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  • Energy

    1. 2. What is Energy? <ul><li>Energy is the ability to do work </li></ul><ul><li>Comes in two forms </li></ul><ul><ul><li>Kinetic </li></ul></ul><ul><ul><ul><li>The energy of a body in motion </li></ul></ul></ul><ul><ul><li>Potential </li></ul></ul><ul><ul><ul><li>The energy that is pent up ready to be let out. In fuels it is chemical energy. </li></ul></ul></ul><ul><ul><li>Changing potential energy into kinetic energy is called the transformation of energy . </li></ul></ul>
    2. 3. Why do we need energy? <ul><li>Food energy enables us to live and work. </li></ul><ul><li>Fuel energy enables us to use machines to do work for us. </li></ul><ul><li>Electrical energy allows us to live the life to which we are accustomed. </li></ul>
    3. 4. How do we get energy? <ul><li>Food energy is ultimately comes from the sun (solar). </li></ul><ul><ul><li>We use photosynthesis to grow crops to feed animals both of which we eat. </li></ul></ul><ul><li>Fuel energy comes from natural resources. </li></ul><ul><ul><li>Most often mined from the earth </li></ul></ul><ul><li>Electrical energy is generated most often by burning fuels. </li></ul><ul><ul><li>Coal </li></ul></ul>
    4. 5. Renewable Energy Sources <ul><li>Renewable energy sources are those that can be replaced within a reasonable amount of time. </li></ul><ul><ul><li>Solar, wind, hydropower and geothermal energy are all renewable and inexhaustible resources. </li></ul></ul><ul><ul><ul><li>Little or no pollution </li></ul></ul></ul><ul><ul><li>Biomass such as wood, miscanthus, and other plant based materials are renewable. </li></ul></ul><ul><ul><ul><li>Usually burned, creates some pollution </li></ul></ul></ul>
    5. 6. Nonrenewable Energy Resources <ul><li>Nonrenewable Energy Resources are those that are harvested from the earth that cannot be replaced in a foreseeable amount of time. </li></ul><ul><ul><li>Fossil Fuels </li></ul></ul><ul><ul><ul><li>Coal, petroleum, natural gas </li></ul></ul></ul><ul><ul><ul><li>Takes millions of years to create. </li></ul></ul></ul><ul><ul><ul><li>Releases large amounts of pollution when burned. </li></ul></ul></ul><ul><ul><li>Nuclear </li></ul></ul><ul><ul><ul><li>Relatively no pollution released when burned, but extremely hazardous waste produced. </li></ul></ul></ul>
    6. 7. How do we measure energy? <ul><li>Gallons of liquid fuel </li></ul><ul><li>Barrels of oil </li></ul><ul><li>Cubic feet of gas </li></ul><ul><li>Watts of power </li></ul><ul><ul><li>Kilowatts (10 3 ), Megawatts (10 6 ), Gigawatts (10 9 ), Tetrawatts (10 12 ), Petawatts (10 15 ) </li></ul></ul>
    7. 8. What are our current energy demands? <ul><li>North America currently uses between 20 and 25 million barrels of oil per day. </li></ul><ul><ul><li>2/3 is used for transportation fuel </li></ul></ul><ul><ul><li>1 barrel of oil yields roughly 20 gallons of gasoline. </li></ul></ul><ul><li>The US uses just under 800,000 megawatts of power every day. </li></ul><ul><li>We burn about 20 trillion cubic feet of natural gas annually. </li></ul>
    8. 10. Breakdown of US energy usage
    9. 11. What are the current energy sources? <ul><li>Fossil Fuels (coal, oil, natural gas) </li></ul><ul><li>Wind </li></ul><ul><li>Solar </li></ul><ul><li>Hydroelectric </li></ul><ul><li>Geothermal </li></ul><ul><li>Biomass </li></ul><ul><li>Nuclear </li></ul><ul><li>Tidal/Wave </li></ul><ul><li>Biofuels </li></ul>
    10. 12. Coal <ul><li>Coal is mined from the earth’s crust. </li></ul><ul><li>a readily combustible black or brownish-black sedimentary rock. </li></ul><ul><li>Formed in ecosystems where plant remains were preserved by water and mud from oxidation and biodegradation. </li></ul><ul><li>Comprised primarily of carbon and hydrogen, and varying amounts of sulfur. </li></ul>
    11. 13. Coal <ul><li>The Chinese mined coalstone for fuel 10,000 years ago at the time of the New Stone Age, or Neolithic Era. </li></ul><ul><li>Outcrop coal was used in Britain during the Bronze Age (2000-3000 years BC), </li></ul><ul><li>However, there is no evidence that the product was of great importance in Britain before the High Middle Ages, after about AD 1000. </li></ul>
