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Microgrids: Come “island” with me

2012 March 27

Santa Rita Jail microgrid

Microgrid technology is an attractive way for military bases, schools, jails, and other electricity customers to pursue energy efficiency and clean energy in tandem. One of the most unique functions of microgrids is their ability to island, or operate autonomously and separated from the larger macrogrid. This function was critical for the Sendai microgrid, when the devastating earthquake hit Japan in March 2011. The Sendai microgrid was able to continue providing reliable power to a number of loads, including a hospital, for two days while the larger macrogrid had halted power supply amidst the disaster aftermath.

Indeed, the official U.S. Department of Energy definition of microgrids emphasizes the importance of islanding functionality, saying: “[a microgrid is] a group of interconnected loads and distributed energy resources within 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.”

On March 22 this year, a local microgrid project officially launched at the Santa Rita Jail in Dublin, just 30 miles east of Berkeley. Power reliability is a primary concern for the jail, which houses about 4,000 inmates. Over the past ten years, the project has slowly been coming to fruition as various power supply technologies and energy efficiency measures have been installed and implemented. The jail has over 1 megawatt of installed solar PV capacity, featuring both rooftop installations and ground-mounted tracking installations.

The jail also has a fuel cell and two back-up diesel generators, and its most recent addition was a 2 megawatt battery. The combination of these technologies allows the jail to significantly reduce its daily purchases from the macrogrid (saving the jail about $100,000 a year) and to operate as an island in the event of a power supply disruption. A switch detects when no voltage is coming from the macrogrid and immediately disconnects the jail from the grid. Simultaneously, microgrid controls and software allow the jail’s suite of backup supply and storage technologies to provide uninterrupted full power to the jail. The jail consulted with Lawrence Berkeley Lab (LBL) a number of times throughout the development of the microgrid, using the lab’s DER-CAM (Distributed Energy Resources-Customer Adoption Model) software to analyze electricity and heat requirements and develop a plan for the jail to meet its needs at minimum cost.

Chief engineer for the Sendai project, Keiichi Hirose of NTT Facilities, visited LBL on March 23 to give a talk on the microgrid development to date and operation during the earthquake period. Their microgrid project features a fuel cell, solar PV, batteries, and two natural gas-fired microturbines for a total peak output of 1 megawatt.

Microgrid in Sendai, Japan

Both the Sendai and Santa Rita microgrid projects benefited from public funding, which helped to get these unique, groundbreaking projects built. The Sendai project received funds from Japan’s New Energy and Industrial Technology Development Organization, and the Santa Rita project received funds from the Department of Energy and California Energy Commission. Indeed, microgrid investment costs are still relatively for many commercial building customers. However, customers with high reliability demands, such as military bases and tactical operations centers, are actively pursuing microgrid solutions (such as the SPIDERS project). As successful experiences accumulate and costs come down for a number of the supply and storage technologies involved, opportunities for other customer applications will arise. Maybe, one day, we’ll all be on the island.

Also trying out NextGEN gallery plug in to show some more photos from my visit to Santa Rita microgrid. The only problem is lack of captions… Click on the photo to show the next one or else they will change automatically.

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