What is renewable energy?

A field of solar panels next to a wind turbine at sunset. — Renewable energy harnesses the wind's strength and sun's heat to generate electricity.

(Image credit: Peter Cade/Getty Images)

Renewable energy comes from sources that are replenished naturally, such as the sun and wind. Traditional energy sources, like coal and oil, are finite and when burned, release carbon in the form of carbon dioxide and methane — two greenhouse gases that significantly contribute to the acceleration of global climate change. Renewable energy, on the other hand, either does not emit carbon or is carbon neutral, meaning it absorbs as much carbon as it emits.

Tapping into sources of renewable energy is a relatively new development in the history of human energy production. Early human ancestors used wood to generate heat energy, then switched to coal, a fuel with higher energy density, as summarized in the textbook "The Cambridge World History" (Cambridge University Press, 2015). Petroleum oil now fuels the majority of the world's transportation industry, including cars, airplanes, boats and trains, according to the U.S. Energy Information Administration (EIA).

Not only are fossil fuels accelerating global climate change, but the supply is limited, so they're not a sustainable source of energy. Industries, countries and individuals around the world are now turning to renewable energy sources, which either do not produce carbon to generate energy or are carbon neutral, to minimize humanity's contribution to climate change and help make sure our planet has energy for the future.

There are a number of ways in which water can be used to create energy. For example, energy can be generated via the free-flow of water in a river or stream, or from water released out of a dam with a higher elevation, according to the U.S. Geological Survey. As the water flows, it turns turbines that generate electricity. Pumped storage is another method of hydropower that involves pumping water into a dam at a higher altitude during off-peak periods and then releasing it to transfer energy to the electricity grid when there is high demand.

Large dams and reservoirs, however, come with environmental concerns of their own, as these large-scale pieces of infrastructure drastically change water flow and affect local ecosystems, according to American Rivers, a nonprofit organization promoting river conservation. For example, the Itaipu Dam, a hydroelectric dam across the Paraná River between Paraguay and Brazil, was constructed in the 1970s and 1980s and has resulted in a 70% loss of biodiversity in the surrounding river habitat, Michigan State University professor Emilio Moran told the German news agency Deutsche Welle in June 2020.

But what about the largest body of water on our planet? Although the ocean contains an abundance of wave power, locating and building an efficient power station in the unforgiving saltwater environment presents huge logistical and financial challenges. Nonetheless, researchers and engineers are developing and testing new energy-capture systems with the goal of finding an efficient way to harness the energy of ocean waves, according to the U.S. Department of Energy.

One method, known as a geothermal heat pump, is used to heat or cool homes and other buildings. This system works by taking advantage of temperatures just a few feet underground where it's a relatively stable 50 to 60 degrees Fahrenheit (10 to 16 degrees Celsius), according to the Environmental and Energy Study Institute. Water-filled pipes are buried between 30 to 100 feet (9 to 30 meters) below ground and are connected to a surface-level pump that circulates the water through the pipes. In cold weather climates, as water is pumped through the warmer pipes in the ground to the cooler pipes in the house, it releases energy in the form of heat, which dissipates into the building, warming it up. Nine out of 10 houses in Iceland heat their houses using this method, according to Iceland's National Energy Authority. Geothermal heat pumps can also be used to help cool buildings down in warmer climates where the below-ground temperature is cooler than the air temperature.

Further below Earth's surface are reservoirs of scalding water under extreme pressure from the tons of rock above. Another method of geothermal energy generation uses deep wells to access this water. As the hot water rises to the surface (driven by the pressure decrease) it turns to steam that creates enough force to turn the turbines of a powerstation, similar to the mechanism of a coal-fired powerstation. These deep geothermal vents produce substantially less toxic gas and 99% less carbon emissions than coal-fired power stations, according to the EIA.

The Environmental and Energy Study Institute, a nonprofit organization promoting sustainable energy, defines biomass as "living or recently dead organisms and any byproducts of those organisms, plant or animal. The term is generally understood to exclude coal, oil and other fossilized remnants of organisms, as well as soils." These biomass products absorb energy and carbon during their lifetime and are then burned for fuel, similar to fossil fuels, or converted into liquid fuel.

Biofuel, or energy created from burning biomass, is one of the more controversial renewable energy options because of its dependence on farms, forests and other ecosystems as sources of biomass. The largest agricultural biofuel industries, for example, turn crops such as sugar cane and soybeans into energy rather than selling the crops as food. But agriculture is a carbon-intense industry, which means those biofuels aren't exactly environmentally friendly. Using food crops for biofuel also threatens food security as biofuel crops affect the price and availability of food crops, according to a 2010 NATO report.

A major impediment to the uptake of renewable energy has been its price tag, but as these technologies mature, their costs have decreased significantly. Between 2010 and 2019, the cost of solar panel technology dropped 82%, followed by concentrating solar power at 47%, onshore wind at 40% and offshore wind at 29%, according to the International Renewable Energy Agency (IRENA), an intergovernmental organization.

"The simple answer is 'yes,'" said Tomas Kåberger, a technology management and economics expert and affiliated professor at Chalmers University in Sweden. The major reason is that industrial technology development has pushed down the price of renewables, particularly wind and solar, allowing them to compete with fossil fuels, Kåberger said. Commercial advances in efficient battery technology, driven by cellphones, laptops and automotive manufacturers, has also led to cost decreases.

We may see a big shift in the next 10 years from fossil fuels to renewable energy, particularly in the electricity generation and transportation industries, said Ken Gillingham, an associate professor of energy economics at Yale University. But in order to accelerate the process, he said, the world needs policy interventions, such as carbon taxes or shifting government subsidies towards energy storage rather than generation.

Sarah Wild is a British-South African freelance science journalist. She has written about particle physics, cosmology and everything in between. She studied physics, electronics and English literature at Rhodes University, South Africa, and later read for an MSc Medicine in bioethics.

Since she started perpetrating journalism for a living, she's written books, won awards, and run national science desks. Her work has appeared in Nature, Science, Scientific American, and The Observer, among others. In 2017 she won a gold AAAS Kavli for her reporting on forensics in South Africa.

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