    12. 14. Coal <ul><li>The price of coal has gone up from around $30 per short ton in 2000 to around $123.50 per short ton as June 25th, 2008 </li></ul><ul><li>World coal consumption is about 6.2 billion tons annually </li></ul><ul><ul><li>about 75% is used for the production of electricity. </li></ul></ul>
    13. 15. Coal <ul><li>The environmental drawbacks to mining and burning coal. </li></ul><ul><li>release of carbon dioxide and methane </li></ul><ul><li>waste products including uranium, thorium, and other heavy metals </li></ul><ul><li>Acid rain </li></ul><ul><li>interference with groundwater and water table levels </li></ul><ul><li>dust nuisance </li></ul><ul><li>subsidence above tunnels, sometimes damaging infrastructure </li></ul><ul><li>rendering land unfit for other uses. </li></ul><ul><li>coal-fired power plants without effective fly ash capture are one of the largest sources of human-caused background radiation exposure. </li></ul>
    14. 16. Oil <ul><li>A naturally occurring, flammable liquid found in rock formations in the Earth consisting of a complex mixture of hydrocarbons of various molecular weights, plus other organic compounds. </li></ul><ul><li>Crude oil varies greatly in appearance - usually black or dark brown </li></ul><ul><li>Usually found in association with natural gas, and saline water </li></ul><ul><li>Crude oil may also be found in semi-solid form mixed with sand </li></ul><ul><ul><li>Athabasca Oil Sands in Canada </li></ul></ul>
    15. 17. Oil <ul><li>84% by volume of the hydrocarbons present in petroleum is converted into energy-rich fuels (petroleum-based fuels) </li></ul><ul><ul><li>gasoline, diesel, jet, heating, and other fuel oils </li></ul></ul><ul><li>Due to its high energy density, easy transportability and relative abundance, it has become the world's most important source of energy since the mid-1950s. </li></ul><ul><li>The 16% not used for energy production is the raw material for many chemical products, including pharmaceuticals, solvents, fertilizers, pesticides, and plastics </li></ul>
    16. 18. Oil <ul><li>Known reserves of petroleum are typically estimated at around 190 km3 (1.2 trillion barrels) without oil sands </li></ul><ul><li>Consumption is currently around 84 million barrels (13.4×106 m3) per day </li></ul><ul><li>At current consumption levels, known recoverable reserves would be gone around 2039 </li></ul><ul><ul><li>Estimate varies greatly </li></ul></ul><ul><ul><li>depending on source </li></ul></ul>
    17. 19. Oil <ul><li>Oil is formed from the preserved remains of prehistoric zooplankton and algea which have settled to the sea (or lake) bottom in large quantities under anoxic conditions. </li></ul><ul><li>Over geologic time this organic matter, mixed with mud, is buried under heavy layers of sediment. </li></ul><ul><li>High levels of heat and pressure cause the organic matter to chemically change during diagenesis, </li></ul><ul><ul><li>first into a waxy material known as kerogen </li></ul></ul><ul><ul><li>then with more heat into liquid and gaseous hydrocarbons in a process known as catagenesis. </li></ul></ul>
    18. 20. Oil <ul><li>The presence of oil has significant social and environmental impacts </li></ul><ul><ul><li>from accidents and routine activities such as seismic exploration, drilling, and generation of polluting wastes not produced by other alternative energies </li></ul></ul><ul><li>Burning oil releases carbon dioxide (CO2) into the atmosphere </li></ul><ul><ul><li>which is credited with contributing to global warming </li></ul></ul><ul><li>Per joule, oil produces 15% less CO2 than coal, but 30% more than natural gas. </li></ul>
    19. 21. Natural Gas <ul><li>Natural gas is a gaseous fossil fuel consisting primarily of methane but including significant quantities of ethane, propane, butane, and pentane </li></ul><ul><ul><li>as well as carbon dioxide, nitrogen, helium and hydrogen sulfide </li></ul></ul><ul><li>In the United States, retail sales are often in units of therms (th) </li></ul><ul><ul><li>1 therm = 100,000 BTU </li></ul></ul>
    20. 22. Natural Gas <ul><li>It is found in oil fields or isolated in natural gas fields and in coal beds </li></ul><ul><li>When methane-rich gases are produced by the anaerobic of non-fossil organic material, these are referred to as biogas </li></ul><ul><li>Sources of biogas include swamps and landfills or sewage sludge and manure </li></ul>
