There is every reason to utilize biomass from thinning wood in production forests for district heating, among other uses. When forests are regularly thinned, and new trees are planted, significantly more CO2 is bound in the forest, write several researchers and a forester in an opinion piece.
August 21, 2024 | Original article in Danish by Niklas Lindstrøm Jørgensen, Danish District Heating Association | Translation: DBDH
In untouched forests, CO2 is continuously released as trees decay. This is avoided in production forests, where trees are thinned and used, for example, as biomass for heat production. According to some researchers, this makes ‘production forests’ better for the climate.
In Denmark’s overall CO2 accounting, burning biomass from production forests to displace fossil fuels makes a lot of sense. When trees are cut and thinned as they age and used for other purposes—such as wood chips for district heating—they have a more positive impact on total CO2 emissions than untouched forests ever could. This is the claim of some researchers and a forester in an opinion piece in Altinget.
According to them, production forests have a more positive effect on the climate because growing trees, which have a high carbon storage capacity, are more abundant than in untouched forests. This is due to the continuous thinning, felling, and replanting of trees.
“Newly established, untouched forests bind much CO2 in the first few years, just like production forests. But thereafter, the binding decreases, and the emissions from decay increase. All biomass in untouched forests eventually rots, causing almost all CO2 to return to the atmosphere. Over a 100-year period, the climate effect of untouched forests is close to zero, except for some carbon storage in the soil,” the researchers write in the opinion piece.
They particularly highlight the substitution effect when biomass from production forests is burned, which is one of the main reasons for the forests’ value. They use straw as an example, but according to the researchers, the same calculations apply to wood chips.
“The substitution effect is enormous, whether you look at how much coal, oil, or natural gas can remain in the ground or the amount of electricity that can be produced,” they argue.
Even in a future with plenty of offshore wind turbines and solar panels, enormous amounts of backup energy will be needed when the wind doesn’t blow and the sun doesn’t shine.
Anders Frandsen, Director of the Danish Forest Association:
An Important Replacement for Fossil Fuels
In recent times, biomass has played an important role in phasing out fossil fuels, particularly from district heating production. But in the future, biomass will—and must—play a smaller role as it is phased out in favor of greener alternatives.
However, even in the future, biomass may still be needed, according to the researchers:
“Even in a future with plenty of offshore wind turbines and solar panels, there will be a need for enormous amounts of backup energy for when the wind doesn’t blow and the sun doesn’t shine,” they argue.
Anders Frandsen, Director of the Danish Forest Association and Chairman of Triangle Energy Alliance, supports this viewpoint.
“Today, we use a lot of biomass from agriculture and forestry for energy in direct combustion. In the short and medium term, there are no alternatives to this unless one wishes to return to fossil fuels, which would make it impossible for Denmark to achieve its ambitious climate goals,” he writes in an opinion piece in GridTech. He continues:
“In the long term, expanding solar, wind, geothermal energy, and improved energy efficiency will reduce the share of biomass used relatively unprocessed directly in the Danish energy sector. We don’t cut trees specifically for biomass for district heating plants.”
Rune Moesgaard, Political Director at the Danish District Heating Association
Strict Requirements for District Heating Biomass
The Danish District Heating Association supports the use of biomass from production forests and, like the researchers, emphasizes that wood chips and straw play a major role in phasing out fossil fuels.
“At the Danish District Heating Association, we see sustainable biomass as part of the solution for producing green heat and electricity. Since the political agreement in 2012, biomass has contributed significantly to freeing Denmark from coal and accelerating the current phase-out of gas—and soon sustainable biomass will also contribute to negative emissions via CCS,” says Rune Moesgaard, Political Director at the Danish District Heating Association.
He further mentions that much of the biomass used in the district heating sector today comes from local forestry or straw producers. Specifically, wood chips account for about 40% of biomass used for district heating production in Denmark. There are also strict sustainability requirements that must be met and documented.
At the same time, Rune Moesgaard emphasizes that trees are not unnecessarily felled to supply wood chips to heating plants. Instead, thinning wood from production forests, which would have been removed anyway to allow the rest of the forest to grow and bind even more CO2, is used.
“Many district heating companies nationwide use local Danish biomass and thus participate in a green and rational symbiosis with Danish forestry. We don’t cut down trees to make biomass for district heating plants—we instead utilize a fraction from the forests,” he says.
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