- China Solar Thermal Alliance

. Introduction ..................................................................................................................................................................................................................................................................................................................

. Benefits of industrial Thermal Energy Storage ................................................................................................................................................................................

. Business cases for industrial Thermal Energy Storage ........................................................................................................................................................

. Cost of industrial Thermal Energy Storage ............................................................................................................................................................................................

.................................................................................................................................................................................................................................................................................................................

One quarter of total final energy consumption in the European Union is consumed by industry. Within that quarter, over 0% is consumed by heating and cooling processes. The continued, wide-scale use of gas, oil, coal, and other fossil fuels for industrial thermal processes leads to an estimated greenhouse gas (GHG) emission of Mt CO equivalent per year, which equates to around 0% of the total industrial GHG emissions and % of total GHG emissions in the EU. Thermal energy storage (TES) can assist in the decarbonisation of industrial heating and cooling, and at the same time increase energy system flexibility and security. The full roll-out of industrial TES could enable a potential ,9 TWh of fossil fuel replacement by renewable energy and/or surplus heat, leading to a reduction of Mt CO equivalent GHG emissions per year.

. Recognition of the role of TES options and benefits in industrial
long-term energy and infrastructure planning.

. Develop a policy framework to deploy a portfolio of TES options, from early breakthrough to nearly commercial technology options at full scale.

. Provide support to targeted R&D programmes for TES technologies to address the identified technical barriers at regional, national and EU levels.

. Share best practices and disseminate knowledge and data actively to industry, policy makers, and other stakeholders through publications, presentations and other forms of media and engagement.

. Develop innovative business models based on, for example, new energy system services and a dynamic energy price structure.

. Develop clear conditions and long-term perspectives for investments in industrial TES.

. Establish independent TES materials testing institutes to support technical development.

. Activate a community sharing best practices to disseminate the advantages and successful demonstration and application of using TES in industries. This community can deliver standardised systems, disseminate information and knowledge, and as a result to help to lower financial risks.

. Introduction

To limit global warming to . degrees, the world must halve GHG emissions over the next decade and reach net zero carbon emissions by 00, as foreseen by the Paris Agreement. To achieve carbon neutrality, in Europe, it is necessary to urgently accomplish the decarbonisation of the industrial energy system.

TES has the potential to play a significant role in industrial energy system conversion and assist in the decarbonisation of industrial energy supply, while at the same time facilitating energy flexibility and security.

In terms of the EU¡¯s decarbonisation objectives, the full roll out of TES in the EU industrial sector could enable a potential of 9 TWh fossil fuel replacement by renewable energy
and/or surplus heat and a GHG reduction of Mt CO equivalent per year [, ].

Industrial TES represents one of the key technologies that can enable the active participation of energy intensive industries in future smart energy systems. This chapter outlines the heating and cooling demand in industrial processing and the range of applications which can benefit from different TES technologies.

. Industrial thermal processing

Industrial energy consumption within the
EU has shown a continuously increasing trend since 0. By 09, industries in the EU were responsible for 0 Mtoe (,0 TWh) of final energy consumption, which corresponds to almost % of the total final energy consumption (,0 Mtoe/,9 TWh) [], with only the transport sector and domestic sector being higher.

Thermal energy demands combined
account for around 0% of the total industrial energy consumption (0 [, ]). As shown in Figure , process heating consumes .9% of the final energy, followed by non-thermal process (9.9%), space heating and hot water (.%), process cooling (.%), and space cooling (0.%) [, ].

Industrial heating and cooling is mainly provided by fossil fuel energy sources, with Natural gas as the most dominant energy source (9%). Renewable energy sources currently provide only 0% of industrial heating and cooling by direct renewable energy use (9% biomass, % others). Renewable energy can also be supplied indirectly through electricity (%) and district heating (%) []. Overall, the continued dominance of natural gas, coal, oil, and other fossil fuels contributed to an estimated industrial GHG emissions of Mt CO equivalent (based on 0 data [] and CO emission factors []), which is around 0%
of the total industrial GHG emissions [].

. High temperature processes (over 00 ¡ãC)
consume almost % of the energy demand, as shown in Figure . Natural gas and coal are often used to achieve these high temperatures.

. in the temperature range of
00¨C00 ¡ãC is primarily generated by natural gas and biomass.

. Lower temperature process heating
(below 00 ¡ãC) is mostly provided by district heating. Space heating and hot water are mainly met by individual gas boilers or local district heating (provided by CHP).

