Energy Storage

Energy storage will be the key topic for our future energy supply system. The energy turnover will ony be successful, if the generated electricity can be stored intelligently. With its innovative storage concepts, the SIJ is already making an important contribution to a reliable energy supply.

Head of Section

Dipl.-Ing. Anette Anthrakidis M.Eng.

Room N101
T: +49.241.6009 53507
F: +49.241.6009 53570
anthrakidis(at) | Homepage |



Experimental test rig for bulk material and heat

Project start: July 2019

A core task for permanently available and cheap electricity is cost reduction in the heat storage of solar energy. The SIJ has developed a new type of air-bulk material heat exchanger which, in contrast to the systems available on the market, is characterized by the direct material contact. The better heat exchange from this direct contact faces the challenges of the fluidic phenomenologies.

In the VESUW project, the system is being promoted to market maturity with local project partners. Special attention is paid to the temperature behavior of the materials (800° temperature difference), the lifespan and operating costs, as well as the optimization of the heat transfer process. This is being researched by combining numerical simulations with extensive experiments on a laboratory scale. The final goal is to transfer innovation to the next level.

Project partners:

  • Hilger GmbH
  • Grenzebach GmbH

Funded by:

  • Federal Ministry for Economic Affairs and Energy

StoreToPower - Phase 1

Storing electricity in high-temperature thermal storage power plants

Duration of the project: 01.01.2019 - 30.09.2021

How can we guarantee the security of supply even without coal-fired power plants? What happens to the power plants after the coal phase-out? How can the phase-out be carried out in a socially acceptable way? StoreToPower can make a significant contribution to the solution of these problems.

In this project, the conversion of a coal-fired power plant into a thermal storage power plant is being planned. A thermal storage power plant represents an enhanced thermal power plant using a thermal storage system that is connected in parallel to the conventional steam generator. The thermal storage system will use electricity in low-price periods to store the electrical energy as sensible heat by electrical heating. As heat storage medium, molten salt or a solid material heated by hot air can be used. At high electricity prices, the heat can be converted back into electricity using the existing infrastructure (steam cycle with turbine, condenser, generator and cooling system). This concept contributes to the use of volatile electricity (rising with the further expansion of the renewable energies in the future) as controllable and secure power. In the long term, it would be possible to completely replace the coal combustion system by the storage system. The aim is to develop and demonstrate low-CO2 or rather CO2-free thermal storage power plants that enable a 100% security of supply with minimum CO2 emissions for the energy transformation process.

The StoreToPower project will be the first of its kind in the world to test such a concept on a power plant belonging to the RWE AG. At the Solar Institute Jülich (SIJ), the project is a direct successor to the I-TESS study from 2017, which was also funded by the Ministry of Economic Affairs, Innovation, Digitalisation and Energy of the State of North Rhine-Westphalia. As part of the current project, SIJ's task is to develop reference concepts for the extension/conversion of coal-fired power plants with combined heat and power generation by means of high-temperature thermal storage and their techno-economic evaluation. Furthermore, a life cycle assessment (LCA) regarding the thermal storage system and dynamic simulations for the electrical heater are carried out. With regard to the economic view, a demand analysis for thermal storage power plants in the European network as well as an estimation of the market potential for thermal storage power plants coupled to district heating networks is necessary. The institute NOWUM Energy of the FH Aachen develops future market potentials by means of different stochastic models and calculates the economic performance considering different electricity price development scenarios on the basis of hourly price forward curves of the next three decades. The achieved results are used for the design and engineering of a pilot plant.


Power-to-heat technologies combined with molten salt storage for the application in industry and in PV-CSP hybrid power plants

Project start: May 2018

The industrial sector accounts for about 30 % of the final energy demand of the Federal Republic of Germany. Of this, about two thirds is used for the generation of process heat, whereby large amounts of waste heat are usually generated. The waste heat is usually generated at a temperature level below the temperature required for the respective processes. The SWS project is therefore investigating a high-temperature heat pump in combination with a molten salt heat storage unit. The heat pump brings waste heat to a temperature of over 500 °C and stores it in the heat storage tank. The storage tank is discharged on demand depending on the connected consumer.

In addition to a high-temperature heat pump, a commercial resistance heater is being investigated as a further power to heat (P2H) technology. This can also be used to charge a thermal storage tank. At the electricity stock exchange, negative electricity prices are regularly observed in times with a large supply of renewable electricity and the resulting oversupply. With the help of the technologies investigated, this surplus electricity can be used and thus additionally contribute to grid stability. Furthermore, the implementation of P2H technologies in CSP power plants (Concentrating Solar Power) will be investigated. This is of particular interest for the location NRW, as industrial companies located here have a high market share in the production of CSP components and also offer services in this area. In addition, the design of these two P2H technologies will be examined in an innovative concept for their application in a PV CSP power plant. In this case, low-cost PV electricity will be temporarily stored in high-temperature heat storage tanks (Carnot battery) for periods without solar radiation and consequently offered according to demand.

project partners:

    • TSK Flagsol
    • German Aerospace Center e. V.

