*3.1. Reproducible Production Technology for MEAs*

In PEM electrolyzers, the MEA is situated between the gas diffusion layers and consists of two porous, gas-permeable electron- and proton-conducting catalyst layers (anode and cathode) that comprise a gas-tight proton-conducting polymer membrane. Iridium oxide and platinum are common catalyst materials. Nafion, a perfluorinated alkyl sulfonic acid, is predominantly used as a proton-conducting material. Nafion is also used as an electron-isolated proton-conducting material for the membrane itself.

For the production of MEAs in the MW scale, it is important that the manufacturing processes used meet the requirements for scalability and production speed. The transfer or decal method outlined in Figure 2 meets these requirements. The process steps used, such as coating a substrate with a catalyst dispersion using a doctor blade or slot die and the subsequent drying, can be carried out in a laboratory or a roll-to-roll process. This also

applies to the subsequent assembly process where the dried catalyst layers are transferred from substrate to a membrane with a hot pressing process.

**Figure 2.** Process steps for producing an MEA using the decal process.

The production of MEAs for PEM water electrolysis faces the challenge of increasing the electrochemical efficiency of the MEAs and structuring the entailed processes in such a way that they are scalable and can be mass-produced. The electrochemical efficiency of MEAs partially depends on the thickness of the membrane used, as the protons flowing through the membrane during cell operation induce ohmic losses. This requirement can be fulfilled using the aforementioned decal process in which the thinnest possible membranes are used during assembly. However, a compromise must be made between membranes that are as thin as possible but still easy to handle in the production process.

Scalable processes, such as slot die or blade coating, are ideal for the industrial-scale coating of a substrate. A disadvantage of blade coating (a form of self-metered coating) is that the homogeneity of the coating cannot always be precisely controlled [70], whereas slot dies (which allow for a pre-dosed coating) can produce highly homogeneous coatings in combination with homogeneous substrates [71]. The possibility of pre-dosing means that the catalyst loading of the electrodes can be precisely adjusted by means of the dosing rate of the pump and the coating speed, provided that the dispersion composition is known. As the MEAs in the stack are connected in series for PEM electrolysis, it is highly important that the electrodes are identical and that the rolls of electrodes being produced from which the electrodes are subsequently cut are also homogenous. The specifications shown in Table 2 were applied for the catalyst loading of the MEAs being produced for the MW electrolysis system.

**Table 2.** Materials used in the construction of the MEAs.


A Premion (Alfa Aesar) IrO2 catalyst was used as the anode catalyst and a Pt/C 60% high surface area (HAS) Ketjen Black (Fuel Cell Store) catalyst was used as the cathode catalyst. The Nafion NR212 membranes were purchased from Chemours. An additional specification was the use of a recombination catalyst to be inserted into the MEA to break down the hydrogen permeating through the membrane with oxygen and thus minimize the safety risk presented by oxy-hydrogen formation during operation of the stack. As previously published methods of use of such recombination systems [72,73] could not be scaled to the required production size, a new method was developed and used for the production process described in the following sections [74].

Dispersions were produced from the catalyst powders that were applied to a fiberglassreinforced polytetrafluoroethylene (PTFE) roll in the roll-to-roll coating system (Figure 3a) by means of a slot die. During drying, it must be ensured that the combination of solvent evaporation and the formation of layers does not lead to layer defects and the flaking of

dried layers [75,76]. The specific machine settings were determined in preliminary tests. After drying, the coated material was rolled up (see Figure 3b) and the electrodes were cut from the roll with dimensions of 32.5 × 32.5 cm2 (see Figure 3c).

After producing the anodes and cathodes, they were assembled together with the Nafion NR212 membranes using hot presses from P/O/Weber. After pressing, the substrates were then removed from the cooled MEAs, which were then completed (see Figure 4).

**Figure 4.** (**a**): After assembly, the substrate could be removed from the electrode; (**b**): A complete and isolated MEA.

For the purpose of quality assurance, samples were taken from the rolls of electrodes to produce MEAs for laboratory cells and for the electrochemical characterization of the MEAs.

