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The award-winning Phase Change Matters blog tracks the latest news and research on phase change materials and thermal energy storage. E-mail tips and comments to Ben Welter, communications director at Entropy Solutions. Follow the blog on Twitter at @PureTemp. Subscribe to the monthly PCM newsletter. Or join the discussion on LinkedIn.

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PCM battery shows promise in home heating system

Ben Welter - Tuesday, September 15, 2020

A home heating system equipped with a PCM battery put up encouraging numbers in a small trial in northern Italy earlier this year. The monthlong test “shows that is possible [for such a system] to supply the whole heating demand of a house reducing close to zero the costs,” says Domenico Feo, who developed the system. The full report, prepared by ThermaLink, a trademark of Sunservice Srl of Treviso, Italy, is available here.

ThermaCubeThe system is composed of a 6 kW solar array, an air/water heat pump and a thermal battery filled with BioPCM Q42, a biobased phase change material supplied by Phase Change Energy Solutions of Asheboro, N.C. A control unit, PCDCube, monitors temperatures and manages energy flow to optimize system performance. In an interview with Phase Change Matters, Feo answered questions about the heat battery, recently rebranded as ThermaCube.

Q: Thermal conductivity has proven to be a challenge in thermal energy storage across most types of PCM. Was conductivity an issue with the required charge/discharge cycles?

A: "As already known, the thermal conductivity of the PCM, especially of the organic one that we use, is low. This is, at the same time, a disadvantage and an advantage. The disadvantage has been minimized in using a heat exchanger made with a flat aluminum panel with the various layers just over 1 inch of distance; in this way we are able to make the entire volume of material work in a very efficient way. Vice versa this is an advantage for the very low heat losses during the non-work phases; in conditions of installations inside the buildings, the temperatures can be maintained for several days."

Q: If faster heat transfer is required, do you envision a redesign of the heat exchanger or a modification of the PCM to meet the demand of the energy transfer?

A: "As manufacturer, we can customize the heat exchanger dimensions and shape in order to achieve our goals, but as always in the industrial scalability, the quantities are mandatory for a good price. We designed a single heat exchanger dimension and multiply it in order to be able to produce the different storage capacities and realize a complete modular range. The transfer of energy can be however accelerated by increasing the flow rate of the fluid and the delta T between the fluid and the melting point, of course there is always a limit to this possibility. There are still studies around this point that need to be better understood."

Q: Would implementing several PCMs of different melting temperatures aid in the overall performance of the TES?

A: "Let's say that we expect a slight drop in performance at lower temperatures, but we don't have many other tests to give you a more general opinion."

Q: How is the PCM temperature measured throughout the entire storage to provide input to the PCDCube? Since the melting/solidification of PCM is not a homogenous process, are multiple measurements necessary to get a realistic status of the PCM?

A: "In the documents that we have published, we do not specify that we have installed two temperature probes, one in the center and another one near the walls and it is evident that, when the final phase of the  discharge of the PCM approaches, the perimeter probe shows a decrease of more sudden temperature than the central one. We, however, assume that the fact of having installed our thermal battery outside the building in a very cold climate, has exaggerated the heat loss despite the low heat transmission."

Q: Have you considered other PCM suppliers/products, since many are located in Europe and the RAL quality organization is based there?

A: "This is a possibility, at least for the distribution of our products in Europe and Asia. Currently we try to separate the supply of the case with exchangers (that we manufacture) from the PCM with direct purchase of the client from the supplier, especially in the larger units."

Q: What is the customer value proposition for this product? What is the expected return on investment/payback period?

A: "This is a $1 million question; the proposal is certainly into the growing wave of the storage market, even the electrical ones for PV systems. (A Tesla Powerwall is cool but not economically advantageous if you don’t pay attention at the payback that is higher than the life of the battery). The best value proposition is to separate production from the consumption of the energy and take advantage of renewable energies which, unfortunately, are linked to the day / night cycle and the outdoor temperature conditions. We see perfect the combination HP + Thermal Battery because we can concentrate the HP working hours during the best outdoor conditions that, for many reasons, are affecting and reducing the performances.  Furthermore, we also see a large market in the use of these thermal batteries in all these existing systems which are undersized or which, due to specific situations of changing use of the building, are no longer able to provide the necessary heating or cooling to the whole plant. About the ROI, this really varies a lot country by country because the cost of the electricity has different rates and peak hours schedules. The industrial needs are sometimes much more interesting and attractive than the residential ones."