    21. 23. Natural Gas <ul><li>Natural gas is a major source of electricity generation through the use of gas turbines and steam turbines. </li></ul><ul><li>Natural gas can be used to produce hydrogen </li></ul><ul><li>Natural gas is supplied to homes, where it is used for such purposes as in natural gas-powered ranges and/or ovens, clothes dryers, and heating/cooling </li></ul><ul><li>Natural gas is a major feedstock for the production of ammonia for use in fertilizer production </li></ul><ul><li>Natural gas also contains and is the primary market source of helium </li></ul>
    22. 24. Wind <ul><li>Wind power is the conversion of wind energy into a useful form, such as electricity, using wind turbines. </li></ul>
    23. 25. Wind <ul><li>The earliest historical reference describes a windmill used to power an organ in the 1st century AD. </li></ul><ul><li>Windmills were used extensively in Northwestern Europe to grind flour beginning in the 1180s, and many Dutch windmills still exist. </li></ul><ul><li>In the United States, the development of the &quot;water-pumping windmill&quot; was the major factor in allowing the farming and ranching of vast areas of North America, which were otherwise devoid of readily accessible water. </li></ul>
    24. 26. Wind <ul><li>The origin of wind is complex. </li></ul><ul><li>The Earth is unevenly heated by the sun </li></ul><ul><ul><li>the poles receiving less energy from the sun than the equator does. </li></ul></ul><ul><ul><li>the dry land heats up (and cools down) more quickly than the seas do. </li></ul></ul><ul><li>The differential heating drives a global atmospheric convection system reaching from the Earth's surface to the stratosphere which acts as a virtual ceiling. </li></ul>
    25. 27. Wind <ul><li>Electricity generated from wind power can be highly variable at several different timescales </li></ul><ul><ul><li>from hour to hour, daily, and seasonally </li></ul></ul><ul><ul><li>this variability can present substantial challenges to incorporating large amounts of wind power into a grid system </li></ul></ul><ul><li>Peak wind speeds may not coincide with peak demand for electrical power </li></ul>
    26. 28. Wind <ul><li>Pumped storage hydroelectricity is a type of hydroelectric power generation used by some power plants for load balancing . </li></ul><ul><li>The method stores energy in the form of water, pumped from a lower elevation reservoir to a higher elevation. </li></ul><ul><ul><li>Low-cost off-peak electric power is used to run the pumps. </li></ul></ul><ul><li>During periods of high electrical demand, the stored water is released through turbines. </li></ul><ul><ul><li>Although the losses of the pumping process makes the plant a net consumer of energy overall, the system increases revenue by selling more electricity during periods of peak demand , when electricity prices are highest . </li></ul></ul>
    27. 29. Wind <ul><li>In 2006 the United States produced/used 26.3 TWh </li></ul><ul><li>We consumed/produced a total of 4105 TWh in 2006 </li></ul><ul><li>Had a total capacity of producing 11,603 MWh in 2006 </li></ul><ul><li>The US has added more wind energy to its grid than any other country </li></ul><ul><ul><li>Wind power capacity grew by 45% to 16.8 GW in 2007 </li></ul></ul><ul><li>Texas has become the largest wind energy producing state </li></ul>
    28. 30. Wind <ul><li>Wind power consumes no fuel for continuing operation, and has no emissions directly related to electricity production. </li></ul><ul><ul><li>Operation does not produce carbon dioxide, sulfur dioxide, mercury, particulates, or any other type of air pollution, as do fossil fuel power sources. </li></ul></ul><ul><li>Wind power plants consume resources in manufacturing and construction. </li></ul><ul><ul><li>During manufacture of the wind turbine, steel, concrete, aluminum and other materials will have to be made and transported using energy-intensive processes </li></ul></ul>
    29. 31. Solar <ul><li>Solar energy is the heat and light radiated from the Sun that powers Earth's climate and supports life </li></ul><ul><li>Solar power refers specifically to the conversion of sunlight into electricity by photovoltaics </li></ul><ul><li>The absorption of solar energy by atmospheric convection and evaporation and condensation of water vapor powers the water cycle and drives the winds. </li></ul>
