People have used biomass energy—energy from living things—to make wood fires for cooking or keeping warm for at least 450,000 years. 

Biomass is organic, meaning it is made of material that comes from living organisms, such as plants and animals. The most common biomass materials used for energy are plants, wood and waste. These materials are called biomass feedstocks. Although people often view biomass as a renewable source of energy, in practice, biomass energy can be a nonrenewable energy source when it is not sustainably managed. 

Biomass contains energy first derived from the sun. Plants absorb the sun’s energy through photosynthesis and convert carbon dioxide and water into nutrients (carbohydrates).

The energy from these organisms can be transformed into usable energy through direct and indirect means. Biomass can be burned to create heat (direct), converted into electricity (direct) or processed into biofuel that can be used as an energy source later (indirect).

Biofuel

Biomass is the only renewable energy source that can be converted into liquid biofuels, such as ethanol and biodiesel. Ethanol is made by fermenting biomass that is high in carbohydrates, such as sugarcane (Saccharum officinarum), wheat and corn (Zea mays). Biodiesel is made by combining an alcohol (methanol or ethanol) with animal fat, recycled cooking fat or vegetable oil.

Biofuel can power vehicles, and countries in Asia, Europe, Africa, Oceania, South America and North America are producing biofuels. While there is concern over biofuel’s performance compared to fossil fuels, biofuels can be just as high quality. They can also be blended with gasoline to efficiently power vehicles and machinery, and vehicles that use a biofuel-gasoline blend have lower greenhouse gas emissions than vehicles that use fossil fuels alone. But ethanol still releases pollutants that form smog, a smoky haze filled with pollutants. 

Ethanol requires acres of farmland to grow biocrops (usually corn). This leaves the acreage unavailable for growing crops for food or other uses. Growing enough corn for ethanol also creates a strain on the environment because of the lack of variation in planting, the high use of fertilizers and the impacts to water quality. 

Ethanol has become a popular substitute for wood in residential fireplaces. When burned, it gives off heat in the form of flames but releases water vapor and carbon dioxide instead of smoke. However, improper use can cause safety hazards.

Hydrogen Fuel Cells

Biomass is rich in hydrogen, which can be chemically extracted and used to generate power and to fuel vehicles. Stationary fuel cells are used to generate electricity in remote locations, including spacecraft.

Hydrogen fuel cells may hold even more potential as a high efficiency alternative energy source for vehicles. Recent research estimates that hydrogen could reduce global carbon dioxide emissions by as much as 1.1 gigatons per year (the world produces roughly 40 gigatons each year). Currently, hydrogen fuel cells are used to power automobiles, forklifts, boats and submarines, and hydrogen fuel cell developers are testing them on airplanes and other vehicles. 

However, there is a debate as to whether this technology will be sustainable or economically realistic. The energy that it takes to isolate, compress, package and transport hydrogen means it may not be practical in all applications. 

Biomass and the Environment

In contrast to fossil fuels, biomass comes from living or recently living organisms. The carbon cycle can continue to exchange the carbon from biomass. Proponents of biofuels argue that because biomass can sequester carbon that would otherwise end up in the atmosphere, creating biofuels is a way to reduce fossil fuel use and combat climate change. It’s why some governments have positioned biomass as a clean alternative to fossil fuels. The reality is more complicated.

It takes decades for trees to grow and replace those that are cut down, limiting the amount of carbon that forests can store. Uprooting or disturbing the soil can be extremely disruptive to the carbon storage process too. Clearing large amounts of land in a short period of time to harvest biomass can release large amounts of carbon into the atmosphere. A steady and varied supply of trees, crops and other plants is vital for maintaining a healthy environment.

Biomass harvesting also has the potential to negatively impact wildlife beyond releasing carbon. For example, harvesting trees may remove important habitats and food supplies on which wildlife depend.

Whether or not biofuels are sustainable depends heavily on the local environments and circumstances. What is sustainable in one area may not be sustainable in another. Determining how to distribute and use biofuels with a specific community is more likely to produce a sustainable product that supports local economies compared to a larger distribution system. The transport needed to export biomass and biofuels can lead to more carbon emissions.

