Eucalyptus Biomass

I’m sure you can tell that I am a big fan of Eucalyptus biomass and firewood.

Being a newcomer to rural Ireland, I was quite surprised that some households in the rural community were buying firewood ! To me it appeared that they could simply grow their own. Cheap winter fuel in the form of Eucalyptus biomass, either for firewood logs or coppice.

My experience with turf has been good, though turf does leave a lot of fine ash to be cleared up most mornings. Burning timber, provided it is dry provides equivalent heat with a fraction of the ash. Although I haven’t yet, as of September 2018, been able to verify that Eucalyptus firewood leaves even less ash than most other varieties such as Ash and Spruce, this is what I am led to believe.

Eucalyptus is ideally suited to biomass in Ireland due to their fast growth rates. Many varieties of Eucalyptus will coppice, giving a high yield over a thirty year lifespan. Eucalyptus is considered to be a perennial biomass crop, i.e. a harvest can be taken each year.

Because Eucalyputs can grow in a wide variety of poor soils, with many varieties thriving in wet ground, they are a commercial proposition on degraded land which otherwise would yield no revenue. Again I am surprised that growing Eucalyptus biomass isn’t more popular.

How does Eucalyptus biomass compare with other varieties as a firewood crop.

Below are my own personal experiences and results of research.

My experience:

  • It’s very noticeable when you burn Ash, just how long it lasts and how much heat it gives off. Likewise when you burn softwood like spruce, it’s very evident how much more quickly it burns, though it does burn hot.
  • Wood needs to be dry before it will burn well. This is important ! Seasoning is a relative term. The summer of 2018 was particularly hot, and a small Irish Alder I cut up for firewood was dry in a few weeks ! It brunt well, not as good as Ash, but certainly it is acceptable firewood.
  • Wood becomes fibrous and tough as it seasons. This is my experience of Ash and Spruce. The chain saw cuts through it with ease when it’s fresh. Try cutting it with the chain saw when it’s been drying for a few months and you would think the saw is blunt.

Eucalyptus Biomass, Does it have a high moisture content 🤔

Early on I was told that Eucalyptus had a high moisture content. Is this true, and does it matter ?
The logs in my experiment are quite small, though you would split them to improve the drying times, which for this experiment I didn’t do. So I am being conservative.

The point I am trying to make in the video about these cheap moisture content devices is, that they are an average across different tree species including hard and softwoods. To get an accurate measurement a more professional device that is species specific would be required.

So in addition to the prong tester, I decided to weigh the log I am testing to further gauge how much moisture it loses.

I’ll update the table below on a weekly basis until the moisture content is 10% or lower

DateMoisture  content (%)Weight (grams)Coments
21 Mar 2022341157Sunny, hot in the poly tunnel
27 Mar 2022301046Sunny, hot in the poly tunnel
4 Apr 202227898I got several moisture content readings from 39% ? To 27% I can only assume that the moisture was coming out to the ends where I was taking the reading. I have recorded the lowest, the weight is well down.
11 Apr 202221804Again I got several different readings ranging from 39% to the lowest which I have put down, 21%
18 Apr 202218743Again I got several different readings ranging from 32% to the lowest which I have put down, 18% Much lower temperatures in the poly tunnel, a mostly cloudy week
25 Apr 20227.1635A range again, from 21% down to 7.1%. I’m putting down the lower. A sunny week and I had the ventilation and one door open in the poly tunnel, so a good airflow.
2 May 202215586Another interesting range ! 15 to 20% Its been cooler this week and when I took the reading it was around 20℃, previously perhaps in the high 30℃ So perhaps this is a more accurate measure, though I will stick with the weight which is now half of what it was 6 weeks ago. The weigh scale is very accurate.
9 May 202217551Well quite remarkable, an increase ? It hasn’t been that sunny and today is a dull damp day, even though, the weight is down, so the moisture content overall must be down. As I say in the video I am a bit dubious of these cheap testers.
16 May 202265146 to 11% today. I think it is becoming a more accurate measurement as it dries out. Interesting report which suggests Eucalyptus can have a moisture content as high as 63% and the weight so far suggest this is the case for my small sample.
23 May 202210502Well these moisture meter readings are bizarre 🙄 The wood is slightly lighter, though the readings I got ranged from 10 to 16%
OngoingI’ve left the log in the poly tunnel and will take a reading every now and then for my own curiosity, though the weight reduction during the last week has dropped off noticeably and I consider this firewood to be more than dry enough to burn in a stove or fire.
30 May 20229478Couldn’t resist 🙂 Moisture 9 to 13%
7 Jun 20229477A lost of only one gram over seven days. The moisture content reading was from 9 to 10%. So I would definitely consider this timber to be less than 5% moisture content, being 58% lighter than when cut.
13 Jun 20229474A range of moisture readings from 9 to 13% The weight isn’t coming down much anymore, so I don’t think the moisture content is as high as 9% now.
23 Jun 202294729 to 14% ! With a lower weight 🙄not credible. Its evident though, that the weight hasn’t reduced much in the last four weeks, so this wood is more than dry enough to burn 😁 and well before the turf has dried out 😉

