The Challenge of the Last Few Percent: Quantifying the Costs & Emissions Benefits of a 100% Renewable U.S. Electricity System
Only two decades ago, some scientists were skeptical we could integrate more than about 20% renewable energy generation on the U.S. power grid. But we hit that milestone in 2020 — so, these days, experts’ sights are set on finding pathways toward a fully renewable national power system. And according to new research published in Joule, the nation could get a long way toward 100% cost-effectively; it is only the final few percent of renewable generation that cause a nonlinear spike in costs to build and operate the power system.
In “Quantifying the Challenge of Reaching a 100% Renewable Energy Power System for the United States,” analysts from the U.S. Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL) and DOE’s Office of Energy Efficiency and Renewable Energy (EERE) evaluate possible pathways and quantify the system costs of transitioning to a 100% renewable power grid for the contiguous United States. The research was funded by EERE’s Strategic Analysis Team.
“Our goal was to robustly quantify the cost of a transition to a high-renewable power system in a way that provides electric-sector decision-makers with the information they need to assess the cost and value of pursuing such systems,” said Wesley Cole, NREL senior energy analyst and lead author of the paper.
Expanding on previous work to simulate the evolution of the U.S. power system at unprecedented scale, the authors quantify how various assumptions about how the power system might evolve can impact future system costs. They show how costs can increase nonlinearly for the last few percent toward 100%, which could drive interest in non-electric-sector investments that accomplish similar decarbonization objectives with a lower total tab.
“Our results highlight that getting all the way to 100% renewables is really challenging in terms of costs, but because the challenge is nonlinear, getting close to 100% is much easier,” Cole said. “We also show how innovations such as lower technology costs, or alternate definitions for 100% clean energy such as including nuclear or carbon capture, can lower the cost of reaching the target.”
Advanced Methods Expand Our Understanding of High-Renewable Grids
This work builds on another Joule article released last month exploring the key unresolved technical and economic challenges in achieving a 100% renewable U.S. electricity system. While some aspects of 100% renewable power grids are well established, there is much we do not know. And because 100% renewable grids do not exist at the scale of the entire United States, we rely on models to evaluate and understand possible future systems.
“With increasing reliance on energy storage technologies and variable wind and solar generation, modeling 100% renewable power systems is incredibly complex,” said Paul Denholm, NREL principal energy analyst and coauthor of the paper. “How storage was used yesterday impacts how it can be used today, and while the resolution of our renewable resource data has improved tremendously in recent years, we can’t precisely predict cloudy weather or calm winds.”
Integrated energy pathways modernizes our grid to support a broad selection of generation types, encourages consumer participation, and expands our options for transportation electrification.
Many prior studies have modeled high-renewable electricity systems for a variety of geographies, but not many examine the entire U.S. grid. And even fewer studies attempt to calculate the cost of transitioning to a 100% renewable U.S. grid — instead, they typically present snapshots of systems in a future year without considering the evolution needed to get there. This work expands on these prior studies with several important advances.
First, the team used detailed production cost modeling with unit commitment and economic dispatch to verify the results of the capacity expansion modeling performed with NREL’s publicly available Regional Energy Deployment System (ReEDS) model. The production cost model is Energy Exemplar’s PLEXOS, a commercial model widely used in the utility industry.
“Over the past couple of years we put a tremendous amount of effort into our modeling tools to give us confidence in their ability to capture the challenges inherent in 100% renewable energy power systems,” Cole said. “In addition, we also tried to consider a broad range of future conditions and definitions of the 100% requirement. The combination of these efforts enables us to quantify the cost of a transition to a 100% clean energy system far better than we could in the past.”
The analysis represents the power system with higher spatial and technology resolution than previous studies in order to better capture differences in technology types, renewable energy resource profiles, siting and land-use constraints, and transmission challenges. The analysis also uniquely captures the ability to retrofit existing fossil plants to serve needs under 100% renewable scenarios and assesses whether inertial response can be maintained in these futures.
What Drives System Costs? Transition Speed, Capital Costs, and How We Define 100%
The team simulated a total of 154 different scenarios for achieving up to 100% renewable electricity to determine how the resulting system cost changes under a wide range of future conditions, timeframes, and definitions for 100% — including with systems that allow nonrenewable low-carbon technologies to participate.
“Here we use total cumulative system cost as the primary metric for assessing the challenge of increased renewable deployment for the contiguous U.S. power system,” said Trieu Mai, NREL senior energy analyst and coauthor of the paper. “This system cost is the sum of the cost of building and operating the bulk power system assets out to the year 2050, after accounting for the time value of money.”
To establish a reference case for comparison, the team modeled the system cost at increasing renewable energy deployment for base conditions, which use midrange projections for factors such as capital costs, fuel prices, and electricity demand growth. Under these conditions, the least-cost buildout grows renewable energy from 20% of generation today to 57% in 2050, with average levelized costs of $30 per megawatt-hour (MWh). Imposing a requirement to achieve 100% renewable generation by 2050 under these same conditions raises these costs by 29%, or less than $10 per MWh. System costs increase nonlinearly for the last few percent approaching 100%
Associated with the high renewable energy targets are substantial reductions in direct carbon dioxide (CO2) emissions. From the 57% least-cost scenario, the team translated the changes in system cost and CO2 emissions between scenarios into an average and incremental levelized CO2 abatement cost. The average value is the abatement cost relative to the 57% scenario, while the incremental value is the abatement cost between adjacent scenarios, e.g., between 80% and 90% renewables. In other words, the average value considers all the changes, while the incremental value considers only the change over the most recent increment.