Figure 5 shows a polarization curve plotted from the characterization measurements, an efficiency curve, and a graph demonstrating the proportional volume of hydrogen in the anode gas. The latter clearly shows that safe operation can be achieved with the MEAs produced, even with small current densities. Within the scope of measurement uncertainty, no hydrogen could be detected as a result of the recombination catalyst being used.

#### *3.2. Compact, Efficient, and Robust Cell Components*

The previously considered MEA is a component that plays the main role in producing hydrogen in electrolyzers. It is here that the electrochemical water splitting reactions and the generation of heat occur due to operational and material-related overvoltages. However, as indicated by the setup of the MEAs, additional cell and stack components are required to produce hydrogen in MW electrolyzers on an industrial scale. The entire assembly of the electrolyzer must support the following process functions:


On the left-hand side of Figure 6 can be seen an exploded view of an electrolysis stack from the Ekolyser project (funding reference no. 03ESP106A) being funded by the Federal Ministry for Economic Affairs and Energy (BMWi). The stack is closed off by two massive end plates through which the media are added and removed and through which the power connection is made. The combination of end plates and tie rods also ensures that the inner components are pressed together. A defined contact pressure helps to ensure that the components are sufficiently sealed and that they have electrical or mechanical contact. The contact pressure is adjusted via the tractive forces in the tie rods. A distinction must be made between two areas: the active cell area and the sealing area. Although the optimal contact pressure on the active cell area is 2–3 MPa [44], the required pressure on the sealants is dependent on the sealing concept. The inner components are the repeating units of the electrolysis stack. A repeating unit always consists of one bipolar unit and one MEA. In Figure 6a, three bipolar units are shown. The MEAs (not shown here) are each arranged between the bipolar units. The active cell area is 300 cm2 (10 cm × 15 cm). In Figure 6b, an assembled electrolysis stack comprising 27 cells can be seen. The stack is designed for an electrical power supply of 50 kW with a maximum operating pressure of 50 bar.

**Figure 6.** Electrolysis stack from the Ekolyser project; (**a**): Exploded view with three bipolar units; (**b**): 27-cell stack, 50 kWel, 50 bar.

Developed as part of the Ekolyser project, the bipolar unit with seven individual components is shown in Figure 7. The central aspect of the bipolar unit is the bipolar plate, which separates the anode and cathode sides of the two adjacent electrolysis cells in a gas-tight manner. The bipolar plate is made of stainless steel 1.4404 (316L) and also features flow distributor structures that are produced by hydroforming to distribute the feed water equally across the active cell area and to remove the produced gases—oxygen on the anode side and hydrogen on the cathode side—with surplus water. The bipolar plate is enclosed on both sides by a polyether ether ketone (PEEK) frame. The frames feature distribution and collector structures for the inflow/outflow of media (water and two-phase flow) from pipes installed at the end plates (see Figure 6b) to the respective cell level. Additional covers made of stainless steel are required to provide mechanical support for sealants (not shown) in the distribution and collector structures. The frame cutouts admit fine distribution structures of varying porosity on the anode and cathode sides. The anode side features a layer of sintered Ti powder. A perforated stainless steel plate is used on the cathode side. In addition, a carbon fiber layer can be found on the MEA side, which is not shown in Figure 7.

**Figure 7.** Bipolar unit consisting of several parts from the Ekolyser project.

A significant drawback of this bipolar unit is the fact that all components must be individually laid on top of each other when assembling the stacks. For the 27-cell stack shown above, the individual parts (including O-rings) amount to around 600 for the repeating units alone. The assembly of the stacks is extremely time-intensive and there is also the potential for sources of error, which can lead to malfunctions in stack operation. These

include leaks outside and within the stack, as well as inhomogeneities in contact pressure distribution. The higher the number of individual components, the greater the likelihood of errors occurring during assembly. The dimensional tolerances of the components and the shifting of components during assembly play a key role in ensuring the quality of the entire assembly.

