Alternative Energy Technologies

Transcription

1 Alternative Energy Technologies James L. Kolar Technologies that remove carbon dioxide from the atmosphere and produce energy without reliance on fossil fuels can play a significant role in sustainably meeting our energy needs John Wiley & Sons, Inc. In last quarter s issue of Environmental Quality Management, I offered some thoughts on how integrating renewable and nonrenewable energy sources could help us meet our energy needs while also reducing emissions of greenhouse gases. In this issue, I follow up with a discussion of several alternative energy technologies that can further these goals. I open with a brief discussion of carbon sequestration, which can help reduce the amount of greenhouse gases in the atmosphere. I then discuss several alternative energy-producing technologies that can help reduce our reliance on traditional fossil fuels such as coal and petroleum. CARBON SEQUESTRATION TO REDUCE GREENHOUSE GASES In 1997, the world s average temperature was the highest since record keeping began in That same year, nearly 80 million more people were added to the world s population. It is believed that the increase in global temperatures can be attributed to a buildup of carbon dioxide and other greenhouse gases in the atmosphere. These gases are generated in large part from the use of carbon-based fuels, such as coal. When these fuels are burned, carbon is converted to carbon monoxide, carbon dioxide, methane, and other hydrocarbons. (Carbon conversions for fossil fuel power plants have an average of 95 to 99 percent efficiencies. 1 ) In response to the increase in global temperatures, the world s nations adopted the Kyoto climate change treaty, which requires the United States to reduce its carbon dioxide (CO 2 ) emissions to 7 percent below 1990 levels by no later than In a series of papers released in 1998, the National Renewable Energy Laboratory (NREL) states that the United States might have to spend over $770 billion to reduce greenhouse gases to this level. Jerry Taylor, director of natural resource studies at the Cato Institute, states that the terms of the Kyoto treaty, if adhered to, would reduce global warming by only 0.18 centigrade which, he argues, is not much bang for the global warming buck John Wiley & Sons, Inc. ENVIRONMENTAL QUALITY MANAGEMENT / Winter 2000 / 45

2 There are two types of carbon sequestration: Capturing carbon dioxide from power plants and other combustion sources is called associated sequestration. Many other scientists argue that the targets established by the Kyoto treaty are far below what is necessary to arrest climate change. By contrast, Linda Baker, in her publication entitled Feeling the Heat: Can the Global Warming Agreement Be Saved?, argues that, given the accelerated rate at which countries are currently producing greenhouse gases, the United States. will actually end up reducing emissions by 35 percent below what would have been accomplished without the Kyoto treaty. Still other experts, including some from the U.S. Department of Energy s Fossil Energy Division, believe that a strong partnership must exist between alternative energy and the technological processes known as carbon sequestering. There are two types of carbon sequestration: Capturing carbon dioxide from power plants and other combustion sources is called associated sequestration. Removing carbon dioxide from the atmosphere regardless of where it originates is called unassociated sequestration. 2 Both types of sequestration will probably be necessary for effective longterm global greenhouse gas control. Other alternative measures including increasing energy supply and enduse efficiency, switching from coal and oil to natural gas where possible, reforestation, and the creation of affordable alternative energy technologies are also important measures. 3 However, a long-term solution to climate change is probably not possible without the use of carbon dioxide capture and sequestration technologies. Capturing Carbon Dioxide: Key Issues Since the early 1970s, air emissions control technology has been available to capture sulfur dioxide (SO 2 ) and particulate matter from fossil fuel power plants. 4 Why not apply carbon dioxide capturing technologies to these same power plants? The answer is that today s carbon dioxide control is extremely expensive and energy intensive; as much as 100 megawatts from a typical 500-megawatt power plant would have to be used for today s CO 2 capturing process. This 20 percent energy requirement would simply not be affordable for most electric customers. However, it may be possible to reduce the energy requirement from 20 to 15 percent if more effective solvents, such as monoethanolamine (MEA), can be used in the process, and if a better integration of carbon dioxide capturing can be applied to existing power plant design. 5 Coal-burning power plants may not be the only source for CO 2 capture technologies. A typical natural gas field contains up to 20 percent CO 2 by volume, most of which must be removed to produce pipeline-quality gas. Refineries for crude oil, along with iron, steel, and petrochemical plants, also are candidates for CO 2 capture. 6 Carbon Dioxide Storage Techniques There are actually four potential CO 2 sequestration methods available: Deep ocean sinks, whereby CO 2 could be piped or injected into deep oceanic waters for up to 1,000 years. Oceans represent the largest potential sink for CO 2 produced by human activities. Oceans already contain an estimated 140,000 billion tons of CO 2. 7 Deep aquifers, including coal seams, where injected CO 2 adheres to the surface of coal. Methane (CH 4 ) could be recovered in a second capturing process. Depleted gas reservoirs are the most promising technology for CO 2 sequestering since the geologic integrity of gas reserves already contains hydrocarbon gases. Depleted oil reservoirs are also feasible since CO 2 is already being inject- 46 / Winter 2000 / ENVIRONMENTAL QUALITY MANAGEMENT James L. Kolar

