I’m going to have to read this report. How does that work? There’s no way cutting down a tree, shipping it and processing it requires a tree-worth of fuel. Yeah, you could let the forest keep growing, but from what I’ve heard it slows down pretty good at a certain point, and eventually starts decaying as well. Maybe way more of it is going to paper than I would have expected?
There’s no way cutting down a tree, shipping it and processing it requires a tree-worth of fuel.
Let’s fact check that:
(TLDR: it seems you’re right)
(Note on gross vehicle weights. I found everything from 80,000 kg at the high end in Canada and 80,000 pounds consistently in the US. That wide range, especially the huge difference between Canada and USA, makes me somewhat suspicious of the following calculations. But I think it still works out in favour of the original assertion.)
Canadian maximum weight limit for semis is 80,000 kg. I’ve seen numbers varying from about 35,000 kg to 80,000 kg, depending on jurisdiction, trailer configuration, and permits, so I’ll use the biggest number.
That leaves an estimated payload of about 64,000 kg. That amount of wood contains about 940,800 MJ of energy.
The payload contains over 600 times the energy required to haul it 100 km. Obviously, there are considerations of actual distance, round trips, logging equipment hauling and use, etc. The numbers can change dramatically based on actual payloads, too, but it seems the lumber has “energy to spare” so to speak.
I’d be a bit more conservative with some of those numbers. I don’t actually know how much they let the logs dry; it could be they’re usually shipped green to avoid damage to them at the site of felling. Furthermore, 1,000km might be a more typical distance for wood to be shipped in Canada, since most of the forest is way up north, far from population centers. We’ve still got comfortably an order of magnitude, though.
Cutting the logs down to size probably takes negligible energy by comparison, and is going to be electricity-based at this point anyway. I’d also have used carbon mass rather than energy, but that’s actually going to work in our favour, because petroleum gets a lot of it’s energy from the hydrogen within it as well, while wood is effectively carbon+water for plant biology reasons.
Oh yeah, it has a lot of holes! Despite the effort I put in, I should have called it what it is: back of the envelope analysis. The only reason I did it was to satisfy my curiosity regarding the initial statement, then felt compelled to share it. :)
I doubt they let the logs dry at all, but the only caloric content I could find for logs assumed air-dried to 20%. I don’t know enough to consider other methodologies like carbon content, etc.
My 100 km was intended as a rate of energy consumption, not an actual hauling distance, but I didn’t make that clear.
I’m going to have to read this report. How does that work? There’s no way cutting down a tree, shipping it and processing it requires a tree-worth of fuel. Yeah, you could let the forest keep growing, but from what I’ve heard it slows down pretty good at a certain point, and eventually starts decaying as well. Maybe way more of it is going to paper than I would have expected?
Let’s fact check that:
(TLDR: it seems you’re right)
(Note on gross vehicle weights. I found everything from 80,000 kg at the high end in Canada and 80,000 pounds consistently in the US. That wide range, especially the huge difference between Canada and USA, makes me somewhat suspicious of the following calculations. But I think it still works out in favour of the original assertion.)
1 m³ of diesel contains 38.68 GJ of energy.. That means 38.68 MJ/litre.
Air dried logs (20%) moisture have 14.7 GJ per tonne. That’s 14.7 MJ/kg.
Ballpark empty weight of a semi truck and trailer is 35,000 pounds (15,876 kg).
Canadian maximum weight limit for semis is 80,000 kg. I’ve seen numbers varying from about 35,000 kg to 80,000 kg, depending on jurisdiction, trailer configuration, and permits, so I’ll use the biggest number.
That leaves an estimated payload of about 64,000 kg. That amount of wood contains about 940,800 MJ of energy.
Average fuel efficiency is 39.5 L/100 km as of 1999. That’s 1,527.86 MJ.
The payload contains over 600 times the energy required to haul it 100 km. Obviously, there are considerations of actual distance, round trips, logging equipment hauling and use, etc. The numbers can change dramatically based on actual payloads, too, but it seems the lumber has “energy to spare” so to speak.
the metric of concern here isn’t GJ, but tonnes of carbon emitted.
“They did the math”. Thanks!
I’d be a bit more conservative with some of those numbers. I don’t actually know how much they let the logs dry; it could be they’re usually shipped green to avoid damage to them at the site of felling. Furthermore, 1,000km might be a more typical distance for wood to be shipped in Canada, since most of the forest is way up north, far from population centers. We’ve still got comfortably an order of magnitude, though.
Cutting the logs down to size probably takes negligible energy by comparison, and is going to be electricity-based at this point anyway. I’d also have used carbon mass rather than energy, but that’s actually going to work in our favour, because petroleum gets a lot of it’s energy from the hydrogen within it as well, while wood is effectively carbon+water for plant biology reasons.
Oh yeah, it has a lot of holes! Despite the effort I put in, I should have called it what it is: back of the envelope analysis. The only reason I did it was to satisfy my curiosity regarding the initial statement, then felt compelled to share it. :)
I doubt they let the logs dry at all, but the only caloric content I could find for logs assumed air-dried to 20%. I don’t know enough to consider other methodologies like carbon content, etc.
My 100 km was intended as a rate of energy consumption, not an actual hauling distance, but I didn’t make that clear.