By Christopher Preble, Senior Fellow and Director, Reimagining US Grand Strategy

Modern militaries require considerable amounts of energy -- and these requirements are likely to grow more onerous in the future. New weapons, including the drones and electronic warfare systems already being used in conflicts, need more energy than previous generations. More energy-intensive weapons, like directed energy weapons, are likely to come into wider use in the coming years because they are significantly cheaper than more traditional methods of delivering ordnance. Militaries should, therefore, ensure access to adequate energy supplies. Most military bases, however, rely on civilian energy infrastructure, which is vulnerable to cyber and physical attacks, natural disasters, and accidents.

The Pentagon has also recognized climate change as a threat not only on its own, but also as a "threat multiplier." Climate change can provoke and intensify some threats already challenging U.S. national security and the safety of U.S. citizens, such as terrorism and infectious diseases. By establishing alternatives to its current reliance on civilian energy grids, most of which are powered by fossil fuels, DOD can kill two birds with one stone: reduce carbon emissions to mitigate the effects of climate change and increase the energy resilience of bases and in-theater operations.

If DOD does not diversify its power supplies for base and in-theater operations, any disturbance to the civilian grid could harm military operations. Unless power plants and transmission grids are built to operate in extreme conditions, major, unprecedented weather events can greatly disrupt energy generation and distribution. In cold weather, for example, turbines in transmission plants, well water needed for oil and gas plants, and hydraulic lines can freeze -- halting power production and damaging infrastructure. Moreover, because burying transmission lines is exorbitantly expensive -- some experts estimate as high as $5 million per mile for high-voltage lines -- most of the United States' civilian power grid remains above ground, making it particularly susceptible to harsh weather. To make matters worse, when extreme weather events occur in areas not acclimatized to that weather, power demand skyrockets, overtaxing grids, causing blackouts, and damaging existing infrastructure.

This occurred in February 2021, when an unprecedented winter storm hit the American South. The storm disrupted power across Texas and brought snow and freezing temperatures to places woefully unprepared for such weather. Just across the border, in northwest Louisiana, Barksdale Air Force Base -- the world's largest bomber base -- was blanketed by 10 inches of snow and sleet. Temperatures around Barksdale fell as low as 1 degree Fahrenheit -- 40 degrees below average. Frozen tree limbs fell on power transmission lines in the surrounding area, cutting power to the base. To fix the infrastructure damage (which included frozen water pipes and impassable roads), the civil engineering squadron at Barksdale moved to 24-hour operations for a full week. If Barksdale had diversified its energy infrastructure beforehand, including building alternatives to civilian energy infrastructure, operations would have returned to normal much sooner.

Building alternatives to civilian energy infrastructure for military bases does not mean that the military would cease to utilize civilian energy systems altogether. In fact, the military could establish systems that, while they would allow a base to be taken off the grid in case of emergency, could serve as a backup or assist in power production during peacetime.

As incidents like the Barksdale case occur more frequently, the U.S. military has begun considering alternatives to ensure it has the energy needed for its bases. One of these alternatives is building microgrids -- localized systems that are capable of producing power without input from external sources. Microgrids could be a path forward both to support a green energy transition and to enhance resilience, allowing military bases to be more autonomous and less reliant on civilian energy infrastructure.

In February 2022, the U.S. Army announced that it would equip each of its 130 bases with microgrids. The microgrid strategy is part of the army's larger climate strategy, in which it aims to reduce its own reliance on fossil fuels and carbon-emitting energy. Building microgrids on critical military installations could also help ensure warfighting capabilities in the face of natural disasters, fuel scarcity, and energy insecurity.

Notably, Tinker Air Force Base in Oklahoma already has a public-private partnership with Oklahoma Gas and Electric (OG&E) dating back to the late 1980s. Tinker leases land -- at no cost -- to OG&E where the company built and maintains a 80-MW peaking generating station, a power station that runs only in times of increased demand. In return, OG&E maintains the electric grid on the base. Tinker gets priority in purchasing power from the plant and can separate itself from the rest of the civilian power grid, if necessary. Essentially, Tinker leveraged future utility payments and free land leases to create a microgrid that can sustain the base in case of an attack or other disruption on the rest of the grid. Tinker, which is in Oklahoma City, is particularly well positioned to have a power generating station that contributes to the civilian grid but whose power can be removed upon attack because of its urban location.

