Biofuels, Solar and Wind as Renewable Energy Systems_Benefits and Risks Episode 1 Part 2 pps

1 Renewable and Solar Energy Technologies 7 The efficiency of solar ponds in converting solar radiation into heat is estimated to be approximately 1:4, assuming a 30-year life for the solar pond (Table 1.2). A 100 ha (1 km 2 ) solar pond can produce electricity at a rate of approximately $0.30 per kWh (Australian Government 2007). Some hazards are associated with solar ponds, but most can be avoided with careful management. It is essential to use plastic liners to make the ponds leakproof and prevent contamination of the adjacent soil and groundwater with salt. 1.5.2 Parabolic Troughs Another solar thermal technology that concentrates solar radiation for large-scale energy production is the parabolic trough. A parabolic trough, shaped like the bot- tom half of a large drainpipe, reflects sunlight to a central receiver tube that runs above it. Pressurized water and other fluids are heated in the pipe and used to gen- erate steam that drives turbogenerators for electricity production or provides heat energy for industry. Parabolic troughs that have entered the commercial market have the potential for efficient electricity production because they can achieve high turbine inlet tempera- ture. Assuming peak efficiency and favorable sunlight conditions, the land require- ments for the central receiver technology are approximately 1,100 ha per1 billion kWh per year (Table 1.2). The energy input:output ratio is calculated to be 1:5 (Table 1.2). Solar thermal receivers are estimated to produce electricity at approxi- mately $0.07–$0.09 per kWh (DOE/EREN 2001). The potential environmental impacts of solar thermal receivers include the ac- cidental or emergency release of toxic chemicals used in the heat transfer system. Water availability can also be a problem in arid regions. 1.6 Photovoltaic Systems Photovoltaic cells have the potential to provide a significant portion of future U.S. and world electrical energy (Energy Economics 2007). Photovoltaic cells produce electricity when sunlight excites electrons in the cells. The most promising photo- voltaic cells in terms of cost, mass production, and relatively high efficiency are those manufactured using silicon. Because the size of the unit is flexible and adapt- able, photovoltaic cells can be used in homes, industries, and utilities. However, photovoltaic cells need improvements to make them economically competitive before their use can become widespread. Test cells have reached ef- ficiencies of about 25% (American Energy 2007), but the durability of photovoltaic cells must be lengthened and current production costs reduced several times to make their use economically feasible. Production of electricity from photovoltaic cells currently costs about $0.25 per kWh (DOE 2000). Using mass-produced photovoltaic cells with about 18% 8 D. Pimentel efficiency, 1 billion kWh per year of electricity could be produced on approximately 2,800 ha of land, and this is sufficient electrical energy to supply 100,000 people (Table 1.2, DOE 2001). Locating the photovoltaic cells on the roofs of homes, industries, and other buildings would reduce the need for additional land by an estimated 20% and reduce transmission costs. However, because storage systems such as batteries cannot store energy for extended periods, photovoltaics require conventional backup systems. The energy input for making the structural materials of a photovoltaic system capable of delivering 1 billion kWh during a life of 30 years is calculated to be approximately 143 million kWh. Thus, the energy input per output ratio for the modules is about 1:7 (Table 1.2, Knapp and Jester 2000). The major environmental problem associated with photovoltaic systems is the use of toxic chemicals, such as cadmium sulfide and gallium arsenide, in their man- ufacture. Because these chemicals are highly toxic and persist in the environment for centuries, disposal and recycling of the materials in inoperative cells could become a major problem. 