3 Exhibit 1. Worldwide CO 2 Storage Potential* Deep Ocean Deep Aquifers Depleted Gas Reservoirs Depleted Oil Reservoirs 5,100 to 100,000 billion tons 320 to 10,000 billion tons 500 to 1,100 billion tons 50 to 700 billion tons *Since the world produces about 22 billion tons of CO2 annually from all energy production, including 5 to 6 billion tons from fossil fuels, the potential storage capacities listed here would be more than adequate. ed into oil reserves to enhance oil recovery. The Department of Energy proposes a trading system whereby CO 2 from power plants, once captured, could be used in the oil recovery industry. 8 Exhibit 1 lists the long-term storage potential of the four sequestration methods. BIOENERGY TECHNOLOGY Bioenergy is emerging as an increasingly promising means of displacing carbon dioxide emissions from fossil fuels. Bioenergy sources, including biomass fuels such as wood, have been valuable and renewable energy sources for many centuries. Wood wastes and even cow dung have been used for heating and cooking since the discovery of fire. Biomass refers to any organic product derived from plants. This can include trees, crops, wood by-products, and even paper. It is the only renewable energy resource that can be converted to liquid fuels. Biomass currently accounts for about 14 percent of the world s energy use and about 35 percent of the energy used in developing countries. 9 A paper authored by L.L. Wright and edited by Frances Sterrett entitled The Biomass Resource Potential of Energy Crops has shown that about 160 million hectares (at acres/hectare) of the 170 million hectares of cropland in the contiguous U.S. states are capable of producing energy crops (e.g., sorghum, alfalfa, kenaf, and corn). Additional data indicate that by 2030, as much as 52 million hectares of cropland may be idled, and as much as 30 million hectares may be permanently removed from crop production, half of which could be used for short rotation woody crops (SRWC) such as farmgrown hybrid poplar trees for the pulp and paper industry. 10 Assuming crop yields were high, bioenergy could displace 6 to 20 percent of U.S. greenhouse gases from burning fossil fuels. In a publication entitled Strategies for Using Trees to Minimize Net Emissions of CO 2 to the Atmosphere, Gregg Marland contends that, in terms of atmospheric CO 2, a tree performs equivalently whether it stores carbon or its conversion to CO 2 displaces some other source of CO 2 that would otherwise be released. Thus, there is actually no difference in atmospheric CO 2 if coal is burned and trees are saved, or if trees are burned and coal is saved. 11 Marland offers an interesting calculation: U.S. emissions of CO 2 from fossil fuels amounted to about 1.3 billion tons of carbon in If we divide this number by the average annual rate at which forests in the contiguous U.S. states sequester carbon, the result is about 1.2 Alternative Energy Technologies ENVIRONMENTAL QUALITY MANAGEMENT / Winter 2000 / 47

