watts, way less energy than the 75 watt new Dual Core desktop which I just sent packing.
Leave in alone and it goes to sleep at less than a watt, not 5 watts like your box or my HP all-in-one printer which gobbles about 10 watts turned off. My previous desktop ran 10 watts in sleep mode. What's wrong with this picture?
Bonus? My new Mac Mini Dual Core is faster on XP than my other new desktop was on Vista, and it's QUIET!
Ron on May 27, 2007 3:55 AMCore Duo, I mean. Circle-slash "Dual Core."
Ron on May 27, 2007 4:20 AMJust about every device you plug into a wall consumes power whether it is on or not.
Why? Simple - the switch usually interrupts the output voltage of the transformer, not the input voltage. This means that power is ALWAYS running through the transformer coil in the machine (nothing but irons, hot plates, and some lights run at a full 120v, just about everything else needs to convert the voltage down. If it doesn't use an adapter, the adapter is just hidden inside the machine as a permanent part)
Why would someone do this? Easy. Ease of use. Remotes need power to receive a signal, so any device with a remote is ALWAYS on. Tv tubes would be as slow to start today as they were in the 50ies if they weren't kept in a "warm" state.
Heck, even your doorbell is hooked to a 12volt transformer which is ALWAYS running (it wouldn't be too safe to run 120volts to something that people mash on that could get wet).
Just turn all your devices off and go watch your power meter spin!
Fortunately, you CAN get some relief by converting some of your computers to lower powered dedicated boxes. Want a file server? Get a network attached storage device instead of a computer. Firewall? Most cable routers do that job and consume a fraction of a computer.
I figure my power bill drops at least 20 dollars a month for each server I take offline and replace with a dedicated brick.
Oh, and LCD displays consume a LOT less power than a tube display just because they don't need to keep an electron gun hot and ready at all times.
Xepol on May 27, 2007 8:27 AMA better solution to the computer supply problem is my home DC power supply idea. Energy is wasted all over the house by those little black power transformers. If it feels warm to the touch, then it's wasting energy. I propose that the UL come up with a home DC power standard. A new electrical socket that has a 3 prong outlet for ground, +5V, +12V. From this, every small electronic device in the house could be powered (including your PC). An efficient, central switching supply would supply the DC power for the house. This would save lots of electricity, but also the waste of every device manufacturer having to include a power supply. The cost of everything would be reduced and we would save electricity in the process.
Larry Bank on May 27, 2007 8:29 AMDude - POST followed by redirect!
:)
I'd love to see that.
GregMagarshak on May 27, 2007 11:14 AMWaste heat from appliances or any or other devices, including computers is not necessarily waste. Waste heat is 100% efficient at heating the space it is situated in....assuming that it indeed needs to be heated, of course. In fact, nearly ALL of the energy consumed by a computer - efficient or not, heats the space it sits in. A computer is basically one big resistive heating element coverting electricity to heat with near perfect efficiency. During heating months, this is a nice side benefit. In the cooling months, well....turn off the A/C and open the window if you really want to save some energy.
Although, in the end, what's the point!? - Electrical power is relatively cheap and ultimately, energy is limitless. Heresy to you!? - Well you really need to read the book "The Bottomless Well" for an actual scientific exploration on the topic. It continues to amaze me how easily most people are influenced by the inept and scientifically clueless media....especially on the perpertually popular topics of energy use and environmental issues.
Pretty cool. I got my mac with the core duo and a month later the core two duo came out. I was pretty mad...
Nick on May 27, 2007 12:16 PMStandby power has had a lot of press coverage lately in the UK and there are now a couple of companies offering solutions:
http://www.oneclickpower.co.uk/
Use power strips where the entire strip turns off automatically when it detects the device using the 'master' socket has gone into standby.
http://www.byebyestandby.co.uk/
Offer radio-remote to turn off their 'smart sockets' from a distance.
Of course in the UK our sockets always have a switch on them too - so the easiest and cheapest way to save standby power is to turn it off at the wall.
Graham Stewart on May 28, 2007 3:32 AMEdison has the last laugh here.
Chui on May 28, 2007 4:51 AMJeff,
Which power supply did YOU buy for your new rig?
Seasonic?
