http://icarb.org/2013/05/06/5th-international-conference-minutes-and-presentations/

1. NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.
Harmonizing Greenhouse Gas Emissions
Estimates for Electricity Generation Systems:
A US approach
ICARB Conference
March 13, 2013
Garvin Heath, PhD
National Renewable Energy Laboratory
s

2. NATIONAL RENEWABLE ENERGY LABORATORY
NREL Snapshot
• Leading clean-energy innovation for 35 years
• 1740 employees with world-class facilities
• Campus is a living model of sustainable energy
• Owned by the Department of Energy
• Operated by the Alliance for Sustainable Energy
Only US national laboratory dedicated solely
to energy efficiency and renewable energy

3. NATIONAL RENEWABLE ENERGY LABORATORY
Scope of Mission
Energy Efficiency Renewable Energy Systems Integration Market Focus
Residential
Buildings
Commercial
Buildings
Personal and
Commercial
Vehicles
Solar
Wind and Water
Biomass
Hydrogen
Geothermal
Grid
Infrastructure
Distributed
Energy
Interconnection
Battery and
Thermal Storage
Transportation
Private Industry
Federal Agencies
Defense Dept.
State/Local Govt.
International

4. NATIONAL RENEWABLE ENERGY LABORATORY
Expertise and Tools for Informed Decisions
• Renewable Integration Analyses for eastern
and western US – production/transmission
planning
• System Advisor Model – software tool for
determining economic value of proposed
solar, wind and geothermal projects
• OPEN EI energy information data platform –
linking and sharing data worldwide
• LCA Harmonization study – consistent basis
to compare life cycle GHG emissions for
energy technologies
Analysis

5. NATIONAL RENEWABLE ENERGY LABORATORY
Why LCA?
Power Sector GHG Emissions (as an example)
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“One third of US CO2 emissions from power sector”
But…
– Only stack emissions considered (typically)
• Renewables assigned ~zero emissions
• Emissions associated with fuel extraction &
transport, chemicals, etc. assigned to different
economic sectors
– Only CO2 emissions counted
(typically)

6. NATIONAL RENEWABLE ENERGY LABORATORY 6
Life cycle assessment (LCA) –
quantifies resource consumption,
energy use, and emissions, from
cradle-to-grave
• Practiced for 40 years
• Methods codified in standards (e.g.,
ISO) and guidelines, though some
methodological issues persist
Selected by IPCC as most appropriate
basis for consistent comparison of
renewable and conventional energy
technologies in Special Report on
Renewables
Quantifying Attributable Impacts
Source: IPCC SRREN

7. NATIONAL RENEWABLE ENERGY LABORATORY
Life Cycle Assessment: A Primer
Major Stages:
• Raw materials, feedstocks and fuels
acquisition
• Equipment manufacture
• Unit siting and construction
• Operation of generating units
• Transmission and distribution
• Materials, fuel, and waste
transportation
• Waste disposal
• Unit decommissioning and disposal
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Metrics
• GHG emissions
• Water consumption and discharges
• Energy use
• Petroleum use
• Raw material consumption
• Air pollutant emissions
• Solid waste
Source: ORNL

8. NATIONAL RENEWABLE ENERGY LABORATORY 8
System Boundary in LCA – Unifying concept with
differing application
non-
renewable
energy
non-
renewable
materials
emissions
energy
final product
net emissions
emissions
emissions
emissions
emissions
emissions
emissionsraw materials
raw materials
energy
energy
energy
energy
energy energy
waste materials
Intermediate
feedstock
Intermediate
feedstock
Intermediate
feedstock
Extraction
process
Process Process
Process
Waste
disposal
Extraction
process
Process
of
Interest
Life cycle system boundary

9. NATIONAL RENEWABLE ENERGY LABORATORY
Depth and Breadth of LCA at NREL
1992 2012
9

10. NATIONAL RENEWABLE ENERGY LABORATORY
Special Issue of Journal of Industrial Ecology on
Meta-Analysis of LCA
Issue Publication date: May, 2012
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Systematic Review and Harmonization of
LCAs of Electricity Generation
Technologies: LCA Harmonization Project

11. NATIONAL RENEWABLE ENERGY LABORATORY
Need for Systematic Review & Meta-Analysis
Context
– Considerable previous work in assessing life cycle
environmental impacts of electricity generation
technologies
• Scrutinized > 2,000 references to date
– Lack of holistic evaluation of this work in a
consistent manner, especially across technologies
– Methodological inconsistency has hampered
cross-study comparisons
– Result is impression amongst decision makers that
state of the science is inconclusive
11