    30. 32. Peak wind speeds may not coincide with peak demand for electrical power 174 PW coming in 10 PW reflected by Atmosphere 35 PW reflected by clouds 7 PW reflected by Earth’s surface 33 PW absorbed by Atmosphere 111 PW radiated to space by Atmosphere 10 PW radiated from earth to space 26 PW absorbed by Atmosphere 40 PW latent heat in water vapor 12 PW Conduction & rising air
    31. 33. Solar <ul><li>A solar cell (or photovoltaic cell) is a device that converts light into direct current using the photoelectric effect </li></ul><ul><ul><li>The photoelectric effect is a quantum electronic phenomenon in which electrons are emitted from matter after the absorption of energy from electromagnetic radiation such as x-rays or visible light </li></ul></ul><ul><li>Photovoltaic cells became invaluable during the “space race” and made possible several significant satellites </li></ul>
    32. 34. Solar <ul><li>Storage is an important issue in the development of solar energy </li></ul><ul><ul><li>modern energy systems usually assume continuous availability of energy </li></ul></ul><ul><ul><li>Solar energy is not available at night, and the performance of solar power systems is affected by unpredictable weather patterns </li></ul></ul><ul><ul><li>storage media or back-up power systems must be used </li></ul></ul>
    33. 36. Hydroelectric <ul><li>Hydroelectricity is a form of hydropower </li></ul><ul><ul><li>is the most widely used form of renewable energy </li></ul></ul><ul><ul><li>Hydroelectricity now supplies about 715,000 MWe or 19% of world electricity </li></ul></ul><ul><li>Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator. </li></ul><ul><li>The US creates 291.2 TW annually </li></ul>
    34. 39. Hydroelectric <ul><li>The major advantage of hydroelectricity is elimination of the cost of fuel. </li></ul><ul><li>Since hydroelectric dams do not burn fossil fuels, they do not directly produce carbon dioxide </li></ul><ul><ul><li>some carbon dioxide is produced during manufacture and construction of the project </li></ul></ul>
    35. 40. Hydroelectric <ul><li>Hydroelectric projects can be disruptive to surrounding aquatic ecosystems both upstream and downstream of the plant site </li></ul><ul><ul><li>For instance, studies have shown that dams along the Atlantic and Pacific coasts of North American have reduced salmon populations </li></ul></ul><ul><li>Water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks </li></ul><ul><li>A further concern is the impact of major schemes on birds </li></ul>
    36. 41. Hydroelectric <ul><li>Another disadvantage of hydroelectric dams is the need to relocate the people living where the reservoirs are planned </li></ul><ul><li>Failures of large dams, while rare, are potentially serious </li></ul>
    37. 42. Geothermal <ul><li>Geothermal energy is heat from within the earth </li></ul><ul><li>We can use the steam and hot water produced inside the earth to heat buildings or generate electricity </li></ul><ul><li>Geothermal energy is a renewable energy source because the water is replenished by rainfall and the heat is continuously produced inside the earth </li></ul>
    38. 43. Geothermal <ul><li>Geothermal energy is generated in the earth's core, about 4,000 miles below the surface </li></ul><ul><li>Temperatures hotter than the sun's surface are continuously produced inside the earth by the slow decay of radioactive particles </li></ul><ul><li>Geothermal energy can sometimes find its way to the surface in the form of: </li></ul><ul><ul><ul><li>volcanoes and fumaroles </li></ul></ul></ul><ul><ul><ul><ul><li>holes where volcanic gases are released) </li></ul></ul></ul></ul><ul><ul><ul><li>hot springs and </li></ul></ul></ul><ul><ul><ul><li>geysers </li></ul></ul></ul>
    39. 44. Geothermal <ul><li>The three main uses of geothermal energy are: </li></ul><ul><li>Direct Use and District Heating Systems which use hot water from springs or reservoirs near the surface. </li></ul><ul><li>Electricity generation in a power plant requires water or steam at very high temperature </li></ul><ul><ul><li>Geothermal power plants are generally built where geothermal reservoirs are located within a mile or two of the surface. </li></ul></ul><ul><li>Geothermal heat pumps use stable ground or water temperatures near the earth's surface to control building temperatures above ground. </li></ul>
