Renewable Energy

At-a-glance

  • Renewable energy is the fastest-growing energy source in the United States, increasing 67 percent from 2000 to 2016.
  • Renewables made up nearly 15 percent of net U.S. electricity generation in 2016, with the bulk coming from hydropower (6.5 percent) and wind power (5.6 percent).
  • Solar generation is projected to climb from 7 percent of total U.S. renewable generation in 2015 to about 36 percent by 2050, making it the fastest-growing electricity source.
  • Globally, renewables made up 24 percent of electricity generation in 2014, much of it from hydropower (17 percent).
  • Renewable ethanol and biodiesel transportation fuels made up over 22 percent of total U.S. renewable energy consumption in 2016, up from 12 percent in 2006.

Renewable Supply and Demand

Renewable energy is the fastest-growing energy source globally and in the United States.

Globally:

  • Nineteen percent of the energy consumed globally for heating, power, and transportation was from renewable sources in 2015 (see figure below). About half came from modern renewables (i.e., biomass, geothermal, solar, hydro, wind, and biofuels) and half from traditional biomass (used in residential heating and cooking in developing countries).
  • Renewables made up 24 percent of global electricity generation in 2014. That’s expected to rise to 31 percent by 2040. Most of the increase will likely come from wind and hydropower.

The International Energy Agency notes that the development and deployment of renewable energy technologies will depend heavily on government policies to make renewable energy cost-competitive.

Estimated Global Renewable Energy Share of Total Final Energy Consumption (2015)

In the United States:

  • Ten percent of the energy consumed across sectors in the United States was from renewable sources in 2016 (10.2 quadrillion Btu out of a total of 97.4 quadrillion Btu). U.S. consumption of renewables is expected to grow over the next 25 years at an average annual rate of 2 percent, higher than the overall growth rate in energy consumption (0.2 percent per year) under a business-as-usual scenario.
  • Renewables made up nearly 15 percent of electricity generation in 2016, with hydro, wind, and biomass making up the majority. That’s expected to rise to 25 percent by 2030. Most of the increase is expected to come from wind and solar. Non-hydro renewables have increased their share of electric power generation from less than 1 percent in 2005 to nearly 7 percent at the end of 2016 while demand for electricity has remained relatively stable.

In the transportation sector, renewable fuels, such as ethanol and biodiesel, have increased significantly during the past decade. E85 (ethanol transportation fuel) is expected to be the fastest growing renewable energy type, growing at an average annual rate of 9.7 percent over the next 25 years, although it starts from a very low base.

In the industrial sector, biomass makes up 98 percent of the renewable energy use with nearly 60 percent derived from biomass wood, 33 percent from biofuels, and nearly 8 percent from biomass waste.

Uncertainty about federal tax credits, fuel prices, and economic growth will influence the pace of U.S. renewable energy source development.

Renewable Energy Drivers

Factors affecting renewable energy deployment include market conditions (e.g., cost, diversity, proximity to demand or transmission, and resource availability), policy decisions (e.g., tax credits, feed-in tariffs, and renewable portfolio standards) as well as specific regulations. At least 176 countries, more than half of which are developing, had renewable energy policy targets in place at the end of 2016.

Businesses with sustainability goals are also driving renewable energy development by building their own facilities (e.g., solar roofs and wind farms), procuring renewable electricity through power purchase agreements, and purchasing renewable energy certificates (RECs).

Policy Drivers

Two federal tax credits have encouraged renewable energy:

  • The production tax credit (PTC), first enacted in 1992 and subsequently amended, is a corporate tax credit available to a wide range of renewable technologies including wind, landfill gas, geothermal, and small hydroelectric. For wind, geothermal and closed-loop biomass, the utility receives a 2.2 ¢/kWh ($22/MWh) credit for all electricity generated during the first 10 years of operation. For wind, with an average total system levelized cost of $64/MWh, the PTC represents a 34 percent cost reduction.
  • The investment tax credit (ITC) is earned when qualifying equipment, including solar hot water, photovoltaics, small wind turbines, is placed into service. The credit reduces installation costs and shortens the payback time of these technologies. The Consolidated Appropriations Act (2016) extended the ITC for three years and phases out the PTC by 2020.

States offer added incentives, making renewables even easier to implement from a cost perspective. 