. Industrial space and process cooling is dominantly provided by electrically driven vapour compression refrigeration.

Conventionally, TES has been applied mainly to balance fluctuation in thermal energy demand, as illustrated in Figure . By charging the TES during low-demand periods and discharging during high-demand periods, a process known as peak shaving, a significant reduction in implemented capacity for the heat supply or chiller system can be obtained. As the capital costs of a heat supply system are driven by its capacity, peak shaving with TES can enable a significant reduction in investment costs. In the example shown in Figure , the peak heating demand is reduced by %.

For electrically driven heating or cooling systems, TES can be applied to provide load shifting i.e, the production of heating or cooling to low-price periods, thus reducing the operational costs and simultaneously alleviating the pressure on the power grid []. This scenario is becoming more and more relevant in a power grid with an increasing share of variable renewable energy sources.

Figure illustrates an electricity-driven steam supply system powered by renewable energy, with various alternatives for steam generation and TES technologies that are relevant in industrial process heat applications []. Such application of power-to-heat technologies and TES paves the way for active participation of energy-intensive industries in the power market, as will be discussed in the following section.

. Thermal Energy Storage in
future fossil-free industries

. Thermal Energy Storage technologies

There are four general methods used to store thermal energy: () sensible heat storage, () latent heat storage,
() sorption heat storage and
() chemical reaction storage.

. TES stores heat by simply changing the temperature of a material to higher level for heat storage or to a lower level for cold storage. Typical sensible heat storage materials include water, thermal oil, rocks, sandstone, clay, brick, steel, concrete and molten salts.

. Latent TES involves a phase change (or phase transition) of the storage material. This type of material is called a phase change material (PCM). The latent heat involved in the phase change process is typically large; for example, it takes 0 times more heat energy to melt kg of ice than it takes to heat up liquid water from to ¡ãC. Typical PCMs include ice, paraffin, fatty acid, sugar alcohol, salt hydrate, inorganic salt and metals.

. TES is based on a reversible gas-solid reaction between a sorbate (gas) and a solid adsorbent or liquid absorbent, typically for application temperatures below 00 ¡ãC. The sorption heat involved in this reversible sorption/desorption process is generally greater than sensible and latent heats [9]. The advantage of sorption is that heat can be stored over long periods of time with minimum heat loss, since the energy is stored in an endothermic reaction instead of a temperature rise and the (charged) material can be stored at room temperature [9].

o Solid adsorbents include porous-structured materials, for example zeolite, silica gel, and activated alumina, which can adsorb/desorb gases, such as water or ammonia vapour.

o Typical liquid absorbent materials are concentrated salt solutions, such as aqueous solutions of LiCl, LiBr and NaOH.

. Chemical reaction TES (also known as Thermochemical TES) is also based on a reversible gas-solid reaction, similar to sorption TES. Correspondingly, it also has the advantage of low storage loss (since the energy is stored in an endothermic reaction instead of a temperature rise), but with potentially even higher storage density and lower costs. The main difference with sorption TES is that the gas is now directly taken up in the crystal lattice of the solid, changing the crystal structure. However, this method of TES is still at a lower stage of development than sorption TES, because the material is more susceptible to mechanical degradation and agglomeration.

Normally a solid inorganic salt and a gas are used as working pair, such as CaCl and water vapour or SrCl and ammonia vapour, for temperatures less than 00 ¡ãC. Other types of chemical reactions include hydroxide formation (e.g. CaO/Ca(OH)) and carbonation (e.g. CaO/CaCO) [0] which are used for higher temperature applications (typically in the range of 0 ¡ãC up to 00 ¡ãC). Finally, oxidation reactions are possible (e.g. BaO/BaO or Fe/FeO), for temperatures ranging from 00 ¡ãC up to ,00 ¡ãC [].

The volumetric energy densities and application temperature ranges of various TES technologies are summarised in Table .

. Very high temperature storage, up to ,00 ¡ãC, is typically achieved using porous solid materials, such as ceramics, stone or sand, with air or hot flue gas used as the heat transfer medium. Research is currently investigating the opportunity for thermochemical heat storage based on redox reactions [].

. High temperature storage between
0¨C0 ¡ãC, can be achieved using molten nitrate salts or solid materials, such as concrete. Researchers are currently exploring the potential of other types of molten salt with the objective of reaching higher temperatures. using hydroxides (e.g., CaO/Ca(OH)) is also under investigation [0].

