Micro is mighty
Why two grids can be better than one
Published In: Intelligent Utility Magazine May/June 2011
DON'T LET THE DIMINUTIVE NAME FOOL YOU. A MICROGRID might sound like a tiny achievement. But designing an affordable, reliable integrated power system that can seamlessly isolate from the nation's power grid during a blackout or sag--and then reconnect just as smoothly--is no small feat.
And, as is the case with any brainy and brawny idea, the microgrid concept didn't materialize overnight.
Congress, jittery about the reliability of national electricity transmission, turned to the U.S. Department of Energy (DOE) for guidance in the late 1990s. What started as a conversation about maximizing distributed generation to relieve stress on an overtaxed grid has evolved into on-the-ground applications. Proponents envision limitless industrial and commercial applications.
"We like to say we bring good ideas to life," DOE senior program manager Steve Waslo said about the government's key role in guiding technologies such as microgrids from the laboratory to the marketplace. "Our philosophy is that when a technology such as the microgrid is ready for prime time, you need to get it out there and test it. That's part of the value added by the Department of Energy."
After years of tinkering, toiling and thorough research, DOE has recently started deploying microgrid technology in school districts, universities, jails, hospitals, laboratories, military bases, industrial parks and a variety of businesses nationwide.
For instance, one California utility will begin testing what it calls a full-fledged microgrid at its corporate headquarters this spring. The Sacramento Municipal Utility District (SMUD), a longtime pioneer with advanced technologies, will be operating a 310-kilowatt baseload microgrid. It couples three 100-kilowatt (kW) reciprocating generators with a 120- ton chiller combined heat and power system and a 10 kW photovoltaic system. The project will also integrate storage technology in the form of a 500kW zinc bromine flow battery. SMUD's system is based on DOE and California Energy Commission (CEC) research and development on microgrid control technologies.
Not just any microgrid
Those initial meetings at the DOE led to the 1999 creation of a microgrid research and development team. Funding for this R&D effort, called the Consortium for Electric Reliability Technology Solutions (CERTS), came from DOE's Office of Electricity Delivery and Energy Reliability and the CEC's Public Interest Energy Research program.
The consortium drew on a list of nationwide specialists, including researchers from DOE's national laboratories and industry, and was led by Bob Lasseter, a professor of electrical engineering at the University of Wisconsin-Madison with a penchant and passion for thinking outside the box.
"We started from very modest origins and have made major contributions to the definition of the microgrid landscape," explained Joe Eto, a staff scientist with the DOE's Lawrence Berkeley Laboratory in California. "The idea was to articulate the basic concepts and then develop and put in the public domain the tools required to advance them."
Early on, these researchers coined the term "microgrid" to describe their project. Just because they had named the idea, however, didn't mean they owned it. Soon, other power system specialists were engineering their own versions of microgrids. Understandably, that prompted the consortium to christen its own unique invention as the CERTS Microgrid.
"We're not claiming to have the only way to organize or control a microgrid," Eto emphasized. "It's the idea of system integration-treating load and generation as a single, distributed system that can operate both connected and as a stand-alone electrical island-that's the umbrella under which all of this fits."
Letting shareholders kick the tires
Taking any new technology from idea to fruition can be a dicey venture. That's why DOE has an overarching strategy that emphasizes teamwork. The strategy is strong on open communication, effective partnerships and common goals.
"The Department of Energy creates strategic teams of technology owners, universities and labs really well," said Waslo, who has more than two decades of experience with the department. "Our strategy is to encourage buy-in, give all stakeholders a voice and focus on problem solving."
With the CERTS microgrid, Waslo said, utilities and other businesses needed to be at the table so they could explain how and why the research needed to be tailored to meet their specific needs. "Those stakeholders have a crystal-clear understanding of their businesses so they can optimize the technology," he said. "That makes for a more efficient use of resources."
DOE's strategy can keep research projects moving forward when they encounter inevitable hardships, such as technical or sponsorship issues or projects that just have too much risk for the private sector to tackle alone. "But the government can bring resources to bear," Waslo said. "We can keep worthwhile projects alive that might not have thrived otherwise."
Microgrid pioneer advances technology
Traditionally, connecting multiple sources of distributed generation to the grid is complicated, expensive and laborious. Not only do utilities require that each connection be separate and meet particular standards, but all distributed generation also has to be automatically shut down if the grid's voltage wavers.
How could the CERTS team overcome these obstacles? Enter microgrid pioneer Bob Lasseter. The University of Wisconsin at Madison professor took the lead in engineering a solution that allows all of the distributed generation to connect to the grid at a single point and to operate 24/7.
First, all distributed generation and local load are tied together on its own feeder using unique interface controls so it presents to the main grid what Lasseter calls a single, well-behaved energy system. In addition, newly developed automatic switching technology lets the intra-connected distributed generation and load disconnect from and reconnect to the grid without a hitch. This feature allows the microgrid to provide high levels of quality power to local loads.
"Our goal is for this to be plug and play," Lasseter said. "That way, you plug it in and it works, without a control system on top of it."
These advances let the researchers move from an economy of scale to an economy of numbers, Lasseter said, because it allows microgrid users to buy dozens of smaller machines instead of a single large one. It could also eliminate an industry's need to invest in backup generators or batteries.
"I do this because I see it as exciting," Lasseter said about his 11 years of CERTS involvement. "The way it's structured, I get to handle the technical part and think about the subjects I enjoy. That's what keeps me engaged."
Passing the ultimate test
To gain acceptance by the appropriately conservative electric utility industry, Eto and the rest of the CERTS team recognized that microgrid technologies could only be proven through demonstration at a full-scale test bed and that the most rigorous evaluations would be those conducted by an electric utility's testing staff.
CERTS was fortunate to find such a research partner in American Electric Power (AEP), one of the largest utilities in the country and one with a long history of path-breaking R&D success, such as the deployment of the nation's first 765-kV transmision lines. Once AEP expressed interest, the CEC and DOE stepped forward with funding. The investor-owned utility ran the initial round of field tests at its John E. Dolan Engineering Laboratories in Groveport, Ohio, from 2006 to 2007. The original CERTS Microgrid Test Bed featured utility inverters and engines manufactured by a company that specializes in small natural-gas-powered generators.
"We came up with the grain of the idea," Lasseter said about nurturing the CERTS Microgrid beyond the incubator stage. "Coming through that struggle, we've watched it grow to be implemented and commercialized. And today, we are seeing it almost reach a tipping point."
Other possibilities the team will be tracking include easing the integration of direct connected synchronous generation, wind, solar and other renewables and giving utilities the opportunity to meet peak needs with offpeak storage.