Renewable energy is energy that is gathered from renewable resources, which are naturally replenished on a human timescale, such as sunlight, wind, rain, tides, waves, and geothermal heat. Renewable energy often provides energy in four important areas: electricity generation, air and water heating/cooling, transportation, and rural (off-grid) energy services.
While many renewable energy projects are large-scale, renewable technologies are also suited to rural and remote areas and developing countries, where energy is often crucial in human development. As most of renewable energy technologies provide electricity, renewable energy deployment is often applied in conjunction with further electrification, which has several benefits: electricity can be converted to heat (where necessary generating higher temperatures than fossil fuels), can be converted into mechanical energy with high efficiency, and is clean at the point of consumption. In addition, electrification with renewable energy is more efficient and therefore leads to significant reductions in primary energy requirements.
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is filtered through Earth’s atmosphere, and is obvious as daylight when the Sun is above the horizon. When the direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. When it is blocked by clouds or reflects off other objects, it is experienced as diffused light. The World Meteorological Organization uses the term “sunshine duration” to mean the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per square meter. Other sources indicate an “Average over the entire earth” of “164 watts per square meter over a 24 hour day”.
The ultraviolet radiation in sunlight has both positive and negative health effects, as it is both a requisite for vitamin D3 synthesis and a mutagen.
Sunlight takes about 8.3 minutes to reach Earth from the surface of the Sun. A photon starting at the center of the Sun and changing direction every time it encounters a charged particle would take between 10,000 and 170,000 years to get to the surface.
Sunlight is a key factor in photosynthesis, the process used by plants and other autotrophic organisms to convert light energy, normally from the Sun, into chemical energy that can be used to synthesize carbohydrates and to fuel the organisms’ activities. What role does renewable energy play in the United States?
Until the mid-1800s, wood was the source of nearly all the nation’s energy needs for heating, cooking, and lighting. From the late 1800’s until today, fossil fuels—coal, petroleum, and natural gas—have been the major sources of energy. Hydropower and solid biomass were the most used renewable energy resources until the 1990s. Since then, the shares of U.S. energy consumption from biofuels, solar, and wind energy have increased.
In 2018, renewable energy provided about 11.5 quadrillion British thermal units (Btu)—1 quadrillion is the number 1 followed by 15 zeros—equal to 11% of total U.S. energy consumption. The electric power sector accounted for about 56% of total U.S. renewable energy consumption in 2018, and about 17% of total U.S. electricity generation was from renewable energy sources.
Renewable energy plays an important role in reducing greenhouse gas emissions. Using renewable energy can reduce the use of fossil fuels, major sources of carbon dioxide emissions.
The consumption of biofuels and other nonhydroelectric renewable energy sources in the United States more than doubled from 2000 to 2018, mainly because of state and federal government requirements and incentives to use renewable energy. The U.S. Energy Information Administration projects that U.S. renewable energy consumption will increase through 2050.