18 June 2015

A few days ago I read this tweet from Nicholas Weaver about laptop fans spinning on a certain web site.

It was sort of a joke. Think European Union energy labeling. Would a random site get an A++ or a D energy efficiency label? Based on what? What a thought!

But as things go, that thought would not leave me alone. There clearly are some applications that routinely will busyloop on a cpu core1. As Nicholas said, there are also some web sites that put a large burden on the processor, too. You can literally feel that as heat on your lap.

How much?

The question is how much power can a power-hungry website consume?

I am ready. I have a pluggable power meter, computer, paper and a pen.

So I set up to work. First I measured2 some baseline power usage levels on my laptop3 with different screen brightness levels:

baseline power usage graphs

From left to right: lowest visible brightness level, screen off, 50% brightness, 50% brightness with browser running and 100% screen brightness.

I decided to use 50% screen brightness for my tests. Notice that the difference between screen off and lowest brightness level seems neglible, which is interesting. I had expected that the backlight would consume significantly more power than screen completely off. (The measurement baseline of screen at 50% intensity with Google Chrome running and a single incognito window open used 10.8 ± 0.7 W.)

Having set up the baseline, time to browse some sites! After gathering data on several randomly chosen sites I divided sites into three groups, low, medium and high power usage:

power usage graphs

From left to right, in low power group: New Scientist, BBC, Apple, YouTube, Google; in medium power group: Vimeo playing a video, YouTube video in fullscreen mode, Vimeo video in fullscreen mode, The Guardian, YouTube video; in high power group: The New York Times.

Power usage by group was

  • Low power group: 10.7 ± 0.9 W
  • Medium power group: 20 ± 3 W
  • High power group: 48 ± 3 W

Considering Nicholas’s comment I was surprised about Forbes being in the low power group. One factor might have been that I have the Flash plugin disabled by default, and there was at least one Flash ad on the Forbes front page. Secondly, I was expecting a more uniform power use distribution, but at least these results were quite stratified. I was also expecting that video sites would be the most power hungry. They weren’t.

The main conclusion based on this very limited sampling is nonetheless clear: there are significant differences in browser power use between web sites. The difference between low and medium group is almost 10 watts and grows to almost 50 watts between low power group and The New York Times site.

Post Scriptum: Does that matter?

The global electricity consumption4 is about 2 terawatts. Even if we assume that 30% of world population use 1 hour a day browsing the web then 10 watts more power would mean a total of 875 megawatts more power consumed, which is only 440 parts per million of the global electricity consumption.

So is 875 MW a large number or not? Perhaps it is better to compare it against power conservation efforts. Let’s take the European Union energy labels for refridgerators as a reference. When the labels were introduced the lowest energy label was an A. Now it is A+++ whose difference is 33 kWh per annum5. This difference multiplied by the number of households in EU-286 totals up to 790 megawatts.

In the same ballpark.

These are just numbers, but I think they show that it is possible that power-hungry websites can potentially consume significant amount of power by end-user computers.


  1. I’m not naming any birds, thundering or not.

  2. Most applications turned off, no Time Machine backups running, battery at 100%, not using the computer during measurements, starting measurements only 10-30 seconds after page load, pausing video until player has cached as much as possible before video plays, measuring power meter visually from a digital display at 5 second intervals for 30 seconds for a total of 7 measurements for each test.

  3. 13” Retina Macbook Pro, 2013 model.

  4. Source: Wikipedia

  5. This is actually normalized to the volume of the refridgerator, but I’m willing to take a chance in taking this difference as a valid average.

  6. 210 million, source: Eurostat




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