Microgrids have been a topic of research at the Lawrence Berkeley National Laboratory since 1996 and at the Electric Power Research Institute since at least 2000.

By Lyn Corum

The US Department of Energy (DOE), often in partnership with the California Energy Commission, has funded research on microgrids since 2000. The driver behind this activity has been the catastrophic utility-grid collapses experienced in the past decade, the resulting financial impacts on businesses, and the need to provide more reliable, energy-efficient, grid-independent power.

The US Conference of Mayors in 2006 created a small flurry of publicity when it called on cities to create energy improvement districts that would set up microgrids. Their concerns were for the businesses in cities on the East Coast, where power outages have become commonplace in the heat of summer months.

But the ongoing research indicates the mayors were a little too hasty in their demands, since advanced control and protection technologies have yet to be proved before microgrids can be widely adopted in the marketplace. Still, the City of Stamford, CT, is enthusiastically making plans to begin work on a microgrid at its city hall.

The distributed generation (DG) industry is providing the power systems for microgrids. But there is a difference between a DG installation at a factory or school and at a microgrid. If a factory is connected to the grid, the generator shuts down at the time grid power is lost. A microgrid, on the other hand, is designed to be automatically islanded when grid power is disrupted and continue generating power for the buildings or residences it serves. It then automatically synchronizes with the grid when power is restored by the local utility.

Buildings are linked through one small combined heat and power (CHP) plant that supplies electricity and heating and/or cooling to all the buildings in the microgrid. The plant may consist of reciprocating engines, fuel cells, microturbines, photovoltaic systems, or small wind turbines, either singly or in any combination. The goal is to provide the linked buildings with more reliable, less expensive, and cleaner power.

Microgrids in Test Phase
The Consortium for Electric Reliability Technology Solutions (CERTS), with funding from the California Energy Commission and the US Department of Energy, has built a microgrid test bed utilizing three 100-kW Tecogen engines running on natural gas. It is now undergoing testing in Columbus, OH, in collaboration with American Electric Power. The goal of the work is to create one aggregated system that the grid sees as a single controlled unit and that meets local needs for reliability and security.

The immediate objective of the test-bed work includes understanding the impact of DG on the grid, including achieving seamless islanding and reconnection. Other objectives include embedding all millisecond-level controls in the microgrid system along with autonomous coordination among the DG resources, protecting sensitive loads from voltage sags and outages, and providing protection techniques for inverters. A report is scheduled for publication in late 2007.

In another DOE-sponsored project, the University of South Alabama and its industry partner Radiance Technology Inc. have developed and are now evaluating the simulation of a fuel-cell-powered microgrid-connected neighborhood over a 12-month project period. The National Renewable Energy Laboratory, in partnership with GE Global Research and Rocky Research, is spending $4.2 million in a 24-month program to develop a microgrid energy-management system and demonstration in Wayne, NJ. Mitsubishi Electric is operating four microgrids in Japan and China.

There are no commercial microgrids operating in the US; a couple of projects come close, but they do not automatically isolate from or reconnect with the grid. The Colonias Project and the Mueller Energy Center, both in Texas, can be considered progenitors. Then there are the optimistic plans in Stamford, CT

Stamford’s Proposed Microgrid
Southwestern Connecticut is just 30 miles from New York City and provides an ideal location for businesses seeking to leave Gotham. A summer heat wave in 2006 forced Connecticut Light & Power (CL&P) to cut power to thousands of Stamford residents and businesses. Given this experience, the City of Stamford is taking the initiative to develop a generating facility in its government center—also known as City Hall—and intends to invite owners of other nearby buildings to hook up to the power plant.

Michael Freimuth, Stamford’s director of economic development, says the growth occurring in southwestern Connecticut is demanding more and more power. While service companies with large electrical demands have been moving into the area, residents have been acquiring electronics with monster power draws. The power demand has become huge, while no new generation has come into the state. The two utilities are now in the distribution business, having sold their generation to private companies. Moreover, building new transmission has become a problem politically due to the not-in-my-backyard syndrome.

Freimuth says the first purpose of the planned generating facility will be to provide critical city services. The emergency operating center is located in the nine-story government center, and the city cannot risk having it go down during power collapses. The building does have an emergency generator, but there is concern the outage may last long enough that the generator will run out of diesel. Furthermore, says Freimuth, the government center offers a cooling facility for seniors and others to escape the summer heat, especially during power outages, and it is critical the air-conditioning system stay operational.

The generating facility might also provide a financing mechanism: Once the microgrid is built, the city intends to sell power through long-term purchase contracts to the businesses surrounding the government center. General Electrical Capital Corp., Pitney Bowes Inc., Xerox Corp., UBS Investment Bank, and the Royal Bank of Scotland are all energy hogs, claims Freimuth. Furthermore, UBS and Royal Bank have data centers that operate 24 hours per day, so they need highly reliable power.

Likewise, hedge-fund companies and other financial institutions are moving to Stamford and out of New York City. Close by the government center, an 80-acre residential/commercial development is being planned, offering further opportunities for the microgrid. All these companies want more reliable, sustainable power either from a source not subject to power outages or as a backup to grid power. Plus they want to go green, Freimuth says.

