The Death Of Fossil Fuels

[dyqik]

At best, photosynthesis is 6% efficient at turning light into biomass,

That's the wrong calculation until we get into a Dyson sphere type situation. Biomass grows by itself, and needs minimal energy input from sources that are otherwise useful to humans. That's different to solar arrays, which cost energy to build.

The opportunity cost for biomass inputs to the fuel production process is low.

Calculating the solar to biomass efficiency is like including the conversion of solar flux into wind in the efficiency of wind power.

I get your point, but I think your overselling it. It's not like farmers sit on their arses for 10/12 months a year never using water, fertiliser, etc.

And I always thought that the trouble with biofuels was the opportunity cost! Just fuel vs food, not fuel vs fuel.

It's really not a clean either/or. There's substantial biomass waste products from food production, and substantial areas that can be used for biomass production that isn't suitable for food production.

And that needs to be compared to the land, material and labor resources used for solar array production and generation.

Hell, how much power can you generate from the grass trimmings discarded from US lawns?

[bjn]

My back of the envelope says you need to use
at least 8x the land to deliver the same motive power with biomass as you do with solar. That land has to be of sufficient quality that you can grow things. Such land is generally not cheap as people want to use that for other things, like food. Yes there is an up front cost of solar panels, but you only need to acquire 1/8th as much land of nearly any quality.

Running farms is not free, you will have to plant, nurture and harvest the biomass like any other crop, Running a solar farm means keeping the panel clean and the weeds off (depending on where you put them) and not much more.

I’m really not feeling it for biomass derived fuels in the general case.

[bjn]

FWIW, solar panels can be had at US$0.12 now (wholesale, bulk orders). The main cost of a solar farm is no longer the panels, but every thing else.

[bjn]

Hell, how much power can you generate from the grass trimmings discarded from US lawns?

I’d put money on it being less than the energy to collect it to be passed onto Martin B’s team to turn it into Jet-A.

[dyqik]

My back of the envelope says you need to use
at least 8x the land to deliver the same motive power with biomass as you do with solar. That land has to be of sufficient quality that you can grow things. Such land is generally not cheap as people want to use that for other things, like food. Yes there is an up front cost of solar panels, but you only need to acquire 1/8th as much land of nearly any quality.

Again, that's just a wrong assumption.

Biomass can grow in places where food isn't economical, and food production produces more waste biomass than food mass.

[dyqik]

Hell, how much power can you generate from the grass trimmings discarded from US lawns?

I’d put money on it being less than the energy to collect it to be passed onto Martin B’s team to turn it into Jet-A.

It's already being collected and delivered to centralized locations by lawn care companies. That energy is already being spent.

Around me, more people have companies come and now their lawns and carry the waste off than don't.

[Grumble]

Obviously the benefit of bio-fuel for aviation is nothing to do with the efficiency of production, doesn’t really matter if it’s 1% efficient, we’re nowhere near electric long haul and maybe never will be.

[Gfamily]

My back of the envelope says you need to use
at least 8x the land to deliver the same motive power with biomass as you do with solar. That land has to be of sufficient quality that you can grow things. Such land is generally not cheap as people want to use that for other things, like food. Yes there is an up front cost of solar panels, but you only need to acquire 1/8th as much land of nearly any quality.

Again, that's just a wrong assumption.

Biomass can grow in places where food isn't economical, and food production produces more waste biomass than food mass.

Yes, but collecting biomass on many of those places is tricky - covering the southern slopes of many mountains with solar panels would be better than trying to grow and collect 'biomass' there - and keeping the sheep from eating the stuff is a bugger too.

[dyqik]

Around me, the problem is stopping biomass growing, not getting it to grow.

Trees grow everywhere, and cover nearly 2/3 of the land area. Farming is 10% of the land area.

[Gfamily]

Around me, the problem is stopping biomass growing, not getting it to grow.

Trees grow everywhere, and cover nearly 2/3 of the land area. Farming is 10% of the land area.

Collecting it though - it needs collecting.

[dyqik]

Around me, the problem is stopping biomass growing, not getting it to grow.

Trees grow everywhere, and cover nearly 2/3 of the land area. Farming is 10% of the land area.

Collecting it though - it needs collecting.

There are trucks moving trees around all the time.

