Overview
The world consumed 3.1×1010 billion barrels of oil in 2007 (nation master) with the United States far surpassing all other oil consuming nations by using 20,680,000 bbl/day. That’s 2.7 times more oil than China, our closest competitor. The primary point of concern regarding global petroleum consumption is the non-renewable status of this crucial energy source since each drop of that 3.1 x1010 billion barrels is one that cannot be replaced. Aside from inevitably “peaking out”, our accelerated usage of petroleum as a fuel and materials source over the past decade has contributed to a myriad of secondary problems including the warming of the troposphere via carbon dioxide emissions (and associated ecological consequences), and economic and political consequences of being dependent on foreign countries for such a vital resource. As such, development of alternative fuel sources is crucial to the construction of a sustainable society.
The primary use (2/3rds) of oil in the United States is transportation (eia.doe.gov) – so it makes sense focus efforts to develop technological alternatives to petroleum in the transportation sector. Conveniently, students are far more interested in alternative fuel vehicles than they are in alternative sources of electric energy (wind, solar, hydro.) since they can envision buying a car far more easily than buying a home and making decisions about mundane gas and electric bills. The rapidly growing alternative vehicle market is a perfect lens through which to examine the science and the affordances and constraints of emerging technologies. These technologies fit into the basic categories of a) relying on petroleum sources but improving fuel efficiency and b) exploiting a fuel source other than petroleum (natural gas, hydrogen, biofuels).
This unit is an elongated case study centered around the school’s parking lot. Students will collect and analyze data regarding the current oil and carbon footprint of the lot as a snapshot of modern consumption and complete the necessary research on fuel alternatives to develop an alternate vision of a sustainable parking lot. As a result students will gain an understanding of the limitations of our current transportation technology, the mechanics of the greenhouse effect and climate change, and be able to comparatively analyze the various alternative fuel technologies currently on the U.S. vehicle market.
Rationale
Energy is the ability to do work
A unit on energy resources cannot begin without a discussion of what we require billions of barrels of liquid energy to accomplish- work. Especially in the usage of energy for transportation, the scientific meaning of work has great resonance. It is the application of force to cause a change in the motion of an object. In 2008, vehicles in the United States were forced into motion for 3 trillion miles along highways (bts.gov.) That distance required significant amounts of work (since Work= Force x distance)
Power is the rate at which work is done (work/time). Newton first captured this measurement in the unit horsepower (how much weight a horse could move in a period of time.) We expect our vehicles to move large masses very quickly- and it is common to see sedans with over 190 horsepower. Oil is the primary transportation fuel because it can be fractionally distilled into various products used for transportation from jet fuel to gasoline (which accounts for about 17 percent of the energy consumed in the United States) to diesel. Additionally, petroleum is relatively easy to extract from the earth’s crust and extremely easy to transport in barrels. But perhaps most importantly, oil contains enough energy density to provide the power we require to accelerate quickly while carry heavy loads (power.)
Despite oil’s significant advantages discussed above that have kept it so cheap and ubiquitous. Significant constraints regarding oil usage are beginning to force us to explore alternative fuels and technologies.
Consequences of our reliance on petroleum for transportation
Depletion: Petroleum (crude oil) is made of combustible hydrocarbons- the molecular remains of dead organisms that rained down and became buried on seafloors over millions of years. Some organic material became buried under enough sediment to create the pressure and heat necessary for conversion into the appropriate length hydrocarbons for use and extraction. It’s rare enough to encounter appropriate conditions for the production of crude oil, but known global reserves also had to have been created in geologic conditions that allowed for it to collect and avoid escape or contamination. While these events occurred in many locations around the globe (98 of 205 countries possess oil reserves- but that also means that 107 do not), the amount of oil in each varies widely. Saudi Arabia far exceeds the rest of the world with 2.7×1011 billion barrels of oil. The United States is 12th in the world with 2.1×1010 billion barrels (cia world factbook).
