Energy Storage

The International Energy Agency's (IEA) "Experts Group on Science in Energy", has identified the development of efficient and cost-effective energy storage as the most important challenge for future R&D activities. Energy storage systems are essential for integrating renewable energies and increasing energy efficiency.

The integration of highly fluctuating energy sources such as wind, photovoltaics or solar thermal energy relies on efficient storage technologies for electrical and thermal energy. The storage of heat and cold is particularly important for increasing efficiency in industrial processes or buildings. Last but not least, electric energy storage systems also play a decisive role in electromobility. ZAE Bayern is internationally recognized for its expertise in the field of energy storage.

This is also reflected in the strong presence in various bodies of the International Energy Agency IEA. Due to the fact that ZAE Bayern has been dealing with energy storage topics since its foundation, they are accompanied in their entire breadth from the basics to implementation.

ZAE Bayern's expertise in the field of thermal and electrical storage can then be used to handle the possibilities of energy storage, which arise from the conversion of thermal to electrical energy (e. g. in the operation of solar thermal power plants) and vice versa (e. g. the integration of wind power through decentralised thermal energy storage systems). Questions can also be answered where thermal and electrical systems play a role, such as the thermal management of batteries.

Fields of Research

Electrical Energy Storage

Stationary electrical energy storage systems contribute decisively to the stability of the grid and the integration of renewable energy technologies into it. ZAE Bayern, in close cooperation with the Chairs of Electrical Energy Storage Technology (TUM-EES) and Technical Electrochemistry (TUM-TEC) of the Technical University of Munich, will therefore significantly intensify its activities in this area. The development of components, e.g. for redox flow systems, is in line with the development of system technology and network integration. ZAE strives to establish itself in this research area with the help of TUM.

Contact

Dr. Mathias Rzepka
+49 89 329442-31
Matthias.Rzepka@zae-bayern.de

Super Capacitors

In the field of energy storage, supercapacitors are clearly superior to batteries in terms of cycle stability and power density. Compared to Li-ion storage, however, supercapacitors have a significantly lower energy density, so that correspondingly large volumes are required for storing large amounts of energy.
ZAE Bayern has the necessary expertise in materials science for synthesis and electrochemical characterization of nanoporous electrode materials. The volume change of the electrodes during charging and discharging processes can also be measured in-operando by means of dilatometry.

Contact
Dr. Gudrun Reichenauer
+49 931 70564-328
gudrun.reichenauer@zae-bayern.de

Thermal Energy Storage

In the field of energy storage systems, ZAE Bayern has so far been primarily investigating thermal storage systems. Research and development focused on the storage of sensitive heat, latent heat storage and thermochemical storage. All areas of research have been dealt with from fundamental questions, e. g. the theoretical limits of storage capacity or material development, to questions of system integration or product development. ZAE Bayern has made a name for itself nationally in the field of thermal energy storage systems through a series of research projects for the BMBF and the BMWi. This is also underlined by the growing number of inquiries from industry. In this context, the main focus is on increasing energy efficiency in industrial production processes.

Particularly noteworthy is the fact that all techniques of thermal energy storage - sensitive, latent and thermochemical - from fundamental questions of material development and characterization to demonstration plants or commercial products are dealt with. In this context, ZAE Bayern's expertise in the field of heat transformation using sorption heat pumps and chillers should also be mentioned. This significantly expands the possible application areas of the storage systems by adapting the required temperature levels.

Contact

Dr. Stefan Hiebler
+49 89 329442-35
Stefan.Hiebler@zae-bayern.de

Heat Storage Systems

Mobile Energy Transport

  • Experimental investigation of sorption equilibria for solid sorbents
  • Dynamic simulation of ad and absorption processes
  • Design of open sorption systems
  • Design and calculation of mobile sorption storages
  • Mobile energy transport through mobile storage facilities (MobS)
  • Construction and measurement of pilot and demonstration plants

Solar air conditioning

  • Dynamic simulation of ad and absorption processes
  • Dynamic system simulation of the plant engineering
  • Design of open sorption systems for heating, cooling and dehumidification
  • Design and calculation of sorption memories
  • Experimental investigations of sorption equilibria
  • Construction and measurement of pilot and demonstration plants

