Editing IPCC:AR6/WGIII/Chapter-6 (section)

==== 6.4.2.6 Bioenergy ====

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Bioenergy has the potential to be a high-value and large-scale mitigation option to support many different parts of the energy system. Bioenergy could be particularly valuable for sectors with limited alternatives to fossil fuels (e.g., aviation, heavy industry), production of chemicals and products, and, potentially, in carbon dioxide removal (CDR) via BECCS or biochar. While traditional biomass and first-generation biofuels are widely used today, the technology for large-scale production from advanced processes is not competitive, and growing dedicated bioenergy crops raises a broad set of sustainability concerns. Its long-term role in low-carbon energy systems is therefore uncertain ( ''high confidence'' ). (Note that this section focuses on the key technological developments for deployment of commercial bioenergy.)

Bioenergy is versatile: technology pathways exist to produce multiple energy carriers from biomass – electricity, liquid fuels, gaseous fuels, hydrogen, and solid fuels – as well as other value-added products ( ''high confidence'' ). Different chemical and biological conversion pathways exist to convert diverse biomass feedstocks into multiple final energy carriers (Figure 6.14). Currently, biomass is mostly used to produce heat, or for cooking purposes (traditional biomass), electricity, or first-generation sugar-based biofuels (e.g., ethanol produced via fermentation), as well as biodiesel produced from vegetable oils and animal fats. Electricity generated from biomass contributes about 3% of global generation. Tens of billions of gallons of first-generation biofuels are produced per year. The processing requirements (drying, dewatering, pelletising) of different feedstocks for producing electricity from biomass are energy-intensive, and when utilising current power plants, the efficiency is around 22%, with an increase up to 28% with advanced technologies ( [[#Zhang--2020|Zhang et al. 2020]] ).

Scaling up bioenergy use will require advanced technologies such as gasification, Fischer-Tropsch processing, hydrothermal liquefaction (HTL), and pyrolysis. These pathways could deliver several final energy carriers starting from multiple feedstocks, including forest biomass, dedicated cellulosic feedstocks, crop residues, and wastes (Figure 6.14). While potentially cost-competitive in the future, pyrolysis, Fischer-Tropsch, and HTL are not currently cost-competitive ( [[#IEA--2018c|IEA 2018c]] ; [[#Molino--2018|Molino et al. 2018]] ; [[#Prussi--2019|Prussi et al. 2019]] ), and scaling-up these processes will require robust business strategies and optimised use of co-products ( [[#Lee--2013|Lee and Lavoie 2013]] ). Advanced biofuels production processes are at the pilot or demonstration stage and will require substantial breakthroughs or market changes to become competitive. Moreover, fuels produced from these processes require upgrading to reach ‘drop-in’ conditions – that is, conditions in which they may be used directly consistent with current standards in existing technologies ( [[#van%20Dyk--2019|van Dyk et al. 2019]] ). Additional opportunities exist to co-optimise second-generation biofuels and engines ( [[#Ostadi--2019|Ostadi et al. 2019]] ; [[#Salman--2020|Salman et al. 2020]] ). In addition, gaseous wastes, or high-moisture biomass, such as dairy manure, wastewater sludge and organic municipal solid waste (MSW) could be utilised to produce renewable natural gas. Technologies for producing biogas (e.g., digestion) tend to be less efficient than thermochemical approaches and often produce large amounts of CO 2 , requiring the produced fuels to undergo significant upgrading ( [[#Melara--2020|Melara et al. 2020]] ).

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[[File:c08ff1ffe65209ee327ad1e6315ceae6 IPCC_AR6_WGIII_Figure_6_13.png]]

'''Figure 6.13 | Costs and potential for different CO''' 2 '''utilisation pathways.''' Source: with permission from [[#Hepburn--2019|Hepburn et al. (2019)]] .

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[[File:31b2a571018212806f9a750b7b4413c6 IPCC_AR6_WGIII_Figure_6_14.png]]

'''Figure 6.14 | Range of advanced bioenergy conversion pathways (excluding traditional biomass, direct heat generation, first-generation biofuels, and non-energy products) based on feedstock, targeted end product, and compatibility with carbon dioxide removal (CDR) via carbon capture and storage (CCS) and soil carbon sequestration.''' Source: modified with permission from [[#Baker--2020|Baker et al. (2020)]] .

A major scale-up of bioenergy production will require dedicated production of advanced biofuels. First-generation biofuels produced directly from food crops or animal fats have limited potential and lower yield per land area than advanced biofuels. Wastes and residues (e.g., from agricultural, forestry, animal manure processing) or biomass grown on degraded, surplus, and marginal land can provide opportunities for cost-effective and sustainable bioenergy at significant but limited scale ( [[#Morris--2013|Morris et al. 2013]] ; [[#Saha--2018|Saha and Eckelman 2018]] ; [[#Fajardy--2020|Fajardy and Mac Dowell 2020]] ; [[#Spagnolo--2020|Spagnolo et al. 2020]] ). Assessing the potential for a major scale-up of purpose-grown bioenergy is challenging due to its far-reaching linkages to issues beyond the energy sector, including competition with land for food production and forestry, water use, impacts on ecosystems, and land-use change ( [[#IPCC--2020|IPCC 2020]] ; [[#Roe--2021|Roe et al. 2021]] ) (Chapter 12). These factors, rather than geophysical characteristics, largely define the potential for bioenergy and explain the difference in estimates of potential in the literature. Biomass resources are not always in close proximity to energy demand, necessitating additional infrastructure or means to transport biomass or final bioenergy over larger distances and incur additional energy use ( [[#Baik--2018|Baik et al. 2018]] ; [[#Singh--2021|Singh et al. 2021]] ).

