A Decade of Transformation: What We Have Learned Since RE Futures Showed What Was Possible
Ten Years After Visionary Renewable Electricity Futures Study Showed an 80% Renewable U.S. Grid Was Possible, NREL Experts Recount How They Have Built on Those Findings in the Decade Since—and What Is Next
June 6, 2022 | By Madeline Geocaris | Contact media relations
The year is 2012.
Wind generation is expanding rapidly in some regions of the United States. Still, wind and solar combined generate less than 3% of the U.S. electricity supply. Natural gas has reached record-low prices, and nearly 25 gigawatts of coal plants will retire over the next two years.
Energy demand and greenhouse gas emissions from the energy sector are increasing, but much of the world has not imagined a clean, renewable-based power grid. Until July of that year.
The National Renewable Energy Laboratory (NREL) released the Renewable Electricity Futures Study, or “RE Futures”—the most comprehensive analysis of a high-renewable U.S. power system at that time.
Results showed the nation’s abundant and diverse renewable energy resources could feasibly, both technically and economically, supply 80% of U.S. electricity in 2050—with a significant fraction from wind and solar. As modeled, the power system could successfully balance supply and demand every hour of the day, in every region—marking a new era in NREL's power grid analysis.
Groundbreaking Findings: A Shift in the Clean Energy Narrative
With funding from the U.S. Department of Energy (DOE), more than 110 experts from 35 organizations came together to explore whether a future U.S. power system with very high levels of renewable electricity generation was possible.
Using its now-publicly available Regional Energy Deployment System (ReEDS) model, NREL explored future power system scenarios at then unprecedented geographic and time resolution, with renewable generation levels ranging from 30% to 90%—focusing on 80%.
"We had been thinking for a while about how we could get to very high levels of renewable energy in our power sector analysis," said Sam Baldwin, chief science officer at DOE's Office of Energy Efficiency & Renewable Energy, who came up with the idea for RE Futures and supported the study from beginning to end. "Studies at the time looked at renewable energy technologies individually, but that didn't consider the natural synergies between solar and wind and other resources like bioenergy, hydropower, and geothermal. It was incredibly fortunate that we had such an outstanding team of researchers across the entire renewable energy and energy efficiency community work on the study."
RE Futures' groundbreaking findings, published across four volumes, not only showed 80% was possible, but also there were many pathways to get there. To make that future a reality would require "a total transformation involving every element of the grid, from system planning through operation."
downloads of RE Futures to date
NREL publications of all time
Greentech Media's Interchange Podcast called RE Futures one of the most impactful pieces of research of the decade: "It was highly influential. … The study changed the narrative around clean energy and guided many studies that followed. It all started with RE Futures."
In the years that followed, NREL has collaborated with diverse organizations in the United States and beyond to explore possible pathways for power grid transformation to 80% or greater renewables—bringing forth new questions, new models, and new data to help find answers. "Over the past decade, our research has largely confirmed the key conclusions from RE Futures and, in some ways, identified that it might have been a conservative snapshot of the future," said Trieu Mai, senior energy analyst at NREL and co-author of the RE Futures study. "From today's vantage point, it will likely be easier to hit 80% renewables—or higher—than what we originally thought."
Here is what NREL's grid analysts have learned in the years since RE Futures.
Clean Energy Costs: Rapid Change Drives a Need for More Consistent Data
After the release of RE Futures, clean energy costs declined much faster than anyone expected.
RE Futures' main scenario assumed a utility-scale solar photovoltaic (PV) system in 2050 would cost between $2,200 and $2,700 per kilowatt. However, by 2020, a utility-scale PV system cost $1,000 per kilowatt.
RE Futures also estimated retail electricity price increases, reaching $29 to $60 per megawatt-hour in 2050 with 80% renewables. Today, studies estimate retail electricity prices of less than $5 per megawatt-hour in 2050 with 80% renewables.