4 Fast-growing crops such as SRWC rapidly deplete soil nutrients, requiring added fertilizer and pesticide applications. tons of carbon per hectare per year. 12 Marland hypothesizes that it would take 1.1 billion hectares of forest to sequester all the carbon we discharge from fossil fuels per year. The evidence of increased carbon dioxide sequestering by biomass is significant. Yet high biomass operational cost, coupled with difficult environmental issues (discussed in the next section), have kept biomass energy from receiving the attention it deserves. Bioenergy Disadvantages Biomass could realistically provide as much as 11 percent of U.S. energy. However, serious environmental and cost issues necessitate further benefit/cost and risk analysis. Cost Because transporting and processing biomass crops and trees for power plant use is expensive, biomass energy currently costs as much as $.08 per kwh to produce. Biomass will not receive more attention until costs can be reduced to around $.04 to $.06 per kwh, thus making biomass competitive with coal. 13 The current high production costs limit biomass s net energy yield to only about 5 percent of U.S. energy needs. Overall, biomass costs are much higher than those associated with burning fossil fuels. Soil Erosion and Pollutant Runoff Soil erosion, which is caused in part by reductions in organic matter and fine clays, results in less plantholding capacity. Such erosion diminishes the productivity of agricultural land and is a serious threat to U.S. and world crop production. 14 Average soil loss from U.S. crop lands currently is estimated to range from 11 to 20 tons per hectare per year. Soil is being replaced at a rate of only 0.5 to 2 tons per hectare per year. 15 Biomass energy production can be expected to exacerbate soil erosion. Losses have been found to be greater from sweetgum, including significant nutrient losses in runoff and subsurface water. 16 Fast-growing crops such as SRWC rapidly deplete soil nutrients, requiring added fertilizer and pesticide applications. Assuming an average pesticide consumption of 2.0 to 3.5 kg per hectare for corn and sorghum biofuel production would result in the use of 31 kg of pesticide per capita per year, or a total exceeding 8 million tons. This is almost 20 times the current use of pesticides in the United States 17 Fertilizers and pesticides contaminate water runoff from cropland, endangering both surface and groundwater resources. Air Emissions According to the Department of Energy, combustion air emissions from wood biofuel can be two to three orders of magnitude higher, on a unit energy basis, than emissions from gas and oil. In addition, wood burning releases up to 14 carcinogens, as well as particulate matter, CO, and NO x. Moreover, the net conversion efficiency of biomass-to-energy is not consistent. It can range from 5 to 80 percent, depending on the boiler design. Bioenergy Advantages Use in Developing Countries As the discussion above indicates, the advantages of biomass as a sustainable alternative fuel are limited. Yet developing countries (e.g., China) can and do benefit. In addition to using available wood to supplement costly and sometimes unavailable coal and oil, many developing countries depend on it for both heat and cooking fuel. Wood chips, bark, and scrap wood are also being used as fuel in electrical energy generation. 48 / Winter 2000 / ENVIRONMENTAL QUALITY MANAGEMENT James L. Kolar