1.7 Geothermal Systems Geothermal energy uses natural heat present in Earth’s interior. Examples are geysers and hot springs, like those at Yellowstone National Park in the United States. Geothermal energy sources are divided into three categories: hydrothermal, geopressured-geothermal, and hot dry rock. The hydrothermal system is the simplest and most commonly used for electricity generation. The boiling liquid underground is produced using wells, high internal pressure drives, or pumps. In the United States, nearly 3,000 MW of installed electric generation comes from hydrothermal resources, and this is projected to increase by 4,500 MW. Most of the geothermal sites for electrical generation are located in California, Nevada, and Utah. Electrical generation costs for geothermal plants in the West range from $0.06 to $0.30/kWh (Gawlik and Kutscher 2000), suggesting that this technology offers potential to produce electricity economically. The US Department of Energy and the Energy Information Administration (DOE/EIA 2001) project that geothermal electric generation may grow three- to fourfold during the next 20–40 years. However, other investigations are not as optimistic and, in fact, sug- gest that geothermal energy systems are not renewable because the sources tend to decline over 40–100 years (Bradley 1997, Youngquist 1997, Cassedy 2000). Exist- ing drilling opportunities for geothermal resources are limited to a few sites in the United States and world (Youngquist 1997). Potential environmental problems of geothermal energy include water shortages, air pollution, waste effluent disposal, subsidence, and noise. The wastes produced in the sludge include toxic metals such as arsenic, boron, lead, mercury, radon, and vanadium. Water shortages are an important limitation in some regions. Geothermal systems produce hydrogen sulfide, a potential air pollutant; however, this could be 1 Renewable and Solar Energy Technologies 9 processed and removed for use in industry. Overall, these environmental costs of geothermal energy appear to be minimal relative to those of fossil fuel systems. 1.8 Biogas Wet biomass materials can be converted effectively into usable energy using anaer- obic microbes. In the United States, livestock dung is normally gravity fed or in- termittently pumped through a plug-flow digester, which is a long, lined, insulated pit in the earth. Bacteria break down volatile solids in the manure and convert them into methane gas (65%) and CO 2 (35%) (Pimentel 2001). A flexible liner stretches over the pit and collects the biogas, inflating like a balloon. The biogas may be used to heat the digester, to heat farm buildings, or to produce electricity. A large facility capable of processing the dung from 500 cows costs nearly $300,000 (EPA 2000). The Environmental Protection Agency (EPA 2000) estimates that more than 2000 digesters could be economically installed in the United States. The amount of biogas produced is determined by the temperature of the sys- tem, the microbes present, the volatile solids content of the feedstock, and the retention time. A plug-flow digester with an average manure retention time of about 16 days under winter conditions (17.4 ◦ C) produced 452,000 kcal/day and used 262,000 kcal/day to heat the digester to 35 ◦ C (Jewell et al. 1980). Using the same digester during summer conditions (25 ◦ C) but reducing the retention time to 10.4 days, the yield in biogas was 524,000 kcal/day, and it used 157,000 kcal/day for heating the digester (Jewell et al. 1980). The energy input per output ratios for these winter and summer conditions for the digester were 1:1.7 and 1:3.3, respectively. The energy output of biogas digesters is similar today (Hartman et al. 2000). In developing countries such as India, biogas digesters typically treat the dung from 15 to 30 cattle from a single family or a small village. The resulting energy produced for cooking saves forests and preserves the nutrients in the dung. The capital cost for an Indian biogas unit ranges from $500 to $900 (Kishore 1993). The price value of a kWh biogas in India is about $0.06 (Dutta et al. 1997). The total cost of producing about 10 million kcal of biogas is estimated to be $321, assuming the cost of labor to be $7/h; hence, the biogas has a value of $356. Manure processed for biogas has fewer odors and retains its fertilizer value (Pimentel 2001). 