The Invisible Trillion · Data Centers: The Cathedrals Nobody Visits

The Power

Data centers use an enormous amount of electricity, and how that power gets delivered is one of the most interesting (and environmentally consequential) parts of the story.

A medium-large data center draws 10 to 50 megawatts. A big one draws 100 megawatts. A giant “hyperscale” campus might draw 500 megawatts or more. For comparison, a nuclear reactor produces about 1,000 megawatts; a typical American house uses about 1.5 kilowatts on average. A single big data center campus, in other words, uses as much electricity as several hundred thousand houses.

This electricity does not arrive by magic. A data center has its own substation, often on-site, where high-voltage power from the grid is stepped down to something the servers can use. From the substation, power flows into the building through enormously thick cables, gets distributed to racks, and ends up running chips.

About half of the power goes to the chips themselves. The other half goes to cooling (fans, pumps, chillers, air handlers), networking equipment, lighting, and conversion losses. The industry measures this efficiency with a metric called PUE, Power Usage Effectiveness, which is the ratio of total facility power to IT power. A PUE of 1.0 would mean every watt goes to the servers and none to overhead. The best modern data centers achieve 1.1 or better. Older ones might be 1.6 or worse — 60% of their power going to cooling and overhead.

Because data centers cannot, absolutely cannot, tolerate power outages, every data center has layers of backup.

First, uninterruptible power supplies, or UPS: giant banks of batteries that can run the whole facility for a few minutes. The moment the grid power hiccups, the UPS takes over, seamlessly. Modern UPS batteries are often lithium-ion, sometimes flywheels, sometimes huge banks of lead-acid batteries the size of rooms.

Second, backup generators. Most data centers have enough diesel generators on-site to run the whole facility for several days. When a grid outage lasts longer than the UPS can handle, the generators start up — a noisy affair — and take over. Data centers have on-site fuel tanks holding tens or hundreds of thousands of gallons of diesel. The generators get tested regularly, which is when you hear them in operation if you’re nearby.

Third, redundant grid connections. A serious data center has power coming from two or more separate substations on two or more separate grid paths, so that a failure of one substation doesn’t take the building down.

The layers of redundancy mean a well-run data center is genuinely reliable. The industry measures uptime in “nines”: 99.99% uptime (“four nines”) means less than an hour of downtime per year. 99.999% (“five nines”) means about five minutes. The best data centers achieve six or seven nines — a few seconds of downtime per year, across everything.

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