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Understanding future emissions from low-carbon power systems by integration of life-cycle assessment and integrated energy modelling

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Michaja Pehl at Potsdam Institute for Climate Impact Research
Michaja Pehl
Anders Arvesen
Anders Arvesen
Anders Arvesen
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Florian Humpenöder at Potsdam Institute for Climate Impact Research
Florian Humpenöder
Alexander Popp at Potsdam Institute for Climate Impact Research
Alexander Popp
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Abstract and Figures

Both fossil-fuel and non-fossil-fuel power technologies induce life-cycle greenhouse gas emissions, mainly due to their embodied energy requirements for construction and operation, and upstream CH4 emissions. Here, we integrate prospective life-cycle assessment with global integrated energy-economy-land-use-climate modelling to explore life-cycle emissions of future low-carbon power supply systems and implications for technology choice. Future per-unit life-cycle emissions differ substantially across technologies. For a climate protection scenario, we project life-cycle emissions from fossil fuel carbon capture and sequestration plants of 78-110 gCO2eq kWh⁻¹, compared with 3.5-12 gCO2eq kWh⁻¹ for nuclear, wind and solar power for 2050. Life-cycle emissions from hydropower and bioenergy are substantial (~100 gCO2eq kWh⁻¹), but highly uncertain. We find that cumulative emissions attributable to upscaling low-carbon power other than hydropower are small compared with direct sectoral fossil fuel emissions and the total carbon budget. Fully considering life-cycle greenhouse gas emissions has only modest effects on the scale and structure of power production in cost-optimal mitigation scenarios.
| Embodied energy use of electricity production as a percentage of lifetime electricity production. Global average values are shown by secondary energy carrier (coloured bars) for capacities built in 2050. Combined model variations over both regions and technology variants (sample minimum, 25th percentile, median, 75th percentile, and maximum, see Methods) are shown as grey boxplots. See also Supplementary Table 1.
| Embodied energy use of electricity production as a percentage of lifetime electricity production. Global average values are shown by secondary energy carrier (coloured bars) for capacities built in 2050. Combined model variations over both regions and technology variants (sample minimum, 25th percentile, median, 75th percentile, and maximum, see Methods) are shown as grey boxplots. See also Supplementary Table 1.
… 
| Specific direct and indirect GHG emissions. Global 2050 average of lifetime emissions over lifetime electricity production (solid coloured bars), for capacities built in 2050 in a 2 °C-consistent mitigation scenario. Model variations (sample minimum, 25th percentile, median, 75th percentile, and maximum, see Methods) across both regions and technology variants are shown as boxplots. Ranges of specific emissions from AR5, from section 7.8.1, Fig 7.6 in ref. 4 are shown as light blue ranges. BECCS is not assessed there. The (median) 2050 CO 2 intensity of electricity production for AR5 scenarios without CCS (technology category T3) reaching 430-480 ppm CO 2 eq (climate category 1) is shown in red as a proxy for the level of specific net emissions (without negative emissions from BECCS) in line with the 2 °C target. See also Supplementary Table 2.
| Specific direct and indirect GHG emissions. Global 2050 average of lifetime emissions over lifetime electricity production (solid coloured bars), for capacities built in 2050 in a 2 °C-consistent mitigation scenario. Model variations (sample minimum, 25th percentile, median, 75th percentile, and maximum, see Methods) across both regions and technology variants are shown as boxplots. Ranges of specific emissions from AR5, from section 7.8.1, Fig 7.6 in ref. 4 are shown as light blue ranges. BECCS is not assessed there. The (median) 2050 CO 2 intensity of electricity production for AR5 scenarios without CCS (technology category T3) reaching 430-480 ppm CO 2 eq (climate category 1) is shown in red as a proxy for the level of specific net emissions (without negative emissions from BECCS) in line with the 2 °C target. See also Supplementary Table 2.
… 
Total global 2050 emissions Both direct and indirect emissions from global power production in 2050 for the Baseline (no climate policy) and the Policy (2 °C-compatible) scenario. Direct fossil fuel CO2 (non-CCS) emissions derive from non-CCS fossil fuel plants, while direct fossil fuel CO2 (imperfect CCS capture) from fossil fuel plants with CCS. See also Supplementary Table 3.
