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A Case Study in Resilient Microgrids

A Case Study in Resilient Microgrids

To smooth the power spikes associated with seasonal fishing while decarbonizing, the city of Cordova partnered with the Department of Energy to modernize its power system.

The city of Cordova, Alaska, is sandwiched between the eastern side of the Prince William Sound and the Chugach Mountains. Despite being located on the mainland, Cordova is only accessible by plane or boat. Its isolated access means Cordova’s electricity system is fully self-sufficient, operating like an islandic state. Even with a population of just over 2,500 people, the city’s energy demands can change rapidly due to electric heating in the winter and a large demand from fishing boats in the summer. 

Looking to smooth the power spikes associated with the seasonal fishing industry while transitioning to clean energy, the Cordova Electric Cooperative partnered with U.S. Department of Energy's (DOE) national labs in 2017 under the Grid-Modernization Laboratory Consortium (GMLC) project that aims to modernize the local power system. As part of the venture, engineers built a digital twin of the system and devised a microgrid to provide stability.

The project offers field validation of technologies for resilient distribution systems. Through the $6.2-million, three-year effort—referred to as the Resilient Alaskan Distribution system Improvements using Automation, Network analysis, Control, and Energy storage or RADIANCE Project—the National Renewable Energy Laboratory (NREL) worked with the Cordova Electric Cooperative, the National Rural Electric Cooperative Association, the Pacific Northwest National Laboratory, the Idaho National Laboratory, and the Sandia National Laboratories to develop and build the Advanced Research on Integrated Energy Systems (ARIES).  

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One project objective was to help reduce the risks associated with transitioning Cordova to clean energy. Often the challenge with clean or renewable energy sources is their variability and limited dispatchability to ramp power generation quickly and at the control of grid operators. In Cordova, when fishing boats come into port to offload their catch, energy usage will spike for a few hours. Hydroelectric power plants have limited ability to accommodate this surge, which is where the diesel generation and battery storage come in.  

Before this project, diesel generators could be used to manage the load capacity of the microgrid and ramp power production quickly and easily to supplement demand peaks the hydroelectric system couldn’t accommodate due to seasonal variations in water flow. By installing batteries in Cordova’s network, the energy storage will be able to better provide power during peaks.  
 

A digital twin and prioritized usage


Cordova’s microgrid must be resilient to meet its own needs and it also must withstand several natural events including annual avalanches, freeze/thaw cycles impacting hydroelectric generation, earthquakes, tsunamis, and volcanic eruptions. The microgrid is made up of 7.8-MW hydro generation from the Humpback Creek and Power Creek hydroelectric power plants, which are fed from glacial melt and rainfall. There is also a 10.8-MW diesel generator at the Orca Power Plant, for which fuel is shipped in on large barges, and 1-MW battery energy storage.  

Researchers built a digital twin, a virtual copy of a real-world object, to better understand the energy needs of Cordova and test measures digitally before implementation. Digital twins are often used to better understand how the object operates and what it needs to stay running. The team started with a digital twin for the power distribution infrastructure, and then expanded to include the power generation systems and calibrated this against the field event data. 

“Our thought process for developing the digital twin was to define whatever we can get through physics and then try to bridge the gap between that and the actual field through some operational data,” explained Mayank Panwar, a senior research engineer in the Power Systems Engineering Center at NREL. 

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The project’s second objective was to improve resilience by dispatchability on the load side. In the North American electricity grid, two large, interconnected networks serve the western and eastern portions of Canada and the United States. Each user is connected to the grid and draws power as required. Since the grid is so large, with several power generation plants throughout, there is no need to coordinate power usage with end users to manage spikes. However, in Cordova, full cooperation from the town and all its energy users is required to maintain stability in the grid.  

“There would be a heads up from the fish cannery to let the grid operators know they were starting and then the utility would bring on the diesel generator to cover the spike in load,” Panwar said. 

Through the installation of 1,200 smart meters, operators have “the ability to connect or disconnect the loads in case the grid goes down or some impact on the grid affects the generation. They can also prioritize the loads so less critical loads can be taken off the grid and the microgrid can operate stably for the maximum amount of time,” said Panwar.

This is a challenge in any islanded microgrid such as Cordova without any external bulk grid connectivity. If the grid goes down, operators must work to bring it back online using generation resources available internally in the microgrid.  

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Cordova’s energy users are split into four groups based on priority. Group A is for critical loads and includes the hospital, electricity control room, airport, fire station, and the U.S. Coast Guard. Group B includes critical commercial loads from May to September, which then shift to group D from October to April.

Group C includes essential loads like medically sensitive residential, and group D includes flexible residential and commercial loads. Under extreme events where load shedding is required, the smart meters allow operators to disconnect noncritical loads to stabilize the grid and bring those users back online systematically to prevent another surge.  

Throughout the RADIANCE Project, the city of Cordova appointed a board comprised of community representatives that is responsible for reviewing and providing input prior to implementation of any improvement measures. The Cordova Electric Cooperative, owned by the people of Cordova, has invested in community engagement to ensure the updates to the microgrid are in the best interest of the community and improve the resilience of their power generation needs. 

Nicole Imeson is an engineer and writer in Calgary, Alberta.  

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