. Medium temperature storage between 00¨C0 ¡ãC, typically uses process steam, combined with pressurised water storage (steam accumulators) for short-term storage (< hour). Solid materials, such as concrete, are a viable option for longer time scales and high storage capacities. Research is currently being undertaken in the use of phase change materials for this temperature range.

. Low temperature storage, less than
00 ¡ãC, that is used in long-term, large-scale storage for district heating applications, is typically provided using water stored in tanks, gravel pits, aquifers or boreholes. Commercially available phase change materials are also used for this temperature range.

. Cold storage, less than ¡ãC, can use different types of phase change materials. is typically used for storage at 0 ¡ãC, whilst organic PCMs (e.g. paraffin) are used for higher temperatures. Salt solutions that have freezing points below 0 ¡ãC are used for cold storage at below 0 ¡ãC. Cold warehouses, take advantage
of the thermal mass of the frozen product, by temporarily lowering the
set-point temperature.

Temperature range, ¡ãC

Volumetric energy density, MJ/m

TRL

Water

0¨C00

High

>00

High

Stones/ceramic/sand []

<,00

High

Concrete []

<00

High

Molten salt,
e.g. NaNO¨CKNO mixtures []

0¨C0

High

Latent
(.T = 0 ¡ãC around melting point)

Aqueous solution,
e.g. CaCl aqueous solution, ethylene glycol aqueous solution

High

Organic PCMs,
e.g. paraffin, fatty acids []

0¨C00

<00

Medium-High

High temperature organic PCMs, e.g. sugar alcohol, dicarboxylic acids []

00¨C00

<00

Low-Medium

Salt hydrate []

0¨C00

Medium

Inorganic salt and metals []

<,000

Medium

Absorption,
e.g. NaOH solution¨C water []

0¨C0

900¨C,0

Low¨CMedium

Adsorption,
e.g. Zeolite¨C water []

0¨C00

0¨C0

Low¨CMedium

Type I,
e.g. CaCl¨CHO, SrCl¨CNH []

0¨C00

00¨C,00

Low¨CMedium

Type II, e.g. CaO/Ca(OH) [0]

<,000

,000¨C,00

Low¨CMedium

Type III, e.g. Fe/FeO []

<,00

,000¨C,000

Low-Medium

Table Volumetric energy densities, application temperature ranges and technology readiness levels (TRLs) of different TES technologies.

. Benefits of industrial
Thermal Energy Storage

The potential for fossil fuel savings and GHG emissions reduction through the integration of TES in the industrial energy system is summarised in Figure . The analysis is based on replacing the used fossil fuels (electricity and district heating have not been considered) with renewable energy and/or surplus heat integration with TES. The roll-out of industrial TES throughout the EU enables a potential of 9 TWh [, ] fossil fuel replacement with renewable energy and/or surplus heat, corresponding to a GHG saving of Mt CO equivalent per year [, ]. For process and space cooling, the potential fossil fuels and GHG emissions reduction will be dependent on the carbon intensity of the purchased electricity.

. Business cases for industrial Thermal Energy Storage

) Industrial process heating or cooling:

a. For high temperature process heat demand (0¨C,00 ¡ãC), typically electric heating in combination with heat storage in porous solids could be used, similar to that used for high temperature Carnot batteries [].

i. Industrial heat pumps in combination with TES [].

c. For industrial cold storage (< ¡ãC), refrigeration systems (e.g. chillers or air conditioning), can provide low-temperature energy to a sensible or PCM cold storage to overcome peaks in cold demand at the start of a new cooling batch/period and to exploit low-cost renewable electricity.

a. Short-term storage, in which surplus heat from batch processes is used to preheat a new batch, to reduce energy input and increase energy efficiency. The storage temperature level varies and hence the most suitable TES technology, depending on the surplus heat available (e.g. in exothermic batch processes in the chemical industry that need a sufficient starting temperature, such as polymerisation or alkoxylation). Short-term storage can also improve the potential of utilising fluctuating industrial surplus sources for district heating [9, 0].

b. Long-term storage, in which surplus heat from an industrial process is stored to provide space heating during winter for the industrial site itself or for export to a district heating network. This requires storage temperatures in the range of 0¨C0 ¡ãC or alternatively an upgrade of the heat stored at lower temperatures or to supply heat customers with low temperature demand.

) Industrial backup storage serves as an uninterruptible thermal supply (UTS) in case other heating options fail. This requires fast response time and high reliability. Today, industry mostly relies on gas-fired boilers as backup. Instead, storage can be used in the form of a backup steam supply, avoiding steam boilers that otherwise would have to be available in standby mode. accumulators are available commercially, while PCM and thermochemical storage options are of interest for future development. For higher temperature options, porous solids would be available, with high temperature PCM and thermochemical material as future options.