"I don't think anybody really envisioned how quickly many of the technology advances would materialize," said Maureen Hand, NREL project lead of RE Futures and now air resources engineer for the California Air Resources Board.
Clean Energy Costs: RE Futures vs. Actual, 2010–2020
In response to the rapid change, NREL launched a new effort in 2015 with support from DOE to ensure energy analyses use consistent, timely assumptions. Two products came out of the effort.
The Standard Scenarios provided a robust suite of defined scenarios for U.S. power sector evolution through 2050, and the Annual Technology Baseline (ATB) included detailed cost and performance data for renewable and conventional technologies. Together, the free, open-source products offered a standard modeling approach to apply to all power system analyses.
Every year, NREL updates and releases the Standard Scenarios and ATB, which are used by energy analysts, modelers, and industry experts. The ATB has had over 85,000 users from 144 countries to date.
NREL is expanding both the Standard Scenarios and ATB to include a broader range of power sector technologies—and in 2020, the ATB included the transportation sector for the first time, offering a template for other sectors.
Electrification: Increasing Demand Could Fundamentally Change How We Operate the Future Grid
To understand whether a high-renewable power system was feasible, RE Futures analyzed future end-use electricity demand in buildings, transportation, and industrial sectors with increasing population and energy efficiency.
It was one of the few power grid studies at the time to consider flexible loads from plug-in electric vehicles, which made up less than 0.2% of vehicles on the road in 2012. RE Futures assumed 40% of vehicles would be electric in 2050.
Today, EVs have broken into the mass market. Ten percent of new cars globally are electric, with over 1.7 million on U.S. roads as of 2020. By mid-2021, plug-in electric vehicle sales surpassed 2 million for the first time.
To dive deep into the potential impacts of widespread electrification in all U.S. economic sectors—commercial and residential buildings, transportation, and industry—NREL launched the multiyear Electrification Futures Study (EFS) with funding from DOE.
NREL conducted groundbreaking national-scale simulations of U.S. power system hourly operations, costs, and emissions to understand the interactions between electrification, demand-side flexibility, and renewable energy deployment.
In the high electrification scenario—now assuming about 86% of vehicles are electric in 2050—the Electrification Futures Study modeled that electric load increases 67% in 2050 and installed capacity would need to double. Flexible loads from EV charging and operations of end-use equipment in buildings and industry help renewable generation meet new electrified demands and reduce annual emissions.
"Building on RE Futures, the Electrification Futures Study found that all sources of grid flexibility—including transmission and inter-regional power transfers, flexible generation, storage, and demand-side sources of flexibility—will likely be important for efficiently operating a power system with high electrification and high renewable energy deployment," said Caitlin Murphy, senior energy analyst at NREL and co-author of the Electrification Futures study.
Transmission: Unlocking a More Resilient, Flexible Grid
The role of the transmission system in a high-renewable power system was an important consideration in RE Futures.
The three major portions of the U.S. power system—the Western Interconnection, the Eastern Interconnection, and the Electric Reliability Council of Texas—operate virtually independently. Their few connections are aging rapidly and present operational challenges with increasing variable generation—offering an opportunity to modernize the grid.
NREL's foundational Western Wind and Solar Integration Study, released in three phases around the time of RE Futures, examined power system operations of integrating up to 35% wind and solar in large portions of the Eastern and Western Interconnections. The studies concluded that it is technically feasible to accommodate 35% wind and solar with operational changes, including much greater coordination of power system operations across larger geographic areas, scheduling generation on a sub-hourly basis, and increasing utilization of existing transmission.
RE Futures revealed that 80% renewable generation would require additional transmission to ensure power system flexibility—and it is more economical to build out transmission from sites with high-quality wind and solar, than to site wind and solar locations with lower-quality resources but closer to the load.
