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Energy Solutions

Biomass Electricity Production: How Green Is It?

Although biomass supporters consider wood chips to be a ‘green’ fuel like wind and solar, burning wood to generate electricity raises public health and efficiency questions

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A wood-chip electricity plant in Vermont. The 50-MW McNeil Generating Station uses woody biomass from regional forests as its main fuel stock, but its efficiency is less than 30%. <p


Image Credit: Shelton Blog
A wood-chip electricity plant in Vermont. The 50-MW McNeil Generating Station uses woody biomass from regional forests as its main fuel stock, but its efficiency is less than 30%. <p


Image Credit: Shelton Blog
Wood chips from logging operations are burned to make electricity at McNeil. Waste heat from the plant is cooled by water from local wells.
Image Credit: Shelton Blog

“On a scale from 1 to 10, how nice are you?”

My nine-year-old neighbor put that question to me recently. He had been asked the question as part of an anti-bullying curriculum at his school, and he was trying it out on other people. I wasn’t sure how to answer it, and neither was he — “niceness” just doesn’t fit on a 10-point scale, in my mind. It did get us to talk a bit about what is nice and what isn’t, though, and he noted that there was less “meanness” at his school following use of the curriculum.

How green is biomass energy?

“On a scale from 1 to 10, how green is energy from biomass?”

What would you say?

Burning biomass for electrical production is, on its surface, attractive. Take the McNeil Generating Station in Burlington, Vermont, as an example. In the 1970s, the Burlington Electric Department (BED) was looking for additional power sources to meet rising demand for electricity. This was the era of the First Energy Crisis, and Three Mile Island. Oil and nuclear weren’t looking so good.

According to the Burlington Electric Department (BED) website, “BED conducted studies to find a fuel source that would be locally available, reliable, cost-effective, non-polluting and publicly acceptable. Wood scored high on all counts. Using wood fuel as a generation source would put money back into the Vermont economy, improve the condition of our forests and provide jobs for Vermonters.”

Fueled by low-quality trees and harvest residues

In 1978, Burlington voters approved a bond authorizing construction, with 71 percent of voters in support. The plant, which began operating in 1984, has a net electrical output of 50 megawatts. (For comparison, Vermont’s nuclear plant, Vermont Yankee, puts out 650 megawatts.) That is nearly enough electricity for Burlington, Vermont’s largest city. In 1989, McNeil was altered to also burn natural gas. According to BED, that allows it to be online more often, thus operating more economically.

Burning wood produces emissions, but BED says that they’re well controlled. Stack devices keep particulate emissions to one-tenth of State limits and one one-hundredth of federal limits. Like other power plants, McNeil uses water for cooling. It draws that water from four wells located near the plant, and releases clean, used water into the Winooski River. Wood ash produced at McNeil is used as a soil amendment.

McNeil’s wood comes from various regional sources. Seventy percent is “whole-tree chips” that according to BED, come from “low-quality trees and harvest residues.” Those include poorly formed trees that don’t have potential to be manufactured into useful products, and tree tops. Those chips are supplemented by sawdust, chips, and bark from local sawmills. McNeil even has a drop-off location for local residents for their wood and yard waste — everything from unpainted lumber waste to trees and limbs.

A different take on the same story

That is the story told by McNeil’s owners, and it’s a pretty good one. For a different reading of this story, I talked with Josh Schlossberg, the communications coordinator for something called the Biomass Accountability Project (see the Partnership for Policy Integrity website for more info). I had heard a few months ago that Josh was very critical of biomass power and in part because he’s an old acquaintance who I know is a committed environmentalist, I wanted to learn more.

“Biomass power should be in a different category than zero-waste, zero-emissions sources like solar and wind,” says Schlossberg, even though he acknowledges that each of those has environmental impacts.

Topping Schlossberg’s list of concerns is public health. McNeil is 400 feet from a residential area of Burlington’s Old North End. Schlossberg quotes the Environmental Protection Agency’s National Emissions Inventory Database as revealing 75 different air pollutants coming from McNeil’s smokestack.

Where there’s fire, there’s smoke

Those emissions include everything from dioxin, carbon monoxide, sulfur dioxide, nitrogen oxides, volatile organic compounds, formaldehyde, chlorine, heavy metals, and particulate matter (PM) 2.5. “PM2.5” is particulate matter 2.5 micrometers in diameter — so small it can’t be seen, and so tiny that it can lodge deep in the lungs, bloodstream, and internal organs. American Cancer Society studies demonstrate there is no safe level of exposure, says Schlossberg.

