Renewable Energy: An Overview


Renewable energy includes many different types of energy sources, such as solar, hydro, wind, geothermal, and biofuels. These sources constantly renew themselves and are considered virtually inexhaustible. In recent years, new focus has been placed on the development and improvement of renewable energy sources. New incentives and regulations have emerged, ranging from funding for research and development of alternative energy sources and production requirements designed to lessen our dependence on petroleum-based fuels, to new air emissions standards and tax credits for implementing renewable energy systems.


Solar energy is a renewable source of energy supplied by the sun. Solar energy can be converted to electricity using photovoltaic (PV) devices, commonly called “solar cells,” or through solar-thermal technologies at solar power plants. Solar cells change sunlight directly into electricity and are made of silicon or other conductive materials. When sunlight hits the solar cell, a chemical reaction takes place resulting in electricity. Solar-thermal technologies in use at solar power plants use the heat from solar thermal collectors to create steam, which powers a generator. According to the U.S. Department of Energy, the greatest potential for solar energy in the U.S. is in Southwestern states, where sufficient solar energy falls on an area of 100 miles by 100 miles to provide all of the nation’s electricity requirements. More than 2 million solar PV devices have been installed in the United States, which produces enough electricity in a year to power more than 12 million homes.


Hydropower, or energy derived from the movement of water, is the most commonly used form of renewable energy in the United States. Water that is moving quickly, such as in a fast-flowing river or from a waterfall, can be utilized for hydropower by channeling the water through pipes toward turbines. As the water moves the turbines, electricity is generated. Hydropower can also be developed by building dams along rivers to create reservoirs and lakes of water. When the demand for electricity is high, the dam is opened, and the water is pushed through turbines generating power. The lakes created by the dam also provide recreational opportunities such as boating and fishing. There are some concerns about the impact dams and turbines have on aquatic life and natural habitats due to changes in the course, flow or temperature of the water. Other more infrequently used methods of producing hydropower include tidal power, wave power, and ocean thermal energy conversion. Tidal power produces energy using the natural movement of water currents and tides. Wave power captures the energy produced from waves. Ocean thermal energy conversion uses the temperature difference between the surface of the ocean and deep ocean waters, called thermal gradients, to produce energy.


Wind, the movement of air, is created when the earth’s air is unevenly heated, and warmer air moves toward cooler air. Wind turbines are used to harness the energy produced by the movement of air, and usually have two or three long blades that spin as the air moves over them. The energy of motion contained in the air is converted to electricity as the blades turn a generator. To create a useable amount of electricity for a large population, several wind turbines placed together on a “wind farm” are necessary. Opponents of wind farms point to the problems inherent with placing these large turbines close to populated areas, the harm they cause to wildlife, and the noise that they generate during operation. In 2016 the United States completed its first offshore wind project and has since developed several more. Offshore wind turbines are mainly located in deep water and use undersea cables to transmit the electricity generated to the electrical grid.


Geothermal energy is heat from within the earth’s core about 4,000 miles below the surface. The heat is continuously produced inside the earth by the slow decay of radioactive particles, a natural process that occurs in all rocks. This heat produces either hot water or steam that is used to heat buildings or water, or to generate electricity in a geothermal power plant. Geothermal energy can also be extracted by pumping water underground to be heated by hot, dry rocks. Steam is then returned to the surface for use in generating electricity. Some drawbacks are that geothermal energy is costly to access unless it is close to the earth’s surface and geothermal technology is limited to mainly volcanically and tectonically active regions.


The agriculture industry has found strong footing in the world of renewable energy through biofuels. These are fuels produced from biomass, or any plant-derived organic matter available on a renewable basis. Biomass includes agricultural food and feed crops, agricultural crop wastes and residues, wood wastes and residues, aquatic plants, animal wastes, municipal wastes and other waste materials.

The two most common types of biofuels for transportation are ethanol and biodiesel. Ethanol is typically produced through a biological process of fermentation of biomass high in carbohydrates. Corn is used most often in the United States. Ethanol is mostly used as a blending agent with gasoline to increase octane and to reduce air emissions. Most vehicles can operate on a gasoline-ethanol blend without any modification. A new type of ethanol- cellulosic ethanol- has recently emerged. This type of ethanol can be produced from a wide variety of biomass materials, most importantly from non-food plant materials. Proponents of cellulosic ethanol argue that it is better than conventionally produced corn-based ethanol because cellulosic ethanol uses non-food portions of renewable feedstock and can be produced from other non-food biomass such as switchgrass, wood products, and by-products of other crops. However, the refining process for cellulosic ethanol is more complex than that for conventionally produced ethanol, making it prohibitively expensive to produce with the current technology.