) For industrial electricity demand,
in addition to batteries, thermal options can provide low-cost solutions to meet the future need for high-power, high-capacity and long-duration storage. Implementation of such TES solutions at industrial sites would have several advantages as these TES systems can deliver both electricity and process heat. Several technologies need to be developed:

a. High temperature Carnot batteries [], using electric heating to store heat in porous solids to 00 ¡ãC.

b. Medium temperature Carnot batteries [], using a heat pump to convert electricity to heat up to 00 ¡ãC. To increase the coefficient of performance, industrial surplus heat may be used as
a heat source for the heat pump.

. Cost of industrial Thermal Energy Storage

The International Renewable Energy Agency [] has published key objectives for industrial TES, including cost (€/kWh) and lifetime (in cycles) as presented in Table . The payback period, which is normally prioritised by industrial investors, is currently long, e.g. ¨C years for a steam accumulator for surplus heat recovery, and up to years for mobile TES systems (e.g. a trailer or a cargo ship filled with PCMs for surplus heat recovery for swimming pools or district heating) []. However, this may change as fossil fuel costs continue to increase.

. heat storage is the most established and cheapest TES method. The cost of sensible storage materials, e.g. water and gravel, are very small compared to other system components. Therefore, the capital cost of sensible TES is dominated by the container, heat exchanger and installation costs. Further reduction in these costs is difficult, although standardisation could reduce installation and integration costs. Large scale TES using water tanks can be less than . €/kWh and 0¨C0 €/m [].
Borehole and aquifer TES are also established technologies, mostly for building applications combined with solar thermal or heat pump technologies, but can also be used for industrial low temperature heating or cooling. Underground TES is possible to implement at very large scale and investment costs can be lower than
0. €/kWh [].

. Latent TES has not yet been widely used in industrial applications, even though there is no significant technology barrier to deploy it. The cost of latent TES generally remains higher than sensible TES. The most cost effective PCMs are approximately 0 €/kWh [] and this will likely reduce in the near future due to the expansion of the market.

. and chemical reaction TES have the potential of very high energy storage density, experience minimal energy loss, while also being cost effective. These storage materials are generally cheap. However, these types of TES systems are currently in the early stages of development and not yet commercially available. Hence it is impossible to estimate their cost, although it is expected that this could be similar to latent TES in the future.

Latent

& Chemical reaction

0.09¨C

¨C0

¨C

Research

Pilot scale
0¨C0

Demonstration <0

,000¨C,000

,000¨C,00

,000¨C,000

,000¨C,00

<00

00¨C,000

,000¨C,000

Table Foreseen objectives of capital cost and lifetime cycles of sensible, latent, sorption and chemical TES for industry [].

. Examples of Industrial Thermal
Energy Storage

Case : Packed bed TES applied to a steel
recycling plant ¨C RESlag project

In steel recycling, a significant amount of surplus heat is wasted in the exhaust gases from an electric arc furnace (EAF). Aiming to increase energy efficiency and reduce the primary energy cost of operation, CIC EnergiGUNE has demonstrated a packed bed TES for surplus heat recovery at ArcelorMittal in Spain, Figure [, ]. Steel slag, a low-cost by-product produced in the same plant, was used as the storage material. The pilot system was installed
at a capacity of MWh, corresponding to
/0 scale of the full plant. The storage volume is m and uses approximately
tons of steel slag. The exhaust gas from the EAF is at ,00 ¡ãC and is used to heat air, which is subsequently used to heat the packed bed TES to 00 ¡ãC. The stored heat can be used for scrap pre-heating, steam production or other recycling plant applications. The project estimated that the full usage of .9 Mton slags in EU steel industrial for surplus heat recovery would lead to kg CO reduction per ton of produced steel. Since steel production generated on average . tons CO/ton steel [], this amounts to a CO reduction of about %.

Hofm¨⊃hl Brewery in Eichstatt, Germany, uses the Merlin ¡®gentle brewery¡¯ process which requires heating for the evaporation process. An area of m of evacuated tube solar collectors were installed with two series-connected m water storage tanks by Solarbayer GmbH, Figure . The system is capable of storing pressurised hot water up to ¡ãC and enables the smart utilisation of heat at different temperatures; it can supply 90 ¡ãC hot water for the bottle washer, 0¨C90 ¡ãC preheating for brewing and domestic hot water and ¨C ¡ãC for space heating. The solar TES system replaced a gas boiler, increasing the share of renewable energy in the plant and reducing carbon emissions, energy consumption and operating costs.

