The Role of Distributed Generation and Combined Heat and Power CHP Systems in Data Centers

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4 Distributed Generation Applications at Data Centers7
DG can be applied in a variety of configurations to meet a hierarchy of facility needs, including
standby/backup power, continuous prime power, and CHP. DG has been successfully employed
in data centers using both fuel cells and other types of prime movers, such as reciprocating
engines, gas turbines, and microturbines. Appendix 1 provides a listing of recent fuel cell
installations in data centers throughout the country. It also includes three case studies of
successful CHP system applications in data centers in New York and California.
4.1 Standby/Backup
The traditional emergency or backup generator is a form of DG. In standby mode, the electric
utility is the primary source of power, and onsite power generation is used only as a backup
during a scheduled shutdown or failure of the utility feed(s). A UPS is used to bridge the time
delay while the standby system starts. This mode of operation is used in more than 99 percent of
network rooms and data centers that have local power generators (see Figure 2) (APC, 2003).
The standard generation technology for this mode is a diesel generator. Emergency diesel
generators are relatively inexpensive; they can pick up load rapidly on start-up, and they are
reliable if properly maintained. Lack of maintenance and testing, however, can reduce system
reliability and lead to the engines failing to start when needed. In addition, diesel generators for
emergency use are very high emitters of pollution and can produce visible smoke, noise, and
odor that can lead to local complaints when a facility tests or is forced to use its generators.
Some data centers are considering a switch to cleaner technologies for backup power, including
gas- or propane-fired engines, microturbines, or fuel cells. These technologies take longer to start
and pick up load than a diesel engine, so they might require additional energy storage in the form
of batteries or flywheels. Fuel-cell-based backup power systems are just emerging as commercial
products. Fuel cell use for backup power is being developed by a number of companies with
remote telecommunications facilities as an early target market. In 2005, a fuel cell product was
introduced into the market that provides backup power to data centers using bottled hydrogen as
a fuel. Another fuel cell product on the market fits within a single 42U Rack and provides 30 kW
of backup power. Fuel cell technology is currently aimed at data center applications where
conventional backup power is impractical and where backup needs are longer than can be
provided by conventional diesel generator-based UPS systems.
4.2 Continuous Prime Power
In continuous prime power mode, DG is the primary source of power, and utility-supplied power
is used primarily as a backup during a scheduled shutdown or failure of the onsite generator. Use
of the utility feed in this way is not free, but most utilities have established standard tariffs for
providing standby power to a customer with its own generator. In some states, these rates are
high enough to discourage customer-sited generation; in other states, standby tariffs are more
7 Information in this section was adapted from APC, 2003.
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