Sustainable Design and Management of Microgrids

Sustainable Design and Management of Microgrids

While microgrids can be a source of renewable and reliable energy for utility distribution systems, significant challenges exist in stable operation and meeting the economic goals of the microgrid owners. Sustainability of microgrids will depend on a sound business model, enabling technology, and regulation policies.

Energy microgrids are a key building block of future smart grids. Microgrids integrate modular energy sources, such as solar, wind, thermal generators, fuel cells, etc., with energy storage devices and both critical and non-critical loads to form low-voltage distribution systems. By definition, a microgrid is a group of interconnected loads, energy storage and generation systems within clearly defined boundaries that act as a single controllable entity with respect to the grid. A microgrid can operate in both grid-connected mode (to support the local distribution system) or operate in islanded mode (to protect users from grid instability). In this context, local generation systems, also known as distributed energy resources (DER), support local thermal and electrical demand while ensuring reliability and power quality with a lower emission footprint. Maintaining this profile relies on the flexibility of advanced power electronics that control the interface between micro generation and storage sources and their surrounding AC system.

While microgrids can be a source of renewable and reliable energy for utility distribution systems, significant challenges exist in stable operation and meeting economic goals of the microgrid owners. Any instability in the microgrid and/or faulty islanding can trigger failure of the surrounding distribution systems. Monitoring microgrid-utility interaction at the point of common coupling with the utility is of utmost importance to detect anomalies and trigger appropriate protection mechanisms at the distribution substation.

Currently, installation and operation of microgrids is cost prohibitive due to expensive energy storage systems and advanced device interfaces that are needed to interact with other distributed energy resources and demand. Complex rule sets are needed for control and management of microgrid infrastructure. Every microgrid seems to have challenges specific to its application and needs. This leads to customization of each microgrid system, which is responsible for higher costs at various stages including design, installation, and commissioning. Microgrid management systems have to rely on extensive and exhaustive data aggregation coupled with complex control procedures. Unfortunately, computational methods in management of energy storage and other microgrid entities are still in development or do not exist. One of the expected advantages of microgrids is having a higher availability compared to the current electrical grid due to localized generation and storage. But lack of robust knowledge discovery techniques makes fault detection and prediction of failures of local generation, storage and power systems a challenge. In addition, high variability and intermittency of power generated from renewable energy sources that pose significant challenges for the stability of the distribution systems, also applies to microgrids.

Sustainability of microgrids will depend on a sound business model, enabling technology and regulation policies. While the technical challenges mentioned above are significant, they are surmountable in various degrees with application of existing technology in various forms. For example, technology applied to distribution system stability can be supplanted into microgrids. Autonomous state estimation methods and markov approaches can be used to diagnose the state of various devices and power systems. Multi-agent systems can be utilized to implement cooperative control or other variations of energy management systems. Intelligent economic dispatch techniques can be used to manage distributed energy resources and storage in microgrids to achieve various goals like net-zero energy or zero emission performance or minimum cost of generation, to name a few. Demand response can also be implemented among demand centers within microgrids or among microgrids. However, without active involvement of utilities, success of microgrids is in doubt. Various opportunities exist for utilities that desire to go up the proverbial "food chain." While providing uninterrupted power is one of the mandates of utilities, new value-added services can be devised for on-demand delivery of active and reactive power at various uptime and throughput levels with desirable renewable content.

Sector-based (residential/commercial/industrial) pricing currently in practice should give way to renewable content or market-based pricing. Pricing can be service-based and derived from various functions already mentioned above. Microgrids offer a low-cost option for investment deferral for upgrades. With the rise in demand and interconnection of fluctuating renewables-based generation, upgrades will be necessary to manage bidirectional power flow in distribution systems. Parts of the distribution feeder can be apportioned into smaller microgrid elements with smart inverters and energy storage systems to contain fluctuations and isolate faults. Utilities must agree on common interconnection standards, testing and certification procedures that can enable microgrid equipment suppliers to streamline processes. Distribution assets should be allowed to participate in energy markets through OpenADR and other standard methods. The aggregator business model or the ESCO model can be further evolved to create entities that can provide energy services and set the foundation for microgrid energy service providers in the distribution system.

While significant research effort is ongoing for the technical feasibility of these approaches, suitable market design and regulatory policies are necessary for the microgrid business to succeed. Ultimately, the future of sustainable microgrids depends on a design and management system that supports a robust business model reduces cost while improving the reliability of our energy infrastructure.

Source: IEEE Smart Grid

SMART GRID Bulletin March 2017

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