Case :
accumulator

is widely used in industrial heating processes, typically at 0 ¡ãC (. bar), 0 ¡ãC ( bar), 0 ¡ãC (0 bar), or even 0 ¡ãC ( bar). requirement often varies with time and a single steam boiler sometimes cannot meet this fluctuating demand. In this case, a steam accumulator can be used during low demand periods to provide steam for heating processes when utilisation is high. During accumulator charging, more steam than needed is generated and the surplus steam is injected into a mass of water for storage, increasing the pressure and temperature of the stored water. During discharge, flash steam is generated as the pressure of the stored water is reduced.

At a large poultry processing plant in Orkanger, Norway, a m steam accumulator has been implemented, Figure 0 [0]. The plant is located in an area where the electricity price is strongly influenced by the high share of variable wind power, and with the help of a smart control system, the steam accumulator will be applied to store steam from an electric boiler during periods with low power prices and to deliver steam to the plant when the demand is high.

Case :
Solid sensible TES for steam grid balancing

A solid sensible TES system is under construction at a Yara chemical plant in Her.ya, Norway, to balance their steam grid, shown in Figure . The ThermalBattery. system is designed, manufactured and installed by EnergyNest []. The plant has a continuous steam demand produced by a CHP-plant and gas boilers. is used in several processes at different temperature levels, and therefore there are three steam grids at different pressure levels. The high-pressure steam at bar
is currently discharged in times of imbalances. The TES material, Heatcrete, is a specially developed high-conductivity material [] and is used to store heat from the high-pressure steam grid in low demand periods. The stored heat is released to the middle and low-pressure steam grids to optimise production. Four ThermalBattery. modules, with a total MWh capacity, are used to achieve 0 charge/discharge cycles per day. The integration of TES allows () energy saving by avoiding producing large amounts of steam; () increasing electricity output from a CHP-plant; () enhancement of the energy supply security as the gas boilers can be used as backup; () a reduction of tons CO emissions per day.

. Challenges and barriers

. Technical challenges

Table introduces the technical challenges for the different types of TES: sensible, latent, sorption and thermochemical.

Section . shows that some innovative
TES technologies have been, and are, currently being demonstrated at either pilot or full-scale within industrial processes, providing evidence of their benefits. Given that these projects have been successful, there is no doubt that TES technologies uptake will increase and take a significant share of the energy storage market. This will be accelerated through addressing the above technical challenges and upscaling the production of TES technologies to reduce their specific costs.

TES

TRL

Main identified technical challenges

Main applications

heat storage

Liquid (tank)

. Increase volumetric thermal density, therefore reduce
space requirements

. Reduce high temperatures, pressures, and corrosion for
molten salts

. Reduce heat losses due to lack of compactness

Hours to days duration of heat or cold storage, where a cheap solution is required, and space-availability is not a challenge

heat storage

Solid

. Increase low gravimetric and volumetric thermal density, therefore reduce space requirements and system weight

. Improve heat exchange process

Hours to days duration of heat or cold storage, where a cheap solution is required, and space-availability is not a challenge

heat storage

Underground (borehole/aquifer)

. Reduce very large area requirement

. Reduce dependence on specific geological conditions

. Reduce high heat losses

. Reduce long start-up time

. Increase limited temperature range

Large-scale seasonal heat storage under 90 ¡ãC where close-to-free heat is available for charging periods

heat storage

Pit

. Reduce space demand at the surface

. Improve storage efficiency and impact of temperature levels
and the general quality of stratification

Large-scale weeks to months heat storage under 0¨C0 ¡ãC where close-to-free heat
is available for charging periods

Phase Change Materials (PCM)

¨C

. Increase heat transfer rates, limiting the charge/discharge rates

. Improve the process of standardisation and commercialisation
of PCMs

. Reduce the need for a customised solution for each application

. Increase PCM durability (number of cycles)

. Improve the purity of thermal storage materials required

Hours to days of heat or cold storage where a compact unit is required

heat storage

Absorption
and adsorption
heat storage

¨C

. Increase materials commercially available for applications
above 00 ¡ãC

. Improve efficiency through utilising cold energy produced

. Reduce gap between charging and discharging temperatures

Hours to months of heat storage where space availability is a challenge

Chemical
heat storage (e.g. salt-based reactions)

¨C

. Increase durability and stability of materials

. Eliminate agglomeration/lumping issues

. Reduce gap between charging and discharging temperatures

Hours to months of heat storage where space availability is a challenge

Table Technical challenges related to the different TES technologies.

