In the middle of the night, while America sleeps, the energy system never stops.
An alarm clock blinks. A street light flickers. Hospital monitors beep. A water treatment plant pumps clean water across the city. Air traffic control towers keep flights moving coast to coast.
Most people never see the system working. They notice it only when it fails.
When a winter storm knocks out power or a heat wave pushes the grid to its limits, energy becomes a matter of security and well-being. Will the lights stay on- Will the water run- Will the hospital have power- In those moments, the invisible system behind daily life is suddenly impossible to ignore.
That system is vast and highly coordinated: Power plants generate electricity, transmission lines carry it across long distances and distribution networks deliver it to homes, schools, hospitals and businesses.
One of the most common ways to measure electricity on that system is the unit of electric power called the megawatt. A megawatt is equal to one million watts and describes the rate at which electricity is produced or consumed. In practical terms, one megawatt can supply enough electricity to power roughly 600 to 1,000 homes, depending on the region and how energy is used.
But the nation's energy future will not be defined by megawatts alone. Keeping the system running - through storms, surges and everyday demands - depends on reliable delivery of electricity, how quickly systems can respond when conditions change and how well different technologies work together when demand rises or disruptions hit.
The future of energy will be built in the spaces between technologies - in how they connect, support one another and respond together.
At the U.S. Department of Energy's (DOE) Argonne National Laboratory, scientists and engineers are working to make the nation's energy system stronger, smarter and more resilient. That means nuclear plants providing steady power, hydropower ramping up in seconds, batteries responding in an instant and a grid that ties it all together. Their work is shaping a future where the energy we depend on is there when we need it most, whether we notice it or not.
Nuclear: The Steady Backbone
Among those interconnected technologies, nuclear provides something the energy system cannot do without: steady, around-the-clock power.
Unlike resources that fluctuate with conditions, nuclear plants are built to run continuously for long stretches of time. In the U.S., nuclear energy supplies about 19% of the nation's electricity. In Illinois, that share is even higher - about 53% of the electricity generated in the state. As demand rises and the overall system becomes more complex, dependable generation helps hold everything together.
"People don't always realize how much of daily life depends on power that is simply there when you need it," said Argonne Nuclear Engineer Amanda Bachmann. "That kind of consistency is one of nuclear's greatest strengths."
That reliability is reflected in how consistently nuclear plants are available to generate electricity. The U.S. nuclear fleet operates at an average capacity factor of about 93%, meaning plants generate electricity nearly all the time, shutting down only for refueling and maintenance. For utilities and grid operators, that kind of predictability is invaluable and provides a stable foundation they can count on as other demands across the system change hour by hour.
Its importance also extends far beyond the grid itself.
Nuclear plants are often major employers in the communities around them, especially in rural areas. They support local tax bases, schools and small businesses, and they create jobs that are both long-term and highly skilled. During refueling outages, when plants temporarily bring in additional workers for maintenance and inspections, local economies often see an additional boost.
"It's a lot more than just the megawatts that these plants offer," Bachmann said. "They're also a major source of support for the communities around them."
At Argonne, nuclear research extends across that broader picture. The laboratory has long played a central role in reactor development, with Bachmann noting that nearly every commercial reactor operating today has some connection back to Argonne's work. Today, researchers are helping industry partners advance new reactor designs, improve fuels and materials, study safety systems and analyze the fuel cycle from beginning to end.
Some of that work focuses on one of the most persistent public questions surrounding nuclear power: What happens after the fuel is used-
Today, used nuclear fuel in the U.S. is generally stored safely at the power plant locations where it is used - first in pools, then in sealed dry casks. Argonne researchers are studying whether used fuel could be recycled and reused, what new infrastructure might be required to support future fuel cycles, and how different approaches might affect cost, storage and long-term management.
