Promoted as clean and climate friendly, and driven by lucrative renewable energy subsidies and tax credits, biomass energy – burning wood and other biological materials to produce heat and power – is on the rise around the United States, with hundreds of new facilities large and small proposed in the past 10 years. However, recent scientific and policy developments recognizing that biomass energy has significant greenhouse gas emissions have blown a major hole in arguments for treating biomass as a favored renewable energy source and could fundamentally reshape its future in the United States.
Until this past decade, the nation’s aging biomass fleet was composed largely of industrial boilers, often located at sawmills and paper mills, which burned manufacturing waste or waste wood to produce industrial heat and power. Some of these facilities also exported electricity to the grid. In recent years, however, there has been a surge of over 200 proposals for new biomass power plants in the United States. Eligible for lucrative renewable energy subsidies and tax credits, most of these proposed plants are stand-alone electricity-generating units, uncoupled from a manufacturing facility, that plan to produce “renewable” power for the grid. Critically, most of them plan to burn wood – wood that is directly sourced from logging operations – rather than waste from paper mills and other wood-processing facilities.
Citizens in the communities where these new biomass facilities are proposed often find the plans alarming. A moderate-sized biomass power plant in the 30-40 megawatt (MW) range (they can exceed 100 MW) is a huge installation, with a 200- to 300-foot smokestack, a wood chip pile 60 feet tall that can cover several acres, and an unending stream of tractor-trailers delivering wood fuel. Cooling towers blow off hundreds of thousands of gallons of water a day as waste steam, water that is often taken from nearby rivers.
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Also to many local residents’ surprise, these biomass power plants emit just as much pollution, and in some cases even more, as coal-fired power plants – tons of particulate matter, carbon monoxide, nitrogen oxides, volatile organic compounds, hydrochloric acid, and carcinogens like formaldehyde and benzene. (1) They also emit carbon dioxide, the primary global warming gas, and lots of it – far more, it turns out, than fossil fuel plants. Burning fuels with low energy density and high water content, biomass power plants are notoriously inefficient and actually emit 40-50% more carbon dioxide per megawatt hour than coal plants, and more than 300% the carbon dioxide of gas plants. (2)
How did something that emits so much conventional pollution, and more greenhouse gases than coal, come to be incentivized as “green” energy?
To some extent, this has been the fault of policymakers who were eager to advance the cause of renewable energy and failed to critically examine biomass power. They accepted the two main arguments usually advanced for biopower’s supposedly benign effect on the climate: first, that the carbon released from burning waste materials such as sawmill trimmings and logging residues (tree tops and branches) is no greater than the carbon released if those materials are left to decompose; and second, that biomass fuels such as switchgrass and trees can be grown and harvested in such a way that each new crop would absorb or “resequester” equivalent carbon as was released by the burning of the previous crop. In either case, there is supposedly no net increase in carbon dioxide emissions – or so the theory goes – and biomass is therefore as “carbon neutral” and “green” in many policymakers’ minds as wind or solar.
There is a major and obvious flaw in each of these propositions. The problem with the burning-is-the-same-as-decomposition argument is that burning takes minutes, while decomposition takes years. (Moreover, decomposition of logging residues helps build long-lived soil carbon stocks for healthy forests.) The problem with the “just wait and it will regrow” argument is even more blatant. Switchgrass crops may indeed be regrown swiftly after harvest, but in fact, there are virtually no biomass facilities using switchgrass or other energy crops as fuel, due to prohibitive costs and logistics. Most existing and proposed biomass plants burn wood, but while it takes mere moments to cut and burn a tree, it takes decades to regrow a new one in its place. This fact is widely recognized when we bemoan the role forest loss plays in driving global warming, yet it goes curiously unnoted in the promotion of wood fuels – indeed, the exact opposite is assumed, and burning wood magically becomes “carbon neutral.”
Perhaps because of growing public concern over the state of our forests, energy companies and the biomass industry have hastened to portray the newly emerging fleet of biomass plants as using mostly logging residues and other waste wood for fuel, attempting to keep greenhouse gas impacts more squarely in the “it would decompose anyway” zone. However, this argument collapses the moment one reads the permit for one of these plants.
Utility-scale biomass energy plants consume huge amounts of wood – about 12,500 green tons per megawatt per year. The air permit for the 75 MW Laidlaw biomass plant in Berlin, New Hampshire, for instance, states the facility will burn 113 tons of “whole logs” an hour
– nearly a million tons a year, or the equivalent of clear-cutting more than an acre of forest every hour. Such prodigious demand far outstrips available logging residues in most regions, meaning that each new facility requires cutting hundreds of thousands, if not millions, of trees each year – trees that would otherwise continue growing and sequestering carbon dioxide out of the atmosphere.
The good news for the planet is that the renewable energy policies rewarding such polluting, forest-threatening power plants were written a number of years ago, and in the interim, as local activists have fought individual plants, the science of carbon accounting for biomass has taken big leaps forward. The results have not been good for the industry.
Given its extensive forest cover and centuries-old tradition of burning wood, New England has been a hotbed of biomass energy development – as well as citizen opposition to it – so it’s not surprising that Massachusetts became the first state to do some actual scientific analysis of the issue. To make sure the state could meet the greenhouse gas reduction goals set in its 2008 Global Warming Solutions Act, Governor Deval Patrick’s administration commissioned the well-regarded Manomet Center to study the carbon impacts of biomass energy. The primary finding was that when biomass plants burn a combination of logging residues and whole trees, the net emissions of carbon dioxide, the primary global warming gas, exceed emissions from an equivalent-sized coal-fired plant for more than 45 years, and exceed emissions from an equivalent gas-fired plant for more than 90 years – even when taking forest regrowth into account.
