Biomass Energy and Cellulosic Ethanol

Farmers standing in switchgrass field

Credit: Gretz, Warren - NREL Staff Photographer

Biomass power comes from plants -- crop and forest residues, corn kernels and stalks, energy crops, perennial grasses, and fast-growing trees like poplars, to name a few. It can be used to make liquid biofuels that serve as alternatives to oil, or to produce heat or electricity to power our homes. Biomass power accounts for roughly half of all the renewable energy produced in the United States, and we use more of it than any other country in the world.

Biomass energy is a double-edged sword, depending on how and where it is produced. It can be produced in ways that reduce global warming pollution or in ways that increase it. It can help clean up the air, water, and soil and protect wildlife, or it can degrade our lands, forests, and water, threaten biodiversity, and harm public health.

Most of the biomass we use commercially today comes from resources that are not sustainable. Our challenge is to ensure that biomass energy is produced in ways that not only reduce global warming pollution, but also protect the environment and do not increase the price of food. In other words, biomass energy should do the job better than the fossil fuels it replaces.

How Biomass Energy Works

Biomass energy is a double-edged sword, depending on how and where it is produced

Plants capture and store the sun's energy as they grow. Today's biomass energy comes from annual row crops, such as corn and soybeans, agricultural leftovers, such as rice husks and pressed sugar cane, and wood, including whole trees, from forests -- a highly problematic source of biomass. Researchers are developing ways to produce energy from special, fast-growing, and higher-yielding "energy crops" such as willow, miscanthus, and switchgrass.

All this plant material can be treated in different ways to produce energy and fuel. Biomass can be:

  • Burned in power plants to produce heat or electricity, with fewer harmful emissions than coal.
  • Fermented to produce fuels, like ethanol, for cars and trucks.
  • Digested by bacteria to create methane gas for powering turbines.
  • Heated under special conditions, or "gasified," to break down into a mix of gases that can be burned for electricity or used to make a range of products, from diesel to gasoline to chemicals.

Environmental Impacts of Biomass Power

Forests, not fuel: Burning trees for energy increases carbon pollution and destroys forests

Most of the biomass energy we use today comes from unsustainable sources that are not an improvement over fossil fuels: ethanol, made by fermenting food crops like corn and sugarcane, which require large amounts of land, water and chemicals to grow; and wood or even whole trees from forests, which are often "co-fired" with coal in power plants, increasing global warming pollution and threatening our forests as well.

Focusing on food crops like corn or soybeans as sources of biofuels can have unintended economic and environmental consequences. Harvesting these crops for biofuels could raise the price of feed for livestock and possibly food as well. Because these crops are grown using large amounts of fertilizer, land, and water, water quality and availability could suffer, due to soil erosion and pollution from fertilizer runoff. All in all, the production of corn ethanol creates more carbon pollution than the oil it is supposed to replace.

Wood can also be a problematic source of biofuels, if it's not sustainably harvested. Demand for wood pellets is expected to increase significantly over the next few years, as European countries strive to meet renewable energy goals of 20 percent by 2020.[1] Pellet manufacturers in the southeastern United States are gearing up to satisfy this growing market, as European suppliers will not be able to meet this demand -- unfortunately, they are increasingly looking to whole trees for energy.

Burning a whole tree not only releases stored carbon -- it takes away the tree's ability to absorb more carbon in the future. Harvesting whole trees for energy increases carbon pollution and degrades our forests, one of our best defenses against global warming. Furthermore, forests in the southern United States already produce more wood and paper products than anywhere else in the world, so increased demand from the bioenergy market could put even more pressure on these overworked ecosystems.

How the United States Can Produce Better Biomass Power

Massachusetts is setting smart standards for biomass energy that define and favor good biomass over bad

Setting standards for how we can maximize the benefits of biomass energy will help the bioenergy industry move towards the most sustainable sources of biomass while continuing to grow and innovate. Only biomass that is carefully chosen, grown responsibly, and efficiently converted into energy can reduce carbon pollution and minimize harmful impacts to our land, water and soil.

The misconception that trees are "carbon neutral" sources of biomass is embedded in many renewable energy policies that promote biomass uniformly, and can often distort the marketplace towards unsustainable sources of biomass like whole trees.

Timber harvest residues -- a portion of tree tops and branches left after logging -- are a more sustainable source of biomass than whole trees. Unlike whole trees, timber residues can be removed, in limited amounts, from a forest, without compromising the health of the soil or wildlife habitat. These small remainders would normally decay on the forest floor and release carbon quickly, unlike a tree, which would continue to act as a carbon sink for decades.

For making liquid fuels, crop wastes, sustainably harvested cover crops, switchgrass, willow, or other non-invasive energy crops that require little fertilizer or irrigation, and are grown on land that is degraded, idle, and not suited for growing food, are attractive alternatives to corn and soybean. These next-generation biofuels have the potential to deliver better environmental performance with less impact on food and feed prices.

