Microgrids are localized grids that can disconnect from the traditional grid to operate autonomously. Because they are able to operate while the main grid is down, microgrids can strengthen grid resilience and help mitigate grid disturbances as well as function as a grid resource for faster system response and recovery. Hospitals, military bases, and campuses have traditionally been the primary users for microgrids given their needs for round the clock energy and required energy loads. However, microgrids, are increasingly being included in community resiliency planning because of their ability to provide continuous power to critical infrastructure and limit the impact of outages by localizing power generation close to critical services. To be most cost-effective, microgrids that are developed to support critical infrastructure have a cluster of critical facilities that will all be serviced by the microgrid in the case of an emergency.
|Woodbridge, CT - Fuel-cell microgrid servicing the town hall, library, fire house, police station, public works, high school, and senior center.|
|Montgomery County, MD - Multiple microgrids servicing public safety headquarters and correctional facilities, and other proposed community microgrids|
|Pittsburgh, PA - Microgrid concept that will serve hospitals, fire and police stations, and places of refuge during outage events|
The three examples above illustrate that microgrids can be formed with different ownership models and technologies to meet needs and policy goals. The traditional microgrid ownership model has been single end-user ownership but there has been a recent shift to multi-stakeholder projects, which helps with overall project economics. More information on ownership models can be found here, and see below for a breakdown in microgrid ownership models by GTM.
In 2016, CHP was the main source of generation in microgrids, and is expected to continue to be a key technology in future microgrid design (Figure 5). In many resiliency projects, a technology like CHP is needed to reliably sustain power over an extended period, supplemented with solar generation. CHP can be an ideal anchor for microgrid systems because of its ability to withstand heavy storms and long outages, while also serving as an enabling technology for integrating renewable energy. As storage costs continue to decline, solar + storage will likely become a stronger candidate for more complex microgrid projects. Several jurisdictions are exploring solar and storage in resiliency and have created supportive resources, such as the roadmap created by New York City:
Figure 5. Existing and Planned Microgrid Capacity by Resource
Nationally, states and local governments are exploring how microgrids can help meet resiliency goals within the existing regulatory framework. Approaches include developing reports considering key concerns, developing a task force to provide recommendations on how to incorporate microgrids in resiliency planning, creating funding opportunities to incentivize microgrid developments, and developing pilot projects.
- Microgrids for Critical Facility Resiliency in New York State: This report was commissioned by the New York State Legislature for the purpose of developing recommendations for the establishment of microgrids. Several state agencies including New York State Energy Research and Development Authority (NYSERDA), the New York State Department of Public Service (DPS), and New York State Division of Homeland Security and Emergency Services (DHSES) collaborated to prepare the report.
- Maryland Resiliency through Microgrids Task Force: This report shares the results of a task force established by the Governor’s office to study the statutory, regulatory, financial, and technical barriers to the deployment of microgrids in Maryland. It includes a roadmap for action to pave the way for private sector deployment of microgrids across the state.
- Resilient Microgrids for Rhode Island Critical Services: This report was prepared for the Rhode Island Office of Energy Resources (OER) in response to their request for support for the design of a program to enhance energy assurance of critical infrastructure through deployment of distributed resources. It describes technologies, procurement strategies, and polices that can contribute to microgrid development.
- Connecticut Microgrid Program: Connecticut was the first state in the nation to deploy a statewide Microgrid Pilot Program in 2013. Today, the state runs a full-scale microgrid program offering incentives for microgrid projects at critical facilities. Funding is typically is applied to design, engineering, and interconnection costs.
Resiliency goals will have an impact on technology choices and required load in microgrid design for critical infrastructure. For instance, relying exclusively on renewable energy resources cannot provide electric power during grid outages with the level of reliability required for emergency loads for an extended period. A beginning step for designing a microgrid is collecting data across all of the facilities on the site to determine the energy needs and assets, as well as determining which critical facilities may already have backup generation systems. A number of technologies are considered to form the optimal generation including combined heat and power systems, renewables, smart grid technologies, energy storage, and traditional backup generators. Microgrids that are designed for resiliency that have black start capability and meet the needs of all critical infrastructure on site during an islanded incident may require additional generation than needed to ensure power in the case failure of one or more generators.
