Interim findings of the Energy Storage Research Initiative
Last week, the 2nd status seminar on energy storage systems took place in Berlin from 22 to 23 April, 2015. The focus was on the following questions: Which contribution can energy storage systems make to the energy transition? How can they be employed economically? And what are the future research priorities? At present, the German Federal Ministry for Economic Affairs and Energy and the German Federal Ministry of Education and Research are funding 186 projects with a total of 202 million euros. During the two-day event, the coordinators presented the interim results of their projects. The research initiative is taking its half-time break. An interim report.
With the conversion of the energy supply system as part of the energy transition, the demand for storage capacity is increasing. This is why the federal government launched the Energy Storage Research Initiative back in 2011. The German Federal Ministry for Economic Affairs and Energy and the German Federal Ministry of Education and Research are funding 186 projects of the initiative with a total of 202 million euros. The research initiative is taking its half-time break. After the first joint status meetings in January 2013, the project participants are now taking stock.
During the event, the questions of what energy storage systems can contribute to the energy transition, and which technological breakthroughs had been achieved, were dealt with. Dr Karl Eugen Huthmacher, Director-General of the department “Provisions for the Future” of the Federal Ministry of Education and Research, said at the opening of the status seminar: “There is no single storage technology, but Germany needs a reliable energy storage system. There are a few promising research approaches.”
The status seminar also addressed the priorities for future research. “Due to the expansion of renewable energies, there will be strong fluctuations in electricity generation. Energy storage systems will become increasingly important for stability,” said Dr Georg Menzen, Head of Energy Research Unit of the Federal Ministry for Economic Affairs and Energy.
The event served as a forum for the presentation of interim project results and gave researchers the opportunity to exchange ideas and to network with other experts.
Cooperation between academia and economy
The status seminar served to present the interim results of the collaborative projects, exchange ideas and network with other experts. The talks were held in eleven topic-oriented technical sessions on the following topics:
- Battery storage systems and energy management aspects
- Power-to-Gas technologies and applications
- Thermal energy storage systems
General findings of the technical sessions
Key observation of the status seminar: the profitability of projects has come to the fore. The leitmotif of many technical sessions, in particular of systems analysis or storage systems in grids: the economic feasibility of energy storage systems depends heavily on the regulatory framework.
Another conclusion was that finding business models is the current challenge that crops up in many projects. Battery demonstration projects are already relatively advanced, and are largely in their pre-field test phases or further.
Components for battery storage systems
Dr Andrea Balducci reported on the development of electric double-layer capacitors with improved electrochemical performance and increased intrinsic safety for application in high-voltage and high-performance systems. As part of the IES project, the research group around Balducci at MEET in Münster, together with Dr Stefano Passerini’s research group at the Helmholtz Institute Ulm and the companies Iolitec and Brandenburgische Kondensatoren, examined all components of supercapacitors in order to improve their overall performance. The aim was to increase both the energy and power density by increasing operating voltage. This was achieved with novel electrolytes. What proved to be an obstacle was that activated carbon with a microporosity that would suit the electrolyte was not available on the market. So they developed a simple and inexpensive manufacturing process using agricultural waste. The researchers also developed a new method for the synthesis of high purity graphene, which has now been patented.
The researchers will apply their insight gained to building a prototype. The prototype is designed for a maximum operating supply voltage of 3.5 V rather than 2.5 V, as would be customary. This will triple the specific energy density at room temperature to 15 Wh/kg. Internal loss resistance should not exceed 5 Ω cm2.
Power-to-Gas session recap
In the Power-to-Gas projects, basic catalyst development through to components and systems will be studied. While doing so, effects that could advance the technology and make it more viable will be taken into account. Forecasts show that some projects could be implemented in a financially profitable way even before 2030, thereby reaching the business case phase.
