Monday, 18 August 2008

Saving Energy

Time for a change from the cycling topics. Our energy bills here seem to have been somewhat higher than before we moved. This was especially true in winter, so we had cavity wall insulation installed in our house today.

It was extremely effective in two of our previous homes and we're hoping for the same savings on the heating bills here.

Cavity wall insulation typically pays for itself in about 3-5 years. Perhaps even quicker if the price of fuel increases. While loft and floor insulation are DIYable, cavity wall insulation isn't.

We've also started measuring the electricity consumption of some of our appliances. To do this we bought the "power calculator" pictured on the right. This purchase was prompted by a recent visitor who commented that our firewall PC would cost more to run for a year than a cheap off the shelf replacement would cost to buy.

Our firewall is actually quite frugal. It's built around a half length ISA embedded 486SLC card on a passive backplane in an old 286 case with 60W power supply. It runs freesco, a tiny linux distribution, and consumes only around 20W. This adds up to about 8 cents of electricity per day for the 16 hours or so that it's usually switched on - around €29 per year. We could buy a replacement box for €20, so our guest is right. The consumption of the plugin appliance style firewall ought to be no more than half this amount, so it would pay for itself in about 18 months which is worthwhile.

I then went on to other things. It turns out that the firewall is a relatively small user of energy. The PC on which I'm typing this (a 1GHz Athlon based machine dating from 2001 - someone else's cast off but fast enough for us because we use Linux) gets through 100W on its own, and the 17" monitor another 55W. It amounts to about 35 cents per day or over €120 of electricity a year. That's nearly a sixth of our entire year's electricity bill !

As a result, I'm also looking into ways of reducing this monster's consumption. A laptop might consume less, but the cost of them makes it unlikely that they'd pay for themselves ever. The same seems to be true for ITX and other smaller form factor PCs.

Replacing the CRT monitor with an LCD of a similar size would probably not help a lot as while it would reduce consumption by 15-20 W when it's on (they typically seem to be quoted as consuming 40W), it would add 5W or so of consumption when it's off. Our current monitor has a proper off switch so consumes nothing when its off. What I have done is to make sure the auto-power off feature of the computer is enabled. If we leave it on and walk away, the monitor goes into low power mode after 10 minutes and the computer goes into standby after an hour.

3 comments:

DrMekon said...

We've been inspired by David MacKay's comments about how worthwhile it is to turn various appliances off. I've developed a habit of turning everything off at the wall last thing at night. Since starting to do it, I've wondered to myself why I ever thought leaving the wireless router on all night was a good idea.

Matt said...

The Intel P4 appears to have been the high water mark in CPU power consumption, and thankfully things now seem to be taking a downturn. We're seeing initiatives from both AMD and Intel with their 'Underclocked Athlon' and Atom ranges, and lower powered motherboard chipsets are also on the horizon.

Laptops - and particularly netbooks - can certainly use a lot less power overall, and have the added advantage that they can be recharged from DC solar or wind sources if a suitable high-efficiency DC-DC converter is used in place of their power pack.

We are also, of course, seeing the rise of the smartphone, upon which one can perform maybe 80% of the web tasks one would currently use a PC for. This proportion will probably increase as more websites become 'portable friendly'. An external keyboard would mean you could at least draft word processing documents on your smartphone, but I'd not want to try spreadsheets on one...!

David Hembrow said...

Thanks for your replies. David MacKay's comments actually include some measurements, which gives them a lot more validity than many of the opinions I've seen.

I have long been skeptical about the huge savings sometimes claimed to be possible by unplugging the likes of mobile phone chargers and I remain skeptical of this (I'm planning to round up the family's chargers and plug them all in at once to see if I can any reading on the power meter from them). However, some things are quite surprising.

My daughter's computer turns out to consumes 11 W when off, or nearly 60 W in standby mode ! That's being unplugged from now on.

The main computer is more of a dilemma. I'm not going to go out and buy a new machine straight away even it will save quite a bit. The environmental cost of the things goes well beyond their power consumption, the payback time for a new machine seems too long, and besides I don't have the money right now.

Even though I once worked on something rather similar, I'm afraid I don't much like the sound of the smartphone either. Actually, I really dislike mobile phones. I do own one these days, as it can be convenient sometimes, but it's usually switched off.

Anyway, I do use spreadsheets sometimes, I do a bit of web development and other stuff on the PC. It also has many gigs of photos, videos and the kid's music collection stored on it, and that requires (for the time being) a proper spinning hard disk, and a proper computer.

It strikes me that it ought to be possible to buy a more efficient power supply and perhaps a more efficient motherboard and processor and chuck that in the same case. However, power supply efficiency figures are difficult to find.