# Thermal energy storage Source: https://ordergroup.co/glossary/thermal-energy-storage/ Last updated: 2026-10-10 > Thermal energy storage (TES) stores heat for later use. How it works, where it pays off and what control and monitoring software it needs. [Energy](https://ordergroup.co/glossary/energy/) 4 min read # Thermal energy storage Also known as: TES, heat storage Definition Thermal energy storage (TES) stores energy by heating or cooling a medium such as water, rock or molten salt, and releases it later as heat, cold or power. It lets a site buy electricity when it is cheap and deliver heat when it is needed. Cite this entry Text "Thermal energy storage". Order Group, Software glossary, 10 October 2026. https://ordergroup.co/glossary/thermal-energy-storage/ HTML `Thermal energy storage - Order Group` Reviewed by [Michał Dżaman](https://ordergroup.co/authors/michal-dzaman/), Co-founder & Head of Backend Last reviewed 10 October 2026 ## How thermal energy storage works IRENA, quoting the European Association for Storage of Energy, defines thermal energy storage as "the temporary storage of energy by heating or cooling a storage medium so that the stored energy can be used at a later time" for power generation, heating or cooling. The medium can be water in a tank, rock or ceramics, a phase change material, or molten salt. IRENA's 2020 outlook groups 13 TES technologies into four families. Sensible storage raises or lowers the temperature of a material. Latent storage uses the heat absorbed or released when a material melts or freezes. Thermochemical storage keeps energy in a reversible chemical reaction, and mechanical-thermal systems combine heat storage with compressed or liquefied air. The same report counts about 234 GWh of TES installed worldwide in 2019 and expects the market to more than triple, to over 800 GWh, by 2030. Molten salt is the most widely used TES technology in the power sector, mainly because concentrated solar power (CSP) plants use it. IRENA puts installed molten-salt capacity at over 21 GWh, with Spain, the United States and South Africa leading at the end of 2019. The thermal stability of the salts limits the maximum operating temperature to 565°C. Industrial heat is a newer use. A unit charges from the grid through electric heaters when power is cheap or in surplus, keeps the heat in insulated tanks, and discharges through a steam generator when a process or a district heating network needs it. Kyoto Group's Heatcube works this way: its standard 52 MWh configuration delivers steam at 150-300°C and the manufacturer quotes round-trip efficiency above 93% at one cycle per day. The two efficiency figures on this page describe different things: IRENA's over 98% in the table below is for molten-salt storage as a technology class, while 93% is Kyoto's figure for a complete Heatcube unit, which charges through electric heaters and discharges through a steam generator. Selected TES technologies (IRENA, Innovation Outlook: Thermal Energy Storage, Table 3) TechnologyFamilyCapacity rangeOperating temperatureRound-trip efficiencyStorage period Water tank (WTTES)SensiblekWh to 1 GWh10 to 90°C50 to 90%Hours to monthsUnderground (UTES)SensibleMWh to GWh5 to 95°Cup to 90%Weeks to monthsSolid state (rock, ceramics)Sensible10 kWh to GWh-160 to 1,300°Cover 90%Hours to monthsMolten saltsSensibleMWh to 5 GWh265 to 565°Cover 98%Hours to daysIce storageLatentkWh to 100 MWh-3 to 3°Cover 95%Hours to days ## What thermal energy storage means for your software A thermal store is a set of tanks, pumps, valves, heaters and a steam generator, and somebody has to decide every few minutes what each of them does. The software around it usually has four layers, and you should know which ones you are buying. The first is control and safety: the plant's control system, which Kyoto calls the BMS of its thermal battery, and the SCADA screens operators use. It reads tank temperatures and levels, pump and valve states and heater power, and it keeps the salt inside its operating range. A molten-salt store cannot be allowed to cool below its lower temperature limit, so heater control, alarms and safe shutdown sequences belong in this layer, and they need testing on real hardware as well as in simulation. The second is the interface to the site. Kyoto's Heatcube connects its BMS to the customer's energy management system (EMS) through a standard industry interface. Your tender should name that interface and the signals that cross it: available heat in MWh, maximum charge and discharge power, steam demand, alarms. If the store will also offer grid services, response time matters too. Heatcube's charge response is under 3 seconds. The third is optimization. The value of TES comes from moving electricity consumption from expensive hours to cheap ones, so the scheduler needs day-ahead and intraday prices, a weather forecast and a forecast of heat demand. Market data feeds fail and change format, so ingestion needs validation, retries and a fallback schedule. The fourth is data and simulation: historian, dashboards and often a [digital twin](https://ordergroup.co/glossary/digital-twin/) used to test charge strategies and to size the next plant before it is built. Molten salt also appears in electrochemical cells, a different technology from the heat stores described here. The article on [molten salt batteries](https://ordergroup.co/blog/molten-salt-batteries/) covers both. Writing the specification? Add Thermal energy storage to your requirements checklist Collect the terms your project touches and get their system requirements in one e-mail, ready for an RFP. Software functions around a thermal store FunctionWhat it handlesQuestion for your supplier BMS and SCADATemperatures, levels, pumps, valves, heaters, alarmsWhich actions are automatic and which need operator approval?EMS interfaceState of charge in MWh, power limits, steam demandWhich protocol, and who owns the signal