Sugarcane plantation to produce ethanol in Brazil
A CHP power station using wood to supply 30,000 households in France

Bioenergy is energy made or generated from biomass, which consists of recently living (but now dead) organisms, mainly plants.[1] Types of biomass commonly used for bioenergy include wood, food crops such as corn, energy crops and waste from forests, yards, or farms.[2] The IPCC (Intergovernmental Panel on Climate Change) defines bioenergy as a renewable form of energy.[3] Bioenergy can either mitigate (i.e. reduce) or increase greenhouse gas emissions. There is also agreement that local environmental impacts can be problematic.

Terminology

Biomass plant in Scotland.

Since biomass can be used as a fuel directly (e.g. wood logs), the terms biomass and biofuel have sometimes been used interchangeably. However, the word biomass usually denotes the biological raw material the fuel is made of. The terms biofuel or biogas are generally reserved for liquid or gaseous fuels respectively.[4]

Input materials

Wood and wood residues is the largest biomass energy source today. Wood can be used as a fuel directly or processed into pellet fuel or other forms of fuels. Other plants can also be used as fuel, for instance maize, switchgrass, miscanthus and bamboo.[5] The main waste feedstocks are wood waste, agricultural waste, municipal solid waste, and manufacturing waste. Upgrading raw biomass to higher grade fuels can be achieved by different methods, broadly classified as thermal, chemical, or biochemical:

Thermal conversion processes use heat as the dominant mechanism to upgrade biomass into a better and more practical fuel. The basic alternatives are torrefaction, pyrolysis, and gasification, these are separated mainly by the extent to which the chemical reactions involved are allowed to proceed (mainly controlled by the availability of oxygen and conversion temperature).[6]

Many chemical conversions are based on established coal-based processes, such as the Fischer-Tropsch synthesis.[7] Like coal, biomass can be converted into multiple commodity chemicals.[8]

Biochemical processes have developed in nature to break down the molecules of which biomass is composed, and many of these can be harnessed. In most cases, microorganisms are used to perform the conversion. The processes are called anaerobic digestion, fermentation, and composting.[9]

Applications

Biomass for heating

This section is an excerpt from Biomass heating system.[edit]
Wood chips in a storage hopper, in the middle an agitator to transport the material with a screw conveyor to the boiler
Biomass heating systems generate heat from biomass. The systems may use direct combustion, gasification, combined heat and power (CHP), anaerobic digestion or aerobic digestion to produce heat. Biomass heating may be fully automated or semi-automated they may be pellet-fired, or they may be combined heat and power systems .

Biofuel for transportation

Based on the source of biomass, biofuels are classified broadly into two major categories, depending if food crops are used or not:[10]

First-generation (or "conventional") biofuels are made from food sources grown on arable lands, such as sugarcane and maize. Sugars present in this biomass are fermented to produce bioethanol, an alcohol fuel which serves as an additive to gasoline, or in a fuel cell to produce electricity. Bioethanol is made by fermentation, mostly from carbohydrates produced in sugar or starch crops such as corn, sugarcane, or sweet sorghum. Bioethanol is widely used in the United States and in Brazil. Biodiesel is produced from the oils in for instance rapeseed or sugar beets and is the most common biofuel in Europe.

Second-generation biofuels (also called "advanced biofuels") utilize non-food-based biomass sources such as perennial energy crops and agricultural residues/waste. The feedstock used to make the fuels either grow on arable land but are byproducts of the main crop, or they are grown on marginal land. Waste from industry, agriculture, forestry and households can also be used for second-generation biofuels, using e.g. anaerobic digestion to produce biogas, gasification to produce syngas or by direct combustion. Cellulosic biomass, derived from non-food sources, such as trees and grasses, is being developed as a feedstock for ethanol production, and biodiesel can be produced from left-over food products like vegetable oils and animal fats.

Production of liquid fuels

Comparison with other renewable energy types

Eucalyptus plantation in India.

