IEEE Electrification Magazine - March 2014 - 98

viewpoint

Average Customer
MWh

TAble 1. distributed Generation (Mwh).
0.25 MWh

1 MWh

24 MWh

50 MWh

0.25 MWh

0.25

0.010

0.005

1 MWh

0.04

0.02

24 MWh

0.48

50 MWh

200

2.08

75 MWh

300

3.13

1.50

points 2 and 3 we have enough on-site
DG to provide power to our system's
average load. as DG continues to be
added or turned on, we exceed the peak
load of our system and find ourselves in
a situation where the microgrid can
generate more power than our system
would ever demand. In terms of reliability, we reach a point where, if we lose
our primary source, we have the means
to keep our entire system running for
as long as our DG sources allow.
an important concept with the
value of reliability and efficiency in a
microgrid is load shedding. In Figure 1,
you can see a third line that is below
our average load and closer to our mission-critical load. One tool that makes a
microgrid vastly more adaptable is a
control system that allows the interconnected loads to shed their nonessential loads. This can be as simple as
physical plant personnel manually cutting power to a nonessential building
or it could be as advanced as a centralized master control that automatically
turns off individual circuits among the
microgrid's interconnected loads.
In Figure 1, we show this concept
with our theoretical customer having
the means to shed load to a new
reduced load level. By doing this, customers can keep just a bit more than
their mission-critical loads operating
using the DG already in use. This ability transitions us to the fourth value of
a microgrid.

Grid support
colored in yellow on the final portion
of Figure 1, we show DG increasing to

I E E E E l e c t r i f i cati o n M agaz ine / MARCH 2014

a point where it exceeds the peak load
of the customer's system. at point
four, we have more generation capacity than our system demands. This
excess capacity can be used to support the local grid. For example, imagine a microgrid at a military base. at a
typical base, a majority of the personnel who work at the base live nearby
in the surrounding communities. If a
major weather event interrupts sources of generation typically feeding
these communities, and the base is
set up like our microgrid in Figure 1,
the base could use its excess DG to
support other loads outside its system
with permission and coordination
with the local utility. In a nonemergency situation, the base could sell its
excess generation to the local utility,
essentially becoming a source of both
load and generation.
With load-shedding capability, a
microgrid can broaden its ability to
support the grid. In Figure 1, there is
enough DG to support the customer's
peak load, but there may be situations
where it is more economical or necessary to reduce the customer's load
and provide additional support for the
local grid. This is the exact situation
that occurred at the University of california San Diego (UcSD). The UcSD
campus has a variety of DG sources
including a fuel cell, combined heat
and power system, solar panels, and
eS. When wildfires took out transmission lines, the local utility asked UcSD
if they could use its DG to stabilize the
grid. UcSD was happy to help and
reduced its load through load

shedding protocols that were already
in place to provide the maximum
support it could by exporting its now
excess DG capacity. This effort helped
keep the grid from collapsing.

Microgrid Costs
We hope this overview helps you see
why there is such momentum building
behind microgrids. large and small
customers hold tremendous potential
to save money by implementing
microgrids of their own. We can dollarize the two benefits for consumers:
1) By using microgrids to become
more efficient, customers can
directly save money by reducing
their power demand (cost savings).
2) By using microgrids to become
more reliable, customers can
indirectly save money by reducing the frequency and duration
of outages (cost avoidance).
If we look for ways that microgrids
could threaten utilities, the most
obvious culprit is the ability for customers to reduce their demand. For
instance, if a large customer decides
to invest in DG, that would, in turn,
reduce the customer's energy
demand and thereby reduce revenues
for the utility. however, it is much
more complicated than that. We illustrate this through the microgrid cost
evaluation tool shown in Table 2. This
is the same tool we use with our customers to evaluate what their realized cost savings would be for using
DG to offset their electricity demand
and improve their reliability.
The argument for microgrids displacing utilities is that customers can
own and operate their own grids cheaper and more reliably than what their
local utility can. We have highlighted
four portions of the economic analysis
shown in Table 2 that highlight why
microgrids are not going to disrupt utilities in the near future. When you run
the numbers, you find out quickly that
the utility still delivers the same value
that led to its creation in the first place.
The rumors of their demise are
extremely premature.

Table of Contents for the Digital Edition of IEEE Electrification Magazine - March 2014