5 Exhibit 2. Bioenergy Crop Acres that Could Be Planted in SRWC and Switchgrass Time Frame Acres/Year Cumulative Acres , , ,000 1,500, ,000 3,000, ,000 5,500,000 Carbon Offset Potential Short rotation woody crops have been found to be the most effective feedstock supply offering the greatest carbon reduction potential. In addition, highefficiency biomass-to-electricity systems have been found to be the conversion technology offering the greatest carbon reduction. If these technologies, such as whole-tree burning, could achieve a linear rate, U.S. carbon emission reductions could progress at about 0.6 percent per year over the next 35 years. 18 Availability of Biofuel Sources The United States has excess crop production capacity, a luxury that many developing countries do not have. In recent years, 50 to 60 million acres of U.S. croplands have been removed from production annually, either for conservation reasons or for supply control. 19 It is reasonable to assume that several million acres could be made available for production of bioenergy crops (e.g., hybrid poplar). Exhibit 2 describes the number of acres of SRWC and switchgrass that could potentially be planted each year, and the cumulative total acres at the end of each time period. Dedicated biomass crops (such as SRWC) for biofuels including ethanol, methanol, and biodiesel fuel from soybean oil when grown on nutrientdepleted agricultural lands, offer the most environmentally beneficial and largest resource for displacing fossil fuels. When used in combination with coal or oil as fuel supplements, biofuels offer the maximum carbon reduction benefit. However, with current power plant technology, achieving a 3 percent reduction in carbon levels would require converting 25,000 Mwe of coal-fired electric power production to biomass power at a conversion efficiency of 33 percent or better. 20 Most biomass technologies are simply not yet affordable when compared to coal and oil. FUEL CELLS Daimler-Chrysler, Ford, General Motors, and Toyota have all announced that they are developing prototype fuel cells to power vehicles. Exhibit 3 describes the lower air emission advantages of a current fuel-cell prototype over fossil-fuel power plants. 21 According to Daimler-Chrysler, its new fuel-cell system has a reforming unit that can easily strip pure hydrogen from any hydrocarbon fuel. 22 With its fuel cell, an on-board fuel processor converts gasoline to hydrogen, carbon dioxide, and water. The hydrogen is used in the fuel cell to make electricity for powering the vehicle. The hydrogen production process begins with a fuel vaporizer that heats the gasoline, converting it from a liquid to a gas. The vaporized gasoline is then processed in a partial oxidation reactor (essentially a metal canister and spark plug). By restricting the air intake, both hydrogen and carbon monoxide are Alternative Energy Technologies ENVIRONMENTAL QUALITY MANAGEMENT / Winter 2000 / 49

6 produced and sulfur in the gasoline is converted into hydrogen sulfide gas. 23 One problem associated with this technology is that carbon monoxide, a byproduct of combustion, contaminates proton exchange membrane (PEM) fuel cells, and along with hydrogen sulfide must be eliminated. In addition, the ongoing problem of how to strip pure hydrogen from hydrocarbon fuels with a reforming technology may or may not be solved. Another technology using molten carbonate fuel cells would seem to have a market in certain applications, such as using hydrogen-rich gas streams from biomass. 24 Little is currently known about PEM vehicle fuel cells, except that they will operate for the 3,000-plus hours required over the 10-year average life of a vehicle. Some results are available using a 250-kW fuel-cell power station with an operating efficiency of 34 percent and target efficiency of 40 percent. 25 Clearly, the technology for alternative energy fuel cells is available. But (at least until very recently) their price was as high as $2 million per unit, making them uncompetitive with nonrenewable energy sources. These costs are now declining. PHOTOVOLTAIC ENERGY SYSTEMS Although invented by Bell Labs in 1954, photovoltaics (PV) have achieved their most notable development and advances as a result of the U.S. space program, from the early Vanguard satellites to today s space shuttle. The basic power of a PV system is the solar cell. Today, a typical crystalline silicon cell is about 100 square centimeters in area. When sunlight strikes the solar cell, it frees electric charge carriers within the cell. These electric charges are separated by an internal voltage, producing an electric current. A metal contact grid on the surface of the cell enables current to flow through an external circuit to produce approximately 1 watt of electric power. 26 Some of the current uses for photovoltaics include wristwatches, calculators, televisions, radios, battery chargers, automobile sunroofs, and swimming pool heating systems. The most obvious environmental advantage of photovoltaics is that they create no air pollution. The main disadvantage is the cost per unit. A residential-sized system costs approximately $18,000, although this is expected to drop to about $4,100 by The current photovoltaic costs of $.17 to $.18 per kwh are expected to decline to about $.10 per kwh within the next few years, 27 and to $.04 per kwh by Most experts agree that successfully using photovoltaics as an alternative energy source will depend on improved efficiencies. They disagree on which of the many promising PV technologies will succeed. Exhibit 3. Fuel Cell versus Power Plant Emissions* Contaminant Utility Emissions (lbs. /Mwh) Fuel Cell (lbs. /Mwh) Oxides of Nitrogen (NOx) Carbon Monoxide (CO) Sulfur Dioxide (SO2 ) Particulates (PM10) Carbon Dioxide (CO2) (lbs./kwh) * Power plant emissions were obtained from actual emission test reports. 50 / Winter 2000 / ENVIRONMENTAL QUALITY MANAGEMENT James L. Kolar

