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DOE Pulse
  • Number 371  |
  • September 10, 2012

Microgrids: So much more than backup energy

There are two prongs to the microgrid work at NREL: innovative research and partnering with industry. Credit: Dennis Schroeder

There are two prongs to the microgrid work
at NREL: innovative research and partnering
with industry. Credit: Dennis Schroeder

Most Americans don't have to think much about energy reliability. We plug in a computer and it powers up; we flip a switch and the lights come on.

While very reliable today, the U.S. electricity grid is old and has gone at least five decades without a significant technological upgrade. DOE's National Renewable Energy Laboratory (NREL) is working with industry on one solution to help maintain a secure, reliable flow of energy: microgrids.

A microgrid is a smaller power grid that can operate either by itself or connected to a larger utility grid. Microgrids can serve areas as small as a few houses, all the way up to large military installations.

"If your home was part of a microgrid, you could continue to receive power even when the utility power goes out," NREL Electrical Engineer Mariko Shirazi said. "It gives you the ability to ride through any disturbances or outages by seamlessly switching over to locally generated power."

A microgrid senses the quality of the power flowing through the grid. In the event of an outage, it can disconnect from the grid at a moment's notice. It can also leverage solar, wind, or stored energy to supplement a dip in the current power supply. If things are running smoothly with the regional grid, a microgrid generating electricity from renewable sources can export that clean energy to the grid for everyone's use.

The major components of a microgrid include a source of power generation, local loads, and electrical switching gear. It might also include inverters and energy storage — all of which sounds easy enough to just connect up to get started, right?

"These technologies are in different stages of maturity; the challenge is to get them all to operate together in a stable, concerted way to accomplish the goals of efficiency, security, and energy reliability — all of which are required from a microgrid," NREL Electrical Engineer Greg Martin said.

NREL works with industry to test microgrid systems by providing the experts as well as the infrastructure to support microgrid testing. The U.S. Department of Defense is also working with NREL researchers to examine using microgrids to improve base reliability. Testing includes using grid simulators, load banks, and generators, all currently at the Distributed Energy Resources Test Facility at the National Wind Technology Center near Boulder, Colorado.

"We use equipment such as a grid simulator to create a virtual electric grid to test equipment that is planned to be connected to a utility," Martin said. "We create outages, or some other kind of electrical phenomenon, to make sure the equipment operates as expected. We basically try to make stuff work while making sure it works the way it's supposed to."

NREL is leading the way in understanding issues in energy systems integration and helping industry work through them. The lab's research tools will get a boost when the Energy Systems Integration Facility (ESIF) is completed later this year.

“ESIF is going to be like our current lab on steroids, and will expand our testing scale to 1 megawatt," Martin said. "We'll be able to test large single components like large utility-scale inverters. We'll also be able to scale up the complexity of our testing. Using the Research Electrical Distribution Bus [REDB], and hardware-in-the loop, we'll be able to connect dozens of sources and loads and be able to test their interactions with each other. Now, we collect single data points. At ESIF, we'll be able to collect high-speed, time-synchronized data at numerous points throughout the REDB."

Using a high-performance computing data center, NREL will be able to simulate entire distribution systems. When testing a microgrid system, engineers can monitor its voltages and frequencies at the point where it joins the distribution system, enabling them to simulate the effect of a microgrid on the larger utility. This is important, because being physically connected to the grid is often not practical — plus, the utility doesn't have to worry about putting an unproven technology on their system.

"ESIF is going to give us more research power, both in the actual electrical power but also in the ability to collect data across all points in the system," Martin said. "It will also offer really awesome visualization that will enable us to look at data coming in from different places, to look at simulations and video feeds, in a really nice, easy, big way. We're sure this visualization capability will help ignite collaborations among NREL, industry, utilities, academia, and government agencies."

Learn more about NREL's Energy Systems Integration testing facilities.

Submitted by DOE’s National Renewable Energy Laboratory