I used to think that the term biomass was used to describe a methane generator. Apparently I am wrong, or the term has since been hijacked.
Biomass refers, these days to use of biological material, probably wood pellets, to replace coal. That is the meaning at Drax power station, which [1] produces about 5% of the UK's electricity, 12% of the renewable electricity.
However, there is a basic assumption here that I am uncomfortable with, that burning wood instead of coal is somehow good replacing bad. I completely accept that perhaps the wood burned would otherwise have been wasted, left to rot and/or burned inefficiently. According to Drax, the decision to move from coal to biomass has slashed the plant’s CO2 emissions by over 80% since 2012. [1].
The assumption that bothers me is that it is assumed that the smokestack emissions are cancelled out by the carbon absorbed by forest regrowth. I'm sorry, since when has that been assumed instantaneous? If it is not instantaneous, where is the guarantee of new growth to absorb that freed CO₂? How long does that take? Apparently, [1] says, between 40 and 100 years. That, then is perilously similar to the disposal issues that a nuclear power plant has. Research carbon debt payback time, please. ¹. One relevant contention is the presumption that a carbon debt is incurred with payback times in the range of 50-100 years and that the urgency of the climate challenge does not allow for this delay. [3, p9]
The principle here is that bioenergy is assumed to be climate neutral. I need to establish quite what we mean by the terms bioenergy and climate neutral. I think the measure of the latter, climate neutral is the tonnage of CO₂e. [3] explains this with regard primarily to the Swedish forests and looks closely at various forest management alternatives, concluding that, among other things, not harvesting the forest at all was worse that the as-is management strategy. In turn, ..based on the findings, there is no support for the proposition to reduce or eliminate harvests from Swedish forests as a climate action [3, p2].
The assumption that wood is necessarily 'good' relies on the fundamental assumption above. If that were to be declared wrong or irrelevant to some regard, then the important figure lies (only) in those products which are not subsequently burnt, such as construction timber and long-term paper products. Everything else becomes suspect, because surely the test has to be that the processing of wood products eventually returns CO₂e to the atmosphere and that this needs to be compared against the tree being left alone. [3] discusses this in detail. Obviously, increased forest area (really, volume) represents more stored carbon.
Worryingly, the idea that forest harvesting causes a carbon debt has become an ”established fact” in contemporary Swedish and European forestry debate – despite being incorrect and/or implausible as shown in this study. [3, p25]. I'm thinking this is an accounting problem. As [3][ says towards the end, many of the studies of forestry start by separating the forest from its environment, which leads to false conclusions.
The term bioenergy is defined as a form of renewable energy that is derived from recently living organic materials known as biomass, which can be used to produce transportation fuels, heat, electricity, and products. [4] As the US Dept of Energy enthuses;
One billion tons of biomass could:
- Produce up to 50 billion gallons of biofuels
- Yield 50 billion pounds of bio-based chemicals and bioproducts
- Generate 85 billion kilowatt-hours of electricity to power 7 million households
- Contribute 1.1 million jobs to the U.S. economy
- Keep $260 billion in the United States.[1]
I think that bioenergy, biomass, biofuel, biopower and bioproduct have been turned into buzzwords with (too) little remaining meaning. In a mixed order, extracting what sense I can: biopower converts biofuels into heat and electricity; Biofuels are liquids and include biodiesel, bioethanol - 'renewable' transportation fuels; generally—and here is where the confusions start—biomass is the start point, which generously includes waste food, waste wood both urban and forest, woody crops, crop wastes, purpose-grown grasses and microalgae. Biomass is any organic material which has absorbed sunlight and stored it in the form of chemical energy (wikipedia). Bioproducts are then things made from biomass in much the same way as we might categorise petroleum-based products.
I think we are deluding ourselves here, or allowing ourselves to be deluded. We grow stuff and in the 'normal' life-cycle this growth would decay in its usual way. Therein lies an assumption that the plane sans humans would remain in balance; fair enough, we agree that it is our interference that is changing that balance. If we abstract biological material then we sometimes delay the decay process. What we call fossil fuels are already stored carbon and we have upset the balance by consuming these. Switching to 'renewables' changes this cycle far less, provided the net effect is to have more renewable than we use, what we might, with a little grin, call net growth. Persuading ourselves that consumption of anything recently alive is suddenly okay is to not understand the processes; we need to measure whatever use we put the material to against the 'natural' decay process. Or, to measure both and then take the difference in our measurements as the test of success or failure. It is clear that reparation requires us to find copious ways to store carbon – in effect, to replace the coal, oil and gas, at least by the measure of carbon. In huge units, gigatonnes of carbon.
So we make bioenergy from biofuel or biomass. How we convert biomass to biofuel can be done by methods classes as thermal (and heat to have one of torrefaction, pyrolysis, and gasification, chemical (mostly coal-based processes) and biochemical (think anaerobic digestion, fermentation, and composting. [wikipedia]. Recognise, please, that an awful lot of biofuel is simply wood, often pelletised as at Drax above — and it is simply burnt, as if replacing coal.
If you wished to compare renewables one measure is the land required for power production densities, which [5] lists as biomass 0.3W/m², wind 1W/m², hydro 3W/m², solar 5W/m². I'm immediately sure that one could argue with how these figures are arrived at and what (else) should be included. Thus one has lifecycle power densities and the figures change somewhat to biomass 0.08W/m², wind 1.84W/m², hydro 0.14W/m², solar 6.63W/m². To which, thanks to [5], I'll add fossil gas at 420W/m², nuclear power at 240W/m², and humans 20W/m² in an urban environment or 0.125W/m² on ice-free land. Which strongly makes a case for nuclear, by that measure.
