Secure energy supply is of great importance for industry and can only be achieved through the optimal use of all available renewable resources in order to meet international climate targets.

The innovation of CORES lies in fields of  identification, evaluation and the design of technically, energetically (in terms of exergy) and economically optimised combinations of renewable energy technologies (selected from waste heat, solar process heat, heat pumps, storage, PV and PVT) to cover the industrial process heat demand with renewable energy technologies. For this purpose, an optimisation algorithm has been developed which combines technology-specific parameters (key performance indicators) for the whole system based on comprehensible evaluation criteria (global performance indicators) thus generating a system optimum. Based on system simulations and their application to three industrial case studies, control concepts for the operation of the technology combinations are derived.

CORES will be jointly organized with 2 consortia from Germany and Switzerland in a D-A-CH-project in order to create synergies in the field of optimised integration of an industrial company into grid-connected (thermal) energy supply as well as in deriving innovative economic evaluation parameters (non-energetic advantages, business and financing models). Through a joint dissemination, target groups (industry, planners, technology providers) in the German-speaking and European area will be addressed and integrated into the development in order to achieve maximum impact.

The Research Unit for Thermodynamics and Thermal Engineering has been dealing with concentrating solar systems (CSP - Concentrated Solar Power) for some time.

In addition to the direct conversion of solar radiation into electrical energy using photovoltaics (PV), the path of energy conversion from solar radiation via high-temperature thermal energy to electrical energy is still a significant alternative. With this, the solar radiation is bundled via line or point concentrators before it hits a thermal receiver. As a result, higher temperatures can be reached than with planar receivers, which enables the thermal energy to be stored at high temperatures and allows the thermal energy to be converted into electrical energy with high efficiencies. In particular, the storage of thermal energy brings advantages over a PV path.

Valuable research collaborations and publications have emerged in the course of research on CSP systems. - Here is a short excerpt:

• U. Leitner:
  "Numerische Analyse der Intensitätsverteilung am Absorber eines pneumatisch vorgespannten Solarkonzentrators";
  Betreuer/in(nen): K. Ponweiser; Institut für Thermodynamik und Energiewandlung, 2009.
• M. Hartl:
  "Pneumatisch vorgespannter Solarkonzentrator - theoretische Betrachtungen und praktische Erfahrungen";
  Betreuer/in(nen), Begutachter/in(nen): K. Ponweiser, F. Rauscher; Institut für Energietechnik und Thermodynamik, 2010; Rigorosum: 11.10.2010.
• C. Diendorfer:
  "System Design and Analysis of Floating Solar Power Plants";
  Betreuer/in(nen), Begutachter/in(nen): M. Haider, F. Rammerstorfer; Institut für Energietechnik und Thermodynamik, 2014; Rigorosum: 25.06.2014.
• M. Lauermann:
  "Pneumatic prestressed solar concentrator - thermal and optical analyses";
  Betreuer/in(nen), Begutachter/in(nen): K. Ponweiser, F. Rauscher; Institut für Energietechnik und Thermodynamik, 2015.
• M. Heigl:
  "Entwicklung des pneumatisch vorgespannten Solarkonzentrators vom Prototyp bis zur Serienreife";
  Betreuer/in(nen), Begutachter/in(nen): K. Ponweiser, R. Willinger; Institut für Energietechnik und Thermodynamik, 2015.
• E. Esmaeili:
  "Electrolytic solar water splitting at elevated temperatures a thermodynamic approach";
  Betreuer/in(nen), Begutachter/in(nen): K. Ponweiser, J. Fleig, A. Werner; Institut für Energietechnik und Thermodynamik, 2017.
• G. Oberndorfer:
  "Sensitiv of Annual Solar Fraction for Solar Space and Water Heating Systems to Tank and Collector Heat Exchanger Parameters";
  Betreuer/in(nen): W. Linzer; Institut für Technische Wärmelehre, 1999.
• G. Fuchs:
  "Measurement and Control of a Pneumatic Solar Concentrator";
  Betreuer/in(nen): K. Ponweiser; Institut für Thermodynamik und Energiewandlung, 2008.
• M. Garcia Ano:
  "Investigation of the Optical Behavior of a Concentrating Solar Collector";
  Betreuer/in(nen): K. Ponweiser; Institut für Thermodynamik und Energiewandlung, 2008.
• V. Layec:
  "Formfinding of inflatable solar concentrators";
  Betreuer/in(nen): K. Ponweiser; Institut für Thermodynamik und Energiewandlung, 2008.
• D. Wertz:
  "Comparison between various concepts of Solar Thermal Power Plants";
  Betreuer/in(nen): H. Walter; Institut für Thermodynamik und Energiewandlung, 2008.
• D. Wagner:
  "Investigation of Solar Cells for a Concentrating Solar Collector";
  Betreuer/in(nen): K. Ponweiser; Institut für Thermodynamik und Energiewandlung, 2009.
• A. Miguez da Rocha:
  "Analysis of Solar Retrofit in Combined Cycle Power Plants";
  Betreuer/in(nen): A. Steiner, M. Haider; Institut für Energietechnik und Thermodynamik, 2010.
• A. Bacher:
  "Auswirkung erhöhter Einspeisung durch Solar- und Windkraftlagen auf die Betriebsweise von Wasserkraftanlagen";
  Betreuer/in(nen): C. Bauer, E. Doujak; E302 - Institut für Energietechnik und Thermodynamik, 2013; Abschlussprüfung: 05/2013.
• L. Panzer:
  "Design and simulation of a solar tower cavity receiver with "solar salt" as heat transfer fluid";
  Betreuer/in(nen): M. Haider; Institut für Energietechnik und Thermodynamik, 2015.
• H. Ernst:
  "Erarbeitung des Festigkeitsnachweises sowie Entwicklung eines Stabilisierungssystems einer Heliofloat Luftkissenplattform";
  Betreuer/in(nen): R. Eisl, M. Haider; Institut für Energietechnik und Thermodynamik, 2018.

