Alternative energy sources are becoming more and more popular and for this reason more and more alternative energy sources are found. Many non-renewable energy sources are being innovated to make them renewable. Three types of new renewable energy sources are mentioned in this research paper. Biomass, compressed air tanks, and fuel cells are all alternative energy sources that can power cars, but fuel cells are the best. Biomass can be used to produce energy, called biopower (Renewable Energy 2008). Biopower is powered by two types of biofuels, which are ethanol and biodiesel (Biofuel Basics). Ethanol is a fermented plant, like corn, that is produced in a process “similar to the production of alcoholic liquors” (Renewable Energy 2008). Biodiesel, “a nontoxic, biodegradable liquid fuel,” is produced from a blend of gasoline and vegetable oil (Renewable Energy 2008). Biopower is produced by burning waste wood and other sources, which then heats water which then turns into steam, which in turn drives a turbine (alternative sources of energy). There are many disadvantages of biopower; to produce biomass a large amount of land and materials is required (Renewable Energy 2008). Biopower releases carbon dioxide, but plants used in biomass use the emitted carbon dioxide (Ibid). Burning biodiesel could also increase emissions of a greenhouse gas called nitrous oxide (Ibid). The future of biopower is that larger countries will use it for heating and cooking rather than energy production (Ibid). The compressed air car has “two pumping hearts” or “separate motors that run at different times”, these motors do this to work more efficiently (CNN). The compressed air turns the pistons, which then turn the vehicle's wheels (Ibid). The only emission provided by the compressed air tank is cold air (the car runs on compressed air). The tank containing the compressed air can be disposed of or recycled with little toxic waste (Environmental Research Letters). According to CNN, compressed air tanks would reduce car production costs by at least 20%. The cost would be reduced because cars will not need cooling systems, fuel tanks and spark plugs (CNN). A prototype car with this new technology sold for almost ten thousand dollars (Car Runs on Compressed Air). One of the 6 most used types of fuel cells is the phosphoric one (Fuel Cells Explained). According to NASA, the different types depend on the different way hydrogen and oxygen combine to form water.