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.

Renewable Electricity Futures

Trieu Mai, Ph.D.

Wind Powering America Webinar

August 15, 2012

NREL/PR-6A20-56118

Renewable Electricity Futures Study (2012). Hand, M.M.; Baldwin, S.; DeMeo, E.; Reilly, J.M.; Mai, T.; Arent, 

D.; Porro, G.; Meshek, M.; Sandor, D., editors. Lead authors include Mai, T.; Sandor, D.; Wiser, R.; Heath, G.; 

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

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

A U.S. DOE-sponsored collaboration among more than 110 individuals from 35 organizations.
WWW.NREL.GOV/RE_FUTURES 2

• RE is a low carbon, low air pollutant, low fuel use, low water 

use, domestic, and sustainable electricity source. 

• To what extent can renewable energy technologies 

commercially available today meet the U.S. electricity 

demand over the next several decades?

Renewable Electricity Futures Motivation

RE Capacity Growth 2000-2010

Source: RE Data Book (DOE 2011) Source: RE Data Book (DOE 2011)
WWW.NREL.GOV/RE_FUTURES 3

Summary of Key Results

• Renewable electricity generation from technologies that are commercially 

available today, in combination with a more flexible electric system, is more than 

adequate to supply 80% of total U.S. electricity generation in 2050–while 

meeting electricity demand on an hourly basis in every region of the country.

• Increased electric system flexibility, needed to enable electricity supply-demand 

balance with high levels of renewable generation, can come from a portfolio of 

supply- and demand-side options, including flexible conventional generation, grid 

storage, new transmission, more responsive loads, and changes in power system 

operations.

• The abundance and diversity of U.S. renewable energy resources can support 

multiple combinations of renewable technologies that result in deep reductions 

in electric sector greenhouse gas emissions and water use.

• The direct incremental cost associated with high renewable generation is 

comparable to published cost estimates of other clean energy scenarios. 

Improvement in the cost and performance of renewable technologies is the most 

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

on 2050 that explores:

o Whether the U.S. power system can supply electricity to 

meet customer demand with high levels of renewable 

electricity, including variable wind and solar generation.

o Grid integration using models with unprecedented 

geographic and time resolution for the contiguous U.S.

o Synergies, constraints, and operational issues associated 

with a transformation of the U.S. electric sector.

Renewable Electricity Futures Introduction
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Renewable Electricity Futures Report

REF is a U.S. DOE-sponsored collaboration with more than 110 

contributors from 35 organizations including national laboratories, 

industry, universities, and non-governmental organizations.

Volume 1 Exploration of High-Penetration Renewable Electricity Futures

Volume 2 Renewable Electricity Generation and Storage Technologies

Volume 3 End-Use Electricity Demand

Volume 4 Bulk Electric Power Systems: Operations and Transmission Planning
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Renewable Electricity Futures Introduction

RE Futures does.... RE Futures does not...

Identify 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 operating 

procedures, evolved business models, or 

market rules that could facilitate high levels

of RE generation.

Identify electric sector characteristics 

associated with high levels of RE generation.

Fully evaluate power system reliability.

Explore a variety of high renewable 

electricity generation scenarios. 

Forecast or predict the evolution of the 

electric sector.

Estimate the associated U.S. electric sector 

carbon emissions reductions.

Assess optimal pathways to achieve a lowcarbon electricity system.

Explore a select number of economic, 

environmental and social impacts.

Conduct a comprehensive cost-benefit 

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 their 

implications.

Provide a definitive assessment of high RE 

generation, but does identify areas for

deeper investigation.
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Modeling Framework

Technology cost & 

performance

Resource availability

Demand projection

Demand-side 

technologies

Grid operations

Transmission costs

Black & Veatch

Technology Teams

Flexible Resources

End-Use Electricity

System Operations

Transmission

ABB inc.

GridView

(hourly production cost)

rooftop PV

penetration

2050 mix

of generators

does it balance

hourly?

Implications 

GHG Emissions

Water Use

Land Use

Direct Costs

Capacity & Generation 

2010-2050
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Scenario Framework
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General Assumptions

• Energy Efficiency: Most of the scenarios assumed significant adoption of energy efficiency 

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

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

petroleum and toward electricity in the form of plug-in hybrid or electric vehicles, partially 

offsetting the electricity efficiency advances that were considered.

• Grid Flexibility: Most scenarios assumed improvements in electric system operations to enhance 

flexibility in both electricity generation and end-use demand, helping to enable more efficient 

integration of variable-output renewable electricity generation.

• Transmission: Most scenarios expanded the transmission infrastructure and access to existing 

transmission capacity to support renewable energy deployment. Distribution-level upgrades were 

not considered. 

• Siting and Permitting: Most scenarios assumed project siting and permitting regimes that allow 

renewable electricity development and transmission expansion with standard land-use exclusions.
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Renewable Resources and Technologies

• Only currently commercial technologies were modeled (no enhanced geothermal, 

ocean, or floating wind systems) with incremental and evolutionary improvements.