An important feature of bioenergy is that it can be used to remove carbon from the atmosphere by capturing CO 2 in different parts of the conversion process and then permanently storing the CO 2 (BECCS or biochar) ( [[#Smith--2016|Smith et al. 2016]] ; [[#Fuss--2018|Fuss et al. 2018]] ) (Chapters 3 and 7, and [[IPCC:Wg3:Chapter:Chapter-12#12.5|Section 12.5]] ). Some early opportunities for low-cost BECCS are being utilised in the ethanol sector but these are applicable only in the near-term at the scale of ≤100 MtCO 2 yr –1 ( [[#Sanchez--2018|Sanchez et al. 2018]] ). Several technological and institutional barriers exist for large-scale BECCS implementation, including large energy requirements for CCS, limit and cost of biomass supply and geologic sinks for CO 2 in several regions, and cost of CO 2 capture technologies ( ''high confidence'' ). Besides BECCS, biofuels production through pyrolysis and hydrothermal liquefaction creates biochar, which could also be used to store carbon as 80% of the carbon sequestered in biochar will remain in the biochar permanently (Chapter 7). In addition to its ability to sequester carbon, biochar can be used as a soil amendment ( [[#Wang--2014b|Wang et al. 2014b]] ).

First-generation bioenergy is currently competitive in some markets though, on average, its costs are higher than other forms of final energy. Bioenergy from waste and residues from forestry and agriculture is also currently competitive, but the supply is limited ( [[#Aguilar--2020|Aguilar et al. 2020]] ). These costs are context-dependent, and regions having large waste resources are already producing low-cost bioenergy ( [[#Jin--2018|Jin and Sutherland 2018]] ). In the future, technology costs are anticipated to decrease, but bioenergy produced through cellulosic feedstocks may remain more expensive than fossil alternatives. Large-scale deployment of early opportunities, especially in the liquid fuel sector, may reduce the technological costs associated with biomass conversion ( [[#IEA--2020g|IEA 2020g]] ). At the same time, the cost of feedstocks may rise as bioenergy requirements increase, especially in scenarios with large bioenergy deployment (Muratori et al. 2020). The costs of bioenergy production pathways are highly uncertain (Table 6.4).

'''Table 6.4 | The costs of electricity generation, hydrogen production, and second-generation liquid fuels production from biomass in 2020.''' These costs are adapted from [[#Bhave--2017|Bhave et al. (2017)]] , Daioglou et al. (2020), NREL (2020a, 2020b), Witcover and Williams (2020), and Lepage et al. (2021).

{| class="wikitable"
|-
|
| Unit

| Low

| Median

| High

|-
| Bioelectricity with CCS

| USD MWh –1

| 74

| 86

| 160

|-
| Bioelectricity without CCS

| USD MWh –1

| 66

| 84

| 112

|-
| Biohydrogen with CCS a

| USD kg –1

| 1.63

| 2.37

| 2.41

|-
| Biohydrogen without CCS a

| USD kg –1

| 1.59

| 1.79

| 2.37

|-
| Liquid biofuels with CCS

| USD gge –1

| 1.34

| 4.20

| 7.85

|-
| Liquid biofuels without CCS

| USD gge –1

| 1.15

| 4.00

| 7.60

|}

a Using cellulosic feedstocks.

• '''Electricity.''' The costs of baseload electricity production with biomass are higher than corresponding fossil electricity production with and without CCS, and are likely to remain as such without carbon pricing ( [[#Bhave--2017|Bhave et al. 2017]] ). The additional cost associated with CO 2 capture are high for conventional solvent-based technologies. However, upcoming technologies such as chemical looping are well-suited to biomass and could reduce CCS costs.

'''•''' '''Hydrogen.''' The costs of hydrogen production from biomass are somewhat higher than, but comparable, to that produced by natural gas reforming with CCS. Further, the incremental costs for incorporating CCS in this process are less than 5% of the levelised costs in some cases, since the gasification route creates a high-purity stream of CO 2 ( [[#Muratori--2017a|Muratori et al. 2017a]] ; [[#Sunny--2020|Sunny et al. 2020]] ). While these processes have fewer ongoing prototypes/demonstrations, the costs of biomass-based hydrogen (with or without CCS) are substantially cheaper than that produced from electrolysis utilising solar/wind resources ( [[#Kayfeci--2019|Kayfeci et al. 2019]] ; [[#Newborough--2020|Newborough and Cooley 2020]] ), even though electrolysis costs are dropping.

