NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by 

Renewable Electricity 

Trieu Mai, Ph.D.PSERC WebinarSeptember 4, 2012NREL/PR‐6A20‐56168

Renewable Electricity Futures Study (2012). Hand, M.M.; Baldwin, S.; DeMeo, E.; 

D.; Porro, G.; Meshek, M.; Sandor, D., editors. Lead authors include Mai, T.; Sand

Augustine, C.; Bain, R.; Chapman, J.; Denholm, P.; Drury, E.; Hall, D.; Lantz, E.; Ma

Hostick, D.; Belzer, D.; Hadley, S.; Markel, T.; Marnay, C.; Milligan, M.; Ela, E.; Hein

A U.S. DOE‐sponsored collaboration among more than 110 individuals from 35 o
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• RE is a low carbon, low air pollutant, low fuel u

use, domestic, and sustainable electricity sourc

• To what extent can renewable energy technolo

commercially available today meet the U.S. elec

demand over the next several decades?

Renewable Electricity Futures Mo

RE Capacity Growth 2000-2010

Source: RE Data Book (DOE 2011) Source: RE D
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Summary of Key Results• Renewable electricity generation from technologies that are com

available today, in combination with a more flexible electric sys

adequate to supply 80% of total U.S. electricity generation in 20

meeting electricity demand on an hourly basis in every region o

• Increased electric system flexibility, needed to enable electricity 

balance with high levels of renewable generation, can come fro

supply‐ and demand‐side options, including flexible convention

storage, new transmission, more responsive loads, and changes 

operations.

• The abundance and diversity of U.S. renewable energy resource

multiple combinations of renewable technologies that result in 

in electric sector greenhouse gas emissions and water use.

• The direct incremental cost associated with high renewable gen

comparable to published cost estimates of other clean energy s

Improvement in the cost and performance of renewable techno

impactful lever for reducing this incremental cost.
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• RE Futures is an analysis of the U.S. electric secto

on 2050 that explores:

o Whether the U.S. power system can supply e

meet customer demand with high levels of reelectricity, including variable wind and solar g

o Grid integration using models with unpreced

geographic and time resolution for the contig

o Synergies, constraints, and operational issues 

with a transformation of the U.S. electric sect

Renewable Electricity Futures Intro
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Renewable Electricity Futures Rep

REF is a U.S. DOE‐sponsored collaboration with more t

contributors from 35 organizations including national l

industry, universities, and non‐governmental organizat

Volume 1 Exploration of High-Penetration Renewable ElectricVolume 2 Renewable Electricity Generation and Storage TechVolume 3 End-Use Electricity DemandVolume 4 Bulk Electric Power Systems: Operations and Trans
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Renewable Electricity Futures Intro

RE Futures does.... RE Futures does nIdentify commercially available RE

generation technology combinations that

meet up to 80% or more of projected 2050

electricity demand in every hour of the year.

Consider policies, new o

procedures, evolved bus

market rules that could 

of RE generation.

Identify electric sector characteristics

associated with high levels of RE generation.

Fully evaluate power sys

Explore a variety of high renewable

electricity generation scenarios.

Forecast or predict the e

electric sector.

Estimate the associated U.S. electric sectorcarbon emissions reductions.

Assess optimal pathway

carbon electricity system

Explore a select number of economic,

environmental and social impacts.

Conduct a comprehensi

analysis.

Illustrate an RE‐specific pathway to a clean

electricity future to inform the development

of integrated portfolio scenarios that

consider all technology pathways and theirimplications.

