Understanding the Role of Biomass in the U.S. Renewable Energy Portfolio



by Dan Esposito


When most people think of renewable energy, images of windmills and solar panels are typically the first to appear, and for good reason—they are visually distinct, produce clean electricity with minimal environmental impact, and have experienced tremendous growth over the last decade. Yet biomass, the historical frontrunner and a continued staple of the non-hydro renewable energy industry, tends to remain an afterthought.1 Arguably the most conceptually complex source of renewable energy, biomass is often attacked as merely acting under the guise of being renewable and clean, leading to the unsustainable clear-cutting of forests and the burning of dirty substances. After hearing such accusations and following the associated debates, how is a purchaser of clean energy supposed to feel, particularly when their product includes some portion of biomass-generated electricity? Do the criticisms have merit, and if so, why does Green-e Energy certify these products?

We begin with the bad news: biomass—defined as organic matter that can be burned for fuel—does emit greenhouse gases when combusted and can also contribute to localized pollution in the form of particulate matter and gases that contribute to acid rain (NOx and SOx).2 Further, left unregulated and unsupervised, bad actors could profit from chopping down whole forests and burning the associated lumber, or from burning waste materials that could emit harmful substances. Taken as a whole, these factors need to be acknowledged, but they do not spell the end for the resource’s potential to be (or rather, remain) a major player in the renewable energy industry.

Biomass that is intelligently procured in a manner in which all of the major players are held to high standards of transparency can be a boon for our planet. First, while biomass does release greenhouse gases, it is carbon neutral in theory—that is, burning a tree releases the same amount of carbon dioxide as the amount it sequestered over its lifetime. Further, it emits much less carbon dioxide and localized pollutants than coal. Finally, when managed properly, biomass is renewable—if, for example, we burn a tree for fuel, we can grow a new one in a generation (as opposed to fossil fuels which take hundreds of millions of years to form). Thus, the effect of biomass on the environment stems not from the resource itself but from how it is sourced and utilized. This is where trusted third-party certification is critical. As we will see, Green-e Energy only certifies the burning of biomass that would otherwise go to waste or result in the net reduction of greenhouse gases.


Gaseous Biomass

One major contributor to climate change stems from a source which seemingly has very little to do with power generation: municipal landfills. These enormous dumping grounds have huge stores of organic material which break down over time, causing landfills to collectively act as one of the nation’s largest emitters of methane—a much more potent greenhouse gas than carbon dioxide. Collecting and burning this gaseous biomass provides “free” electricity (as the gas would otherwise escape into the atmosphere) and helps to mitigate climate change by converting the methane to carbon dioxide.

Similarly, the methane release from livestock farms is immense and inevitable barring a sharp decline in American meat and dairy consumption. Manure from these farms are traditionally collected in open lagoons until they are needed as fertilizer, where they emit methane, exude an odor, and contribute to runoff. As an alternative, farmers can collect the manure in an anaerobic digester—a sealed container which heats the manure and collects the resultant methane gas for burning on-site. In addition to electricity, the farmer receives a nutrient-rich fibrous product which has less of an odor and a reduced risk of runoff.

Most gaseous biomass comes from the above two sources. Since it is typically derived from a waste product and would otherwise enter the atmosphere without intervention, burning it provides a positive outcome that meets Green-e Energy’s high standards for renewable energy.


Nongaseous Biomass

While gaseous biomass is largely derived from the above two generally accepted sources, its nongaseous form must meet much stricter eligibility standards to prevent malpractice in the industry. For example, with few exceptions, whole trees are not an eligible source of biomass under the Green-e Energy National Standard. If such a restriction did not exist, the biomass industry would have an incentive to purchase timber for electricity generation; this could raise prices for wood-based products and lead to higher rates of deforestation. Similarly, healthy agricultural crops are not eligible to keep actors in the industry from purchasing food and farmlands as a means of procuring biomass, since doing so could put great pressure on food prices and availability. Nongaseous biomass can also be dangerous to local communities if not properly sourced, since tainted organic materials can release toxins and other harmful pollutants when burned. For this reason, biomass containing nontrivial levels of plastics, paints, metals, or other harmful chemicals is ineligible (i.e. the entire category of municipal solid waste is excluded).

Most nongaseous biomass deemed eligible by the Green-e Energy National Standard comes from taking advantage of waste materials resulting from other practices as opposed to harvesting the biomass from a dedicated source. While whole trees are generally excluded from eligibility, exceptions include Christmas trees (which typically go to waste after their use during the holiday season) and trees felled by natural causes. Tree limbs and other woody waste may also be used under certain circumstances, such as when procured using best management practices as part of a forest sustainability plan or when trimming to prevent overgrowth onto existing roads and right-of-ways. Waste materials from other timber-based production (i.e. paper production) is also eligible, such as “black liquor,” a substance resulting from pulp and paper processing, mill residues, and other waste woods. Further, damaged agricultural crops that are no longer fit for human consumption are eligible under the National Standard, since these crops would otherwise go to waste. Other materials such as solid animal and organic waste also meet Green-e Energy’s criteria, assuming they do not contain chemicals that would be dangerous upon incineration.

