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Pint-Sized Power Producers

Pint-Sized Power Producers

Today's microturbines are currently about 25% to 30% efficient, but by the end of 2006, their efficiency could hit 40%. a government-sponsored program is working with utilities, energy service companies, industrial manufacturers, and equipment suppliers to develop new concepts and designs.

Microturbines can help the nation move toward a new energy economy.

Good things often come in small packages. Case in point: microturbines. About the size of a refrigerator, they can generate as much as 500kW of power with virtually no emissions.

Stephen Waslo, senior project manager for the Department of Energy (DOE), envisions microturbines as the solution to America's inadequate electricity infrastructure. Like reciprocating engines, they can lessen the country's dependence on the grid by providing on-site power through distributed generation.

“We have a 10- to 15-year window where equipment like microturbines can carry us through a transition period to new energy situations and a new energy economy,” Waslo says. “As time goes on and our need for electricity grows, even peaking units that operate 300 hr a year may not be adequate. We may have to consider equipment that runs for a longer period of time.”

New technologies are currently under development to address the nation's transmission problems. Researchers have invented a lightweight transmission conductor that can double or triple a transmission line's carrying capacity without constructing new transmission towers. While it may take years for the technology to take off, microturbines are already commercially available and ready to meet the country's current power needs. About 3,000 have already been shipped worldwide.

Design Issues.

Today's microturbines are currently about 25% to 30% efficient, but by the end of 2006, their efficiency could hit 40%. The U.S. government plans to invest up to $60 million in the DOE's Advanced Microturbine Program, along with an equal amount of cost share from the industry. The program is working with utilities, energy service companies, industrial manufacturers, and equipment suppliers to develop new concepts and designs. For example, Southern California Edison has teamed up with the DOE to develop a high-efficiency hybrid fuel cell/microturbine unit (see “The Hybrid” on page 48). This market could also be fueled by President Bush's $1.2 billion Freedom Fuel initiative, which hopes to reverse America's growing dependence on foreign oil by developing the technology needed for commercially viable hydrogen-powered fuel cells. This fuel cell technology could power vehicles, homes and businesses with reduced pollution or greenhouse gases. Combined with his Cooperative Automotive Research (CAR) initiative, Bush has proposed a total of $1.7 billion for fuel cell research over the next five years.

Fuel cells and microturbines once traveled on parallel paths of development. After studying both technologies, the DOE deemed fuel cells as the more appropriate solution to power cars. Researchers then started developing microturbines for the stationary market. After years of microturbine research, the DOE expects to achieve some major milestones this year.

“We are looking at the next generation microturbine,” says Debbie Haught, DOE microturbine program manager. “It would be less costly, have lower maintenance, and retain or perhaps lessen its already low emissions profile.”

Teams of contractors are now developing innovative equipment designs, and the DOE is building and testing the prototypes. Rather than starting from scratch and shooting for 40% efficiency, the teams are focusing on the immediate goal of 35%. The DOE has already begun to test turbines in the 200kW to 300kW class with an expected efficiency of 35%, but they're not yet market-ready. In order to meet the 40% goal, manufacturers are looking at integrating new ceramics into existing microturbines so they can run at a higher temperature.

Scientists at the Oak Ridge National Laboratory, Roane County, Tenn., are also researching new materials for recuperators, which help extract heat from the hot gases produced by the unit. Without one of these large metal heat exchangers, a microturbine's efficiency would plummet to about 15% to 17%, Haught says. Recuperators, however, make up a significant percentage of the initial expense of the microturbine; manufacturers are looking at different strategies to drop the cost. Stainless steel is the current material of choice, but since it has a specific temperature limit, it's likely it won't be able to withstand the higher temperatures that come with a more efficient microturbine. As a result, the Oak Ridge scientists are studying different materials that can behave like thin foil sheets of metal yet tolerate high temperatures. By discovering new materials for the recuperators and integrating new ceramics into existing microturbines, the DOE hopes to achieve energy and cost savings.

“In general, you can reduce cost by increasing production levels or looking at the design of the individual components,” Haught says. “Looking at some of the market projections, you will get some cost reductions as more units are sold. Also, as you start to learn how they perform, you can generally find ways to reduce costs.”


Microturbines, which operate in grid-connected, stand-alone, and dual modes, often power small commercial buildings. Manufacturing plants also use microturbines to ensure reliable temperature and process control.

“Minimal investment in a microturbine can save a plant millions of dollars in lost production and lost revenues,” Waslo says. “If you are making tire cord in a polymer plant, and something happens and you lose temperature control, you can freeze up a whole furnace and lose a couple weeks of production due to downtime. In the case of a drug manufacturing plant, if you lose one batch, it could be a multi-million dollar loss.”

