# Sensible heat storage: Science and technology

Why the oldest storage trick needs no scarce minerals

Source page: https://www.materialinsights.org/energy/e_sensible_heat/sg-sci/

What this tab covers The physics and chemistry: how the energy is stored, which materials it needs (scarcity, toxicity, recyclability) and what makes it age.

Sensible heat stores hold energy by making a cheap, plentiful material hotter: water, rock, sand, brick, carbon or molten salt. The physics is simple and well proven, and the materials are among the least scarce of any storage technology.

#### Mechanism
Favourable

Energy goes in as heat and raises the temperature of a solid or liquid; the amount stored is mass times specific heat times the temperature rise. Water stores 4.2 kJ per kg per degree C, but only between about 20 and 80 C, so a tonne swung by 60 C holds about 70 kWh. Solids can run much hotter: the Pornainen sand battery in Finland keeps 100 MWh in about 2,000 t of crushed soapstone, roughly 50 kWh per tonne, and brick and carbon stores run at over 1,000 C, with Antora quoting up to 2,400 C for its carbon blocks (company figure).^[2](https://polarnightenergy.com/news/worlds-largest-sand-battery-now-in-operation/)^[6](https://energy-storage.news/thermal-storage-company-rondo-plans-90gwh-ramp-up-of-heat-battery-gigafactory)^[9](https://www.steel-technology.com/news/antora-energy-launches-ready-to-scale-industrial-decarbonization-technology-establishes-new-ultra-high-temperature-record)^[13](https://nso-journal.org/articles/nso/full_html/2024/03/NSO20230051/T2.html)^[28](https://www.energy-storage.news/antora-energy-closes-us550-million-series-c-to-scale-us-thermal-battery-deployment/)
 Specific heat, water / rock 4.2 / 0.9-1.1 kJ per kg per C^[13](https://nso-journal.org/articles/nso/full_html/2024/03/NSO20230051/T2.html) Water, 60 C swing about 70 kWh per tonne (calculated)^[13](https://nso-journal.org/articles/nso/full_html/2024/03/NSO20230051/T2.html) Pornainen soapstone store 100 MWh in about 2,000 t, about 50 kWh/t (calculated)^[2](https://polarnightenergy.com/news/worlds-largest-sand-battery-now-in-operation/) Top storage temperature, company data Rondo up to 1,500 C; Antora above 1,800 C demonstrated (2023), up to 2,400 C quoted (2026)^[6](https://energy-storage.news/thermal-storage-company-rondo-plans-90gwh-ramp-up-of-heat-battery-gigafactory)^[9](https://www.steel-technology.com/news/antora-energy-launches-ready-to-scale-industrial-decarbonization-technology-establishes-new-ultra-high-temperature-record)^[28](https://www.energy-storage.news/antora-energy-closes-us550-million-series-c-to-scale-us-thermal-battery-deployment/)

#### Material scarcity and toxicity
Favourable

No critical or conflict minerals are needed. Water costs about USD 0.005 per kg and rock USD 0.02 to 0.3 per kg. Several developers use waste: Kraftblock's pellets are up to 85% recycled material, mainly steel slag, and Pornainen's soapstone is an offcut from fireplace making. Rondo says its bricks are made of oxygen, silicon and aluminium, and Antora calls its carbon blocks earth-abundant (company statements). The exception is molten nitrate salt, which is corrosive and freezes if allowed to cool.^[4](https://polarnightenergy.com/news/new)^[6](https://energy-storage.news/thermal-storage-company-rondo-plans-90gwh-ramp-up-of-heat-battery-gigafactory)^[7](https://ceramics.org/wp-content/bulletin/2023/pdf/articles/F-kraftblock_mar23_hi-res.pdf)^[13](https://nso-journal.org/articles/nso/full_html/2024/03/NSO20230051/T2.html)^[20](https://www.businesswire.com/news/home/20231024478018/en/Antora-Energy-Announces-U.S.-Thermal-Battery-Manufacturing-Facility)
 Material cost, water / rock USD 0.005 / 0.02-0.3 per kg^[13](https://nso-journal.org/articles/nso/full_html/2024/03/NSO20230051/T2.html) Recycled content, Kraftblock pellets up to 85%^[7](https://ceramics.org/wp-content/bulletin/2023/pdf/articles/F-kraftblock_mar23_hi-res.pdf)