Algal Fuel

Algae, whose most familiar form is seaweed, is a unique organism that has potential as a source of biomass energy. The high fat content of algae makes it a great candidate for biofuel. Biofuel from algae is known as green crude and is considered a renewable source of energy.

Since algae can grow in places that other crops cannot and does not require soil, it does not reduce the amount of arable land that could potentially be used to grow food crops. Algae can grow in ocean water and nonpotable water, so it does not deplete freshwater resources, and it takes up much less space than other biofuel crops. 

Although algae does release carbon dioxide when burned, as it grows, it releases oxygen and absorbs pollutants and carbon dioxide since it uses carbon dioxide during photosynthesis. It is possible to capture carbon dioxide emissions from fossil fuel or ethanol production and use it to produce algae.

While there is potential for algae as a biofuel, there are still roadblocks preventing full implementation. One factor is that researchers still have a lot to learn about algae. For instance, scientists have not sequenced the genomes of all algae species and need to learn more about their biology. Scalability is another limitation. While algae can produce biofuel, it has only been done on a small scale. Larger scale operations remain prohibitively expensive. Major investments would be needed to produce algae biofuel on a scale that would actually reduce emissions.

Recent research has also called into question algae’s environmental impact. In looking holistically at large-scale implementation of algae biofuel production, the emissions saved do not appear to balance the emissions required to build and operate the necessary facilities. However, researchers also believe this issue can be mitigated with further research and development.

People and Biomass

Advantages

If well managed, biomass can be a clean, renewable energy source. Its initial energy comes from the sun, and plant and algae biomass can regrow in a relatively short amount of time. Trees, crops and municipal solid waste are consistently available and can be managed sustainably. If trees and crops are sustainably farmed, they can offset carbon emissions when they absorb carbon dioxide through respiration. Many biomass feedstocks, such as switchgrass (Panicum virgatum), can be harvested on marginal lands or pastures, where they do not compete with food crops.

Unlike other renewable energy sources, such as wind and solar, biomass energy is stored within the organism and can be harvested when needed.

Bioenergy is especially important to people who do not have a steady source of electricity. Lack of electricity can mean limited economic growth and reduced social services from agriculture, healthcare, education and other sectors. Using bioenergy can help bring reliable electricity to rural and remote areas.

Disadvantages

If biomass feedstocks are not replenished as quickly as they are used, they can become nonrenewable. A forest, for instance, can take well over 100 years to re-establish itself. This is still a much, much shorter time period than it takes to form fossil fuel sources such as peat, the precursor to coal. It can take about 900 years for just a meter (about 3 feet) of peat to replenish itself.

Most biomass requires arable land to develop. This means that land used for biofuel crops, such as corn and soybeans, is unavailable to grow food or provide natural habitats. In addition to removing habitats for wildlife, the production of biofuels also removes land used for agriculture, which can present issues of food availability.

Forested areas that have matured for decades (so-called “old-growth forests”) sequester more carbon than newly planted areas. If forested areas are not sustainably cut, replanted and given time to grow and sequester carbon, the trees do not grow fast enough to offset the carbon released from cutting them down and using the wood for fuel.

Another disadvantage is that biomass has a lower “energy density” than fossil fuels. Depending on the type of biomass, it might be half or mostly water. About 50% of wood biomass is water, which is lost in the energy conversion process. Converting biomass into pellets (as opposed to wood chips or larger briquettes) can increase the fuel’s energy density and make it more advantageous to ship.

Burning biomass also releases emissions, including carbon dioxide and other pollutants. If these pollutants are not captured and recycled, burning biomass can exceed the number of pollutants released by fossil fuels. Even if biomass is produced in a renewable way—for example, if trees are replanted to replace ones that are cut down—this does not automatically make that product carbon neutral. Quantifying the carbon emissions associated with biofuels is not simple, creating some difficulty in determining the true impact of biofuels on climate change. 

The health risks associated with emissions include strokes, respiratory conditions like lung cancer and cardiovascular illnesses. Pollution associated with the production and use of biofuels disproportionately harms marginalized groups, such as people of color, those with low income, rural communities, women and children.

People in rural areas in low- to middle-income countries are particularly vulnerable because they use biomass more often. Throughout much of the world, biomass is used as a source of heat and for cooking within homes. This puts over 2 billion people at risk from pollution because of their close proximity to where the biomass is being burned.