Life Cycle Greenhouse Gas Emissions from Electricity Generation: Update

Photo by Dennis Schroeder, NREL 22610

Life Cycle Greenhouse Gas Emissions

from Electricity Generation: Update

As clean energy increasingly becomes

part of the national dialogue, lenders,

utilities, and lawmakers need the most

comprehensive and accurate information

on greenhouse gas (GHG) emissions from

various sources of energy to inform

policy, planning, and investment decisions.

Since the National Renewable Energy Laboratory (NREL)

published original results from the Life Cycle Assessment

Harmonization Project (Heath and Mann 2012), it has

updated estimates of electricity generation GHG emissions

factors as part of several recent studies. This fact sheet

updates an earlier version (NREL 2013).

Systematic Review

NREL considered approximately 3,000 published life cycle

assessment studies on utility-scale electricity generation

from wind, solar photovoltaics, concentrating solar power,

biopower, geothermal, ocean energy, hydropower, nuclear,

natural gas, and coal technologies, as well as lithium-ion

battery, pumped storage hydropower, and hydrogen storage

technologies. A systematic review, comprising three rounds

of screening by multiple experts, selected references that met

strict criteria for quality, relevance, and transparency.

Less than 15% of the original pool of references passed

this review process.

The addition of battery and hydrogen storage technologies

introduces a unique set of challenges and assumptions to

the compilation of emissions factors. The primary challenges

stem from the fact that storage technologies are

characterized by two diﬀerent types of capacity

• Energy Capacity: how much energy a given resource

can store, denoted in units of kilowatt hours (kWh)

• Power Capacity: how much energy a given resource

can deliver, denoted in units of kilowatts (kW).

Life Cycle Assessment

of Energy Systems

Life cycle assessments (LCA) can help quantify environmental

burdens from “cradle to grave” and facilitate more-consistent

comparisons of energy technologies.

Figure 1. Generalized life cycle stages for energy

technologies

Background Economy

Operation

Combustion

Maintenance

Operations

Downstream

Dismantling

Decommissioning

Disposal and

Recycling

Upstream

Resource Extraction

Material Manufacturing

Component Manufacturing

Construction

Fuel Cycle

Resource Extraction/

Production

Processing/Conversion

Delivery to Site

Life cycle GHG emissions from renewable electricity generation

technologies are generally less than from those from fossil fuel-

based technologies, according to evidence assembled from

the LCA Harmonization project. Further, the proportion of GHG

emissions from each lifecycle stage diﬀers by technology. For

fossil-fueled technologies, fuel combustion during operation

of the facility emits the vast majority of GHGs. For nuclear and

renewable energy technologies, most GHG emissions occur

upstream of operation.

Source: Sathaye et al. 2011

Life Cycle Greenhouse Gas Emissions from Electricity Generation: Update 1

Also, certain storage technologies, especially lithium-ion

batteries, can be designed to operate for a variety of grid

services, such as time-shifting or frequency regulation.

To align the estimates of GHG emissions impacts from

the storage technologies with those of other generation

technologies, we considered only references that

enabled the calculation of emissions per unit of electricity

delivered over the lifetime of the storage system.

Thus, we have excluded references that report only

emissions factors per unit of power capacity.

Published estimates of life cycle GHG emissions for biomass,

solar (photovoltaics and concentrating solar power),

geothermal, hydropower, ocean, wind (land-based and

oﬀshore), nuclear, oil, and coal generation technologies

as well as storage technologies are compared in Figure 2.

These estimates are drawn from three groups of studies:

• Studies conducted as part of NREL’s Life Cycle Assessment

Harmonization Project (“Life Cycle Assessment

Harmonization,” NREL, https://www.nrel.gov/analysis/life-

cycle-assessment.html)

• U.S. Department of Energy “vision” studies, including

Hydropower Vision (DOE 2016), Wind Vision (DOE 2015),

Geothermal Vision (Millstein et al. 2019) and On the

Path to SunShot (Wiser et al. 2016)

• Grid-scale lithium-ion battery and hydrogen fuel cell

stationary storage literature compiled under the Los

Angeles 100% Renewable Energy Study (Nicholson

et al. 2021)

1,800

1,600

1,400

1,200

1,000

800

600

400

200

-200

-400

-600

-800

-1,000

-1,200

-1,400

-1,600

Life Cycle Greenhouse Gas Emissions (g CO

e/kWh)

Biopower

Photovoltaic

Concentrating Solar Power

Geothermal Energy

Hydropower

Ocean Energy

Wind Energy

Pumped Hydropower Storage

Hydrogen Storage

Lithium-Ion Battery Storage

Nuclear Energy

Natural Gas

Oil

Coal

276

(

)

(

)

Estimates

References

149

186

(

)

(

)

* Avoided emissions, no removal of

GHGs from the atmosphere

Electricity Generation

Technologies Powered by

Nonrenewable Resources

Electricity Storage

Technologies

Electricity Generation Technologies

Maximum

Median

Minimum

Single Estimate for

Hydrogen

Single Estimates

with CCS

164

(

)

(

)

Figure 2. Life cycle greenhouse gas emission estimates for selected electricity generation and storage

technologies, and some technologies integrated with carbon capture and storage (CCS).

