7 Jul 2026
I thank the Renewable Thermal Collaborative (RTC) for organising a webinar highlighting some of the recent achievements of thermal energy storage technologies. Conceptually thermal-energy storage is quite simple. You heat up a material and it stores energy either in the form of sensible heat, latent heat (phase change) or thermochemically.
At medium grade, with temperatures of up to 400C, these systems are hard to beat as they can provide industrially useful heat. This stored heat is highly valuable in food processing and bio refining industries because process temperatures rarely exceed 200C. Besides food processing there are several other industries that can use medium grade heat for drying and preheating.
Since heat is used in all industries, it is the single unifying theme of the entire manufacturing sector and residential too because many electrical appliances are performing temp control work. Thermal energy storage technology is therefore highly suitable to meet these industrial and residential needs and this differentiates it from traditional chemical batteries like Li or Na ion which store chemical energy and are reliant on way more expensive materials.
While this discussion focussed on sensible heat based energy storage and recovery all thermal energy storage systems have to face the same engineering challenge , that is, how to store and extract power most efficiently. Power transfer in heat based systems scale with area so during engineering of these systems we want to maximise the heat transfer area while minimising the volume.
The real appeal of these technologies is, as Antorra energy and Magaldi group demonstrated, that they can use relatively cheap materials like sand and graphite to store massive quantities of energy — on gigawatt scale. This cost benefit is undeniable and one of the biggest advantages of thermal energy technology.
Of particular interest to me was Magaldi Group's demonstration of using fluidised bed technology that can speed up the heat transfer process in sand and make charging and discharging faster thereby improving the power density.
While 400C is relevant for food processing and other industrial applications,at slightly higher temperatures, thermal energy batteries approach the gravimetric energy density of chemical batteries at 140 watt/Kg. Theoretically higher energy densities are possible because sand is also a high temp phase change material but the problem is that higher temperatures place very tough demands on materials that have to store what would essentially be confined lava. Therefore it's unlikely that the densities are going to improve further with sensible heat technology for portable storage.
For industrial heat requirements Antorra has already demonstrated temperatures in excess of 2000C pushing the boundaries of what is possible with thermal storage.
But for thermal-energy tech to realise its full potential a couple of things need to happen. Right now the these systems have demonstrated that they can work but reliance on electrical energy to heat the thermal storage blocks is a big bottleneck.
Solar PV devices have terrible conversion efficiency. Wind is much better but nothing beats concentrated sunlight in raw heat power transmission. If the problem of manufacturing lenses could be solved then it might be possible to store solar thermal energy directly inside blocks easily achieving heat efficiencies of 80% or more. Depending upon thermal mass of the battery final charge temp could be adjusted, though with direct solar it's unlikely to move past 1200C, which may not be such a bad thing as it relaxes the load on materials.
While the first problem is solvable with good engineering and improved manufacturing capabilities the second problem of converting this heat into useful work is much more challenging. Carnot limitations severaly cap the amount of work that can be extracted from heat. Even if they approach the energy density of Li ion they will be unable to produce equivalent useful work. On the whole it does balance out. Because even with carnot limitations you can easily achieve work output exceeding solar and approaching wind. But can we do better?
Electricity is useful in its own way. It's easier to transport and work with. It also has its own peculiarities with materials but the best solution would be solar heat to electricity, if it can somehow be managed. That would overcome the limitations of solar PV and still be able to produce electrical energy or clean fuels for direct transport. This is going to be very tough but it is within the realm of possibility and definitely a direction that is worth exploring through simulations and scientific discourse before an investment can be justified.
There might be another way to make thermal storage more appealing. Could it be possible to build new thermodynamic cycles that operate on low grade heat and focus on system level efficiencies rather than raw work output per cycle? In combined heat and power plants system efficiency easily reaches 80-90%. But could it be possible to use heat recovery to drive additional work and improve net output? This is a big question that needs to be answered decisively.
I'm excited by the idea of thermal batteries because they offer a promising alternative to electrical power systems. However the thermal energy ecosystem is not yet as mature as the chemical battery ecosystem and there are a few issues that will need ironing out before this technology becomes truly revolutionary.
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Akshat Jiwan Sharma
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