Q: What are your plans for a commercial rollout?

A: "We are completing the Italian sales force and are looking for international distributors. Our goal is to propose the range of products at an international level with distribution agreements for the case only with exchangers; it will obviously be our responsibility to direct the partner to some reliable and high-quality PCM manufacturers. Obviously, those who will quickly give us the opportunity to build pilot plants, demonstrating the technology, will have an advantage in introducing them into the market and in the exclusivity of the contractual relationship."

PCM briefing: Ice Energy files for bankruptcy; Viking Cold has opening for thermal engineer

Ben Welter - Monday, February 10, 2020

Ice Energy, the Santa Barbara, Calif., company that made and distributed ice-based thermal energy storage systems, has filed for bankruptcy. The company's Ice Bear system makes ice at night when demand for electricity is low and capacity is abundant. During the day, the stored ice is used to provide cooling. Details of the Chapter 7 bankruptcy, filed in December, are sparse. The company's website is no longer active. Over the years, Ice Energy had won several major energy storage and distribution contracts with utilities, and had begun marketing a smaller version of the Ice Bear system aimed at retail customers. 

Viking Cold Solutions has an opening for a chemical/thermal engineer in Houston. The engineer will "conduct research in Thermal Science, Storage/Heat Transfer and Phase Change Materials (PCM) for low temperature applications (<10⁰C)."

Axiom Exergy has secured more than $1 million in orders for the Axiom Cloud, a software platform that helps manage energy consumption in supermarkets and cold storage facilities that use the company's PCM-powered thermal storage systems.

• The 2020 Advancements in Thermal Management conference, to be held Aug. 6-7 in Denver, has issued a call for presentations. Topics include thermal materials, thermal modeling and characterization and measurement of thermal materials. Abstracts are due Feb. 12.

EnergyNest will install a large thermal energy storage battery at a Senftenbacher brick factory in Austria. The system will temporarily store excess energy in the form of hot air from a tunnel furnace. The stored heat be converted to steam and later reused in production.

Devan Chemicals, the Belgium-based developer of finishing technologies for textiles, introduced its Tones of Cool Bio technology at the Heimtextil trade show in Frankfurt, Germany, last month. The technology "stimulates the textile to dissipate redundant heat from the body and to instantly reduce the body temperature," the company says. The phase change materials "are derived from sustainable, natural sources.

Registration is open for the 23rd Microencapsulation Industrial Convention to be held June 8-11 in Rotterdam, Netherlands.

Research roundup: Analysis of hysteresis method in EnergyPlus; pinecone biochar; passive cooling; thermal responses of concrete slabs; more

Ben Welter - Thursday, August 15, 2019

From Applied Thermal Engineering:

Application and sensitivity analysis of the phase change material hysteresis method in EnergyPlus: A case study

From Scientific Reports:

A promising form-stable phase change material prepared using cost effective pinecone biochar as the matrix of palmitic acid for thermal energy storage

From Applied Energy:

Geometry-induced thermal storage enhancement of shape-stabilized phase change materials based on oriented carbon nanotubes
Passive cooling through phase change materials in buildings. A critical study of implementation alternatives

From Cement and Concrete Composites:

Thermal responses of concrete slabs containing microencapsulated low-transition temperature phase change materials exposed to realistic climate conditions

From Solar Energy Materials and Solar Cells:

Preparation and thermal properties of low melting point alloy/expanded graphite composite phase change materials used in solar water storage system
Frost and high-temperature resistance performance of a novel dual-phase change material flat plate solar collector

From Energy:

Novel micro-encapsulated phase change materials with low melting point slurry: Characterization and cementing application

From IOP Conference Series: Materials Science and Engineering:

Thermal performances and characterization of microencapsulated phase change materials for thermal energy storage

From Journal of Physics: Conference Series:

Effect of thermal performance on melting and solidification of lauric acid PCM in cylindrical thermal energy storage

From Construction and Building Materials:A sodium acetate trihydrate-formamide/expanded perlite composite with high latent heat and suitable phase change temperatures for use in building roof

From Materials Research Express:

Investigation of magnesium nitrate hexahydrate based phase change materials containing nanoparticles for thermal energy storage

From Journal of the Brazilian Society of Mechanical Sciences and Engineering:

Selection of phase change material for solar thermal storage application: a comparative study

From Renewable Energy:

Experimental study on the thermal performance of a grey water heat harnessing exchanger using phase change materials

From International Journal of Energy Research:

Climate applicability study of building envelopes containing phase change materials

New dorm at Massachusetts college features 18,000+ square feet of PCM mats

Ben Welter - Thursday, August 15, 2019

Garfield passive house elements

A new dormitory at Williams College in Massachusetts is equipped with 18,200 square feet of mats filled with phase change material.