The lab's nuclear work also reaches beyond electricity generation. Researchers are studying chemical separation methods that can help recover valuable isotopes from used nuclear fuel for medical applications. Some of those isotopes are used in imaging procedures that help doctors diagnose disease, while others support treatments used in cancer care. It is another example of how nuclear science can have an impact far outside the power system, not only keeping electricity flowing but also contributing to technologies that help save lives.
"Nuclear medicine is literally a lifesaver," Bachmann said. "We use these materials in imaging and in cancer care, so it's a powerful example of how nuclear science can improve lives far beyond electricity generation."
Even with its established role in the energy system, nuclear still faces challenges, especially around construction costs, timelines and workforce development. But its value as a stable foundation for the grid remains clear. In a future defined by rising demand and growing complexity, that kind of dependability will be essential.
Hydropower: Flexibility in Motion
If nuclear helps anchor the energy system with steady power, hydropower adds another kind of strength: flexibility.
Hydropower uses moving water to generate electricity, but its value to the U.S. electric system goes beyond how much power it produces. It is one of the grid's most reliable resources and one of the fastest to respond when conditions change. When demand rises, when another source drops unexpectedly, or when the system needs help recovering from an outage, hydropower can ramp up quickly.
"Hydropower is very flexible," said Vladimir Koritarov, director of Argonne's Electric Power Systems department. "You can dispatch it easily and quickly, and because you have storage, you can store water and use it when you need more electricity."
That flexibility matters because not all power plants respond the same way. Some are designed to run steadily over long periods. Hydropower, especially plants with reservoirs, can increase or decrease output much faster. Water stored behind a dam can be held back when demand is lower and released when more electricity is needed. That gives grid operators an important tool for balancing supply and demand throughout the day.
In the U.S., hydropower provides about 6% to 7% of electricity generation, though that can vary depending on how much water is available in a given year. But hydropower's importance is larger than that share alone suggests because of the role it plays in keeping the system balanced and dependable.
Hydropower comes in many forms. Large dams may be the most familiar example, but hydropower also includes smaller facilities, run-of-river plants and pumped storage systems.
At Argonne, much of the laboratory's hydropower work focuses on how to operate these systems as effectively as possible. Researchers model the operation of individual plants, reservoirs and cascaded systems, where water released from one facility affects what happens downstream at the next. Those tools help operators decide when to store water, when to release it and how to coordinate across multiple plants so the resource is used efficiently.
"Our goal is to maximize utilization of water to maximize the generation of electricity," Koritarov said.
Argonne is a leader in pumped storage hydropower (PSH) research, which Koritarov emphasized is especially important because PSH functions as a storage technology. PSH uses two reservoirs at different elevations. When electricity is abundant, water is pumped uphill to the upper reservoir. When electricity is scarce, that water is released back downhill through turbines to generate much needed power. Essentially, the system stores energy by storing water.
That makes PSH especially useful in a grid that increasingly needs flexibility. It allows operators to shift electricity from times of low demand to times of high demand, providing power when and where it's needed most. It can also provide large amounts of stored energy for longer periods than many battery systems. In the U.S., pumped storage can supply about 22 gigawatts of power at once - roughly enough to serve millions of homes - and store about 553 gigawatt-hours of energy, making it one of the country's largest forms of long-duration storage.
"Pumped storage can provide a lot of energy storage and a large amount of dispatchable capacity," Koritarov said. "That is key for the flexible, reliable and affordable operation of the power system."
Argonne's work in this area includes technical studies, cost models and market analysis aimed at understanding where PSH can provide the most value and what is slowing broader adoption. Even as the grid becomes more complex, Koritarov sees hydropower, especially PSH, as essential because it adds something increasingly valuable: the ability to move fast when the system needs it most.
Batteries: The Grid's Multipurpose Tool
If hydropower adds flexibility through water, batteries offer versatility and reliability for the grid.