A renewable portfolio standard requires electric utilities to deliver a certain amount of electricity from renewable or alternative energy sources by a given date. State standards range from modest to ambitious, and qualifying energy sources vary. Some states also include “carve-outs” (requirements that a certain percentage of the portfolio be generated from a specific energy source, such as solar power) or other incentives to encourage the development of particular resources. Although climate change may not be the prime motivation behind these standards, they can deliver significant greenhouse gas reductions and other benefits, including job creation, energy security, and cleaner air. Most states allow utilities to comply with the renewable portfolio standard through tradeable credits that utilities can sell for additional revenue.

In states with a renewable portfolio standard, utilities consider cost, intermittency and resource availability in choosing technologies that satisfy this requirement.

In the U.S. transportation sector, The Energy Policy Act of 2005 created a Renewable Fuel Standard that required 2.78 percent of gasoline consumed in the United States in 2006 to be renewable fuel.

The Energy Independence and Security Act of 2007 created a new Renewable Fuel Standard, which increased the required volumes of to 36 billion gallons by 2022, or about 7 percent of expected annual gasoline and diesel consumption above a business-as-usual scenario.

Types of Renewable Energy

Renewable energy comes from sources that can be regenerated or naturally replenished. The main sources are:

  • Water (hydropower and hydrokinetic)
  • Wind
  • Solar (power and hot water)
  • Biomass (biofuel and biopower)
  • Geothermal (power and heating)

All sources of renewable energy are used to generate electric power. In addition, geothermal steam is used directly for heating and cooking. Biomass and solar sources are also used for space and water heating. Ethanol and biodiesel (and to a lesser extent, gaseous biomethane) are used for transportation.

Renewable energy sources are considered to be zero (wind, solar, and water), low (geothermal) or neutral (biomass) with regard to greenhouse gas emissions during their operation. A neutral source has emissions that are balanced by the amount of carbon dioxide absorbed during the growing process. However, each source’s overall environmental impact depends on its overall lifecycle emissions, including manufacturing of equipment and materials, installation as well as land-use impacts.

Water

Large conventional hydropower projects currently provide the majority of renewable electric power generation. With nearly 1,100 gigawatts (GW) of global capacity, hydropower produced an estimated 4,100 terawatt hours (TWh) of the 24,659 TWh total global electricity in 2016

The United States is the third-largest producer of hydropower after China and Brazil. In 2011, a much wetter than average year in the U.S. Northwest, the United States generated 7.9 percent of its total electricity from hydropower. The Department of Energy has found that the untapped generation potential at existing U.S. dams designed for purposes other than power production (i.e., water supply and inland navigation) represents 12 GW, roughly 15 percent of current hydropower capacity.

Hydropower operational costs are relatively low, and hydropower generates little to no greenhouse gas emissions. The main environmental impact is that a dam to create a reservoir or divert water to a hydropower plant changes the ecosystem and physical characteristic of the river.

Water power captures the energy of flowing water in rivers, streams, and waves to generate electricity. Conventional hydropower plants can be built in rivers with no water storage (known as “run-of-the-river” units) or in conjunction with reservoirs that store water, which can be used on an as-needed basis. As water travels downstream, it is channeled down through a pipe or other intake structure in a dam (penstock). The flowing water turns the blades of a turbine, generating electricity in the powerhouse, located at the base of the dam.

Hydroelectric Power Generation

Small hydropower projects, generally less than 10 megawatts (MW), and micro-hydropower (less than 1 MW) are less costly to develop and have a lower environmental impact than large conventional hydropower projects. In 2016, the total amount of small hydro installed worldwide was 78 GW. China had the largest share at 51 percent. China, Italy, Japan, Norway and the United States are the top five small hydro countries by installed capacity. Many countries have renewable energy targets that include the development of small hydro projects.

Hydrokinetic electric power, including wave and tidal power, is a form of unconventional hydropower that captures energy from waves or currents and does not require dam construction. These technologies are in various stages of research, development, and deployment. In 2011, a 254 MW tidal power plant in South Korea began operation, doubling the global capacity to 527 MW. By the end of 2016, global capacity was about 536 MW.

Low-head hydro is a commercially available source of hydrokinetic electric power that has been used in farming areas for more than 100 years. Generally, the capacity of these devices is small, ranging from 1kW to 250kW.