Jonas Aichinger from Stadtwerke Mainz reported on the progress made in the flagship project “EnergieparkMainz”. In this joint research project, the entire process chain of Power-to-Gas technology is being tested for hydrogen electrolysis purposes. Electricity from different sources, such as wind power, balancing energy or the spot market, will be used to produce hydrogen via PEM electrolysis. This is then compressed by a new ionic compressor. A pressure accumulator with a capacity of approximately 1,000 kg is used for storage – this corresponds to approximately 33 megawatts. A so-called hydrogen refuelling station completes the system. Natural gas grid feed-in is being tested as well. The system installation is now largely completed. Compressor and trailer filling have already been in operation, and the accompanying research on operational strategies in the electricity market has started. The system will be officially inaugurated on 2 July 2015.
PEM electrolysis in the laboratory
Basic research and testing of PEM electrolysers, including high-performance ones, shall become possible in the TEZEL test centre. Dr Arne Fallisch from the Fraunhofer Institute for Solar Energy Systems ISE gave a lecture on the current status of planning and equipment installation. A unique test environment is being built on a total of 750 m² of laboratory area. A 1-MW-electrolysis test rig was supplied for the short and long-term characterisation of pressure electrolysis cell stacks. The system allows for tests with currents of up to 4,000 A on 30 to 120 cells, and cell areas of up to 2,000 cm². Another 200-kW test rig is being used for the long-term characterisation of pressure electrolysis cell stacks (up to approx. 30 cells, 4,000 A) and the investigation of long-term effects. Work on the control room is largely finalised.
However, the hydrogen storage facility is still in its planning phase. The analysers are mostly available. A computer tomograph is being delivered in June. The researchers expect that regular test operation can be started in early 2016.
Energy management aspects of battery storage systems
Dieter König from the Technical University of Dortmund informed about the research project Die Stadt als Speicher (The city as a storage system). Until 2017, scientists from research institutes, energy utilities, and the industry will analyse the increasing divergence of rural areas, with decentralised energy generation, such as wind and solar, and urban areas with a high energy consumption and relatively low production. “The money that cities can put to work for the integration of renewable energy is the already existing thermal storage capacity for cogeneration and the increasingly flexible consumers,” said Mr König. The researchers’ approach: to use the combined flexibility of urban areas as a virtual storage system. To this end, they are examining the potential under real conditions, and they are evaluating different operating and communication strategies. In addition, the researchers are developing appropriate strategies to avoid additional grid loads with virtual energy storage systems, and business models for operation itself.
From the technical session to the thermal storage system
Dr Stefan Henninger reported on progress made in the HyAktiv project. Researchers at the Fraunhofer Institute for Solar Energy Systems ISE are developing an open sorption thermal storage system based on activated carbon and water. For the researcher from Freiburg, a major advantage over the well-known zeolite/water systems is the relatively low charging temperature: “An activated carbon storage system should do fine at a charging temperature of 120 °C, while zeolite storage systems usually require over 160 °C,” said Dr Stefan Henninger. Therefore, zeolites cannot be used in many solar thermal applications or local heating systems. Activated carbon is also inexpensive, and it has a favourable CO2 balance when produced using renewable raw materials. The material properties are easy to control via the manufacturing process. The disadvantage is the lower enthalpy, leading to a lower storage density. As a conservative estimate, Dr Stefan Henninger expects that storage densities of roughly 120 kWh/m3 can be reached.
Based on economic and energy-related considerations, Dr Stefan Henninger does not see the area of application in seasonal storage systems, but rather in monthly or weekly storage systems and in so-called peak-shifting - for example, in combination with CHP plants or local heating networks.
When the project started, there were critical voices asking whether or not the hydrophobic raw material could even be hydrophilised to a sufficient extent. It was also unclear if it would adequately withstand many cycles. Both issues have never been properly studied. During the project, the researchers produced evidence that the material indeed reaches the necessary adsorption capacity, and that this capacity declined by less than 10 percent after 50 cycles.
Demonstration of the storage system to start in 2016
Currently, the HyAktiv researchers are shaping the system. The activated carbon based on coconut is extruded into a honeycomb-like body using binders and additives. This allows for a high storage density combined with good throughflow properties. At the end of the project in 2016, the researchers aim to demonstrate the functionality of a storage system on a laboratory scale.