#### Degradation and ageing
Favourable

There is no chemistry to wear out, so capacity barely fades. The real loss is heat leaking through insulation, which matters most for seasonal stores: in Danish pit stores, losses linked to charging and discharging range from 6% to 24% a year. Hot solids can crack or crumble under repeated heating, and salts corrode tanks. In an EU-funded test Kraftblock had run 4,700 cycles with no degradation observed, against a target life of over 30 years (10,000 to 15,000 cycles); Polar Night Energy designs for 30 or more years (company figure).^[3](https://polarnightenergy.com/reference/solution-for-clean-energys-big-problem/)^[8](https://cordis.europa.eu/project/id/190167786/reporting)^[10](https://www.solarthermalworld.org/news/seasonal-pit-heat-storage-cost-benchmark-30-eurm3)
 Annual heat loss, Danish pit stores 6-24% of heat charged and discharged^[10](https://www.solarthermalworld.org/news/seasonal-pit-heat-storage-cost-benchmark-30-eurm3) Cycle test, Kraftblock 4,700 cycles, no degradation observed (EU project report)^[8](https://cordis.europa.eu/project/id/190167786/reporting) Design life over 30 years (Kraftblock target; Polar Night Energy, company figure)^[3](https://polarnightenergy.com/reference/solution-for-clean-energys-big-problem/)^[8](https://cordis.europa.eu/project/id/190167786/reporting)

#### Variants compared^[1](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2020/Nov/IRENA_Innovation_Outlook_TES_2020.pdf)^[2](https://polarnightenergy.com/news/worlds-largest-sand-battery-now-in-operation/)^[3](https://polarnightenergy.com/reference/solution-for-clean-energys-big-problem/)^[5](https://www.ess-news.com/2025/10/20/rondo-energys-100-mwh-solar-powered-heat-battery-now-operational/)^[9](https://www.steel-technology.com/news/antora-energy-launches-ready-to-scale-industrial-decarbonization-technology-establishes-new-ultra-high-temperature-record)^[10](https://www.solarthermalworld.org/news/seasonal-pit-heat-storage-cost-benchmark-30-eurm3)^[12](https://escholarship.org/uc/item/5r60c449)^[19](https://www.siemensgamesa.com/global/en/home/press-releases/190612-siemens-gamesa-inauguration-energy-system-thermal.html)^[25](https://www.osti.gov/pages/servlets/purl/2496207)^[28](https://www.energy-storage.news/antora-energy-closes-us550-million-series-c-to-scale-us-thermal-battery-deployment/)

| Variant | Typical temperature | Example size or deployment | Main use |
|---|---|---|---|
| **Hot-water tanks** | 20-80 C | Widespread; cheapest medium | Homes, district heating |
| **Seasonal pit stores** | up to about 90 C | Vojens, Denmark: 210,000 m3 of water | Summer solar heat for winter |
| **Aquifer stores (ATES)** | usually below 25 C | over 2,800 systems worldwide | Building heating and cooling |
| **Molten salt** | up to 700 C targeted | over 21 GWh installed (IRENA 2020) | Solar thermal power plants |
| **Sand and rock** | 400-750 C | Pornainen 100 MWh (2025); Siemens Gamesa Hamburg 130 MWh pilot (2019) | District heat; power pilot |
| **Brick and carbon** | above 1,000 C; up to 2,400 C quoted (company figures) | Rondo 100 MWh in California (2025); Antora 5 GWh at Big Stone, South Dakota (company data, 2026) | Industrial steam and heat |
| **Building thermal mass** | room temperature (21-24 C band) | pre-cooling cut cooling costs 5-12% on a modelled day in a US office | Pre-heating or pre-cooling |