Pumped storage hydropower plants use inexpensive electricity (typically overnight during periods of low demand) to pump water from a lower-lying storage reservoir to a storage reservoir located above the power house for later use during periods of peak electricity demand. Although economically viable, this strategy is not considered renewable since it uses more electricity than it generates.

Hydroelectric Power Generation

Wind

Wind was the second largest renewable energy source (after hydropower) for power generation. Wind power produced more than 3 percent of global electricity in 2016 with 487 GW of global capacity. Capacity is indicative of the maximum amount of electricity that can be generated when the wind is blowing at sufficient levels for a turbine. Because the wind is not always blowing, wind farms do not always produce as much as their capacity. With more than 149 MW, China had the largest installed capacity of wind generation in 2016. The United States, with 82 GW, had the second-largest capacity; Texas, Iowa, Oklahoma, Kansas, and California were the top five wind-power-producing states.

Although people have harnessed the energy generated by the movement of air for hundreds of years, modern turbines reflect significant technological advances over early windmills and even over turbines from just 10 years ago. Generating electric power using wind turbines creates no greenhouse gases, but since a wind farm includes dozens or more turbines, widely-spaced, it requires thousands of acres of land. For example, Lone Star is a 200 MW wind farm on approximately 36,000 acres in Texas.

Average turbine size has been steadily increasing over the past 30 years. Today, new onshore turbines are typically in the range of 1.5-3.5 MW. The largest production models, designed for off-shore use can generate more than 9.5 MW; some innovative turbine models under development are expected to generate more than 15 MW in offshore projects in the coming years. Due to higher costs and technology constraints, off-shore capacity, approximately 14.4 GW in 2016, is only a small share of total installed wind generation capacity.

Evolution of Wind Turbines

Solar 

Solar energy resources are massive and widespread, and they can be harnessed anywhere that receives sunlight. The amount of solar radiation, also known as insolation, reaching the Earth’s surface every hour is more than all the energy currently consumed by all human activities each year. A number of factors, including geographic location, time of day, and weather conditions, all affect the amount of energy that can be harnessed for electricity production or heating purposes.

Solar energy can be captured for electricity production using:

  • A solar or photovoltaic cell, which converts sunlight into electricity using the photoelectric effect. Typically, photovoltaics are found on the roofs of residential and commercial buildings. Additionally, utilities have constructed large (greater than 100 MW) photovoltaic facilities that require anywhere from 5 to 13 acres per MW, depending on the technologies used.
  • Concentrating solar power, which uses lenses or mirrors to concentrate sunlight into a narrow beam that heats a fluid, producing steam to drive a turbine that generates electricity. Concentrating solar power projects are larger-scale than residential or commercial PV and are often owned and operated by electric utilities.

Solar hot water heaters, typically found on the roofs of homes and apartments, provide residential hot water by using a solar collector, which absorbs solar energy, that in turn heats a conductive fluid, and transfers the heat to a water tank. Modern collectors are designed to be functional even in cold climates and on overcast days.

Electricity generated from solar energy emits no greenhouse gases. The main environmental impacts of solar energy come from the use of some hazardous materials (arsenic and cadmium) in the manufacturing of PV and the large amount of land required, hundreds of acres, for a utility-scale solar project.

Concentrating Solar Power

Biomass

Biomass energy sources are used to generate electricity and provide direct heating, and can be converted into biofuels as a direct substitute for fossil fuels used in transportation. Unlike intermittent wind and solar energy, biomass can be used continuously or according to a schedule. Biomass is derived from wood, waste, landfill gas, crops and alcohol fuels. Traditional biomass, including waste wood, charcoal and manure, has been a source of energy for domestic cooking and heating throughout human history. In rural areas of the developing world, it remains the dominant fuel source.  Globally in 2016, traditional biomass accounted for about 9.1 percent of total energy consumption. The growing use of biomass has resulted in increasing international trade in biomass fuels in recent years; wood pellets, biodiesel, and ethanol are the main fuels traded internationally.