. Non-technical barriers

The identified non-technical barriers are represented below (Figure ), divided into four categories: market, operational, financial, and legislative.

. Recent trends and innovations in Thermal Energy Storage technologies

The cases described in Chapter demonstrate a growing interest in the application of TES, with collaborative research solving some critical issues and reducing costs. Recent trends and innovations in TES for industrial exploitation of renewable energy are mainly related to the development of advanced storage materials and configurations, as well as the implementation of established technologies on an unprecedented scale to fit industrial applications. The development of advanced simulation tools to improve and accelerate the design and implementation of integrated energy systems with TES, also provides greater opportunity for efficient exploitation.

Solid sensible TES provides a robust and safe means for storing high-temperature heat. Solid TES technologies that have been gaining interest lately include concrete storage and packed bed storage. The Norwegian company EnergyNest has developed and demonstrated a modular
TES system based on specially developed high-conductivity concrete, called Heatcrete.. The technology was recently implemented in the steam grid of a chemical plant in Norway, as discussed in Chapter . Other foreseen applications of this technology are at the Austrian brick manufacturer Senftenbacher [] and the Dutch Sloecentrale combined cycle power plant [].

Packed bed storage using rock, slag-based materials or sand is finding new applications within the Carnot battery concept, which will be discussed in more detail in the following section. In the SIEMENS Gamesa's Carnot battery pilot plant [], a packed bed basalt rock storage at 0 ¡ãC is used. The storage has a thermal capacity of 0 MWh and a heating power of 0 MW. Packed bed TES is also used for surplus heat recovery at the ArcelorMittal steel recycling plant in Spain, discussed in Chapter .

PCM materials can provide heat at
constant temperature, which makes PCM very interesting for applications such as industrial steam storage. A new development in is the increasing interest in high temperature PCM materials, with melting temperatures above 00 ¡ãC, such as nitrate salt eutectics, dicarboxylic acids, sugar alcohols and even metal PCMs [].

Substantial research has been undertaken in recent years to improve the thermal conductivity and thus the rate of charging/discharging of PCMs by adding conductive filler materials []. This has led to a more compact and cheaper storage system since less heat transfer surface area (e.g. metal fins) is needed.

Furthermore, new high-temperature resistant encapsulating materials are being developed [], increasing the application potential of high-temperature PCM.

Composites of thermochemical and sorption materials are also being developed, which is promising for high energy density and long-term stability. R&D is investigating the benefits of using salt-in-porous host matrix composite materials and their innovative preparation techniques [9], aiming to increase energy storage density and enhance the sorption/reaction stability and longevity. In addition, coating technologies are developed to protect thermochemical materials from agglomeration or pulverising.

The feasibility of such a technical solution has been demonstrated by the Swedish company SaltX , who haves developed a nano-coated salt for use in a thermochemical energy storage system called EnerStore. This salt demonstrates a high number of charging and discharging cycles with low-cost material [0]. The principle is based on the thermochemical reactions between calcium oxide and
water/steam. The storage system consists
of two tanks as shown in Figure .

During charging, calcium hydroxide in the first tank is heated up to 00 ¡ãC, which leads to evaporation of the water and therefore drying of the salt. Dry salt (calcium oxide) remains in the first tank while the water is condensed and stored in the second tank, representing the charged state of the storage system. For discharging, water or steam is added to the salt, resulting in a chemical reaction, converting calcium oxide to calcium hydroxide, releasing heat at 0 ¡ãC. A SaltX system has been demonstrated in a Power-To-Heat pilot that was built at the Vattenfall CHP plant in Berlin in the winter of 0/9 and has been in use since March 09, delivering thermal energy into the long-distance heating network of Berlin []. It has a storage capacity of 0 MWh and is charged with electricity from the grid. The overall Power-To-Heat efficiency reached is % to %, with a theoretical maximum of 9%. The discharge rate and level can be controlled with high precision.

The development of simulation models can effectively support the implementation of TES in integrated industrial energy systems with thermal energy storage. Simulation studies are important because they allow the reliable and rapid design of TES systems and sensitivity analysis for innovative configurations. For example, in the field of latent heat storage, a simulation-based system design performance evaluation has been recently presented [, ].