• '''Liquid biofuels.''' First-generation sugar-based biofuels (e.g., ethanol produced via fermentation) or biodiesel produced from vegetable oils and animal fats, are produced in several countries at large scale and costs competitive with fossil fuels. However, supply is limited. The costs for second-generation processes (Fischer-Tropsch and cellulosic ethanol) are higher in most regions ( [[#Li--2019|Li et al. 2019]] ). Technological learning is projected to reduce these costs by half ( [[#IEA--2020g|IEA 2020g]] ).

Large-scale bioenergy production will require more than wastes/residues and cultivation on marginal lands, which may raise conflicts with SDGs relevant to environmental and societal priorities ( [[#Heck--2018|Heck et al. 2018]] ; [[#Gerten--2020|Gerten et al. 2020]] ) (Chapter 12). These include competition with food crops, implications for biodiversity, potential deforestation to support bioenergy crop production, energy security implications from bioenergy trade, point-of-use emissions and associated effects on air quality, and water use and fertiliser use ( [[#Fajardy--2018|Fajardy and Mac Dowell 2018]] ; [[#Fuss--2018|Fuss et al. 2018]] ; [[#Tanzer--2019|Tanzer and Ramírez 2019]] ; [[#Brack--2020|Brack and King 2020]] ). Overall, the environmental impact of bioenergy production at scale remains uncertain and varies by region and application.

Alleviating these issues would require some combination of increasing crop yields, improving conversion efficiencies, and developing advanced biotechnologies for increasing the fuel yield per tonne of feedstock ( [[#Henry--2018|Henry et al. 2018]] ). Policy structures would be necessary to retain biodiversity, manage water use, limit deforestation and land-use change emissions, and ultimately optimally integrate bioenergy with transforming ecosystems. Large-scale international trade of biomass might be required to support a global bioeconomy, raising questions about infrastructure, logistics, financing options, and global standards for bioenergy production and trade (Box 6.10). Additional institutional and economic barriers are associated with accounting of carbon dioxide removal, including BECCS ( [[#Fuss--2014|Fuss et al. 2014]] ; [[#Muratori--2016|Muratori et al. 2016]] ; [[#Fridahl--2018|Fridahl and Lehtveer 2018]] ).

Lifecycle emissions impacts from bioenergy are subject to large uncertainties and could be incompatible with net-zero emissions in some contexts. Due to the potentially large energy conversion requirements and associated GHG emissions (Chapters 7 and 12), bioenergy systems may fail to deliver near-zero emissions depending on operating conditions and regional contexts ( [[#Elshout--2015|Elshout et al. 2015]] ; [[#Daioglou--2017|Daioglou et al. 2017]] ; [[#Staples--2017|Staples et al. 2017]] ; [[#Hanssen--2020|Hanssen et al. 2020]] ; [[#Lade--2020|Lade et al. 2020]] ). As a result, bioenergy carbon neutrality is debated and depends on factors such as the source of biomass, conversion pathways and energy used for production and transport of biomass, and land-use changes, as well as assumed analysis boundary and considered time scale ( [[#Zanchi--2012|Zanchi et al. 2012]] ; [[#Wiloso--2016|Wiloso et al. 2016]] ; [[#Booth--2018|Booth 2018]] ; [[#Fan--2021|Fan et al. 2021]] ). Similarly, the lifecycle emissions of BECCS remain uncertain and will depend on how effectively bioenergy conversion processes are optimised ( [[#Fajardy--2017|Fajardy and Mac Dowell 2017]] ; [[#Tanzer--2019|Tanzer and Ramírez 2019]] ).

Acceptability of bioenergy is relatively low compared to other renewable energy sources like solar and wind ( [[#Poortinga--2013|Poortinga et al. 2013]] ; [[#Ma--2015|Ma et al. 2015]] ; [[#Peterson--2015|Peterson et al. 2015]] ; [[#EPCC--2017|EPCC 2017]] ) and comparable to natural gas ( [[#Scheer--2013|Scheer et al. 2013]] ). People also know relatively little about bioenergy compared to other energy sources ( [[#Whitmarsh--2011a|Whitmarsh et al. 2011a]] ; [[#EPCC--2017|EPCC 2017]] ) and tend be be more ambivalent towards bioenergy compared to other mitigation options ( [[#Allen--2013|Allen and Chatterton 2013]] ). People evaluate biomass from waste products (e.g., food waste) more favourably than grown-for-purpose energy crops, which are more controversial ( [[#Plate--2010|Plate et al. 2010]] ; [[#Demski--2015|Demski et al. 2015]] ). The most pressing concerns for use of woody biomass are air pollution and loss of local forests ( [[#Plate--2010|Plate et al. 2010]] ). Various types of bioenergy additionally raise concerns about landscape impacts ( [[#Whitmarsh--2011a|Whitmarsh et al. 2011a]] ) and biodiversity ( [[#Immerzeel--2014|Immerzeel et al. 2014]] ). Moreover, many people do not see biomass as a renewable energy source, possibly because it involves burning of material.

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