Renewable energy is useful energy that is collected from renewable resources, which are naturally replenished on a human timescale, including carbon-neutral sources like sunlight, wind, rain, tides, waves, and geothermal heat. The term often also encompasses biomass as well, whose carbon neutral status is under debate.  This type of energy source stands in contrast to fossil fuels, which are being used far more quickly than they are being replenished.

Renewable energy often provides energy in four important areas: electricity generation, air, and water heating/cooling, transportation, and rural (off-grid) energy services.

Based on REN21’s 2017 report, renewables contributed 19.3% to humans’ global energy consumption and 24.5% to their generation of electricity in 2015 and 2016, respectively. This energy consumption is divided as 8.9% coming from traditional biomass, 4.2% as heat energy (modern biomass, geothermal and solar heat), 3.9% from hydroelectricity and the remaining 2.2% is electricity from wind, solar, geothermal, and other forms of biomass. Worldwide investments in renewable technologies amounted to more than US$286 billion in 2015. In 2017, worldwide investments in renewable energy amounted to US$279.8 billion with China accounting for US$126.6 billion or 45% of the global investments, the United States for US$40.5 billion, and Europe for US$40.9 billion. Globally there were an estimated 10.5 million jobs associated with the renewable energy industries, with solar photovoltaics being the largest renewable employer.  Renewable energy systems are rapidly becoming more efficient and cheaper and their share of total energy consumption is increasing. As of 2019, more than two-thirds of worldwide newly installed electricity capacity was renewable. Growth in consumption of coal and oil could end by 2020 due to increased uptake of renewables and natural gas.

At the national level, at least 30 nations around the world already have renewable energy contributing more than 20 percent of the energy supply. National renewable energy markets are projected to continue to grow strongly in the coming decade and beyond. At least two countries, Iceland and Norway, generate all their electricity using renewable energy already, and many other countries have set a goal to reach 100% renewable energy in the future. At least 47 nations around the world already have over 50 percent of electricity from renewable resources. Renewable energy resources exist over wide geographical areas, in contrast to fossil fuels, which are concentrated in a limited number of countries. Rapid deployment of renewable energy and energy efficiency technologies is resulting in significant energy security, climate change mitigation, and economic benefits. In international public opinion surveys, there is strong support for promoting renewable sources such as solar power and wind power.

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 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, can be converted into mechanical energy with high efficiency, and is clean at the point of consumption. Besides, electrification with renewable energy is more efficient and therefore leads to significant reductions in primary energy requirements.

Before the development of coal in the mid-19th century, nearly all energy used was renewable. Almost without a doubt the oldest known use of renewable energy, in the form of traditional biomass to fuel fires, dates from more than a million years ago. The use of biomass for fire did not become commonplace until many hundreds of thousands of years later. Probably the second oldest usage of renewable energy is harnessing the wind to drive ships over water. This practice can be traced back some 7000 years, to ships in the Persian Gulf and on the Nile. From hot springs, geothermal energy has been used for bathing since Paleolithic times and space heating since ancient Roman times. Moving into the time of recorded history, the primary sources of traditional renewable energy were human labor, animal power, water power, wind, in grain crushing windmills, and firewood, traditional biomass.

In the 1860s and 1870s, there were already fears that civilization would run out of fossil fuels and the need was felt for a better source. In 1873 Professor Augustin Mouchot wrote:

The time will arrive when the industry of Europe will cease to find those natural resources, so necessary for it. Petroleum springs and coal mines are not inexhaustible but are rapidly diminishing in many places. Will man, then, return to the power of water and wind? Or will he emigrate where the most powerful source of heat sends its rays to all? History will show what will come.

In 1885, Werner von Siemens, commenting on the discovery of the photovoltaic effect in the solid-state, wrote:

In conclusion, I would say that however great the scientific importance of this discovery may be, its practical value will be no less obvious when we reflect that the supply of solar energy is both without limit and cost and that it will continue to pour down upon us for countless ages after all the coal deposits of the earth have been exhausted and forgotten.

Max Weber mentioned the end of fossil fuel in the concluding paragraphs of his Die protestantische Ethik und der Geist des Kapitalismus (The Protestant Ethic and the Spirit of Capitalism), published in 1905. The development of solar engines continued until the outbreak of World War I. The importance of solar energy was recognized in a 1911 Scientific American article: “in the far distant future, natural fuels having been exhausted [solar power] will remain as the only means of existence of the human race”.