Sorption processes for energy saving

  • Open sorption systems with solid and liquid sorbents
  • Applications for heating, cooling, dehumidifying and drying
  • Storage of thermal energy
  • Experimental investigation of sorption equilibria for solid and liquid sorbents
  • Dynamic simulation of ad and absorption processes
  • Design of open sorption systems and sorption storages
  • Construction and measurement of pilot and demonstration plants

Contact

Dipl.-Ing. Eberhard Lävemann
+49 89 329442-18
Eberhard.Laevemann@zae-bayern.de

Projects

Seasonal Heat Accumulators

Heat storage unit

The cost-efficient long-term storage of heat is a key technology in the provision of heating energy from strongly fluctuating renewable energies such as solar radiation. In order to guarantee the highest possible proportion of solar energy in the heat supply, it is necessary to compensate for the time lag between high levels of solar radiation in summer and high heating demand in winter when solar radiation is comparatively low with the storage tank. The low number of 1-2 storage cycles per year also places very tough constraints on construction costs in order to provide an economically acceptable solution. Today, these requirements can only be met by large underground thermal energy storage facilities such as large thermally insulated water tanks, geothermal probes, aquifer or gravel/water storage facilities. For underground reservoirs, geothermal heat probes and gravel/water reservoirs, there must be no flowing groundwater in the storage area in order to minimise heat losses.

Due to the hydrogeological situation, a 6000 m3 underground concrete tank was therefore used as a hot water storage tank in the Ackermannbogen solar local heating project in Munich, the sidewalls and roof were assembled with precast concrete elements. Inside, the storage tank is lined with stainless steel sheet metal to prevent vapour diffusion through the walls, which on the one hand would cause a high heat loss and on the other hand would lead to moisture penetration of the thermal insulation. The storage tank floor is insulated with foam glass gravel, wall and ceiling with a filling of expanded glass granulate (0.50-0.70 m thick). The reservoir was then filled with soil outside and is now integrated into a hill in the green area next to the residential quarter.

Another very cost-effective solution is the geothermal probe storage tank, which can be built both in unsaturated subsoil and in stagnant groundwater. Due to the limited transmission capacity of geothermal probes, a buffer storage tank must be included in the storage system. In the solar local heat project in Attenkirchen, a hybrid storage tank was used for the first time, in which an underground hot water storage tank with a volume of 500 m³ is in the centre of a geothermal probe storage tank (90 probes, 2 m distance, 30 m deep). The internal hot water storage tank is thermally coupled with the geothermal probe field. No waterproof inner lining is used and the entire storage tank is only thermally insulated at the top. By serial connection of the two systems and a loading from the inside to the outside, or rather a discharge in the opposite direction, a horizontal layering is created and thus heat losses are minimized.

As it does not require a buffer tank, this combination unites the operating advantages of a water storage tank with the economic advantages of the geothermal probe storage tank. Like the geothermal probe storage tank, the hybrid storage allows the storage tank to be adapted to an increased demand by adding probes.

Contact

Dipl.-Phys. Lars Staudacher
+49 89 329442-41
Lars.Staudacher@zae-bayern.de

Mobile Sorption Storage Systems for the Use of Industrial Waste Heat

 sorption storage

Waste heat from industrial processes is often emitted to the environment at high temperatures and with high outputs because it cannot be used on site at the present time. Mobile sorption storages are an option to utilize this thermal energy. ZAE Bayern carried out a project funded by the Federal Ministry of Economics in cooperation with Hoffmeier Industrieanlagen in Hamm and the waste incineration plant Hamm Betreibergesellschaft. The project started in December 2009 and was completed in 2013.

The aim of the project was to develop a mobile heat accumulator on the grounds of an open sorption process and to build and operate a demonstration plant.

The storage tank was designed as a fixed bed zeolite filling. During charging, hot air flows through it. In this process, water vapour is expelled from the zeolite. During unloading, a cool, humid air stream flows into the accumulator. Water vapour from the air is adsorbed on the zeolite. The adsorption heat released heats up the air, which in turn releases its heat to a subsequent process. The storage tank is mounted on a container swap body and transported on a semi-trailer.

