The Biomass Boondoggle
Background
I wrote this some time ago to document an analysis that I did of the land use requirements for different kinds of renewable energy, including various types of biomass, wind and solar.
I expressed these requirements as “percents of Scotland”, my country, the northern part of Great Britain.
Scotland constitutes about 1/3 of the land mass of Great Britain, eight million hectares or 80,000 sq km; and holds just under 10% of the population, a little over 5 million. So by European standards, our population density is quite low, so if biomass energy made sense anywhere in Europe it should make sense here. Read on to see if it does.
This blog will be edited down to form a Bylines Scotland article, but will stay here in its unexpurgated form to provide more detail of the analysis and assumptions for those who want to follow them up.
Key message
It’s hard to avoid the conclusion that biomass energy is a boondoggle designed to divert to rich landowners subsidies that should be being spent developing high energy-density green energy solutions, and on rewilding nature.
The unexpurgated detail!
How best to produce energy from your woodland? Plant solar panels and wind turbines on one percent, use as much timber as you need to insulate your house to Passiv Haus standards, burn the scrap in your pellet or log burner, and rewild the rest!
As a physicist I’ve always been very sceptical about biomass energy. The reason for that isn’t sentimentality or any distaste for intensive forestry. It goes back to physics fundamentals.
The best energy is high grade, high quality energy that can be easily stored and harnessed to do a lot of work. There’s a lot of that sort of energy in nuclear fuel. There’s a lot in the sun. There is a lot in hydrocarbons, quite a lot in hydrogen. There’s a lot in a lithium battery. (The eagle eyed will have noticed that I’m now talking energy density here, not just energy.) The first things a good physicist wants to understand in an energy system is the energy density, the second is the conversion efficiency in the various stages of the energy delivery process. The third is whether the proposition thus revealed violates the second law of thermodynamics!
Energy density is my problem with biomass energy. There are clues a-plenty if we look for them. The 3.2 metres of peat depth at Carrifran Wildwood took over 10,000 years to accumulate. That’s a rate of one millimetre every three years. How long does a 1mm thick bit of peat take to burn? Less than three years! The fossil fuels we have burnt in the last two hundred years took well over 200 million years to be created. We’re burning them a million times faster than they were created. That million to one ratio is essentially the conversion efficiency between sunlight and fossil fuels! Then there is another factor of two to three efficiency loss if we burn the fossil fuels to create electricity.
Another clue is that pre-modern non-tropical civilisations mostly cleared their forests in their unremitting search for firewood to keep warm and to make charcoal for iron and steel production.
By comparison, the conversion efficiency of the photovoltaic cells in a modern solar panel is over 20% in optimum conditions. Solar panels are five orders of magnitude more efficient than the fossil fuel process at extracting energy from sunlight, and they produce high grade electrical energy directly.
In all the enthusiasm for biomass energy, we seldom hear land areas or energy efficiency or energy density discussed. That’s not surprising – because if they were, it would be a short conversation, that would lead to biomass energy being abandoned as a serious national-level contender. (It has its uses at the margins, particularly off grid and in woodland communities, but not as a primary fuel for a modern country.) Let me show why.
The table below shows how much energy we can get out of different forms of biomass, per hectare, and for solar and wind power. This is then converted into the number of hectares needed to produce one giga-watt of thermal power (assuming 100% efficiency) and one giga-watt of electrical power (assuming conversion efficiency of 1/3, which is optimistic because it’s higher than reported values. Sources are [1] and [2].)
The last column shows the number of Scotlands we would need to cover with each form of biomass to generate 5 GW of electricity. 5 GW is more or less the upper limit of Scotland’s current consumption – but expect that figure to rise a lot when we all drive electric cars and use heat pumps to heat our houses. So we could meet Scotland’s current electricity needs with home grown biomass if we were to cover a quarter of Scotland – that’s two million hectares, our current area of woodland is one and a half million - with intensively harvested miscanthus.
Applying that to the whole of the UK, which is about three times the area of Scotland and consumes about 40 GW of electricity, you’d need to cover 2/3 of the UK with intensively harvested miscanthus to provide the UK’s electricity needs from biomass. If you did what Drax claim to do, which is only to use wood thinnings and waste, you’d need 13 times the area of Scotland, or over four times the area of the UK, to provide the UK’s electricity.
We can’t meet our energy needs with home-grown biomass.
It might be more useful to use biomass to replace natural gas for domestic heat. This is the proposal in the Common Weal Common Home Plan[3], combined with solar thermal and a massive insulation programme (using Scottish wood!) If we assume that we can reduce heat demand by 40% with insulation, and the remaining requirement is split 50/50 between biomass and solar thermal, then we need to replace 30% of the calorific value of the gas we use just now with biomass.