NREL built on that finding a few years later in the Eastern Renewable Generation Integration Study (ERGIS). Using new high-performance computing capabilities and innovative visualization tools, NREL examined operations of the Eastern Interconnection—the largest power grid in the world—at the five-minute timescale with 30% wind and solar. Results showed the power system could operate at those levels, but flows of power across the Eastern Interconnection could change more rapidly and frequently—requiring greater coordination of regional grid operations.
ERGIS was the capstone of a family of detailed NREL-led grid integration studies of 30%–35% wind and solar, leading to studies with higher levels as U.S. renewable generation has increased.
In 2020, wind produced 8.4% of U.S. electricity, or enough to power more than 31 million homes—tripling since RE Futures was released. Most of the growth has taken place in Midwest and Southwest states, with Iowa, North Dakota, and Kansas generating enough wind and solar power to meet half of their electricity demand. Transmission upgrades have not kept up with the dramatic growth.
To understand the value of strengthening ties between the Eastern and Western grids, NREL launched the Interconnections Seam Study. Using enhanced computational and visualization capabilities first demonstrated in ERGIS, NREL modeled conceptual transmission designs under different scenarios through the year 2038.
"With variable renewable resources becoming a larger share of our nation's electricity supply, the ability to transfer those resources across regions could be incredibly valuable—whether that's in periods of power system stress, like extreme weather, or during a typical day to take advantage of the best available resources," said Greg Brinkman, NREL senior research engineer and co-author of the Interconnections Seam Study and RE Futures.
Results showed that, under all designs and scenarios, uniting the Eastern and Western U.S. electric grids would strengthen the power system's ability to share generation resources and flexibility across regions—providing reliable electricity and seeing cost savings.
And NREL did not just explore expanding transmission across the U.S. grid. NREL took it to the continental level with the North American Renewable Integration Study, which modeled greater power-system coordination across all of North America and between regions within each country through 2050.
As modeled, expanding international transmission would provide up to $30 billion (2018 $US) of net value to the continental power system between 2020 and 2050—increasing power system reliability and enabling exchange of load and renewable generation diversity between regions.
The NREL team has also expanded its grid integration research beyond North America and offered expertise to India, the Philippines, Vietnam, China, and more—even informing country-specific and international clean energy plans.
Today, 70% of U.S. transmission lines are 25 years old or older or at full capacity. RE Futures' emphasis on the need for expanded transmission still rings true, with Congress and regulators at the Federal Energy Regulatory Commission urging to rebuild America's critical infrastructure, including transmission expansion—which could pay for itself multiple times over.
Energy Storage: The Unexpected Player in a Low-Carbon Grid
When RE Futures was released, energy storage was equivalent to 2% of U.S. power capacity, nearly all of which was pumped-storage hydropower.
Still, RE Futures saw energy storage as another potentially important contributor of power system flexibility to support large-scale deployment of wind and solar. The study estimated there could be 152 gigawatts of storage capacity in 2050, with most new storage additions coming from compressed air energy storage and pumped-storage hydropower. Lithium-ion batteries were not on the radar at the time because they averaged nearly $1,200 per kilowatt-hour.
However, lithium-ion battery prices rapidly fell in the subsequent years due to the rise of battery-powered EVs—dropping to about $130 per kilowatt-hour in 2020—and several other storage technologies entered the market. In addition, more instances of power system disruptions due to weather disasters drove a greater focus on maintaining a reliable and resilient power system. Suddenly, storage was poised to play a bigger role than expected.
NREL launched the multiyear Storage Futures Study with support from DOE's Energy Storage Grand Challenge. By adding new storage capabilities to ReEDS, NREL studied how much value storage could provide to the grid and behind the meter, how much could be economically deployed, and how high storage levels might impact power system operations.
Unlike RE Futures, the study focused primarily on the potential of lithium-ion batteries, given their recent and anticipated cost declines with the oncoming proliferation of EVs.