Provide a definitive asse

generation, but does idedeeper investigation.
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Modeling Framework

Technology cost &

performanceResource availabilityDemand projectionDemand‐sidetechnologiesGrid operationsTransmission costs

Black & Veatch

Technology Teams

Flexible ResourcesEnd‐Use ElectricitySystem OperationsTransmission

A

G

(hourly 

rooftop PVpenetration

2050 mix

of generators

Implications

GHG Emissions

Water Use

Land Use

Direct Costs

Capacity & Generation2010‐2050
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Scenario Framework
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General Assumptions• Energy Efficiency: Most of the scenarios assumed significant adoption of ener

(including electricity) measures in the residential, commercial, and industrial s

• Transportation: Most of the scenarios assumed a shift of some transportation 

petroleum and toward electricity in the form of plug‐in hybrid or electric vehi

offsetting the electricity efficiency advances that were considered.

• Grid Flexibility: Most scenarios assumed improvements in electric system ope

flexibility in both electricity generation and end‐use demand, helping to enab

integration of variable‐output renewable electricity generation.

• Transmission: Most scenarios expanded the transmission infrastructure and a

transmission capacity to support renewable energy deployment. Distribution‐not considered.

• Siting and Permitting: Most scenarios assumed project siting and permitting r

renewable electricity development and transmission expansion with standard 
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Renewable Resources and Techno

• Only currently commercial technologies were modeled (no enhanced 

ocean, or floating wind systems) with incremental and evolutionary im

• RE characteristics including location, technical resource potential, and 

characteristics were considered.

Biopower ~100 GW

Solar CSP ~37,000 GW

Geothermal ~36 GW

•Stand‐alone•Cofired with coal

•Trough•Tower

•Hydrothermal

With thermalstorage
Key Results
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A Transformation of the U.S. Electric

RE generation from technologies that are commerc

today, in combination with a more flexible electric 

more than adequate to supply 80% of total U.S. ele

generation in 2050—while meeting electricity dem

hourly basis in every region of the country.
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0%

10%20%30%40%50%60%70%80%90%

100%

Baseline

30% RE

40% RE

50% RE

60% RE

% of Total Generated Electricity

Percent 

Renewable generation resources could adequately supply 80% 

electricity generation in 2050 while balancing hourly supply a

Baseline scenario 80% RE‐ITI scenario

RE‐ITI scenarios
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The abundance and diversity of RE resources can support m

combinations of RE technologies to provide 80% generation 

• Technology deployment depends on scenario assumptions, but in all ca

resources existed to compensate for assumed variations in access to tra

flexibility, resource availability, technology costs, and electricity deman

• Constraints to transmission result in greater PV, offshore wind, and biop

• Constraints to system flexibility result in greater dispatchable technolog

storage and CSP with thermal storage.

• Constraints to resource accessibility result in greater wind and solar dep

Low‐Demand rangesencompass results forTechnology Improvement andConstrained scenarios
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All regions of the country could contribute substantial 

electricity supply in 2050

80% RE‐ITI scenario
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0

100200300400500600700800

Jul-16 00:00

Jul-16 12:00

Jul-17 00:00

Jul-17 12:00

Jul-18 00:00

Jul-18 12:00

Jul-19 00:00

Jul-19 12:00

Power (GW)

Date

0

100200300400500600700800

Jul-16 00:00

Jul-16 12:00

Jul-17 00:00

Jul-17 12:00

Jul-18 00:00

Jul-18 12:00

Jul-19 00:00

Jul-19 12:00

Power (GW)

Date

CurtaWindPVGas CGas CHydrCSPBiopCoalGeotNucleShiftLoad

0

100200300400500600700800

Apr-27 00:00

A

pr-27 12:00

A

pr-28 00:00

A

pr-28 12:00

A

pr-29 00:00

A

pr-29 12:00

A

pr-30 00:00

A

pr-30 12:00

Power (GW)

Date

CurtaWindPVGas Gas HydrCSPBiopCoalGeoNuclShiftLoad

0

100200300400500600700800

Apr-27 00:00

A

pr-27 12:00

A

pr-28 00:00

A

pr-28 12:00

A

pr-29 00:00

A

pr-29 12:00

A

pr-30 00:00

A

pr-30 12:00

Power (GW)