7 Regardless of which technology wins out, the cost of energy from photovoltaics remains higher than for most alternatives. In order to succeed, it will be necessary to drive up production and expand markets through aggressive marketing and commercialization. GEOTHERMAL POWER Geothermal power is the only renewable energy that does not rely on direct or converted solar energy. All applications of geothermal energy draw on hydrothermal reservoirs, large pools of water trapped in underground rock and heated by the earth s core. Hydrothermal reservoirs are located from 100 meters to several kilometers below the earth s surface, where the temperatures can be as high as 400 C. The reservoirs are tapped for their energy by geothermal heat pumps, with small power plants converting the hot fluids to electricity and then reinjecting the cooler water back into the reservoir. (Geothermal should not be confused with solar thermal power, which uses solar towers for electrical generators.) Geothermal power production in 1993 was estimated to be 7,000 megawatts. In the near future, it is expected to grow to nearly 15,000 megawatts. It is particularly important in Japan, China, and Hungary, which today have a combined capacity of 11,730 megawatts of geothermal power. 29 The main barrier to further development of geothermal power is economics; costs are not expected to fall as dramatically as those of solar or wind power. The U.S. Department of Energy suggests, however, that hot dry rock technology, which utilizes encrusted lava rock, could make geothermal more affordable because it offers lower drilling and well completion costs. This approach potentially could provide more than 2.3 million megawatts of energy for 200 years at $.05 to $.06 per kwh. 30 WIND POWER Wind power is still only a minimal provider of energy. Its current cost of $.06 or more per kwh cannot compete with the coal and petroleum prices of $.05 per kwh that we saw during the 1990s. However, recent petroleum cost increases, if sustained, could make wind power more affordable. 31 In addition, the cost of wind power has decreased substantially. According to the U.S. Department of Energy, in 1980 electricity from wind power cost consumers $0.35 per kwh; thus, current prices represent a drop of well over 80 percent. 32 Wind power offers significant environmental benefits. Every billion kw hours of electricity produced from wind instead of fossil fuels offsets nearly 6 million pounds of air pollutants and a billion pounds of carbon dioxide. Smog-related problems from urban areas could be reduced significantly by adding wind power plants to their primary energy mix. There currently are sizable wind farm projects operating in California, Iowa, Maine, Minnesota, Montana, New York, Wisconsin, and Wyoming. The largest of these projects is located in southwestern Minnesota, where 143 wind turbines operated by Northern States Power Company (NSP) generate 107 megawatts of electricity for 40,000 residential customers. This project was undertaken largely in response to a 1993 mandate by the state legislature, which required NSP to produce 425 megawatts of wind-powered electricity and 125 megawatts of biomass power by CONCLUSION The United States continues to depend primarily on fossil fuels such as coal and petroleum to meet our energy needs. These sources still account for 60 percent of the energy consumed in the United States. Wind power is still only a minimal provider of energy. Alternative Energy Technologies ENVIRONMENTAL QUALITY MANAGEMENT / Winter 2000 / 51