Two storage tanks were planned for the demonstration plant, which were manufactured by Hoffmeier Industrieanlagen. The heat is supplied by the waste incineration plant in Hamm and used in a drying process of the company Jäckering Mühlen- und Nährmittelwerke, which is about eight kilometres away. The sites were equipped with stations for loading and unloading the storage tank. These are ventilation systems consisting of fans, filters and heat exchangers. The plants went into operation in the first quarter of 2012.

Contact

Dipl.-Ing. Eberhard Lävemann
+49 89 329442-18
Eberhard.Laevemann@zae-bayern.de

Materials research for thermochemical storage systems

foto thermochemical storage

In order to achieve the goals of integrating renewable energies and increasing energy efficiency in the future, efficient and cost-effective thermal energy storage technologies must be developed. Thermochemical heat and cold storage systems can provide the highest storage capacities of all thermal storage technologies.

The aim of a project funded by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) was to establish a laboratory for the characterisation and evaluation of thermochemical storage materials in thermal energy storage applications.

For the characterization of thermochemical storage materials, suitable laboratory equipment should be purchased and put into operation to determine the material properties and reaction parameters. For the investigation of stability of thermochemical storage materials, an ageing test stand was set up. The hydrothermal cycle stability and the stability of the material against the influence of harmful gases were investigated. For the application-oriented assessment of thermochemical storage materials, a modular test stand was designed, constructed and put into operation, which was able to determine the boundary conditions of the various applications (cold, heat and high temperature storage). Finally, experimental proof of the effective storage capacity of various materials for the seasonal storage of solar heat should be provided.

The project, which began in October 2011, opened up the possibility of deepening theoretical and practical knowledge in the field of thermochemical energy storage. The results obtained in the experimental set-ups contributed to an improved understanding of the mechanisms underlying material ageing and to predictions on the stability of the materials. Finally, by standardizing material characterization and measurement under defined reference conditions, storage materials could be compared.

Contact

Dipl.-Ing. Eberhard Lävemann
+49 89 329442-18
Eberhard.Laevemann@zae-bayern.de

Development of innovative PCM

 PCM Storage -phase change materials-

Phase change materials (PCM) are used to store thermal energy as they can store large quantities of heat in small temperature ranges. In practice, materials with a solid-liquid phase change have been used in the past, as the storage density is particularly high in relation to the storage volume. However, a substance that is sometimes solid and sometimes liquid must be encapsulated in a suitable way for the application. Encapsulation is always a cost factor in the construction of storage facilities and can possibly also reduce the effective storage density significantly.

Against this backdrop, ZAE Bayern is investigating various possibilities for the production of dimensionally stable PCM using polymer technology as part of the ENFoVerM project ("Development of novel PCM, dimensionally stable PCM and PCM composite materials with improved thermal conductivity"). The aim of the work is to develop substances that melt on a molecular level but remain macroscopically solid.

How can you picture that? With "regular" PCM, a solid-liquid phase change takes place. In the solid state, the "components" of the substance, i. e. ions, molecules or polymers, are bound, i. e. fixed in their mutual position, and thus give the body an external shape. Above a characteristic temperature, the melting temperature, these rigid bonds are released, the components can move against each other: the material loses its outer shape and melts. The substance absorbs the melting energy. When cooling below the melting temperature, the bonds are re-formed and this energy is released again. The material can thus be used as a thermal storage medium.

ZAE is investigating various options for the production of polymer-based, dimensionally stable PCM. In comb polymers, the teeth of the comb function as the actual phase change material, while the ridge back ensures external stability. In polymer blends, dimensional stability is achieved by embedding small droplets in a matrix of solid material. Unbranched block copolymers can act as stable PCMs when an amorphous-crystalline transition of a block takes place while the second block provides crosslinking of the polymers and thus dimensional stability.

In the ENFoVerM project, further topics at material development levels will be investigated. These are studies on PCM mixtures, polymer-based PCMs and the improvement of the thermal conductivity of PCM by appropriate additives. In addition, an attempt is being made to develop a superordinate, theoretical understanding of the interrelationships at PCM.

Contact

Dr. Stefan Hiebler
+49 89 329442-35
Stefan.Hiebler@zae-bayern.de

ZAE Bayern

We work at the interface between knowledge-based basic research and applied industrial research. Under the motto "Excellent Energy Research - Excellent Implementation", we realize complete innovation packages that build on synergies between generation, storage and efficiency measures.

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