Jeffrey Perkins and Allison Donnelly, ERS
The DOE's definition of a microgrid is 'A group of interconnected loads and distributed energy resources (DER) with clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid [and can] connect and disconnect from the grid to enable it to operate in both grid-connected or island mode.' The concept is not new – originally, microgrids were used for locations that were too remote to connect to the national grid. A later development was to use microgrids to keep portions of the grid running during power outages. Even if its neighbors were out of power, a customer on a microgrid could disconnect or 'island' itself from the larger grid and generate enough power for some of its critical functions. For this reason, university campuses, large hospital complexes, and military installations were early adopters of the technology. While the high cost of owning, operating, and maintaining a microgrid has limited the interest in and growth of the market today, companies that manufacture key equipment for the grid are working to make the development of microgrids more accessible.
At 10:00 p.m. on Thursday, September 21, 1989, Hurricane Hugo made landfall along the South Carolina coast. The category 4 storm was estimated to be 600 miles in diameter and the storm surge was over 20 feet at its worst. By early Friday the storm center had left South Carolina and was diminishing in intensity just west of Charlotte, North Carolina. At the time, Hugo was the second-strongest hurricane to hit the East Coast north of Florida and was the strongest hurricane on record to make landfall in South Carolina. There had been extensive preparation in coastal areas, including evacuations of the barrier islands, which kept loss of life to a minimum. However, since a storm of this intensity had not been seen in that region, especially inland, the local infrastructure was not ready to handle it. By daybreak that Friday the impact on the electric grid was abundantly clear: In South Carolina there was no power east of Interstate 95. One utility had 400 transmission towers and 5,000 poles down, 570 miles of transmission lines destroyed, and 1,200 transformers damaged. Another experienced 1,670 miles of transmission lines out of service with 905 poles damaged, 709 poles in need of replacement, and 382 damaged transmission towers.
In the weeks that followed, the region began the long process of recovery and evaluation of what happened. As reports were written, one theme was clear: resiliency, or the ability of the grid to bounce back quickly after a major disturbance, was a problem. While reports lauded the efforts of the utility crews in rebuilding, there were a few key takeaways of relevance: 1) The ability to generate power with some form of distributed generation was of tremendous value. For example, only one radio station in the region stayed on the air in the aftermath and that was due to their
- The ability to generate power with some form of distributed generation was of tremendous value. For example, only one radio station in the region stayed on the air in the aftermath and that was due to their back-up generator.
- With hundreds of thousands of customers without power, independent power producers – consisting mainly of small, distributed generation units that were fairly new to the scene in 1989 – were the first to be able to reconnect to the grid, and customers proximate to them were among the first to receive power.
- For these and other reasons, the value of having some form of 'sub-networks' was mentioned repeatedly in the weeks and months that followed.
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