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In Search of Alternatives

Engineers and scientists at the National Renewable Energy Lab seek ways to wean us from fossil fuels by developing more environmentally friendly and sustainable energy sources such as solar, wind, biomass, and hydrogen

By Ken Freed

Engineers at the National Renewable Energy Laboratory (NREL) in Golden, Colorado go to work every day knowing their efforts help the world develop viable options to replace fossil fuels. "The high cost of fossil fuels is driving development of alternatives fuel sources like biomass," says John Sheehan, senior engineer at the National Bioenergy Center, based in the Alternative Fuels User Facility, one of almost 20 buildings on the main NREL campus.

At some point, alternative energy sources will become primary sources when petroleum supplies drop below the point of being cost-effective to extract from the ground, Sheehan reasons. "Some say that may happen as early as 2010, and others think it’s still 30 to 40 years away, or more. It’s hard for industry to make business decisions with that much uncertainty, but we know that eventually the oil will run out, so we need to get ready." This explains why NREL engineers push the gamut of alternative fuels seen as possible replacements for fossil fuels and offer some of the best perspective on them.

NREL was first established under the U.S. Department of Energy (DOE) in 1974 as the Solar Energy Research Institute, opening its Golden research center in 1977. The institute later became NREL in 1991 when President George H.W. Bush designated it a national laboratory, placing the facility on a par with Sandia National Laboratory and Los Alamos National Laboratory. NREL’s official mission: to develop renewable energy and energy efficiency technologies and practices, advance related science and engineering, and transfer knowledge and innovations to address the nation's energy and environmental goals.

Midwest Research Institute and Battelle manage NREL for the U.S. Department of Energy. The laboratory in Golden employs about 1100 researchers, engineers, analysts, and administrative staff and serves as the home base of visiting professionals, graduate students, interns, and leased workers. Engineers and scientists pursue 50 areas of technology investigation, including photovoltaics, wind energy, biomass-derived fuels and chemicals, energy-efficient buildings, advanced vehicles, solar manufacturing, industrial processes, solar thermal systems, hydrogen fuel cells, superconductivity, geothermal energy, distributed energy generation, and waste-to-energy technologies.

Biomass as Fuel

John Sheehan defines biomass as any plant matter, including trees, grasses, agricultural crops, or other biological material. The fibrous material can be used as a solid fuel to drive a boiler or steam turbine, or the plant matter can be converted to liquid or gaseous forms in a biomass refinery for producing electric power, heat, chemicals, or renewable fuels. NREL’s biomass research and development efforts feature four main activities: biomass sources identification and characterization, thermochemical and biochemical biomass conversion technologies, bio-based products development, and biomass process engineering and analysis.

NREL serves as the lead national laboratory of the virtual National Bioenergy Center, which supports and coordinates national biomass research activities for the Office of the Biomass Program under DOE's Office of Energy Efficiency and Renewable Energy (EERE). In this capacity, NREL collaborates with private industry, academic research institutions, and other governmental agencies to promote research, development, and commercialization of biomass technologies.

Wind Power Well on its Way

Wind power for electricity generation is already proving itself for reducing greenhouse gases, says Brian Parsons, project manager for wind applications at the NREL Wind Technology Center, based north of Golden. "If you really want to stop global warming, you need to count on wind power as one of the important alternative solutions."

Parsons addresses the economic challenges related to wind energy: "Wind power generation makes the most sense in areas with steady high-velocity winds, such as the Dakotas." For locations with less wind, because wind speeds tend to increase with altitude, mounting turbine blades on higher towers is being explored. Because the greatest demands for wind power come in less windy rural areas, NREL is cooperating with the wind industry to test and deploy low-wind-speed turbines for use at sites both on and off the electric grid. They also work with private wind technology companies to improve the overall reliability and durability of wind turbines and blades. The Wind Technology Center operates a testing facility where equipment can be stressed to the equivalent of many years of use in a short time.

Solar Energy Seeking Higher Efficiency

Meanwhile, Thomas Surek, photovoltaics (PV) program manager on the main NREL campus, says solar electricity production is moving speedily toward wide-scale, cost-effective deployment. "We’re working with leading companies in America and worldwide to improve PV cell efficiencies and lower production costs." Right now, solar energy production is adopted chiefly in secondary markets, mainly homes and businesses off the primary electricity grid. "Within five to ten years, because of the technical leadership of NREL, we expect to count the PV program as a major success story for renewable energy."

In offering an overview of NREL’s solar energy initiatives, Surek says about 80 percent of DOE funding for solar energy research and development comes to NREL directly or passes through NREL to other facilities, such as Sandia, which takes a leading role in solar systems engineering and integration. "Most solar energy companies can’t afford large research facilities of their own, so we provide DOE funds to work in partnership with the PV industry for long-term, high-risk, high-payoff research, development, and testing of PV components and systems."