Extraction of crude oil is heavily limited by drilling and extraction technology. Currently producers only get 35-50% of the oil out of a deposit, though this efficiency is expected to increase with development of technology capable of recovering remaining heavy crude oil (steam flushes and otherwise.) Regardless of how efficient technology becomes, it is clear that the biological and geologic conditions responsible for creating crude oil were finite and that crude oil is non-renewable and cannot be exploited indefinitely.
In 1956 M.King Hubbert predicted that U.S. oil production would peak in the 1970s. He was correct- and the United States now imports about 60% of the oil it consumes. While the United States has already “peaked out” in terms of oil production, predictions for a global oil production peak still range from having already occurred to 2018 (science daily peak oil). Peak oil is difficult to predict because The Organization of Petroleum Exporting Countries (OPEC), who control 75% of the world’s proven oil reserves, frequently change the amount of proven reserves. This fuzzy math makes it difficult to asses the true status of oil reserves.
Climate Change etc.: Vehicles that run on standard unleaded gasoline emit about 20lbs of carbon dioxide (170 cu. ft.) for every gallon of gasoline consumed (fueleconomy.gov). Despite the fact that other atmospheric gases have higher warming potentials, carbon dioxide is the most important anthropogenic greenhouse gas because of its ubiquity. Annual CO2 emissions have grown between 1970 and 2004 by about 80%, from 21 to 38 gigatonnes (Gt), and it represented 77% of total anthropogenic GHG emissions in 2004 (2007, IPCC). The result of such significant increases in carbon dioxide concentrations in the atmosphere is unequivocal warming of the climate system “as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level” (2007, IPCC). Despite the fact that carbon dioxide and temperature have both fluctuated throughout history on Earth, it is clear that current fluctuations are anthropogenic. The 2007 IPCC report clearly states that “global atmospheric concentrations of CO2, CH4 and N2O have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years, with a radiative forcing of +1.6 [+0.6 to +2.4].”
Large scale increases in tropospheric carbon dioxide result in global climate change via the greenhouse effect. Energy enters the earth as solar radiation is absorbed by the surfaces of the planet and converted eventually to outgoing infrared radiation (heat.) As the concentration of carbon dioxide (and other greenhouse gases) increase in the lowest layer of the atmosphere (the troposphere), they trap infrared radiation which leads to increased energy storage in the troposphere and the myriad secondary and tertiary consequences from droughts to floods to increased geographic range of infectious disease, and altered biological communities.
Alternatives
Due to the two reasons above as well as more immediate and compelling reasons put forth by the EPA/DOT to save money ($300-$2,000 per year) and strengthen national energy security by reducing American dependence on foreign oil, it is imperative to explore sustainable transportation technologies.
An interesting point of appreciation regarding all energy sources we’ll consider in this unit is that they share a common origin; the sun. Petroleum and other fossil fuels are the decomposed and compressed remains of ancient plants whose biomass was converted from carbon dioxide using the sun’s power for photosynthesis billions of years ago. It’s no surprise that the burning of that modified biomass in the form of diesel, gasoline, and natural gas emits carbon (as carbon dioxide, monoxide, and methane) that was sequestered from the atmosphere so long ago. We now use modern plants such as corn, sugar cane, and jatropha for biofuels. These plant stocks have converted solar energy into biomass we can process into alcohols and oils for combustion engines. Assuming the electricity powering a plug-in electric vehicle is non-fossil fuel, it still ultimately depends on the sun. If the electricity was derived from hydroelectric power, the sun’s pull manifest as evaporation and transpiration and the sun’s influence in creating wind is responsible for replacing water at places along a watershed where it can flow and be captured to produce current. In the case of other electric sources, the sun’s energy has been converted more parsimoniously from photons directly to current by photovoltaic cells. Perhaps the sun’s energy was instead concentrated to single points where the tremendous heat vaporizes liquids that can then turn turbines to produce current. No matter what we choose at the fill station, we are ultimately plugging into the sun.