1.9 Ethanol and Energy Inputs The average costs in terms of energy and dollars for a large modern corn ethanol plant are listed in Table 1.4. In the fermentation/distillation process, the corn is finely ground and approximately 15 L of water are added per 2.69 kg of ground corn. After fermentation, to obtain a liter of 95% pure ethanol from the 8% ethanol and 92% water mixture, the 1 L of ethanol must be extracted from the approximately 13 L of the ethanol/water mixture. To be mixed with gasoline, the 95% ethanol must be 10 D. Pimentel Table 1.4 Inputs per 1,000 L of 99.5% ethanol produced from corn a Inputs Quantity kcal × 1000 Dollars $ Corn grain 2,690 kg b 2,550 b 287.36 Corn transport 2,690 kg b 322 c 21.40 d Water 15,000 L e 90 f 21.16 f Stainless steel 3 kg g 165 h 10.60 d Steel 4 kg g 92 h 10.60 d Cement 8 kg g 384 h 10.60 d Steam 2, 546, 000kcal i 2,546 i 21.16 j Electricity 392 kWh i 1,011 i 27.44 k 95% ethanol to 99.5% 9 kcal/L l 9 l 0.60 Sewage effluent 20 kg BOD m 69 n 6.00 Distribution 331 kcal/L ◦ 331 20.00 ◦ Total 7,569 $436.92 a Output: 1 L of ethanol = 5,130 kcal. b Pimentel (2003). c Calculated for 144 km roundtrip. d Pimentel (2003). e 15 L of water mixed with each 2.69 kg of grain. f Pimentel et al. (2004b). g Estimated. h Newton (2001). i Illinois Corn (2004). j Calculated based on the price of natural gas. k $.07 per kWh (USCB 2004–2005). l 95% ethanol converted to 99.5% ethanol for addition to gasoline (T. Patzek, personal communi- cation, University of California, Berkeley 2004). m 20 kg of BOD per 1,000 L of ethanol produced (Kuby et al. 1984). n 4 kWh of energy required to process 1 kg of BOD (Blais et al. 1995). o DOE (2002). further processed and more water removed, requiring additional fossil energy inputs to achieve 99.5% pure ethanol (Table 1.4). Thus, a total of about 12 L of wastewater must be removed per liter of ethanol produced, and this relatively large amount of sewage effluent has to be disposed of at an energy, economic, and environmental cost. To produce a liter of 99.5% ethanol uses 43% more fossil energy than the energy produced as ethanol and costs 44c/ per L ($1.66 per gallon or $2.76 per gallon in- cluding the subsidy) (Table 1.4). The corn feedstock requires more than 33% of the total energy input. In this analysis the total cost, including the energy inputs for the fermentation/distillation process and the apportioned energy costs of the stainless steel tanks and other industrial materials, is $436.92 per 1,000 L of ethanol produced (Table 1.4). The largest energy inputs in corn-ethanol production are for producing the corn feedstock, plus the steam energy, and electricity used in the fermentation/distillation process. The total energy input to produce a liter of ethanol is approximately 7,570 kcal (Table 1.4). However, a liter of ethanol has an energy value of only 5,130 kcal. Based on a net energy loss of 2,440 kcal of ethanol produced, 43% more fossil energy is expended than is produced as ethanol. 1 Renewable and Solar Energy Technologies 11 1.10 Grasslands and Celulosic Ethanol Tilman’s research (Tillman et al. 2006) has merit in the explanation of field exper- iments with various combinations of species of natural vegetation, and the produc- tivity of diverse experimental systems. The outstanding, 30-year effort by the Land Institute in Kansas (Jackson 1980) to develop multi-species perennial ecosystems that deliver high productivity for long periods has been de facto endorsed by Tillman et al., albeit without acknowledgement. However, there are concerns about two items. First, the statement by Tillman et al. that crop residues, like corn stover, can be harvested and utilized as a fuel source. This would be a disaster for agricultural ecosystems. Without the protec- tion of crop residues, soil loss may increase as much as 100-fold (Fryrear and Bilbro 1994). Already the U.S. crop system is losing soil 10 times faster than sus- tainability (NAS 2003). Soil formation rates are extremely slow or less than 1 t/ha/yr (NAS 2003, Troeh et al. 2004). Increased erosion will facilitate soil-C oxidation and contribute to the greenhouse problem (Lal 2003). Tillman et al. assume about 1,032 L of ethanol can be produced through the con- version of the 4 t/ha/yr of grasses harvested. However, Pimentel and Patzek (2007) reported a negative 50% return in switchgrass conversion. Based on the optimistic data of Tillman et al., and converting all 235 million ha of U.S. grassland into ethanol, only 12% of U.S. petroleum would be provided (USDA 2004, USCB 2004–2005). In addition, to achieve the production of this much ethanol would mean displac- ing about 100 million cattle, 7 million sheep, and 4 million horses now grazing on 324 million ha of U.S. grassland and rangeland (USDA 2004, Mitchell 2000). Already overgrazing is a problem on U.S. grasslands and a similar problem exists worldwide (Brown 2001). Thus, the assessment of the quantity of ethanol that can be produced on U.S. and world grasslands by Tillman et al. appears to be unduly optimistic. 