While technically a carbon-neutral fuel source, burning biomass with a high carbon intensity (i.e. old forests) could lead to significant carbon emissions with it taking a century or more for new organic material to sequester the same amount of carbon. Staying true to our mission to only certify products that mitigate climate change and help build a sustainable energy future, Green-e may have to reevaluate the eligibility of certain sources of biomass if new research on their carbon intensities is brought to light by the EPA or another highly regarded research authority.3 At a minimum, we require facilities burning biomass to be in compliance with all state and federal laws concerning air emissions.

Biomass also serves a unique role among sources of renewable energy—it can be “co-fired” (i.e. burned as fuel) with non-renewable sources like coal to reduce the emissions of existing power plants. By utilizing existing infrastructure and retrofitting gas and coal-fired plants to also accept some portion of biomass, significant cost savings and emissions reductions can be achieved in the near-term. Power generated in this manner also produces renewable energy certificates, but strict standards are in place to ensure that only the percent of energy generated from the biomass is counted as renewable supply.


Green-e Energy and Industry Trends

Data from the Energy Information Association (EIA) and Green-e Energy’s annual verification reports show similar trends within the biomass industry: namely, that biomass-fired electricity is on the rise in absolute terms, yet is falling in its share of the overall national renewable energy portfolio. For instance, Green-e Energy has seen its share of biomass-generated RECs fall from 14.65% in the 2011 reporting year to an estimated 10.52% in 2014, despite contributing over 100,000 more RECs in 2014. Over the years, about three quarters of all Green-e certified biomass-fired electricity has been sourced from its non-gaseous form. Similarly, EIA data shows that biomass made up 29.21% of all renewable generation in 2011 (including wind, solar, geothermal, but not hydro, even when low-impact) but only 22.88% in 2014, despite adding nearly 8 million more megawatt-hours of generation in 2014.

These statistics suggest that the biomass industry is healthy, increasing steadily in our national energy portfolio as well as in the quantity that has achieved Green-e Energy certification. They also demonstrate the remarkable speed at which wind and solar are expanding, since these capacity additions have led the overall share of biomass to fall despite its significant growth. The graph below—built using the EIA’s Electricity Data Browser—illustrates the growth of four major sources of renewable energy over the last fifteen years. We notice that while the growth of biomass appears stagnant relative to the other resources, it contributes a sizable and consistent supply of electricity to our nation’s renewable generation portfolio.



The significant and steady share of biomass in the renewable energy industry has two important implications. First, despite being a more complex and contentious resource than wind or solar, biomass is a vital part of our nation’s renewable energy portfolio and will continue to be an important driver of the renewable energy market. Second, as the industry continues to grow, rigorous third-party certification such as that provided by Green-e Energy will become ever more important for ensuring that biomass is sourced intelligently and responsibly with all parties maintaining transparency and being held accountable. When buying Green-e certified renewable energy, you can be confident that any portion generated from biomass was procured using sustainable practices.

For more information about our certification process and specifications for resource eligibility, please see the Green-e Energy National Standard. For information about getting certified under Green-e Energy, please visit the Green-e website.


Dan Esposito joined CRS in May 2015 as a Green-e Energy Verification Associate. He is currently pursuing a Master of Public Affairs and a Master of Science in Environmental Science at Indiana University-Bloomington, with a focus on energy policy analysis. He has a Bachelor in Science in Physics and Mathematics from the University of Dayton. Dan is interested in the design and analysis of policy with regard to the advancement of clean energy and the mitigation of climate change.


  1. Conventional hydroelectric power is generally ineligible from Green-e Energy certification. The vast majority of existing dams are too old to meet the eligibility criteria of the Green-e Energy National Standard, since the Standard only certifies facilities that began operation within the last fifteen years. New impoundments are ineligible in order to protect river ecosystems from further disruption. For examples of hydropower meeting the eligibility criteria for Green-e certification, see the Green-e Energy National Standard.
  2. Biomass is defined by the Energy Information Association (EIA) as “organic nonfossil material of biological origin constituting a renewable energy source.” Examples of biomass include wood, crops, animal wastes, and gases (methane and carbon dioxide) originating from the breakdown of organic material by microorganisms.
  3. From the Green-e Energy National Standard: “At a future time when the EPA, or other similarly reputable authority, releases findings on biogenic carbon dioxide emissions, and the carbon intensity of certain types of biomass may be determined with reasonable accuracy, then Green-e Energy may reevaluate the eligibility of biomass resources used to generate renewable electricity. Emerging technologies generating electricity from byproducts and waste streams may be eligible for Green-e Energy, however such technologies should be able to demonstrate that procurement and use of their fuel has a favorable carbon balance” (p.4).