Garfield House, completed in time for the first students to move in this month, is designed to achieve Passive House PHIUS+ certification and LEED Gold certification. It features R-38 walls, R-60 roofs, triple-pane windows, high-efficiency energy recovery ventilation units, drainwater heat recovery and a 50 kw photovoltaic array.

The Infinite R PCM mats, made by Insolcorp LLC of New London, N.C., will help keep the passively cooled building comfortable when the weather is warm. The PCM is a salt hydrate with a peak melting point of 73 degrees F and a thermal storage capacity of about 170 joules per gram. The mats are deployed within Garfield's interior walls and above ceilings.

Jacob Higginbottom Jacob Higginbottom, director of higher education design at SGA in Boston, was project manager. He first learned about the potential use of phase change material in building envelopes and interiors in March 2018.

"A member of our team had run across the Infinite R product at a trade show and our client was looking for ways to introduce passive cooling techniques since it’s their campus standard to build residence halls without active cooling," said Higginbottom, right. "Upon research we convinced the client that this could help and they decided to give it a try."

Garfield House has no active cooling system. Did that present any special challenges?

"The fact that Garfield did not have cooling wasn’t necessarily a challenge for the PCM, but perhaps was more of an opportunity for the project itself," said Mick Dunn, Insolcorp president. "The project wasn’t without a cooling source altogether. The design team implemented well-designed ERV/ventilation to leverage cool overnight temperatures. As part of the Passive House design process, some issues were identified with cooling and being able to maintain comfort without the introduction of A/C. So we worked with them to analyze a suitable amount of PCM to help address that cooling issue and help negate the need for investment in mechanical cooling other than ventilation.

"We’ve had numerous applications where the PCM has been used with no active cooling. Most of these have been very large industrial applications where the PCM has been used to control peak plant temperatures in buildings with very high internal heat loads. The results have been very good, and we’ve seen reductions as much as 10 to 15F compared with baseline temps. Sometimes we’ll be using a higher temp PCM to promote natural re-freezing. In more conventional occupied office/housing applications we’d typically still be looking for some kind of mechanical cooling mechanism such as ventilation if air conditioning is not present. And we’d probably be more likely to consider this as a viable strategy in climates such as California or New England than say Florida where humidity and overnight temperatures are very high."

The engineering firm Thornton Tomasetti of New York conducted whole building energy modeling in WUFI Passive, the program required by the Passive House Institute US (PHIUS). The models project cooling demand of 0.74 kBtu per square foot per year and a cooling load of 1.64 Btu per hour per square foot. A PCM thermal simulation model projects a peak cooling reduction of 10 degrees F.

Will the building's actual performance be measured against these metrics in the first year of occupancy?

Elsa Mullin, senior sustainability consultant at Thornton Tomasetti, says PHIUS "does not require post-occupancy measurement and verification after initial occupancy."

Higginbottom said LEED certification for the design portion is completed. All construction requirements have been submitted and he expects a LEED Gold certificate from the U.S. Green Building Council by the end of the month.

He said the use of PCM won't be a factor in the certification process.

"A building like this can easily achieve LEED Gold without the use of this material," he said. "PCM was introduced to address thermal comfort. Active cooling does not dramatically affect the building energy consumption in a use type like this (most loads come from domestic HW and plug loads and ventilation fans which are still required irrespective of cooling design)."

It's the first time Higginbottom has used PCM in a project. He hopes to use it in future projects.

"The interesting part about this product is the ability to fine-tune a building towards net zero or net positive and also to flatten out the demand for cooling and possibly downsize equipment in the future and save money on operating and up front costs," he said. "We would like to have more research to back that up, but it’s a speculation on our part that this would be a benefit to building owners’ first costs and life-cycle costs."

