The main transportation tools in modern society are cars, ships and airplanes, which are vehicles for land, water and air transportation respectively. Needless to say, it takes energy to run these vehicles.
The first energy carrier for transportation is petroleum or oil, which provided about 95% of all the energy consumed in transportation in the world and 90% in the USA in 2011. Oil is a liquid fuel, which has high energy capacity, easy to transport, and easy to handle. But oil is a fossil fuel. It was formed from plants and animals that lived on the earth millions of years ago. The resources of oil are limited and non-renewable. As global demand for oil is increasing and worldly oil production will peak in the near future and then decline, the world simply cannot produce enough oil to meet the demands of oil for transportation.
The second energy carrier for transportation is natural gas. Natural gas as a transportation fuel can be either compressed natural gas (CNG) or liquefied natural gas (LNG). There were about 14 million natural gas vehicles in the world in 2011, which accounted for about 1.4% of all vehicles running on the road. Natural gas vehicles are more expensive than gasoline-powered vehicles. But natural gas has a price advantage over oil and emits fewer greenhouse gases when burned. Because huge supply is available domestically in the USA and around the world, current and predicted future price of natural gas is much lower than that of gasoline on an energy equivalent basis. With such a price advantage as a fuel, natural gas vehicles, especially those of heavy-duty trucks and high-mileage vehicles like transit-buses and taxis, will continue to grow in the coming years.
The third energy carrier for transportation is electricity. Electricity is clean, which doesn’t cause air pollution to the driving area. Some trains and a few of cars are running on electricity. There seem no big problems to produce enough electricity for present and future use because electricity can be generated from nuclear power, solar energy, wind, tidy, water force etc., as well as from coal, natural gas and oil. But there are several barriers for widely using electricity cars. First, the energy capacity of batteries is low. Generally an electricity car can only run about 100 miles. Second, it takes hours to recharge the batteries. It can be argued that the first problem could be solved with development of more effective batteries in the future; and the second problem could be solved with building up national net of battery stations: people change their batteries at the battery stations rather than wait for the batteries to be recharged. However, key materials for making rechargeable batteries are expensive and non-renewable.
The fourth energy carrier for transportation is hydrogen. Hydrogen is widely used in space transportation, for example, sending satellites and people into space by rockets. There are also a few cars running on hydrogen. The advantage of hydrogen is clean with water as the only waste. But hydrogen is not easy to handle. The tank of a car that can store hydrogen must be able to contain high pressure, which is a technological challenge. And since hydrogen is highly flammable, cars running on hydrogen have special safety issues. It seems that in the near future, hydrogen would not be able to become a popular transportation fuel.
The fifth energy carrier for transportation is liquid biofuels. Biofuels, such as ethanol, butanol and biodiesel, are fuels produced from living organisms or biomass. Since energy in biofuels originates from solar energy through photosynthesis, biofuels are renewable. Liquid biofuels can be conveniently used in current petroleum used vehicles. The problem facing biofuels is how to produce large quantity of biofuels with low and competitive price. Current ways of producing biofuels from corn, soybean, and other crops are not the solution for the future, because their production costs are high and potentials limited. It seems the future lies in genetically modified or created bacteria or algae, which will be able to directly produce biofuels by using sunlight, water and carbon dioxide.
As renewable fuels, biofuels will play more and more important roles in transportation.
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The above is one of my 8 to 10 minute Toastmasters speeches.