1.11 Methanol and Vegetable Oils Methanol can be produced from a gasifier-pyrolysis reactor using biomass as a feedstock (Hos and Groenveld 1987, Jenkins 1999). The yield from 1 ton of dry wood is about 370 L of methanol (Ellington et al. 1993, Osburn and Osburn 2001). For a plant with economies of scale to operate efficiently, more than 1.5 million ha of sustainable forest would be required to supply it (Pimentel 2001). Biomass is generally not available in such enormous quantities, even from extensive forests, at acceptable prices. Most methanol today is produced from natural gas. Processed vegetable oils from soybean, sunflower, rapeseed, and other oil plants can be used as fuel in diesel engines. Unfortunately, producing vegetable oils for use in diesel engines is costly in terms of economics and energy (Pimentel and Patzek 2005). A slight net return on energy from soybean oil is possible, if the soybeans are grown without commercial nitrogen fertilizer. The soybean under 12 D. Pimentel favorable conditions will produce its own nitrogen. Even assuming a slight net en- ergy return with soy, the total United States would have to be planted to soybeans just to provide soy oil for U.S. trucks! 1.12 Transition to Renewable Energy Despite its environmental and economic benefits, the transition to large-scale use of renewable energy presents several difficulties. Renewable energy technologies, all of which require land for collection and production, will compete with agriculture, forestry, and urbanization for land in the United States and world. The United States is at maximum use of its prime cropland for food production per capita today, but the world has less than half the cropland per capita that it needs for a diverse diet (0.5 ha) and adequate supply of essential nutrients (USDA 2004). In fact, more than 3.7 billion people are already malnourished in the world (UN/SCN 2004, Bagla 2003). With the world and US populations expected to double in the next 58 and 70 years, respectively, all the available cropland and forestland will be required to provide vital food and forest products (PRB 2006). As the growing U.S. and world populations demand increased electricity and liquid fuels, constraints like land availability and high investment costs will restrict the potential development of renewable energy technologies. Energy use based on current growth is projected to increase from the current U.S. consumption of 102 quads to approximately 145 quads by 2050. Land availability is also a problem, with the US population adding about 3.3 million people each year (USCB 2007). Each person added requires about 0.4 ha (1 acre) of land for urbanization and highways and about 0.5 ha of cropland (Vesterby and Krupa 2001). Renewable energy systems require more labor than fossil energy systems. For example, wood-fired steam plants require several times more workers than coal-fired plants (Giampietro et al. 1998). An additional complication in the transition to renewable energies is the rela- tionship between the location of ideal production sites and large population cen- ters. Ideal locations for renewable energy technologies are often remote, such as deserts of the American Southwest or wind farms located kilometers offshore. Al- though these sites provide the most efficient generation of energy, delivering this energy to consumers presents a logistical problem. For instance, networks of dis- tribution cables must be installed, costing about $179,000 per km 115-kV lines (DOE/EIA 2002). A percentage of the power delivered is lost as a function of electrical resistance in the distribution cable. There are complex alternating cur- rent electrical networks in North America, and 3 of these are tied together by DC lines (Nordel 2001). Based on these networks, it is estimated that electricity can be transmitted up to 1500 km. A sixfold increase in installed technologies would provide the United States with approximately 46 quads (thermal) of energy, less