The objective of this R&D project was to develop and engineer a 10 MWth high temperature heat recovery from a cement plant and to allow the transport of the heat to industrial customers, which are more than 1.5 km away from the heat source. Crossing public terrains with a heat transport piping at this temperature level has never been implemented before in Austria. The context calls for maximized standards of reliability and safety. As cement plants typically shut down for several weeks in winter, the question of heat storage is of key importance. Environmental compatibility is important in terms of emissions but also to water protection, as the site is situated in a touristic area next to a lake. Only environmentally benign fluids such as H₂O or CO₂ are acceptable as heat transport medium.

For the Overall concept, almost 30 interconnections of the subsystems heat extraction fluid, storage system and district heating system were analyzed thermodynamically and with regard to the technical and economic optimum. From these, we technically designed four (4) concepts in the sense of a basic design and compared analyzed them economically. (K0, K5, K9, K10).

Figure 1 shows the temperature/duty diagram.

Figure 2 shows the process flow diagram of the basic concept K0 without storage.

For the heat extraction, the comparison between the approaches “dust-loaded smooth tube heat exchanger” and “ceramic hot gas filter + finned tube heat exchanger” has shown financial advantages for the finned tube variant. For the techno-economic project concept, the smooth tube variant was nevertheless chosen, because on the one hand, the technical risk is lower and on the other hand, the internal material flows can be better organized.

For the heat transport over 1.5 km (heat link), a district heating system based on steam has clearly emerged as the techno-economically most advantageous solution (Figure 3). This was opposite to the original assessment at the start of the project. The project team was able to work out a technically feasible route between the waste heat source and the potential industrial customers.

We analyzed several types of heat storage. The aim of a heat storage system is, on the one hand, to optimize operation and, on the other hand, to maximize the use of waste heat and thus avoid CO₂ emissions with a temporal decoupling of generation and consumption. The load profiles of the waste heat and the heat demand vary greatly and are not in the same direction. A storage allows supply and demand to be matched.

In the project, a distinction was made between operational storage (6 MWh), day storage (330 MWh) and long-term storage (> 4 GWh). The number of storage cycles increases with decreasing storage size. For the operational storage variant, Ruths steam storage (K5) and pressurized water storage (K10) were evaluated techno-economically. For day storage or larger high-temperature storage (K9), a gravel storage was developed, simulated, tested in the laboratory of the TU Wien and evaluated techno-economically. For long-term storage with use up to seasonal storage, gravel storage and pit water storage were evaluated.