Producing these biofuels in large quantities will require policies that reward farmers who grow environmentally sustainable biomass, and carefully manage their land for yield and ecological benefits like wildlife habitat, cleaner water and healthier soils. NRDC is working to protect and monitor existing programs that help farmers grow sustainable biomass, and supports performance-based policies and market-based mechanisms –- such as voluntary sustainable certification programs like the Roundtable on Sustainable Biofuels (RSB) -- that directly reward good conservation practices.

States like Massachusetts are leading the way and showing that setting smart standards for biomass energy is critical to reducing carbon pollution and protecting forests, both locally and on a national level. The Massachusetts standards define and favor good biomass over bad, and will greatly limit the ability of the industry to carry out whole-tree timber harvests to fuel biomass facilities. At the same time, Massachusetts' standards will incentivize the use of short-rotation crops, wood waste and reclaimed wood, and timber harvest residues, all of which can reduce carbon emissions and are sustainable sources of biomass energy.

Advantages of Biomass Energy

  • Farmers and foresters already produce a great deal of residue. While much of it is needed to protect habitat, soil, and nutrient cycles, tens of millions of tons and more could be safely collected with the right management practices. Every year in the United States, roughly 39 million tons of crop residues go unused.[2]
  • Unlike coal, biomass produces no harmful sulfur or mercury emissions and has significantly less nitrogen -- which means less acid rain, smog and other toxic air pollutants.
  • Over time, if dedicated biomass is sustainably managed, converting it to energy can result in low or no net carbon emissions, provided that the carbon released is rapidly absorbed back from the atmosphere by biomass re-growth.
  • Using biofuels in our cars and airplanes can potentially produce less global warming pollution than petroleum-based fuels, and allows us to invest our energy dollars at home rather than in foreign oil.
  • Switchgrass, a promising source of biofuels, is a native, perennial prairie grass that is easier to grow responsibly than most row crops. If planted in such a way that it does not replace native habitat or take land out of food production, switchgrass and other sustainably managed energy crops have the potential to reduce erosion and nitrogen runoff, and increase soil carbon faster when mowed than when standing.
  • Many ethanol refineries are owned by farmer-cooperatives, which help preserve the economic vitality of rural communities.

What's Around the Corner for Biomass Energy

  • Aggressive action to develop advanced biofuels by 2015 could allow America to produce, by 2050, the equivalent of the oil we currently import from the Persian Gulf. If at the same time we make our vehicles more efficient and make plug-in hybrids widely available, biofuels could help virtually eliminate our demand for gasoline.
  • Flexible-fuel vehicle requirements are being considered at the national level that will prompt manufacturers to equip all new cars and trucks for both gasoline and biofuels within about a decade.
  • Alternative aviation fuels are being tested and approved for use in both commercial and military aircraft; several large airlines have made commitments to source these fuels if they are produced sustainably.[3]
  • International sustainability standards for biomass have been developed and are now available to producers. The Roundtable on Sustainable Biofuels (RSB) launched a global sustainability standard in 2011. The standard provides a comprehensive and rigorously-tested basis for independent certification and applies to all types of biomass feedstock in every region of the world along the supply chain. Widespread adoption of credible sustainability standards and certification is essential to reducing future environmental, cultural and social harm.[4]
  • Improved high-tech "gasification" systems could bring down the cost of biomass energy to 5 cents per kilowatt-hour.
  • Farmers will develop new and broadly sustainable biomass cropping systems and find innovative ways to manage their farms to increase yields, improve degraded and marginal soils, and protect critical ecosystems. Researchers are testing the ability of fast-growing, cost-efficient trees such as poplar and eucalyptus, and grasses such as switchgrass and alfalfa, to be harvested as biofuels.
  • More states will follow the lead of Massachusetts and establish smart policies that put bad biomass off limits and incentivize the use of sustainable biomass.

Learn More


Agricultural Marketing Resource Center
The AgMRC (Agricultural Marketing Resources Center) "is an electronic, national resource for producers interested in value-added agriculture."
AgSTAR Handbook
The EPA's AgSTAR program has a comprehensive handbook on developing biogas technology. The site includes FarmWare, a free decision-making software package that can help you assess the feasability of biogas on your farm.
Alternative Fuels and Advanced Vehicles Data Center (AFDC)
The US Department of Energy's Alternative Fuels and Advanced Vehicles Data Center (AFDC, formerly known as the Alternative Fuels Data Center) provides a wide range of information and resources to enable the use of alternative fuels, in addition to other petroleum reduction options such as advanced vehicles, fuel blends, idle reduction, and fuel economy.
ATTRA - National Sustainable Agriculture Information Service
ATTRA - National Sustainable Agriculture Information Service is managed by the National Center for Appropriate Technology (NCAT) and is funded under a grant from the United States Department of Agriculture's Rural Business-Cooperative Service. It provides information and other technical assistance to farmers, ranchers, Extension agents, educators, and others involved in sustainable agriculture in the United States.
Farm Energy
A helpful website from the Environmental Law and Policy Center that outlines the incentives offered in the current Farm Bill and monitors the development of new ones.
Renewable Fuels Association (RFA)
Website of the Renewable Fuels Association (RFA), the national trade association for the U.S. ethanol industry.
State Agricultural Overview
State-by-state agricultural statistics from the USDA National Agricultural Statistics Service.

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