Total global 2050 emissions Both direct and indirect emissions from global power production in 2050 for the Baseline (no climate policy) and the Policy (2 °C-compatible) scenario. Direct fossil fuel CO2 (non-CCS) emissions derive from non-CCS fossil fuel plants, while direct fossil fuel CO2 (imperfect CCS capture) from fossil fuel plants with CCS. See also Supplementary Table 3.
… 
Differences between global indirect emissions a,b, Differences between the Policy (2 °C-compatible) and Baseline (no climate policy) scenarios over time (a) and cumulated from 2010 to 2050 (b). Indirect emissions include those from construction, operation (except fuel burning), LULUC, and upstream and biogenic CH4 emissions. See also Supplementary Table 4.
Differences between global indirect emissions a,b, Differences between the Policy (2 °C-compatible) and Baseline (no climate policy) scenarios over time (a) and cumulated from 2010 to 2050 (b). Indirect emissions include those from construction, operation (except fuel burning), LULUC, and upstream and biogenic CH4 emissions. See also Supplementary Table 4.
… 
Impact on optimal technology choice a,b, Electricity production by technology for two variants of the Policy (2 °C-compatible) scenario, accounting only for direct emissions or all indirect emissions (a) and differences between the two variants in 2050 (b). Accounting for the effect of indirect emissions (upstream and biogenic CH4, LULUC and life-cycle CO2 emissions) reduces electricity production by about 3 EJ yr⁻¹ in 2050 (a). Technologies with comparatively high specific indirect emissions (gas, hydropower and bioenergy) produce significantly less electricity, which is largely offset by increased production from technologies with lower specific indirect emissions (wind, nuclear and CSP) (b). See also Supplementary Table 6.
Impact on optimal technology choice a,b, Electricity production by technology for two variants of the Policy (2 °C-compatible) scenario, accounting only for direct emissions or all indirect emissions (a) and differences between the two variants in 2050 (b). Accounting for the effect of indirect emissions (upstream and biogenic CH4, LULUC and life-cycle CO2 emissions) reduces electricity production by about 3 EJ yr⁻¹ in 2050 (a). Technologies with comparatively high specific indirect emissions (gas, hydropower and bioenergy) produce significantly less electricity, which is largely offset by increased production from technologies with lower specific indirect emissions (wind, nuclear and CSP) (b). See also Supplementary Table 6.
… 
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Articles
https://doi.org/10.1038/s41560-017-0032-9
© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
1Potsdam Institute of Climate Impact Research, PO Box 60 12 03 Potsdam, Germany, . 2Industrial Ecology Programme and Department of Energy and
Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway. 3Center for Industrial Ecology, Yale School for Forestry
and Environmental Studies, New Haven, CT, USA. *e-mail: michaja.pehl@pik-potsdam.de; gunnar.luderer@pik-potsdam.de
The Paris Agreement of COP21 confirmed the goal of limiting
global temperature increase well below 2 °C and acknowledged
the need to achieve net greenhouse gas neutrality during the
second half of the century1. Previous research based on integrated
energy–economy–climate models has shown that achieving these
targets cost-effectively requires a rapid, almost full-scale decarbon-
ization of the electricity system by mid-century2,3. In electricity pro-
duction, ample low-carbon alternatives are available4 and electricity
is a potential substitute for fossil-based fuels in all economic sectors,
which leads to final energy electricity shares of 25–45% in stringent
mitigation scenarios2.
The life-cycle assessment (LCA) literature illustrates that all
energy transformation technologies are associated with upstream
energy demands and corresponding indirect (that is, not caused by
fuel-burning on site) greenhouse gas (GHG) emissions4–7. Concerns
have been voiced that these can impair the emission reduction
potential of low-carbon technologies6,8,9. However, LCA studies of
electricity mostly focus on impacts on a per-kilowatt-hour basis
in static settings, typically neglecting technology improvements in
electricity generation technologies, as well as the effects of concur-
rent decarbonization measures in other sectors of the energy system
and the economy6,10,11.
