Due to the growing interest in climate change, the environment, and energy security, woody biomass is receiving more and more attention as a renewable energy source. Though it still accounts for only a small portion of energy use worldwide, woody biomass is one of the top candidates for oil equivalents and a fast growing source of renewable energy. As a result, using biomass as an energy source has come under extensive scrutiny. Woody biomass has become the topic of intense debates and controversy as questions have been raised regarding its sustainability, cost-effectiveness, and greenhouse gas impact.
As the demand for biomass has grown, so has the number of criticisms and misconceptions about it. One of the often heard complaints is that the burning of biomass as fuel releases CO2 and other greenhouse gases (GHG), contributing to global warming, making it no better than fossil fuels. In reality, woody biomass is a carbon neutral energy source. For this to be understood, it is necessary to look at the entire cycle, not just the combustion of the fuel. Trees are part of an atmospheric cycle. As they grow, they absorb carbon from the atmosphere temporarily storing it. When a tree dies, the same amount of carbon that it absorbed during its lifetime is released back into the atmosphere as it decomposes, adding no new carbon to the atmosphere. When woody biomass is burned to produce energy, it releases that same amount of carbon that would have naturally been released if the tree had been left to decompose on the forest floor.
Though woody biomass is a carbon neutral energy source, research has found that it also has several other environmental benefits as well. A study from the Pacific Research Institute found that biomass energy production contributes to healthy forests and reduces the potency of the CO2 that would otherwise be naturally released.
“The total amount of carbon that is sequestered in terrestrial biomass affects the amount of carbon in the atmosphere,” said Dr. Gregory Morris, director of Green Power Institute. “Energy production from forest fuels contributes to forest health and fire resiliency, thereby increasing the amount of carbon that is stored on a sustainable basis in the earth’s forests.”
Also, biomass energy production can change the timing and relative mix of carbon forms associated with the disposal of the biomass resources emitted into the atmosphere.
“As a greenhouse-gas, reduced carbon (CH4) is 25 times more potent than oxidized carbon (CO2) on an instantaneous, per-carbon basis,” said Dr. Morris. “Therefore the form in which carbon is transferred from the biomass stock to the atmospheric stock is critically important from the standpoint of greenhouse forcing impact.”
It is important to realize that much of the biomass that is converted to energy would otherwise be landfilled or left in the forest and eventually decompose or burn in a wildfire. Both ultimately lead to GHG emissions with higher levels of potency than if it had been burned in a controlled boiler.
“Compared to combustion in a controlled boiler, open burning entails poor combustion conditions and gives rise to significant emissions of carbon in reduced form,” said Dr. Morris. “This elevates the greenhouse-gas potency of the emissions. Biomass burial in a landfill or agricultural field leads to even greater emissions of reduced carbon than open burning. Although the emissions from landfills are delayed, the greenhouse-gas potency of the emissions over the long term is much greater.
Beyond its positive affects on GHG emissions, the use of biomass also contributes to forest health in another way. There has been concern that increased biomass energy production would lead to deforestation. However, forests need to be properly managed to remain healthy. This includes thinning to prevent overcrowding and the removal of underbrush and fallen trees. Overgrown forests can become unhealthy and have a higher susceptibility to disease, pest and wildfires. Biomass energy production can encourage sustainably managed and maintained forests and help offset the costs to do so by paying for removal of overgrowth and residuals.
Despite the benefits provided to forests by biomass harvesting, some have taken to using the slippery slope argument that biomass power producers might run out of residuals, start using higher grade timber and be the cause of increased deforestation. However, this ignores the fact that part of what makes biomass energy affordable is that it utilizes cheap residuals. Buying expensive timber would not be profitable for anyone, let alone affordable. Bob Cleaves, president and CEO of the Biomass Power Association (BPA) said the biomass power industry cannot generate enough revenue to pay for its fuel, much less pay for higher value fiber like chip and pulpwood.
“We can’t afford biomass, let alone merchantable timber,” he said.
If biomass plants run out of sources of forest residuals and byproducts, they shut down. Already 20% of the California biomass fleet has become non-operational due to a lack of residuals, Bob said.
For this reason, it is important that the nearby resources be considered carefully when the location for a biomass plant is being chosen. On a national basis, there is an abundant supply of wood residues, byproducts and slash available. A report on wood energy sources and uses from the U.S. Forest Service’s Forest Products Laboratory (FPL) said that there is enough wood readily available in the U.S. to provide up to 10% of the nation’s energy use from wood.
“We could increase use significantly, without depleting our timber resource, by using material not now used, such as logging residues, manufacturing residues, land-clearing residues, urban wood residues, and wood from insect, disease and fire-killed trees,” said the report. “Nationwide, volume of annual wood growth exceeds the volume that is cut.”
At present, biomass power provides more than half of the renewable “green” electricity in the U.S. – around 8,500 megawatts per year which provides enough electricity to light about 8.5 million homes – and roughly 4% of the country’s total energy use. The demand for renewable energy sources is only going to increase from this point. More than half of the states have already passed legislation that requires a portion of electricity be produced from renewable sources by 2020. A federal standard is also being considered. If passed, it will create an even higher demand than there is now for renewable energy sources.
In spite of the research that shows woody biomass to be a sustainable and renewable alternative to fossil fuels and the growing need for just such a resource, there are still a number of obstacles in the way of it being recognized as such and utilized to its full potential. These include a lack of infrastructure for marketing wood fuel products, emphasis on non-wood fuels in research and subsidy programs, and failure to give due credit to environmental, national security, and economic benefits of using wood fuels. If these obstacles are overcome, woody biomass could become key to energy security and an answer to climate change concerns.