Significantly, choosing a vehicle that achieves an efficiency of just 5 more miles per gallon can prevent 17 tons of greenhouse gases from entering the atmosphere over the lifetime of the vehicle. Knowing the importance of fuel economy, the government set fuel economy standards Corporate Average Fuel Economy (CAFE) as part of the “Energy Policy Conservation Act,” enacted into law by Congress in 1975. The law authorizes the EPA to enforce a minimum standard for the sales weighted average fuel economy, expressed in miles per gallon (mpg), of a manufacturer’s fleet of passenger cars or light trucks with a gross vehicle weight rating (GVWR) of 8,500 lbs. or less, manufactured for sale in the United States, for any given model year. The standard set for 1985 was 27.5mpg where it has remained since. President Obama raised C.A.F.E. standards to 35.5mpg by 2016. Several technologies exist that respond to the fuel crisis simply by increasing a vehicle’s fuel efficiency. While these technologies reduce the rate of global warming and petroleum depletion by combusting less carbon to accomplish the same amount of work, they cannot realistically be considered sustainable because they still rely on nonrenewable resources.
Hybrid electric vehicles
The most fuel efficient vehicles in some classes for the 2009 model year are hybrid-electric vehicles (HEVs). The Toyota Prius gets 48mpg in the city and 45mpg on the highway. Hybrid electric vehicle options exist in most vehicle classes including compact and midsize cars, pickup trucks and sports utility vehicles. Hybrids run on internal combustion engines (as do conventional vehicles) but have a secondary electric motor that can be used for low speeds off of a battery that charges using the kinetic energy typically lost when coasting and braking. HEVs do not need to be plugged into external sources of electricity or recharged. Hybrid vehicles rely upon 3 main technologies to conserve fuel, they are regenerative braking , electric motor/drive assist, and automatic start/shutoff. Regenerative Braking is a technology that allows the “electric motor to apply resistance to the drivetrain causing the wheels to slow down. In return, the energy from the wheels turns the motor, which functions as a generator, converting energy normally wasted during coasting and braking into electricity, which is stored in a battery until needed by the electric motor.” (fuel economy.gov) The electric motor is useful in providing power to assist the engine in accelerating, passing, or hill climbing. Providing extra short-term power from electricity rather than increased fuel injection allows a smaller, more efficient engine to be used. The electric motor can also be used alone for low-speed driving (where internal combustion engines are least efficient). Lastly, automatic start/shutoff. prevents idling by automatically turning off the combustion engine when coming to a stop. Idle Free Philly reports that “thirty seconds of idling can use more fuel than can use more fuel than turning off the engine and restarting it. “ Automatic start/shutoff prevents fuel wasting (and the air pollution issues) (CAC).
The federal government is offering a tax incentives for HEVs and some states offer additional incentives.
Electric Vehicles
Vehicles that rely entirely on an electric motor are called electric vehicles. Because their engines are not powered by the residual energy from braking/motion as stored in a battery, electric vehicles offer a convenient entry into discussing all energy sources used to produce electricity These include hydroelectricity, solar energy, wind energy, and geothermal energy (to some extent) as alternatives to coal and nuclear power. Here are some brief points about each. Because electric vehicles do not combust any fuel, there are zero emissions from these vehicles. Although electric vehicles (EVs) are not direct pollution sources, they can still significantly contribute to global warming, acid rain, and other air pollution issues depending on how the electricity they plug into has been generated.
Coal: Coal is the primary source of U.S. electricity production (54%), followed by nuclear (21%), hydropower (11%), natural gas (9%), oil (2%), and non-hydro renewables (3%). A typical coal plant burns 1.4 million tons of coal each year. That adds up to 840 million tons of coal each year. Coal-fired power plants burn coal to heat water into steam. The steam turns turbines that produce electricity through the movement of electromagnets. Coal is the world’s most abundant fossil fuel (Miller, 2005) but accounts for over 1/3 of the world’s annual carbon dioxide emissions and also releases sulfur dioxide, particulates, radioactive dust, and toxic metals like mercury, arsenic and lead into the atmosphere. The mining of coal (especially by removing mountaintops) creates incalculable damage to ecosystems by disrupting topography and hydrology and uses huge amounts of space and water in the process.
