A report published this week by WSL, the Swiss Federal Institute for Forest Snow and Landscape Research, calculates Switzerland could double the amount of energy it gets from burning biomass to 97 peta joules (PJ) a year, with 50 PJ coming from wood combustion.
In 2019, Switzerland generated 41 PJ of energy burning wood. This represented 4.3% of Switzerland’s total energy consumption. Taking this to 50 PJ would boost energy from wood combustion to 5.2%.
Currently, woody biomass in Switzerland is mainly combusted to produce heat (95%) and, to a small extent, electricity (5%) in combined heat and power. One advantage of electricity from wood combustion is its ability to provide peak supply. Unlike solar and wind, wood can be stored and burned when needed. On-off sources of electricity like this are a critical element of grid balancing as more volatile renewables are added.
The report also highlights risks and challenges of using biomass for energy, which include limited raw materials and competition for them, high production and logistic costs, negative environmental impacts, suboptimal use of raw materials and carbon emissions, especially for wood.
Optimising the process requires those involved in the business of burning to follow the rules. Ultimately, the system has to ensure a new tree is planted for every one burned or the material burned must be destined to rot and release. Wood used as material, to build a house for example, locks up carbon and has a far better emissions profile than combustion of the same wood. It is vital to follow the proper cascade of material use before burning, says the report. In addition, defining wood waste is key but not clear cut. For example, those benefiting from wood burning may have a different definition of waste wood to those using wood chips to make particle board.
Another challenge is the high emissions and air pollution generated. Wood burning (368 g CO2/kWh) has higher emissions than hard coal (338 g CO2/kWh) or diesel (267 g CO2/kWh) – figures from Volker Quaschning. And like all combustion, wood burning produces particulates and NOx.
The main argument justifying the sustainability of wood and other biomass combustion is the potentially cyclical nature of it. Every time a tree is burned another is planted. Sustainability rests largely on the incentives created to plant more carbon sequestering plants. Also waste wood might as well be burned for heat rather being left to release carbon as it lies on the ground and rots.
In 2019, hundreds of scientists wrote a letter to a number of world leaders urging them not to undermine climate goals by shifting from burning fossil fuels to burning trees to generate energy.
Their main arguments include rule breaking. In recent years, there has been a misguided move to cut down whole trees (rather than only burn waste wood) or to divert large portions of stem wood for bioenergy, releasing carbon that would otherwise stay locked up in forests. In addition they argue that government subsidies for burning wood promote a false solution that is replacing real carbon reductions. Companies are shifting from fossil energy to wood, which increases warming, as a substitute for shifting to solar and wind, which would truly decrease warming.
In some places, including Japan and French Guiana, there are proposals not just to burn wood for electricity but to burn palm or soybean oil. Producing these fuels requires expansion of palm
or soybean production that leads to clearing of carbon dense tropical forests and reduction of their important carbon sink, both of which add carbon to the atmosphere.
To avoid these harms, governments must end subsidies and other incentives that today exist for the burning of wood whether from their forests or others, write the scientists. The European Union needs to stop treating the burning of biomass as carbon neutral in its renewable energy standards and in its emissions trading system. Japan needs to stop subsidising power plants to burn wood. And the United States needs to avoid treating biomass as carbon neutral or low carbon as the new administration crafts climate rules and creates incentives to reduce global warming. Trees are more valuable alive than dead both for climate and for biodiversity. To meet future net zero emission goals, your governments should work to preserve and restore forests and not to burn them, concludes the letter.
The difference between burning a tree or coal is largely temporal. There isn’t much difference between coal (a very old tree) and wood from a new one. In both cases a former tree is being turned into energy, usually heat. In the end it largely comes down to incentives. The incentive to plant a new tree is higher with wood than with coal, although in theory a tree could be planted every time its coal equivalent is burned. In some ways this might be easier to monitor. The case for burning waste wood that would otherwise rot is clearer from an emissions perspective. However, it’s open to cheating. Who defines waste wood? And is rotting waste wood actually worthless? “Besides growing trees and other plants, if you had to pick one other thing that was key in the forest, it would be dead wood,” said Lori Hennings, a senior natural resources scientist in the US.
WSL report (in English)
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