Page 38 - Energize December 2022

TECHNICAL

For large-scale computing, the data centre would require 20 to Rack level FC power
30 MW. This would require considerable space for storage of fuel, With a centralised prime power system only 20% of the fuel
either hydrogen or natural gas, if allowing for 48 to 72 hours of energy input at a power plant reaches the servers. Energy is lost as
backup power. it travels down the wire. In a data centre, these losses are found in
One advantage of integrating fuel cells as a backup power the power plant, transmission, substation, transformation and AC
source is that a complete redesign of the data centre would be to DC conversion at the servers. A data centre that uses distributed
unnecessary. Fuel cells would replace diesel generators by using generation, as opposed to the traditional architecture which relies
similar electrical infrastructure, redundancies and support systems on the electrical grid, has the potential to lower overall electrical
which are already in place. costs. With fuel cells located at server racks, a method known as
Early FC models used bottled hydrogen gas, but later used a a Distributed Fuel Cell (DFC), the losses are limited to the power
variety of liquid fuels. A recent development is the self-recharging conversion in the cell itself.
fuel-free hydrogen FC incorporating an electrolyser which FCs can be brought closer to the servers. In this case, a FC of
generates hydrogen from water when surplus energy is available several kW can be used to power one or more racks. This design
and uses the stored compressed hydrogen as a fuel when the eliminates the entire power distribution system in the data
power supply is absent. centre and replaces it with a fuel distribution network, resulting
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in a significant reduction in infrastructure costs. Power failures
Prime power generation due to FC malfunctions are limited to a couple of racks, which
There are several possible ways to incorporate fuel cells for prime modern data centre software can tolerate. Having FCs close to the
power generation in data centres. servers makes direct DC power distribution possible. This can also
eliminate the AC power supply unit in servers, currently used to
Utility power level convert AC input to internal DC power.
FCs can be used to replace the utility’s power supply, with the data Linking individual rack-based FC makes it possible to do things
centre disconnected from the electric grid. Existing deployments such as load balancing and fail-over. Not every rack will be full
are typically of this type and use a few MW-rated SOFCs. Larger and/or have the same energy requirements, so one FC will have
FCs tend to have better efficiencies, but the impact of failure a surplus, while another will be at its limit. To avoid having to add
is large. This design requires a power distribution system like new FCs, loads can be shared, and if one fails, others can provide
traditional data centres. power to ensure energy requirements are met.
Many fuel cells systems are currently configured to use natural
gas. Hydrogen fuel cells could also be used with on-site electrolysis
or delivered hydrogen. Delivered liquid hydrogen and hydrogen
pipelines would likely be more appropriate for large prime power
generation. Most current installations use natural gas from a gas
distribution pipeline.
One advantage to this approach is that a massive redesign of
the data centre electrical infrastructure would not be required. On-
site generation offers opportunities for combined heat and power,
potential for grid independence, and cost savings by eliminating
some parts of the uninterruptable power supply backup system.
This approach has been used by a number of large data centre
operators in the United States, such as Apple, Google, AT&T,
Microsoft and many others. 5

Figure 1: A 3 MW hydrogen FC system consisting of a pair of 40-foot-long
shipping containers, each holding 18 PEM fuel cells (Microsoft). Figure 2: Conventional and rack power systems

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