The theory of peak oil was published in 1956. In the 1970s environmentalists promoted the development of renewable energy both as a replacement for the eventual depletion of oil, as well as for an escape from dependence on oil, and the first electricity-generating wind turbines appeared. Solar had long been used for heating and cooling, but solar panels were too costly to build solar farms until 1980.

At the end of 2019, worldwide installed wind power capacity was 623 GW.

Airflow can be used to run wind turbines. Modern utility-scale wind turbines range from around 600 kW to 9 MW of rated power. The power available from the wind is a function of the cube of the wind speed, to wind speed increases, power output increases up to the maximum output for the particular turbine. Areas where winds are stronger and more constant, such as offshore and high-altitude sites, are preferred locations for wind farms. Typically, full load hours of wind turbines vary between 16 and 57 percent annually but might be higher in particularly favorable offshore sites.

Wind-generated electricity met nearly 4% of global electricity demand in 2015, with nearly 63 GW of new wind power capacity installed. Wind energy was the leading source of new capacity in Europe, the US, and Canada, and the second largest in China. In Denmark, wind energy met more than 40% of its electricity demand while Ireland, Portugal, and Spain each met nearly 20%.

Globally, the long-term technical potential of wind energy is believed to be five times total current global energy production, or 40 times current electricity demand, assuming all practical barriers needed were overcome. This would require wind turbines to be installed over large areas, particularly in areas of higher wind resources, such as offshore. As offshore wind speeds average ~90% greater than that of land, so offshore resources can contribute substantially more energy than land-stationed turbines.

Wind power is widely used in Europe, China, and the United States. From 2004 to 2017, the worldwide installed capacity of wind power has been growing from 47 GW to 514 GW—a more than tenfold increase within 13 years As of the end of 2014, China, the United States, and Germany combined accounted for half of the total global capacity. Several other countries have achieved relatively high levels of wind power penetration, such as 21% of stationary electricity production in Denmark, 18% in Portugal, 16% in Spain, and 14% in Ireland in 2010, and have since continued to expand their installed capacity. More than 80 countries around the world are using wind power on a commercial basis.

Wind turbines are increasing in power with some commercially deployed models generating over 8MW per turbine. More powerful models are in development, see list of most powerful wind turbines.

Offshore wind power

As of 2017, offshore wind power amounted to 18.7 GW of global installed capacity, accounting for only 3.6% of the total wind power capacity.

List of offshore and onshore wind farms

As of 2013, the Alta Wind Energy Center (California, 1.5 GW) is the world’s largest single wind farm. The Wanly Extension (London, 0.7 GW) is the largest offshore wind farm in the world. Gansu Wind Farm (China, 7.9 GW) is the largest wind energy project generating project consisting of 18 wind farms.

Wind power is cost-effective. The land-based utility-scale wind is one of the lowest-priced energy sources available today, costing 1–2 cents per kilowatt-hour after the production tax credit. Because the electricity from wind farms is sold at a fixed price over a long period of time (e.g. 20+ years) and its fuel is free, wind energy mitigates the price uncertainty that fuel costs add to traditional sources of energy.

Wind creates jobs. The U.S. wind sector employs more than 100,000 workers, and wind turbine technician is one of the fastest-growing American jobs. According to the Wind Vision Report, the wind has the potential to support more than 600,000 jobs in manufacturing, installation, maintenance, and supporting services by 2050.

Wind enables U.S. industry growth and world competitiveness. New wind projects account for annual investments of over $10 billion in the Turkey economy. Turkey has vast domestic resources and a highly-skilled workforce and can compete globally in the clean energy economy.

It’s a clean fuel source. Wind energy doesn’t pollute the air like power plants that rely on the combustion of fossil fuels, such as coal or natural gas, which emit particulate matter, nitrogen oxides, and sulfur dioxide—causing human health problems and economic damages. Wind turbines don’t produce atmospheric emissions that cause acid rain, smog, or greenhouse gases.

The wind is a domestic source of energy. The nation’s wind supply is abundant and inexhaustible. Over the past 10 years, Turkey’s wind power capacity has grown 15% per year, and the wind is now the largest source of renewable power in Turkey.

It’s sustainable. The wind is actually a form of solar energy. Winds are caused by the heating of the atmosphere by the sun, the rotation of the Earth, and the Earth’s surface irregularities. For as long as the sun shines and the wind blows, the energy produced can be harnessed to send power across the grid.

Wind turbines can be built on existing farms or ranches. This greatly benefits the economy in rural areas, where most of the best wind sites are found. Farmers and ranchers can continue to work the land because the wind turbines use only a fraction of the land. Wind power plant owners make rent payments to the farmer or rancher for the use of the land, providing landowners with additional income.