Monday, June 29, 2020

A Burning Question: Trees Into Electricity?


Ancient humans probably learned first about fire by watching a forest burn.  One would think that in this era of nuclear and solar energy, the very old-fashioned alternative of burning wood for power is pass√©, but one would be wrong.  A recent article on the Wired website points out that biomass-fueled power plants are enjoying a comeback both in the U. S. and Europe, but for different reasons.  And the reasons are controversial.

Burning wood releases the greenhouse gas carbon dioxide, so other things being equal, generating electricity with solar or nuclear power is ecologically friendlier for that reason alone.  However, every tree on the planet has a natural life cycle, and before humans came along, the fate of many trees was to perish in a lightning-ignited forest fire.  We now know that such fires are a normal way for forests to renew themselves, and nature is not taken by surprise when a forest burns.  A few years later seedlings have sprouted into trees and the scars are largely healed. 

But in places like California, where residents of forested areas have promoted fire-prevention efforts that allow a buildup of dead trees and underbrush, the inevitable fires that nevertheless result can prove even more devastating than if people had just left nature to itself.  So a movement has arisen in that state to cut down dead trees and burn them in biomass plants, so much so that California leads the nation in the number of biomass-to-electricity facilities.

At first glance, this looks like a win-win situation.  The forests are better managed with those dead trees pruned away, the electric grid gets some much-needed power plants, and the local job markets benefit through the creation of labor-intensive logging and chipping activities.  But critics point out that burning any kind of biomass has a carbon footprint we could avoid, and the carbon sequestered in dead trees doesn't contribute to global warming.

I suppose somebody could get a grant to figure out exactly what mix of benign neglect, active harvesting of dead or even living trees, and biomass energy production would lead to the optimum of electricity and minimum carbon footprints, but even if you could figure it out, other factors would intervene before you could optimize things. 

Such factors include politics, both domestic and abroad.  In the Southeast U. S., where attitudes toward forests are more commercial than esthetic, it turns out there is a booming business in planting and harvesting pine forests to make wood pellets for export to Europe.  In a controversial decision, the European Union decided to designate biomass-fueled power plants as renewable energy, and now European countries are importing lots of wood pellets from the U. S. to burn for electricity.

Back when we lived in New England a couple of decades ago, a friend of ours started a business selling wood-pellet stoves for home heating.  As long as the pellets were made locally, they were cheaper per heating unit than fuel oil, which was the only alternative for many homes.  But somehow I doubt that shipping wood pellets across the Atlantic is as cost-effective as shipping oil, or even coal.  But it's renewable, and that label is valued increasingly by an ecologically-conscious public willing to pay more for it.

If you consider the life cycle of a particular tree, there is a good but not certain chance that it will perish in a forest fire some day.  In prehistoric natural forests, this fate was probably more common than it is today in California's fire-protected forests, but as recent years have shown, it's impossible to prevent all forest fires.  And when an artificially-protected forest choked with dead trees and dry underbrush does catch fire, the resulting conflagration can be a lot worse than if we had just walked away from the place a few dozen years ago and let nature do its own burning at its own pace.  But people with million-dollar homes in the middle of a forest don't want to do that, and so you get the situation that California faces now, where many forests resemble powder kegs waiting for a match.

If you look at the situation from a sustainable-energy perspective, it seems to me that biomass energy fits the description better than many other so-called sustainable options.  Over the long term, here's what happens.  Trees use sunlight, water, carbon dioxide, and a few other things to make cellulose.  Either before or after the tree dies, people come along and chip up the tree and burn it for power, releasing the carbon dioxide back into the air.  But other trees will come along some day and grab that same carbon dioxide and repeat the cycle.  Sounds pretty sustainable to me.

One practical problem in the way of going completely biomass for our electricity is that biomass plants don't scale very well.  Just as an example, the largest biomass plant in Texas has a capacity of only 100 megawatts (MW).  The smallest natural-gas plant in Texas has a capacity of 176 MW, and the largest can put out 2051 MW, comparable to the two nuclear plants in Texas.  The fact of the matter is that it takes a whole lot of wood chips to make not that much energy, and so far, most biomass plants in the U. S. have been built not simply to produce power, but to achieve other ends as well:  reduction of dead-tree mass, employment, and so on. 

So we probably shouldn't envision a future in which all our power comes from burning trees.  There just aren't enough trees to go around for that.  But in situations where labor, forestry policies, and politics coincide, biomass energy can both make sense and do some good.  It's not all good, but it's not all bad either, like most things in life.  And in burning wood for fuel, we are doing something that humanity has done since the dawn of time. 

Sources:  The Wired story by Jane Braxton Little entitled "The Debate Over Burning Dead Trees to Create Biomass Energy" appeared at https://www.wired.com/story/the-debate-over-burning-dead-trees-to-create-biomass-energy/ on June 27, 2020.  I also referred to the Wikipedia article "List of power stations in Texas" and some websites promoting the economy of wood pellets over oil, such as https://www.woodpellets.com/support/save-money-woodpellets.aspx. 

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