Although the Tinker model can help ensure energy resilience on bases, it still faces an enormous vulnerability: reliance on fossil fuels. U.S. bases tap into civilian energy production and distribution. In cases of disruption, they can draw on emergency diesel generators as backups. Both energy sources are powered by fossil fuels. In a recent Military Review article, Maj. Nicholas Barry, USA, and Dr. Surya Santoso, an electrical engineering professor at the University of Texas-Austin, noted that fuel reliance is particularly dangerous for forward operating bases (FOBs) because fuel supply in any potential near-peer conflict "cannot not be guaranteed." In other words, fuel convoys to overseas bases or operations have been costly in previous conflicts. In a future conflict, the risks associated with fuel supply could be insurmountable.

Even though the United States has focused on domestic sourcing of energy, as long as the U.S. military relies upon fossil fuels to power its bases, any disruption to global fossil fuel supplies will drive up costs and divert resources from other warfighting priorities. That is precisely what has occurred during the last few years. High energy prices in Europe and Asia following the Russian invasion of Ukraine -- and again with the Houthi shipping attacks (and U.S. retaliation) on the Red Sea -- have forced the U.S. miliary to pay more for its energy than anticipated. Even though DOD has been working to reduce its oil consumption, it is now paying more for oil than in previous years. In 2019, the Defense Logistics Agency (the DOD agency that handles fuel distribution for the U.S. military and civilian contractors) distributed approximately 94.2 million barrels of oil, valued at $12.1 billion; in 2023, the same agency distributed 79.5 million barrels, worth $13.3 billion.

Another possibility for powering base microgrids is the use of small modular reactors (SMRs). U.S. military bases have limited capacity to turn to nuclear power as a backup energy source in the event of outages. This is surprising given that the U.S. military -- the Nuclear Navy, specifically -- has nearly 70 years of experience using nuclear fission to generate power. Until recently, however, the other service branches did not see much value in nuclear power.

Nonetheless, concerns about domestic bases' vulnerability to disruptions on the civilian grid have motivated some analysts to begin exploring alternatives. In 2011, a paper published by the National Defense University's Institute for National Strategic Studies made the case for DOD's investing in small nuclear reactors. Notably, authors Richard B. Andres, a professor of cybersecurity strategy and policy at the National War College, and Hanna L. Breetz, a professor at Arizona State University who focuses on alternative energy policy, made only passing mention of the importance of reducing greenhouse gas emissions as a rationale. Instead, they focused on the security challenges posed by continued reliance on traditional energy sources and the need for DOD to diversify its power sources.

A Defense Science Board study in 2016 predicted that "the U.S. military could become the beneficiaries of reliable, abundant, and continuous energy through the deployment of nuclear energy power systems," and urged DOD to explore such options. In response, DOD initiated Operation Pele, named after the Hawaiian god of fire, and tasked it with a mission "to design, build, and demonstrate a prototype mobile nuclear reactor within five years."

Eight years later, in September 2024, engineers at the Idaho National Laboratory (INL) broke ground on a transportable nuclear reactor. The prototype high-temperature gas-cooled mobile microreactor is designed to be transported in four 20-foot shipping containers. Assembly is scheduled to begin in February 2025, and the final, fully assembled reactor will be delivered to INL by 2026.

The idea of deploying SMRs on military bases does have detractors. Professor Alan Kuperman at the University of Texas-Austin's Nuclear Proliferation Prevention Project warned of the risks posed by nuclear power plants, especially on army forward operating bases. Kuperman noted how missile attacks on U.S. FOBs, for example, would have a high probability of hitting and damaging the reactors, possibly releasing harmful radiation. Kuperman is even more skeptical of the power supplies on fixed installations on domestic facilities, which, he notes, will still rely on power from the civilian grid, and thus will not create the "island" of invulnerability that SMR boosters claim. Kuperman concludes that the Pentagon's several nuclear power programs amount to "a huge subsidy to an industry on grounds that make no sense to anyone with even basic knowledge of the subject."

Ed Lyman, director of nuclear power safety at the Union of Concerned Scientists, similarly challenges the rationale for expanding the use of nuclear energy, following decades of resistance owing to safety and security concerns, and because other energy sources are widely available. Even defenders of SMRs admit that they are less economical than large reactors. There is also the perennial problem of waste storage. Contrary to some claims, SMRs do not generate considerably less waste than standard reactors relative to the amount of power that they generate.

