Life-cycle greenhouse gas emissions of energy sources

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 of energy sources through life-cycle assessment. These are usually sources of only electrical energy but sometimes sources of heat are evaluated.<ref>"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.</ref> 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.<ref name="NREL-LCA1" /> 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

Life-cycle greenhouse gas emissions of electricity supply technologies, median values calculated by IPCC<ref name="IPCC 2014 Annex III" />

Life cycle CO₂ equivalent (including albedo effect) from selected electricity supply technologies according to IPCC 2014.<ref name="IPCC 2014 Annex III">"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.</ref><ref>"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.</ref> Arranged by decreasing median (gCO₂eq/kWh) 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.

UNECE". unece.org. Retrieved 26 November 2021.</ref>

Lifecycle CO₂ emissions per kWh, EU28 countries, according to UNECE 2020.<ref name=":0"/>

Technology		gCO2eq/kWh
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 <ref>"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)</ref>	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:

• PC — pulverized coal
• CCS — carbon capture and storage
• IGCC — integrated gasification combined cycle
• SC — supercritical
• NGCC — natural gas combined cycle
• CSP — concentrated solar power
• PV — photovoltaic power

Bioenergy with carbon capture and storage

As of 2020 whether bioenergy with carbon capture and storage can be carbon neutral or carbon negative is being researched and is controversial.<ref>"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.</ref>

Studies after the 2014 IPCC report

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.<ref name="Nature-2008.09" />

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.<ref>"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.</ref>

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 gCO₂eq/kWh, with an average of 53 gCO₂eq/kWh.<ref>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.</ref> 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 gCO₂eq/kWh),<ref>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.</ref> 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 gCO₂eq/kWh).

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.<ref name=":0" />

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 gCO₂eq/kWh.<ref>"Les émissions carbone du nucléaire français : 4g de CO₂ le KWH".</ref>

Cutoff points of calculations and estimates of how long plants last

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:<ref>"WindEconomics: Extending lifetimes lowers nuclear costs". Archived from the original on 18 May 2020. Retrieved 4 May 2020.</ref> 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.<ref>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.</ref> Some nuclear plants can be used for 80 years,<ref>"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.</ref> but others may have to be retired earlier for safety reasons.<ref name="bellona.org">"Nuclear plant lifetime extension: A creeping catastrophe". Bellona.org. 30 March 2020. Archived from the original on 21 June 2020. Retrieved 25 June 2020.</ref> As of 2020 more than half the world's nuclear plants are expected to request license extensions,<ref>"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.</ref> and there have been calls for these extensions to be better scrutinised under the Convention on Environmental Impact Assessment in a Transboundary Context.<ref name="bellona.org"/>

Some coal-fired power stations may operate for 50 years but others may be shut down after 20 years,<ref>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.</ref> or less.<ref>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.</ref> 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.<ref>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.</ref>

Lifecycle emissions from heating

For residential heating in almost all countries emissions from natural gas furnaces are more than from heat pumps.<ref>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.</ref> 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.<ref>"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.</ref>

Fossil gas bridge fuel controversy

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.<ref>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.</ref> 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.<ref>"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.</ref>

Missing life cycle phases

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<ref name="Warner + Heath, JoIE" /> 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.<ref>"A Record 26 States Removed Dams in 2019". American Rivers. Archived from the original on 7 August 2020. Retrieved 30 July 2020.</ref> 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.<ref>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.</ref> 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,<ref>http://srren.ipcc-wg3.de/report/IPCC_SRREN_Annex_II.pdf Archived 27 June 2013 at the Wayback Machine pg 40</ref> does however include the contribution of facility decommissioning with an "Added facility decommissioning" global warming potential in the full nuclear life cycle assessment.<ref name="Warner + Heath, JoIE" />

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.<ref>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.</ref> 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.<ref>Marshall, Michael. "No, Wind Farms Are Not Causing Global Warming". Forbes. Archived from the original on 24 September 2020. Retrieved 30 July 2020.</ref>

See also

• Bioenergy with carbon capture and storage
• Carbon capture and storage
• Carbon footprint
• Climate change mitigation
• Efficient energy use
• Low-carbon economy
• Nuclear power proposed as renewable energy

External links

• National Renewable Energy Laboratory. LCA CO₂ emissions of all present day energy sources.
• Wise uranium CO₂ calculator