12. NATIONAL RENEWABLE ENERGY LABORATORY
Need for Systematic Review & Meta-Analysis
Context
– Considerable previous work in assessing life cycle
environmental impacts of electricity generation
technologies
• Scrutinized > 2,000 references to date
– Lack of holistic evaluation of this work in a
consistent manner, especially across technologies
– Methodological inconsistency has hampered
cross-study comparisons
– Result is impression amongst decision makers that
state of the science is inconclusive
LCA Harmonization Study goals
– Understand range of published results
– Reduce uncertainty and inconsistency around
estimates of environmental impacts of electricity
generation technologies
– Make the information useful to decision makers in
the near term
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13. NATIONAL RENEWABLE ENERGY LABORATORY
Major Outcomes
Contribution to important studies
– IPCC SRREN: comprehensive assessment of
estimates of GHG emissions from electricity
generation technologies (renewable and
conventional)
– Renewable Electricity Futures: 80% RE by
2050
Contribution to science
– Special issue of Journal of Industrial
Ecology on meta-analysis of LCAs
• Publication date early May, 2012
• 8 articles from project in special issue
– Special sessions at International LCA
conferences on meta-analysis
of energy LCAs
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14. NATIONAL RENEWABLE ENERGY LABORATORY
Literature Review Counts
Note: Some double counting is inherent in the Totals given that some references investigate more than one technology.
Note2: The counts represent progress to-date and will differ from final results once the project is completed.
Technology Category
References
Reviewed
Passing the
First Screen
Passing the
Second
Screen
Providing Life
Cycle GHG
Emissions
Estimates
Biopower 369 162 84 52
Coal 273 192 110 52
Concentrating solar power 125 45 19 13
Geothermal 46 24 9 6
Hydro 89 45 11 11
Natural gas 251 157 77 40
Nuclear 249 196 64 32
Ocean energy 64 30 6 5
Oil 68 45 19 10
Photovoltaics 400 239 75 26
Wind 231 174 72 49
Totals 2165 1309 546 296
% of total reviewed 60% 25% 14%
% of those passing first screen 42% 23%
% of those passing second screen 54%
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15. NATIONAL RENEWABLE ENERGY LABORATORY
Large Variability for Some Techs,
RE Considerably Lower than Fossil
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IPCC SRREN
SPM Fig 8

16. NATIONAL RENEWABLE ENERGY LABORATORY
Lit. Review Methods and Caveats
Methods
Literature collection
– > 2,000 reviewed
– Exhaustive search of English
language publications
– All pub types (articles, reports,
conf papers, theses…)
Literature screening
– Quality methods of LCA and
GHG accounting
– Transparency of reporting
inputs, assumptions, and results
– Relevance of evaluated
technology today/near future
Caveats
Distributions of literature estimates
– Not assessment of likelihood
– Not a prediction, though newer
designs included
– Might not capture true min., max.,
or central tendency (countered by
repeated study of many
technologies)
Limited to available literature
– Not all technology variations
studied or studied frequently
Technologies considered in isolation
– System impacts typically not
studied (↑reserves for ↑ wind)
– Typically do not consider fleet of
existing units (could weight
technologies by deployment to
estimate)
– Land use change not considered
(or removed)
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17. NATIONAL RENEWABLE ENERGY LABORATORY
Harmonization Methods
Types of Harmonization
System Harmonization
– System boundaries
– GWPs
– GWIs (full harmonization)
Technological Harmonization
– Plant performance
characteristics (eff., CF,)
– Lifetime
Geographic Harmonization
– Solar resource
Method
1. Proportional adjustment of
denominator of:
2. Addition or subtraction for
system boundary
3. Full harmonization:
Recalculation of GWI x
material mass (activity) for
whole LCI
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GWP weighted
lifetimeGHG
GHG
I PR LT Aη
−
=
× × × ×

18. NATIONAL RENEWABLE ENERGY LABORATORY
Crystalline PV – Published estimates
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0
50
100
150
200
250
all values mono-crystalline
silicon
(m-Si)
poly-crystalline
silicon
(p-Si)
amorphous
silicon
(a-Si)
cadmium
telluride
(CdTe)
nano- crystalline
dye sensitized
(DSC)
concentrator ribbon
silicon
cadmium selenide
quantum dot
(QDPV)
LifeCycleGHGEmissions(gCO2e/kWh)
count: 124 30 56 12 13 4 6 2* 1
references: 26 9 15 3 3 1 2 2 1
KEY TO BOX PLOT
MAX
75th
MEDIAN
25th
MIN