    Funded by:

    • Ministry of Economic Affairs, Innovation, Digitization and Energy of North Rhine-Westphalia using EFRE-funds

    TESS 2.0

    Thermal electricity storage for the electricity market 2.0

    Project duration 01.10.2017 – 30.09.2020

    The storage of high temperature heat with subsequent generation of electricity in steam power processes is known from solar thermal power plants. In these applications, the high temperature heat is collected by concentrating solar collectors. The idea behind thermal electricity storage is to charge the storage unit with surplus electricity from the grid using a power-to-heat concept instead of solar energy. The Solar-Institut Jülich is developing multiTESS (multifunctional thermal electricity storage), a storage concept for a decentralized and flexible supply of electricity and heat. In contrary to the conventional power-to-heat approach, the thermal power storage unit of multiTESS stores high temperature heat at up to 1000 °C and can be partially converted back into electricity in a thermal power process. The base of the multifunctionality of multiTESS is the flexible choice of heat source and heat sink (see Figure 1). As heat source, electric heating or waste heat can be used. The heat sink can also be designed flexibly, and, in addition to electricity, heat at different temperature levels can be provided.

    In the TESS 2.0 project, the Power-to-Power&Heat usage chain of the multiTESS concept is demonstrated for the first time in the form of a pilot plant (see Figure 2). The BMWi-funded project benefits from the expertise of the industrial partners Dürr Systems AG, Kraftanlagen München GmbH and Otto Junker GmbH. The emphasis of TESS 2.0 is on the generation and process control of 1000 °C hot air, the storage of the high temperature heat, as well as the integration of the reconversion of electricity and heat extraction. The project partner Otto Junker GmbH has developed an innovative heating concept for the generation of high-temperature heat (state of the art: 750 °C). Dürr System AG is responsible for the conceptual design and construction of the likewise novel ceramic storage tank. The detailed planning of the plant concept was largely carried out by Kraftanlagen München GmbH. The Solar-Institut Jülich is the project initiator, functions as project coordinator, provides support in concept planning and conducts the scientific studies after completion of the pilot plant.

    During the tests, we investigate the operating performance of the individual components and optimise the process control in the overall system. The objective of the project is to create an innovative and primary energy-saving overall system by combining the individual components.




    Indirect solar-heated reformer for methanol production

    Duration of the project: 01.12.2016 - 31.12.2019

    In the "INDIREF" project, a process for indirect solar heated reforming for the production of methanol from carbon dioxide and natural gas was further developed. The conventional production of synthesis gas, which is the basic resource for many chemical products (e.g. methanol), causes significant carbon dioxide emissions today. By using concentrated solar radiation and the in process possibility of CO2 recycling, the release of carbon dioxide can be greatly reduced. The "INDIREF" technology offers a high potential for the intensified use of renewable solar energy in the chemical industry in the future.

    The project focused on the development of an indirectly heated reforming reactor combined with a modified solar receiver for this application. Both components were technically implemented and tested under solar conditions in Synlight Juelich (artificial sun of DLR). In parallel, a process simulation model was created and validated based on test results. On the basis of the simulation model, the process was virtually upscaled to evaluate the technical and economic potential for a market launch.

    The solar mixed reformation with the INDIREF reactor system has successfully been demonstrated in 2019 at the Synlight facility in Juelich. The most important goals, such as high CH4 and CO2 conversion rates and the targeted reaction temperatures were safely achieved, which confirmed the feasibility of the concept. Important results for further development and market introduction of the technology were obtained and prepared for use in follow-up projects.

    Project partners:

    • German Aerospace Center (DLR) e. V.
    • Hilger GmbH
    • Hille & Müller GmbH

    Funded by:

    • Ministry of Economic Affairs, Innovation, Digitization and Energy of North Rhine-Westphalia using EFRE-funds


    Evaluation of the Dispatchability of a Parabolic Trough Collector System with Concrete Storage

    Link zur EDITOR-Homepage: EDITOR

    Projektlaufzeit: 01.10.2015 bis 30.09.2018

    Die Zielsetzung von EDITOR ist es, die Grundlastfähigkeit sowie Leistungsfähigkeit eines solarthermisches Systems, das für kontinuierlichen Betrieb konzipiert ist, zu demonstrieren und zu verifizieren. Während der Projektlaufzeit wird ein System bestehend aus einem mittelgroßen Parabolrinnenkollektor, Betonwärmespeicher und Kessel auf Zypern errichtet. Mit dem System wird Sattdampf produziert und in das Dampfsystem eines Getränkeherstellers eingespeist.

    Der Parabolrinnenkollektor erhitzt mit einem innovativen Vakuumreceiver ein neuartiges, umweltfreundliches Thermoöl auf über 400 Grad Celsius. Ein innovatives neues Betonwärmespeichersystem speichert die gewonnene Wärme, um diese in Zeiten ohne (ausreichender) Direktsolarstrahlung für die Produktion von Sattdampf zu nutzen.

    Im Projekt werden sowohl die technischen Aktivitäten der Installation, Inbetriebnahme und dem Betrieb der Anlage, als auch kommerzielle Gesichtspunkte, wie zum Beispiel die Machbarkeit hinsichtlich Hochskalierung, die Identifizierung von zukünftigen Kunden und der begleitende Kommunikationsprozess mit dem potentiellen Markt, umgesetzt.