In terms of CO₂ savings and economy, the available waste heat of 70 to 90 GWh (depending on the concept) would have a theoretical CO₂ emission avoidance potential of up to 22,000 tons (22 kT) of CO₂ per year. The analyzed variants with operational storage (K5 and K10), with day storage (K9), or without storage (K0) allow waste heat to be used in the range of 42 GWh annually to 65 GWh annually (47 to 72% of the maximum potential).

The following key data are the essential input variables for the profitability of the project:

• investment costs,
• running costs (operating costs),
• economic observation period (useful life),
• interest rate,
• specific fuel costs,
• substituted amount of primary energy,
• funding (especially invest funding),
• other costs avoided (e.g. taxes per kWh or per tonne of CO₂) based on the amount of primary energy and emissions avoided.

Based on the key data applicable to the project in 2021, it was unfortunately not possible to demonstrate an economic feasibility for any of the concepts examined. For even larger heat storage systems, the economic viability deteriorated under the prevailing framework conditions. The project team worked out which changes in the framework conditions would make implementation possible.

Acknowledgments:

The Austrian Climate and Energy Fund funded this project.

Due to the complexity of the energy systems of continents, countries, etc., it is unlikely that top-down approaches on their own are sufficient to achieve the necessary energy transition. Therefore, it is proposed here to develop sustainable energy solutions for a type of regions. In the research focus (FSP) 1 of the ResearchLab regions with a population of about 2500 inhabitants (limited to Austria) will be analyzed with the aim to supply them decentrally with renewable energy sources. To achieve this the import of electricity and heat produced with fossil fuels shall be minimized and the regionally available emission-neutral energy sources shall be used instead.

The project aim was to increase the flexibility of heating networks with the help of a thermal energy storage device.

The investigation was done for the thermal centre Dürnrohr of the company EVN. This thermal centre provides heat for different industrial companies as well as for district heating of the regions Tulln and St. Pölten with the help of an incineration plant and the plant unit of the coal fired power plant Dürnrohr which was still in operation (at the end of the project the power plant was decommissioned). During this project four different thermal energy storage technologies are analysed as thermal energy storage units.

In particular the daily morning peak which was compensated by fossil fuels (coal and natural gas) should be managed in the future in a CO₂-neutral and sustainable way by the integration of a thermal energy storage device.

The aim of the project was a detailed techno-economic design of the investigated thermal energy storage technologies to get a solid technical and economic basis for a targeted selection of an optimal thermal energy storage concept for the heating centre Dürnrohr.

IET is working on a novel technology for floating Solar Power Plants, called HELIOFLOAT.

The project is inserted into a doctoral college and the research is done in cooperation with several national and foreign partners. Currently a project application for national funding and patent applications are pending.

The Motivation for Solar Offshore solutions is that Europe lacks adequate available land for significantly large contributions of solar power; only Spain has a significant available inland surface with high direct normal irradiance (DNI). Europe’s solar potential is dramatically increased if one considers a coastal strip of 30km around the coasts of southern Spain, Malta, Lampedusa, Italy, Peloponnes Peninsula (Greece), Crete or Cyprus. Offshore solar generation has two advantages compared to land based systems: the possibility of a relatively effortless tracking around a vertical axis (cost advantage) and the possibility of using seawater for cooling (cost and efficiency advantages). The basic hope of the HELIOFLOAT concept is that these advantages will counterbalance the challenges, costs and difficulties linked to the offshore arrangement.

The main technical features for HELIOFLOAT are:

• The solar platform units are supported and stabilized through a combination of spar buoys, a truss system and a pneumatic support system
• Concentration technology will be either the established HELIOTUBE pre-stressed pneumatic concentrator technology (PPC) or alternate options
• Heat carrier fluid will be either organic heat transfer fluid or direct steam
• Power Platform is separated from solar platform units. It is of conventional and proven Oil & Gas type platform design. It contains control room, steam turbine, generator, seawater cooled condenser, balance of plant and an optional thermal energy storage system.

Due to running patent application no more detail can be given at this point in time.