Batteries store electricity when supply is available and release it when demand exceeds what the grid can supply. They can provide backup power during outages and also help utilities delay expensive upgrades to infrastructure, such as transmission and distribution lines. The objective is straightforward, but there is much complexity in execution. For example, exactly where the storage is placed can make a significant difference in both cost and performance. Batteries have widespread applications across mobility, grid, and in support of other legacy and emerging energy technologies - all of which are crucial to national security.
Sue Babinec, Argonne program lead for stationary storage, says that batteries have become essential to electric grid operation, especially as demand continues to grow and the power mix changes.
"Batteries have two primary roles for the grid," Babinec said. "They make the grid more reliable, and they help enable new sources of electricity."
These needs are growing quickly. Utilities face rising demand from across the economy, including a new category of large, power-hungry users: data centers. Unlike many traditional loads, data centers have high continuous demand around the clock and have very little tolerance for interruption. The challenge is that while new demands are expanding rapidly, building new large-scale generation or upgrading the grid takes years.
"For data centers, the key issue is speed to power," Babinec said. "They need reliable electricity now, but the grid simply cannot grow quickly enough. Batteries can help bridge that gap by enabling firm capacity from intermittent power sources and by ensuring the reliability and quality of power that is essential to data centers."
That kind of flexibility - the ability to store electricity when it is available and deliver it quickly when conditions change - is already changing how parts of the country manage risk. After the severe winter storm that caused widespread outages in Texas in 2021, large-scale battery deployment in the state accelerated. Babinec pointed to that example as a sign of how quickly storage has moved from a promising option to a practical grid tool.
Most batteries used on the grid today are lithium-ion, the same broad technology used in many rechargeable electronics and portable applications. But grid batteries are designed for a different job. Where other applications often prioritize packing as much energy as possible into a compact, lightweight battery, grid storage emphasizes low cost, long life and the ability to charge and discharge reliably over many years.
"For the grid, it has to be low-cost, it has to last for many cycles and many years, and typically the entire capacity will be used every time - day in and day out," Babinec said.
Those requirements are shaping Argonne's battery research when it comes to providing the best solutions for stationary storage. One path is improving lithium-ion batteries by substituting in lower-cost, more abundant materials. Another is sodium-ion batteries, which could build on existing manufacturing methods that are similar to lithium-ion while relying on a more abundant element: sodium. Argonne is also working on the redesign of lead-acid batteries for the grid, as well as longer-duration storage systems that could provide power at very low cost for days rather than hours.
Supply chains are central to that work. Researchers are looking not only at battery performance, but also at where materials come from, what it takes to extract and process them, and whether the U.S. can build enough manufacturing capacity to meet future demand.
"Supply chain is everything today," Babinec said. "It's not enough to develop a battery that works well in the lab. You also have to ask whether the raw materials are available, whether they can be processed economically at scale, and whether the manufacturing base exists to produce the technology where and when it's needed."
Argonne is also researching battery recycling and second-life applications. A battery that no longer meets the performance demands of its first use may still be useful in a stationary grid setting. Reusing or recycling those batteries can help stretch valuable materials further and reduce pressure on new supply.
The lab's work spans battery materials, chemistry and electrochemistry, and makes use of world-class facilities and cutting-edge tools to move promising ideas toward application. Researchers use the Advanced Photon Source, a DOE Office of Science user facility at Argonne and one of the brightest light sources in the world, to study what is happening inside batteries as they operate. They also use the Materials Engineering Research Facility to scale up promising materials and artificial intelligence (AI) to speed materials discovery and battery life prediction.
"We're not here to just do research," Babinec said. "We're here to turn discoveries into something practical and manufacturable so that it can make an impact."
The Grid: Holding it All Together
If batteries can respond in an instant, the U.S. electrical grid is what puts that capability to work across the entire energy system.
For David Sehloff, an Argonne principal energy systems engineer focused on infrastructure systems, the grid is more than a network of wires. It is the system that connects electricity generation, transmission and distribution - moving power from where it is produced to where it is needed. And as demand grows, that system is becoming more complex, more stressed and more essential.