Land requirement

The surface power production densities of a crop will determine how much land is required for production. The average lifecycle surface power densities for biomass, wind, hydro and solar power production are 0.30 W/m2, 1 W/m2, 3 W/m2 and 5 W/m2, respectively (power in the form of heat for biomass, and electricity for wind, hydro and solar).[11] Lifecycle surface power density includes land used by all supporting infrastructure, manufacturing, mining/harvesting and decommissioning.

Another estimate puts the values at 0.08 W/m2 for biomass, 0.14 W/m2 for hydro, 1.84 W/m2 for wind, and 6.63 W/m2 for solar (median values, with none of the renewable sources exceeding 10 W/m2).[12]

Bioenergy with carbon capture and storage (BECCS)

Carbon capture and storage technology can be used to capture emissions from bioenergy power plants. This process is known as bioenergy with carbon capture and storage (BECCS) and can result in net carbon dioxide removal from the atmosphere. However, BECCS can also result in net positive emissions depending on how the biomass material is grown, harvested, and transported. Deployment of BECCS at scales described in some climate change mitigation pathways would require converting large amounts of cropland.[13]

This section is an excerpt from Bioenergy with carbon capture and storage.[edit]
Diagram-of-Bioenergie power plant with carbon capture and storage (cropped).jpg (description page)

Bioenergy with carbon capture and storage (BECCS) is the process of extracting bioenergy from biomass and capturing and storing the carbon, thereby removing it from the atmosphere.[14] BECCS can be a "negative emissions technology" (NET).[15] The carbon in the biomass comes from the greenhouse gas carbon dioxide (CO2) which is extracted from the atmosphere by the biomass when it grows. Energy ("bioenergy") is extracted in useful forms (electricity, heat, biofuels, etc.) as the biomass is utilized through combustion, fermentation, pyrolysis or other conversion methods.

Some of the carbon in the biomass is converted to CO2 or biochar which can then be stored by geologic sequestration or land application, respectively, enabling carbon dioxide removal (CDR).[15]

The potential range of negative emissions from BECCS was estimated to be zero to 22 gigatonnes per year.[16] As of 2019, five facilities around the world were actively using BECCS technologies and were capturing approximately 1.5 million tonnes per year of CO2.[17] Wide deployment of BECCS is constrained by cost and availability of biomass.[18][19]: 10 

Climate and sustainability aspects

Alternative system boundaries for assessing climate effects of forest-based bioenergy. Option 1 (black) considers only the stack emissions; Option 2 (green) considers only the forest carbon stock; Option 3 (blue) considers the bioenergy supply chain; Option 4 (red) covers the whole bioeconomy, including wood products in addition to biomass.[20]
This section is an excerpt from Sustainable energy § Bioenergy.[edit]

The climate impact of bioenergy varies considerably depending on where biomass feedstocks come from and how they are grown.[21] For example, burning wood for energy releases carbon dioxide; those emissions can be significantly offset if the trees that were harvested are replaced by new trees in a well-managed forest, as the new trees will absorb carbon dioxide from the air as they grow.[22] However, the establishment and cultivation of bioenergy crops can displace natural ecosystems, degrade soils, and consume water resources and synthetic fertilisers.[23][24] Approximately one-third of all wood used for traditional heating and cooking in tropical areas is harvested unsustainably.[25] Bioenergy feedstocks typically require significant amounts of energy to harvest, dry, and transport; the energy usage for these processes may emit greenhouse gases. In some cases, the impacts of land-use change, cultivation, and processing can result in higher overall carbon emissions for bioenergy compared to using fossil fuels.[24][26]

Use of farmland for growing biomass can result in less land being available for growing food. In the United States, around 10% of motor gasoline has been replaced by corn-based ethanol, which requires a significant proportion of the harvest.[27][28] In Malaysia and Indonesia, clearing forests to produce palm oil for biodiesel has led to serious social and environmental effects, as these forests are critical carbon sinks and habitats for diverse species.[29][30] Since photosynthesis captures only a small fraction of the energy in sunlight, producing a given amount of bioenergy requires a large amount of land compared to other renewable energy sources.[31]

Second-generation biofuels which are produced from non-food plants or waste reduce competition with food production, but may have other negative effects including trade-offs with conservation areas and local air pollution.[21] Relatively sustainable sources of biomass include algae, waste, and crops grown on soil unsuitable for food production.[21]

Environmental impacts

Bioenergy can either mitigate (i.e. reduce) or increase greenhouse gas emissions. There is also agreement that local environmental impacts can be problematic. For example, increased biomass demand can create significant social and environmental pressure in the locations where the biomass is produced.[32] The impact is primarily related to the low surface power density of biomass. The low surface power density has the effect that much larger land areas are needed in order to produce the same amount of energy, compared to for instance fossil fuels.