Average UK gas consumption[4] for heating is about 50-60 GW. Assuming Scotland would need only a population share, or 8.5 % of the UK level – maybe a bit optimistic given it’s colder here – our current gas consumption for heating would be 5 GW. With the measures proposed by Common Weal, we’d need 1.5 GW each of thermal biomass and solar thermal, and save 2 GW with better insulation. This is getting into the realms of the possible. On this basis we could heat Scotland with wood thinnings and waste from four million hectares of woodland which also fed a radically increased wood industry – possibly replacing all of our imported construction timber with Scottish wood. (The UK imports 80% of its construction timber.) Alternatively, cover 600,000 hectares with miscanthus plantations. To heat the whole of the UK on the same basis, multiply that by 12, so you’d need 1/3 of the UK covered with miscanthus to replace gas for heating.
Is biomass carbon neutral? No matter how you dress it up, without carbon capture and storage, when you burn wood, you’re discharging CO2 into the atmosphere[5]. If and when CCS technology is mature and available at scale, capacity will be limited; there are better things to do with expensive CCS capacity than burying trees! And to cap it all, burning biomass is a huge health risk – it puts far more particulates into the atmosphere than coal power stations or diesel cars[6].
It does seem that the way carbon is accounted for (discussed elsewhere), it is legitimate to regard biomass as carbon neutral AS LONG AS the forestry is run sustainably – in other words, you have enough woodland to meet the demand without the carbon stock in the wooded areas depleting. But better to use the timber for construction, so that the carbon in it is sequestered for the long term rather than being recycled through the atmosphere. The thing we must avoid, though, is allowing the wood to decay in a way that emits methane. Methane has a much stronger global warming effect than CO2, and anything that increases methane emissions is bad news.
But this is where we get to the nub of the problem. Because biomass is eligible for green energy subsidies, the subsidies are driving demand. Demand for biomass is increasing faster than the supply. You need a huge area of forest to feed a power station. Drax, at 3 GW electrical output, apparently draws on four million hectares of forest – half the area of Scotland or 1/6 of the area of the UK, to give the UK only 1/10 or less of its electricity. The demand for wood pellets is rising so fast it can no longer be satisfied by sawmill offcuts. American forests are being clear-felled to feed the pellet factories[7]. There are better uses for land, and for wood, and for the water needed for irrigation.
Bioenergy is a desperately inefficient use of land. If you simply want to generate green electricity, cover one percent of the land area with solar panels, plant a wind turbine, use as much of the wood as you need to insulate your house as well as you possibly can, use the offcuts in your wood-pellet burner, and leave the rest of the trees to grow. Don’t burn the timber. Use it to insulate houses. This not only sequesters the carbon in the timber long term, but also reduces the amount of energy we need for heating!
We need to take a whole-system view of forestry and how it relates to the ecosystem, our society, the economy, and climate. Country-scale bio-energy and carbon sequestration need country-scale forests, involve country-scale opportunity costs, and demand country-scale trade-offs. Basically those trade-offs say it’s a bad idea to use biomass at country scale. Opportunistic use at local level is fine. But the problem is that when biomass starts driving demand, instead of just using waste and offcuts, it causes massive problems and affects, mostly badly, seven of the planetary boundaries[8]: climate change, biodiversity loss, nitrogen cycle, land use, freshwater, atmospheric aerosols and chemical pollution.
Who is making the country-scale trade-offs on land use, biodiversity, water management, use of the timber, use of available carbon capture and storage (CCS) reservoirs, and the opportunity cost of all of these – and on what criteria?
It’s hard to avoid the conclusion that biomass energy is a boondoggle designed to divert to rich landowners subsidies that should be being spent developing high energy-density green energy solutions, and on rewilding nature.
[1] http://www.basisbioenergy.eu/fileadmin/BASIS/D3.5_Report_on_conversion_efficiency_of_biomass.pdf
[2] https://www.forestresearch.gov.uk/tools-and-resources/biomass-energy-resources/reference-biomass/facts-figures/potential-yields-of-biofuels-per-ha-pa/
[3] https://commonweal.scot/our-common-home
[4] Estimates based on https://gridwatch.co.uk/gas
[5] https://www.biofuelwatch.org.uk/axedrax-campaign/ It’s hard to find an independent view on this!
[6] https://www.biofuelwatch.org.uk/wp-content/uploads/Drax-and-air-quality-briefing_final.pdf
[7] https://insideclimatenews.org/news/10072020/wood-pellet-business-booming-scientists-say-’s-not-good-climate?utm_source=InsideClimate+News&utm_campaign=9ae33eaa10-&utm_medium=email&utm_term=0_29c928ffb5-9ae33eaa10-327825809
[8] Rockström et al, Planetary Boundaries: Exploring the Safe Operating Space for Humanity, Ecology and Society Vol 14 No 2 Art 32, 2009. https://www.ecologyandsociety.org/vol14/iss2/art32/
Thank you for this article.