Wood (including pellets) is in the vast majority of cases the worst energy source and heat source.
German Environment Agency (Umweltbundesamt)
“Sustainable wood” here does not mean industrial wood production. That is what the document says:
For waste wood, the balance only accounts for the expenses for processing and transport. Furthermore, despite the discussion about “carbon debts” in the energetic use of forest wood (Agostini, Giuntoli & Boulamanti, 2013; et al., 2017), it assumes that the removal of forest wood is greenhouse-gas-neutral due to sustainable forestry in Germany. Thus, only the energetic expenses for harvesting and transporting the wood are counted.
This comes from this document, page 61: https://www.umweltbundesamt.de/sites/default/files/medien/1410/publikationen/2019-11-07_cc-37-2019_emissionsbilanz-erneuerbarer-energien_2018.pdf
(Note: The Umweltbundesamt is Germany’s central environmental authority, roughly comparable to the US EPA.)
On top of that comes particulate matter, especially with wood.
Illuminating on the topic of “sustainable wood” is also this three-minute audio piece:
Are wood stoves really climate-neutral? | MDR.DE
Experts are calling for a move away from wood stoves, because wood performs worse than hard coal when burned. The science editor spoke with the scientist Dominik van Pinxteren and the author Peter Wohlleben. https://www.mdr.de/wissen/audios/sind-holzoefen-wirklich-klimaneutral-102.html
(MDR is Mitteldeutscher Rundfunk, a public broadcaster serving the central German states of Saxony, Saxony-Anhalt and Thuringia.)
An open letter from science
More than 500 scientists have called on the European Union and the United States to abandon the burning of wood for energy. Among the signatories, alongside researchers from Harvard, Stanford and the University of Oxford, are scientists from Germany, such as from the Potsdam Institute for Climate Impact Research, Humboldt University Berlin and the University of Göttingen.
The original letter “Letter Regarding Use of Forests for Bioenergy” of 11 February 2021 is available at http://link.euwid.de/0q2zy.
Volker Quaschning - Carbon dioxide emissions
And to round off the topic, the article by Volker Quaschning, German engineering scientist and professor of renewable energy systems at the University of Applied Sciences (HTW) in Berlin:
Specific carbon dioxide emissions of various fuels
The various fossil energy sources produce different amounts of carbon dioxide when burned. These values are decisive for calculating carbon dioxide savings. https://www.volker-quaschning.de/datserv/CO2-spez/index.php
Notes on the article
Volker Quaschning defines “sustainable” via the quantity balance. Only as much wood is burned as regrows in the same period. Only then does the fuel count as CO₂-neutral. The table therefore lists wood with 0 g CO₂/kWh in the row “Wood¹)”. Precondition: growth ≥ removal. This definition leaves four points open that would even speak in favor of burning wood.
The time reference is missing. “Can regrow” does not say how long that takes. A tree needs 60 to 100 years. During this time, the CO₂ is already in the atmosphere. The article blanks out this carbon amortization period.
The reference to origin is missing. Whether the wood comes from sustainable forestry, from clear-cutting or as imported pellets from overseas remains open. The article calculates in a blanket way.
The text does not resolve footnote ¹). It stands for “sustainable wood use”. The only explanation is provided by the one sentence at the end. But every number is missing.
The table contradicts its own text. Quaschning writes: “Natural fuels such as peat or wood have very high specific emissions if they are not used sustainably.” But the table shows 0 g CO₂/kWh for wood¹). That is a calculated ideal case, not a realistic average value.
In short: The article defines “sustainable” purely physically as a closed carbon cycle. It says nothing about time periods, origin or practical implementation. That is why the sentence at the end reads: “In reality, this applies only in exceptional cases.” That is the actual statement of the article.
Wood ranks among the worst fuels
Burning it harms the climate more than almost any other energy source.