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Life-cycle greenhouse gas emissions of energy sources

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See also: Emission intensity

Greenhouse gas emissions are one of the environmental impacts of electricity generation. Measurement of life-cycle greenhouse gas emissions involves calculating the global warming potential (GWP) of energy sources through life-cycle assessment. These are usually sources of only electrical energy but sometimes sources of heat are evaluated.[1] The findings are presented in units of global warming potential per unit of electrical energy generated by that source. The scale uses the global warming potential unit, the carbon dioxide equivalent (CO2e), and the unit of electrical energy, the kilowatt hour (kWh). The goal of such assessments is to cover the full life of the source, from material and fuel mining through construction to operation and waste management.

In 2014, the Intergovernmental Panel on Climate Change harmonized the carbon dioxide equivalent (CO2e) findings of the major electricity generating sources in use worldwide. This was done by analyzing the findings of hundreds of individual scientific papers assessing each energy source.[2] Coal is by far the worst emitter, followed by natural gas, with solar, wind and nuclear all low-carbon. Hydropower, biomass, geothermal and ocean power may generally be low-carbon, but poor design or other factors could result in higher emissions from individual power stations.

For all technologies, advances in efficiency, and therefore reductions in CO2e since the time of publication, have not been included. For example, the total life cycle emissions from wind power may have lessened since publication. Similarly, due to the time frame over which the studies were conducted, nuclear Generation II reactor's CO2e results are presented and not the global warming potential of Generation III reactors. Other limitations of the data include: a) missing life cycle phases, and, b) uncertainty as to where to define the cut-off point in the global warming potential of an energy source. The latter is important in assessing a combined electrical grid in the real world, rather than the established practice of simply assessing the energy source in isolation.

Global warming potential of selected electricity sources

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Life-cycle greenhouse gas emissions of electricity supply technologies, median values calculated by IPCC[3]
Life cycle CO2 equivalent (including albedo effect) from selected electricity supply technologies according to IPCC 2014.[3][4] Arranged by decreasing median (g/kWh CO2eq) values.
Technology Min. Median Max.
Currently commercially available technologies
Coal – PC 740 820 910
Gas – combined cycle 410 490 650
Biomass – Dedicated 130 230 420
Solar PV – Utility scale 18 48 180
Solar PV – rooftop 26 41 60
Geothermal 6.0 38 79
Concentrated solar power 8.8 27 63
Hydropower 1.0 24 22001
Wind Offshore 8.0 12 35
Nuclear 3.7 12 110
Wind Onshore 7.0 11 56
Pre‐commercial technologies
Ocean (Tidal and wave) 5.6 17 28

1 see also environmental impact of reservoirs#Greenhouse gases.

Lifecycle GHG emissions, in g CO2 eq. per kWh, UNECE 2020[5]
Lifecycle CO2 emissions per kWh, EU28 countries, according to UNECE 2020.[5]
Technology g/kWh CO2eq
Hard coal PC, without CCS 1000
IGCC, without CCS 850
SC, without CCS 950
PC, with CCS 370
IGCC, with CCS 280
SC, with CCS 330
Natural gas NGCC, without CCS 430
NGCC, with CCS 130
Hydro 660 MW [6] 150
360 MW 11
Nuclear average 5.1
CSP tower 22
trough 42
PV poly-Si, ground-mounted 37
poly-Si, roof-mounted 37
CdTe, ground-mounted 12
CdTe, roof-mounted 15
CIGS, ground-mounted 11
CIGS, roof-mounted 14
Wind onshore 12
offshore, concrete foundation 14
offshore, steel foundation 13

List of acronyms:

Bioenergy with carbon capture and storage

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As of 2020 whether bioenergy with carbon capture and storage can be carbon neutral or carbon negative is being researched and is controversial.[7]

Studies after the 2014 IPCC report

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Individual studies show a wide range of estimates for fuel sources arising from the different methodologies used. Those on the low end tend to leave parts of the life cycle out of their analysis, while those on the high end often make unrealistic assumptions about the amount of energy used in some parts of the life cycle.[8]