My research:

  • Generally conifer, Ash, Oak, Beech and the other mainstays of the Irish firewood market need to be seasoned for at least a year unless kiln dried. It’s suggested that Eucalyptus be seasoned for a couple of years. It grows at least twice as fast as the other species, so that shouldn’t be an issue. NOTE what I say above though, everything is relative and subject any tree wood to hot dry conditions and it will dry out more quickly than in cold damp conditions.
    My current view after burning some of my Eucalyptus wind fall is that it will require no more seasoning / drying that Ash, Spruce or Alder all of which I have personally cut and burnt.
  • BTU values for Eucalyptus suggest equivalent heat value to Oak, though there are over 700 varieties which grow in various habitats from the coast to the high mountains and everything in-between. Therefore it is likely that the BTU values will differ depending on the variety. A general rule of thumb would be the heavier the wood the more dense it is, and therefore the more heat it will produce per given volume. White Ash produces about 60% more BTU than white pine and about 30% less than Oak. NOTE these figures will always only be a guide ! trees even of the same variety will differ to some degree or another.
  • I would generally consider Eucalyptus biomass coppice varieties such as Gunnii to be equivalent to Willow (sallys). The Ash comparable firewood log varieties as the Nitens, Viminalis and Johnstonii.
  • Those that burn Eucalyptus as firewood love it. The caveat is that you need to process it within a week or so of cutting it down, assuming you are splitting it with an axe. DON’T leave three metre logs in your mini forest to season. The wood will become fibrous and tough. As above though, my experience has been similar with native species such as Ash and Spruce.
    If you process it within a week or so and store it in a log store with a poly carbonate roof, then it will dry out in a year easily.  Cut up logs will have more surface area exposed for moisture to evaporate from. The shed / greenhouse I built in Scotland could reach temperatures of over 50℃ during the summer, and often over 30℃ on a sunny day during the winter. It was a simple wood structure, though with a polycarbonate roof and windows.
  • “Overall, eucalyptus is a good choice for firewood. The wood produces heat somewhat comparable to oak and it leaves a nice bed of hot coals.”
  • “Eucalyptus firewood is known for burning very hot.”

Climate change

Is having an impact. This is no longer a debate. Sustainable heating fuel is therefore going to be more valuable in the near future. Ash dieback is affecting the mainstay of the Irish biomass (firewood) industry, and a good substitute, in fact a better alternative is growing Eucalyptus trees as Eucalyptus biomass.

Eucalyptus planted for biomass and firewood is a sustainable carbon neutral fuel.

There have been some good years and bad since I first started planting my mini forest; check out some of the videos in my YOUTube playlist Trees & the Environment to see what my mini forest looks like now