To counter this problem, the development of a "one-component bipolar unit" was initiated as part of the Energy Lab 2.0 and LLEC projects. Another aspect to consider was that only cost-effective, readily available raw materials should be used. The active cell area also had to be significantly increased to approximately 1000 cm2 in order to advance development towards MW electrolysis. The starting components for the newly developed bipolar unit are shown in Figure 8. A distinguishing feature of the bipolar unit is that all of its components are comprised of Ti. According to Lædre et al. [77], Ti is a material that exhibits good corrosion stability under electrolysis conditions. To counteract degradation effects, an additional coating may need to be applied to the contact areas of the MEA. The setup shown in Figure 8 reveals a simple central plate with drill holes and elongated holes for the supply of media. The double-sided simple frames merely contain holes that enable media to pass through. Three-part expanded metal sandwiches are inserted into the frame interiors. The elongated holes in the center plate allow the media to flow in and out of these areas. The expanded metal sandwiches serve as flow distributors. A Ti fleece acting as a fine distribution structure can be found on the anode side of the bipolar unit.

All previously described components are connected to each other in an interlocking manner by means of diffusion welding. This process takes place in a vacuum oven in which the stacked components are heated by thermal radiation up to a temperature close to enabling phase transition (882 ◦C for Ti). When the desired temperature is reached, a defined pressure is applied to the components through a mobile stamp in the oven.

As is shown in Figure 9, the stack assembly can be handled manually and easily by two people. Simple assembly aids in the form of plastic rods enhance the positioning accuracy of the components. The repeating units now comprise the following components: a bipolar unit, flat gasket, carbon fiber sheet, and an MEA. In Figure 9c, a fully assembled short stack can be seen. The performance and long-term behavior of the stack in operation has yet to be determined and will be documented and discussed in a later publication. The nominal power of a stack with 70 cells of this type will be in the range of 400 kW.

**Figure 9.** Manual stack assembly with one-part bipolar plate; (**a**): MEA; (**b**): bipolar unit; (**c**): interlocked stack.

#### *3.3. Design and Setup of the Test Facility*

On the basis of interdisciplinary approaches, Jülich researchers and engineers work on electrolysis technologies at various stages of development. A relatively new technology for industrial-scale application is polymer electrolyte membrane water electrolysis, which features dynamic operation and a high overload capacity. A new test facility, which is unique in this way, was developed in close collaboration with the Canadian company Greenlight, which is schematically illustrated in Figure 10. The test facility allows for the comprehensive characterization of PEM electrolysis stacks with an electrical output of up to 500 kVA with current intensities of up to 4000 ADC/10,000 ADC. The pressures can be flexibly adjusted between 4 bar and 50 bar for the anode and cathode circuits. Characterization can thus be flexibly performed at various pressure levels with balanced pressure or differential pressures.

**Figure 10.** Process overview of the MW electrolysis system.

The main features of the test facility are as follows: power electronics enable the conversion of 400 VAC mains electricity into direct voltage up to 125 VDC. The anode and cathode are each fitted with their own gas/water circuits, which are used for heating and cooling the stack as well as supplying it with water. The gas separators also separate the converted water from the produced gas in the circuits and can regulate the produced gases at pressures of up to 50 bar by means of membrane pressure regulators. Therefore, the gas can be made available for consumers or temporary storage. For stable and disruption-free electrolysis operation, the regulation of pressure to minimize the differential pressure between the two gas circuits is very important. The deionized fresh water required for electrolysis is supplied by an in-house system and introduced to the test stand using a booster pump in accordance with the current operating pressure. In addition to regulating pressure, the temperature is also optimally regulated, which has a significant influence on achieving optimal operation and helps to compensate for highly dynamic load changes and the resulting waste heat as quickly as possible.

Comprehensive recording and processing of the measurement data allows for automated operation under predefined load profiles and ensures the transfer of data to overarching control systems of EnergyLab and LLEC living labs, which are described in the following sections. Data are connected to the control systems of the LLEC, which enables optimal electrolysis operation in terms of energy efficiency and performance in the entire network of systems by means of a specially initiated data exchange in the Jülich virtual local area network (VLAN). The protocol used for the data exchange is based on the message queuing telemetry transport (MQTT) network protocol. The MQTT is very well suited for large networks of systems with high data transfer rates, as is predominantly the case with automation technology. Therefore, it is important that all units in the LLEC are equipped with an MQTT protocol. All required data are collected and evaluated centrally with the LLEC's control systems. To enable optimized operation in the entire network of systems, the desired values must be transferred to the available systems in addition to the evaluated data. This again takes place using the MQTT protocol to ensure optimized control at the highest control level. The electrolyzer itself is then capable of regulating the desired values and can implement the provisions of the LLEC's control system. Safety-based limits for the LLEC's desired values are integrated into the test stand control system and help protect the personnel and systems.

