Basics of Renewable Fuels
Renewable fuels are fuels that humans can make or harvest
Biomass provides a source of biofuels from recently grown plants including corn, wood, and algae
Hydrogen is another potential renewable fuel that is carbon-free. Hydrogen can be classified as green, blue, or gray, depending on where it is sourced from
In contrast to fossil fuels, formed and stored over millions of years, humans can make or harvest renewable fuels from current solar energy cycles. Wood harvested to make fire is an example of a renewable fuel.
Newer forms of renewable fuels include biofuels and hydrogen fuel produced from renewable sources. Scientists and engineers are striving to replicate the strengths of fossil fuels, particularly for transportation, while avoiding the hazards of greenhouse gas emissions.
Biofuels and biodiesel
Biomass is a general term for the material derived from plants that were recently alive, rather than dead for millions of years. This matter can include edible biomass (corn, wheat, etc), non-edible biomass (wood, grass, waste, etc.), algae, agricultural products, agricultural waste products, and more.
Biofuels are the secondary fuels derived from biomass. Ethanol, for example, is produced through the fermentation of corn, beets, and other sugar-containing plants. Biodiesel is produced through a chemical process that converts oils and fats into a liquid fuel that can be burned in a diesel engine.
While biofuels are renewable and can be regrown, they can use a great deal of land, water, and other resources, including chemicals. Growing plants for energy can compete with agricultural food production and can spur tropical deforestation.
Hydrogen is a carbon-free fuel, and a combustion reaction with hydrogen produces only water as a byproduct. But as with electricity, whether hydrogen is “renewable” depends on how it is produced.
A color-coded system classifies hydrogen sources. Gray hydrogen, the current method for producing hydrogen fuel, converts natural gas into hydrogen and carbon dioxide, resulting in significant carbon emissions. Green hydrogen would use renewable energy, such as solar or wind-generated electricity, to split water into oxygen and hydrogen on a large scale. This technology is still in development, but shows promise as a future alternative. Blue hydrogen would continue to produce hydrogen from natural gas, but would capture and store the carbon dioxide emissions instead of releasing them into the atmosphere. See our climate change module to learn more about carbon dioxide capture.
Hydrogen fuel faces the challenge of being a very small, light, and flammable gas, which makes it difficult to store and transport.
Other renewable fuel opportunities
As researchers strive to replace fossil fuels, several other renewable fuel possibilities are being explored. These include synthetic fuels made directly from carbon dioxide from the atmosphere (which would theoretically close the fuel cycle by recycling the waste carbon dioxide), and other chemicals such as ammonia. These technologies are still in the research phase, but could see greater attention in the near future.
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Questions for deeper thinking
Is “renewable” a good term for these types of fuels? What does it take for something to be “renewable”?
How do the costs of biofuel production and use compare to those of fossil fuels? Now consider the environmental costs of each type of fuel and how their extraction, land use, and waste contribute to our larger systems.
Sources and further reading
Page last updated: August 31, 2022