Anyone who installs a small-scale renewable-energy system typically has the opportunity to sell power back to the neighborhood utility company. But the transaction isn’t as simple as it sounds.
Electric utilities, whose business is providing bulk power at a profit rather than purchasing it piecemeal, generally resist such arrangements through unfavorable rate structures and other obstacles. Besides fearing the loss of revenue from users in their home territories, utility companies often worry about the quality of the locally produced power and the negative effects it might have on their regional grid networks.
That’s all changing, however, thanks to governmental regulations introduced in recent years that are forcing utility providers to buy distributed power that is produced in their districts.
Enter the mighty microgrid
Electrical engineers are in the process of developing optimal ways to link small-scale producers to the nationwide grid at the lowest cost. The solution to this surprisingly thorny technical problem—microgrid technology—could go a long way toward helping to modernize and stabilize the national grid, says Robert H. Lasseter, Emeritus Professor of Electrical Engineering at the University of Wisconsin, Madison.
Lasseter—the person generally credited with coining the term ‘microgrid’—describes the devices as small, smart, self-contained electrical power-distribution networks that link multiple local loads and sources.
By 2015, market research firms project that the worldwide microgrid equipment and systems market will generate more than $3 billion in annual revenue.
These microgrids, which generally have capacities under 10 megawatts (MW), can provide highly reliable power for commercial buildings, industrial facilities, residential neighborhoods, college campuses, and military bases, while retaining the ability to operate independently as “energy islands.”
What’s more, they don’t require a connection to the grid and can easily incorporate on-site renewable energy sources, such as solar panels and wind turbines, to reduce peak loads and supply power.
The U.S. Department of Energy (DOE) is currently spending $55 million to support eight microgrid projects. In addition to the U.S., microgrid research and development projects are underway in Europe, Japan, and China. By 2015, market research firms project that the worldwide microgrid equipment and systems market will generate more than $3 billion in annual revenue.
Big benefits from going small
“The benefits of microgrid technology,” Lasseter continues, “include reduced energy losses, greater efficiency, and the availability of reliable high-quality power.”
Small, local power units lower line losses—the power lost during electrical transmission over long-distance cables—by locating generation near demand, he says.
On-site power generation in the meantime often releases significant amounts of waste heat, which can be used for heating and cooling buildings, refrigeration through absorption chilling, and heating water. Such combined heat and power systems can boost overall “efficiencies from around 35 percent to as high as 85 percent,” Lasseter states, with parallel reductions in carbon dioxide greenhouse gas emissions.
“Microgrids are also good for providing high-reliability, high-quality power for enterprises that need uninterrupted power supplies,” he adds. Lasseter further notes, “You need a fast switch to protect the loads from events like power outages or voltage fluctuations.” The local power systems, via the newly “islanded” microgrid, take the power load until utility power returns.
Perhaps one of the greatest advantages of microgrids is that they can be better adapted than the central grid to meet the needs of the future. Rather than having to wait for utility companies to build capital-intensive, full-scale power plants, microgrids can enlarge the overall electricity supply rapidly and cost-effectively using relatively small local generators.
Two kinds of microgrids
Unfortunately, implementing microgrids is not so straightforward. Most vendors rely on digital computers and communications to streamline operations. Lasseter faults this approach for its reliance on external communications links, which may be unreliable.
In contrast, Lasseter is a key member of a federally supported R&D team—the Consortium for Electric Reliability Technology Solutions (CERTS)—that is developing an alternative microgrid technology that communicates significant grid changes automatically via alterations in the frequency of the power signal itself.
Many experts believe that microgrids could serve as the key building blocks for efforts to build a smart and truly flexible national grid.
If a CERTS Microgrid encounters a utility grid disturbance, it separates and isolates itself seamlessly with little or no disruption to the power quality or internal loads. When the utility grid returns to normal, the CERTS Microgrid then automatically resynchronizes and reconnects itself in an equally seamless fashion.
In addition, he continues, “Our way is plug and play. This means that a distributed energy resource unit can be placed at any point within the microgrid without re-engineering its controls.”
The CERTS project is sponsored by the DOE Office of Electricity Delivery and Energy Reliability and the California Energy Commission. Researchers taking part in the R&D effort come from four national laboratories, nine American universities, and eight company and power industry organizations.
First full microgrid test near
The first test of full CERTS Microgrid functionality is slated to start in the spring at Santa Rita Jail, an inmate facility in Dublin, California, about 40 miles east of San Francisco.
During the past decade, members of the CERTS team, in cooperation with Pacific Gas & Electric, have undertaken a series of installations and efficiency measures to transform the facility into a “green jail” with a bona fide, fully functional intelligent microgrid. These installations include a 1.2-MW rated rooftop photovoltaic system, a 1-MW molten carbonate fuel cell that incorporates a combined heat and power system, two 1.2-MW diesel generators, a 4-MW-hour lithium-ion storage battery, and a fast disconnect switch.
Many experts believe that microgrids could serve as the key building blocks for efforts to build a smart and truly flexible national grid that features two-way communications, electric vehicle charging, and the ability to reduce energy use when regional power supplies run short or electricity prices spike.
Illustration by Gavin Potenza