<

Stones/ceramic/sand []

<,

Concrete []

<

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

¨C

<

(.T = ¡ãC around melting point)

<

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

¨C

<

-

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

¨C

<

Salt hydrate []

¨C

<

Inorganic salt and metals []

<,

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

¨C

¨C,

Low¨C

Adsorption,
e.g. Zeolite¨C water []

¨C

¨C

Low¨C

Type I,
e.g. CaCl¨CHO, SrCl¨CNH []

¨C

¨C,

Low¨C

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

<,

,¨C,

Low¨C

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

<,

,¨C,

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

. Benefits of industrial
Thermal Energy Storage

The potential for fossil fuel savings and GHG emissions reduction through the integration of 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 . The roll-out of industrial throughout the EU enables a potential of 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 (¨C, ¡ãC), typically electric heating in combination with heat storage in porous solids could be used, similar to that used for high temperature Carnot batteries [].

b. For medium temperature hot water and
process steam demand (up to ¡ãC),
multiple options exist:

i. Industrial heat pumps in combination with [].

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 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 [, ].

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 ¨C ¡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 solutions at industrial sites would have several advantages as these systems can deliver both electricity and process heat. Several technologies need to be developed:

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

b. temperature Carnot batteries [], using a heat pump to convert electricity to heat up to ¡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 , 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 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 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 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 using water tanks can be less than . €/kWh and ¨C €/m [].
Borehole and aquifer 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 is possible to implement at very large scale and investment costs can be lower than
. €/kWh [].

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

. and chemical reaction 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 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 in the future.

& Chemical reaction

.¨C

.¨C

.¨C

¨C

¨C

¨C

Pilot scale
¨C

Demonstration <

,¨C,

,¨C,

,¨C,

,¨C,

,¨C,

,¨C,

¨C,

,¨C,

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

. Examples of Industrial Thermal
Energy Storage

Case : Packed bed 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 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
/ 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 , ¡ãC and is used to heat air, which is subsequently used to heat the packed bed to ¡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 . 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¨¹hl 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 ¡ãC hot water for the bottle washer, ¨C ¡ãC preheating for brewing and domestic hot water and ¨C ¡ãC for space heating. The solar 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 ¡ãC (. bar), ¡ãC ( bar), ¡ãC ( bar), or even ¡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 []. 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 :
sensible for steam grid balancing

A solid sensible 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 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 charge/discharge cycles per day. The integration of 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 : sensible, latent, sorption and thermochemical.

Section . shows that some innovative
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 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 technologies to reduce their specific costs.

heat storage

heat storage

heat storage

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

heat storage

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

heat storage

¨C

heat storage

¨C

. Increase materials commercially available for applications
above ¡ãC

¨C

Table Technical challenges related to the different technologies.

. Non-technical barriers

Typical non-technical barriers include: a lack of awareness of the potential of the technology, lack of knowledge of implementation and operation, high costs,
or lack of incentives that support its uptake.
Additionally, often a company investing in the technology may not be the one that obtains the greatest benefits, for example, load shifting might not benefit the owner of the but rather the grid operator, depending on the power pricing scheme.

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

The share of renewable energy sources supplying the power grid is increasing rapidly, and the demand for removing fossil energy sources is more urgent than ever. One of the main non-technical barriers is the lack of awareness of solutions, particularly as a means of providing flexibility at the interface with a renewable energy-based power grid. In general, the benefits of compared to battery technology, including lower costs, suitability for large-scale applications, longer lifetime, and use of common and abundant materials, as well as the minimal environmental impact of most technologies.

Integration and operation of is more complex compared to batteries, with thermal power, temperature, and pressure demands needing to be considered.
Until recently, variability in electrical
power prices has been low, reducing the viability of investments in adopting , however, this is now changing with the potential future introduction of power tariffs and increasing energy price variation. These factors support the further demonstration that can provide an increased return on investment, both financially and environmentally.

