Correction: This story has been updated to reflect the fact that Gartner doesn't include x86 servers in its definition of PCs.

If everyone decided to log onto their PCs at once, would we have a global brown out?

Good chance of it. I did some rough calculations recently and estimated that it would take about 112.8 gigawatts if everyone in the world decided to start typing in Word and/or sending emails out at the same time – and use all of the servers

That’s more than the capacity of the U.S. commercial nuclear reactors combined (100 gigawatts) or the power provided by all of the coal plants installed in China in 2006 (90 gigawatts). And if everyone decided to start playing Doom III or downloading pirated copies of Hellboy II, power consumption would climb. The fumes would give Beijing’s air an even greater resemblance to the consistency of Progresso minestrone soup.

Here’s how I came up with the numbers: There are more than 1 billion PCs plugged in these days, according to estimates from firms like Gartner (see this CNET story). Gartner includes desktops, notebooks and servers in its definition of PCs. An average desktop consumes 114.7 watts, according to the U.S. Environmental Protection Agency statistics forwarded by Barbara Grimes, a PR rep for Climate Savers (Wint-O-Green flavor). An LCD monitor consumes about 41.5 watts. Thus, together a typical desktop will consume 156.2 watts in active mode.

There is wiggle room here, of course. If you use an Energy Star desktop (108.8 watts) and LCD (27.8 watts), active power consumption goes down to 136.8 watts (see Payoff About a Year for Energy Efficient Computers). But not everyone has that. And if you use a traditional CRT monitor (73.4 watts, or 35.1 watts for the Energy Star version), it goes the other way, and CRTs remain a big part of the base in emerging markets.

But for our purposes, let’s just use the rough estimate of 156 watts. Not trying for the Fields Medal here.

Notebooks clock in at 19.5 watts (regular) and 16.4 (Energy Star), so let’s rate them at 18 watts.

The EPA numbers didn’t include servers, but I’ve looked at some stats and 170 watts seems about right. It varies according to processor count and age.

Now, desktops account for roughly 60 percent to 70 percent of the installed base; notebooks account for 30 percent to 40 percent. Thus, the average blended PC power consumption comes to between 109.2 watts – (156 watts X 0.6 market share) + (18 watts x 0.4 market share) – using a 60-40 split, and 114.6 watts using a 70-30 split.

Multiply those numbers by a billion and you get 100.8 gigawatts and 114.6 gigawatts. The halfway point is 107.7 gigawatts.

That number doesn't even include servers. With a conservative estimate of 30 million servers out there (more than 7 million have shipped in each of the last five years, according to IDC and Gartner), and an average energy consumption of some 170 watts, servers add another 5.1 gigawatts, bringing the total to 112.8 gigawatts.

You might say that’s unrealistic. Not everyone logs on all at once. True, but the installed base is growing rapidly. Gartner says there will be 2 billion PCs in use by 2014. Ergo, the number of PCs turned on at any given time also will double by then. (Roughly 310 million PCs will ship this year, according to eminent PC analyst Richard Shim.)

And if you want to add in Xboxes (187 watts) and LCD TVs (200-plus watts) that figure keeps climbing.

This explains why power-saving chips and software are hot technologies for greentech VCs, according to Venture Power, a newsletter we publish. Powervation ($10 million in the fourth quarter of 2007), Verdiem ($12 million in the second quarter), CamSemi ($8 million in the second quarter) and CHiL Semiconductor ($17 million in the second quarter) are some of the most recent beneficiaries.

The views in this opinion piece are not connected with Greentech Media News.

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