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COMPUTING SCIENCE

The Computer and the Dynamo

Brian Hayes

The Coal-Burning Internet

It wasn't hard to trace the story back to its source. Typing the words "8 percent computer electricity consumption" into a search engine produced lots of leads. (The search engine told me how many seconds it spent on the query, but not how many kilowatt-hours.) All trails led to Peter Huber and Mark P. Mills, writers and consultants who publish a newsletter called Digital Power Report. In particular, I was directed to an article of theirs titled "Dig More Coal—The PCs Are Coming," which appeared in Forbes in 1999.

The Forbes article includes all the essential elements of the story: "At least 100 million nodes on the Internet, drawing from hundreds to thousands of kilowatt-hours per year, add up to 290 billion kWh of demand. That's about 8% of total U.S. demand. Add in the electric power used to build and operate stand-alone (unnetworked) chips and computers, and the total jumps to about 13%. It's now reasonable to project that half of the electric grid will be powering the digital-Internet economy within the next decade."

Other statements of Huber and Mills are no less electrifying. Utilities have to burn a pound of coal, they calculate, for every two megabytes of data moving across the Internet. A "server farm" housing computers that serve Web pages has the power needs of a small steel mill. And then there is their most provocative claim: A Palm Pilot connected to the Internet consumes as much energy as a household refrigerator. (Of course that power doesn't come out of AAA batteries; it's the handheld unit's share of the power used by Internet routers and servers.)

Unfortunately, Huber and Mills don't always make it easy to trace the line of reasoning that led them to their conclusions. As far as I can tell, the Palm Pilot–refrigerator equation is not explained anywhere. The extrapolation from 8 or 13 percent today to 50 percent a decade hence is also presented without any supporting documentation. (Moreover, another version of this prediction says 30 to 50 percent in two decades.)

The longest and most explicit presentation of these ideas appears in a report titled The Internet Begins with Coal, authored by Mills alone. Even there, however, certain blanks remain unfilled. A crucial starting point for the numerical estimates is an assumption that "your typical PC and its peripherals require about 1,000 watts of power," but the documentation for this number is vague and confusing. A footnote mentions as one source of information an "online configuration tool" provided by a manufacturer of uninterruptible power supplies, but that tool's rating for the configuration that Mills discusses is not 1,000 watts but only 205 watts. Mills then remarks: "The 1,000 W figure for the PC nominally accounts for the power needs of otherwise unaccounted microprocessor devices on the network." Those devices remain unaccounted, so that four-fifths of the power drain attributed to PCs comes from unidentified "behind-the-wall components."

Figure 1. Estimates of power consumption . . .Click to Enlarge Image

This shadow world of unseen power loads is also mentioned in the Forbes article. "For every piece of wired hardware on your desk," Huber and Mills write, "two or three pieces of equipment lurk in the network beyond—office hubs and servers, routers, repeaters, amplifiers, remote servers and so forth." Taken literally, this statement implies that there are 200 or 300 million hubs, routers, etc.—two or three for each of the 100 million desktop computers that Huber and Mills count as being connected to the Internet. The preponderance of hidden devices is hard to fathom, since the Internet has a treelike structure, in which the leaf nodes—desktop PCs—ought to be more numerous than machines along the trunk and branches. Elsewhere, Huber and Mills themselves assume there are only 7 million routers and Web servers.

Such gaps in documentation are no definitive refutation of the Huber and Mills thesis, but they don't inspire great confidence. Neither does the provenance of the report. The Internet Begins with Coal was published by an organization called the Greening Earth Society, where Mills serves as science advisor. The name of this group might evoke images of the Green Party and Greenpeace, but the agenda is rather different. The name reflects a conviction that higher concentrations of atmospheric CO2 are "beneficial to humankind and all of nature," because they promote plant growth. The society was created by the Western Fuels Association, a consortium of electric utilities and coal-mining companies, whose main business, of course, is digging up C and combining it with O2. Both the society and the association argue that coal-fired power plants will remain essential to continued prosperity; in particular, they disparage the notion that the Internet will usher in a new economy without smokestacks, where demand for electricity would remain static or decline.

The fact that an argument serves the publisher's economic interest certainly does not invalidate the argument. But when interests and arguments are so closely aligned, readers can be expected to give the supporting evidence rather careful scrutiny.








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