Another setting for microturbines is supermarkets, which have coincident electrical and thermal loads. Microturbines can generate the supermarket's baseload power and reduce the store's electrical needs by supplying chilled water to cool the refrigerated display cases. Compared to a coal-fired plant that runs at 35% efficiency with a 7% to 8% line loss, a distributed energy system like a microturbine can top 70% to 80% efficiency with no line loss in combined heating and cooling applications. Stephanie Hamilton, manager of Southern California Edison, a California utility that has tested 13 microturbines at the University of California-Irvine, says the most desirable market for microturbines is that of combined heat and power (CHP) applications. By using the excess heat generated by a microturbine, a user can drive up efficiency and drive down cost. For example, the Hilton Garden Inn in Chesterton, Ind. can warm the swimming pool and spa, provide hot water for the laundry, offer hot showers to its guests, and heat parts of the building by converting the microturbines' waste heat into energy. According to the Energy Information Administration (EIA), about 40% of a hotel's typical energy usage is used for water heating. The natural gas-powered microturbines at the Hilton Garden Inn generate 90kW of electricity, which provides a third of the hotel's electricity needs. NiSource Energy Technologies, Merrillville, Ind., installed the three microturbines in a small dedicated building that architecturally blends in with its surroundings. Robert Kramer, chief scientist for NiSource, says the microturbines even helped keep the power and heat running at the hotel when a thunderstorm knocked out power to the rest of the surrounding area.

“Normally, the three microturbines are synchronized to the grid, but on loss of grid power, they very quickly isolate from the grid and supply critical loads within the hotel,” Kramer says.

Because many chain hotels and grocery stores may have similar designs and sizes, NiSource can develop pre-packaged applications that will lower on-site engineering costs. Haught of the DOE says packaged systems will not only save time, but also build consistency.

“You don't want one person to deliver a microturbine and another person to deliver the air conditioning unit and then have someone spend a lot of engineering hours trying to figure out how to make the two work together,” Haught says.

By developing packaged systems for the hotel industry, the microturbine market could take off, she says.

“If you installed a microturbine in one Hilton and saw a benefit, you could then outfit every Hilton that made sense,” she says. “You could see how they would start to proliferate pretty fast.”

Fueling the future.

Regions of the country with high electricity rates but moderately low natural gas prices, such as California, are ideal for microturbines. By 2020, the EIA expects the use of natural gas for distributed generation to more than double. Microturbines can also burn a number of other fuels, such as waste gas, landfill gas, or propane, at high- and low-pressure levels, says Hamilton of Southern California Edison.

“Landfill gas is a free fuel or a very cheap fuel,” she says. “You are also cleaning up the emissions because otherwise the fuel would be either flared or vented to the atmosphere. As a potent greenhouse gas, it's very methane-rich.”

While landfill gas is a zero-cost fuel, it has a higher capital cost than natural gas. Unlike natural gas, which is compressed and then fed directly into a microturbine, landfill gas must first be treated through moisture removal and the extraction of other trace impurities. In the long run, however, landfill gas is a less expensive fuel for the microturbines. In California, landfill-gas fired microturbines can produce electricity for 5 to 6 cents a kWh, compared to about 8 or 9 cents a kWh for natural gas and 14 cents a kWh for grid power.

“The cost of electricity is relatively low in areas with coal-fired plants, such as the Midwest, but high in areas with natural gas-fired plants, like California,” says Jeffrey Pierce, executive vice president of SCS Energy. “With the fuel costs free, regions are separated from the natural gas price. It improves the economics.”

Creating a niche business.

SCS Engineers, an environmental engineering company, broke into the microturbine market about a year-and-a-half ago. The Long Beach, Calif.-based firm established a new division called SCS Energy to install microturbines at California landfills. Because SCS was well versed in landfill projects, the firm could more easily learn how to handle and pretreat the landfill gas for microturbine use.

“As an environmental engineering company, the microturbine market helped us merge our two lines of business together,” Pierce says. “Microturbines allowed us to expand our environmental practice to an energy practice as well.”

By using a renewable fuel to power the microturbines, SCS Energy can apply for state and federal grants, production incentives, tax credits and low-interest loans. So far, the company has secured more than $2 million in funding and now has eight microturbine installations under its belt. With a 20-year background in the power business, Pierce says could quickly adapt to the new technology. Since many of the other team members weren't familiar with power generation, however, he provided them with on-the-job training. While the manufacturers maintain the microturbine, it's up to the SCS Energy team to do the balance of the plant.

“The microturbine is like the engine in the car,” he says. “We are an assembler like General Motors as contrasted to just a guy that makes the engine. They provide the engine in the car, but we put everything else around it.”

In order to get a microturbine up and running, the company has to get interconnection approval from the local electrical utility, apply for an environmental permit and order the equipment from the manufacturer. All the steps involved in a large-scale power project are also necessary in a small installation, Pierce says.

“I think a lot of people look at the effort that's required and think that it's not worth going through the effort to complete a small project, but we've made a business of it, and it's been successful,” he says. “You really have to keep pushing every step of the way to drive a project to completion.”

From authorization to power production, a typical project takes between four to seven months to get online, Pierce says. By installing microturbines at a landfill, however, SCS Energy can help its clients reduce or nearly eliminate their electricity costs. The microturbines are tied into the utility in parallel and continuously produce on-site power to meet the landfill's needs.

“Some people buy a microturbine and use it for standby power,” he says. “Our projects all work just the opposite. Your standby power is the utility. You never have to worry about power outages caused by microturbine downtime.”