Long-distance transport of biomass have been criticised as wasteful and unsustainable,[33] and there have been protests against forest biomass export in Sweden[34] and Canada.[35]

Generally, bioenergy expansion fell by 50% in 2020. China and Europe are the only two regions that reported significant expansion in 2020, adding 2 GW and 1.2 GW of bioenergy capacity, respectively.[36]

Almost all available sawmill residue is already being utilized for pellet production, so there is no room for expansion. For the bioenergy sector to significantly expand in the future, more of the harvested pulpwood must go to pellet mills. However, the harvest of pulpwood (tree thinnings) removes the possibility for these trees to grow old and therefore maximize their carbon holding capacity.[37]: 19  Compared to pulpwood, sawmill residues have lower net emissions: "Some types of biomass feedstock can be carbon-neutral, at least over a period of a few years, including in particular sawmill residues. These are wastes from other forest operations that imply no additional harvesting, and if otherwise burnt as waste or left to rot would release carbon to the atmosphere in any case."[37]: 68 

By country

See also

References

  1. ↑ "Bioenergy Basics". Energy.gov. Retrieved 2023-05-25.
  2. ↑ "Biomass – Energy Explained, Your Guide To Understanding Energy". U.S. Energy Information Administration. June 21, 2018.
  3. ↑ "Renewable Energy Sources and Climate Change Mitigation. Special Report of the Intergovernmental Panel on Climate Change" (PDF). IPCC. Archived (PDF) from the original on 2019-04-12.
  4. ↑ "Biofuels explained - U.S. Energy Information Administration (EIA)". www.eia.gov. Retrieved 2023-01-23.
  5. ↑ Darby, Thomas. "What Is Biomass Renewable Energy". Real World Energy. Archived from the original on 2014-06-08. Retrieved 12 June 2014.
  6. ↑ Akhtar, Krepl & Ivanova 2018.
  7. ↑ Liu et al. 2011.
  8. ↑ Conversion technologies Archived 2009-10-26 at the Wayback Machine. Biomassenergycentre.org.uk. Retrieved on 2012-02-28.
  9. ↑ "Biochemical Conversion of Biomass". BioEnergy Consult. 2014-05-29. Retrieved 2016-10-18.
  10. ↑ Pishvaee, Mohseni & Bairamzadeh 2021, pp. 1–20.
  11. ↑ Smil, Vaclav (2015). Power density : a key to understanding energy sources and uses. Cambridge, Massachusetts. pp. 26–27, 211, box 7.1. ISBN 978-0-262-32692-6. OCLC 927400712.{{cite book}}: CS1 maint: location missing publisher (link)
  12. ↑ Van Zalk, John; Behrens, Paul (2018-12-01). "The spatial extent of renewable and non-renewable power generation: A review and meta-analysis of power densities and their application in the U.S." Energy Policy. 123: 86. doi:10.1016/j.enpol.2018.08.023. hdl:1887/64883. ISSN 0301-4215.
  13. ↑ National Academies of Sciences, Engineering, and Medicine 2019, p. 3.
  14. ↑ Obersteiner, M. (2001). "Managing Climate Risk". Science. 294 (5543): 786–7. doi:10.1126/science.294.5543.786b. PMID 11681318. S2CID 34722068.
  15. 1 2 National Academies of Sciences, Engineering (2018-10-24). Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. doi:10.17226/25259. ISBN 978-0-309-48452-7. PMID 31120708. S2CID 134196575. Archived from the original on 2020-05-25. Retrieved 2020-02-22.