. Recent trends and innovations in Thermal Energy Storage technologies

The cases described in Chapter demonstrate a growing interest in the application of , with collaborative research solving some critical issues and reducing costs. Recent trends and innovations in 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 , also provides greater opportunity for efficient exploitation.

sensible heat storage

sensible provides a robust and safe means for storing high-temperature heat. technologies that have been gaining interest lately include concrete storage and packed bed storage. The Norwegian company EnergyNest has developed and demonstrated a modular
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 ¡ãC is used. The storage has a thermal capacity of MWh and a heating power of MW. Packed bed 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 ¡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 [], 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 []. 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 ¡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 ¡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 / and has been in use since March , delivering thermal energy into the long-distance heating network of Berlin []. It has a storage capacity of MWh and is charged with electricity from the grid. The overall Power-To-Heat efficiency reached is % to %, with a theoretical maximum of %. The discharge rate and level can be controlled with high precision.

The development of simulation models can effectively support the implementation of in integrated industrial energy systems with thermal energy storage. Simulation studies are important because they allow the reliable and rapid design of 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 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 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.

Integration of can also contribute to the phase-out of existing fossil fuel power plants run. This applies in particular to coal power plants that are under pressure to close down as part of national CO reduction plans.

The study I-Tess focuses on 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 % 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 []. A prototype storage system, using basalt that is heated to ¡ãC, has been demonstrated at the scale of 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

Despite the huge potential of in the renewable energy transition, wide-scale uptake is still slow. A major bottleneck at present is the lack of knowledge on their potential applications and benefits. This has led to an exclusion of options in business model development and long-term implementation which has hampered further adoption and advancement of industrial . To overcome this, and allow for greater exploitation in order to contribute to industrial decarbonisation, multiple parallel actions are recommended. These activities involve many different stakeholders, such as Policy Makers, R&D Institutes, Developers, Contractors, Investors and others. A distinction is made between actions that should start immediately, mainly focusing on demonstration and awareness (pre-commercial phase P), and actions that should start in the near term, related to the starting of the commercialisation phase (commercial phase C).

. Policy actions

. Provide support to the demonstration and scale up of innovative and commercially promising industrial 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 technologies to address the technical barriers identified in Chapter on regional, national and EU levels. (P)

. Take full account of the potential advantages of 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 , essential for knowledge sharing and the wider implementation of the technology. (P)

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

(C)

. Technical actions

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

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

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

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

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

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

(P)

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

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

. Business actions

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

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

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. Parnell J., . How Siemens Gamesa Could Give Coal Plants a Second Life [Online]. Available: https://www.greentechmedia.com/articles/read/how-siemens-gamesa-could-give-coal-plants-a-second-life (accessed: Sep. ).

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

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

Professor Herbert Zondag
TNO, Westerduinweg ,
LE Petten, Netherlands

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

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

a

.%
Non-thermal process

.%
Process heating > ¡ãC

.%
Space cooling

.%
Space heating
and hot water

.%
Process cooling <- ¡ãC

.%
Process cooling -¨C ¡ãC

.%
Process heating ¨C ¡ãC

.%
Process cooling ¨C ¡ãC

.%
Process heating ¨C ¡ãC

.%
Process heating ¡ãC

b

%
Others (renewable)

%
Biomass

%
Others
(fossil)

%
Coal

%
Oil

%
District heating

%
Natural gas

%
Electricity

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 : 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 technologies [].

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

Figure Industrial application scenarios of .

Section

. Implementation of Thermal Energy Storage in industry

Figure Fossil fuel and GHG emissions reduction through integrating industrial .

Section

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

Figure Solar-water in Hofm¨¹hl Brewery, Germany [].

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

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

Section

temperature PCM prototype at TNO Laboratory, Petten, Netherlands.

Section

investment costs

Lack of awareness
on the potential of
as a source of flexibility and security of supply

Lack of incentives specifically directed
at

Lack of legislation
on the usage of new
materials and systems in terms of transportation, operation and environment

Lack of sufficiently competent engineers
for systems

Lack of
materials databases
with uniform
KPI metrics

Figure Non-technical barriers hindering the implementation of .

Figure SaltX thermochemical energy storage system [].

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

Section

Section

Section

Section