Research roundup: Surface functionalization of composite PCM; EnergyPlus optimization; direct expansion solar heat pump; more

Ben Welter - Friday, April 26, 2019

From Applied Surface Science:

Effects of surface functionalization on thermal and mechanical properties of graphene/polyethylene glycol composite phase change materials

From Applied Energy:

Facile flexible reversible thermochromic membranes based on micro/nanoencapsulated phase change materials for wearable temperature sensor
Shape-remodeled macrocapsule of phase change materials for thermal energy storage and thermal management
Investigation on the thermal performance of a high temperature packed bed thermal energy storage system containing carbonate salt based composite phase change materials
Toward a new method for the design of combined sensible/latent thermal-energy storage using non-dimensional analysis
Strategic control and cost optimization of thermal energy storage in buildings using EnergyPlus
Adaptive measures for mitigating urban heat islands: The potential of thermochromic materials to control roofing energy balance

From Solar Energy Materials and Solar Cells:

Poly(styrene-co-divinylbenzene-co-acrylamide)/n-octadecane microencapsulated phase change materials for thermal energy storage

From Renewable and Sustainable Energy Reviews:

Recent advances in direct expansion solar assisted heat pump systems: A review
Review on nanoporous composite phase change materials: Fabrication, characterization, enhancement and molecular simulation

From Energy and Buildings:

Experimental Testing of Phase Change Materials in a Warm-Summer Humid Continental Climate

From International Journal of Energy Research:

Development of pentadecane/diatomite and pentadecane/sepiolite nanocomposites fabricated by different compounding methods for thermal energy storage

From Applied Thermal Engineering:

Heat transfer performance of graphene nano-platelets laden micro-encapsulated PCM with polymer shell for thermal energy storage based heat sink

From Journal of Applied Polymer Science:

Investigations on thermal properties of microencapsulated phase‐change materials with different acrylate‐based copolymer shells as thermal insulation materials

From Solar Energy:

Experimental investigation on the impact of thermal energy storage on the solar still performance coupled with PV module via new integration

From Thermochimica Acta:

Nanoencapsulated phase change material with polydopamine-SiO2 hybrid shell for tough thermo-regulating rigid polyurethane foam

From International Journal of Heat and Mass Transfer:

Optimization of the detailed factors in a phase-change-material module for battery thermal management

From Journal of Traffic and Transportation Engineering :

A review on the best practices in concrete pavement design and materials in wet-freeze climates similar to Michigan

From Case Studies in Thermal Engineering:

Study of a passive solar air heater using palm oil and paraffin as storage media

From Acta Microscopica:

Preparation of Graphene Hybrid Material and Thermal Properties of Polymer Composites

Research roundup: Ternary hydrated salt mixture; earth-air heat exchanger; shape-stabilized fly ash composite PCM; more

Ben Welter - Monday, October 01, 2018

From Energy Conversion and Management:

Two types of composite phase change panels containing a ternary hydrated salt mixture for use in building envelope and ventilation system
Research on cooling performance of phase change material-filled earth-air heat exchanger
An experimental investigation of the phase change process effects on the system performance for the evacuated tube solar collectors integrated with PCMs

From Solar Energy:

Carbon based material included-shaped stabilized phase change materials for sunlight-driven energy conversion and storage: An extensive review

From Applied Thermal Engineering:

Experimental Study of Water Solidification Phenomenon for Ice-on-Coil Thermal Energy Storage Application Utilizing Falling Film

From Powder Technology:

Preparation and thermal properties of stearic acid-benzamide eutectic mixture/expanded graphite composites as phase change materials for thermal energy storage

From International Communications in Heat and Mass Transfer:

Experimental and numerical study of melting of the phase change material tetracosane

From Particuology:

Effect of particle size on the thermal performance of NaNO3/SiO2/C composite phase-change materials

From Materials Chemistry and Physics:

Low-cost, shape-stabilized fly ash composite phase change material synthesized by using a facile process for building energy efficiency

From Construction and Building Materials:

Preparation and thermal properties of encapsulated ceramsite-supported phase change materials used in asphalt pavements

From Applied Energy:

Hottgenroth adds PCM module to building simulation software

Ben Welter - Monday, April 23, 2018

Hottgenroth software PCM menuThe latest versions of Hottgenroth modeling software include simulation of phase change materials in buildings.