The aim of the SANBA project is to develop a so-called anergy or low-temperature heating and cooling system (<30°C) for the future use of a former military camp and to answer open research questions based on this task. Key elements are the use of industrial low-temperature waste heat from processes in a neighbouring dairy plant as well as the development of refurbishment and conversion concepts for the listed monument buildings. In a first step and as a core content of this industrial research project, after a comprehensive investigation of the site, new and communicating simulation tools have been developed to cope with the complex situation of the area, consisting of different heat sources, protected and potential new buildings, different temperature levels and times of energy demand, different uses of the buildings, etc. The concept of the anergy grid comprises (I) the heat recovery from the wastewater of the neighbouring dairy plant, (II) integration of locally available renewable energy sources, (III) energy storage aspects, (IV) the special challenge of different building standards of the old protected buildings vs. newly built buildings with different usages (living, commercial, education), and therefore different supply temperatures and demand characteristics, and (V) moderate cooling via Free Cooling.

The project SANBA is part of the NEFI thematic model region that positions energy intensive and manufacturing industries and their decarbonization in the center of a long-term innovation process to boost technological development. SANBA contributes to the NEFI-innovation fields Energy Efficiency & New Processes and Renewable Energy & Storage & DSM.

 

During the last years, several concepts for thermodynamic power storage have been published. This so-called Electro-thermal energy storage (ETES) also has the titles “pumped thermal energy storage” (PTES) and “Carnot-Battery”.

The Institute of Energy Systems and Thermodynamics (IET) is participating in two projects with partners from the USA.

ETES technologies have the following in common:

• electricity is stored as thermal energy (TES),
• the technology is site-independent,
• depending on the temperature levels, one or two thermal reservoirs are needed,
• in general, two reverse thermodynamic cycles are needed (heat pump cycle for charge and power cycle for discharge).

The thermal storage temperature levels may be above or below ambient temperature. In the case that we choose ambient temperature for the lower temperature, only one thermal storage for high temperature is needed.

In a simple set-up, electrical resistance heating (instead of a heat pump cycle) charges the high-temperature storage.

The combination of a water-steam based Rankine cycle with electric heating and thermal energy storage (TES) yields the special case of a thermal storage power plant (TSPP).

The attached figures show the concepts for both CO₂ and H₂O based concepts.

Acknowledgments:

This publication is partly based upon

• work supported by ARPA-e, in program DAYS project DE-AR0000996 with prime awardee Echogen Power Systems,
• work supported by the Department of Energy under Award Number DE-FE0032024 with prime awardee Electric Power Research Institute EPRI,
• several projects supported by FFG, the Austrian Research Funding Agency (the first generation of research and test rigs).

The Institute of Energy Systems and Thermodynamics (IET) has been working on the development of particle based high temperature heat storage systems (Thermal Energy Storage – TES). By 2020 this work has produced four (4) patents, ~15 publications, 6 laboratory scale test rigs, two (2) pilot plants and one (1) license agreement.

The original idea targeted the thermal storage in adiabatic compressed air energy storages (ACAES). Very soon, it became evident that the concept is also applicable in Concentrated Solar Power (CSP), Electro-thermal Energy Storage (ETES) in conjunction with steam and sCO₂ cycles (also named Carnot batteries or PTES - Pumped Thermal Energy Storage) and for industrial heat storage.

All mentioned applications need an indirect particle/fluid heat exchanger, which is optimized for (a) maximized overall thermal performance, hence counter-current characteristic; (b) minimized auxiliary power; (c) minimized costs, hence maximized heat transfer and heat transmission coefficients.

ETES cycles have the additional requirement (d) that the particle suspension flow has to be reversible in order to allow a fast switch from charge to discharge operation and that suspension plug flow is of utmost importance.

IET has developed two basic heat exchanger designs. The original concept, also named sandTES_1.0, was based on longitudinal flow of particles along the tubes. A more recent development called sandTES_2.0, is based on transversal flow across the tubes.

Both concepts use the patented approaches of a 2-stage fluidization grid (for stable and even distribution of fluidization air) and the use of valve-controlled air cushions downstream of the freeboard. The air cushions are obligatory for efficient reversal of particle flow in ETES applications. They are also essential for installing a plug-flow flow behavior on particle side.

sandTES_1 with longitudinal particle flow has the advantage of constant cross section in particle flow direction and the absence of 180° tube bends. It is well suited for applications such as ACAES where fluid side heat transfer is limited and where a high cross section in the tubes is needed due to moderate fluid pressures.

sandTES_2 with transversal flow of particles has the advantages of maximum design flexibility for optimizing both particle and fluid mass flux densities. The transversal flow also allows for the use of transversal helicoid fins, which allow multiplying the outer-diameter based (equivalent) heat transfer coefficient by a factor between 4 to 6 (compared to plain tube). Given that the auxiliary power of a sandTES heat exchanger is directly proportional to the bed volume, high heat transmission coefficients have a high impact on both performance and cost.