Date

Electricity supply and demand can be balanced in ever

year in each region with 80% electricity from renewab

80% RE‐ITI scenario

Baseline scenario

Peak →

Off‐Peak → 
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A more flexible electric power system is needed to enable 

demand balance with high levels of RE generation

• Maintaining sufficient capacity on the system for plannin

• Relying on demand‐side interruptible load, conventional 

(particularly natural gas generators), and storage to mana

operating requirements

• Mitigating curtailment with storage and controlled chargi

vehicles

• Operating the system with greater conventional power p

• Relying on the dispatchability of certain renewable techn

biopower, geothermal, CSP with storage and hydropower

• Leveraging the geospatial diversity of the variable resour

output ramping

• Transmitting greater amounts of power over longer dista

electricity demand profiles and meet load with remote ge

• Coordinating bulk power system operations across wider 

System flexibility can be increased using a broad portfolio of supply‐ and 

options, including:
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Firm capacity provided by some RE gener

conventional generators, and storage

Installed capacity is sufficient to meet summer afternoon p

diverse reserves

0

200400600800

1,0001,2001,400

Installed Capacity (GW)

Storage
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Additional planning and operational challenges include mademand periods and curtailment of excess electricity

• Operational challenges for high renewable scenarios are most a

demand periods (e.g., spring).

• There is greater thermal power plant ramping and cycling, as we

curtailment of excess renewable generation (8‐10% of wind, sol

hydropower curtailed in 2050).

• Storage and demand‐side options (e.g. PHEV charging) can help 

mitigate these challenges, e.g., 100‐150 GW of storage and 28‐48 GW 

load deployed in 2050 for the (low demand) 80%‐by‐2050 RE scenarios.

80% RE‐ITI scenario
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As RE deployment increases, additional transmission infrasrequired

• In most 80%‐by‐2050 RE scenarios, 110‐190 million MW‐miles of new transmi

• AC‐DC‐AC interties are expanded to allow greater power transfer between asy

• However, 80% RE is achievable even when transmission is severely constraine

which leads to a greater reliance on local resources (e.g. PV, offshore wind).

• Annual transmission and interconnection investments in the 80%‐by‐2050 RE 

B$5.7‐8.4/year, which is within the range of recent total investor‐owned utilit

expenditures.

• High RE scenarios lead to greater transmission congestion, line usage, and tra

losses.

80% RE‐ITI scenario
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High renewable electricity futures can result in deep reducsector greenhouse gas emissions and water use

80% RE scenarios lead to:

~80% reduction in 2050 generation from both coal‐fired and natural ga

~80% reduction in 2050 GHG emissions (combustion‐only and life cycle

~50% reduction in electric sector water use

Gross land use totaling <3% of contiguous U.S. area

Other related impacts include visual, landscape, noise, habitat, and e

05

10152025

2010 2020 2030 2040 2050

Annual Electric Sector Consumption 

(Quads)

Year

80% RE (NG) 80% RE (coal) Baseline (NG) Baseline (coal)

Gr

BiomasAll OthAll OthTransmTotal Co2009 CoMajor RGolf Co

80% RE scenarios

* USDA 2
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Incremental cost associated with high RE generation is com

published cost estimates of other clean energy scenarios

• Comparable to incremental cost for clean energy and low carbon scenarios 

EPA

• Reflects replacement of existing generation plants with new generators and 

requirements (combustion turbines, storage, and transmission) compared t

(continued evolution of today’s conventional generation system)

• Assumptions reflect incremental or evolutionary improvements to currentl

technologies; they do not reflect U.S. DOE activities to further lower these 

$0

$20$40$60

2010 2020 2030 2040 

Real 2009$/MWh

Core 80% RE (ReEDS) EIA 2009cEPA 2009a EIA 2010bEPA 2010 EIA 2011a

EIA 2011b

Increase in retail electricity price relative to reference/baseline

Source: Renewable Electricity Future
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• Cost is less sensitive to the assumed electric system constraints (transmis

resource access).