Since the 2014 IPCC study some geothermal has been found to emit CO2 such as some geothermal power in Italy: further research is ongoing in the 2020s.[9]

Ocean energy technologies (tidal and wave) are relatively new, and few studies have been conducted on them. A major issue of the available studies is that they seem to underestimate the impacts of maintenance, which could be significant. An assessment of around 180 ocean technologies found that the GWP of ocean technologies varies between 15 and 105 g/kWh of CO2eq, with an average of 53 g/kWh CO2eq.[10] In a tentative preliminary study, published in 2020, the environmental impact of subsea tidal kite technologies the GWP varied between 15 and 37, with a median value of 23.8 g/kWh),[11] which is slightly higher than that reported in the 2014 IPCC GWP study mentioned earlier (5.6 to 28, with a mean value of 17 g/kWh CO2eq).

In 2021 UNECE published a lifecycle analysis of environmental impact of electricity generation technologies, accounting for the following impacts: resource use (minerals, metals); land use; resource use (fossils); water use; particulate matter; photochemical ozone formation; ozone depletion; human toxicity (non-cancer); ionising radiation; human toxicity (cancer); eutrophication (terrestrial, marine, freshwater); ecotoxicity (freshwater); acidification; climate change, with the latter summarized in the table above.[5]

In June 2022, Électricité de France publishes a detailed Life-cycle assessment study, following the norm ISO 14040, showing the 2019 French nuclear infrastructure produces less than 4 g/kWh CO2eq.[12]

Cutoff points of calculations and estimates of how long plants last

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Because most emissions from wind, solar and nuclear are not during operation, if they are operated for longer and generate more electricity over their lifetime then emissions per unit energy will be less. Therefore, their lifetimes are relevant.

Wind farms are estimated to last 30 years:[13] after that the carbon emissions from repowering would need to be taken into account. Solar panels from the 2010s may have a similar lifetime: however how long 2020s solar panels (such as perovskite) will last is not yet known.[14] Some nuclear plants can be used for 80 years,[15] but others may have to be retired earlier for safety reasons.[16] As of 2020 more than half the world's nuclear plants are expected to request license extensions,[17] and there have been calls for these extensions to be better scrutinised under the Convention on Environmental Impact Assessment in a Transboundary Context.[16]

Some coal-fired power stations may operate for 50 years but others may be shut down after 20 years,[18] or less.[19] According to one 2019 study considering the time value of GHG emissions with techno-economic assessment considerably increases the life cycle emissions from carbon intensive fuels such as coal.[20]

Lifecycle emissions from heating

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For residential heating in almost all countries emissions from natural gas furnaces are more than from heat pumps.[21] But in some countries, such as the UK, there is an ongoing debate in the 2020s about whether it is better to replace the natural gas used in residential central heating with hydrogen, or whether to use heat pumps or in some cases more district heating.[22]

Fossil gas bridge fuel controversy

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See also: Energy policy of China, Energy in India, and Energiewende

As of 2020 whether natural gas should be used as a "bridge" from coal and oil to low carbon energy, is being debated for coal-reliant economies, such as India, China and Germany.[23] Germany, as part of its Energiewende transformation, declares preservation of coal-based power until 2038 but immediate shutdown of nuclear power plants, which further increased its dependency on fossil gas.[24]

Missing life cycle phases

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See also: Electrical grid

Although the life cycle assessments of each energy source should attempt to cover the full life cycle of the source from cradle-to-grave, they are generally limited to the construction and operation phase. The most rigorously studied phases are those of material and fuel mining, construction, operation, and waste management. However, missing life cycle phases[25] exist for a number of energy sources. At times, assessments variably and sometimes inconsistently include the global warming potential that results from decommissioning the energy supplying facility, once it has reached its designed life-span. This includes the global warming potential of the process to return the power-supply site to greenfield status. For example, the process of hydroelectric dam removal is usually excluded as it is a rare practice with little practical data available. Dam removal however is becoming increasingly common as dams age.[26] Larger dams, such as the Hoover Dam and the Three Gorges Dam, are intended to last "forever" with the aid of maintenance, a period that is not quantified.[27] Therefore, decommissioning estimates are generally omitted for some energy sources, while other energy sources include a decommissioning phase in their assessments.

