Chapter 14.3 Renewable Energy for Transportation

1. Chapter 14.3Renewable Energy for Transportation • BIOFUELS • complex organic matter (mainly plants) can be processed to make fuels for vehicles • ethyl alcohol • production has doubled since 2000 • biodiesel • industry has grown 3x in the same time period

2. ethanol • produced by the fermentation of sugars and starches (usually grain, sugar cane, or sugary fruits) • production costs make ethanol more expensive than gasoline until oil costs more than $55 per barrel • corn-based fuels provide another market for the crop • 2005-06: 4.3 billion gallons of ethanol used for fuel in U.S. (accounting for 14% of corn crop) • production credit of 51 cents per gallon helps to make ethanol competitive

3. ethanol benefits? • with corn cropland needed for animal feed and export, there is very little room for expansion of ethanol industry • questionable energy efficiency of corn-based ethanol: • requires fossil fuel energy to produce, transport, and process corn • recent analysis suggests that replacing gasoline with ethanol reduces greenhouse gas emissions only 13% • with negligible environmental benefits, main reason for using ethanol is to reduce dependence on oil • production of ethanol from sugar is much less costly

4. ethanol as substitute • mixtures of alcohols and gasoline should help countries meet their domestic fuel demands as demand continues to rise • ethanol works as a substitute for methyl tertiary butyl ether (MTBE) • MTBE is a petroleum derivative that has been used to make fuel burn cleaner • both ethanol and MBTE improve air quality when they are a part of reformulated gasoline • many metropolitan areas depend on these additives to help them meet Clean Air Act standards • unfortunately, MBTE is a carcinogen in animals and has been showing up in water supplies

5. biodiesel • mix of 20% soybean oil in normal diesel fuel, but any natural oil or fat can be mixed with an alcohol to make the fuel • sales have reached 75 million gallons, which is comparable to diesel from fossil fuels (partly due to a sizeable tax credit) • potential exists for most any organic waste to be converted to biodiesel • Ex. factory in Missouri converts wastes from Butterball turkey-processing plant to biofuels

6. hybrid electric vehicles • combine a conventional gasoline engine and a battery-powered electric motor to achieve substantial improvements in fuel economy • examples: • Toyota Prius—55 mpg • Honda Insight—56 mpg • most of today’s hybrids are versions of standard gasoline engines, combined with a large battery • two electric motors work as generators that charge the battery as the car slows down • car starts out under electric power, then kicks on gasoline engine as speed increases • at stops and down hills, gasoline engine shuts off

7. hydrogen • conventional car engines can be run on hydrogen gas in the same manner as they are now able to run on methane • neither carbon dioxide nor hydrocarbon pollutants are produced • main byproduct is water vapor, along with some nitrogen oxides (NOx) • problem with hydrogen is that it is extremely abundant as an element, but not in the energy-rich gas form • can be extracted from water, but requires input of significant amounts of energy

8. production of hydrogen • plants have split water for millions of years to provide H ions for photosynthesis • 2 proposed methods of mimicking plants: • 1. use a catalyst (titanium dioxide is receiving most attention) to absorb visible light and split water • has worked with an efficiency of 8.5% (reaching 10% would achieve the DOE’s standard as a useful catalyst) • 2. pass an electrical current through water and cause the water molecules to dissociate (electrolysis) • some suggest that solar energy (collected by solar troughs) in the southwest U.S. should be used to power electrolysis • hydrogen produced could then be transported via underground pipelines (some of which already exist)

9. fuel cells • an alternative to burning hydrogen in internal combustion engines is using it in fuel cells • fuel cells would produce electricity and power an electric motor • hydrogen or some other fuel is chemically combined with oxygen to create an electrical potential • to power vehicle, fuel cells are combined into a fuel cell stack • vehicle would require: a hydrogen storage device, a cooling system, and a device to force oxygen into the fuel cells • obstacles include high cost and lack of infrastructure for hydrogen refueling