Bioenergy is an important part of the U.S. renewable energy program because it can help improve energy and economic security while at the same time enhancing rural economic development. Biofuels are liquid fuels that are produced from plant materials and are a renewable source of energy. These fuels can include a range of products from biodiesel to ethanol and butanol. Energy can also be produced from biogases like hydrogen or methane which, when combusted, produce heat energy. Plant material can be used to produce electricity as well by replacing coal in power plants.