Along with the other prominent values of the paper, the median value presented of 12 g CO2-eq/kWhe for nuclear fission, found in the 2012 Yale University nuclear power review, a paper which also serves as the origin of the 2014 IPCC's nuclear value,[28] does however include the contribution of facility decommissioning with an "Added facility decommissioning" global warming potential in the full nuclear life cycle assessment.[25]

Thermal power plants, even if low carbon power biomass, nuclear or geothermal energy stations, directly add heat energy to the earth's global energy balance. As for wind turbines, they may change both horizontal and vertical atmospheric circulation.[29] But, although both these may slightly change the local temperature, any difference they might make to the global temperature is undetectable against the far larger temperature change caused by greenhouse gases.[30]

See also

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References

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  1. ^ "Full lifecycle emissions intensity of global coal and gas supply for heat generation, 2018 – Charts – Data & Statistics". IEA. Archived from the original on 24 June 2020. Retrieved 30 July 2020.
  2. ^ Nuclear Power Results – Life Cycle Assessment Harmonization Archived 2 July 2013 at the Wayback Machine, NREL Laboratory, Alliance For Sustainable Energy LLC website, U.S. Department Of Energy, last updated: 24 January 2013.
  3. ^ a b "IPCC Working Group III – Mitigation of Climate Change, Annex III: Technology - specific cost and performance parameters - Table A.III.2 (Emissions of selected electricity supply technologies (gCO 2eq/kWh))" (PDF). IPCC. 2014. p. 1335. Archived (PDF) from the original on 14 December 2018. Retrieved 14 December 2018.
  4. ^ "IPCC Working Group III – Mitigation of Climate Change, Annex II Metrics and Methodology - A.II.9.3 (Lifecycle greenhouse gas emissions)" (PDF). pp. 1306–1308. Archived (PDF) from the original on 23 April 2021. Retrieved 14 December 2018.
  5. ^ a b c "Life Cycle Assessment of Electricity Generation Options | UNECE". unece.org. Retrieved 26 November 2021.
  6. ^ "The 660 MW plant should be considered as an outlier, as transportation for the dam construction elements is assumed to occur over thousands of kilometers (which is only representative of a very small share of hydropower projects globally). The 360 MW plant should be considered as the most representative, with fossil greenhouse gas emissions ranging from 6.1 to 11 g CO2eq/kWh" (UNECE 2020 section 4.4.1)
  7. ^ "Report: UK Government's net-zero plans 'over-reliant' on biomass and carbon capture". edie.net. Archived from the original on 12 August 2020. Retrieved 4 May 2020.
  8. ^ Kleiner, Kurt (September 2008). "Nuclear energy: assessing the emissions". Nature. 1 (810): 130–131. doi:10.1038/climate.2008.99.
  9. ^ "CO2 emissions from geothermal power plants: evaluation of technical solutions for CO2 reinjection" (PDF). Archived (PDF) from the original on 4 November 2020. Retrieved 30 July 2020.
  10. ^ Uihlein, Andreas (2016). "Life cycle assessment of ocean energy technologies". The International Journal of Life Cycle Assessment. 21 (10): 1425–1437. doi:10.1007/s11367-016-1120-y.
  11. ^ Kaddoura, Mohamad; Tivander, Johan; Molander, Sverker (2020). "life cycle assessment of electricity generation from an array of subsea tidal kite prototypes". Energies. 13 (2): 456. doi:10.3390/en13020456.
  12. ^ "Les émissions carbone du nucléaire français : 4g de CO2 le KWH".
