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You’ve undoubtedly seen the headlines and stories about the huge amounts of electrical power that artificial intelligence (AI) and its computational centers use. A sampling of the claims and forecasts give you a sense of what you need to know:
- “Global Datacenter Critical IT power demand will surge from 49 Gigawatts (GW) in 2023 to 96 GW by 2026, of which AI will consume ~40 GW” (SemiAnalysis)
- “Many new AI data centers are expected to consume 100 megawatts each, according to a recent Morgan Stanley analysis” (Bloomberg)
- “EA forecasts that data centers’ total electricity consumption could reach more than 1,000 terawatt-hours (TWh) in 2026” (Data Center Frontier)
- “Data centers could consume between 4.6% and 9.1% of US electricity by 2030, according to an analysis by the Electric Power Research Institute” (Carbon Credits)
While the numbers are all over the place, and forecasts of the future are always suspect (a reality that is rarely stated explicitly), the message is clear: data centers and AI are power beasts.
However, that’s only the visible, attention-grabbing part of the bigger story. The less-know aspect is that for data centers in general and AI in particular, a power outage — even for a fraction of a second — is a very bad thing, period. If local power goes out, sags, brown-outs, or glitches, the data center must go on as if nothing had happened. These centers are looking for 99.99999% uptime (seven 9s) which is much higher than the customary five or even six 9s of hi-uptime reliability systems.
As a result, these data centers require full-scale generator-based backups, typically about one or two megawatts per generator; a large or so-called hyperscale center will have several of these units in parallel. For example, at a suburban Chicago data center run by Stream Data, more than two dozen generators built by Cummins are installed to provide the 32 megawatts of power needed to maintain the center’s servers and other systems. Depending on location and available resources, these generators are usually powered by on-site diesel fuel or piped-in natural gas.
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It’s the transition period between primary line power being Ok and not OK that is especially critical. These megawatt-class generators do not come online instantly but take anywhere from a minute to several minutes to start up, check themselves, synchronize, and provide power. For that interim period when they are in start-up transition mode, they are 100% reliant on battery power via a battery energy storage system (BESS).
The overall generator plus battery arrangement is therefore configured as a true uninterruptible power supply (UPS) system to ensure a seamless transfer from primary-utility- power to backup generator power. As the batteries are not needed for a long time, their overall energy-storage requirements (kW-hr) are relatively modest, but their power-delivery ratings (kW) must be high enough to run the entire data center, even if only for a shorter period.
The main components in the power backup and distribution arrangement are (Figure 1):
- Emergency Generator – Supplies power when utility power is not available.
- Utility Power – Main power source for the facility.
- Automatic Transfer Switch – Routes utility or emergency generator power to switch gear.
- Switch Gear – Routes utility or emergency generator power throughout the system.
- BESS-based Uninterrupted Power Supply – Consists of the battery bank, charger and inverter.
Utility power is routed through the automatic transfer switch and into the switchgear, which is configured into critical and non-critical supplies. Critical supplies are components such as data centers, security centers, and UPS that cannot have power interrupted. When utility power is lost in the facility, the UPS supplies power to the security and data center.
If the power loss is more than a few seconds duration, the generator starts and the automatic transfer switch transfers to emergency power, while the switch gear routes power to critical and non-critical loads. The UPS transfers to normal operation, while the data center and security are powered by an emergency generator. When normal power is resumed, the automatic transfer switch routes power to utility, and critical and non-critical loads are powered.
Using this procedure, the data center itself and security see no power interruption and continue to operate normally through power loss. (Local workstations may have their own individual UPS backup units to keep them powered for a short period).
Not an under-the-desk backup unit
Although data centers look clean and almost antiseptic with rows of modular racks and enclosures that can be assembled on-site, the backup generator subsystem presents a very different story. They come with installation and management issues and need to be started periodically as a basic health check.
They are also large and expensive: a megawatt-class diesel generator weighs about 5000 kilograms (without fuel), has a 5 × 1.5-meter footprint and 2.5-meter height, starts with a standard 1000-liter fuel tank, and costs about $1 to $2 million not including shipping and installation (Figure 2). That’s just the generator, of course, as the BESS is a separate unit, with its own installation considerations. Leading vendors include Cummins, Caterpillar, ABB, Siemens, and Schneider Electric.
Unlike the data-center racks, it is usually assembled and tested at the vendor site, then shipped by rail or truck to the datacenter site. That site must be prepared with a suitable concrete pad and clearance for access, cabling, and more.
There’s a large irony aspect associated with the need for these backup generator units. Although data-center operators would like to “go green” and get their basic power exclusively, or primarily, from renewable sources — especially for their new installations — the huge power demands make that a very difficult option. Then, the non-green nature of the entire backup generator subsystem completely undermines that objective (see The Wall Street Journal, “How Big Data Centers Are Slowing the Shift to Clean Energy”). It looks like those big, nasty, ancient, fossil-fueled sources of power are still very much needed.
Once again, the “Law of Unintended (or Unforeseen) Consequences” (also known as the “ripple effect”) is a factor. In the case of these data centers, it is present on a very large scale and can’t be ignored. It joins the hard reality that when it comes to power and energy, there’s no such thing as a free lunch.
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