Using Hot Sand To Store Energy
As communities, cities, and states develop ambitious energy efficiency and decarbonization goals, energy storage is an increasingly critical component of our energy economy. Renewable energy sources like solar and wind are changing how we power our buildings, industries, and grid; however, they are intermittent ― we need continuous power even after the sun sets or the wind dies down. As such, energy storage is critical to ensuring continuous power and allows energy producers to take full advantage during times of overgeneration on sunny (or windy) days.
When it comes to short-duration energy storage, lithium-ion batteries are considered the front-runner, but batteries are not the whole story. Our buildings, businesses, industries, and grid need more storage, at lower cost, for longer durations, and at larger capacities than batteries can provide to displace fossil fuels for a sustainable future.
To meet this energy storage challenge, researchers at the National Renewable Energy Laboratory (NREL) are in the late stages of prototype testing a game-changing new thermal energy storage technology that uses inexpensive silica sand as a storage medium. Economic Long-Duration Electricity Storage by Using Low-Cost Thermal Energy Storage and High-Efficiency Power Cycle (ENDURING) is a reliable, cost-effective, and scalable solution that can be sited anywhere.
The ENDURING Mechanism: Storable, Electrically Heated Sand Delivers On-Demand Electricity
ENDURING uses electricity from surplus solar or wind to heat a thermal storage material — silica sand. Particles are fed through an array of electric resistive heating elements to heat them to 1,200°C (imagine pouring sand through a giant toaster). The heated particles are then gravity-fed into insulated concrete silos for thermal energy storage. The baseline system is designed for economical storage of up to a staggering 26,000 MWh of thermal energy. With modular design, storage capacity can be scaled up or down with relative ease.
Particle thermal energy storage systems can be constructed with existing infrastructure from retired coal and gas power plants. Image by Al Hicks and Besiki Kazaishvili, NREL
When energy is needed, the hot particles are gravity-fed through a heat exchanger, heating and pressurizing a working gas inside to drive the turbomachinery and spin generators that create electricity for the grid. The system discharges during periods of high electricity demand and when limited solar photovoltaic or wind power are available, such as early in the morning and evening, during dinner preparation, and when TVs are on. Once discharged, the spent, cold particles are once again fed into insulated silos for storage until conditions (and economics) are appropriate again for charging.
How Hot Sand in a Silo Is Revolutionizing Energy Decarbonization
ENDURING offers several advantages relative to other electricity storage technologies.
As a storage medium, abundant silica sand is stable and inexpensive at $30‒$50/ton, and has a limited ecological impact both in extraction and end of life. For comparison, lithium-ion batteries have an exceptional energy storage density ― important for certain sectors such as transportation, where weight matters ― but it comes at a high cost. Particle thermal energy storage is a less energy dense form of storage, but is very inexpensive ($2‒$4 per kWh of thermal energy at a 900°C charge-to-discharge temperature difference). The energy storage system is safe because inert silica sand is used as storage media, making it an ideal candidate for massive, long-duration energy storage.
ENDURING systems have no particular siting constraints and can be located anywhere in the country. These systems may also be constructed using existing infrastructure from retired coal- and gas-fired power plants.
ENDURING technology can support the expansion of renewable energy generation across our country. Building these cost-effective particle thermal energy storage systems around the United States could help utilities to continue using solar and wind without running the risk of destabilizing the grid or needing to curtail renewable energy generation. Particle thermal energy storage will also provide energy reserves so our communities can better navigate through extended weather events, whether a week-long cold front or a summer heat wave.
Multiple Potential Economical Use Cases Support Decarbonization by 2050
The Biden Administration seeks to achieve a carbon-free power sector by 2035 and a net zero emissions economy by 2050. Zhiwen Ma, principal investigator of the ENDURING project, sees an important role for particle thermal energy storage in achieving these goals. “While decarbonization of electricity has a clear path, decarbonization of the whole economy ― which includes things like building heat and industrial processes ― is more challenging because natural gas is very cheap, making it hard to displace,” he said. “Decarbonizing industrial processes and building heat is very tough.”
Converting renewable electricity into heat is one way to decarbonize these sectors. Ma sees an opportunity for particle thermal energy storage to play a role in cost-effectively supplanting natural gas. By using a heat pump, one unit of electricity is transformed into two to three units of heat, which can be stored in the particle thermal energy storage system and then later delivered to the end user (depending on the coefficient of performance of the heat pump or the use of an emerging pumped thermal energy storage technology). These technologies can be used for building and industry process heating to replace coal or natural gas.
In addition to providing grid storage and building heat, ENDURING offers a steady source of heat for industrial and chemical processes that are otherwise incompatible with the intermittency associated with solar and wind power.
According to NREL researcher Patrick Davenport, the economic environment, decarbonization goals, and technology have aligned for particle thermal energy storage. “Sand and concrete silos with refractory insulation are very inexpensive materials that can lead to low-cost energy storage,” he said. “Traditional four-hour storage technologies don’t scale well to the grid or city scale. Now that we are in need of large-scale energy storage, this technology makes a lot of sense.”
