Microgrids: An Emerging Technology to Enhance Power System Reliability
- Written by Siddharth Suryanarayanan and Elias Kyriakides
Pilot projects are exploring the potential of microgrids to make power systems less vulnerable to costly disruptions. Yet, if the grid is to be made much more decentralized, large investments in technology and training will be needed, and standards, such as IEEE 1547.4, will have to be developed.
Catastrophes, natural or man-made, that affect critical infrastructures have a profound effect on the society. Recent ones have included the major power outage in the San Diego area in September 2011, which occurred when a 500 kV line in Arizona tripped, and which caused more than 11 million liters of sewage to spill into the Los Peñasquitos lagoon; the Japanese earthquake and tsunami that led to the Fukushima nuclear disasters in March 2011; and Hurricane Irene in August 2011, which left 7 million customers without electricity in the U.S. areas affected; and the tragic explosion at the Evangelos Florakis naval base in Cyprus in July 2011, which killed 13 and injured several dozens more, destroying at the same time the neighboring main generating station of the country. In the aftermath of such events, large portions of the centralized electricity grid are compromised, subjecting huge sections of the population to erratic supply, with prolonged and frequent power cuts and lowered electricity supply reliability.
In addition to the immediate inconveniences and costs of the outages themselves, rebuilding efforts after such disasters are hugely affected if electricity remains unpredictable. No society can recover and rebuild with efficiency when critical sources are compromised.
How can customers make themselves less vulnerable to such widespread unreliability in electricity supply? For some, part of the answer will lie in an emerging paradigm of the electricity grid known as the microgrid. This refers to a smaller electricity grid with access to all the essential assets of a larger grid such as generators, transmission lines, substations and switchgear. Today and in the immediate future, to be sure, microgrids represent a tiny fraction of power systems. Pike Research expects the total installed capacity of the world's microgrids to grow to just 4.7 GW in 2017 from 1.1 GW now. Note, however, that this estimate is based largely on North America, where microgrid planning got big boosts from the U.S. stimulus bill of 2008 and from the Department of Energy's Smart Grid Initiative. Anecdotal evidence from other parts of the world—notably the role played by Japan's Sendai microgrid following a 2011 earthquake and tsunami in the Tohoku region—suggest that microgrids already are playing a role in making electricity supplies more robust during grid crises. Specifically, the microgrid located at Tohoku Fukushi University in Sendai performed remarkably well in keeping the loads supplied when the rest of the system was compromised.
Imagine now an electricity infrastructure that is highly decentralized, with many microgrids catering to clusters of end-user loads, as opposed to one centralized generating station serving as the supply center. If, or when, a disastrous system event strikes a part of this decentralized infrastructure, then this infrastructure is inherently capable of isolating that damaged or compromised part, while keeping the rest of the system isolated from the catastrophic event. A cluster of microgrids avoids single-points-of-failures in the electricity grid, thus increasing the reliability and security of electricity supply to the end-users. The part that is compromised can then be rectified with greater help from the parts of the electricity grid that are not affected.
Wide integration of microgrids can be achieved by means of evolving control and communication systems in engineering. Besides providing greater reliability of supply, microgrids will have several other advantages, including the opportunity to integrate some "greener" but smaller-capacity electricity sources, such as photovoltaics, in the grid. Microgrids are providing the basis for new operating philosophies such as virtual power plants, where many small consumers of electricity can be aggregated to reduce consumption and sell unused electricity into the grid at times of peak demand.
But this vision also presents challenges. One is socio-economic. History suggests that fundamentally redesigning any critical infrastructure requires subsidies and government involvement. Active participation of the for-profit private business sector is also required. According to the 2012 Pike study, the worldwide market opportunity in microgrids is expected to reach US$ 17.3 billion by 2017. There will have to be heavy initial investment in information technology infrastructure, updated or novel sensing and protection technologies, and in personnel training.
So far, microgrids have been realized at the distribution voltage level, but they may be extended to higher voltage levels too, where they have the potential to comprise large fractions of power grids. With enhanced information technology to improve sensing, control and monitoring, it is easier to imagine the larger grid being sectionalized into self-sustaining microgrids whose electrical boundaries may be defined by expected levels of reliability. Thus, microgrids may evolve from being a niche application to encompass large portions of the interconnected grid.
Understandably, this vast transformation in the operation of future power systems needs to be achieved through a series of pilot projects to study and overcome technical, economic and social challenges. The United States Department of Defense, through the Smart Power Infrastructure Demonstration for Energy Reliability and Security (SPIDERS) program, is engaged in investigations on supplying various U.S. bases by means of microgrids. Europe is also investing significantly in a modernized electricity grid, for example in the context of the European Union's More MicroGrids project. Besides illuminating technical issues, such projects also will shed light on social challenges—reactions of large corporate and small residential consumers; their receptiveness to the next generation of the smart grid, and the net social benefits microgrids can yield.
Development of operating standards is crucial, if utilities are to be convinced that intentional islanding of the larger grid into microgrids during system crises is useful and non-detrimental. The IEEE 1547.4 is one such forward-looking standard.
Surveying recent disruptions from the naval base explosion in Cyprus to the September 2011 outage in the western U.S. grid, it seems evident that if electricity supplies were not so dependent on centralized power stations and assets, customers would experience greater electrical reliability. This is the promise of microgrids.