The test facility shown in Figure 11a enables the integration of various PEM electrolysis stacks up to an electrical power input of 400 kW for an active cell area of up to 1200–3000 cm2 if the power electronics reserve is expanded for currents of up to 10,000 ADC.


**Figure 11.** Electrolysis facility with first stack in the pilot plant; (**a**): PEM electrolysis test facility (GREENLIGHT); (**b**): 400 kW PEM stack (IEK-14, FZJ); (**c**): IGBT-based AC/DC converter (AIXCOM).

From a safety perspective, the legal and operational provisions were implemented, adherence to which was confirmed by successful inspections of the Technical Supervisory Association (TÜV), particularly in the areas of explosion protection and pressure equipment. From a technical standpoint, many of the required inspections were performed with the aid of a safety-oriented programmable logic controller (PLC).

The entire electrolysis system is part of a technical center that is equipped with the necessary facilities for the supply of media and energy, as well as the forward transport, conditioning, and removal of all products from the electrolysis process. The technical center also features the technical facilities required for ventilation and the safe removal of media, as well as a control room in which all measurements are recorded and processed.

*3.4. Energy Lab 2.0: Real-Life Laboratory and Simulation Platform for the Energy-Related Testing of Sustainable Conversion and Storage Technologies*

Energy Lab 2.0 [78] is a large-scale research infrastructure of the Helmholtz Association. Its mission is to develop technological solutions for a smart and integrated energy system for a defossilized future. Energy Lab 2.0 allows for technology-oriented research on a demonstration scale in order to successfully integrate renewable energy (RE) into the power grid.

In particular, all relevant components of a future energy system are considered, namely RE generation, storage and grid integration, and power-to-X conversion technologies (X = gas, liquid, heat)—all complemented with a comprehensive system analysis. At Karlsruhe Institute of Technology (KIT), the majority of the components have been set up. Moreover, certain components are located at the German Aerospace Center (DRL) in Stuttgart (Germany) and Forschungszentrum Jülich (Jülich, Germany), respectively (see Figure 12).

**Figure 12.** Energy Lab 2.0 at Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany; Photo: M. Breig and A. Bramsiepe (KIT).

For the Karlsruhe site, research at the Energy Lab 2.0 can be subdivided into three major areas: (1) the solar power storage park mainly focuses on short-term energy storage via different types of batteries, whereas the plant network (2) targets chemical energy carriers (power-to-molecules), and (3) the Smart Energy System Simulation and Control Center (SEnSSiCC) focuses on power hardware, the power grid, and consumers/prosumers both experimentally and via simulations. In order to investigate and demonstrate the coupling of the different components, plants are interconnected and can be operated within a smart grid design of interest (see Figure 13). Furthermore, power-to-heat is focused on at the DLR (Stuttgart, Germany), whereas major research is conducted on electrolysis at Forschungszentrum Jülich (Jülich, Germany).

3.4.1. The Solar Power Storage Park of the Energy Lab 2.0

A solar power storage park was built at KIT back in 2014. This storage park includes a 1 MWp photovoltaic (PV) system, as well as smaller storage systems. In addition, a 1.5 MWh Li-ion battery and an 800 kWh redox flow storage system were integrated into the park as part of the Energy Lab 2.0 project. Storage systems on a large scale will only be used when their deployment is economically-viable. Economic viability is not only influenced by the investment costs but also by the lifetime and design of the systems, the system control, and system design, including their overall efficiency. The impact and optimization potential of these aspects in terms of the economic viability of the systems are being investigated as part of various projects centered around the Energy Lab 2.0. Efficiency losses in such storage systems can occur, for instance, due to the high cooling and heating requirements. In order to reduce these losses, an innovative cooling concept was developed for the 1.5 MWh Li-ion battery, which was integrated into a concrete structure. The thermal