Early Achievements and ENDURING Promise
The ENDURING project is seeing promising progress and early interest. The team recently won the American Society of Mechanical Engineers Advanced Energy Systems Division and Solar Energy Division 2021 First-Place Best Paper Award and several U.S. Department of Energy technology funding awards. Patents on concentrating solar power integration have been awarded, and several more are being filed.
The ENDURING prototype heaters and heat exchangers are currently undergoing testing in high-temperature conditions. If the prototype tasks are successful this fall, Ma is confident that ENDURING technology will offer great potential to support renewable integration for future carbon-free energy supply.
Ma is not the only one who sees promise: NREL and clean-energy technology firm Babcock & Wilcox have an exclusive intellectual property option agreement to license the ENDURING particle thermal energy storage technology. Babcock & Wilcox are among several industry and academic research partners that contributed to the ENDURING project, including General Electric, Allied Mineral Products, Worley, Purdue University, and Colorado School of Mines.
Learn more about NREL thermal systems and concentrating solar power research.
Article courtesy of NREL.
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Workers transport soil containing rare earth elements for export at a port in Lianyungang, Jiangsu province, China.
China Stringer Network | Reuters
Like the U.S., Europe is also feeling the pressure to keep China sweet in order to maintain supplies of rare earth elements, which are vital for its strategic industries in the region such as auto production, green energy and defense.
Europe is heavily dependent on China for supplies of the world’s 17 rare earth elements and has been looking to calm stormy waters with Beijing over supplies, while looking for alternative sources of critical minerals — including in its own back yard.
That’s a long process, however, and for now, Europe is as vulnerable as other major consumers of rare earths, and particularly the U.S., when it comes to Beijing’s ability to turn the tap off on supplies.
Officials from Germany and the Netherlands are in Beijing this week for talks with their Chinese counterparts on China’s controls on rare earths exports and semiconductor chips which have made European industries vulnerable to global supply chain disruptions.
China dominates the rare earths market from mining to refining, with data from the International Energy Agency showing that, in 2024, China was responsible for 59% of the world’s rare earths mining, 91% of its refining and 94% of the manufacuring of permanent magnets which are commonly used in electric vehicles, wind turbines, industrial motors, data centers and defense systems.
As the world’s single largest supplier of a component that’s critical to so much manufacturing, China’s dominance has made “global supply chains in strategic sectors – such as energy, automotive, defense and AI data centres – vulnerable to potential disruptions,” the IEA noted.
That potential for disruption came to the fore this year when, in April and October, Beijing announced licensing requirements, and later export controls, on its rare earth supplies and technologies.
Those controls were suspended for a year as a result of a trade truce reached in October between China and the U.S. reached but major rare earth importers such as the U.S. and EU, which imports around 70% of rare earth supplies — and almost all of its rare earth magnets — from China, are all too aware of its vulnerabilities to geopolitical disruptions.
Barriers to diversification
Last month, European Commission President Ursula von der Leyen announced that the bloc was launching the “RESourceEU” plan aimed at reducing reliance on critical raw materials from China “in the short, medium and long term.” She said the bloc could do this by recycling existing raw materials, such as those in batteries, and by joint purchasing to stockpiling.
Von der Leyen also said the EU would boost investment in strategic projects “for the production and processing of critical raw materials here in Europe,” and would speed up work on critical raw materials partnerships with countries like Ukraine, Australia, Canada, Kazakhstan, Uzbekistan, Chile and Greenland.
“The world we face today rewards speed, not hesitation, because today’s world is unforgiving. And the global economy is completely different than it was even a few years ago. Europe cannot do things the same way anymore. We learned this lesson painfully with energy; we will not repeat it with critical materials,” she said, referencing the bloc’s reliance, before the Ukraine war, on Russian oil and gas.
Valdis Dombrovskis, European Commissioner for Economy and Productivity, told CNBC Monday that the bloc was working to diversify its rare earth supplies but that this would take time.
“I would say there is some positive news, so China has suspended now for 12 months those additional export controls, which were announced in October, which gives us some time. But I also would say it emphasizes the need for the EU to diversify its rare earth and critical minerals supplies, because of many on those rare earths, we are depending more than 90% on China’s supplies,” Dombrovskis said.
Necessity the mother of invention?
Europe itself has reserves of rare earth materials with deposits found in Turkey, Sweden and Norway but the problem is that it doesn’t have the operations to mine those materials, let alone refine and process them — unlike China, which has decades of experience, investment and infrastructure that has fueled its global processing dominance.
Europe is also more encumbered with long approval processes and environmental standards when it comes to mining, meaning any regional plans to develop those rare earth deposits could take years. Public opposition is also a factor that has not shackled China.
A view of the NEO magnetic plant in Narva, a city in northeastern Estonia. A plant producing rare-earth magnets for Europe’s electric vehicle and wind-energy sectors.