    40. 45. Geothermal <ul><li>The direct use of hot water as an energy source has been happening since ancient times </li></ul><ul><li>After bathing, the most common direct use of geothermal energy is for heating buildings through district heating systems </li></ul><ul><ul><li>Hot water near the earth's surface can be piped directly into buildings and industries for heat. </li></ul></ul>
    41. 46. Geothermal <ul><li>Geothermal plants require high temperature water sources </li></ul><ul><ul><li>(300 to 700 degrees Fahrenheit) </li></ul></ul><ul><li>hydrothermal resources that may come from either dry steam wells or hot water wells </li></ul><ul><li>We can use these resources by drilling wells into the earth and piping the steam or hot water to the surface </li></ul><ul><ul><li>Geothermal wells are one to two miles deep </li></ul></ul>
    42. 48. Geothermal <ul><li>Geothermal heat pumps use the Earth's constant temperatures to heat and cool buildings </li></ul><ul><li>temperatures above ground change a lot from day to day and season to season </li></ul><ul><li>temperatures in the upper 10 feet of the Earth's surface hold nearly constant between 50 and 60 degrees Fahrenheit. </li></ul><ul><li>soil temperatures are usually warmer than the air in winter and cooler than the air in summer </li></ul><ul><li>They transfer heat from the ground (or water) into buildings in winter and reverse the process in the summer </li></ul>
    43. 49. Biomass <ul><li>Biomass refers to the burning or refining of plant materials to generate heat (directly) or electricity (indirectly) </li></ul><ul><li>Examples of biomass include: </li></ul><ul><ul><li>Wood </li></ul></ul><ul><ul><li>Miscanthus </li></ul></ul><ul><ul><li>Corn </li></ul></ul><ul><ul><li>Soybeans </li></ul></ul><ul><ul><li>Switchgrass </li></ul></ul><ul><ul><li>Sugarcane </li></ul></ul><ul><ul><li>Palm oil </li></ul></ul>
    44. 50. Biomass <ul><li>Biomass currently supplies approximately 1,700 MW of power to the grid </li></ul><ul><ul><li>0.5 percent of the U.S. electricity supply. </li></ul></ul><ul><li>This level of biomass power generation avoids approximately 11 million tons per year of CO2 emissions from fossil fuel combustion </li></ul>
    45. 51. Biomass <ul><li>Draw backs to biomass include the release of greenhouse gasses as the fuel is burned </li></ul><ul><li>Food vs. Fuel debate </li></ul><ul><ul><li>Using food sources as a fuel source </li></ul></ul><ul><ul><li>1/3 of the corn gown in the US is exported to other countries as a food source </li></ul></ul><ul><li>Water resources needed to convert biomass to liquid fuel </li></ul>
    46. 52. Nuclear <ul><li>Nuclear power is any nuclear technology designed to extract usable energy from atomic nuclei via controlled nuclear reactions </li></ul><ul><ul><li>The most common method today is through nuclear fission </li></ul></ul><ul><ul><li>other methods include nuclear fusion and radioactive decay </li></ul></ul><ul><li>All methods involve heating water, which is then converted by a turbine into electricity or propulsion </li></ul><ul><ul><li>Today, more than 15% of the world's electricity comes from nuclear power </li></ul></ul><ul><ul><li>Over 150 nuclear-powered naval vessels have been built </li></ul></ul>
    47. 53. Nuclear <ul><li>Electricity was generated for the first time by a nuclear reactor on December 20, 1951 at the EBR-I experimental station near Arco, Idaho </li></ul><ul><ul><li>initially produced about 100 kW </li></ul></ul><ul><li>A general movement against nuclear power arose during the last third of the 20th century </li></ul><ul><ul><li>based on the fear of a possible nuclear accident </li></ul></ul><ul><ul><li>fears of radiation </li></ul></ul><ul><ul><li>nuclear proliferation </li></ul></ul><ul><ul><li>opposition to nuclear waste production </li></ul></ul><ul><ul><li>transport and final storage </li></ul></ul>