Nuclear Energy: Nuclear energy is the second most common source of electricity produced in the United States. In 2005 103 commercial nuclear power plants were operational in the United States and 14 were decommissioned with radioactive waste stored on site. Nuclear energy is still relatively new. The first nuclear reactor was built by Enrico Fermi in 1942, and the first commercial reactor became operational a little more than a decade later in 1957. One big advantage of nuclear power is that it does not emit any greenhouse gases. Fission reactors use controlled chain reactions in which fuel pellets made of Uranium (where the concentration of radioactive uranium-235 is enriched from the .7% occurring in nature to 3%.) Neutrons split the nuclei of radioactive isotopes, liberating large quantities of heat and more neutrons in the process that split more nuclei in a reaction that proceeds exponentially unless controlled very carefully by neutron absorbing control rods. Aside from the fancy science that occurs in the reactor’s core, a nuclear power plant works simply and in much the same way as a coal-fired power plant. The heat generated in the core turns water to steam which turns a turbine to generate electricity. The challenges that nuclear power plants pose to the environment are very different from those of coal plants.
Some of the biggest concerns regarding nuclear power are how to keep reactors safe and reactions under control and what do do with spent highly radioactive waste. Two nuclear accidents are largely responsible for the dissolution of interest in nuclear energy that occurred in the United States during the 80’s and 90’s. A meltdown of a core at Three Mile Island in Pennsylvania due to a bungled reaction to a routine malfunction in 1979. The devastating explosion and dispersal of radioactive material that resulted from a core meltdown in Chernobyl, Ukraine in 1986 made the world think twice about the consequences of nuclear power. Nuclear accidents actually pose far less risk than the radioactive waste that is produced as a side product of the fission reactions. Many of the fission products are themselves radioactive and give off alpha and beta radiation as they reach nuclear stability. Isotopes with short half-lives give off radiation very quickly and pose immediate health risk while those with longer lives pose more of a distributed health risk, but must be contained and manage for geologic spans of time. The federal government had promised nuclear energy companies long-term waste management beginning in the 1980’s, but never has succeeded in approving an acceptable site. Yucca Mountain, the most likely site was killed by the Obama administration in 2010 after concern over water infiltration. All high level radioactive waste is stored at the site of each reactor.
Despite initial optimism about nuclear power in the 1950’s (Eisenhower administration), the United States lost interest in constructing new reactors after the Three Mile Island and Chernobyl safety scares. No new nuclear power plants were ordered between 1978 and 2009. But because of new safety and production technologies, increased electric demand, higher prices for oil and coal, and concerns about climate change, the Obama administration supports the expansion of nuclear power. They have offered $37 billion in new loan guarantees to support building new reactors (construction on one in Georgia has begun.)
Wind Power: One very promising alternative to coal and nuclear power plants for electricity generation is wind. It is one of the fastest growing energy sources around the world. Currently only 2% of U.S. electricity is wind generated, but this figure may rise to 20%. by 2030 (according to the DOE). Proposed projects for 2010-2016 in the wind sector far outstrip electricity generation (in GW) by coal (according to the National Energy Technology Laboratory.) 1-2% of the sun’s energy is converted to wind on Earth as the planet heats unequally and gases in the atmosphere move in response to pressure differences. Geographic features can impact the use of turbines to convert wind into electricity. For example, buildings and uneven terrain can cause turbulence, but the windy side of mountains can compress air into a tunnel with higher wind speeds like those that exist at the tops of mountains, hills, and ridges. Placement of wind turbines is important for optimal electricity production. The main components of a wind turbine are the rotor (blades), hub, gear box, generator, and tower. Rotor blades are designed to make wind speed up as it moves over them and new turbines have the ability to respond to wind direction. Initial concerns about noise from turbines have been allayed as the produce less emissions than the average home or office environment.
