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facilities to supplement their utility
supply, akin to how power utilities
ramp up and down their generating
capacity throughout the day to meet
expected demand from consumers
and business.
Unfortunately, the use of generating
sets does not address the problem
of peaks arising from more dynamic
CPU utilization that is characterized
by a higher peak to average power
ratio, which is of shorter duration
and occurs with a higher frequency.
For this the solution is to provide
battery power storage. The principle
here is simple, the batteries supply
power when demand peaks and are
recharged during periods of lower
utilization. This approach, referred
to as peak shaving, is illustrated by
figure 3, which shows how a server
rack that would normally require
16kW of power can operate with
8-10kW of utility power. Indeed,
if utility power is constrained, the
Figure 3. By profiling power demand and employing battery storage it is possible to manage peak
demand using power stored during low utilization periods
Figure 4. CUI’s rack-mount ICE hardware for intelligent power
switching and battery storage
the supply system and causing
power outages. This leads planners
to add additional capacity to provide
a safety buffer. Consequently it
is not surprising to find that the
average utilization in data centers
worldwide is less than 40% purely
by taking account of peak demand
modeling plus the additional
buffering - this figure drops further
when redundancy provisions are
also included.
Unlocking underutilized
power supply capacity
The peak versus average-power
consumption issue discussed
above clearly locks up considerable
power capacity. Where peaks occur
at predictable times and have a
relatively long duration, data centers
typically use local power generating
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