The striking result across the six phases of the Storage Futures Study is that energy storage deployment has the potential to increase significantly—reaching at least five times today's capacity in 2050. These storage levels would enable integrating at least 80% renewables on the U.S. grid. As modeled, lithium-ion batteries will likely continue to dominate near-term deployments, but other technologies like closed-loop pumped hydropower and fuel cells for long-duration storage could become more cost-competitive in the future.
"Each phase of the Storage Futures Study indicated a potential coming wave of energy storage," said Nate Blair, NREL principal investigator of the study. "Overall, we find energy storage could play an important role in a flexible, resilient, low-carbon future grid."
Study results revealed energy storage could not only help the future grid operate more efficiently by meeting peak demand but also increase the use of new and existing transmission lines. At the same time, it could offset the need to build new polluting power plants.
"Since RE Futures, a new framework has emerged for storage deployment," said Paul Denholm, senior energy analyst at NREL and co-author of RE Futures and the Storage Futures Study. "This framework links storage duration with the value of services it can provide to the grid. As shorter-duration storage applications are met and storage costs continue to decline, opportunities for longer-duration storage will grow. In the future, we could see multiday or even seasonal storage."
Although energy storage is still a small fraction of the U.S. power sector today, NREL expects it will likely exceed what RE Futures thought and play an integral role in determining the cost-optimal grid mix of the future.
100% Clean Energy: Setting Sights on a New Target
By 2019, the cost of PV had dropped 71% for distributed PV and 80% for utility-scale PV since RE Futures. The 2 millionth solar PV system was installed in the United States, with an additional million installed by summer 2021. The cost of wind decreased 40% since RE Futures, even as performance improved.
U.S. electricity generation from renewable sources (23%) exceeded coal-fired generation (20%) for the first time in 2019—marking a new era in our energy landscape.
As of December 2020, more than 260 large corporations and 200 cities and counties in the United States pledged to meet 100% of their electricity needs with renewables over the coming decades—including Los Angeles, whose city council announced in 2016 a goal of 100% clean energy by 2045.
To determine data-driven pathways to reach this ambitious goal, the Los Angeles Department of Water and Power partnered with NREL on the Los Angeles 100% Renewable Energy Study (LA100).
NREL scaled up its modeling and analysis capabilities to unprecedented levels. The team ran millions of simulations of future scenarios to evaluate a range of how LADWP's power system could evolve to 100% renewables—while maintaining reliable power for LA customers. The study was the most comprehensive, detailed analysis to date of an entirely renewable-based grid as complex as LA's.
Results showed LA's goal is achievable as soon as 2035 with rapid deployment of wind, solar, and storage technologies this decade—showing it is possible to go even further than RE Futures' then-visionary 80% target. And the same methodology from LA100 can be used for more cities seeking insights on the road to clean and equitable energy futures.
But LA100 also revealed that the most challenging—and costly—part of reaching a fully renewable grid is the final stretch: the last 10%–20% of energy demand that cannot be easily served by wind, solar, and conventional storage, but is crucial to maintaining reliability in the face of extreme events.
A few months after LA100's release, NREL published new research looking at that challenge at the national scale. NREL again used the ReEDS model, now including additional enhancements to quantify how different assumptions about how the power system might evolve can impact future system costs. The results show costs can increase nonlinearly for the last few percent toward 100%, which could drive interest in non-electric-sector investments that achieve similar decarbonization objectives with a lower total tab.
Energy Justice: Ensuring All Communities Reap the Benefits of Cleaner Grids
When RE Futures was published, energy justice had relatively recently emerged as a crosscutting research discipline for NREL, but the underlying challenge had existed for decades.
Power system planning has historically focused on prioritizing costs and efficiency over the experiences of some communities. Vulnerable communities have long endured the negative aspects of energy—like pollution, higher proportional household spending on energy bills, and utility shutoffs—without as many opportunities to access benefits like rooftop solar panels, energy efficiency programs, and well-paying energy jobs. Recently, efforts like the federal government's Justice40 Initiative have built momentum around making sure the benefits of cleaner power systems are delivered broadly to all communities—and this was a critical component of NREL's LA100 study.