[Gfamily]

Around me, the problem is stopping biomass growing, not getting it to grow.

Trees grow everywhere, and cover nearly 2/3 of the land area. Farming is 10% of the land area.

Collecting it though - it needs collecting.

There are trucks moving trees around all the time.

Old mature trees are sequestered CO2 over several decades (if not centuries) - Old stuff is probably better left to sequester longer rather than burn and release now (particularly if it's chopped and chipped and sent across the Atlantic in big ships to be burned at Drax)

[dyqik]

This is all secondary forest that's grown in the last century. Mostly in the last 50 years.

It grows back in a few years.

[Gfamily]

This is all secondary forest that's grown in the last century. Mostly in the last 50 years.

It grows back in a few years.

Yes, but probably not as CO2 efficient as taking last year's maize growth (already harvested with the 'corn' extracted) and using that to process to bio-fuel.

I may have* read that cellulose is more easily processed than lignin)

* or maybe I read the opposite

[Martin_B]

Yes, but probably not as CO2 efficient as taking last year's maize growth (already harvested with the 'corn' extracted) and using that to process to bio-fuel.

I may have* read that cellulose is more easily processed than lignin

+1

[Martin_B]

make liquid hydrocarbons from plants, it’s a biofuel and not an efuel.

Apologies if it's the wrong terminology; blame the marketing guys (who use the terms pretty interchangeably).

[bjn]

My back of the envelope says you need to use
at least 8x the land to deliver the same motive power with biomass as you do with solar. That land has to be of sufficient quality that you can grow things. Such land is generally not cheap as people want to use that for other things, like food. Yes there is an up front cost of solar panels, but you only need to acquire 1/8th as much land of nearly any quality.

Again, that's just a wrong assumption.

Biomass can grow in places where food isn't economical, and food production produces more waste biomass than food mass.

No it’s not. You are farming plants, you need to be able to do it in places you can plant, nurture and harvest the stuff at scale. Mountainsides, gullies, isolated patches of land in urban landscapes are not those. Flatish land you can run mechanised agricultural equipment on will be. Fast growing bio mass won’t be trees, it will be some form of grass or bush you want to harvest regularly. Switch grass or hemp or similar.

[bjn]

This is all secondary forest that's grown in the last century. Mostly in the last 50 years.

It grows back in a few years.

Yes, but probably not as CO2 efficient as taking last year's maize growth (already harvested with the 'corn' extracted) and using that to process to bio-fuel.

I may have* read that cellulose is more easily processed than lignin)

* or maybe I read the opposite

Using current agricultural waste is probably the best option. But you want some of that to go back into the soil regardless.

[dyqik]

My back of the envelope says you need to use
at least 8x the land to deliver the same motive power with biomass as you do with solar. That land has to be of sufficient quality that you can grow things. Such land is generally not cheap as people want to use that for other things, like food. Yes there is an up front cost of solar panels, but you only need to acquire 1/8th as much land of nearly any quality.

Again, that's just a wrong assumption.

Biomass can grow in places where food isn't economical, and food production produces more waste biomass than food mass.

No it’s not. You are farming plants, you need to be able to do it in places you can plant, nurture and harvest the stuff at scale. Mountainsides, gullies, isolated patches of land in urban landscapes are not those. Flatish land you can run mechanised agricultural equipment on will be. Fast growing bio mass won’t be trees, it will be some form of grass or bush you want to harvest regularly. Switch grass or hemp or similar.

Loads of flattish land is available here. All that woodland I mentioned used to be agricultural land

[Grumble]

The 2024 CfD auction seems to have gone well, although only one onshore wind farm in England. Hopefully more next year, probably not been enough time since the change of policy for potential projects to get themselves in order.

[IvanV]

This is all secondary forest that's grown in the last century. Mostly in the last 50 years.

It grows back in a few years.

Yes, but probably not as CO2 efficient as taking last year's maize growth (already harvested with the 'corn' extracted) and using that to process to bio-fuel.

I may have* read that cellulose is more easily processed than lignin)

* or maybe I read the opposite

If what dyqik says is true, it makes you wonder why the biomass extraction from forests mostly goes on in the SE and NW of the USA, rather than in places in the NE where they seemingly have huge amounts of wasteland they don't know what to do with. Maybe the trees grow faster in those other parts of the USA.