#### Sources

1. [Innovation Outlook: Thermal Energy Storage](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2020/Nov/IRENA_Innovation_Outlook_TES_2020.pdf) IRENA, 2020
2. [World's largest Sand Battery now in operation (Pornainen press release, company data)](https://polarnightenergy.com/news/worlds-largest-sand-battery-now-in-operation/) Polar Night Energy, 2025
3. [Solution for clean energy's big problem (Pornainen reference, company data)](https://polarnightenergy.com/reference/solution-for-clean-energys-big-problem/) Polar Night Energy, 2025
4. [New industrial Sand Battery filled with soapstone equal to 1,000 fireplaces](https://polarnightenergy.com/news/new) Polar Night Energy, 2024
5. [Rondo Energy's 100 MWh solar-powered heat battery now operational (news report of company claims)](https://www.ess-news.com/2025/10/20/rondo-energys-100-mwh-solar-powered-heat-battery-now-operational/) ESS News, 2025
6. [Thermal storage company Rondo plans 90GWh ramp-up of heat battery gigafactory (news report of company plans)](https://energy-storage.news/thermal-storage-company-rondo-plans-90gwh-ramp-up-of-heat-battery-gigafactory) Energy-Storage.news, 2023
7. [Kraftblock thermal energy storage from upcycled industrial by-products (ACerS Bulletin feature)](https://ceramics.org/wp-content/bulletin/2023/pdf/articles/F-kraftblock_mar23_hi-res.pdf) American Ceramic Society Bulletin, 2023
8. [KRAFTBLOCK: scalable, modular, high temperature thermal energy and power storage (EIC Accelerator, periodic report)](https://cordis.europa.eu/project/id/190167786/reporting) European Commission CORDIS, 2025
9. [Antora Energy launches ready-to-scale industrial decarbonisation technology, establishes new ultra-high temperature record](https://www.steel-technology.com/news/antora-energy-launches-ready-to-scale-industrial-decarbonization-technology-establishes-new-ultra-high-temperature-record) Steel Technology, 2023
10. [Seasonal pit heat storage: cost benchmark of 30 EUR/m3](https://www.solarthermalworld.org/news/seasonal-pit-heat-storage-cost-benchmark-30-eurm3) solarthermalworld.org, 2019
11. [High-Temperature Aquifer Thermal Energy Storage (HT-ATES) Projects in Germany and the Netherlands: Review and Lessons Learned (Dobson et al., Energies 18(23) 6292)](https://escholarship.org/uc/item/5r60c449) eScholarship (LBNL), 2025
12. [Study on the hybrid energy storage for industrial park energy systems, Table 2: thermal storage materials (National Science Open 3(3))](https://nso-journal.org/articles/nso/full_html/2024/03/NSO20230051/T2.html) National Science Open, 2024
13. [Siemens Gamesa inaugurates electric thermal energy storage system (press release)](https://www.siemensgamesa.com/global/en/home/press-releases/190612-siemens-gamesa-inauguration-energy-system-thermal.html) Siemens Gamesa, 2019
14. [Antora Energy announces U.S. thermal battery manufacturing facility](https://www.businesswire.com/news/home/20231024478018/en/Antora-Energy-Announces-U.S.-Thermal-Battery-Manufacturing-Facility) Business Wire, 2023
15. [Large-scale simulation-based parametric analysis of an optimal precooling strategy for demand flexibility in a commercial office building (Lu, Adetola and Bhattacharya, Energy and Buildings)](https://www.osti.gov/pages/servlets/purl/2496207) PNNL / OSTI, 2024
16. [Antora Energy closes US$550 million Series C to scale US thermal battery deployment (news report of company data)](https://www.energy-storage.news/antora-energy-closes-us550-million-series-c-to-scale-us-thermal-battery-deployment/) Energy-Storage.news, 2026

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_sensible_heat/index.md)
- [Overview](https://www.materialinsights.org/energy/e_sensible_heat/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_sensible_heat/correlation/index.md)
- [Engineering and performance](https://www.materialinsights.org/energy/e_sensible_heat/sg-eng/index.md)
- [Economics](https://www.materialinsights.org/energy/e_sensible_heat/sg-econ/index.md)
- [Impact and additionality](https://www.materialinsights.org/energy/e_sensible_heat/sg-impact/index.md)
- [What to track](https://www.materialinsights.org/energy/e_sensible_heat/tracking/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_sensible_heat/links/index.md)