component activation of the concrete structure and the use of groundwater to control the temperature of the batteries by indirect water cooling ensure minimized system operating costs (through increased efficiency) and a long lifetime for the battery modules as a result of the enhanced temperature control. There also exists the potential to optimize redox flow batteries (RFBs) in terms of efficiency [79]. In addition, research on intelligent operating strategies is being conducted on RFBs and Li-ion batteries. In the majority of cases, the operator of a Li-ion storage system is provided with information on the state of charge. However, the actual state of charge and the battery's usable energy depend on the system's discharge capacity. A model that is capable of self-learning during operation is currently being developed and would be able to provide information on the state of energy of the entire storage system. Furthermore, one of the smaller storage systems is being operated to replicate a Li-ion storage system in a multifamily home and is virtually connected to a part (30 kWp) of the 1 MWp PV system.

**Figure 13.** Interacting components: power generation, transformation, and storage in the Energy Lab 2.0 plant network (power-to-X) coupled with energy systems analysis on the theoretical and experimental levels in the Energy Lab 2.0 Smart Energy System Simulation and Control Center. Solid lines—physically-implemented coupling in the Energy Lab 2.0; dashed lines—data and model exchange; blue lines—electricity; green lines—chemicals; red lines—heat; yellow lines—data and models.

Li-ion batteries are subject to particularly strong degradation if they are in a high state of charge for a long period of time. This can be reduced through an intelligent operating strategy [80,81]. PV and load forecasts are both vital components for arriving at such intelligent operating strategies. Currently research is being conducted to determine which type of PV forecasting methods are best suited for intelligent charging strategies [82].

#### 3.4.2. Power-to-Molecules in Decentralized and Highly Efficient Plants

In the future energy system, "power-to-molecules" technologies will be an important piece of the overall puzzle, not only as an option for chemically-storing electrical energy, but also as a source for CO2-neutral fuels and chemical feedstocks. Within the plant network of the Energy Lab 2.0, there is a focus on the synthesis of hydrocarbons—namely methane and Fischer–Tropsch-based fuels—from CO2 and H2. Although green hydrogen can be obtained through electrolysis, non-fossil CO2 must be captured from the air (direct

air capture—DAC), generated from biomass, or separated from unavoidable industrial point sources that cannot be decarbonized, for example, by electrification. At the Energy Lab 2.0, a PEM electrolysis unit (100 kWAC nominal power, operating pressure of up to 47 bar) and a high-temperature reversible steam electrolysis/fuel cell unit (electrolysis mode: 150 kWAC; fuel cell mode: H2: 25 kWAC, CH4: 20 kWAC) are used to investigate integration into certain process chains. Within the Kopernikus Project "P2X", funded by the German Federal Ministry of Education and Research, a high-temperature co-electrolysis system will be installed. In order to capture CO2 from ambient air, DAC is integrated into the plant network, for example, within the framework of the Power-Fuel project funded by the German Federal Ministry for Economic Affairs and Energy.

Predetermined by the local and temporal availability of both non-fossil CO2 and green electricity in a future defossilized energy system solely based on renewable energy, power-to-molecule process chains must be tolerant to input fluctuations (not only in terms of minutes but also on a day/season scale) and intensified, also allowing for decentralized application. Dynamic operation and process intensification are the major objectives investigated in the synthesis plants at the Energy Lab 2.0, namely the three-phase methanation [83] (output equivalent to 100 kW) and eFuel synthesis plants (1 bpd Fischer–Tropsch products).

While conventional plants for eFuel synthesis, for example, via the Fischer–Tropsch (FT) route, are designed for steady-state operation due to several hurdles such as hot-spot formation; in contrast, process intensification enables the reactor's volume and plant's complexity to be reduced [84]. This is why, in the eFuel synthesis plant (INERATEC GmbH) of the Energy Lab 2.0, a modular microchannel-based reactor is used. Projects utilizing the Energy Lab 2.0 s infrastructure investigate the benefits of process-intensified and modular equipment on the design of the process chain. For example, in the PowerFuel project, the required tank size for buffering the hydrogen produced from renewable sources was investigated. The results show that it is possible to drastically reduce the intermediate tank size due to the ability of the microchannel-based FT reactor and of the eFuel synthesis plant in general to operate under reduced feed within a response time of a few minutes [85].