8 While this dependence on fossil fuels has as yet shown few signs of decline, there is little doubt that the 1997 Kyoto Treaty has created a more favorable climate for alternative energy sources worldwide by emphasizing the need to reduce greenhouse gas emissions to curb global climate change. Thus far, U.S. policies for lowering greenhouse gas emissions have stressed only energy efficiency and conservation. Other options are clearly available, however. Carbon sequestration and additional tree planting can effectively reduce carbon dioxide in the atmosphere. Also deserving of attention are market-based strategies such as carbon taxes, emissions trading, promoting of alternative energy sources, and use of less carbon-intensive fossil fuels. Alternative energy technologies have the proven ability to offset increasing emissions of carbon dioxide and other greenhouse gases. For any of these alternatives to achieve importance, however, there must be supportive government policy. Congress must increase and sustain funding for development of these energy sources. The burden of providing government funding for alternative energy technology does not have to be placed solely on the taxpayer. Major funding offsets are now being established through partnerships with utility companies, builders, private investors, state government agencies, and cities. Currently, the highest profile alternative energy program in the United States is the Million Solar Roofs Program, which was launched in Modeled after similar initiatives in Japan and Europe, the U.S. program aims to install one million rooftop PV systems by Alternative energy sources, if made affordable and used in combination with carbon sequestration technologies, can provide major and sustainable environmental benefits. When properly integrated with our existing fossil fuel-based system, they can also be a major contributor to this country s overall energy management program. NOTES 1. Joyce, J. (1998). Carbon conversion (CREST paper). 2. U.S. Department of Energy, Fossil Energy Division. (1997). Series of reports entitled Global Climate Change, Sequestering Carbon. 3. Id. 4. Scrubber control systems and fabric filter baghouse technology are used in power plants worldwide. 5. Incorporating carbon dioxide capturing into existing power plants is important since the number of new plant construction proposals is continuing to decline, in part because of stringent federal Clean Air Act requirements. 6. U.S. Department of Energy, Fossil Energy Division. (1997). Series of reports entitled Global Climate Change, Sequestering Carbon. 7. U.S. Department of Energy, Fossil Energy Division. (1997). Ocean sequestration technology. 8. Id. 9. Wright, L.L. (1995). The biomass resource potential of energy crops. In F. Sterrett (Ed.), Alternative fuels and the environment. 10. Id. 11. Marland, G. (1993). Strategies for using trees to minimize net emissions of CO2 to the atmosphere. 12. Id. 13. Virginia Tolbert of Oak Ridge National Laboratory states that municipal wood wastes are being looked at today as a resource, while biomass costs are simply too high. 14. Worldwatch Institute. (1998). State of the world (pp. 8 9). 15. New York State College of Agriculture. (1984). Biomass energy. 16. Tolbert, V. (1997). Environmental effects of growing short rotation woody crops on former agricultural lands. Oak Ridge National Laboratory. 17. Giampietro, Ulgaiti, & Pimental. (1997). Feasibility of large-scale biofuel production. Oak Ridge National Laboratory. 18. Wright, L.L., & Hughes, E.E. (1995). U.S. carbon offset potential using biomass energy systems. Oak Ridge National Laboratory. 19. Oak Ridge National Laboratory. (1998). Evolution of the fuel ethanol industry: Feedstock availability and price. 20. Wright, L.L. (1993). Biomass energy for carbon mitigation by year Oak Ridge National Laboratory. 21. ONSI Corp. (1997). The PC25 C fuel cell. International Fuel Cells. 22. Dickerman, T. (1997). Technology to fuel fuel cells. American Hydrogen Association. 23. Id. 24. Mauro, R. (1998). Gaining perspective on fuel cells. National Hydrogen Association. 25. Id. 52 / Winter 2000 / ENVIRONMENTAL QUALITY MANAGEMENT James L. Kolar

9 26. Department of Energy. (1988). Photovoltaics: Converting sunlight to electricity. 27. Worldwatch Institute. (1994). Power surge. 28. Renewable Energy Policy Project. (1997). Project Contest. 29. Worldwatch Institute. (1994). Power surge (pp ). 30. Department of Energy. (1994). Geothermal: Program overview. 31. Worldwatch Institute. (1994). Power surge, (pp ). 32. Department of Energy. (1998). Wind energy program overview (pp. 1 4). James L. Kolar has over 25 years experience as a pollution control professional in air quality, solid waste, and hazardous waste. He is a Registered Environmental Manager (REM #8006) who currently works as a senior pollution control specialist with the Minnesota Pollution Control Agency in St. Paul. He can be reached at jim.kolar@pca.state.mn.us. Alternative Energy Technologies ENVIRONMENTAL QUALITY MANAGEMENT / Winter 2000 / 53

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