IEEE Power & Energy Magazine - Grid Edge 2023 - 98

energy flow path through alternative distribution lines for
re-energizing load centers after damage to a part of the
power system) and mobile energy storage system (MESS).
This article addresses deployment and utilization of advanced
MESS to enhance reliability and resilience of energy
supply.
Fossil fuel-based portable emergency generators (diesel
or gas) have traditionally been used during system outages
to restore service to a segment of a power distribution system.
Being part of a mobile fleet, these generators provide
flexibility in managing restoration of impacted sites and
for supplying groups of customers to temporarily deliver
power to critical sites before the system is back to a normal
operating condition.
The restoration time could last several hours or-in
more severe conditions-several days, exposing impacted
customers to significant pollution from the noise
and emission of diesel/gas generators. The need for clean
electricity and regulatory limitations on operating time
of diesel generators suggests finding alternative approach
for meeting electricity needs during the outage
recovery time.
A mobile energy storage system (MESS) as a cleaner
replacement for diesel/gas generators has mostly been
available in very small sizes (a few hundred watts or kilowatts);
which is not adequate to supply all critical loads
of an industrial or a commercial customer or multiple
customers-in a safe and scalable way-through existing
(unimpacted) distribution system assets (such as service
transformers or lines connecting neighbor customers in
a segment).
Two challenges normally affect the use of small portable
battery-powered backup power supplies for utility
customers:
✔ A significant effort may be needed to reconfigure
customer connections by separating and isolating
supply paths to dedicate the portable backup unit to
given loads, and
✔ An increase in the size and number of household devices
or business usage that would be considered part
of the critical load groups.
The preference is to maintain the normal power delivery
path from the utility to the end-critical customers as much
as possible, rather than re-configuring the connection. Using
a properly sized MESS that has microgrid capability
for both grid connected and islanded operation, the only
required change is to swap the input with a mobile clean
energy source. This approach also reduces the effort for
restoring customer connection, when the grid is back, by
seamless transfer to a healthy grid.
With increasing adaption of large grid-scale batteries,
the capabilities of MESS technologies have grown rapidly
in both system sizes and maturity of products. However,
additional effort is needed to make the technology scalable
for supplying larger systems and be on par or superior to
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ieee power & energy magazine
the capabilities of typical portable/emergency diesel generators
in ease of interconnection and control capabilities for
acceptance and adoption by utilities and fleet managers as
promising alternatives for outage management and reliability/resilience
services. The fundamental features expected
from a MESS are:
(i) Reliable and dependable technology that is is immediately
available to supply electrical loads.
(ii) Mobility and the ability to be relocated from one
site to another frequently to cover widespread outage
areas with non-coincidental outage patterns.
(iii) Plug-and-play standard connection to a site to
minimize preparation time needed to quickly reenergize
service supplies to customers.
(iv) An easy to use and reliable automated control and
monitoring platform for streamlining the process
of start/stop or changing control modes. This process
reduces the burden on an operator especially
during stressful outage recovery time.
As the technology is becoming commercially available
at the utility scale, utility and fleet owners need
to integrate MESS into their asset portfolio properly,
including defining a new planning process for scheduling
and tracking utilization of the new assets for outage
recovery and grid preparedness - as the primary
use case. The business justification for the total cost
of ownership requires an understanding of all feasible
secondary use cases to increase the utilization factor in
normal business days (also referred to as business case
for blue sky conditions).
Several use cases for outage recovery and emergency
response are presented in this article. A benchmark system
is used to describe the functionality of the mobile energy
storage system for each specific use case and how the technology
will impact overall grid preparedness for weatherdriven
outages.
Paradigm Shift
After a long history of relying upon diesel generators for
energy supply during outages or at remote customer locations,
the time has come to re-think the alternatives. While
the alternative technology should have similar or superior
technical capabilities to portable diesel generators (e.g.,
mobility, blackstart function, long supply duration), it must
be more environmentally friendly and economically justifiable.
Table 1 presents a high-level comparison between
a portable diesel generator versus a MESS from technical
and environmental perspectives. Advanced control functions
and automation capabilities embedded in a MESS
will facilitate utilization for a wider spectrum of gridconnected
and outage applications, enabling the stacking
of applications and increased value-proposition of the unit.
Incorporating multiple use cases by staking applications is
critical for building a stronger business case for MESS and
its financial justification.
April 2023
IEEE Power & Energy Magazine - Grid Edge 2023

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