Notes for Figure 2: The number of estimates is greater than the number of references

because many studies considered multiple scenarios. Numbers reported in parentheses

pertain to additional references and estimates that evaluated technologies with CCS.

Life Cycle Greenhouse Gas Emissions from Electricity Generation: Update 2

Table 1 includes the median values for four life cycle phases

(one-time upstream (e.g., materials acquisition and plant

construction), ongoing combustion (where applicable),

ongoing noncombustion (e.g., operation and maintenance),

and one-time downstream (e.g., plant decommissioning

and disposal/recycling)) as well as a total life cycle emissions

factor. These results show that total life cycle GHG emissions

from renewables and nuclear energy are much lower and

generally less variable than those from fossil fuels.

For example, from cradle to grave, coal-ﬁred electricity

releases about 20 times more GHGs per kilowatt-hour

than solar, wind, or nuclear electricity (based on median

estimates for each technology).

Note that because diﬀerent numbers of references may be

used in the calculation of each entry in Table 1, the sum of

the median estimates of each life cycle phase for a given

generation technology might not equal the median of the

total life cycle emissions factors (the sum of the medians

need not equal the median of the sums). Indeed, the sum of

the individual phase median values may be greater than the

median total, as is the case with concentrating solar power.

Generation

Technology

RenewableStorage

Nonrenewable

EPRI 2013

Renewable Electricity

Futures Study 2012

Kim et al. 2012

Hsu et al. 2012

NREL 2012

Burkhardt et al. 2012

Eberle et al. 2017

DOE 2016

IPCC 2011

DOE 2015

DOE 2016

Nicholson et al. 2021

IPCC 2011

Whitaker et al. 2012

Khan et al. 2005

Warner and Heath 2012

O’ Donoughue et al. 2013

~10

6.9

1.9

0.74

1.8

2.5

0.53

0.12

0.004

0.34

0.07

3.4

1.9

0.7

0.02

7.4

486

840

1001

—

389

1010

Biomass

Photovoltaic

Geothermal

Ocean

Nuclear

Natural gas

Oil

Coal

Hydropower

Wind

Concentrating

Solar Power

Pumped-

storage

hydropower

Lithium-ion

battery

Hydrogen

fuel cell

~28

6.2

3.0

2.0

0.8

One-Time

Downstream

One-Time

Upstream

Total

Life

Cycle

Ongoing

Combustion

Sources

Ongoing

Non

Combustion

Notes for Table 1

All values are in grams of carbon dioxide

equivalent per kilowatt-hour (g CO

e/kWh)

Thin ﬁlm and crystalline silicon

Tower and trough

Land-based and oﬀshore

Light-water reactor (including

pressurized water and boiling water) only

NR = Not Reported.

See Also

General information about life cycle assessments: “Life Cycle

Assessment Harmonization,” NREL,

https://www.nrel.gov/analysis/life-cycle-assessment.html

Data visualization and data downloads: “LCA Harmonization,”

OpenEI, https://openei.org/apps/LCA/

Additional distributional statistics and subtechnology

emissions factors augmenting Table 1:

https://data.nrel.gov/submissions/171

Table 1. Median Published Life Cycle Emissions Factors for Electricity

Generation Technologies, by Life Cycle Phase

Funding for this fact sheet was

provided by the Joint Institute

for Strategic Energy Analysis

in support of its Energy and

Atmospheric Systems Catalyzer,

a collaborative eﬀort that

explores the multidirectional

relationships across climate,

air quality, and energy systems.

Life Cycle Greenhouse Gas Emissions from Electricity Generation: Update 3

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References

Burkhardt III, John J., Garvin Heath, and Elliot Cohen. 2012. “Life Cycle

Greenhouse Gas Emissions of Trough and Tower Concentrating Solar

Power Electricity Generation: Systematic Review and Harmonization.”

Journal of Industrial Ecology 16(S1): S93-S109. https://doi.

org/10.1111/j.1530-9290.2012.00474.x

DOE (U.S. Department of Energy). 2015. Wind Vision: A New Era for

Wind Power in the United States. Appendix J. U.S. Department of

Energy. DOE/GO-102015-4557. https://doi.org/10.2172/1220428

———. 2016. Hydropower Vision: A New Chapter for America’s First

Renewable Electricity Source. Appendix G. U.S. Department of Energy.

https://doi.org/10.2172/1330494

Eberle, Annika, Garvin Heath, Scott Nicholson, and Alberta Carpenter.

2017. Systematic Review of Life Cycle Greenhouse Gas Emissions

from Geothermal Electricity. Golden, CO: National Renewable Energy

Laboratory. NREL/TP-6A20-68474. https://doi.org/10.2172/1398245

EPRI (Electric Power Research Institute). 2013. Literature Review

and Sensitivity Analysis of Biopower Life-Cycle Assessments and

Greenhouse Gas Emission. Palo Alto, CA: Electric Power Research

Institute. 1026852. https://www.epri.com/research/products/1026852

Heath, Garvin A., and Margaret K. Mann. 2012. “Background and

Reﬂections on the Life Cycle Assessment Harmonization Project.”