What we do with biomass makes a difference by this measure too. For example corn plantations producing 10 tonnes per hectare will then produce 0.26W/m² if processed to ethanol, but a far larger 0.6W/m² if used for combustion, mostly because the whole plant is used. You should read [5] entirely, perhaps progressing to read material form Vaclav Smil, Smil noted in 2018 that coal, oil, and natural gas still supply 90% of the world's primary energy. Despite decades of growth in newer renewable energy technologies, the worldwide proportion of energy supplied by fossil fuels had increased since 2000.[4] He emphasises that "the greatest long-term challenge in the industrial sector will be to displace fossil carbon used in the production of primary iron, cement, ammonia and plastics" which account for 15% of the total fossil fuel consumption globally.[6] Smil favours reducing demand for fossil fuels through energy conservation, and calls for having the price of energy reflect its real costs including greenhouse gas emissions.[7] Ouch. There's a target for Cop26.
I am struck by the gains (in terms of carbon capture) that could be made by extraction of CO₂ at the point of generation, as reported in essay 368.
Vaclav Smil [6] records that the world’s fossil-fuel-based energy system ... now has an annual throughput of more than 7 billion metric tons of hard coal and lignite, about 4 billion metric tons of crude oil, and more than 3 trillion cubic meters of natural gas. This adds up to 14 trillion watts of power. And we propose to displace this system within the odd decade. Dream on.
So there's the fossil fuel, but that is also from Smil. But these are quite clearly not cumulative figures but annual figures. Our demand for energy continues to rise.
This second chart, from the same sources, I've presented in 'relative' format to show the shift away from traditional biomass (red), coal, oil and gas — the next several bands of colour. If we assumed that all of the renewables behaved as oil, the fastest changing market shown, then we require many simultaneous changes, because between 1940 and 1975 oil grew only 30% in relative terms, form 12% to 42% of what we used for energy. If renewables (even including nuclear) are to displace fossil fuels we need to change the demand, not just the supply. What is more, those changes need to be far more extreme than I think we have realised. Look at this another way; the supply of all non-fossil fuel reduces the growth of demand by only 10 years. Essay 367 showed that the UK has reduced its total demand (such that 2012 = 1965) but that position is rare. At the same time, UK demand per head is enormous.
Looking at the growth of low-carbon sources,at the best gradient we've had shown, the mid-eighties, it will take another 40 years to only reach 30%, double what we have now. But if we talk about Cop26 targets, that's several times too slow. Smil is right, this sort of change is slow.
It appears that, if we ever become serious in intention to reduce climate change, we need several fronts of attack simultaneously. A drastic reduction in energy demand and at the same time a drastic change in how we generate energy. I do not see the nations of the world responding to any crisis in a collective manner and, though that is what we need, I begin to think that the collective response for which we have been looking is simply not going to occur.
This may be a version of the north-south divide within the UK only writ larger; that the advantaged determine to keep that advantage. Thus I now think it is likely that each nation will do its own thing and make its own policies to reduce its impact — and then trumpet this to its neighbours. To change policy in Asia or South America or Africa requires changes that are so drastic that the history of corruption says to me that no financial solution will work; if we really want change we're actually going to have to go and show how the changes must occur. That could easily look like invasion. How we make change worthwhile for those who've never had what Europe has had is a whole new game, because they're not going to settle for less than a huge leg up if change is actually to occur. Man is the problem and it looks as though the doomsayers may yet be right. A disaster that reduced the global population by a half would be a step forwards and backwards at the same time; forwards only if the remainder were able to change behaviour to a sustainable one.
We really don't deserve to survive.
DJS 20210929
top pic from [1]
Albert Hall-sized storage domes for wood pellets at Drax power station, North Yorkshire, UK. (Courtesy: Kate Ravilious)
² ³ ⁴ ⁵ ⁶
[1] https://physicsworld.com/a/biomass-energy-green-or-dirty/
[2] https://www.researchgate.net/publication/313792157_Carbon_debt_and_payback_time_-_Lost_in_the_forest
[4] https://www.energy.gov/eere/bioenergy/bioenergy-basics [US.gov, not gov.uk]
[5] https://en.wikipedia.org/wiki/Bioenergy
1 Carbon debt payback time In later years the potential contribution of forest bioenergy to mitigate climate change has been increasingly questioned due to temporal displacement between CO2 emissions when forest biomass is used for energy and subsequent sequestration of carbon in new biomass. Also disturbance of natural decay of dead biomass when used for energy affect the carbon dynamics of forest ecosystems. These perturbations of forest ecosystems are summarised under the concept of carbon debt and its payback time. Narrative reviews demonstrate that the payback time of apparently comparable forest bioenergy supply scenarios vary by up to 200 years allowing amble [ample] room for confusion and dispute about the climate benefits of forest bioenergy. This meta-analysis confirm that the outcome of carbon debt studies lie in the assumptions and find that methodological rather than ecosystem and management related assumptions determine the findings. The study implies that at the current development of carbon debt methodologies and their lack of consensus the concept in it-self is inadequate for informing and guiding policy development. At the management level the carbon debt concept may provide valuable information directing management principles in a more climate benign directions.
[6] https://spectrum.ieee.org/a-skeptic-looks-at-alternative-energy A Vaclav Smil sample from 2012. Delicious, and an illustration of what happens with(out) biased reporting and/or vested interest. He writes; Perhaps the most misunderstood aspect of energy transitions is their speed. Substituting one form of energy for another takes a long time. He then lists progress for the US, all of which rather points up that any 2030 target (2050, whatever, but in your lifetime) is going to take a drastic change in speed that we have not yet seen, ever.