Are laptops more energy economical than desktops?

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Assuming you only charge your laptop battery when you are using the laptop, are you then getting 'free energy' when running on the battery?


Offline turnipsock

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Are laptops more energy economical than desktops?
« Reply #1 on: 19/01/2008 01:04:58 »
power is lost when charging the battery, so laptops are less efficient.

Also, laptop technology is usually is more expensive than desktop stuff, if you want the same performance.

I've worked with people that have asked for laptops and never taken them out of the docking station...why?
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Offline Simulated

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Are laptops more energy economical than desktops?
« Reply #2 on: 19/01/2008 02:31:01 »
I'd say desktops are better. Not sure why. Just a hunch.

Maybe cuz when my laptop worked it was on 24/7 lol



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Are laptops more energy economical than desktops?
« Reply #3 on: 19/01/2008 03:19:19 »
It depends what you mean by 'energy economical'.

As Turnipsock suggests, charging and discharging batteries loses energy (as we are discussing in another thread, it generates heat, and the generation of heat or sound is a direct indication of loss of energy).

On the other hand, part of the design criteria of laptops is that they should be able to run as long as possible on battery power (as long as possible turns out not to be very long at all once the batteries are of a certain age, but with new batteries, you should get a few hours work out of them with batteries).  For this reason, there are all sorts of technologies that are used with laptops to try and minimise power consumption in other ways (reducing clock speed for less processor intensive applications, putting components to sleep when they have not been used for a while).  All of these have a slight adverse impact on performance, but give longer battery life, and so are using less energy.  These technologies could be implemented on desktops (some even are, but often the users disable them because they want maximum performance), but generally the criteria for desktops is geared more towards performance and less towards power saving.

So, in theory, you could make a desktop more energy efficient than a laptop; but given the market sectors the two types of machines are geared towards, in practice laptops are usually more energy efficient than desktops.
« Last Edit: 19/01/2008 03:22:35 by another_someone »



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Are laptops more energy economical than desktops?
« Reply #4 on: 19/01/2008 16:36:52 »
OK, if we are going to look at how to build an energy efficient desktop (and as I build my own these days, so energy efficiency is one of the criteria, not only because I would rather reduce my energy costs, but because energy=heat, and I'm using the computers in a room that often gets hot in summer, so keeping them cool is important to me).  I don't say I do everything to minimise energy - there are always trade-offs, but it is one factor I always keep in mind.

Firstly, if you can get hold of a processor that was designed for a laptop, and a motherboard that will suit that processor, so much the better.  Not always easy, since most suppliers assume people are looking for raw performance, and not energy efficiency.

Secondly, on modern computers, that are often geared for games playing, the graphics card is going to consume far more energy that the actual processor.  If you are not going to be playing games (and that is not what I buy computers for), then go for the slowest and simplest graphics card you can (many mother boards come with integrated graphics cards, and these will do file).

Likewise, don't buy the fastest processor, since speed=energy=heat.  Think carefully what your processing needs actually are, and buy accordingly.  For many applications, buying more memory will gain you more speed advantage than buying a faster processor.  Also, a processor with a bigger on chip cache, but slower clock speed, will still be faster and more efficient for many applications.

Adding exta hard disks, etc. will also consume extra power, but less so than the processor or graphics cards, and they only consume power when they are actually in use, so simply having them in the box will not cost any significant power.  The biggest problem with having extra hard disks, etc., is that even if you don't use them much, the power supply has to be rated to allow for the possibility that they will all be used at once.  Then again, you can generally select hard disks that are more power efficient (but again, there is often a trade-off between power and performance).

Think carefully about the power supply you buy.  If you are building a super duper computer with the latest and fastest graphics cards, and lots of other add ons, then you will need at least a 500W power supply, and that power supply will probably be rated at least 80% efficiency (so you could be losing 20% of the energy as heat) when at full load.  The problem is the power supplies tend to be less efficient when at lower loads, so if you only need a 300W power supply (as most high end machines 5 years ago would have been rated at), then buying a 300W power supply to supply 300W is more efficient that buying a 500W power supply to supply 300W.  On the other hand, buying too small a power supply can harm your machine, and at very least might shorten its life span - so it is a calculation you need to make carefully.

When you have put the machine together, there are a number of things you can change in the BIOS, or using utility programs, to improve its efficiency.

Firstly, most modern motherboards allow you to tweak the processor clock speeds and voltage to increase performance (and so consume more power), but some will allow you to tweak them to reduce performance (and so reduce power).  Many of the modern ones can be quite clever, and adjust the processor speeds depending on the demands being made upon it, so the processor speeds up when you are doing something processor intensive and slows down when you are not.

There are also various other tweaks you can often do that (like laptops) will switch off components when not in use (e.g. the most common is to shut down the display if nothing has happened for 5 minutes).

Also, switching off the capability for wake on LAN, or wake on modem, or wake on keyboard, will all reduce power consumption when the machine is soft powered down.

What most laptops can do, but I have not seen a desktop do yet, is to save RAM to hard disk, and then totally power down when it it quiescent.

Oh, and one last point - don't use Microsoft Vista - Vista needs more memory, faster processor, and faster graphics cards than any previous version of Windows or than Linux, and all of this generates heat, and consumes energy.

And, ofcourse, if you are in an air conditioned building, and your computer is using more energy than it needs to, then it is generating more heat than it needs to, so the air conditioning is working harder to dissipate the heat, so you then have a second energy hit; first to generate the heat, and the second to get rid of it.
« Last Edit: 19/01/2008 17:04:06 by another_someone »