Journal of Industrial Ecology 16(S1): S8–S11. https://doi.org/10.1111/

j.1530-9290.2012.00478.x

Hsu, David D., Patrick O’Donoughue, Vasilis Fthenakis, Garvin A.

Heath, Hyung Chul Kim, Pamala Sawyer, Jun-Ki Choi, and Damon E.

Turney. 2012. “Life Cycle Greenhouse Gas Emissions of Crystalline

Silicon Photovoltaic Electricity Generation: Systematic Review and

Harmonization.” Journal of Industrial Ecology 16(S1): S122–S135.

https://doi.org/10.1111/j.1530-9290.2011.00439.x

Khan, Faisil I., Kelley Hawboldt, and M.T. Iqbal. 2005. “Life Cycle

Analysis of Wind–Fuel Cell Integrated System.” Renewable Energy

30(2): 157–177. https://doi.org/10.1016/j.renene.2004.05.009

Kim, Hyung Chul, Vasilis Fthenakis, Jun-Ki Choi, and Damon E. Turney.

2012. “Life Cycle Greenhouse Gas Emissions of Thin-ﬁlm Photovoltaic

Electricity Generation: Systematic Review and Harmonization.” Journal

of Industrial Ecology 16(S1): S110–S121. https://doi.org/10.1111/

j.1530-9290.2011.00423.x

Millstein, Dev, James McCall, Jordan Macknick, Scott Nicholson,

David Keyser, Seongeun Jeong, and Garvin Heath. 2019. GeoVision

Analysis Supporting Task Force Report: Impacts—The Employment

Opportunities, Water Impacts, Emission Reductions, and Air Quality

Improvements of Achieving High Penetrations of Geothermal

Power in the United States. Golden, CO: National Renewable Energy

Laboratory. NREL/TP6A20-71933. https://doi.org/10.2172/1524769

Nicholson, Scott, David Keyser, Marissa Walter, Greg Avery, and

Garvin Heath. 2021. “Chapter 8: Greenhouse Gas Emissions.” In The

Los Angeles 100% Renewable Energy Study, edited by Jaquelin

Cochran and Paul Denholm. Golden, CO: National Renewable Energy

Laboratory. NREL/TP-6A20-79444-8. https://www.nrel.gov/docs/

fy21osti/79444-8.pdf

NREL (National Renewable Energy Laboratory). 2012. Life Cycle

Greenhouse Gas Emissions from Solar Photovoltaics. Golden, CO:

National Renewable Energy Laboratory. NREL/FS-6A20-56487.

https://doi.org/10.2172/1056745

———. 2013. Life Cycle Greenhouse Gas Emissions from Electricity

Generation. Golden, CO: National Renewable Energy Laboratory.

NREL/FS-6A20-57187. https://doi.org/10.2172/1062479

O’Donoughue, Patrick R., Garvin A. Heath, Stacey L. Dolan, and Martin

Vorum. 2014. “Life Cycle Greenhouse Gas Emissions of Electricity

Generated from Conventionally Produced Natural Gas: Systematic

Review and Harmonization.” Journal of Industrial Ecology 18(1):

125–144. https://doi.org/10.1111/jiec.12084

Sathaye, Jayant, Oswaldo Lucon, John Christensen, Atiq Rahman,

Fatima Denton, Junichi Fujino, Garvin Heath et al. 2011. “Renewable

Energy in the Context of Sustainable Energy.” In IPCC Special Report

on Renewable Energy Sources and Climate Change Mitigation. O.

Edenhofer et al., eds., Cambridge University Press. https://www.ipcc.

ch/site/assets/uploads/2018/03/Chapter-9-Renewable-Energy-in-the-

Context-of-Sustainable-Development-1.pdf

Warner, Ethan S., and Garvin A. Heath. 2012. “Life Cycle Greenhouse

Gas Emissions of Nuclear Electricity Generation: Systematic Review

and Harmonization.” Journal of Industrial Ecology 16(S1): S73–S92.

https://doi.org/10.1111/j.1530-9290.2012.00472.x

Whitaker, Michael, Garvin A. Heath, Patrick O’Donoughue, and Martin

Vorum. 2012. “Life Cycle Greenhouse Gas Emissions of Coal-Fired

Electricity Generation: Systematic Review and Harmonization.” Journal

of Industrial Ecology 16(S1): S53–S72. https://doi.org/10.1111/j.1530-

9290.2012.00465.x

Wiser, Ryan, Trieu Mai, Dev Millstein, Jordan Macknick, Alberta

Carpenter, Stuart Cohen, Wesley Cole, Bethany Frew, and Garvin A.

Heath. 2016. On the Path to SunShot: The Environmental and Public

Health Beneﬁts of Achieving High Penetrations of Solar Energy in the

United States. Golden, CO: National Renewable Energy Laboratory.

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NREL/FS-6A50-80580 • September 2021