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Microgrids: Reliable Power in a Small Package

In 1996, a sagging power line in Oregon brushed against a tree; within minutes, 12 million customers in eight states lost power. Such is the vulnerability of today's electricity grid, in which a disturbance can propagate instantly through large portions of the system.

To address this vulnerability, Environmental Energy Technologies Division (EETD) scientists are helping to develop a new approach to power generation in which a cluster of small, on-site generators serve the electricity, heating, and cooling needs of office buildings, hotels, small industrial facilities, and possibly even homes. Called a microgrid, this new approach could help slake the nation's growing thirst for electricity-predicted to jump by almost 400 gigawatts by 2025-without overburdening aging transmission lines or building the 1,000 new power plants that would be required to meet this demand. Microgrids may make statewide blackouts a thing of the past or at least ensure that service to critical equipment and facilities is maintained during outages.

"Catastrophic loss of power to all systems like the 1996 blackout should be impossible," says Chris Marnay, an EETD scientist. "If we sat down today to devise a power system from scratch, our design wouldn't resemble the one we have."

Instead of relying solely on large power plants, the nation's electricity system could meet a portion of the demand for power using small generators such as ordinary reciprocating engines, microturbines, fuel cells, and photovoltaic systems. A small network (microgrid) of these generators, each of which typically produces no more than 500 kilowatts, could power a postal sorting facility, a commercial office building, or potentially a whole grouping of customers.

Chris Marnay (left) and Ryan Firestone of Berkeley Lab's Environmental Energy Technologies Division stand in front of generators that power and heat a laboratory at BD Biosciences in San Diego CA.

Figure 1. Chris Marnay (left) and Ryan Firestone of Berkeley Lab's Environmental Energy Technologies Division stand in front of generators that power and heat a laboratory at BD Biosciences in San Diego CA. The Consortium for Electric Reliability Technology Solutions (CERTS) is studying this project as an early example of on-site power generation.

The microgrid appears to the larger power grid as if it's any other single customer. And it can quickly switch between operating on or off the larger grid; when the grid offers cheap electricity, the microgrid can purchase it, but if prices rise or there's a power failure, the microgrid can isolate itself and continue to serve its participants. It can also temporarily shed unimportant equipment such as refrigerators during power shortages, ensuring uninterrupted power to the critical computers, communications infrastructure, and control systems that drive today's economy.

"Everything is interdependent. For example, if vital communications go down, other sectors falter," Marnay says. "But if sensitive equipment is powered locally, our vulnerable, centralized power system becomes much less critical and is a less attractive terrorist target."

Microgrid Pioneers

The microgrid concept is being pioneered by the Consortium for Electric Reliability Technology Solutions (CERTS), a collaboration of national lab, university, and industry participants convened by the U.S. Department of Energy in 1999 to explore ways to improve power system reliability. The consortium, which is also supported by the California Energy Commission and centered at Berkeley Lab, is developing several innovative strategies in addition to microgrids, including managing power grids in real time. CERTS is also researching how the emerging competitive electricity market affects reliability.

CERTS will conduct the first microgrid bench test in early 2004, in which three microturbines and several end loads will be linked together at a utility-grade testing facility. If this test succeeds, it will be followed in 2005 by the first microgrid field test.

Marnay and colleagues are also developing a computer model that predicts who is most likely to adopt a microgrid and why. Their work underscores the fact that air-quality regulatory restrictions, building code constraints, and site limitations mean that some microgrids will be able to use only clean, quiet generators, instead of the natural-gas-fired reciprocating engines and microturbines being installed today.

A microgrid's many advantages will likely win fans. One selling point is the possibility of capturing waste heat to serve energy loads. Between 60 and 80 percent of the energy consumed by power plants isn't converted to electricity, or leaks away between the generator and the socket. The heat that power plants produce, unlike the electricity, is neither transportable nor easy to use locally. But in a microgrid, waste heat could feed a small, adjacent heat load such as a water heater. In a microgrid, "We'd place power generation where heat is needed, rather than where we can conveniently discard it," Marnay says.

Recovered waste heat could also cool and dehumidify buildings, using thermally activated processes. This is doubly advantageous. Cooling buildings places tremendous strain on the power grid; if a microgrid shares some of this load, it will help both the microgrid customer and everyone using the larger grid.

This leads to another selling point. Microgrids could become "model citizens" on the larger power grid, injecting power and other services into the system, rather than from it. This would lessen stress on the overall system during periods of high demand and help maintain local service quality.

This transformation will not happen overnight, but it demonstrates how microgrids-along with increased end-use energy efficiency, improved energy transmission, and use of renewable resources-can help shepherd the nation from decades of centralized power generation to a new era of decentralized, flexible, and environmentally friendly power generation.

— Dan Krotz

For more information, contact:

  • Chris Marnay
  • (510) 486-7028; fax (510) 486-7976

This research is funded by the Consortium for Electric Reliability Technology Solutions.

Dan Krotz is a writer in Berkeley Lab's Public Information Department.

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