Biodiesel is an alternative fuel for use in diesel engines that is made from fats or oils such as animal fats and new or used vegetable oils. The most commonly used oils are soybean, rapeseed and sunflowers. Biodiesel is created in a process called transesterification where glycerin is separated from the fat or oil. This process creates two products – biodiesel and glycerin (used to make soap). It is usually blended with petroleum diesel in ratios of 2 percent, 5 percent or 20 percent, but can also be used as pure biodiesel. Biodiesel is one of the most common types of biofuels in the United States and can be used in most diesel engines without any modification. It is clean-burning, domestically produced and a renewable source of energy. The use of algae as a renewable fuel source has been growing in popularity in recent years and many companies are searching for ways to make producible at commercial level to be processed into biodiesels. Other forms of energy can be produced from biomass as well. According to the U.S. Department of Energy, bioenergy technologies use biomass resources to produce a variety of energy related products including electricity, liquid, solid and gaseous fuels, heat, chemicals, and other materials.  In 2018 energy from biomass, which includes biomass waste, biofuels, and wood, made up 45% of the total renewable energy consumed.

Major Statutes

Agricultural Improvement Act of 2018

The Agricultural Improvement Act of 2018 authorized mandatory funding for various programs listed under the Energy Title that are aimed at benefitting the bioenergy and biofuels industry. This included funding for programs such as the Biobased Markets Program, Biorefinery Assistance Program, Bioenergy Program for Advanced Biofuels, Rural Energy for America Program, and the Carbon Utilization and Biogas Education Program. The Act also expanded the previous definitions of what constitutes renewable chemicals and biobased products to allow for more innovative developments in renewable energy.

Food, Conservation and Energy Act of 2008

The Food, Conservation, and Energy Act of 2008 included several energy-related provisions. Among other things, it established the Biomass Crop Assistance Program which encourages the production of feedstocks for cellulosic ethanol, provides multi-year contracts to growers of dedicated energy crops, and creates incentives for the production, storage and transportation of biomass to bioenergy facilities. The Act also established a sugar-to-ethanol program, and provided millions of dollars for a biobased marketing program, and a Biodiesel Education Program. Finally, the Act established the Rural Energy for America Program which provides grants and loans to farmers for the purpose of purchasing renewable energy systems and making energy efficiency improvements.

Energy Independence and Security Act of 2007

The Energy Independence and Security Act of 2007 was designed to improve vehicle fuel economy and reduce U.S. dependence on oil. It increased the Renewable Fuel Standards created by the Energy Policy Act of 2005 by nearly five times and extended the requirements through 2022. Additionally, it aimed to reduce the demand for fuel by setting a new national fuel economy standard of 35 miles per gallon for passenger cars and light trucks by 2020. Other provisions of the act were aimed at increasing efficiency in homes and businesses.

Energy Policy Act of 2005

The Energy Policy Act of 2005 was the first major energy legislation to be enacted since the Energy Policy Act of 1992. The Energy Policy Act of 2005 includes a variety of incentives and programs to encourage the development and production of alternative fuels. One of the most important was the creation of the Renewable Fuel Standards (RFS), which requires refiners, blenders and importers of gasoline to blend a certain amount of renewable fuels with gasoline each year. The initial requirements were to incorporate approximately 4 billion gallons of renewable fuels in 2006, increasing over time to 7.5 billion gallons in 2012. However, the RFS requirements were increased and extended by the Energy Independence and Security Act of 2007. The new RFS requires 9 billion gallons to be blended in 2008, and increases that requirement to 36 billion gallons by 2022. A refiner, blender or importer of gasoline can meet the RFS requirements through the purchase or trade of “credits.” Credits can be earned by producing over the baseline requirements. Those refiners that produce more than they are required can sell their credits to gasoline suppliers and importers. This allows suppliers to meet the RFS requirements while using less renewable fuel than required.

American Jobs Creation Act of 2004

The American Jobs Creation Act of 2004 authorized the Volumetric Ethanol Excise Tax Credit, providing blenders with a $0.51/gallon credit for every gallon of ethanol that is blended with gasoline. It serves as an incentive to the petroleum industry to blend ethanol into gasoline and helps to make ethanol more affordable to consumers. The tax applied through December 2010, was renewed for another year, and expired on December 31, 2011.

Farm Security and Rural Investment Act of 2002

The Farm Security and Rural Investment Act of 2002 was the first farm bill to contain an energy title. It included provisions that are designed to increase federal government purchase and use of biobased products through the BioPreferred program. Additionally, USDA provides opportunities for the development of biofuels and other renewable energy through loan guarantee programs.

Biomass Research and Development Act of 2000

The Biomass Research and Development Act of 2000 was first authorized by the Agricultural Risk Protection Act of 2000. The act directed the Departments of Energy and Agriculture to coordinate on biomass research and development, and establish a technical advisory committee.  That committee is known as the Biomass Research and Development Board and Technical Advisory Committee. Its main function is to coordinate with other federal programs, and promote the use of biobased industrial products. The Biomass Research and Development Initiative awards competitive grants, contracts and financial assistance to those who research and develop low cost and sustainable biobased Industrial products. Funds have been appropriated to the Department of Energy and the Department of Agriculture through these programs.

The Biomass Research and Development Act was repealed by the Food, Conservation, and Energy Act of 2008, but reauthorized by the Agricultural Improvement Act of 2018.