Integrated energy–economy–climate modelling approaches
estimate cost-optimal long-term strategies to meet the emissions
constraints implied by climate targets3. Whereas direct combustion
emissions as well as CH4 from fossil fuel extraction and indirect
land-use change emissions are accounted for by many state-of-the-
art modelling systems, other indirect emissions, in particular those
related to energy required for the construction of power plants
and the production and transportation of fuels and other inputs
(defined here as embodied energy use, EEU), are not considered in
the optimization. We investigate to what extent this omission leads
to incomplete internalization of externalities.
A previous study by Hertwich et al.5 used prospective LCA to
compare similar scenarios in terms of environmental impacts,
but relied on exogenous scenarios for technology deployment,
and focused on non-climate environmental impacts to assess co-
benefits and trade-offs of climate change mitigation. Daly et al.9 and
Scott et al.12 investigated the influence of national climate policy on
domestic and non-domestic indirect GHG emissions and found
them to have a large potential for carbon leakage, as the ratio of
emissions caused domestically and overseas shifts to the latter due
to imports of goods and services. However, their analysis consid-
ered only the United Kingdom, based carbon intensities on aggre-
gate input–output relationships rather than process detail, and did
not account for policy-induced non-domestic emission reductions
in the context of coordinated international climate change mitiga-
tion efforts. Portugal-Pereira et al.13 included LCA emission coef-
ficients in an integrated assessment model (IAM) and studied the
effect of taxing indirect emissions on the electricity mix. However,
they considered only the Brazilian electricity system and used static
LCA coefficients.
In this study, we present consistent and detailed modelling of
EEU and indirect GHG emissions for global scenarios of future
electricity systems. By linking an IAM with EEU coefficients from a
prospective LCA model, we can provide a holistic and detailed per-
spective on future life-cycle greenhouse gas emissions of low-carbon
technologies and power systems in the context of a universal climate
change mitigation regime, thus closing an important research gap14–16
by quantifying these emissions and their effect on the choice of low-
carbon technologies in mitigation scenarios. This study combines
results from the REMIND model17,18, which details energy use and
Understanding future emissions from low-carbon
power systems by integration of life-cycle
assessment and integrated energy modelling
Michaja Pehl 1*, Anders Arvesen 2, Florian Humpenöder1, Alexander Popp1, Edgar G. Hertwich 3
and Gunnar Luderer1*
Both fossil-fuel and non-fossil-fuel power technologies induce life-cycle greenhouse gas emissions, mainly due to their embod-
ied energy requirements for construction and operation, and upstream CH4 emissions. Here, we integrate prospective life-
cycle assessment with global integrated energy–economy–land-use–climate modelling to explore life-cycle emissions of future
low-carbon power supply systems and implications for technology choice. Future per-unit life-cycle emissions differ substan-
tially across technologies. For a climate protection scenario, we project life-cycle emissions from fossil fuel carbon capture and
sequestration plants of 78–110gCO2eq kWh−1, compared with 3.5–12gCO2eq kWh−1 for nuclear, wind and solar power for 2050.
Life-cycle emissions from hydropower and bioenergy are substantial (∼ 100gCO2eq kWh−1), but highly uncertain. We find
that cumulative emissions attributable to upscaling low-carbon power other than hydropower are small compared with direct
sectoral fossil fuel emissions and the total carbon budget. Fully considering life-cycle greenhouse gas emissions has only
modest effects on the scale and structure of power production in cost-optimal mitigation scenarios.
NATURE ENERGY | VOL 2 | DECEMBER 2017 | 939–945 | www.nature.com/natureenergy 939
The Nature trademark is a registered trademark of Springer Nature Limited.
... Addressing global climate change necessitates an energy transition towards a lowcarbon system, and NPPs present a promising solution in this respect. According to a comprehensive study by Pehl et al. (2017), life-cycle emissions from NPPs are projected to be as low as 3.5-12 gCO2eq kWh−1 by 2050. In stark contrast, the same study estimates that fossil fuel carbon capture and sequestration plants will emit substantially higher levels of greenhouse gases (GHGs) in the 78-110 gCO2eq kWh−1 range. ...
... In stark contrast, the same study estimates that fossil fuel carbon capture and sequestration plants will emit substantially higher levels of greenhouse gases (GHGs) in the 78-110 gCO2eq kWh−1 range. This numerical comparison effectively underscores nuclear power's significantly lower carbon footprint, thereby highlighting its considerable environmental advantages (Pehl et al., 2017). ...
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