• RE characteristics including location, technical resource potential, and grid output 

characteristics were considered.

Biopower ~100 GW

Solar CSP ~37,000 GW

Geothermal ~36 GW

Hydropower ~200 GW

Solar PV ~80,000 GW

(rooftop PV ~700 GW)

Wind ~10,000 GW

•Stand-alone

•Cofired with coal 

•Trough

•Tower

•Hydrothermal

•Run-of-river

•Residential

•Commercial

•Utility-scale

•Onshore

•Offshore fixed-bottom

With thermal

storage
Key Results
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A Transformation of the U.S. Electricity System

RE generation from technologies that are commercially available 

today, in combination with a more flexible electric system, is 

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

generation in 2050—while meeting electricity demand on an 

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% RE40% RE50% RE60% RE70% RE80% RE90% RE

% of Total Generated Electricity

Percent RE

Wind

PV

CSP

Hydropower 

Geothermal

Biomass

Natural Gas

Coal

Nuclear

Variable 

Generation

Renewable generation resources could adequately supply 80% of total U.S. 

electricity generation in 2050 while balancing hourly supply and demand

Baseline scenario 80% RE-ITI scenario

RE-ITI scenarios
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The abundance and diversity of RE resources can support multiple 

combinations of RE technologies to provide 80% generation by 2050

• Technology deployment depends on scenario assumptions, but in all cases examined, RE 

resources existed to compensate for assumed variations in access to transmission, grid 

flexibility, resource availability, technology costs, and electricity demand.

• Constraints to transmission result in greater PV, offshore wind, and biopower deployment.

• Constraints to system flexibility result in greater dispatchable technology deployment, e.g., 

storage and CSP with thermal storage.

• Constraints to resource accessibility result in greater wind and solar deployment.

Low-Demand ranges 

encompass results for 

Technology Improvement and 

Constrained scenarios 
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All regions of the country could contribute substantial renewable 

electricity supply in 2050

80% RE-ITI scenario
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Power (GW)

Date

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Power (GW)

Date

Curtailment

Wind

PV

Gas CT

Gas CC

Hydropower

CSP

Biopower

Coal

Geothermal

Nuclear

Shifted Load

Load

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Apr-27 00:00Apr-27 12:00Apr-28 00:00Apr-28 12:00Apr-29 00:00Apr-29 12:00Apr-30 00:00Apr-30 12:00

Power (GW)

Date

Curtailment

Wind

PV

Gas CT

Gas CC

Hydropower

CSP

Biopower

Coal

Geothermal

Nuclear

Shifted Load

Load

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Power (GW)

Date

Electricity supply and demand can be balanced in every hour of the 

year in each region with 80% electricity from renewable resources*

80% RE-ITI scenario

*Full reliability analysis not conducted in RE Futures

Baseline scenario

Peak →

Off-Peak → 
WWW.NREL.GOV/RE_FUTURES 17

A more flexible electric power system is needed to enable electricity supplydemand balance with high levels of RE generation

• Maintaining sufficient capacity on the system for planning reserves

• Relying on demand-side interruptible load, conventional generators 

(particularly natural gas generators), and storage to manage increased 

operating requirements

• Mitigating curtailment with storage and controlled charging of electric 

vehicles 

• Operating the system with greater conventional power plant ramping

• Relying on the dispatchability of certain renewable technologies (e.g., 

biopower, geothermal, CSP with storage and hydropower)

• Leveraging the geospatial diversity of the variable resources to smooth 

output ramping

• Transmitting greater amounts of power over longer distances to smooth 

electricity demand profiles and meet load with remote generation

• Coordinating bulk power system operations across wider areas.

System flexibility can be increased using a broad portfolio of supply- and demand-side 

options, including:
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Firm capacity provided by some RE generators, 

conventional generators, and storage

Installed capacity is sufficient to meet summer afternoon peak demand from 

diverse reserves

0

200

400

600

800

1,000

1,200

1,400 Installed Capacity (GW)

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

• Operational challenges for high renewable scenarios are most acute during lowdemand periods (e.g., spring).

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

curtailment of excess renewable generation (8-10% of wind, solar, and 

hydropower curtailed in 2050).

• Storage and demand-side options (e.g. PHEV charging) can help shift loads to 

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

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 infrastructure is 

required

• In most 80%-by-2050 RE scenarios, 110-190 million MW-miles of new transmission lines are added.

• AC-DC-AC interties are expanded to allow greater power transfer between asynchronous interconnects.

• However, 80% RE is achievable even when transmission is severely constrained (30 million MW-miles)—

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 scenarios range from 

B$5.7-8.4/year, which is within the range of recent total investor-owned utility transmission 

expenditures.

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

losses.

