Factors such as increasing occurrences of natural disasters, the ongoing threat of cyberattacks and growing awareness of inadequate, outdated or failing grid infrastructure all compel future development in technology to provide power continuity. Traditional standby generation is no longer adequate.
Microgrids provide a platform to keep the power on and operate critical assets over long periods of time while isolated from a damaged or failed grid. Microgrids can generally better manage distributed power generation by providing optimal control, dynamic stability and balancing the demand and generation on a small but critical scale.
Early microgrids for the military focused on providing intelligent mobile power distribution to support power reliability and fuel savings on military forward operating bases. The high cost of safe and reliable access to fuel in combat situations led the US Army to consider energy alternatives and resource management strategies.
The reliability of continuous power for force support is paramount to troop safety and keeping forward operating bases operating around the clock. The system was able to become self-sufficient through a demand-managed microgrid that not only transformed independently operating generators, but also reduced fuel consumption at forward operating bases by more than 30%.
A more resilient, responsive infrastructure is critical beyond military requirements. Power resiliency—the ability to sustain power and recover from adverse events—is critical across a host of industries and businesses, including utility, healthcare, industrial and governmental applications.
In other geopolitical areas, basic electrification remains a critical driver for microgrid innovations and their applications. Globally, over one billion people still lack access to electricity. For these communities, microgrids provide a viable platform for bringing electricity to the developing world.
A microgrid is defined as a group of interconnected loads and distributed energy resources within clearly defined electrical boundaries that act as a single controllable entity with respect to the grid. In essence, microgrids are standalone electrical power systems that consist of multiple generating assets and often storage sources supplying loads that can be powered independent of the primary utility transmission and distribution grid.
Two of the greatest benefits of microgrid technology are increased reliability and power quality to large critical loads like mega-scale data centers and hospital districts. Onsite generation already exists in these loads and microgrid technology enhances the reliability by sourcing the loads in addition to transmission and distribution systems.
Increasingly, microgrids are further leveraged to effectively accelerate the adoption of distributed renewable energy sources that are intermittent, which reduces global dependence on fossil fuels while lowering climate-damaging carbon emissions.
Despite these many benefits, some technical and regulatory issues must still be addressed to realise the full potential of microgrid systems. Economic barriers include the high cost of building microgrids from scratch, the cost of upgrading legacy equipment and infrastructure to operate microgrids, net metering issues, regulatory and market issues, the high cost of components, difficulty in quantifying the benefits, funding and maintenance.
Technical challenges include technology immaturity, upgrading legacy generator controls, addressing complex energy imbalances to ensure optimal control, islanded microgrid protection and ensuring cybersecurity needs. Lastly, as communications become faster and more data intense, microgrid systems must also adapt to current real-time network demands and interfaces.
In most current microgrid designs, a few key components can be outlined. The microgrid is tied to the upstream grid via a point of interconnection is managed by different controller architectures. Of greatest importance are the microgrid’s local controllers, different from the device controllers, which are typically configured for energy storage, photovoltaics, engine-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, 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.
These technical considerations help define the microgrid’s functions and control system. Constraints are considered in detail to help fine-tune chosen microgrid components and sizes.
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.
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
- a 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
Renewable energy assets, if desired, can also be incorporated into the microgrid design.
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, Eaton.Click below to share this article