In 2016, global biomass electric power capacity stood at 112 GW. In 2015, the United States had 16 GW of installed biomass-fueled electric generation capacity. In the United States, most of the electricity from wood biomass is generated at lumber and paper mills using their own wood waste; in addition, wood waste is used to generate the heat for drying wood products and other manufacturing processes. Biomass waste is mostly municipal solid waste, i.e., garbage, which is burned as a fuel to run power plants. On average, a ton of garbage generates 550 to 750 kWh of electricity. Landfill gas contains methane that can be captured, processed and used to fuel power plants, manufacturing facilities, vehicles and homes. In the United States, there is currently more than 2 GW of installed landfill gas-fired generation capacity at more than 600 projects.

In addition to landfill gas, biofuels can be synthesized from dedicated crops, trees and grasses, agricultural waste and algae feedstock; these include renewable forms of diesel, ethanol, butanol, methane and other hydrocarbons. Corn ethanol is the most widely used biofuel in the United States. Roughly 36 percent of the U.S. corn crop was diverted to the production of ethanol for gasoline in 2016, up from 20 percent in 2006. Gasoline with up to 10 percent ethanol (E10) can be used in most vehicles without further modification, while special flexible fuel vehicles can use a gasoline-ethanol blend that has up to 85 percent ethanol (E85).

Closed-loop biomass, where power is generated using feedstocks grown specifically for the purpose of energy production, is generally considered to be carbon dioxide neutral because the carbon dioxide emitted during combustion of the fuel was previously captured during the growth of the feedstock. While biomass can avoid the use of fossil fuels, the net effect of biopower and biofuels on greenhouse gas emissions will depend on full lifecycle emissions for the biomass source, how it is used, and indirect land-use effects. Overall, however, biomass energy can have varying impacts on the environment. Wood biomass, for example, contains sulfur and nitrogen, which yield air pollutants sulfur dioxide and nitrogen oxides, though in much lower quantities than coal combustion.

Geothermal

At least 82 countries used direct geothermal power in 2016. Geothermal provided an estimated 157 TWh globally in 2016, one half in the form of electricity (with an estimated 13.5 GW of capacity) and the remaining half in the form of heat. (Total global electricity generation in 2016 was 24,659 TWh).

In the United States, 17.4 billion kWh of geothermal electricity was generated in 2016, making up about 5 percent of non-hydroelectric renewable electricity generation, but only 0.4 percent of total electricity generation. Seven states generated electricity from geothermal energy: California, Hawaii, Idaho, Nevada, New Mexico, Oregon and Utah. Of these, California accounted for 80 percent of this generation.

Traditional geothermal energy exploits naturally occurring high temperatures, located relatively close to the Earth’s surface in some areas, to generate electric power and for direct uses such as heating and cooking. Geothermal areas are generally located near tectonic plate boundaries, where there are earthquakes and volcanoes. In some places, hot springs and geysers have been used for bathing, cooking and heating for centuries

Generating geothermal electric power typically involves drilling a well, perhaps a mile or two in depth, in search of rock temperatures in the range of 300 to 700°F. Water is pumped down this well, where it is reheated by hot rocks. It travels through natural fissures and rises up a second well as steam, which can be used to spin a turbine and generate electricity or be used for heating or other purposes. Several wells may have to be drilled before a suitable one is in place and the size of the resource cannot be confirmed until after drilling. Additionally, some water is lost to evaporation in this process, so new water is added to maintain the continuous flow of steam. Like biopower and unlike intermittent wind and solar power, geothermal electricity can be used continuously. Very small quantities of carbon dioxide trapped below the Earth’s surface are released during this process.

Enhanced geothermal systems use advanced, often experimental, drilling and fluid injection techniques to augment and expand the availability of geothermal resources.

Geothermal Power Station

U.S. Renewable Resource Availability

The following maps from the DOE National Renewable Energy Laboratory depict the relative availability of renewable energy resources throughout the United States.

  • Wind resources are abundant in the Great Plains, Iowa, Minnesota, along the spine of Appalachian Mountains, in the Western Mountains and many off-shore locations.
  • Solar photovoltaic and concentrating solar power resources are the highest in the desert Southwest and diminish in intensity in a northward direction.
  • The best biomass resources are in the upper central plains (corn) and forests of the Pacific Northwest.
  • Traditional geothermal resources are concentrated in the Western United States.

U.S. Wind Resource Map

U.S. Photovoltaic Solar Resources

U.S. Biomass Resource

U.S. Geothermal Resource