19. NATIONAL RENEWABLE ENERGY LABORATORY
Crystalline PV – Harmonization steps
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1. Lifetime average module efficiency (solar energy converted to DC
electricity)
a) 13% mono
b) 12.3% multi
2. System lifetime: 30 yrs
3. Irradiation: 2,400 kWh/m2/yr
4. Performance ratio (ratio of AC electricity produced to DC-rated module
efficiency and irradiation)
a) rooftop + Bldg-integrated = 0.75
b) ground = 0.8

20. NATIONAL RENEWABLE ENERGY LABORATORY
Crystalline PV – As-Published
20
0
50
100
150
200

21. NATIONAL RENEWABLE ENERGY LABORATORY
Crystalline PV – Module Efficiency
21
0
50
100
150
200

22. NATIONAL RENEWABLE ENERGY LABORATORY
Crystalline PV – System Lifetime
22
0
50
100
150
200

23. NATIONAL RENEWABLE ENERGY LABORATORY
Crystalline PV – Irradiation
23
0
50
100
150
200

24. NATIONAL RENEWABLE ENERGY LABORATORY
Crystalline PV – Performance Ratio
24
0
50
100
150
200

25. NATIONAL RENEWABLE ENERGY LABORATORY
Crystalline PV– Harmonized vs. Published
25
0
50
100
150
200

26. NATIONAL RENEWABLE ENERGY LABORATORY
Crystalline PV– Harmonized vs. Reported
26
0
50
100
150
200
250
Reported Harmonized Reported Harmonized Reported Harmonized Reported Harmonized Reported Harmonized
LifeCycleGHGEmissions(gCO2e/kWh)
All Studies mono-Si multi-Si Ground-mounted Roof-mounted
Estimates: 41 13 28 11 30
References: 13 4 13 5 9

27. NATIONAL RENEWABLE ENERGY LABORATORY
Published Estimates for Harmonized Techs
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28. NATIONAL RENEWABLE ENERGY LABORATORY
Methodological Harmonization Reduces
Variability and Clarifies Central Tendency
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29. NATIONAL RENEWABLE ENERGY LABORATORY
Lessons learned
– Significant set of existing literature (490 passing screens,
and counting!)
• Meta-analyses of LCA literature are rare, but opportunity to gain insight from
existing literature is considerable
– Considerable variability within pool of studies analyzed
• Variability across technologies within a class can be significant
• Variability within technologies can also be significant
• Variability across technology classes significant, but yet not analyzed
– Best performed after harmonizing studies within technologies/classes
– Probably not appropriate to compare broad technology classes given significant
variability across technologies within those classes
– Methodological inconsistency is prevalent
• Many dimensions of inconsistency can be harmonized
• Some are “legitimate” differences in assumptions
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30. NATIONAL RENEWABLE ENERGY LABORATORY
Lessons learned (II)
Harmonization can
• Reduce variability
• Increase consistency
• Facilitate cross-study comparisons
• Identify key drivers
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31. NATIONAL RENEWABLE ENERGY LABORATORY
Harmonization Caveats and Responses
For some users, only system harmonization is appropriate
– For others, results after all steps of harmonization useful
Transparent results and methods
Results express variability around a modern reference system
Outline approaches to adjust our results to other assumptions
Not a true sensitivity analysis
Most effective harmonization steps help identify influential
parameters (for NG  efficiency, fuel cycle methane leakage)
Precision vs. accuracy
– Accuracy still an issue for NG: missing factors, new science
Recommended research

32. NATIONAL RENEWABLE ENERGY LABORATORY
Acknowledgements and Pointers
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Funding from US DOE / EERE
Special Issue on Meta-Analysis of LCA
http://jie.yale.edu/LCA-meta-analysis
• NG article pending response to peer review
comments
NREL LCA Harmonization project
www.nrel.gov/harmonization
Data visualization and download:
en.openei.org/LCA

33. NATIONAL RENEWABLE ENERGY LABORATORY
Contributors
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NREL: Ethan Warner, Patrick O'Donoughue,
Stacey Dolan, David Hsu, John Burkhardt,
Pamala Sawyer, Martin Vorum, Elliot Cohen,
BNL (PV): Vasilis Fthenakis, Hyung Chul Kim,
Symbiotic Engineering (coal): Michael Whitaker

34. NATIONAL RENEWABLE ENERGY LABORATORY
Leading the Way to a Clean Energy Future
Garvin.Heath@nrel.gov