    48. 54. Nuclear <ul><li>In nuclear power plants the heat is provided by nuclear fission inside the nuclear reactor </li></ul><ul><li>When a relatively large fissile atomic nucleus is struck by a neutron it forms two or more smaller nuclei as fission products, releasing energy and neutrons in a process called nuclear fission </li></ul><ul><li>The neutrons then trigger further fission creating a chain reaction </li></ul><ul><li>When this nuclear chain reaction is controlled, the energy released can be used to heat water, produce steam and drive a turbine that generates electricity </li></ul><ul><ul><li>The chain reaction is controlled through the use of materials that absorb and moderate neutrons </li></ul></ul><ul><li>While a nuclear power plant uses the same fuel, uranium-235 or plutoniam-239, a nuclear explosive involves an uncontrolled chain reaction </li></ul>
    49. 56. Nuclear <ul><li>(1) The Nuclear Fuel Cycle begins when uranium is mined, enriched, and manufactured into nuclear fuel </li></ul><ul><li>(2) Which is delivered to a nuclear power plant. </li></ul><ul><li>(3) After usage in the power plant, the spent fuel is delivered to a reprocessing plant or to a final repository for geological disposition </li></ul><ul><li>(4) In reprocessing 95% of spent fuel can be recycled to be returned to usage in a power plant </li></ul>
    50. 57. Nuclear <ul><li>Spent fuel is highly radioactive and needs to be handled with great care and forethought </li></ul><ul><li>Spent fuel rods are stored in shielded basins of water (spent fuel pools), usually located on-site </li></ul><ul><li>After a few decades some on-site storage involves moving the fuel to a dry cask storage </li></ul><ul><li>where the fuel is stored in steel and concrete containers until its radioactivity decreases naturally </li></ul>
    51. 58. Nuclear <ul><li>Nuclear power drastically reduces harmful emissions over fossil fuel based power plants </li></ul><ul><li>It is the most efficient power source we currently have </li></ul><ul><li>However, the potential for disaster is very high </li></ul><ul><li>The waste is very difficult to manage </li></ul>
    52. 59. Tidal/Wave <ul><li>Tidal power , sometimes called tidal energy , is a form of hydropower that converts the energy of tides into electricity or other useful forms of power </li></ul><ul><li>Tides are more predictable than wind energy and solar power </li></ul>
    53. 60. Tidal/Wave <ul><li>Tidal power can be classified into two main types: </li></ul><ul><li>Tidal stream systems make use of the kinetic energy of moving water to power turbines, in a similar way to windmills that use moving air </li></ul><ul><ul><li>This method is gaining in popularity because of the lower cost and lower ecological impact compared to barrages. </li></ul></ul><ul><li>Barrages make use of the potential energy in the difference in height between high and low tides </li></ul><ul><ul><li>Barrages suffer from very high civil infrastructure costs, a worldwide shortage of viable sites, and environmental issues </li></ul></ul>
    54. 62. Tidal/Wave <ul><li>Wave power refers to the energy of ocean surface waves and the capture of that energy to do useful work </li></ul><ul><li>Wave energy is produced when electricity generators are placed on the surface of the ocean. </li></ul><ul><li>The energy provided is most often used in desalination plants, power plants and water pumps. </li></ul><ul><li>Energy output is determined by wave height, wave speed, wavelength, and water density. </li></ul><ul><li>To date there are only a handful of experimental wave generator plants in operation around the world. </li></ul><ul><li>Portugal has built the world's first commercial wave farm </li></ul>
    55. 65. Biofuels <ul><li>Biodiesel </li></ul><ul><ul><li>Made from corn oil, palm oil, soybean oil </li></ul></ul><ul><li>Ethanol </li></ul><ul><ul><li>Made from sugar cane, corn, miscanthus </li></ul></ul><ul><li>Methane </li></ul><ul><ul><li>Derived from landfills and animal waste </li></ul></ul>
    56. 66. Biofuels <ul><li>Brings up many issues </li></ul><ul><ul><li>Food vs fuel </li></ul></ul><ul><ul><ul><li>Using food supplies to generate energy </li></ul></ul></ul><ul><ul><li>Technology gaps </li></ul></ul><ul><ul><ul><li>The need to develop abilities to create ethanol from cellulose </li></ul></ul></ul><ul><ul><li>Carbon emissions </li></ul></ul><ul><ul><ul><li>While biofuels reduce greenhouse gas emissions, they do not eliminate them </li></ul></ul></ul>
    57. 67. Go to these Websites <ul><li> </li></ul><ul><li>www. carbonfootprint .com/ calculator .aspx </li></ul><ul><li> calculator /?src=f1 </li></ul>