Despite these additional challenges, microgrids have already proven to provide consistent power during times of emergency. The Hurricane Sandy Rebuilding Task Force identifies microgrid systems as a means of mitigating the sprawling impacts of weather related disaster. Examples include:
- With a 15 megawatt (MW) combined heat and power generator as well as 5.3 MW of solar, Princeton University’s microgrid kept its campus live for three days while power was cut during Hurricane Sandy.
- South Oaks Hospital, a 245-bed healthcare facility on Long Island, remained disconnected from the grid for fifteen days after Sandy with the help of its 1.25 MW combined heat and power generator and 47 kilowatts (kW) of solar. The hospital accepted patients from other sites that lost power during the storm.
- TECO's CHP plant at Texas Medical Center in Houston, the world’s largest medical center, improves the center’s ability to operate in an emergency. The CHP system was able to provide all of the power and thermal energy to the campus during a hot summer day in 2010, when the Texas grid experienced all-time high energy demand and faced numerous grid disruptions.
As with all distributed generation with large load profiles, microgrids require electrical, communication and controls infrastructure that can add costs to the project. Depending on the size and complexity of the microgrid, specialized protection equipment may also be needed. NYSERDA has developed a benefit-cost assessment (BCA) model for assessing the economic viability of microgrids at critical facilities based on the specific attributes of each site and taking into account the benefits and costs of providing essential services during a prolonged emergency. The model also estimates a range of other potential benefits, including energy cost savings; savings in the development of energy generation, transmission, or distribution capacity; power quality benefits; and environmental benefits (see Figure 6 below).
Figure 6. Excerpt from NY Prize Spreadsheet Model for Community Microgrid Cost Benefit Analysis
This benefit-cost framework is also detailed in the Evaluation of New York Prize Stage 1 Feasibility Assessments final report. This report highlights the objective of the NY Prize microgrid feasibility studies, provides background on the technical approach used in the analysis, and also outlines fundamental considerations for microgrid planning. These considerations can provide high-level guidelines on the key factors to idenify when considering and moving forward with a microgrid project. This information all feeds into the benefit-cost analysis and project-specific technical issues, which provide more detailed information that can be used in later stages of specific microgrid projects.
The 2014 NYSERDA report Microgrids for Critical Facility Resiliency in New York State also highlights the key attributes that generally lead to a successful microgrid project. These attributes may be highly sought after in certain microgrid deployments, but not all owner's may benefit equally. These can be useful in the initial stages of project formulation, and are shown in the table below:
|Clustering of CI sites in close proximity||Reduced infrastructure costs|
|Existing electric or thermal distribution infrastructure that can be re-utilized||Reduced infrastructure costs|
|A consistent and significant need for electrical energy||High degree of asset utilization improves economic return (e.g., generators never sit idle)|
|Capacity limitations in the zone or network area of the microgrid||Demand (capacity) savings that benefits the macrogrid|
|Requirement for distribution capital expenditures that can be deferred or avoided by this microgrid||Distribution utility capital expenditure savings|
|The ability of the microgrid to provide ancillary services (NYISO market)||Lowering the capital and operating costs of the transmission system|
|The ability of the microgrid to provide distribution level services (voltage control, feeder loading relief)||Lowering the capital and operating costs of the distribution system|
- Distributed Energy Resources Customer Adoption Model (DER-CAM) - A customer adoption model of DER based on economic, technical, and environmental metrics. The model aims to minimize the cost of operating distributed generation resources, including CHP.
- Microgrid Design Toolkit (MDT) - A software tool that assists microgrid designers in the preliminary stages of microgrid design. The model uses user-defined objectives focused on the cost, performance, and reliability of various DERs.
- Hybrid Optimization of Multiple Energy Resources (HOMER) - A software package that provides a framework for optimizing a set of distributed energy resources in order to simplify the process for identifying least-cost options for microgrids.
- RETScreen Clean Energy Management Software (RETScreen) - A software system that provides project feasibility and energy performance analysis for energy efficiency, renewable energy and cogeneration projects.