“We included PCM in our components properties and can now calculate the given or taken energy hourly for every single room in an complete 3D model,” said Björn Wolff, industrial technology engineer at Hottgenroth Software GmbH & Co., Cologne, Germany.

“Especially for cooling loads it’s important to take the specific mass and heat capacity into account," Wolff explained. "Our simulation is for the dynamic simulation of heat and cooling loads using worldwide climate data. If you know specific values of them we can also simulate renewable energies like PV, heat pumps, CHP, solar thermal, ice storage etc."

https://www.hottgenroth.de/M/SOFTWARE/SolarPVSimulation/Gebaeude-Simulation/Seite.html,73283,80430

PCM briefing: Pitt professor gets $500,000 grant to study effectiveness of prosthetic liners

Ben Welter - Friday, December 22, 2017

Goeran FiedlerGoeran Fiedler, assistant professor of prosthetics and orthotics at the University of Pittsburgh, has been awarded a $500,000 grant from the U.S. Department of Defense to study temperature control liners for prosthetics. The liners use phase change material to reduce the body’s tendency to sweat. The study will follow participants over 12 months to determine whether the liners decrease the risk of pressure sores, accidental falls and other problems.

Axiom Exergy has been named to Food Logistics' FL100+ Top Software and Technology Providers list. The award recognized Axiom for its PCM-based "refrigeration battery," now in operation at a Whole Foods Market in Los Altos, Calif., and scheduled for installation at a Walmart store in San Diego.

HeatVentors has won 2017’s international PowerUp! competition for innovative energy start-ups. The Hungarian company's PCM-based thermal energy storage system is designed to cut energy use by up to 40 percent.

A thousand tons of rock will be used to store excess thermal energy in Siemens Gamesa's Future Energy System under construction in Hamburg, Germany.

• Registration is open for the Unleashing Innovation Summit 2018 to be held March 12-13 in Amsterdam. The goal of the event is to  "bring together cross-industry innovation leaders to share information on the latest trends and strategies relating to creating an ecosystem and culture of innovation within an organisation."

• The agenda has been posted for the Smart Fabrics Summit in Washington, D.C.  The April 24 event is hosted by the U.S. Department of Commerce and the Industrial Fabrics Association International. Topics include "Smart Fabrics Standards: A Government Regulator’s Perspective" and  "Trends in Public-Private R&D Partnerships on Smart Fabrics."

Maryanne Waweru-Wanyama, a Kenya-based journalist and blogger, offers a fresh take on Warmilu's IncuBlanket. The product uses packs filled with sodium acetate trihydrate to keep infants warm for up to five hours.

New version of EnergyPlus features updated PCM module

Ben Welter - Tuesday, October 17, 2017

The latest version of EnergyPlus modeling software includes an updated module for measuring the impact of phase change material on energy use in buildings.
 
Developed by the U.S. Department of Energy, EnergyPlus is an energy simulation program that can be used to calculate heating and cooling load in a building, based on detailed information about the building’s physical make-up and mechanical systems.
 
With the support of a $100,000 grant from the Department of Energy, Jeremiah Crossett, chief technology officer of NRGsim Inc., worked with Dr. Edwin Lee of the National Renewable Energy Laboratory to incorporate the updated PCM module into EnergyPlus.
 
The PCM module was originally developed more than five years ago by Ramprasad Chandrasekharan, then a graduate student in mechanical engineering at Oklahoma State University. Crossett assumed responsibility for the module soon after, debugging the FORTRAN code and modifying the logic to include the effects of subcooling and hysteresis. He began using the module in a customized version of EnergyPlus on all PCM modeling projects he worked on. The module, however, was not compatible with public versions of EnergyPlus, which was converted to the C++ programming language in 2014.
 
Jeremiah CrossettCrossett, right, sought the DOE grant to fund the conversion of the PCM module to C++ so that it could be incorporated into EnergyPlus. The module features two major improvements to the original PCM module.
 
“The new model includes the effects of hysteresis,” Crossett said. “The input object is called Material Property Phase Change Hysteresis and includes two [temperature/enthalpy] curves. Instead of going up and down in the slope of a single curve, the model either stores the energy in the storage range and then releases it when the model hits the heating curve. Or the model hits the heating curve immediately, depending on the properties of the actual phase change material. This model takes into account the histories of building surface temperatures, on into the current. It does a better job of accounting for the phase change material’s performance over time.
 