BED accurately characterizes McNeil emissions as being below regulatory thresholds, but the plant is still burning wood. Where there’s smoke there’s fire, and vice versa — and BED can’t possibly keep all the smoke from entering the air and ultimately the lungs of residents.

Schlossberg is also concerned about the wood supply demanded by McNeil and other similar biomass facilities, either built or proposed. When McNeil is running at full load, it consumes 76 tons of whole-tree chips per hour, according to BED, or the equivalent of 30 cords of firewood. It uses 400,000 tons of chips per year, the energy equivalent of 800,000 barrels of oil.

Wood use competes with other markets

Although BED says that McNeil uses low-quality trees as fuel, Schlossberg says that its use is competing with other possible outcomes for those trees: pulpwood (for paper), firewood, and leaving them in the forest. While the market determines where the trees end up, Schlossberg worries that the demand for electricity puts a strain on the forest and increases prices for other commodities, especially home heating wood.

How much woody biomass is available for burning? According to BED’s website, Northern Vermont could conservatively produce about one million tons of wood chips per year — enough to power two McNeil plants. While that indicates that there is some excess capacity in the woody biomass market, it doesn’t sound to me like an unlimited capacity. There are numerous biomass plants proposed for New England, and Northern Vermont could only handle one more.

Schlossberg quotes Department of Energy (DOE) statistics saying that biomass provides 0.9 percent of electrical needs nationwide. That’s a respectable showing, but it reveals that we would need a lot more biomass to make a dent in our oil, gas, and coal consumption (DOE, in its latest forecast, sees biomass electricity tripling by 2035). To this point, he dug up an interesting statistic from Harper’s magazine: if we cut down every tree in the U.S., it would meet our energy needs for one year. We don’t know what Harper’s assumed in getting that number, but it’s impressive all the same, in the devastation that would be caused for just one year of energy.

Maximizing efficient use of a (very) limited resource

A discussion of biomass wouldn’t be complete without carbon. Biomass proponents say that it is carbon-neutral: for every tree burned at McNeil and similar plants, another tree replaces it in the forest. While that may be true, climate change is an urgent issue today, and it will take decades for that new tree to grow and absorb carbon. Schlossberg, also notes that “Burning stuff is what has gotten us into the climate change problem to begin with.”

Given that our woody biomass is a limited resource, thermal electric stations like McNeil have a serious limitation: efficiency. Any power plant that extracts only electricity from a fuel source will typically be about 33 percent efficient. BED doesn’t publish efficiency figures, but according to Schlossberg, McNeil’s efficiency when burning biomass may be as low as 20 percent. The rest of the heat energy in the fuel is wasted as heat. Removing all that waste heat is the job of cooling towers using water.

Heating with firewood in a modern, efficient wood stove gives an efficiency of about 80 percent. That doesn’t help us with our lightbulbs and dishwashers, though. However, there has recently been a push for new cogeneration plants from biomass: combined-heat-and-power (CHP) plants that generate electricity and then use the waste heat to heat and cool homes and businesses in the area. These plants can run at an overall efficiency of 70 percent or better. Both wood heat and biomass-fueled CHP produce air pollution, so public health concerns remain, however.

Trying to head off a construction boom

Schlossberg says that he and organizations he works with don’t have a position on wood heat and biomass CHP. So far, they’re focusing on biomass power plants, and trying to head off what threatens in parts of the country to become a construction boom for them. At the very least, Schlossberg says, he’d like those plants to try to stand on their own without taxpayer funding.

Do you have an answer — how green is biomass energy, on a scale from 1 to 10? I know it’s tempting to throw up one’s hands and spout coprolalia, but stick with me for future columns as I explore other uses of biomass to meet our energy needs.

Tristan Roberts is Editorial Director at BuildingGreen, Inc., in Brattleboro, Vermont, which publishes information on green building solutions. Read more Energy Solutions columns, including columns by Alex Wilson, for whom Tristan is filling in, on the Energy Solutions homepage. You can also keep up with Alex’s adventures on sabbatical at ATWilson.com.

11 Comments

  1. Russ Chapman | | #1

    The Forestry side of it
    "for every tree burned at McNeil and similar plants, another tree replaces it in the forest. While that may be true, climate change is an urgent issue today, and it will take decades for that new tree to grow and absorb carbon."