  16. ↑ Smith, Pete; Porter, John R. (July 2018). "Bioenergy in the IPCC Assessments". GCB Bioenergy. 10 (7): 428–431. Bibcode:2018GCBBi..10..428S. doi:10.1111/gcbb.12514. hdl:2164/10480.
  17. ↑ "BECCS 2019 perspective" (PDF). Archived (PDF) from the original on 2020-03-31. Retrieved 2019-06-11.
  18. ↑ Rhodes, James S.; Keith, David W. (2008). "Biomass with capture: Negative emissions within social and environmental constraints: An editorial comment". Climatic Change. 87 (3–4): 321–8. Bibcode:2008ClCh...87..321R. doi:10.1007/s10584-007-9387-4.
  19. ↑ Fajardy, Mathilde; Köberle, Alexandre; Mac Dowell, Niall; Fantuzzi, Andrea (2019). "BECCS deployment: a reality check" (PDF). Grantham Institute Imperial College London.
  20. ↑ Cowie, Annette L.; Berndes, Göran; Bentsen, Niclas Scott; Brandão, Miguel; Cherubini, Francesco; Egnell, Gustaf; George, Brendan; Gustavsson, Leif; Hanewinkel, Marc; Harris, Zoe M.; Johnsson, Filip; Junginger, Martin; Kline, Keith L.; Koponen, Kati; Koppejan, Jaap (2021). "Applying a science‐based systems perspective to dispel misconceptions about climate effects of forest bioenergy". GCB Bioenergy. 13 (8): 1210–1231. doi:10.1111/gcbb.12844. hdl:10044/1/89123. ISSN 1757-1693. S2CID 235792241.
  21. 1 2 3 Correa, Diego F.; Beyer, Hawthorne L.; Fargione, Joseph E.; Hill, Jason D.; et al. (2019). "Towards the implementation of sustainable biofuel production systems". Renewable and Sustainable Energy Reviews. 107: 250–263. doi:10.1016/j.rser.2019.03.005. ISSN 1364-0321. S2CID 117472901. Archived from the original on 17 July 2021. Retrieved 7 February 2021.
  22. ↑ Daley, Jason (24 April 2018). "The EPA Declared That Burning Wood Is Carbon Neutral. It's Actually a Lot More Complicated". Smithsonian Magazine. Archived from the original on 30 June 2021. Retrieved 14 September 2021.
  23. ↑ Tester 2012, p. 512.
  24. 1 2 Smil 2017a, p. 162.
  25. ↑ World Health Organization 2016, p. 73.
  26. ↑ IPCC 2014, p. 616.
  27. ↑ "Biofuels explained: Ethanol". US Energy Information Administration. 18 June 2020. Archived from the original on 14 May 2021. Retrieved 16 May 2021.
  28. ↑ Foley, Jonathan (5 March 2013). "It's Time to Rethink America's Corn System". Scientific American. Archived from the original on 3 January 2020. Retrieved 16 May 2021.
  29. ↑ Ayompe, Lacour M.; Schaafsma, M.; Egoh, Benis N. (1 January 2021). "Towards sustainable palm oil production: The positive and negative impacts on ecosystem services and human wellbeing". Journal of Cleaner Production. 278: 123914. doi:10.1016/j.jclepro.2020.123914. ISSN 0959-6526. S2CID 224853908.
  30. ↑ Lustgarten, Abrahm (20 November 2018). "Palm Oil Was Supposed to Help Save the Planet. Instead It Unleashed a Catastrophe". The New York Times. ISSN 0362-4331. Archived from the original on 17 May 2019. Retrieved 15 May 2019.
  31. ↑ Smil 2017a, p. 161.
  32. ↑ Climate Central 2015.
  33. ↑ IFL Science 2016.
  34. ↑ Forest Defenders Alliance 2021.
  35. ↑ STAND.earth 2021.
  36. ↑ "World Adds Record New Renewable Energy Capacity in 2020". /newsroom/pressreleases/2021/Apr/World-Adds-Record-New-Renewable-Energy-Capacity-in-2020. Retrieved 2021-11-22.
  37. 1 2 Brack, D. (2017) Woody Biomass for Power and Heat Impacts on the Global Climate. Research Paper - Environment, Energy and Resources Department.

Sources

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