Solar Power: Active harvesting of the sun’s energy for conversion to electricity is accomplished by two primary means. The first is the use of photovoltaic cells to create electric current. Photovoltaic cells are silicon wafers that have been doped (intentionally introduced to impurities) with boron and phosphorus. When solar radiation strikes the doping atoms, electrons are released and pass through silicon crystal acting as a semiconductor. The circuit is constructed in such a way that electrons flow in one direction and create direct current that can be used to charge an electric vehicle. Silica, the raw material containing silicon is cheap to extract from the Earth’s crust and abundant, PV cells offer the only direct conversion of solar energy to electrical energy, and the sun provides so much energy to the surface of the Earth that theoretically only a 100×100 mile area is required to supply all of the U.S. electricity needs. Currently, solar cells supply only about .05% of the world’s electricity. The reason that we fall short is that PV panels do not yet have the efficiency necessary. Researchers are trying different layers of thin films to collect the optimum range of wavelengths, and changing the fill factor to balance the amount of space on the cell used to collect energy with the space needed to conduct it.
Another way to convert solar energy into electricity is solar thermal system. These system collect and transform radiant solar energy into heat which can be used to create electricity in the same way as coal and nuclear power plants. In solar thermal plants, sunlight is collected and focused on reservoirs of liquids that become superheated and boil water through heat exchange.
Batteries: Both HEV and EV are limited by their ability to store and efficiently use electric energy in batteries. The development of low-cost, long-life, and high-power energy storage systems is a crucial (and overlooked) part of alternative energy development. Most vehicles use lead-acid batteries, but these are proving to be too heavy and poor in terms of energy density (40Wh/kg) for the performance needed. Nickel-Cadmium batteries are slightly better, but are still considered low in terms of energy density and additionally contain toxic components (Cd) of concern during disposal. The ideal battery would weigh nothing, take up no space, provide infinite voltage over an infinite lifetime, but the closest we’ve come are Nickel-Metal Hydrides, and the more promising Lithium ion batteries use intercalation compounds to create huge surface area (sort of) where electrons can be stored and released. There are, however, safety concerns associated with the high voltage and the decomposition of the electrolyte.
Biofuels
Biofuels are fuels made from plants and have a lot in common with petroleum fuels that are the remains of ancient plants. Biofuels for transportation fall into two categories. Ethanol is an alcohol fermented from starch molecules. Vehicles can run on either 10% or 85% ethanol, but vehicles that run on 85:10 ethanol:gasoline blends are called flexible fuel vehicles (FFV) and have modified engines. Biodiesel a dried and processed fatty acid modified from plant oils and can be used in vehicles that are capable of running on diesel fuel. Biofuels are popular in the United States because they support the local farm economy and absorb carbon from the air as they grow so are part of a closed loop fuel cycle (in positive contrast to the open carbon cycle resulting from burning fossil fuels.)
Ethanol production in the United States has expanded from about 1.7 billion gallons in 2001 to approximately 8–9 billion gallons in 2008. This is largely due to the following advantages that ethanol fuels possess. First they are cleaner burning both in terms of greenhouse gas emissions (especially carbon dioxide) and in terms of carbon monoxide, particulate matter (which contributes to air quality and health problems), and sulfur dioxide (a major reactant in acid deposition.) Biofuels are especially advantageous relative to fossil fuels (gasoline, diesel) in terms of the greenhouse effect and climate change because they offset the carbon emitted during combustion with the sequestration that occurs during growth of the fuel material. Additionally biofuels can be produced (grown and processed) domestically whereas the majority of petroleum must be imported from other countries. Secondary benefits of domestic biofuel production include reduction of petroleum imports, decreased foreign conflict, increased self- sustainability, and creation of American jobs.