    • protarget AG
    • Cyprus University of technology
    • CADE Soluciones de Ingeniería, S. L.
    • Deutsches Zentrum für Luft- und Raumfahrt e. V.

    Gefördert durch:

    • Bundesministerium für Bildung und Forschung


    Integration of thermal electricity storage into existing coal-fired power plants

    Project duration: 01.10.2015 - 31.12.2016

    The transformation of the German electricity system to renewable, fluctuating forms of generation will pose major challenges for a wide range of players in the coming decades. In the I-TESS project the extent to which thermal storage can contribute to the demand-oriented provision of electricity and heat as well as to the stabilization of the power grid is analyzed. In addition to the use of old coal-fired power plants for the construction of new types of thermal electricity storage power plants, the integration of thermal storage into existing coal-fired power plants also plays a decisive role. The latter could drastically increase the flexibility of today's coal-fired power plants and thus make a decisive contribution to demand-driven electricity production. In addition to technical aspects, another focus of the project is on estimating the investment costs and the economic prospects.

    For further information (in German), please klick here.


    Building-integrated thermal storage for the load management of electricity grids with a high share of renewable energy sources

    Project duration: September 2013 - June 2017

    As the energy system is decarbonized, electricity grids are increasingly permeated by fluctuating renewable energy sources. This makes it urgently necessary to provide cost-effective electricity storage or corresponding load management options.

    Within the framework of this project, the Solar Institute Jülich of the University of Applied Sciences Aachen, together with its research partners Viessmann, DuPont de Nemours, RWTH Aachen University and Infrawest, is investigating the option of energy storage by buildings heated with heat pumps and equipped with thermal storage capacity as an interface between the electricity and heating markets. The aim is to significantly increase the energy storage capacity with integrated latent heat storage materials. A successful implementation requires the inclusion of the following aspects: Adaptation of the low-temperature heat source, anticipatory control and building-related load management, thermal comfort, required and permissible temperature levels. It will be determined how electricity purchase prices have to be adjusted to the over- or undersupply, so that a refinancing of the additional investments is achieved.

    If the project is successfully completed, the market will have a system at its disposal which, on the one hand, can activate a high level of negative balancing power (approx. 5 GW for 1 million plants) in a decentralised manner. On the other hand, it can provide a passive storage capacity of several 100 GWh to compensate for fluctuations in renewable energy sources.

    Project Funding: Federal Ministry of Education and Research


    Cross-process heat management in production plants - the example of UPM's paper mill in Hürth

    Project duration: 01.09.2011 - 30.06.2015

    The aim of the project is a comprehensive increase in the energy efficiency of the paper mill. The new technology required is to be exemplary for the entire paper industry and other branches of production. To achieve this goal, an innovative heat/water storage system patented by UPM will be integrated into the existing large-scale plant. This system will recover the heat that has not been used in the production process to date in a comprehensive and, if necessary, time-decoupled manner. In addition to energy savings, considerable savings in fresh water and waste water are expected. Furthermore, the temperature of the waste water can be significantly reduced. The project thus combines environmental protection with an increase in the competitiveness of the production facility.

    The Solar Institute Jülich of the Aachen University of Applied Sciences is carrying out the scientific analysis and optimisation calculations and is supporting the partners UPM, Pöyry and Wallstein.

    Supported by:

    • European Union
    • Ministry for Climate Protection, Environment, Agriculture, Nature and Consumer Protection of North Rhine-Westphalia


    Increasing the cost-effectiveness, utilisation factor and flexibility as well as operating time of the storage system in the Solar Tower Jülich

    Project duration: 1 July 2010 – 31 December 2013

    With the solar thermal experimental power plant Jülich (Solar Tower Jülich), the world's first power plant of this kind was built in Germany. This project serves to improve the utilisation of storage technology and reduce the associated power plant operating costs. The focus of this project is to use new numerical simulation tools to increase the cost-effectiveness, the degree of utilization, the flexibility and the operating time of the storage system. The optimisations shall result in an innovative storage system concept that is predestined for use in solar tower power plants.

    Project partners:

    •     KBA-MetalPrint GmbH | KBA
    •     Kraftanlagen München GmbH | KAM


    High Temperatures heat Exchange and Storage

    Project duration: 01.10.2010 - 31.12.2016

    The idea of using sand as a storage medium for thermal energy is the basis of this project. The resistance at high temperatures, the high availability and the low material prices make sand an excellent storage material. The aim of the project is to develop a process for transferring heat from air into sand at up to 700°C.

    In cooperation with the DLR, the properties of various sands and bulk materials were tested in laboratory experiments for their suitability as heat transfer medium and as heat storage material. Based on these tests, a test facility for direct heat transfer from air to sand was developed and tested. It is used to investigate the behavior of sand during operation.

    This heat exchanger is designed to be used in solar power plants as volatile thermal heat storage system. Further applications such as industrial heat recovery are conceivable.

    Project partners:
    •    DLR

    Funded by:
    •    Federal Ministry for Economic Affairs and Energy