In a study conducted at KIT, the eFuel synthesis plant of the Energy Lab 2.0 was simulated in AspenDynamics within the framework of the aforementioned PEM electrolyzer plant (160 kWAC overload situation), the 50 m<sup>3</sup> hydrogen tank (which corresponds to up to 2300 Nm<sup>3</sup> H2) and an assumed 320 kWp PV field with experimentally-determined power profile data of the solar power storage park (two weeks in the spring of 2015). The electrolyzer in this scenario was assumed to instantaneously follow the PV profile (with a 10 min temporal resolution). Only the ramp-up was capped in the model, as at least 40% of the nominal load was required to run the system experimentally. It was shown that the control strategy applied for the synthesis plant significantly influences the number of required shutdowns enforced by the unsteady supply of electrical energy and, thus, hydrogen in such a scenario. When running the synthesis plant under steady-state conditions, its operating time can be as low as 35% and 48% when applying constant H2 feed equivalent to 150 kWel or 115 kWel electrolyzer load, respectively. In contrast, when running the synthesis plant dynamically, depending on the hydrogen production rate or a desired tank pressure level (see Figure 14), the operating time can be significantly increased to 70% or even 83%, respectively.

For dynamic synthesis operation, it was also shown via experiments on a relevant lab scale (H2 feed equivalent to 500 Wel electrolyzer load) that the ability of micro-structured reactors to cope with feed fluctuations does not influence the product quality, nor does it induce complete hydrogen consumption in the FT reactor, which could harm the catalyst due to the presence of the remaining CO. This is affected by the possibility of effectively controlling the reactor temperature [86].

**Figure 14.** AspenDynamics results for hydrogen supply from the 50 m<sup>3</sup> hydrogen buffer tank and the pressure in the tank as a function of time with underlying PV data of two weeks in spring 2015. The scenario considers the dynamic operation of the electrolyzer and pressure-dependent control of the synthesis plant. Low pressure limit for running the synthesis plant: 25 bar.

#### 3.4.3. The Smart Energy System Simulation and Control Center

The necessary coupling of various energy sectors in future and the fluctuation in the generation of power from renewable energy sources present an enormous challenge regarding the control and operation of future energy systems. In order to perform control and monitoring tasks under the most realistic conditions possible, the Smart Energy System Simulation and Control Center (SEnSSiCC) [87] was established as part of the Energy Lab 2.0 project. The SEnSSiCC brings together work on information technologies and the corresponding research aspects of the Energy Lab 2.0 (see Figures 13 and 15).

The following sub-labs form the SEnSSiCC: the Smart Energy System Control Laboratory (SESCL), which acts as a representation of the real power grid of the future where the most important energy systems are flexibly interconnected through a busbar matrix, ensuring that experimental configurations can be quickly changed; the Energy Grids Simulation and Analysis Laboratory (EGSAL), where the topography of future energy grids is simulated with the virtual integration of components [88] that are not available at KIT's Campus Nord; the Energy Lab 2.0 s Control, Monitoring and Visualization Center (CMVC), where software tools are being developed for the control room of future energy grids [89]; and the power hardware-in-the-loop (PHiL) laboratory test environment, which enables real hardware components to be integrated into a simulated 1 MVA grid and subjected to stress tests, as in [90]. The SEnSSiCC is complemented by the Living Lab Energy Campus (LLEC, see the next chapter), also a research infrastructure of the Helmholtz Association. Three experimental buildings with identical constructions are connected to the SEnSSiCC in terms of electrical technology and data and thus expand the portfolio of energy technology systems used for experiments.