"The grid really touches everything that we rely on in daily life," Sehloff said. "It supports homes, businesses, industry and the infrastructure systems that make modern life possible."
In the U.S., the electric system is not a single machine but a vast network of regional systems, transmission corridors and local distribution lines. It was built to deliver reliable power under changing conditions, but those conditions are shifting. Electricity demand is rising again after years of relatively flat growth. In addition to the load added by data centers, transportation, buildings and industry are becoming more electrified. Grid owners and operators are being asked to plan for all of that while facing uncertainty about how fast new demand will arrive and where it will appear.
That makes planning one of the grid's biggest challenges. Building new transmission takes time - often many years - because of engineering studies, siting, permitting and construction. But waiting too long can leave utilities and communities without the capacity they need. Moving too quickly can mean investing in expensive infrastructure that does not get used as expected.
"One of the hard questions is how to plan for a future when you do not know exactly how much demand is coming or where it will show up," Sehloff said.
At Argonne, researchers are developing tools to help answer that question. Some of that work focuses on long-term planning: building tools to study how the grid may evolve over the next decade or more, where new transmission could provide the most value and how planners can prepare for growth while minimizing risk. For example, Argonne's models can help utilities decide where to build new power lines so they can handle future demand without overbuilding or leaving communities underserved. Some work focuses on operations: how the system behaves minute to minute, and how operators can respond when conditions change suddenly.
Another major part of the work is resilience. Argonne researchers study how the grid is affected by hazards such as extreme heat, hurricanes and other disruptive events. They model how equipment can fail, how disruptions can cascade through a system and how outages in one kind of infrastructure can affect others.
That matters because the grid does not operate in isolation. Electric power is tied to water systems, natural gas networks, communications and transportation. A power outage can disrupt water pumping and fuel delivery. At the same time, problems in those systems can feed back into the electric system. Understanding those interdependencies is a major part of Argonne's grid research.
"These infrastructure systems are deeply connected," Sehloff said. "If one goes down, the effects do not necessarily stay contained."
To study those interactions, Argonne combines infrastructure modeling with advanced computing and AI. Researchers are also drawing on the laboratory's advanced computing ecosystem, including resources at the Argonne Leadership Computing Facility, a DOE Office of Science user facility, to speed up complex grid analysis. Sehloff said newer machine learning and AI approaches are helping researchers examine far more scenarios than traditional modeling alone would allow, making it possible to identify which conditions deserve the closest analysis.
Argonne's grid research is meant to inform real-world planning and operations. The laboratory collaborates with utilities, state agencies and federal partners to help translate analysis into planning and decision-making, with a focus on how the grid performs under pressure and how it can recover when something goes wrong.
"The challenge is not only keeping the system operating day to day," Sehloff said. "It is making sure the system can adapt as demand changes and remain resilient when it is tested."
Beyond Generation: A Connected Energy Future
Bringing all of Argonne's energy work together requires seeing these technologies as parts of a larger whole. Nuclear, hydropower and batteries each contributes something different. The grid is what allows those technologies to function as a system rather than as separate parts. As the demands on that system continue to grow, the ability to plan, coordinate and respond will matter as much as the power source itself.
Together, those technologies, and the people advancing them, point to an energy future that goes beyond generation and is built on connection.
Amber Rose is a science writer and editor for Argonne specializing in coverage of chemical sciences and engineering, materials science, microelectronics and physics. She holds a master's degree in chemistry from the University of California San Diego. Rose joined Argonne in 2024 and has been a science writer for more than 3 years. She previously worked as a science writer for the University of Illinois Urbana-Champaign Grainger College of Engineering.
The Argonne Leadership Computing Facility provides supercomputing capabilities to the scientific and engineering community to advance fundamental discovery and understanding in a broad range of disciplines. Supported by the U.S. Department of Energy's (DOE's) Office of Science, Advanced Scientific Computing Research (ASCR) program, the ALCF is one of two DOE Leadership Computing Facilities in the nation dedicated to open science.