list?SchedulerPrices, weather, heat demand, charge planWhat happens when the price feed is missing?Data platformTime series, history, reportsWho owns the data and where is it hosted?Simulation and planningPlant performance, sizing, what-if scenariosIs the model calibrated with measured data? ## From our projects We worked with Kyoto Group for three and a half years on industrial IoT and digital twin software for its molten-salt thermal storage, taking it from a UX/UI MVP to a SCADA-based system that monitors and controls the flow of energy in real time. In the 2024 phase the scope included what Kyoto calls the BMS of its thermal battery: control of the valves, pumps and the flow of hot fluid in the salt store. Around it the team worked on secure cloud infrastructure for the plant's devices and sensors, surveillance with infrared cameras and image recognition, and management dashboards. The system also collected weather data and analyzed energy prices. The stack was React.js, Python and AWS, with Terragrunt and Jenkins for infrastructure. Two lessons from that work carry over to any TES project. Market data APIs, ENTSO-E among them, returned inconsistent file formats and were not always available, so the price feed needed validation and a fallback. Data quality from the plant also has to be settled at the start, because the simulation and the scheduler depend on it. From our projects [KYOTO - Industrial IoT & Digital Twin for Thermal Energy Storage Why our team flew to Oslo every two weeks: the story of KYOTO's industrial IoT and digital twin project for thermal energy storage, and its results.](https://ordergroup.co/case-studies/kyoto-digital-twin-software/) Where to get it - [Kyoto Group](https://www.kyotogroup.no/heatcube) Kyoto Group makes Heatcube, a molten-salt thermal battery for industrial heat. We built software for its control and monitoring. ## Related terms - [BMS](https://ordergroup.co/glossary/bms/) Battery management system A battery management system (BMS) is the electronics and software that monitor a battery's cells, including voltage, temperature and state of charge, balance them and disconnect the battery when it leaves safe limits. In buildings, BMS can also mean a building management system. - [Digital twin](https://ordergroup.co/glossary/digital-twin/) A digital twin is a software representation of a physical asset or process, kept in sync with it through live data, so operators can monitor it, simulate changes and sometimes control it without touching the real equipment. - [SCADA](https://ordergroup.co/glossary/scada/) Supervisory control and data acquisition Supervisory control and data acquisition (SCADA) is a class of industrial control systems that collects real-time data from field devices and sensors, presents it to operators and sends control commands to equipment across a plant or network. ## Read more on the blog - Article [Battery Energy Storage System (BESS): How It Works and What Software It Needs](https://ordergroup.co/blog/battery-energy-storage-system/) - Article [Molten Salt Batteries - Salt in Batteries?](https://ordergroup.co/blog/molten-salt-batteries/) - Article [Managing Surplus Renewable Energy with Energy Storage Systems](https://ordergroup.co/blog/surplus-renewable-energy-storage/) - Article [Why Is Flexibility Such a Valuable Trait in Software Development?](https://ordergroup.co/blog/flexibility-software-development/) ## Sources 1. [Innovation Outlook: Thermal Energy Storage (2020)](https://www.irena.org/Publications/2020/Nov/Innovation-outlook-Thermal-energy-storage) - International Renewable Energy Agency (IRENA) 2. [Heatcube - molten-salt thermal battery, technical data](https://www.kyotogroup.no/heatcube) - Kyoto Group AS 3. [Norbis Park - Heatcube #1](https://www.kyotogroup.no/customers/norbispark) - Kyoto Group AS Michał Dżaman reviewed this entry. Ask how it applies to your project. [Ask an engineer](https://ordergroup.co/contact-us/) ## FAQ ![Michał Dżaman](https://ordergroup.co/media/images/T02DHCC1Z-USU629221-c8b7d6d66b56-512.format-webp.webp) Michał Dżaman Co-founder & Head of Backend [Talk to an engineer](https://ordergroup.co/contact-us/) ### What is the difference between thermal energy storage and a battery? A battery stores electricity and returns electricity. A thermal store converts electricity (or solar or waste heat) into heat and usually returns heat or steam, so it fits sites that need process heat or district heating. Turning stored heat back into electricity is possible, as in CSP plants, but it costs efficiency. ### How efficient is molten salt thermal storage? IRENA lists round-trip efficiency above 98% for molten-salt storage. Kyoto quotes over 93% for Heatcube at one cycle per day. Ask your supplier what the figure includes, for example heater and steam generator losses and heat lost while the store stands idle. ### What software does a thermal energy storage plant need? At minimum a control system for the store (Kyoto calls it the BMS of its thermal battery) with SCADA screens for control and safety, an interface to the site's EMS, and a scheduler that charges on cheap hours using price and weather forecasts. Larger projects add a data platform and a simulation model or digital twin. ### Can thermal storage earn money on the grid? It can when it charges fast enough to follow grid signals. Kyoto planned to use Heatcube's rapid charging response at Norbis Park in Aalborg to take part in the flexible reserve market. The software then also has to receive activation signals and report delivered flexibility. Building a system that depends on Thermal energy storage? See how we build software for this domain, with case studies and the stack we use. [See Energy Hub](https://ordergroup.co/energy-hub/) Requirements checklist For each term we send the definition and what it requires from your software. Free, no sales call needed. Your checklist is empty. Use the plus next to a term to add it.