  13. ^ "WindEconomics: Extending lifetimes lowers nuclear costs". Archived from the original on 18 May 2020. Retrieved 4 May 2020.
  14. ^ Belton, Padraig (1 May 2020). "A breakthrough approaches for solar power". BBC News. Archived from the original on 3 May 2020. Retrieved 4 May 2020.
  15. ^ "What's the Lifespan for a Nuclear Reactor? Much Longer Than You Might Think". Energy.gov. Archived from the original on 9 June 2020. Retrieved 24 June 2020.
  16. ^ a b "Nuclear plant lifetime extension: A creeping catastrophe". Bellona.org. 30 March 2020. Archived from the original on 21 June 2020. Retrieved 25 June 2020.
  17. ^ "Planning for long-term nuclear plant operations - Nuclear Engineering International". www.neimagazine.com. Archived from the original on 7 August 2020. Retrieved 4 May 2020.
  18. ^ Cui, Ryna Yiyun; Hultman, Nathan; Edwards, Morgan R.; He, Linlang; Sen, Arijit; Surana, Kavita; McJeon, Haewon; Iyer, Gokul; Patel, Pralit; Yu, Sha; Nace, Ted (18 October 2019). "Quantifying operational lifetimes for coal power plants under the Paris goals". Nature Communications. 10 (1): 4759. Bibcode:2019NatCo..10.4759C. doi:10.1038/s41467-019-12618-3. ISSN 2041-1723. PMC 6800419. PMID 31628313.
  19. ^ Welle (www.dw.com), Deutsche. "Climate activists protest Germany's new Datteln 4 coal power plant | DW | 30.05.2020". DW.COM. Archived from the original on 21 June 2020. Retrieved 25 June 2020.
  20. ^ Sproul, Evan; Barlow, Jay; Quinn, Jason C. (21 May 2019). "Time Value of Greenhouse Gas Emissions in Life Cycle Assessment and Techno-Economic Analysis". Environmental Science & Technology. 53 (10): 6073–6080. Bibcode:2019EnST...53.6073S. doi:10.1021/acs.est.9b00514. ISSN 0013-936X. PMID 31013067.
  21. ^ Johnson, Scott K. (25 March 2020). "Few exceptions to the rule that going electric reduces emissions". Ars Technica. Archived from the original on 5 June 2020. Retrieved 30 July 2020.
  22. ^ "Is hydrogen the solution to net-zero home heating?". the Guardian. 21 March 2020. Archived from the original on 4 August 2020. Retrieved 25 July 2020.
  23. ^ Al-Kuwari, Omran (10 April 2020). "Unexpected opportunity for natural gas". Asia Times. Archived from the original on 6 May 2020. Retrieved 4 May 2020.
  24. ^ "Speech by Federal Chancellor Angela Merkel at the 49th World Economic Forum Annual Meeting in Davos on 23 January 2019". Website of the Federal Government. Archived from the original on 5 March 2021. Retrieved 24 March 2021.
  25. ^ a b Warner, Ethan S.; Heath, Garvin A. (2012). "Life Cycle Greenhouse Gas Emissions of Nuclear Electricity Generation: Systematic Review and Harmonization". Journal of Industrial Ecology. 16: S73–S92. doi:10.1111/j.1530-9290.2012.00472.x. S2CID 153286497.
  26. ^ "A Record 26 States Removed Dams in 2019". American Rivers. Archived from the original on 7 August 2020. Retrieved 30 July 2020.
  27. ^ How long are dams like Hoover Dam engineered to last? What's the largest dam ever to fail? Archived 4 August 2014 at the Wayback Machine. Straightdope.com (11 August 2006). Retrieved on 2013-02-19.
  28. ^ http://srren.ipcc-wg3.de/report/IPCC_SRREN_Annex_II.pdf Archived 27 June 2013 at the Wayback Machine pg 40
  29. ^ Borenstein, Seth (5 October 2018). "Harvard study says wind power can also cause some warming". Science. Archived from the original on 11 October 2018. Retrieved 10 October 2018.
  30. ^ Marshall, Michael. "No, Wind Farms Are Not Causing Global Warming". Forbes. Archived from the original on 24 September 2020. Retrieved 30 July 2020.
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