    Great story and you did a great job of addressing the many issues facing the industry. Thank you! I would like to add, however, that the above statement is a bit misleading. Most trees absorb carbon quite rapidly in their early stages of life, in many cases even faster than old growth would. An increased carbon absorbsion rate CAN be achieved in a well managed forest.

    Here's another way of looking at it. I presume that not all the material coming to this plant is from managed forests. These means much of the material coming in is from trees that didn't reach their full potential in life. IF all the material that was accepted here came from well managed forests (or for that matter, if all forests became managed someday) how many plants could the State of VT support. I think in some cases folks who are against biomass plants, weather intentionally or not, are able to use the challenges that managed forestry faces to their advantage. If we solved the un-managed forest issue would that not change this playing field entirely?

  2. User avater
    Tristan Roberts | | #2

    sustainable forestry
    Tom, you raise an important issue. Frankly, I would like to understand it better, so for this article I chose not to delve into it very much. I hope to return to it in more depth for another article.

    The idea that young trees absorb carbon faster than older ones is one I've heard before, and it does seem like there is some validity to it. I am not sure, though, where the validity of that idea meets the idea that you are burning a large tree with a lot of carbon in it today -- and how long will it take for new trees to re-absorb that carbon? Perhaps there is a middle ground. In other words, I suspect that we could get more biomass fuel out of our forests with good management, but how much?

    I understand that there has been some experimentation with supplying McNeil with fast-growing willow farming. This harkens back to the old-world craft of coppicing. Again, I don't know a lot about how well this has gone, or how it works carbon-wise -- if anyone has more information, please make a note of it!

  3. David Meiland | | #3

    Good post Tristan. The state
    Good post Tristan. The state of Washington has pushed biomass power, and the issue of emissions now vs. recapture later has been brought up. I haven't read any real conclusions on that issue. In some cases, the choice is wood vs. coal, in others it might be wood vs. wind. Seems to me that ultimately humanity is going to have to get by without digging anything out of the ground, and without burning anything either. Best to start working on that now...

  4. Matthew Amann | | #4

    Seriously?
    Where would our stuff come from David? Those Solar panels and wind turbines DEPEND on EXTRACTION, like it or not. It is a necessary part of living and will never be overcome. The fact is, at least wood has some carbon EXTRACTION already built into it, while not being pure carbon like coal, and good things can happen to forest when thinned after our historical mismanagement.

  5. David Meiland | | #5

    Matthew
    Stretch your paradigm and imagine a world with less stuff, possibly a LOT less. The current approach is to dig resources out of the ground (plastics and metals) and then use energy dug out of the ground and burned to process them into mostly short-lived products that are then thrown back on the ground (and sometimes buried, sometimes not). Sure, everyone would like to keep on doing this, but for how much longer will it be feasible, even if you ignore environmental quality entirely? Resources become depleted. What is your expectation for how things will look in, say, 100 years?

  6. John Bos | | #6

    Sent by mistake
    I inadvertently sent my previous comment before it was completed. If possible, I'd like you to not post the incomplete comment and allow me to complete it.

    Thanks for your consideration.

    John Bos

  7. User avater GBA Editor
    Martin Holladay | | #7

    Response to John Bos
    John,
    I'm not sure what you mean by "my previous comment," but all comments can be edited by the original poster.

  8. Mark Heslep | | #8

    Burning stuff?
    Interesting tale on the woodchips plant. But, "Burning stuff is what has gotten us into the climate change problem to begin with", says Schlossberg? No, 'burning stuff' buried long ago deep underground is the issue. Lines like "there is no level of safe exposure" is crackpottery, as it can not be falsified. Just as it would be to say, "there is no safe limit of Schlossberg references in articles". How about some comments from an energy or environmental engineer instead of a 'communications coordinator' next time?

  9. User avater
    Tristan Roberts | | #9

    response to Mark
    Hi Mark, note that I'm going to explore biomass in future columns and quote other perspectives. This is simply a start.

    "No level of safe exposure" means that lab testing has exhausted the lowest limits of exposure that could be tested, and health issues were found. How would you phrase that, or how would you test it, etc? There are some things that simply aren't safe... at any speed.

  10. Russ Chapman | | #10

    Helpful report
    Helpful?

  11. Bob Coleman | | #11

    seems like
    the answer is, biomass burning itself is not bad, unless you implement it poorly, in large scale and compete against other fuel source uses

    often green questions like these leave out the part about how the solution is implemented.
    the solution itself is generally here nor there until you factor in the implementation....

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