In particular for industrial thermochemical heat storage systems, modelling is helpful in the design and development stages, since operational kinetics of thermochemical reactions for reactor and process design can be predicted by advanced non-parametric models []. Moreover, the efficiency of the overall system can be increased by the integration of sorption units as part of hybrid sorption/compression chillers. Such a solution can allow an increase of exploitation of renewable energy sources by combined thermal and electrical energy, especially for low-temperature TES applications, such as food processing [].

Electrification of industrial processes has become an important focus for research and applications, because of the CO reduction targets and increasing shares of solar and wind energy in the electricity supply. However, powering a wide range of industrial processes by electricity rather than through the combustion of fuels creates issues related to intermittent electricity supply and grid capacity, a challenge which can be addressed through energy storage []. So far, there has been a lack of location-independent, cost-effective storage systems, capable of absorbing and releasing large amounts of electrical energy with minimal losses. To fill this gap, PXP (Power-to-X-to-Power) systems are proposed as a promising solution. PXP systems convert electrical energy into other forms of energy (such as compressed air, thermal energy and/or hydrogen), which can be stored efficiently and reconverted into electrical power when needed.

A low-cost option for Power-to-X-to-Power is , also known as Carnot battery solutions [, ]. These batteries convert electricity into heat during the charging process and store the energy in the form of heat. During the discharging process, the stored heat is converted back into electricity. In addition, part of the stored heat can be used directly for industrial process heating. An example of such a concept has been recently implemented by SIEMENS. The SIEMENS Gamesa's Carnot battery thermal storage pilot plant in Hamburg, shown in Figure , went into operation in summer 09 and is operated by Hamburg Energie GmbH []. The plant uses packed bed basalt rock storage charged with air via an electric heater and a blower. The stored heat is converted back into electricity using a steam Rankine cycle, with a reported efficiency of % and a maximum of . MW electrical power.

The study I-Tess focuses on TES integration in existing power plants as part of Germany's transition to a coal-free energy supply []. The project aims to use existing storage concepts, with an electric heater powered by surplus electricity when available. When there is a lack of available electricity, the system uses steam cycles from existing coal power plants for the
heat-to-power conversion.

The German Aerospace Centre, DLR, the University of Applied Sciences FH Aachen and the RWE Power AG are working on the StoreToPower project, a pilot plant to develop a heat storage power plant in Rheinisches Revier []. The plant will combine an existing coal power plant with high-temperature storage, including an electrical heater and steam generator, to deliver about 0% of the steam used in the steam cycle of the coal power plant, possibly extending the system to a storage only system after the end of coal utilisation.

SIEMENS Gamesa is one of the leading organisations working on the retrofitting of coal power plants, through the integration of a standalone system for providing electricity, heat or process steam with fluctuating renewable electricity as the input [9]. A prototype storage system, using basalt that is heated to 0 ¡ãC, has been demonstrated at the scale of 0 MW, as mentioned above. This storage enables the repurposing of a fossil fuel power stations to energy storage plants by employing the existing turbomachinery as part of the storage concept. At the same time, it can be used
to provide heat for industrial processes.

. Proposed actions

. Policy actions

. Recognise that electrification of industrial processes strongly enhances the need for heat storage, since most of the energy demand in the process industries is in the form of thermal energy. (P)

. Provide support to the demonstration and scale up of innovative and commercially promising industrial TES technologies and business models in various industrial processes on regional, national and EU levels, to encourage greater adoption of technologies which have been shown to be potentially beneficial in their applications. (P)

. Provide support to targeted R&D programmes for TES technologies to address the technical barriers identified in Chapter on regional, national and EU levels. (P)

. Take full account of the potential advantages of TES in comparison with other forms of energy storage, including the abundance of available and recyclable materials, lower costs when scaled up, and low carbon-footprint. (P)

. Provide support to the dissemination of best practices for industrial TES, essential for knowledge sharing and the wider implementation of the technology. (P)

. Ensure energy efficiency, storage and flexibility are embedded as an integral part of EU, national, regional, and local energy transition plans. (P)

. Develop clear conditions and long-term perspectives for investments in industrial TES to support longer term investment. (C)

. Establish independent TES materials testing institutes to support technical development. (C)

. Technical actions

. Conduct R&D projects on TES, focusing on the technical barriers identified in Chapter . (P)