Another advantage of the proposed project is its contribution to clean air, notes Freimuth. “We’re in a high-emissions attainment area, making it difficult to build. The combination of energy efficiency, demand-side management, renewable power, and cogeneration will produce low-emission, highly efficient power.”

However, the city—or any entity in Connecticut for that matter—must wait for the state to pass legislation establishing energy-independence districts (EIDs) before it can pitch the microgrid concept to neighboring businesses. Without an enabling law, any entity laying a power line over or under a public right of way becomes a utility. The proposed legislation failed last year and was reintroduced in 2007.

Guy Warner, owner of Pareto Energy in Stamford, is partnering with that city to create the microgrid at the government center. “We’re encouraging companies to come together,” he says.

In his vision, Warner says, the planned microgrid system would be composed of a combination of technologies that would provide 100% of the power needed by the government center. Most critically, the grid would serve as backup, says Freimuth. Energy-efficiency retrofits and demand-side management partnered with demand response or voluntary curtailment during peak periods, would reduce power needs by 20%. Another 20% of the power would be generated by sustainable resources: thermal-energy storage, fuel cells in CHP mode, and solar photovoltaics. The 60% remainder would be additional CHP in the form of gas-fired reciprocating engines. The waste heat would be used for both heating and cooling.

Photo: Xtreme Power Solutions

Once utility service arrives, the trailers can be moved to other locations.

Financing will be fairly easy, says Warner, through tax-free private equity bonds. Once the microgrid is built and operating, it could be sold to a utility—in this case CL&P—which would operate and maintain it. Warner says CL&P has been supportive of the state legislation. Furthermore, he points out, a lot of DG has been installed in the state, and CL&P has supported it.

Freimuth says the first thing to be done once the legislation passes and is signed into law is establish an EID by municipal ordinance and form a board of directors. The EID can then be marketed to the nearby companies.

The bottom line, states Freimuth, is that utility bills continue to go up yearly—10% last year, 15% this year. A microgrid would be a nifty way of controlling those bills through cost economies, he adds.

The Texas Colonias
Along the southern and southwestern borders of Texas there are concentrations of very poor Mexican-American communities known as colonias, many of which have no basic services. The State of Texas and the DOE are providing approximately $200,000 to fund a pilot project to test the ability of bringing reasonably priced electricity to 20 colonias homes. Another $200,000 will go to extend the microgrid to 100 homes. The Texas State Energy Conservation Office (SECO), along with the Texas Engineering Experiment Station (TEES), is managing the development of the prototype portable microgrid.

Xtreme Power Solutions, a Kyle, TX–based company, was awarded $2 million by the Texas Emerging Technology Fund to accelerate commercialization of its large-scale load-leveling products. One of its products—a power-storage cell—will be integrated into a package capable of many different applications.

TEES, affiliated with the Texas A&M University System, developed and designed the system for the colonias in partnership with Xtreme Power Solutions. The pilot will operate for six months at 20 homes to make sure the power system is working properly and then expand to include up to 100 homes.

Dub Taylor, director of SECO, says the colonias are located in unincorporated communities built up along the borders. Attempting to restrict and control development, the state legislature passed a law that prevents utilities from providing electricity until the communities have water and sewer services. While older colonias have electricity, the newer developments do not. Instead, residents use candles, open fires, or portable gas generators, which compromise air quality and safety.

Taylor says SECO started thinking about a solution to the issue after a congressman inquired about installing solar panels on the roofs of colonias homes. However, he notes, there was the reality that such a high-value product could walk off in the middle of the night. Taylor says SECO has worked with Xtreme Power off and on over two years, and he happened to mention the problem over lunch one day with Xtreme staff. They suggested using the storage system Xtreme Power was developing. Taylor then brought in TEES to design a clean, transportable power source for a group of homes.

Michael Breen, chief financial officer at Xtreme Power, says the company has been developing applications that include a power cell, a charger, and an inverter for six or seven years. The company is pursuing patents for these systems.

The prototype microgrid, sized at 20 kW, consists of a hybrid generator, four inverters, wind and solar systems, and up to 40 kWh of power storage, all hooked into a trailer-mounted distribution panel large enough to provide 1–2 kW for each home. The battery storage capacity of 40 kWh is capable of serving 10–20 homes.

The generator is fired by biodiesel fuel provided under contract with a local company that produces it from scrap wood. The generator and the wind and solar systems will charge the power cell, with the generator picking up when the wind and solar systems are not producing power. The 3-kW Bergey wind turbine will be on a 35-foot tower installed in the vicinity of the trailer. The 900-watt solar system, consisting of three 300-watt panels, will be mounted on adjustable racks on top of the trailer.

While there are utility distribution lines in the area, this system is not allowed to connect to them. Xtreme Power will bury new distribution lines and connect them to trailer-park stations and meters installed on each house.

Dean Schneider, manager for energy and environmental sustainability at TEES, says the power cell is 98% efficient. The trailer will be located within 1,000 feet of the houses. “We want to minimize line losses, so the efficiencies of the inverters become critical since the overall efficiency has a direct impact on cost,” explains Schneider. The goal is to provide power to each dwelling at 20 cents to 25 cents per kilowatt-hour.