**Figure 15.** Smart Energy System Simulation and Control Center within the Energy Lab 2.0. Photo: M. Breig (KIT).

The Smart Energy System Control Laboratory focuses on the support of developments and innovations in the field of smart grids under realistic conditions. The SESCL is a laboratory in which state-of-the-art energy technology systems and new control algorithms are developed and tested [91]. This laboratory is galvanically isolated from the public grid, so that the control algorithms can be approved and investigated in limit ranges (frequency, voltage). In addition, it is possible to control operating points approaching the limits of stability. Such experiments would not be possible using the public grid, as the risk of a complete grid failure is too high. In order to conduct experiments on low-voltage networks under realistic conditions, the laboratory provides a number of energy systems, such as electricity generators (e.g., PV systems, wind power units), electrical machines, generators, inverters, storage systems (e.g., Li-ion batteries), and charging stations, that can be very flexibly interconnected by taking into account the physical properties of the connecting lines to form a micro-grid with a variable topology. To model the operating behavior of the cable/overhead lines, the laboratory features real means of transmission and line replicas that physically simulate this behavior using discrete resistor–inductor–capacitor (RLC) components. In terms of the interconnection, flexibility is ensured by a matrix of alternating and direct current busbars and contactors that are controlled by a centralized automation system. Load shedding and the addition of further producers and consumers, or a combination of the two (prosumers) can be achieved very easily.

### *3.5. Living Lab Energy Campus: Integrated Research Platform for Energy-Related Coupling of Pioneering Conversion, Distribution, and Storage Technologies*

The Living Lab Energy Campus (LLEC) project is an integrated research platform (see Figure 16) for the coupling of electrical, thermal, and chemical energy flows through an intelligent sensor and control system. Various production, distribution, and storage systems are integrated into the energy supply of the research campus and are then monitored and optimally controlled according to predefined constraints by an adaptive, cloud-based, and model-predictive IT platform. In addition, digital models have been developed for different energy grids, energy demonstrations, and various building types. The demonstrations include various photovoltaic systems, two large Li-ion batteries, a low-temperature waste heat network, and a hydrogen sector with a high level of sector coupling. A large number of sensors collect data via the fluctuating energy flows at the research site. A special significance is attached to achieving an optimal interaction between humans and technology.

**Figure 16.** Living Lab Energy Campus: living lab and research platform.

A thermal energy center (WVVZ) designed as a modular system supplies the campus with electrical energy and heat. To this end, gas mixtures comprised of natural gas with biogas and hydrogen are used in the installed gas engines. An additional low-temperature network uses waste heat from the JUWELS supercomputer to supply heat to the surrounding buildings by means of heat pumps and simultaneously investigate the electrical and thermal utilization of the network, as well as potential resource savings. Various photovoltaic systems form the basis of the renewable energy supply and are integrated into the energy system in the form of conventional rooftop installations, free-standing modules, and modules fixed to the building façade. The fluctuations in the energy feed that occur are offset by two large Li-ion batteries. At the same time, these batteries serve as an uninterruptible power supply for a selection of sensitive research infrastructures. The LLEC was recently expanded to encompass research issues surrounding vehicle-to-grid (V2G) systems. Various bidirectionally operable charging infrastructures for electric research vehicles are currently being established.

One system- and process-related focus of the LLEC is the long-term and seasonal storage of renewable energy using hydrogen from the MW electrolysis system. As is shown in Figure 1, hydrogen and oxygen from the water electrolysis process each flow through a pressure-resistant pipeline, with only the hydrogen flowing into a pressure tank as additional storage. The hydrogen can also be stored in LOHCs. The loading and unloading of the LOHC takes place in a novel one-reactor system, which for the first time, demonstrates both process steps in a system with a performance of 300 kWp. The level of heat required for hydrogenation is approximately 300 ◦C and is obtained from the waste gas of the gas engines. The heat that is generated during dehydrogenation is supplied to the heat supply system on campus. Significantly higher rates of storage efficiency are achieved through this type of sector coupling. All forms of storage enable the stockpiling of gases over many weeks and months before hydrogen can be used to generate electricity and heat in the WVVZ's gas engines, and hydrogen and oxygen are able to do the same in an alkaline fuel cell.

As they are incorporated in a climate-neutral office complex, all of the energy systems can be monitored in the Data and Energy Services Lab, where researchers are also able to plan and evaluate future energy system experiments together with their colleagues from the technical infrastructure department.