Total bulk power system cost at a 5% discount rate (left) for the seven base scenarios and levelized average and incremental CO2 abatement cost (right) for those scenarios. The 2050 renewable (RE) generation level for each scenario is listed on the x-axis. The system costs in the left figure are subdivided into the four cost categories listed in the figure legend (O&M = operations and maintenance). The purple diamond on the y-axis in the left plot indicates the system cost for maintaining the current generation mix, which can be used to compare costs and indicates a system cost comparable to the 90% case.
Total bulk power system cost at a 5% discount rate (left) for the seven base scenarios and levelized average and incremental CO2 abatement cost (right) for those scenarios. The 2050 renewable (RE) generation level for each scenario is listed on the x-axis. The system costs in the left figure are subdivided into the four cost categories listed in the figure legend (O&M = operations and maintenance). The purple diamond on the y-axis in the left plot indicates the system cost for maintaining the current generation mix, which can be used to compare costs and indicates a system cost comparable to the 90% case. NREL
Notably, incremental abatement costs from 99% to 100% reach $930/ton, driven primarily by the need for firm renewable capacity — resources that can provide energy during periods of lower wind and solar generation, extremely high demand, and unplanned events like transmission line outages. In many scenarios, this firm capacity was supplied by renewable-energy-fueled combustion turbines, which could run on biodiesel, synthetic methane, hydrogen, or some other renewable energy resource to support reliable power system operation. The DOE Energy Earthshots Initiative recently announced by Secretary of Energy Jennifer M. Granholm includes the Hydrogen Shot, which seeks to reduce the cost of clean hydrogen by 80% to $1 per kilogram in one decade — an ambitious effort that could help reduce the cost of providing renewable firm capacity.
“When achieving a 100% renewable system, the costs are significantly lower if there is a cost-effective source of firm capacity that can qualify for the 100% definition,” Denholm said. “The last few percent cannot cost-effectively be satisfied using only wind, solar, and diurnal storage or load flexibility — so other resources that can bridge this gap become particularly important.”
Capital costs are the largest contributor to system costs at 100% renewable energy. Future changes in the capital costs of renewable technologies and storage can thus greatly impact the total system cost of 100% renewable grids. The speed of transition is also an important consideration for both cost and emission impacts. The scenarios with more rapid transitions to 100% renewable power were more costly but had greater cumulative emissions reductions.
“Looking at the low incremental system costs in scenarios that increase renewable generation levels somewhat beyond the reference solutions to 80%–90%, we see considerable low-cost abatement opportunities within the power sector,” Mai said. “The trade-off between power-sector emissions reductions and the associated costs of reducing those emissions should be considered in the context of non-power-sector opportunities to reduce emissions, which might have lower abatement costs — especially at the higher renewable generation levels.”
“The way the requirement is defined is an important aspect of understanding the costs of the requirement and associated emissions reduction,” Cole said. “For instance, if the 100% requirement is defined as a fraction of electricity sales, as it is with current state renewable polices, the cost and emissions of meeting that requirement are similar to those of the scenarios that have requirements of less than 100%.”
Additional Research Can Help the Power Sector Understand the Path Forward
While this work relies on state-of-the-art modeling capabilities, additional research is needed to help fill gaps in our understanding of the technical solutions that could be implemented to achieve higher levels of renewable generation, and their impact on system cost. Future work could focus on key considerations such as the scaling up supply chains, social or environmental factors that could impact real-world deployment, the future role of distributed energy resources, or how increased levels of demand flexibility could reduce costs, to name a few.
“While there is much left to explore, given the energy community’s frequent focus on using the electricity sector as the foundation for economy-wide decarbonization, we believe this work extends our collective understanding of what it might take to get to 100%,” Cole said.
Learn more about NREL’s energy analysis and grid modernization research.
Article courtesy of the NREL, the U.S. Department of Energy
Global renewable developer and energy giant RWE has halted its US offshore wind operations “for the time being” because of the “political environment” the Trump administration has created.
RWE, Germany’s biggest electricity producer, said in March that it had dialed back its US offshore wind activities. But now, CEO Marcus Krebber said in a speech transcript, which he’ll deliver at the company’s Annual General Meeting in Essen on April 30, that its US offshore wind business is now closed (but it wasn’t all bad news):
In the US, where we have stopped our offshore activities for the time being, our business in onshore wind, solar energy, and battery storage has so far been developing very dynamically. At the start of this year, we reached an important milestone when our US generation capacity hit the 10 gigawatt mark. The construction of a further 4 gigawatts is secured.