Most of the test rigs are dedicated to the analysis of heat transfer, flow characteristic and of system characteristic. One test rig was designed to perform accelerated erosion testing which has the objective to proof that in HTX-applications with no chemical reaction and small particles operated at low fluidization grade (multiple of minimum fluidization velocity) finned tubes are compatible with an operational life of more than 20 years. The experimental work on heat transfer and suspension flow behavior was supported by numerical analysis based on the CPFD code Barracuda. These simulations aimed on the system level for understanding of what is needed for establishing plug flow behavior in horizontal flow FB HTX’s.

Acknowledgments:

Our work was partly supported by

• several projects supported by FFG, the Austrian Research Funding Agency (the first generation of research and test rigs),
• work supported by ARPA-e, in program DAYS project DE-AR0000996 with prime awardee Echogen Power Systems,
• work supported by the DOE Solar Technologies Office, in  project award CPS 38476 “Compact Counterflow Fluidized Bed Particle Heat Exchanger” with prime awardee Sandia National Laboratories,
• work supported by the Department of Energy under Award Number DE-FE0032024 with prime awardee Electric Power Research Institute EPRI.

At TU Wien, the main contributors were Karl Schwaiger, Peter Steiner and Stefan Thanheiser, who themselves were supported by numerous Master- and Bachelor students in their final theses.

In a research cooperation, the IET supports the company Hydrotaurus GmbH in the development of a reciprocating engine with CO2 as the working medium, which is always in the supercritical state. The machine is to be used to convert low-temperature thermal energy (low-temperature heat) into mechanical energy as much as possible.

During a work cycle, the working medium exchanges mechanical energy with a hydraulic system, in which hydraulic oil is brought from a low to a high pressure level. In an idealized way, the changes in the state of the working medium during the cyclic process result in a rectangular shape in a state diagram in which the pressure is plotted against the specific volume (p,v-diagram).

At the given temperature levels of heat supply and heat release, the geometry of the reciprocating piston machine must be designed in a way that the area inscribed by the cyclic process is as large as possible. In the figures, two cyclic processes are shown as examples in a p,v and a T,s diagram (the latter plots temperature versus entropy).

Nowadays, energy suppliers and process industries are confronted with challenging social and legal requirements to decarbonize, increase energy efficiency and enhance sustainability measures. This results in a growing expansion of renewable energy technologies like solar thermal, photovoltaic or wind power plants. As a consequence, a temporal mismatch between energy supply and demand has to be addressed with flexible solutions, for example energy storages. Currently only a few storage technologies take advantage of the synergies of combined thermal and electrical energy storage.

In the project SyndETES a transient open water-steam cycle is proposed as a system that exploits these synergies. Starting point is the Carnot-battery concept, which stores electrical energy as thermal exergy. In SyndETES this concept is further evolved. Thus, aside from electrical energy, industrial waste heat is utilized as energy source. During high demand periods the stored energy is flexibly released either directly as process heat or as electrical energy, e.g. with a steam turbine.

The overarching goal of SyndETES is an economic and technical evaluation of the proposed system designs. Frameworks and frame conditions are developed in cooperation with a stakeholder pool of experts for the integration of SyndETES-systems into industrial processes. Economic feasibility and operational characteristics shall be assessed. Also, a comparison with a reference system is conducted and shall provide further insight. Finally, further steps to increase the technology readiness level are derived.

The project „Zweifeldspeicher“ (“Two-Field Storage”) deals with the innovative design and operation of seasonal Borehole Thermal Energy Storages (BTES). State-of-the-art BTES are operated in a cyclic way, where the heating and cooling demand is covered from the same BTES field. The “Two-Field Storage” approach splits the BTES in two fields with different temperature levels: one field covers the heating demand, while the cooling demand is covered by the second field. The project team is confident that this approach will yield in a higher efficiency both for heating and cooling. The “Two-Field Storage” approach also makes additional heatsources and –sinks accessible for the thermal storage concept. This one-year project (“Sondierung”) will elaborate the necessary innovations in the fields of BTES prediction and control engineering as well as the technical-economical basics for the conceptual design of a full-scale test and demo site. This demo site will be accompanied by a follow-up F&E&I project.