This central finding was reinforced by a similar study conducted in the Southeast, which examined biomass fuel sourced from fast-growing pine plantations and concluded, “the expanded biomass scenario creates a carbon debt that takes 35-50 years to recover.”
The findings of both this study and the Manomet study carry extra weight given that each had a co-author from the Biomass Energy Resource Center, a group dedicated to promoting small-scale biomass energy installations.
The scientific reality revealed by these two studies, and a number of others that have emerged in the past two years, is that when it comes to biomass power’s relative contribution to global warming, the treatment of biomass as “carbon neutral” couldn’t be further from the truth. Industry claims notwithstanding, there is no quicker way to move carbon into the atmosphere – the opposite of what we want – than through utility-scale biomass energy plants that burn millions of trees per year.
In response to the Manomet Study, Massachusetts dramatically reduced its subsidies to biomass power, finalizing the regulations in August 2012. The state’s Department of Energy Resources’ new policy is the first in the nation to acknowledge that utility-scale biomass plants emit massive amounts of carbon dioxide, and thus should not be subsidized as renewable energy to meet the state’s greenhouse gas reduction goals. Recognizing that electricity-only biomass plants are only about 24% efficient, less even than the 33% efficiency of old line coal-fired plants, the new regulations require biomass power plants to be at least 50% efficient before receiving half a renewable energy credit (REC) per megawatt hour, and 60% efficient to receive a full credit. This standard for the RECs, which are worth millions of dollars to a utility-scale plant, can only be met by smaller facilities that utilize waste heat for thermal energy in addition to generating electricity.
The new Massachusetts regulations had an almost immediate impact on the industry. The Russell Biomass project in Russell, Massachusetts, a 50-megawatt wood-burning power plant under development since 2005, was abruptly cancelled less than two months after the new rules were announced.
The Russell project was Exhibit A for the type of tree-burners designed to produce electricity for the grid, with a section in the plant’s air permit stating that it would burn 250,000-350,000 tons of whole tree fuel per year, along with municipal wood fuel, stump grindings, and pallet grindings. “Under the final DOER regulations, the project is not technically and economically viable because of the required 50-percent efficiency, coupled with the new forest biomass fuel supply limitations,” said Russell Biomass partner John Bos. “We are unable to modify the plant design as permitted.”
The new Massachusetts regulations could provide a template for other states that are serious about reducing emissions from the power sector. High efficiency is one commonsense standard that most people can agree on for renewable energy, and simply requiring that plants meet a stringent efficiency standard in order to qualify for renewable energy credits would do much to reduce the stampede of biomass power development now underway.
Action by the states could also soon be coupled with federal action. At the Environmental Protection Agency, a panel commissioned by the agency to examine the greenhouse gas impacts of biomass energy has concluded that biomass energy cannot a priori be considered carbon neutral, but depends on a number of factors – including whether forests are used as fuel.
It remains to be seen whether EPA will resist the heavy politicization of this issue and write science-based rules that make biomass power plants responsible for the carbon they emit. The moment is ripe, however, for policymakers – including President Obama, who espoused a newly awakened concern over climate change during his second inaugural speech and recent State of the Union – to acknowledge that a renewable energy policy that accelerates forest cutting and CO2 emissions is worse than no policy at all.
(1) Pollution emission rates are expressed as pounds of pollution per million Btu of boiler capacity (lb/MMbtu). EPA’s “clearinghouse” for air permits (at https://cfpub.epa.gov/RBLC/) contains data on emissions limits for the lowest-emitting facilities. The clearinghouse data show overlap in the permitted emission rates for coal- and biomass-burning facilities for each pollutant, with the exception of sulfur dioxide, which is usually emitted at a higher rate by coal plants (although biomass plants burning construction debris that contains gypsum wallboard residues can have relatively high sulfur emission rates). The range of rates at the five lowest-emitting coal facilities and the five lowest-emitting biomass facilities in the clearinghouse with boilers 100 MMbtu/hr and greater are as follows:
Filterable PM10 Coal: 0.01 to 0.12 lb/MMBtu; Biomass: 0.0125 to 0.025 lb/ MMBtu
Nitrogen oxides (NOx) Coal: 0.067 to 0.07 lb/ MMBtu; Biomass: 0.065 to 0.15 lb/ MMBtu
Carbon monoxide (CO) Coal: 0.02 to 0.135 lb/ MMBtu; Biomass: 0.1 to 0.33 lb/ MMBtu
Emissions of hazardous air pollutants (HAPs) including heavy metals, hydrochloric acid, and organic contaminants including benzene and formaldehyde are estimated using EPA emissions factors for biomass combustion (https://www.epa.gov/ttnchie1/ap42/ch01/final/c01s06.pdf), with totals that range from 10 to more than 40 tons of HAPs per facility.
(2) Biomass has a lower energy content per unit carbon than fossil fuels, emitting around 213 pounds of CO2 per MMBtu heat content, in contrast to coal (~206 lb CO2/MMBtu) and natural gas (~117 lb CO2/MMBtu; https://www.eia.gov/electricity/annual/html/epa_a_03.html). Besides its relatively low energy content, biomass tends to have high moisture content, about 45 percent by weight for green wood chips. Energy is required to drive off that moisture before useful heat can be generated for the boiler, which further degrades facility efficiency. Our review of multiple biomass permit applications reveals that peak efficiency of biomass power plants is around 24%, whereas a coal plant is around 34% efficient and a gas plant using combined cycle technology can be around 45% efficient (https://www.eia.gov/electricity/annual/pdf/epa.pdf, efficiency calculated from data in Table 8.2). The combined effect of these factors is that a biomass plant emits about 3,029 lb CO2 per megawatt-hour (MWh), versus a typical coal plant (2,086 lb CO2/MWh), or a combined cycle natural gas plant (883 lb CO2/MWh).