Here are some energy yields per year from various crops grown in the UK. It is not news that miscanthus grass is the best potential yield, at 63 MWh/ha/per year. That is calorific value at a moisture content at which the crop is typically used, and there may be some energy input required to reduce it to that moisture content.

So, as a sample calculation, how much land to produce the UK's present electricity consumption of 266 TWh? Well, what would be the conversion rate of calorific value of the crop to electricity? Call it 50%, if we do very well. So that seems to come to 81,000 sq km. That compares with 170,000 sq km of agricultural land in the UK, which is 70% of the total land area of the UK of 244,000 sq km. That agricultural area would include upland grazing, much of which would not be suited to such biomass cultivation. Reading this source, about 10,000 sq km of agricultural land is categorised as "severely disadvantaged", which includes upland pasture and other highly infertile land neverthless used for agriculture. (100ha is 1 sq km).

Another comparison might be petroleum products consumed by transport in the UK, which was 43m metric tonnes in 2022. 1 toe (tonne-of-oil-equivalent) is 11.6 MWh. So that amounts to 500 TWh of transport fuel per year we use. Again we have an issue of what would be the conversion rate of calorific value of fuel to biofuel, and from this source that seems to be typically around 50%. So we conclude that to grow the UK's transport fuel from biomass would require about 150,000 sq km. If we want to grown both our electricity consumption and transport fuel, then that requires 230,000, which is close to the entire land area of the UK.

I think I once calculated that for Drax to source all of its wood from the UK, via commercial forestry, it would require a land area equal to Devon and Cornwall laid to forestry. And that's in part because wood is less efficient per hectare than miscanthus. Just for the output of Drax.

It is apparent that the UK cannot meet its energy needs from biomass grown on its own land area, and that any appreciable contribution would require large proportions of our agricultural land laid to biomass. Of course, the UK only meets 60% of its food requirements from its own land, and changes to the agricultural funding system in the pipeline from the previous government will likely reduce this further. So that might make you think land is becoming free for biomass. But this is about improving the agricultural environment in terms of biodiversity, not converting it to monocultural biomass cultivation.

Clearly other places can do better. Plenty of places with higher crop yields than the UK, being cool, low insolation, and actually mostly having very much water either, as some high yield crops might demand. Central Chile for example is notable as the place where trees in commercial forestry grow faster than just about anywhere else. Travelling through the extensive continuous monocultural eucalyptus and pinus radiata plantations you find in this part of Chile is a profoundly unpleasant and distressing experience, especially the eucalyptus as pretty much nothing else grows in a eucalyptus plantation, and it is so dusty in those plantations. I do not wish that kind of extensive monocultural agriculture/forestry on anyone. I have also encountered extensive pinus radiata plantations in New Zealand, and eucalyptus in Portugal, where the trees grow almost as fast, and just as horrible there.

[bjn]

Thanks for that Ivan. I was going to do something similar but hadn’t had the time to get to it. Just looking at the hardest to abate use case, which is aviation, the UK used 11million MToe last year. So that would be about 37,000 square km of land by your calculations.

[dyqik]

The answer to the question Ivan poses in the first sentence is much more political in Massachusetts than economic.

The lots of land involved are small, owned by small towns and individuals. There are lots of nimbys. Towns reach decisions by voting at meetings where every voter in the town who turns up to the meeting has a vote (meetings frequently go on over several evenings in a row).

This is the same reason that there isn't significant farming here. Or wind turbines, except offshore. There's a decent amount of solar though, as the unit size for that is much smaller.

Obviously no one expects biomass to be a major element of fueling for general sectors like "transportation".

[bjn]

This paper goes into the energy efficiency of a range of fuels derived from electricity, being H2, 'e-gasoline' and 'e-gasoline with direct air capture', comparing them to a just using electricity. The Sankey diagram sums it up nicely. Just use batteries if you can. My guestimate of 10% efficiency for e-fuels was pretty close.

[dyqik]

It's a minor point, but those engine efficiencies are for ICE cars, though. You can do a fair bit better for marine diesel (55%) and jet engines (~40%) - such that you'd be competitive with hydrogen fuel cells for efficiency, and with much easier integration into existing systems.