than half of current US consump- tion (Table 1.1). This level of energy production would require about 159 million ha 1 Renewable and Solar Energy Technologies 13 of land (17% of US land area). This percentage is an estimate, and could increase or decrease depending on how the technologies evolve and energy conservation is encouraged. Worldwide, approximately 473 quads of all types of energy are used by the population of more than 6.5 billion people (Table 1.1). Using available renewable energy technologies, an estimated 200 quads of renewable energy could be pro- duced worldwide on about 20% of the world land area. A self-sustaining renewable energy system producing 200 quads of energy per year for about 2 billion people (Ferguson 2001) would provide each person with about 5,000 L of oil equivalents per year, approximately half of America’s current consumption per year, but an increase for most people of the world (Pimentel et al. 1999). The first priority of the US energy program should be for individuals, communi- ties, and industries to conserve fossil fuel resources and reduce consumption. Other developed countries have proved that high productivity and a high standard of living can be achieved with the use of half the energy expenditure of the United States (Pimentel et al. 1999). In the United States, fossil energy subsidies of approximately $40 billion per year should be withdrawn and the savings invested in renewable energy research and education to encourage the development and implementation of renewable technologies. If the United States became a leader in the development of renewable energy technologies, then it would likely capture the world market for this industry (Shute 2001). The current subsidies for ethanol production total $6 billion per year (Koplow 2006). This means that the subsidies per gallon of ethanol are 60 times greater than the subsidies per gallon of gasoline! 1.13 Conclusion This assessment of renewable energy technologies confirms that these techniques have the potential to provide the nation with alternatives to meet nearly half of future U.S. energy needs. To develop this potential, the United States would have to commit to the development and implementation of non-fossil fuel technologies and energy conservation. People in the U.S. would have to reduce their current energy consumption by more than 50% and this is entirely possible. Eventually we will be forced to reduce energy consumption. The implementation of renewable energy technologies now would reduce many of the current environmental problems asso- ciated with fossil fuel production and use. The United States’ immediate priority should be to speed the transition from the reliance on nonrenewable fossil energy resources to reliance on renewable energy technologies. Various combinations of renewable technologies should be developed consistent with the characteristics of the different geographic regions in the United States. A combination of the renewable technologies listed in Table 1.3 should pro- vide the United States with an estimated 46 quads of renewable energy by 2050. 14 D. Pimentel These technologies should be able to provide this much energy without interfering with required food and forest production. If the United States does not commit itself to the transition from fossil to re- newable energy during the next decade or two, the economy and national security will suffer. It is of critical importance that U.S. residents work together to conserve energy, land, water, and biological resources. To ensure a reasonable standard of living in the future, there must be a fair balance between human population density and use of energy, land, water, and biological resources. References American Energy. (2007). America’s Solar Energy Potential. 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(Washington, DC: Population Reference Bureau) [...]... growth of world crude oil production between 18 80 and 19 70 proceeded at 6.6% per year Sources: lib.stat.cmu.edu/DASL/Datafiles/Oilproduction.html, US EIA 22 T.W Patzek 18 0 16 0 World Oil Production US Oil Consumption Petroleum, EJ/Year 14 0 12 0 10 0 80 60 27 0 billion gallons of ethanol per year 40 20 0 20 00 20 20 20 40 20 60 20 80 21 0 0 21 2 0 21 4 0 21 6 0 21 8 0 22 00 Fig 2. 