This Weyerhaeuser paper mill in Kentucky installed a highly efficient 88 MW biomass CHP system in 2001.
Earlier this month, Massachusetts Governor Deval Patrick proposed revisions to the state’s Renewable Portfolio Standard (RPS) that would restrict the eligibility of wood-burning biomass electricity generators to qualify for renewable energy credits (RECs). The regulations are now being reviewed for comment by a committee within the state legislature and should go into effect early this summer.
The Massachusetts RPS requires that retail electricity suppliers within the state derive a certain share (6 percent in 2011, rising at 1 percent per year) of their power from renewable sources, either directly or through the purchase of RECs.
The proposed revision to the state RPS comes in response to an independent study by the Manomet Center for Conservation Sciences commissioned by the Massachusetts Department of Energy Resources (DOER), which found that large-scale biomass-fired electricity would result in a 3 percent increase in greenhouse gas (GHG) emissions by 2050 as compared with coal generation. Based on this finding, reliance on biomass to meet the RPS proves inconsistent with other state environmental priorities, including the Global Warming Solutions Act, which calls for ambitious economy-wide GHG emission reductions of 25 percent below 1990 levels by 2020 and 80 percent reductions by 2050.
The proposed regulations would grant RECs only to biomass plants that could prove lifecycle GHG emission reductions of at least 50 percent over 20 years. This would include reductions from both the capture of carbon dioxide during the growth of the fuelwood as well as the GHG emissions from fuel combustion for electricity generation.
The Manomet study on which the Massachusetts revisions are based has come under criticism for its findings that biomass generation emits high levels of GHGs, in contrast to the widely held assumption that biomass generation is carbon neutral. The debate arises primarily from differences in biomass GHG accounting methods: critics of the study argue that carbon captured during the growth of fuelwood and carbon sequestration in the broader forest landscape beyond the harvested stand should be included in the analysis. In its response to these critiques, the Manomet Center defends its original method, stating that the metric of concern for biomass generation is not lifecycle emissions of the entire landscape, but rather the change in net emissions from biomass generation compared to a baseline scenario in which fuelwood is not harvested.
The new regulations also include stringent efficiency standards for biomass plants under the RPS, requiring 40 percent overall plant efficiency to qualify for half of a REC per megawatt-hour, and 60 percent efficiency for a full REC. The press release from the Patrick administration states that this measure is intended to steer the biomass industry toward smaller-scale production through combined heat and power (CHP) facilities that capture waste heat from electricity generation for heating and cooling purposes, rather than large-scale biomass electricity generation which currently operates at just 20–25 percent efficiency. None of the biomass plants that are currently selling electricity in the state, nor the several plants proposed in western Massachusetts, are expected to meet these efficiency requirements.
In addition to emission and efficiency provisions, the regulations limit fuel types for RPS eligibility. In particular, the standards aim to protect the integrity of forest ecosystems by restricting forest-derived fuels to forest residues, small amounts of biomass collected through forest thinning techniques, and forest salvage resulting from storms or pest infestations. The regulations also limit the weight of fuel that can be removed from forests to prevent loss of soil nutrients derived from woody matter.
Even as the Massachusetts government takes aggressive steps to reframe its environmental regulations, the debate over biomass remains far from resolved at the national level. Last year, the U.S. Environmental Protection Agency (EPA) proposed a Prevention of Significant Deterioration (PSD) rule that would allow the agency to regulate biomass and fossil fuel GHG emissions equally. However, under pressure from biomass proponents, including the National Alliance of Forest Owners (NAFO), EPA Administrator Lisa Jackson granted a three-year deferral of biomass GHG regulations to allow time for additional scientific analysis.
The commitment of the Massachusetts government to meet its ambitious GHG reduction targets through regulations informed by scientific evidence should serve as an example to the rest of the country. Biomass generation may indeed be able to contribute to the coming decarbonization of the electricity sector, but this will require the kind of regulatory guidance that Massachusetts is beginning to provide.