In LA, almost 50% of census tracts are designated as disadvantaged. Recognizing this, the city of Los Angeles identified environmental justice as both a key motivation and an intended outcome for the study.
The LA100 study results revealed that while all communities in Los Angeles will share in the benefits of the clean energy transition, improving equity in participation and outcomes requires intentionally designed policies and programs.
The study also revealed the importance of embedding the community in the research process to ensure results reflect local concerns and priorities.
"Every phase of the LA100 study was guided by the LA100 Advisory Group, which included members of LA neighborhood councils, industry, city government, and others," said Jaquelin Cochran, NREL principal investigator of LA100. "We also worked directly with the broader community through one-on-one listening sessions with different environmental justice groups and public outreach events presented in both Spanish and English to ensure Spanish-speaking Angelenos could participate."
After the LA100 study's release, LADWP again joined forces with NREL in 2021 on the new LA100 Equity Strategies project, which picks up where LA100 left off to ensure the city's transition to 100% carbon-free power is equitable.
The project will analyze how to improve or expand LADWP programs to achieve equity for disadvantaged communities, incorporating what community members themselves feel is needed to achieve more equitable outcomes. LA100 Equity Strategies will include a robust community engagement process with the goal of producing community-tailored results.
"NREL's vision means leading an energy transition in which solutions are inclusively designed and benefits are equitably distributed," said Kate Anderson, LA100 Equity Strategies lead at NREL. "With LA100 Equity Strategies, we are continuing our mission-driven work to support communities in becoming active participants in advancing their energy visions."
The Next Decade: Decarbonization Goals Drive Rapid—and Equitable—Clean Energy Deployment
Today, RE Futures' vision of 80% renewable energy for the United States is closer than ever, with ambitious federal emissions-reduction targets and ever-decreasing clean energy costs.
"It's incredible what we can achieve together when we put our minds to it," said Ryan Wiser, co-author of RE Futures and senior scientist at Lawrence Berkely National Laboratory. "RE Futures helped us imagine a U.S. economy powered by clean, renewable energy and gave us the fortitude to pursue the scientific advancements needed to see that vision through. What once seemed far-fetched has become normal as we think about deep, economy-wide decarbonization."
Between RE Futures and 2020, U.S. wind, solar, and geothermal generation increased at an annual compound growth rate of 15%. If we are able to overcome future challenges and this rate continues, wind, solar, and geothermal could produce enough electricity to meet all current U.S. electricity demand by 2035.
As the power system has undergone immense change, NREL has made analytical advances that enable studying future scenarios with greater detail and complexity—answering more questions about the future power grid and earning R&D 100 Awards. ReEDS just surpassed 1,000 external users since it became publicly available in 2019.
"The past decade we have learned a lot about potential energy transition solutions, and falling technology costs have opened the door to new possibilities," said Doug Arent, executive director of strategic public-private partnerships at NREL. "Now we are broadening our scope to the transformational level, focusing on how to increase the speed and scale of clean energy economies around the world through continued research, partnerships, and knowledge sharing."
NREL is accelerating energy system decarbonization both globally through the Net Zero World Initiative and 21st Century Power Partnership and domestically through a variety of initiatives, including Accelerating Clean Energy at Scale. These broad-scale collaborations signal growing readiness to move from theoretical explorations to real-world deployment of clean energy solutions.
While there has been great progress since RE Futures, work still remains.
The energy transition has brought new, critically important questions that were not studied in RE Futures: siting considerations, energy equity concerns, and policy, regulatory, and market design challenges. Plus, there are still several technical considerations that need to be explored for integrating large amounts of renewables, like how to maintain inertia or fault protection on the grid—services that are traditionally supported by conventional generators.
"These are complex, multidisciplinary challenges," Trieu Mai said. "These questions will require more collaboration and next-level power grid analysis over the coming decade. Just imagine the next decade of breakthroughs."