4 The estimated decline of conventional petroleum... population in 20 06 The short-lived rate peak around 19 78 was caused by OPEC limiting its oil production 2 Can the Earth Deliver the Biomass-for-Fuel we Demand 21 35 Exponential projection Logistic projection RFA data 2 017 − Bush’s Goal Billion gallons per year 30 25 20 15 10 5 0 19 80 19 85 19 90 19 95 20 00 20 05 2 010 2 015 20 20 Fig 2. 2 By an exponential extrapolation of ethanol production during the last 7 years... years at 18 .5% per year, one may arrive at 35 billion gallons per year in 2 017 The less optimistic logistic fit of the data plateaus at 14 billion gallons per year Where will the remaining 21 billion gallons of ethanol come from each year? Sources: DOE EIA, Renewable Fuels Association (RFA) Oil production rate, (HHV) EJ/year 10 3 10 2 10 1 10 0 10 1 1880 19 00 19 20 19 40 19 60 19 80 20 00 20 20 Fig 2. 3 Exponential... 0 .18 kg/kg of EtOH, the highest ethanol yield is 3.5 – 4.4% of ethanol in water The higher heating value (HHV) of ethanol is 29 .6 MJ kg 1 (Patzek, 20 04) The HHV of wheat straw is 18 .1 MJ kg 1 (Schmidt et al., 19 93) and that of lignin 21 . 2 MJ kg 1 (Domalski et al., 19 87) With these inputs the first-law (energy) efficiency of Iogen’s facility is η= 0 .28 × 29 .6 ≈ 20 % 1 × 18 .1 + 0 .18 × 2. 4 × 15 /0.787 − 0 .15 ... 0 .15 × 21 . 2 (2 .1) Table 2 .1 Yields of ethanol from cellulose and hemicellulose Step Cellulose Hemicellulose Dry straw Mass fraction Enzymatic conversion efficiency Ethanol stoichiometric yield Fermentation efficiency EtOH Yield, kg 1 kg ×0.38 ×0.76 ×0. 51 ×0.75 0 .11 1 1 kg ×0 .29 ×0.90 ×0. 51 ×0.50 0.067 Source: Badger (20 02) 8 Biomass feedstock composition and property database Department of Energy, Biomass... sulfuric acid and steam Iogen’s patented enzyme then breaks the cellulose and hemicelluloses down into six- and 2 Can the Earth Deliver the Biomass-for-Fuel we Demand 16 29 × 10 4 Iogen data Prediction Cumulative production, gal EtOH 14 12 10 8 6 4 2 0 0 50 10 0 15 0 20 0 25 0 300 350 Days from April 1, 20 04 Fig 2 . 12 Ethanol production in Iogen’s Ottawa plant Extrapolation to one year yields 15 8 000 gallons... Beith Ha’arva 5MW (e) solar pond power plant (SPPP): Progress report Solar Energy, 45, 24 7 25 3 Tillman, D., Hill, J & Lehman, C (20 06) Carbon-negative biofuels from low-input high-diversity grassland biomass Science, 314 , 15 98 16 00 Trainer, F E (19 95) Can renewable energy sources sustain affluent society? Energy Policy, 23 , 10 09 10 26 Troeh, F R., Hobbs, J A & Donahue, R L (20 04) Soil and water conservation.. .1 Renewable and Solar Energy Technologies 17 Repetto, R (19 92) Accounting for environmental assets Scientific American, June, 26 6(6) 94 10 0 Sagrillo, M (20 06) Telecommunication Interference from Home Wind Systems Retrieved May 27 , 20 06, from http:www.awea.org/faq/sagrillos/ms telint 0304.html Sawin, J L (20 04) Mainstreaming renewable energy in the 21 st century Worldwatch Paper 16 9 (Washington,... Appendix 2, as a short-lived but violent disturbance of terrestrial ecosystems on the Earth 4 All global population increase since 19 40 2 Can the Earth Deliver the Biomass-for-Fuel we Demand 25 16 0 Oil production rate, EJ/year 14 0 12 0 10 0 80 60 40 20 0 10 00 −500 0 500 Years, AD 10 00 15 00 20 00 Fig 2. 7 World crude oil production plotted on the same time scale as Fig 2. 6 At today’s rate of fossil and nuclear... www.eere .energy. gov/biomass/progs/searchl.egi, accessed July 25 , 20 07 2 Can the Earth Deliver the Biomass-for-Fuel we Demand 31 30 Kgs of Steam/Gallon Anhydrous EtOH Theoretical Practical Iogen Demand 25 20 15 10 5 0 0 5 10 15 Volume % of Ethanol in Water Fig 2 .13 Steam requirement in ethanol broth distillation The 3.7% broth requires 2. 4 times more steam than a 12 % broth Source (Jacques et al., 20 03) . lib.stat.cmu.edu/DASL/Datafiles/Oilproduction.html, US EIA 22 T.W. Patzek 20 00 20 20 20 40 20 60 20 80 21 0 0 21 2 0 21 4 0 21 6 0 21 8 0 22 00 0 20 40 60 80 10 0 12 0 14 0 16 0 18 0 Petroleum, EJ/Year 27 0 billion gallons. by OPEC limiting its oil production. 2 Can the Earth Deliver the Biomass-for-Fuel we Demand 21 1980 19 85 19 90 19 95 20 00 20 05 2 010 2 015 20 20 0 5 10 15 20 25 30 35 Billion gallons per year Exponential. Seidel, T. (20 02) . Renewable energy: current and potential issues. Bioscience, 52 ( 12 ), 11 11 11 20 Pimentel, D., Pleasant, A., Barron, J., Gaudioso, J., Pollock, N., Chae, E., Kim, Y., Lassiter, A., Schiavoni,