Photos: Xtreme Power Solutions

Above: Power lines are installed in a trench at a colonia. Below: Power pedestals in the colonias feature 15- to 30-amp circuits.

The two renewable systems are a one-to-one offset to the biodiesel-fueled generator and will reduce its run time by two-thirds, Schneider says. The team anticipates that to keep costs down the generator will only operate between seven and eight hours, allowing the storage system to provide needed power the remainder of the day. Schneider says running a generator 24 hours per day is very expensive, and this system can reduce running time while still producing electricity continuously for the 24-hour period.

A billing system is still being worked out, but Schneider suggests one model being considered. A resident would go to Western Union or another payment center and pay for a given amount of watt-hours, and his account would be credited.

Once installed, this prototype system will allow the team to study the economic viability and determine realistic costs. Production models in the next phase, which will be installed at 100 homes in large containers rather than on trailers, are expected to be similar but will not have the test instrumentation or the wind and solar systems because of their higher costs and because they are location dependent—one can’t get wind or solar everywhere, Schneider notes.

Breen points out that once utility electrical service arrives, the trailer or production container can easily be moved to another location. This system has other applications and promises to be an ideal setup to provide electricity following disasters caused by hurricanes or floods, for example, where electricity has to be restored as soon as possible. Xtreme Power has designed smaller systems that could replace gasoline generators in remote locations. Power-cell systems in the multi-megawatt size could be installed in industrial sites for backup or supplemental power.

Mueller Energy Center
Austin Energy, an innovative municipal utility in Austin, TX, is building highly efficient small power plants on the sites of new developments. These plants may well foretell the future for many utilities—at least municipal utilities. The company recently constructed a 4.3-MW cogeneration plant adjacent to the new Dell Children’s Hospital in Austin. A second plant development is lined up for a new mall in Austin.

Austin Energy is also on the frontier of climate protection along with the city it serves. In service of the goal to reduce greenhouse gas emissions, the utility is committed to powering 100% of city facilities with renewable resources by 2012, achieving 700 MW in savings through energy efficiency and conservation by 2020, and meeting 30% of all energy needs through renewable resources by 2020, including 100 MW of solar power.

Furthermore, it will seek to achieve carbon neutrality on any new generation units through lowest-emission technologies and carbon sequestration and offsets and by establishing a carbon-dioxide cap and reduction plan for all utility emissions.

Austin Energy has been a fairly traditional utility with a mixture of coal, gas-fired, and nuclear generation and has recently added a smattering of wind and biomass generation. It serves 380,000 customers and has a peak upper load of 2,300 MW.

Larry Alford, the utility’s manager of distributed generation, describes how the Mueller Energy Center came about. Seton Healthcare Network was planning to build a children’s hospital in Austin when representatives approached Austin Energy at a DOE road show the utility sponsored on CHP and DG. Seton, a not-for-profit provider of health care services in central Texas, was interested in including a CHP plant at the hospital. In Alford’s words, “an intensive collaborative effort ensued, culminating in plans for the Mueller Energy Center.”

Now completed, the 475,000-square-foot Dell Children’s Hospital was built to serve central Texas. It was developed on 32 acres of the 700-acre Mueller Development that once constituted the Robert Mueller Municipal Airport. In partnership with the hospital and at a cost of $18 million, Austin Energy built and will own and operate the Mueller Energy Center adjacent to the hospital. Power is supplied to the hospital at prevailing electric rates. The chilled-water and steam rates were negotiated.

Equipped with a 4.3-MW gas-fired Solar Mercury turbine and a heat-recovery steam generator all operating in combined-cycle mode, plus electrical and absorption chillers and a backup emergency generator with blackstart capability, the plant is capable of providing all the hospital’s power, air conditioning, water, and steam needs. The plant will export power to the grid while supplying the hospital with its projected peak load of 2.3 MW. If the grid goes down, the emergency generator will blackstart the plant to provide power in island mode.

A chilled-water trunk line is being built for a district cooling loop to provide air conditioning to other buildings in the redevelopment area as they are built and staffed. The University of Texas is building the Dell Research Institute nearby and will connect with the chilled-water trunk line as well.

Alford says there are no current plans to provide power to other buildings, since the hospital will eventually expand. Already in the works is an MRI building that will be added to the hospital. A footprint was designed with future hospital growth in mind and allows for another turbine, additional chillers, and another emergency generator, Alford says.

Austin Energy has a similar project on the former IBM campus in Austin, where a mixed-use development called Domain is being created. It includes retail space, high-end shopping malls, offices, residences, and parks. The utility bought a chiller plant at the site, then added a CHP plant with a 4.5-MW Solar Centaur turbine and a 2,500-ton absorption chiller that is fired from the exhaust of the turbine. The plant will serve the Domain occupants. The $8.3 million project was cost-shared, with the DOE providing
$3 million.

California-based writer Lyn Corum specializes in topics related to energy and technology.

DE - September/October 2007