NREL’s solar energy staff focuses near term on improving current technologies, particularly crystalline silicon (CS) solar cells, which represent about 90 percent of today’s market. "We work with existing solar companies to improve efficiencies and reduce the costs of CS cells," Surek says. "By extending their reliability and performance, we hope to extend the warranty on CS electricity generation products from 20 to 25 years out to 30 years or more, making them more cost-effective to deploy." An oddity in the current market, he notes, is that most of the world’s solar CS cells are manufactured by American companies, but few of these are sold and installed in the U.S. Europe, India, and China comprise the largest markets for solar cells.

Long term R&D efforts, Surek states, focus on thin-film technologies along with high-efficiency cell concentrators. Thin-film cells use materials like copper indium diselinide, cadmium telluride, and amorphous silicon. Down the road will come semiconductors made from advanced forms of carbon nitrates. "Over the past decade, these materials have been emerging from niche applications into the mainstream," especially flexible roofing tiles for commercial and residential structures. "Now industry is scaling up for mass production with a real promise for significantly lower costs than crystalline silicon, which itself has seen dramatically lower costs in recent years."

Surek pins his highest hopes on the high-efficiency cell concentrators. A CS cell today only converts a fraction of the sunlight it sees to usable electricity, dissipating the rest to heat. Because different solar cell materials respond to different frequencies of the light spectrum, researchers are learning how to stack these cells between transparent membranes so that each compound cell can become more productive. CS cells typically have an efficiency rating of 25 percent in the lab under optimal conditions, but only 12 to 15 percent in the field. By comparison, thin-film cells average 19 percent efficiency in the lab and only 7 to 10 percent in the field. Stacking these cells into a concentrator cell has increased efficiency to 37 percent in the lab and 25 percent in the field. Teams are working on increasing the efficiency beyond 40 percent.

Supporting the photovoltaic research, NREL also is engaged in concentrating solar light using parabolic trough technology. By using a parabolic reflector to increase the intensity of the light shining on a cell, the electricity output can be increased.

Apart from electricity generation, NREL is working with the industry on solar heating, seeking to lower the cost of water heating systems. Lab researchers assist companies with prototype development on new polymer systems, helping to characterize the systems’ performance with accelerated materials durability testing. This work comes through NREL's Center for Buildings and Thermal Systems, also on the Golden campus.

Hydrogen to Power Vehicles

Hydrogen fuel cell technologies will be in place by 2015 for most types of vehicles, predicts Carolyn Elam, senior project leader for hydrogen production in NREL’s Electrical and Hydrogen Technologies and Systems Center. "Reaching that target means getting the cost of fuel cells down along with lowering the cost of hydrogen production. There’s still quite a bit to be done, but the evidence from dramatic reductions in price recently and the experience from the vehicles already on the road says we can do it."

Elam says NREL chiefly focuses on development of hydrogen delivery and storage systems to prepare for the day when fuel-cell vehicles will fill American roads. Currently, only about 100 prototype hydrogen fuel cell vehicles operate in America, she notes, and fueling stations concentrate in New York, Florida, Michigan, and California. "Storage has been identified as one of the biggest challenges to the success of hydrogen fuel cells.” Toward that end, DOE will provide more than $575 million to support hydrogen storage research projects as part of President Bush’s Hydrogen Fuel Initiative. About $150 million of this will enable the formation of three Hydrogen Centers of Excellence at NREL, Los Alamos, and Sandia. Each site will integrate the expertise of its staff with experts from industry and academia.

NREL will focus on two formats of hydrogen storage, liquid cryogenic hydrogen and solid compressed hydrogen. Liquid cryogenic hydrogen poses the most problems, since it requires cold temperatures in the range of 23 degrees Kelvin and pressures in the range of 10,000 pounds per square inch. "Keeping the cold temperature without a loss of pressure is very difficult and very expensive," Elam explains. Venting problems with cold hydrogen storage not only cost money for consumers, but may pose dangers from leaking hydrogen gas. "These are some of the reasons we’re not yet seeing mass production of hydrogen vehicles." As a solution, NREL scientists and engineers will work with industry to develop solid storage materials like carbon nanotubes and metal hyrdrides that can absorb hydrogen like a sponge absorbs water.

A related question is whether hydrogen will be extracted at special industrial plants, like gasoline is now extracted from petroleum at refineries, or if the extraction technology can be simplified enough that hydrogen refueling stations will double as extraction facilities. As for whether hydrogen should be extracted from water or fossil fuels, Elam says water extraction is ultimately most desirable, but extracting hydrogen from natural gas is currently most effective, with 50 to 60 percent efficiency. Therefore, the industry will probably start with natural gas extraction and then migrate to water extraction as fast as possible. Another option is to extract hydrogen from biomass wastes, which could reduce landfill use.

We hear the pros and cons of all these forms of renewable energy every day in the press. NREL engineers and scientists are working diligently to see that they all reach their potential and take their rightful place in the assortment of energy alternatives needed to lessen our dependence on fossil fuels. "It’s amazing the advances we’re making at NREL that the general public hasn’t heard about," concludes Parsons. "We’ve made a very good start, but give us time and see what happens."

Ken Freed is a freelance writer in Denver, Colorado

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