• Electricity prices in high RE scenarios are largely insensitive to projections 

prices and fossil technology improvements.

• Lower RE generation levels result in lower incremental prices (e.g., 30% R

shows no incremental cost relative to the baseline scenario).

• Cost figures do not reflect savings or investments associated with energy 

assumptions in the low‐demand Baseline and 80% RE scenarios.

-$20 -$10 $0 $10 $20

Fossil-HTI

Higher Fossil Fuel

Lower Fossil Fuel

High Demand

Constr. Res.

Constr. Flex.

Constr. Trans.

80% RE-NTI

Difference in 2050 Electricity Price 

Relative to 80% RE-ITI 

[Real 2009$/MWh]

80% RE-ETI

-$20 -$10 $0 $1

Higher Fossil Fuel

High Demand

Difference in 2050 Electricity 

Relative to Baseline (low-dem

[Real 2009$/MWh] 

Lower FoFossil-HT

Improvement in cost and performance of RE technolog

impactful lever for reducing the incremental cost
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No insurmountable long‐term constraints to RE technology capacity, materials supply, or labor availability were identif

• 80% RE generation in 2050 requires additions of ~20 GW/year in 2011‐20

in 2021‐2040, and ~40 GW/year in 2041‐2050 (higher under High‐Deman

• These installation rates are higher than U.S. capacity additions in 2010 (7 

GW) and would place challenges on RE industries.

• Recent U.S. and worldwide growth demonstrate the scalability of RE indu

• More informed siting practices and regulations can reduce industry scale

80% RE‐ITI scenario
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With higher demand growth, high levels of renewable 

present increased resource and grid integration challe

• Higher demand growth generally implies an increased need for new gene

transmission capacity in both the baseline and 80% RE scenarios.

• More renewable generation capacity, particularly wind and PV, is needed

greater industry scale‐up and resource access challenges.

• Additional flexible supply‐ and demand‐side capacity (e.g., storage, natur

turbine power plants, and interruptible load) is also needed.

• While higher demand growth shows greater increases in electricity prices

incremental cost associated with high renewable generation levels decrea

baseline also increase).

• Cost‐effectiveness of energy efficiency vs. supply‐side options was not ev
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Future Work Needed• A comprehensive cost‐benefit analysis is necessary in order to b

the economic and environmental implications of high renewabl

futures relative to today’s electricity system. Today’s system is 

conventional technologies and alternative futures in which othe

energy are deployed at scale.

• Further investigation of the more complete set of issues around 

power system reliability is needed because RE Futures only part

implications of high penetrations of renewable energy for syste

• Improved understanding of the institutional challenges associat

integration of high levels of renewable electricity, including dev

market mechanisms that enable the emergence of flexible techand mitigate market risks for a range of stakeholders, including 

developers, is important.

• Analysis of the role and implications of energy research and dev

activities in accelerating technology advancements and in broad

portfolio of economically viable future renewable energy supply 

supply‐ and demand‐side flexibility tools is essential.
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Summary of Key Results• Renewable electricity generation from technologies that are com

available today, in combination with a more flexible electric sys

adequate to supply 80% of total U.S. electricity generation in 20

meeting electricity demand on an hourly basis in every region o

• Increased electric system flexibility, needed to enable electricity 

balance with high levels of renewable generation, can come fro

supply‐ and demand‐side options, including flexible convention

storage, new transmission, more responsive loads, and changes 

operations.

• The abundance and diversity of U.S. renewable energy resource

multiple combinations of renewable technologies that result in 

in electric sector greenhouse gas emissions and water use.

• The direct incremental cost associated with high renewable gen

comparable to published cost estimates of other clean energy s

Improvement in the cost and performance of renewable techno

impactful lever for reducing this incremental cost.
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A future U.S. electricity system that is largely powe

renewable sources is possible, and further work is w

investigate this clean generation pathway.

www.nrel.gov/RE_Futures