Lawrence Berkeley National Laboratory

Research on microgrids in the U.S. has taken a somewhat different path than parallel efforts in Japan and Europe, and this distinction is often noted in international research forums. In general, reliability and power quality in North America is poor compared to other developed countries. For example, in the U.S., the average annual expected outage duration is a few hours, whereas in Japan, it is only a few minutes. Power quality problems in the U.S. are both large scale, such as the August 2003 blackout, and local, such as damaging voltage sags. Meeting the increasingly demanding requirements of a modern digital economy would then seem to offer a more daunting challenge for the U.S. than elsewhere, and certainly, concern that the existing power delivery system will prove inadequate for future gourmet requirements has been a motivating driver of U.S. research. This objective tends to translate into a desire for microgrids to seamlessly island when grid power is interrupted or its quality is inadequate, and to (also seamlessly) reconnect when normal service has been restored. In a sense, the microgrid is perceived as acting as an uninterruptible power supply (UPS), and sometimes even as a competitor to existing UPS options. Nonetheless, this difference is often over-stated, and the other threads that motivate microgrid research also exist in the U.S., e.g. the desire to expand renewable generation and the need to increase the efficiency of fossil-fired generation by the useful local application of waste heat in combined heat and power (CHP) systems, Further, over time, the differences are blurring as concerns about climate change increasingly dominate objectives worldwide. This article describes the CERTS Microgrid, which is almost certainly the best known U.S. example, and also briefly mentions some other U.S. microgrid research.