Thanks!
Charles
Charles Nadeau on May 28, 2007 9:03 AMJeff,
Are you running Vista on your gaming machine? I've held off thus far from upgrading my gaming box to Vista because of the FPS lost and the total lack of DirectX 10 games.
Is it the right time to go ahead and do the upgrade?
Karthik on May 28, 2007 9:10 AMdnm, electrical heating is actually far more efficient then most other forms. Electrical energy is only about 25%-33% more expensive then natural gas here (assuming my math is right when converted to joules), and due to the need to exhaust the combustion byproducts, most furnaces are only 75% efficient in the best of times, and high efficiency furnaces cost several times more.
Even if the electricity is generated using natural gas, what do you think will be more efficient, a small number of plants operated by companies with engineers maintaining the equipment, or each and every single furnace which hopefully gets occasional maintenance (but has an individual loss well under the cost of hiring aforementioned engineer)
As to the comment that the heat isn't in the most ideal location, my house has these things called convection currents which take care of the heat distribution within individual rooms, averaging the heat reasonably well.
My office's temperature is roughly the same in the various places I have measured, (within a degree) and is heated primarily by the computers contained therein as it's the only occupied room for many hours during the day (I don't mind the rest of the house being much colder while unoccupied, nor do the cats, they just curl up in my office with me) -- I do have a couple fans in my office, but I do not run them in the winter.
During the winter I run distributed computing projects at certain times of the day (like a poor man's thermostat), during the summer I do not.
power strip with switches
Why isn't the above device not popular in US?
I could hardly find it in walmart....
But I think they are pretty standard to include switches in strips in Asia, esp in HK...
US_wonderer on June 13, 2007 6:47 AMto US_wonderer, maybe you need to look better with those squinty little eyes. you can find them everywhere in teh US
HK_wonderer on July 1, 2007 10:40 AMim looking for some power supply in the 200watt range, that has a very high efficiency and under 30$ , for a server that runs 24/7, my current load is 48 watts idle, and around 100 at load, 98% of the time its at idle or near idle, i was looking at the seasonic SS-200SFD, anyone has any better recommendations for an atx case?? it needs to have excellent realiability, i dont want it blowing up and starting a fire
rsxhitman on May 7, 2008 6:31 AM@Dave:
Direct electrical heating is not as efficient as a heat exchanger that is powered with electricity.
Here is the problem: If we save money via using more efficient power supplies, our energy company WILL increase our rates. Its as simple as 1+1=2. And its as guaranteed as the sun will rise in the East.
An example? We had a major drought in the southeast USA and were forced(!) to stop using water (or really really skimp on its use) for almost every purpose. What happened? People obeyed, the majority of us, and our local water utilities saw major reductions in revenue. How to make up that lost revenue? Increase our rates.
Thanks. Wouldnt shock me (no pun intended) that our electric companies would do the VERY SAME THING -- if we were to have figured out how to save 30% on our electric bills.
The entire system is broken. Before we figure out how to save electricity usage and water usage, etc - we need to first fix our political and civil systems.
Mike on July 11, 2009 10:14 AMI'm using a Pico120 regulator on the MB with a separate brick. This reduced my idle Watts from 47 to 35 for the server - it will pay for itself in 4 years! I'm running an AMD 4850e dual 2.5gz processor in a motherboard with nvidia 7025/630 chipset and 2 WD 500mb green disks (mirrored). With such low power its trivial to keep it cool (and quiet - a 68W in series resistor slows the case fan down nicely as there isn't a PSU fan.)
sybaseguru on July 23, 2009 8:35 AMJeff Atwood,
First off, I'm a [now sophomore] CS and Phil major, and a fairly new reader to your blog (since January) and I must say I really enjoy it.
But as of lately, your blog has been displayed in a different font, one that is much harder for me to read. Is this something you did, or something I did by accident?
Simon Sarris on February 6, 2010 10:07 PMFunny how it's often the power supply that can get overlooked, not in terms of output - you gotta run your components and try to be safe for the next video card upgrade - but in terms of actual consumption.
Brandon on February 6, 2010 10:07 PMThe comments to this entry are closed.
Subscribe in a reader
Subscribe via email
|
|
Traffic Stats |