Xinhua News Agency | Xinhua News Agency | Getty Images
The need to diversify from China quickly could cause officials to lower those barriers, however and there are already signs of action, with Europe’s first rare earth magnet production plant being opened in Estonia in September. Backed by funding from both Canada and the EU, the plant’s raw materials are coming from Australia and Malaysia.
“There’s probably a lot more deposits in Europe but … there are barriers to bringing that online,” Willis Thomas, principal consultant at CRU Group, told CNBC.
“But if we’re getting into a world where risks are being realized on trade tensions, I think that that will continue to push everyone to build out the supply chain and a bit more resilience on it, but it does take some time, and there’s limited expertise.”
What’s also worrying for Europe is that being unable to control the sources and supply of raw materials could mean that its technological and green ambitions suffer.
“Europe’s race towards net zero and digital leadership depend on materials it does not control,” Hamed Ghiaie, professor of Economics and Public Policy at ESCP Europe, and Filippo Gorelli, an analyst at Nexans, said in analysis for the World Economic Forum.
“For decades, Europe treated raw materials as a commodity issue, rather than a strategic one. That complacency is becoming costly,” they added.
“What is at stake is climate targets and economic resilience. Shortages of rare earths, gallium or germanium could slow semiconductor fabrication, AI development and even wind-power installation. In short, Europe cannot build a green or digital future on supply chains it doesn’t control,” they concluded.
Aviation startup Electra made history last month when its EL2 became the first hybrid-electric Ultra Short Take-off and Landing (uSTOL) aircraft to successfully complete helicopter-like take-offs and landings at the Watertown International Airport.
Founded to provide affordable air travel without airports, emissions, or noise, Electra’s stated goal was to build an aircraft that could deliver on the promises of eVTOL aircraft at a significantly reduced cost compared to its more drone-like competitors. In that context, the demonstration at Watertown isn’t a publicity stunt, but part of concerted effort to validate Electra’s uSTOL performance under real-world conditions at a commercial airport — exactly the kind of place that regional operators, cargo carriers, and emergency responders actually fly in and out of.
Hitting those marks now will help Electra clear a path for FAA certification and prove that the company can deliver on the $9 billion worth of promises its made (so far).
“Electra is grateful to the team at Watertown International Airport for enabling this demonstration of the EL2’s Ultra Short capabilities in an off-runway capacity,” explains Tom Carto, director of market development at Electra. “Our Ultra Short aircraft will offer the potential to increase the use of general aviation airports and expand the capacity of larger hubs by enabling takeoffs and landings on ramps and taxiways instead of runways, feeding in regional connections without adding to runway congestion. These transformative and practical capabilities will open the door to Direct Aviation and point-to-point connections in a way that will make it easier for people to get from the where they are to where they want to go.”
The EL2’s innovative “blown lift” design features eight electric motors on the plane’s wings, enabling take-off and landing in as little as 150 feet.
Electra says the final version of its aircraft will be able operate from airfields as small as 300 x 100 ft (90 x 30 m), or about one-tenth the length of a standard airport runway. That means that, even if these eSTOL aircraft don’t open up quite as many spaces for air travel as eVTOLs, do, they’ll still be extremely flexible – and more than capable of operating from the roofs of many existing buildings and parking structures.
Obviously
And, of course, the Air Force wants one.
NOTE: in response to some of the comments, I want to point out that the Electra is capable of sustained, electric-only powered flight and uses the genset for remote operations/extended range. I should have made that clearer. This is arguably more EREV than EV.
SOURCES | IMAGES: Electra; via Oswego County Business.
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The US Department of Energy’s Loan Programs Office (LPO) closed a $1 billion loan to restart Three Mile Island Unit 1, a nuclear reactor at Three Mile Island in Londonderry Township, Pennsylvania.
The money is being loaned to Constellation Energy Generation, which is renaming the 835 megawatt (MW) Three Mile Island Unit 1 the Crane Clean Energy Center. Constellation said in September 2024 that it would restart the reactor under a power purchase agreement with Microsoft, which needs more clean power to feed its growing data-center demand.
The project is estimated to cost around $1.6 billion, and the DOE says the project will create around 600 jobs. The reactor is expected to start generating power again in 2027.
Three Mile Island Unit 1 (in the foreground in the photo above) went offline in 2019 because it could no longer compete with cheaper natural gas, but it wasn’t decommissioned. It’s capable of powering the equivalent of approximately 800,000 homes. It’s on the same site as the Unit 2 reactor (in the background in the photo above) that went into partial nuclear meltdown in 1979, and is known as the worst commercial nuclear accident in US history.
When asked about the loan’s timing, Greg Beard, senior adviser to the Loan Programs Office, told reporters on a call that it would “lower the cost of capital and make power cheaper for those PJM [Pennsylvania-New Jersey-Maryland] ratepayers.” Data centers are driving up electricity costs for consumers.
Read more: DOE props up dying coal with $625M days after Wright mocks clean energy subsidies
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