. Undertake techno-economic studies of the benefits of TES and its applications (P), including:

o Use of TES in renewable power-to-heat (hot/cold)-to-power applications (Carnot batteries)

o Use of TES in renewable power-to-heat (hot/cold), to match fluctuating electricity supply to electrified industrial heat demand

o Use of solar thermal and geothermal storage to satisfy fluctuating
heat demand

o The recovery, storage and use of industrial surplus heat

o Use of thermal storage in cooling
and the industrial cold chain

o Use of thermal storage as a reliable backup in case of failure of other heating technologies

. Identify and share applications in
which TES has an advantage (economic, environmental, operational) over other forms of energy storage (batteries or hydrogen). (P)

. Develop and operate TES demonstration projects and provide open access
results and data. (P)

. Share best practices and disseminate knowledge and data actively to industry, policy makers, and other stakeholders through publications, presentations and other forms of media and engagement. (P)

. Develop accessible TES materials databases with uniform KPI metrics. (C)

. Work with regulators, professional bodies and industry to develop standardised TES systems. (C)

. Business actions

. Promote and develop new business models to support the exploitation
of TES. (C)

. Promote and develop dynamic price structures, adjust the energy system regulatory framework, tariffs, and taxation to accommodate TES and energy flexibility. (C)

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Dr Hanne Kauko and Dr Alexis Sevault
SINTEF, P.O. Box 0 Torgarden,
NO- Trondheim, Norway

Dr Salvatore Vasta
Advanced Energy Institute (ITAE)
¡°Nicola Giordano¡±,
Salita Santa Lucia Sopra Contesse, ,
9 Messina ME, Italy

Professor Herbert Zondag
TNO, Westerduinweg ,
LE Petten, Netherlands

Dr Anton Beck and Dr Gerwin Drexler-Schmid
Austrian Institute of ,
Giefinggasse , 0 Vienna, Austria

Dr Nelson Rene Garc¨ªa Polanco
CIRCE, Dinamiza Business Park,
Ranillas Avenue D Building,
st Floor. 00, Zaragoza, Spain

Dr Zhiwei Ma and Professor Tony Roskilly
Durham Energy Institute, Durham University,
Stockton Road, Durham, DH LE

The writers wish to thank the EERA Joint Programme Energy Storage and particularly
Karin Rindt (CTU/CVUT),
Francesca De Giorgio (CNR), and Francesco Mercuri (CNR)
of the Sub Programme ¡°Thermal Energy Storage¡±
for their support in producing this white paper and to DLR, Brenmiller Energy, EnergyNest, SaltX, Lumenion and SIEMENS Gamesa for their generosity in
allowing the use of these images.

. The role of Thermal Energy Storage in industry decarbonisation and energy system sustainability

9.9%
Non-thermal process

.%
Process heating >00 ¡ãC

0.%
Space cooling

.%
Space heating
and hot water

0.%
Process cooling <-0 ¡ãC

0.%
Process cooling -0¨C0 ¡ãC

.%
Process heating 00¨C00 ¡ãC

.%
Process cooling 0¨C ¡ãC

.%
Process heating 00¨C00 ¡ãC

.%
Process heating <00 ¡ãC

%
Others (renewable)

%
Others
(fossil)

%
Coal

%
Oil

%
District heating

9%
Natural gas

Figure (a) Breakdown of final energy consumption by industries in the EU; (b) Breakdown of energy sources for industrial heating and cooling [][].

The statistics, trends and recommendations in this document apply to the countries now in the EU and the UK. However, the term ¡®EU¡¯ will be used throughout for conciseness.

Not including COVID impact.

Figure Peak shaving with TES: charging during low-demand periods and discharging during high-demand periods (.SINTEF).

Figure Electricity-driven steam supply system powered by renewable energy, with various alternatives for steam generation and TES technologies [].

Figure illustrates several classes of application of TES in future, fossil-free industries, with an active role in a renewables based power system.

Figure Industrial application scenarios of TES.

Section

. Implementation of Thermal Energy Storage in industry

Section

Figure CIC Energigune packed bed TES at the ArcelorMittal steel recycling plant [, ].

Figure Solar-water TES in Hofm¨⊃hl Brewery, Germany [].

Figure 0 accumulator ( m) implemented at a large poultry processing plant in Orkanger, Norway [0].

Figure Four module ThermalBattery. before insulation and cladding, during assembly at site in Norway [].

Section

Figure Non-technical barriers hindering the implementation of TES.

Figure SaltX thermochemical energy storage system [0].

Figure SIEMENS Gamesa¡¯s Carnot-battery thermal storage pilot plant in Hamburg [].

Section