Looking ahead.

Microturbines have the potential to generate clean reliable energy, but at a cost. Right now, microturbines generally cost about $1,000/kW, which is one-tenth the price of fuel cells but double the cost of reciprocating engines.

“If you look at dollars per kilowatt in a microturbine, it seems to be pretty high, but people can afford to buy them,” Waslo says. “It's just the culture, the ability to readily adapt, combine cooling, heating and power, and deal with environmental issues, siting, and interconnection to the grid. I think once people are more comfortable with these issues, you'll see the microturbine market dramatically improve.”

Sidebar:The Hybrid

Southern California Edison has tested a groundbreaking concept that has merged two technologies. The multi-million dollar device, which has been dubbed the “Hybrid,” combines a fuel cell and a microturbine to bring about significantly higher efficiencies. Unlike microturbines, which are the size of refrigerators, the 60,000-lb unit is 30 ft long, 10 ft wide and 12 ft tall.

“It's the first of its kind,” says John Leeper, project manager for Southern California Edison. “The reason why it is so exciting is that you can achieve very high efficiencies in small sizes, which are comparable to large combined cycle plants. You are producing power in the fuel cell and then the heat from the fuel cell is powering the microturbine. The fuel cell supplants the combustor.”

Southern California Edison integrated a Siemens-Westinghouse solid oxide fuel cell with an Ingersoll-Rand microturbine in 1999. The result is a high-efficiency pressurized fuel cell with virtually no emissions.

The 200kW hybrid is a proof-of-concept demonstration and is not grid-connected. Because of its high temperature design, the machine must be run at base load 24/7. Engineers have come from around the world to visit the Hybrid, which resides at the National Fuel Cell Research Center at the University of California-Irvine. While it could someday become a commercially available technology, it's still in the early design stage.

Manufacturers, however, are now building newer versions of the Hybrid. Fuel Cell Energy teamed up with Capstone Turbine Corp. to develop the Direct Fuel Cell/Turbine technology (shown above) and is now testing two hybrid-powered power plants. The Siemens Power Generation Group has also announced plans to build two hybrid power plants for operation in Europe.

Sidebar: What is a Microturbine?

Microturbines are small combustion turbines with outputs between 25kW and 500kW. About the size of a refrigerator, they are well suited for stationary energy generation applications. Small commercial buildings, such as hotels, stores, and restaurants, can use microturbines to produce electricity and heat. They burn a wide variety of fuels like natural gas, kerosene, propane, methanol, diesel, and “waste fuels,” such as landfill and digestor gas. The main components of a microturbine include the turbine, recuperator, compressor, and electrical generator, as shown in the diagram below.

Sidebar: Microturbine Market

The microturbine market quadrupled in 2000, but experienced modest growth in 2001. Shipments of microturbines in the 30kW to 300kW range increased 15% in 2001 to 1,400 units. Industry analysts and manufacturers, however, forecasted that shipments could reach up to 5,500 units. Primen, an energy market research company, concluded that they failed to take into account the following problems when predicting the 2001 increase.

  • Higher-than-projected natural gas prices made the technology uncompetitive with grid-supplied power.

  • The end of California's power crisis slowed down the market for microturbines.

  • Utility rules, standby fees, and other tariff issues significantly raised the actual cost of deploying distributed energy systems.

  • Equipment didn't always run as advertised, and developers and vendors ran into technical problems. Honeywell Power Systems also announced that they were ceasing operations and buying back all their products in the field in August 2001.

  • Vendors and project developers failed to realize the high relative cost of project development for technologies in the 30kW to 75kW size range.

  • Energy users, expecting a decline in energy costs due to retail competition, hesitated to move to distributed generation, especially with a new technology.

Sidebar: Ins and Outs of Microturbines

While reciprocating engines have been around for many decades, fuel cells and microturbines are relatively new technologies. Here are some pros and cons of using a microturbine as a stationary application.


  • Small footprint

  • Good efficiencies, especially with cogeneration

  • Low emissions and low maintenance costs, compared with reciprocating technology

  • High-speed operation with no low-frequency vibration

  • Simple design with a minimum of moving parts

  • Fuel flexibility

  • Increased heat output for absorption chilling or other heat uses


  • Reduced power output and efficiency at higher ambient temperatures and elevation

  • High capital cost

  • Unknown equipment lifetime

Sidebar: Department of Energy's Microturbine Goals

The Department of Energy is working with Capstone Turbine Corp., General Electric, Ingersoll-Rand, Solar Turbines, and UTC to create the next generation microturbine. The DOE has the following five goals for its ultra-clean, high-efficiency microturbine designs.

  • High Efficiency — Fuel-to-electricity conversion efficiency of at least 40%

  • Environment — NOx < 7 ppm (natural gas)

  • Durability — 11,000 hr of reliable operations between major overhauls and a service life of at least 45,000 hr

  • Cost of Power — System costs < $500/kW, costs of electricity that are competitive with the alternatives, including grid, for market applications

  • Fuel Flexibility — Options for using multiple fuels like diesel, ethanol, landfill gas, and bio-fuels

TAGS: Design
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