“In the previous version, what would happen is any time temperatures would fall and then rise again, and rise and then fall again, any time temperatures were not fully linear, [the module] would show additional energy consumption. Essentially, you had this single curve and as it would get cooler it would drop the heat back into the space. So say your material’s melting at 74, 75 Fahrenheit, and you’re saving on cooling energy, and then it drops down to 73, and now it drops all the heat right back into the space. So now you’ve got more energy you’ve got to deal with in your cooling system. That’s not how it actually works in the real world. …
 
“That caused a whole lot of studies, done by many, many different people over the years, to be wrong. It essentially gave a false indication that phase change materials don’t work nearly as well as they really do. …
 
“[The new module also] models subcooling and supercooling. Each PCM has a theoretical melt and freeze point. That’s normally how these products are rated. Some companies call it a Q-value. Other companies just say it as a number, such as a phase change 23 or a phase change 29 in degrees Celsius. But in the real world, how these products actually perform is that there’s some amount of subcooling: the freezing point is not identical to the melting point. You can have supercooling as well, where once your material is frozen, you have to reach a point above the theoretical melting point in order to melt it. This model allows the thermal simulation to have different melting and freezing points. ...         

"Now that EnergyPlus can accurately model PCM's performance in real buildings," Crossett said, "it is well-suited for evaluation of PCM technologies for energy codes such as California's Title 24 and green building standards such as ASHRAE 189.1."

Here's a screen grab of a portion of the new EnergyPlus PCM module:

Crossett and Lee completed work on the module in August. Version 8.8.0, released on Sept. 30, is available for free at https://energyplus.net/downloads. They plan to publish a paper on their work later this year.

Over the next six months NRGsim plans to work with PCM manufacturers to add their products to a database for the EnergyPlus program, based on the ASTM C1784-14 protocol, "Standard Test Method for Using a Heat Flow Meter Apparatus for Measuring Thermal Storage Properties of Phase Change Materials and Products."

PCM briefing: Solar-powered micro cold rooms; Axiom Exergy's jazz connection

Ben Welter - Wednesday, September 13, 2017

• The German company Covestro is providing technology for use in solar-powered micro cold rooms in India. The cold rooms employ phase change material to keep produce cool until it can be transported from farm to market. Eight hundred units will be built in the Indian state of Telangana over the next two years. 

• In an interview with the San Jose Mercury News, Anthony Diamond talks about the musical connection he shares with Axiom Exergy co-founder Amrit Robbins. They met as undergrads at Stanford University. "I play saxophone, he’s actually a trumpet player," Diamond said. "He was like, the best jazz trumpet player on campus. So whenever I had a gig, I would call him, and vice-versa. We had an opportunity to collaborate a lot within that context. I knew that I worked really well with him and we were a really great team."

• Heat battery maker Sunamp Ltd. is one of 15 European scaleups selected to give presentations in California next week at Startup Europe Comes to Silicon Valley

Pelican BioThermal has opened a service center in Puerto Rico. The center will serve as a depot for the company’s Credo on Demand rental program and enable customers to receive and return reusable temperature controlled packaging systems.

Facebook has announced that its cloud campus in Odense, Denmark, will be connected to a neighborhood district heating system. The company expects the system will warm 6,900 homes.

Evelyn Wang, director of MIT’s Device Research Laboratory and an internationally recognized leader in phase change heat transfer on nanostructure surfaces, has been named associate department head of operations in the school's Department of Mechanical Engineering.  

Long-Qing Chen, professor of engineering science, mechanics and mathematics at Penn State University, has been awarded a Humboldt Research Award by the Alexander von Humboldt Foundation of Germany. Chen will work with Jürgen Rödel, professor of materials science and engineering at the Technische Universität Darmstadt, on areas of mutual interest, including multiferroic thin films and phase change materials.

MIT researchers are taking a look at 3,000-year-old technology that could help reduce the use of fossil fuels. Under the proposal, electric resistance heaters would convert excess electricity into heat. The heat would be stored in a large mass of firebricks, which can retain heat for long periods if they are enclosed in an insulated casing. The heat could be used directly for industrial processes, or it could feed generators that convert it back to electricity when the power is needed.