U.S. policymakers debating the widespread adoption of nuclear power -- either SMRs at fixed facilities in the United States, or mobile, very small modular reactors on FOBs abroad -- are likely to weigh concerns about safety against the military's need to reduce the vulnerability of its bases to disruptions and enhance resilience. But the goal of reducing greenhouse gas emissions by transitioning away from carbon-based fuels is also likely to be considered.

Solar microgrids provide yet another alternative for the U.S. military to diversify energy production. Installing solar panels on domestic bases clearly has some benefits. First, solar microgrids do not require a consistent supply of fossil fuels, mitigating both carbon emissions and the vulnerability associated with fossil fuel supply. Second, solar energy does not raise the same concerns about the proliferation of nuclear material and storage of dangerous nuclear waste.

But solar energy is not all sunshine. Solar cells are highly dependent on the weather and the amount of solar irradiation present in the area in which they are installed. Solar-based microgrids would clearly be effective in areas that rarely see rain or clouds and have high solar irradiation, like the American Southwest, but they would be much less productive elsewhere. The reliability of solar energy is also more uncertain than alternatives like fossil fuels or nuclear energy; while rolling blackouts have occurred with extreme weather events -- like the 2021 storm that hit Barksdale -- a grid that relies on solar energy alone would produce nearly no power under stormy skies.

Nevertheless, even with its drawbacks, solar energy could still be a promising path forward. Solar technology is improving rapidly; panels are more efficient and costs are declining relative to alternatives. From 2010 to 2019, solar panels became 37% more efficient, and around that same time residential installation costs fell by 90%. Although solar energy production depends on clear skies, it is notably less dependent on temperature; even though winter weather often means shorter sunlight hours, solar cells are actually more efficient in colder temperatures. Still, to truly overcome the volatility of solar power, solar cell technology would need to be paired with significant battery storage in the event that power is needed on overcast days or at night. Today's batteries are not yet capable of storing such large amounts of energy as to make solar-based microgrids unassailable -- but that might change. Since the rapid global expansion of electric vehicle sales from 2% of all car sales in 2018 to 18% in 2024, battery technology has already advanced and is predicted to continue its improvements. New methods such as solid-state storage and sodium-ion technology will most likely make battery storage cheaper and more efficient.

Clearly, DOD sees solar energy as a potential pathway forward. The Joint Forces Training Base in Los Alamitos, California, installed a hybrid solar microgrid to enhance resilience against energy disruptions on the base. This microgrid consists of 26 MW of solar, batteries, and backup diesel generators. As with Tinker and other microgrids, when the power generated by Los Alamitos is not needed for base operations, the energy is distributed throughout the nearby San Diego region. At present, Los Alamitos would be self-sustaining for 14 days on this microgrid in the event of a civilian grid failure, which is comparable to other microgrids that rely solely on fossil fuels.

As the world enters a period of energy transition, renewable energy and technological advancements can help ensure that the U.S. military has access to the energy that it needs across both its domestic and overseas bases. By working to reduce its carbon emissions, DOD can simultaneously make its bases safer from outages, enhancing energy resilience as it reduces reliance on civilian grid infrastructure.

Attacks on civilian electric grids have been and will continue to be common -- from January to August in 2024 alone, 1,162 cyberattacks occurred on U.S. utilities. The United States' civilian power infrastructure is particularly vulnerable as more Americans use "smart" appliances. Each appliance, gadget, or electronic device that connects both to the internet and the electric grid (like smart thermostats or electric vehicles), provides an entry point for cybercriminals to attack energy systems. Rather than try to strengthen the entire U.S. civilian energy grid, DOD can instead focus on mitigating its reliance on civilian systems.

In a paper for the Watson Institute's Cost of War Project, Neta Crawford, an expert on the human and financial costs of war, concluded that DOD was the "world's largest institutional user of petroleum and correspondingly, the single largest institutional producer of greenhouse gasses." Limiting carbon emissions by developing alternative energy sources serves the military's interests by reducing its vulnerability to supply disruptions. With natural disasters increasingly impacting normal base operations, the military has an added incentive to combat its dependence on civilian power supplies. As the U.S. military works to ensure reliable access to the energy that it needs, DOD should continue investing in renewable energy alternatives. Remaining dependent on fossil fuels and continuing to be a major producer of climate-changing emissions would amount to becoming its own worst enemy.