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As the number of people in the world keeps growing, so does our need for energy. Some energy sources, specifically fossil fuels like coal and oil, are in limited supply. Once we use up what's in the ground, they will be gone forever. Other energy sources, such as wind, water power, and solar energy, are called renewable energy, because they will regenerate over and over again as we use them. Ethanol is one form of renewable energy that is becoming widely used. Ethanol is a form of alcohol that can be burned in engines just like gasoline. But unlike gasoline, which is made by distilling crude oil, ethanol is made from the starchy parts of plants. Most ethanol in this country is created through fermentation of corn. Microscopic yeast cells break down the starch and water, creating ethanol and carbon dioxide gas. In addition to being a renewable fuel, ethanol helps to reduce air pollution. When anything burns in air, molecules of that substance combine with oxygen. Gasoline is a substance made of carbon and hydrogen. When it burns, some, but not all, of the carbon atoms combine with oxygen to make carbon dioxide (CO2). Hydrogen in the gasoline combines with more of the air's oxygen to make water (H2O). There isn't enough oxygen left to combine with the remaining carbon atoms. Deadly carbon monoxide gas (CO) is the result. Like gasoline, ethanol is made of carbon and hydrogen, but in addition it contains its own supply of oxygen. When ethanol burns with gasoline, its "extra" oxygen atoms combine with the "extra" carbon atoms to reduce or even eliminate CO in the exhaust gases. In some parts of the U.S., ethanol is mixed with gasoline at 1 part ethanol to 9 parts gasoline to help reduce air pollution. No adjustment is needed for a car's engine to burn this mixture. Some new cars are designed to burn fuel blends of up to 80 percent ethanol. Ethanol costs more to make than gasoline. New production technologies may bring the price of ethanol down in the coming years. Another disadvantage is that a gallon of ethanol doesn't hold as much chemical energy as a gallon of gasoline. So even though ethanol burns more cleanly than gasoline, a car won't go as many miles per gallon.