He went on to say that renewables have created regional value and jobs, but that the company remains “cautious given the political developments.” RWE has introduced more stringent requirements for future US investments:
All necessary federal permits must be in place. Tax credits must be safe harbored and all relevant tariff risks mitigated. In addition, onshore wind and solar projects must have secured offtake at the time of the investment decision. Only if these conditions are met will further investments be possible, given the political environment.
About half of RWE’s installed renewable capacity is in the US, where it’s the third-largest renewable energy company through its subsidiary, RWE Clean Energy. RWE holds the rights to develop US offshore wind projects in New York, Louisiana, and California.
RWE paid $1.1 billion for the New York lease area in 2022, where it’s meant to develop the 3 gigawatt (GW) Community Offshore Wind with the UK’s National Grid. Community Offshore Wind was projected to come online in the early 2030s and expected to power more than a million homes.
The developer paid $5.6 billion for the Louisiana lease in the Gulf of Mexico in 2023 as the lone bidder for development rights, and the Canopy Offshore Wind project off Northern California was not expected to be completed for another decade.
Read more: Trump admin halts $5 billion NY offshore wind project mid-build
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It’s that time of year again, time for events across the country to show off electric vehicles at Drive Electric Earth Month.
Drive Electric Earth Month is an offshoot of Drive Electric Week, a long-running annual tradition hosting meetups mostly in the US, but also occasionally in other countries. It started as Drive Electric Earth Day, but since not every event can happen on the same day, they went ahead and extended it to encompass “Earth Month” events that happen across the month of April. It’s all organized by Plug In America, the Sierra Club, the Electric Vehicle Association, EV Hybrid Noire, and Drive Electric USA.
Events consist of general Earth Day-style community celebrations, EV Ride & Drives where you can test drive several EVs in one place, and opportunities to talk to EV owners and ask them questions about what it’s like to live with an EV, away from the pressure of a dealership.
This month, there are 158 events registered across the US and 1 in Mexico (including one online webinar about things to consider when purchasing an EV).
Events have been happening all month, but the biggest weekend is this upcoming one, APril 26-27.
One really neat event was the Asheville event, which showcased the resiliency of EVs in an area devastated by Hurricane Helene, which was made more severe by climate change. That event was attended by the Rivian R1T which famously got dragged 100 feet submerged in mud and came out running fine.
But the bulk of the events happened on the weekends surrounding Earth Day, April 22, so there were several last weekend and will be even more this upcoming weekend.
There are plenty of events in the big cities where you’d expect, but Plug In America wanted to highlight a few of the events in smaller places around the country. Here’s a sampling of upcoming events:
- Big Island EV – Cruise and Picnic in Waimea, HI on April 26, 10am-1pm – EV drivers will congregate in various places around the Big Island (Kona, Waimea, Waikoloa and Hilo), then drive up Saddle Road to the Gil Kahele Recreation Area on Mauna Kea for a potluck and a chance to talk about the experience of owning EVs on the Big Island.
- Santa Barbara Earth Day 2025 and Green Car Show in Santa Barbara, CA on April 26-27, 11am-8pm – This is part of Santa Barbara’s Earth Day celebration, which routinely attracts 30,000 participants and is one of the longest-running Earth Day celebrations on the planet. The Green Car Show includes ride & drives and an “Owners Corner” where owners can showcase their EVs and attendees can check them out and ask questions.
- Earth Day’25 – EV’s role in a sustainable future in Queretaro City, Mexico on April 26, 9am-4pm – The sole Mexican event, this is a combined in-person/online seminar at the Querétaro Institute of Technology.
- Norman Earth Day Festival in Norman, OK on April 27, 12-5pm – Another municipal Earth Day festival, with hands-on activities for kids to learn about the environment. A portion of the parking lot reserved for an EV car show for EV owners who pre-register to show off their vehicles.
- Oregon Electric Vehicle Association Test Drive & Information Expo in Portland, OR on April 27, 10am-4pm – This one is at Daimler Truck’s North American HQ, and will have several EVs for test drives, owner displays (including DIY gas-to-EV conversions), and keynote presentations by EV experts. They’ll even have a 1914 Detroit Electric EV available for test rides!
- And, we at Electrek want to give a shoutout to Rove’s EV Drive Days in Santa Ana 10am-3pm April 28 – ROVE is the company behind the “full-service” EV charging concept that we’ve talked about several times here on Electrek, and we like what they’re doing for EV charging. They’ve hosted a few community events, and this is their contribution to Earth Month.
Each event has a different assortment of activities (e.g. test drives won’t be available at every event, generally just the larger ones attended by local dealerships), so be sure to check the events page to see what the plan is for your local event.
These events have offered a great way to connect with owners and see the newest electric vehicle tech, and even get a chance to do test rides and drives in person. Attendees got to hear unfiltered information from actual owners about the benefits and trials of owning EVs, allowing for longer and more genuine (and often more knowledgeable) conversations than one might normally encounter at a dealership.
And if you’re an owner – you can show off your car and answer those questions for interested onlookers.
To view all the events and see what’s happening in your area, you can check out the list of events or the events map. You can also sign up to volunteer at your local events, and if you plan to show off your electric car, you can RSVP on each event page and list the vehicle that you plan to show (or see what other vehicles have already registered).
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