Concerns about biofuels still exist and include… market competition between the food and fuel industries leading to higher prices, performance concerns based on chemical differences between gasoline and ethanol (vapor pressure, octane rating), and perhaps most concerning is the lower energy density of ethanol which reduces torque, acceleration, and miles per gallon of ethanol vehicles. From a consumer perspective, the availability of biofuels at fueling stations limits the range of vehicles that cannot fall back on E10 gasoline.
Biodiesel is a liquid fuel made up of various fatty acid esters that has physical characteristics similar to petroleum diesel (flash point 100-170C, 77% C, 12%H, 11%O by weight, specific gravity .88). Biodiesel is synthesized from renewable sources such as new and used vegetable oils (soy) and animal fats. Biodiesel is made by reacting fats and oils with an alcohol (methanol) to produce fatty acid methyl esters. Glycerin is produced as a co-product and is usually salvaged and sold to cosmetic/pharmaceutical industries. The advantages of biodiesel are that it is less polluting than petroleum diesel, can be produced domestically, and is compatible with existing diesel engines. One limitation is that when biodiesel is made from fresh oil, it competes for raw material (soy) with food and other industries potentially driving up prices or encouraging monoculture. Diesel-powered vehicles get 30-35% better fuel efficiency than gasoline vehicles because of the energy efficiency of diesel engines and a 10% advantage in the energy density of diesel relative to gasoline. The federal government encourages the purchase of diesel vehicles (but not biodiesel vehicles specifically since there are no dedicated biodiesel vehicles on the market) by offering a tax incentive for qualifying vehicles. There were 6 diesel vehicles available in the 2009 market in the compact, midsize, small station wagon and SUV classes.
Ethanol vehicles that run on E85 (a mixture of 85% ethanol and 15% gasoline) make up the largest segment of alternative fuel vehicles in the 2009 market by far. There are well over 50 models available. Ethanol gasoline is cheaper than petroleum gasoline, but is less energy dense so the annual fuel costs are actually higher because a tank of E85 will not move a car as far as a tank of gasoline. There is a huge amount of innovation in the ethanol market. While ethanol was first made by fermenting crops high in sugar and starch like corn and sugar cane, competition for these crops drove up the price of all products containing them. Since that time, researchers have developed techniques for fermenting ethanol from waste components of crops like the stalk cellulose and have investigated ethanol production from plants that are not part of our food system such as switchgrass and jatropha. The availability of E85 fuel is severely restricted to the corn belt.
Fuel Cells
Fuels cells use electrochemical reactions to produce power. They are promising because there are zero carbon emissions, and environmentally clean, offer high efficiency, low noise. In fuel cells hydrogen combusts with oxygen to create water. Liberated ions respond to a semi permeable membrane to create current and come together at the anode to produce waste water. Fuel cells can be put into series to produce the voltage needed (car batteries use a 12V battery just to turn on.) Fuel cells do need to be supplied with fuel. Hydrogen does not occur in high enough concentration naturally to use air as a source, and even though oxygen does- all other components of the atmosphere (nitrogen, water vapor, carbon dioxide etc.) are essentially contaminants. Hydrogen is currently purified from either water (causing competition with other industries) or from hydrocarbons in fossil fuels (resulting in cancellation of the zero carbon emissions advantage.) There are various fuel cell cars on the market today including the Ford Focus, and Hyundai Santa Fe.
Objectives
This curriculum unit was developed for use in a senior year Environmental Science elective course. It follows a unit exploring global warming and climate change as well as non-renewable energy resources with a special focus on oil. The unit targets the following Pennsylvania Academic Standards for Science and Technology and advances student’s content knowledge of earth systems, energy, and technology as well as their understanding of the nature of science. This unit further affords students opportunities to advance their scientific thinking about defining a problem and testing solutions according to a model.