Electrical energy storage
Electrical energy storages are essential for the reorganization of the energy system. In this field, we focus on the development of batteries and SuperCaps. The applications of batteries are numerous and range from compact mobile entertainment and communication devices, batteries for hybrid and electrical vehicles through to storages for renewables with MW/MWh capacities. The common development goal of these fields of applications is an ideally high energy and power density, which means short loading and unloading times. A reliable operation and a long durability are further features.
Redox-flow batteries are a pioneering technology for the energy storage with high outputs (megawatts). The stored energy is held in external tanks and can be converted in the conversion unit when needed. They offer the possibility of individually adjusting power (kW) and energy (kWh) of the application. The applications range from the storage of renewables from fluctuating renewable energy sources and the possible usage as almost continuously available energy storage in the grid through to the uninterruptible power supply.
Rechargeable lithium-ion batteries are increasingly used in all areas of daily life and also gain importance as stationary temporary energy storage.
Advantages of the lithium-ion battery include its low self-discharge rate, the fact that there is no considerable memory effect and its high energy density. Especially the electric mobility in form of e-cars or e-bikes makes use of the high energy density in order to achieve a long range. In addition to the development of materials, their processing and process engineering, battery management and monitoring as well as investigations into the security of these energy storages are also at the focus of the Fraunhofer Energy Alliance.
With their very high power density and related short retrieval and charging times, double-layer capacitors are an alternative or complement to battery technologies. Researchers at Fraunhofer are committed to improve these SuperCaps by using new materials and coating technologies.
Chemical energy storage
Against the background of an increasing interconnection of different fields, the conversion of electrical energy into chemical energy plays an important role. For example, Fraunhofer’s researchers are working on relevant power-to-gas procedures, which make it possible to chemically store energy in form of hydrogen or methane.
Mechanical energy storage
In addition to pumped-storage power plants, compressed air energy storages have become well-established as industrial plants for stationary electromechanical storage of energy. Experts of the Fraunhofer Energy Alliance develop applications for the usage of this technology at a smaller scale (5-50MWel).
Thermal energy storage
As latent heat accumulators, phase-change materials (PCM) increase the heat capacity of buildings and ensure a stable and pleasant indoor climate. In production, its operating temperature can be adjusted from -10°C to 80°C (14°F to 176°F). Of particular importance is the usage in lightweight construction, as they can be directly integrated in the plaster or dry construction panel in form of microcapsules. Besides buildings, PCM can also be used in any application where there is need for a high heat storage capacity in a small area, for example in heat exchangers or water heaters. Experts at Fraunhofer also work on pumpable high performance refrigerants like ice suspensions for use in process and transportation cooling or in the food industry.
Absorption and adsorption processes also make heat and cold storage possible. This so-called sorptive or thermochemical heat storage provides the advantage of achieving a very high storage density and covering a wide range of temperatures. Moreover, thermal energy losses during the storage period are minimized.
Micro Energy Harvesting is a relatively young discipline in the field of mobile power supply of small devices and in off-grid applications. Especially thermoelectric and piezoelectric energy conversion methods are applied here. In thermoelectric energy conversion, a temperature gradient is converted into electrical energy.
Piezoelectric energy conversion is based on the generation of voltage by pressure and vibrations. When monitoring the function in moving or remote plants, systems designed by the Fraunhofer Energy Alliance can provide power for the radio transmission of sensor signals.
Fuel cells are a promising technology for the future energy supply. The Fraunhofer Energy Alliance develops new system components both for fossil and renewable fuels like ethanol, biogas or hydrogen. These include electrode membranes for high-temperature fuel cells as well as polymer electrolyte membranes and electrocatalysts for direct alcohol or reformate fuel cells.
Our member institutes conduct research on innovative testing procedures, especially for the automotive application of fuel cells and offer customers appropriate measuring services. A further field of research are systems for the (electro)chemical provision of hydrogen.