INTELLIGENT GREEN TECHNOLOGY
A typical microgrid energy system.
Microgrid system operating modes.
generator control, load connection,
or general system coordination and
communication. Local control of assets
enables faster, semi-autonomous or
autonomous control of the microgrid
devices to better maintain operation
within connected equipment limits.
Local controllers scale, normalise
and manage control, operational and
monitoring data flow to an upstream
system controller. This controller and a
human machine interface then oversee
connections to the upstream grid,
including system configuration, POC
monitoring and application selection and
control functionality.
Typically, a microgrid can connect and
disconnect from the grid to enable it to
operate in both grid-connected and island
modes. The technology available allows
microgrids to function with distributed
generation assets during times when the
grid is healthy and operating properly,
while also having the capability to physically
disconnect from the grid and operate in an
islanded mode for extended periods of time,
powering critical infrastructure.
Designing a micro-grid
Many questions can arise while exploring
microgrid sizing and design options. To
understand each specific context, many
factors must be explored, among them
the existing electrical infrastructure if
any, load profile and growth, utility rates,
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existing generation assets, generator
control capabilities. A feasibility study is
used to identify and define the microgrid
project for optimal technical features use
cases and economic return.
A feasibility study should attempt to
answer in very simple terms whether
or not a microgrid makes good sense to
employ in a specific circumstance and if so,
what configuration and components are
optimal to meet the specific power needs
of the given scenario. The feasibility study
process walks customers through these
concerns step-by-step - first determining
critical needs and requirements, then
developing a microgrid plan and finally
outlining more specific technical aspects
and recommendations.
Initial screening questions might
touch upon functionality requirements,
existing load and generation information,
automation infrastructure availability,
utility requirements, generation
preferences, and other security, legal and
commercial aspects.
For example, the screening
might attempt to uncover functional
specifications by exploring critical load
requirements as well as any load shedding,
demand response or black start outage
mode operation needs.
Peak electrical and thermal load
profiles, load types and profiles must be
identified prior to the design. During the
screening, further assessment of existing
generation and automation systems,
including their scope, functionality and
interfaces, should be pursued in-depth to
determine more specific microgrid assets
and system topology.
Each critical asset facilities and
present applications must be identified
and addressed in the study in terms of
their energy needs and the criticality
of each asset. Based on these identified
power-critical assets, load sizes and
profiles, the location of supply and storage
infrastructure necessary to adequately
support critical assets will be identified
and designed into the proposed system.
Another aspect of the feasibility study
should cover economic analysis. It is
important to explore whether or not a
microgrid solution will be economically
feasible. The feasibility study can
help to define the type of appropriate
microgrid components and their sizes
to more effectively control cost. Optimal
component sizes minimise the levelised
cost of energy for shorter payback
duration. Renewable energy assets, if
desired, can also be incorporated into
the microgrid design. With all analysis
complete, a comprehensive and tailored
energy reliability plan can be developed
for the microgrid implementation.
The resulting feasibility report
comprehensively details the following:
Intended functionality of the proposed
microgrid and its scope
Existing system assets to serve the
load profile
Proposed design
Details on distributed energy resources
including renewable energy sources
Recommendations for suitable energy
storage technologies
Sizing based on the microgrid
requirements
Overview of operational modes and
control strategies within the design
Detailed cost estimates for
ascertaining benefits
The distributed energy resources,
renewable or not should be selected
based on what is most appropriate for the
system’s goals, be it generators, energy
storage, solar, or other renewables.
Existing and future distributed energy
resources such as solar, wind, combined
heat and power, fuel cells and energy
storage are evaluated. Additionally,
the type and availability of the fuel to
power other distributed generation
assets is evaluated under the foreseeable
contingencies and environmental rules.
Excerpted from, Making microgrids work:
Practical and technical considerations to
advance power resiliency, by Martin Baier,
Engineering manager; Vijay Bhavaraju,
Principal engineer, corporate research
and technology; William Murch, Director
of services, microgrid energy systems;
Sercan Teleke, Senior engineer, microgrids
and renewables, all at Eaton.
Issue 15
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