The burning question of bioenergy’s green pedigree

Scientists challenge the assumption that burning wood is carbon neutral

A bio-power plant fuelled by wood waste | nostal6ie/Shutterstock

(Editor's note: One paragraph of this story was changed November 6 to clarify that the Nexterra co-generation plant at UBC still produces heat using wood waste.)

If the City of Vancouver is serious about becoming 100% carbon-free by 2050, it might need to rethink its plans to replace natural gas with bioenergy for heating.

The strategy aims to begin phasing out natural gas for heating in new buildings, starting in 2030. One alternative to natural gas for heating is biomass (wood waste energy). The city and Creative Energy have tried to get approval for a district energy system that would use wood waste instead of natural gas to produce heat for buildings. The BC Utilities Commission has repeatedly rejected it because it would be a monopoly that would not be in the public interest.

Creative Energy owner, Ian Gillespie, could not be reached for comment. However, a city official confirmed that the city is still working with Creative Energy.

But is burning wood to generate heat better for the environment than burning natural gas?

Not according to 65 American scientists who wrote a letter last year to the U.S. Senate to oppose a plan to designate wood energy as a carbon-neutral energy source on par with solar power.

“Burning forest biomass to make electricity releases substantially more carbon dioxide per unit of electricity than does coal,” their letter states.

But Mark Jaccard, who leads the School of Resource and Environmental Management at Simon Fraser University, vehemently disagrees.

“Burning wood waste has zero emissions,” he said. “All of the carbon that goes into the atmosphere came from the atmosphere via photosynthesis. There is no long-run increase in CO2 or other GHGs [greenhouse gases] in the atmosphere from burning wood.

The IPCC [Intergovernmental Panel on Climate Change] has been clear on this for 20 years.”

But even the IPCC states that the carbon neutrality of wood energy cannot be assumed.

“The IPCC guidelines do not automatically consider biomass used for energy as ‘carbon neutral,’ even if the biomass is thought to be produced sustainably,” its website states.

The Environmental Protection Agency likewise states: “biogenic CO2 emissions will have zero net atmospheric impact only in cases where – over some time period and at some spatial scale – carbon sequestration equals carbon emissions.”

The B.C. government assumes energy from wood to be carbon neutral, so it is not subject to carbon taxes. Although wood produces GHGs when burned for either heat or producing power, it gets a green credit because it is a renewable resource – one that soaks up CO2 when a tree grows.

Because trees absorb carbon, if wood is burned, it is considered to be a loop that produces no net carbon, according to the prevailing wisdom of many environmental scientists. Not all environmental scientists agree, however.

Philip Duffy, a physicist who served as senior adviser to the U.S. Global Change Research Program for the White House under the Barack Obama administration, now heads the Woods Hole Research Center, an American climate change think tank. He is among the 65 scientists who objected to wood energy being designated carbon neutral.

In an email to Business in Vancouver, he said life-cycle analysis of the burning of wood does result in net GHGs that are lower than for burning fossil fuels, but only if a perfect balance is achieved through forests that are managed sustainably in perpetuity – something that simply cannot be assumed.

“Burning wood is not carbon neutral,” he wrote. “The immediate effect is to add a lot of CO2 to the atmosphere, along with other dangerous pollutants.

“If the forest where the wood comes from is fully regrown, which typically takes something like 50 years, much but not all of the emitted CO2 will be absorbed by the growing forest. But during the intervening decades, damage (melting of ice sheets, thawing of permafrost, etc.) will have been done by the elevated atmospheric CO2 levels.”

One alternative to wood waste combustion is turning it into syngas, which occurs when wood is heated and starved of oxygen to create a gas that can be burned, either to produce heat or to power turbines to create electricity.

That has been tried at the University of British Columbia (UBC), with partial success, with its $27.4 million Bioenergy Research Demonstration Facility. Built in collaboration with Vancouver’s Nexterra and General Electric (NYSE:GE), the bioenergy plant was designed as a cogeneration plant that would produce both heat and power for the campus using wood waste.

The plant currently supplies 25% of the campus’ heat, using wood waste. But after only 160 hours of operation, the system experienced a failure in equipment that cleans up the syngas before it is burned to produce power.

The plant is still producing heat using wood waste, and it is still producing power, but not with syngas made from wood. It is using renewable natural gas from FortisBC, at a hefty premium, to produce power.

The wood waste UBC uses to heat its campus is cheaper than natural gas, but only because it pays $55 per tonne in carbon taxes on natural gas. In addition to the $30 per tonne that all British Columbians pay for using fossil fuels, it pays an additional $25 as part of the B.C. government’s carbon-neutral mandate for the public sector.

David Woodson, UBC’s managing director of energy and water services, says the new bioenergy plant, in conjunction with a conversion of the university’s heating system from steam to water, has reduced the campus’ GHG profile.

“The combined bioenergy plant and hot water conversion … are two main projects that have allowed UBC to reduce its greenhouse gas emissions by 34% since 2007,” Woodson said, “and that’s despite the campus growing by over 20% in campus space over the same time.”

But that GHG reduction is based on the assumption that wood as an energy source is carbon neutral.

“I would argue that it is a bad idea to invest in infrastructure that may not result in any climate benefit,” Duffy said. “If the city wants to do something that will have a positive climate benefit they should adopt wind and/or solar power.”

nbennett@biv.com