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Renewable Energy

Renewable energy is energy from sources we cannot run out of. Some types of renewable energy, like wind and solar power, come from sources that are not depleted when used. Others, like biomass, come from sources that can be replenished. Common types of renewable energy are wind, solar, hydropower, biomass and geothermal. Renewable energy has two advantages over the fossil fuels that provide most of our energy today. First, there is a limited amount of fossil fuel resources (like coal, oil and natural gas) in the world, and if we use them all we cannot get any more in our lifetimes. Second, renewable energy produces far less carbon dioxide (CO2) and other harmful greenhouse gases and pollutants. Most types of renewable energy produce no CO2 at all once they are running. For this reason, renewable energy is widely viewed as playing a central role in climate change mitigation and a clean energy transition.


Renewable vs. carbon-free

Most kinds of renewable energy are also “carbon-free”: they do not emit CO2 or other greenhouse gases into the atmosphere. Because of this, and because renewables like wind and solar power are so popular in climate activism, the terms “renewable energy” and “carbon-free energy” are sometimes confused. But not all renewable energy is carbon-free, and not all carbon-free energy is renewable.

Biofuels and bioenergy are renewable: we can regrow plants that we burn for fuel. But they are not necessarily carbon-free. Growing plants absorbs CO2; burning plants releases CO2. The total impact on CO2 in the atmosphere depends on how sustainably the bioenergy is produced.

Nuclear energy is carbon-free: a nuclear power plant does not emit any CO2, or any other greenhouse gases. But it is not renewable. Nuclear reactors use uranium, and if we run out of uranium, we can never get it back.


Transforming the Electric Grid

Some types of renewable energy can provide fuel for transportation (e.g. biofuels) or heating and cooling for buildings (e.g. geothermal). However, most renewable energy is used to make electricity. In 2018, renewable energy sources made up 26% of the world’s electricity, and that number is rising every year. More than 60% of renewable electricity worldwide comes from hydropower, which has been widely used since the invention of the electric grid, but today wind and solar power are growing fastest.

Renewable energy presents great challenges and opportunities for electricity generation. Some renewable energy sources, such as wind and solar, are “variable,” meaning the amount of electricity they make changes depending on the amount of wind or sunlight available. This can cause problems for system operators, particularly when there is a mismatch between the amount of electricity demanded and the amount of wind or sun available. Another challenge is that the best places to generate renewable energy are often far away from the areas that use that electricity. For these reasons, adding much more renewable energy to our electric grid will require other changes, including more energy storage, backup generation, strategies to match electricity use with times of high power generation, and infrastructure for long-distance power transmission.

A Growing Source of Energy

Renewable energy also needs to compete with well-established and cheap fossil fuels. Renewable energy has grown quickly over the last decade, driven by policy support (tax incentives, R&D funding and mandates requiring the use of renewables) and falling costs (especially in solar photovoltaics and wind turbines). Globally, wind and solar electricity grew from just 32 terawatt-hours in 2000 to 1,857 terawatt-hours in 2018: more than enough to power the entire country of India. Nonetheless, together they still only provide 7% of electricity worldwide. As societies work to lower their greenhouse gas emissions, renewable energy is expected to play a large role, especially if we switch more heating and transportation to run on electric power and solve the problem of affordable, large-scale energy storage. How much of our energy we ultimately get from renewables will also depend on their ability to compete with other low-carbon technologies, such as nuclear, carbon capture and storage and hydrogen.


Infographic: Types of renewable energy. Today, 26% of the world’s electricity, and much less of the world’s heat and transportation fuel, comes from renewable sources. Here’s how it breaks down. Data is for 2017 and excludes non-electricity energy like heat and transportation fuel. Source: The International Energy Agency 2019 World Energy Outlook.
Click here to see data from the infographic above in a table.
Type of energy Description Percent of global electricity production
Electricity from all non-renewable sources includes fossil fuels like coal, oil and natural gas, as well as nuclear power 74%
Hydropower Using flowing water to turn a turbine, like in a dam 16%
Wind power Using wind to turn a turbine 5%
Bioenergy Burning plants and other organic matter as fuel 3%
Solar photovoltaics Using light from the sun to generate electricity 2%
Geothermal energy Using the natural heat below the Earth’s surface, usually to heat and cool buildings but sometimes to make electricity less than 1%
Other, rarely used types of renewables Includes wave and tidal energy and solar thermal energy less than 1%

Data for all numbers comes from the International Energy Agency 2019 World Energy Outlook

Photo credit: Justin Lim on Unsplash

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