80% RE-ITI scenario
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High renewable electricity futures can result in deep reductions in electric 

sector greenhouse gas emissions and water use

80% RE scenarios lead to: 

~80% reduction in 2050 generation from both coal-fired and natural gas-fired sources

~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 ecosystem concerns

0

5

10

15

20

25

2010 2020 2030 2040 2050

Annual Electric Sector Consumption 

(Quads)

Year

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

Baseline (NG) Baseline (coal)

Gross Land Use Comparisons 

(000 km2) 

Biomass 44-88

All Other RE 52-81

All Other RE (disrupted) 4-10

Transmission & Storage 3-19

Total Contiguous U.S. 7,700

2009 Corn Production* 350

Major Roads** 50

Golf Courses ** 10

80% RE scenarios

* USDA 2010, **Denholm & Margolis 2008
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Incremental cost associated with high RE generation is comparable to 

published cost estimates of other clean energy scenarios

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

EPA

• Reflects replacement of existing generation plants with new generators and additional balancing 

requirements (combustion turbines, storage, and transmission) compared to baseline scenario 

(continued evolution of today’s conventional generation system)

• Assumptions reflect incremental or evolutionary improvements to currently commercial RE 

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

$0

$20

$40

$60

2010 2020 2030 2040 2050

Real 2009$/MWh

Core 80% RE (ReEDS) EIA 2009c

EPA 2009a EIA 2010b

EPA 2010 EIA 2011a

EIA 2011b

Increase in retail electricity price relative to reference/baseline

Source: Renewable Electricity Futures (2012) 
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• Cost is less sensitive to the assumed electric system constraints (transmission, flexibility, RE 

resource access).

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

prices and fossil technology improvements.

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

shows no incremental cost relative to the baseline scenario). 

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

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 $10 $20

Higher Fossil Fuel

High Demand

Difference in 2050 Electricity Price 

Relative to Baseline (low-demand, ITI)

[Real 2009$/MWh] 

Lower Fossil Fuel

Fossil-HTI

Improvement in cost and performance of RE technologies is the most 

impactful lever for reducing the incremental cost
WWW.NREL.GOV/RE_FUTURES 24

No insurmountable long-term constraints to RE technology manufacturing 

capacity, materials supply, or labor availability were identified

• 80% RE generation in 2050 requires additions of ~20 GW/year in 2011-2020 , ~30/GW/year 

in 2021-2040, and ~40 GW/year in 2041-2050 (higher under High-Demand scenario).

• These installation rates are higher than U.S. capacity additions in 2010 (7 GW) and 2009 (11 

GW) and would place challenges on RE industries.

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

• More informed siting practices and regulations can reduce industry scale-up challenges.

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

present increased resource and grid integration challenges

• Higher demand growth generally implies an increased need for new generation and 

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

• More renewable generation capacity, particularly wind and PV, is needed; it will result in 

greater industry scale-up and resource access challenges. 

• Additional flexible supply- and demand-side capacity (e.g., storage, natural gas combustion 

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

• While higher demand growth shows greater increases in electricity prices, the direct 

incremental cost associated with high renewable generation levels decreases (the prices in 

baseline also increase).

• Cost-effectiveness of energy efficiency vs. supply-side options was not evaluated.
WWW.NREL.GOV/RE_FUTURES 26

Future Work Needed

• A comprehensive cost-benefit analysis is necessary in order to better understand 

the economic and environmental implications of high renewable electricity 

futures relative to today’s electricity system. Today’s system is largely based on 

conventional technologies and alternative futures in which other sources of clean 

energy are deployed at scale.

• Further investigation of the more complete set of issues around all aspects of 

power system reliability is needed because RE Futures only partially explores the 

implications of high penetrations of renewable energy for system reliability.

• Improved understanding of the institutional challenges associated with the 

integration of high levels of renewable electricity, including development of 

market mechanisms that enable the emergence of flexible technology solutions 

and mitigate market risks for a range of stakeholders, including project 

developers, is important.

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

activities in accelerating technology advancements and in broadening the 

portfolio of economically viable future renewable energy supply options and 

supply- and demand-side flexibility tools is essential. 
WWW.NREL.GOV/RE_FUTURES 27

Summary of Key Results

• Renewable electricity generation from technologies that are commercially 

available today, in combination with a more flexible electric system, is more than 

adequate to supply 80% of total U.S. electricity generation in 2050–while 

meeting electricity demand on an hourly basis in every region of the country.

• Increased electric system flexibility, needed to enable electricity supply-demand 

balance with high levels of renewable generation, can come from a portfolio of 

supply- and demand-side options, including flexible conventional generation, grid 

storage, new transmission, more responsive loads, and changes in power system 

operations.

• The abundance and diversity of U.S. renewable energy resources can support 

multiple combinations of renewable technologies that result in deep reductions 

in electric sector greenhouse gas emissions and water use.

• The direct incremental cost associated with high renewable generation is 

comparable to published cost estimates of other clean energy scenarios. 

Improvement in the cost and performance of renewable technologies is the most 

impactful lever for reducing this incremental cost.
WWW.NREL.GOV/RE_FUTURES 28

A future U.S. electricity system that is largely powered by 

renewable sources is possible, and further work is warranted to 

investigate this clean generation pathway.

www.nrel.gov/RE_Futures