- Also called:
- alternative energy
- Key People:
- T. Boone Pickens
- Daniel G. Nocera
renewable energy
What is renewable energy?
How is renewable energy different from nonrenewable energy?
What are the main types of renewable energy?
Is nuclear power considered renewable?
News •
renewable energy, usable energy derived from sources that are naturally replenished, including the Sun (solar power), wind (wind power), rivers (hydroelectric power), hot springs (geothermal energy), tides (tidal power), and biomass (biofuels). Unlike fossil fuels, including natural gas, coal, and petroleum, which are finite and require millions of years to form, renewable energy sources are continually renewed on human timescales. Because they generally produce lower emissions of greenhouse gases and air pollutants than fossil fuels, renewable-energy technologies have become increasingly important in efforts to combat the growing climate crisis and to meet global energy demands while reducing environmental impacts.
In the early 21st century, renewable energy emerged as one of the fastest-growing sectors of the world energy economy. Hydroelectric power, solar power, and wind power account for most renewable electricity generation, with other forms contributing in regions where local conditions are favorable, such as geothermal energy in volcanically active areas and tidal power along suitable coastlines. The expansion of renewable energy has been driven by technological innovation, declining costs, energy-security concerns, and efforts to limit climate change.
Types
Renewable energy is obtained from several naturally replenishing sources, each relying on different processes to convert natural energy flows into usable electricity, heat, or fuel. Major types include:
" height="20" alt="HEW Logo">
- Solar power: Uses sunlight to generate electricity or heat through photovoltaic panels and solar thermal technologies
- Wind power: Generates electricity using wind turbines driven by moving air
- Hydroelectric power: Produces electricity by harnessing the energy of flowing or falling water
- Wave power: Captures energy from the motion of ocean waves to produce electricity
- Geothermal power: Uses heat from the Earth’s interior for electricity generation and direct heating applications
- Biofuels: Converts plant material, agricultural waste, and other organic matter into heat, electricity, or transportation fuels
Nuclear power is often grouped with low-carbon energy sources because nuclear reactors generate electricity with very low direct greenhouse gas emissions. However, nuclear energy is generally not considered renewable because it depends on finite supplies of uranium and other nuclear fuels. Unlike sunlight, wind, flowing water, or geothermal heat, these fuels are not replenished on human timescales.
The problems of fossil fuels
At the beginning of the 21st century, about 80 percent of the world’s energy supply was derived from fossil fuels such as coal, petroleum, and natural gas. Fossil fuel combustion has a number of negative environmental consequences. Furthermore, the burning of fossil fuels releases carbon dioxide (CO2), one of the main greenhouse gases that cause global warming. Carbon dioxide released from fossil fuel combustion had been stored underground for millions of years in coal, petroleum, and natural gas deposits. Burning these fuels transfers that stored carbon rapidly into the atmosphere, altering Earth’s carbon cycle and contributing to the greenhouse effect.
Fossil-fueled power plants emit air pollutants such as sulfur dioxide, particulate matter, nitrogen oxides, and toxic heavy metals such as mercury, chromium, and arsenic. Fossil-fueled vehicles emit nitrogen oxides, carbon monoxide, and particulate matter. Exposure to these pollutants can cause heart disease, asthma, and other human health problems. In addition, emissions from fossil fuel combustion are responsible for acid rain, which has led to the acidification of many lakes and consequent damage to aquatic life, leaf damage in many forests, and the production of smog in or near many urban areas.
Fossil fuels are finite resources; most estimates suggest that the proven reserves of oil are large enough to meet global demand at least until the middle of the 21st century. Depleted reserves of conventional oil fields have caused some producers to turn to heavy oil and tar sands, the recovery and refinement of which carry significant ecological and economic costs. Although the petroleum industry has long minimized the ecological and climate impacts of fossil fuel combustion, the depletion of conventional sources of crude oil and other fossil fuels remains an incentive to invest in alternative energies. See also peak oil theory.
The trusted destination for professionals, college students, and lifelong learners.
SUBSCRIBE
Growth of renewables in the 21st century
In a historic first, renewable energy surpassed coal as the world’s leading source of electricity in the first half of 2025.
Renewable energy sources accounted for nearly 20 percent of global energy consumption at the beginning of the 21st century, largely from traditional uses of biomass such as wood for heating and cooking. By 2015 about 16 percent of the world’s total electricity came from large hydroelectric power plants, whereas other types of renewable energy (such as solar, wind, and geothermal) accounted for 6 percent of total electricity generation. Some energy analysts consider nuclear power to be a form of renewable energy because of its low carbon emissions; nuclear power generated 10.6 percent of the world’s electricity in 2015.
Growth in wind power exceeded 20 percent and photovoltaics grew at 30 percent annually in the 1990s, and renewable energy technologies continued to expand throughout the early 21st century. Between 2001 and 2017 world total installed wind power capacity increased by a factor of 22, growing from 23,900 to 539,581 megawatts. Photovoltaic capacity also expanded, increasing by 50 percent in 2016 alone. The European Union (EU), which produced an estimated 6.38 percent of its energy from renewable sources in 2005, adopted a goal in 2007 to raise that figure to 20 percent by 2020. By 2016 some 17 percent of the EU’s energy came from renewable sources. The goal also included plans to cut emissions of carbon dioxide by 20 percent and to ensure that 10 percent of all fuel consumption comes from biofuels. The EU was well on its way to achieving those targets by 2017. Between 1990 and 2016 the countries of the EU reduced carbon emissions by 23 percent and increased biofuel production to 5.5 percent of all fuels consumed in the region. In the United States numerous states have responded to concerns over climate change and reliance on imported fossil fuels by setting goals to increase renewable energy over time. For example, California required its major utility companies to produce 20 percent of their electricity from renewable sources by 2010, and by the end of that year California utilities were within 1 percent of the goal. In 2008 California increased this requirement to 33 percent by 2020, and in 2017 the state further increased its renewable-use target to 50 percent by 2030.
