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“GET – GREEN EFFICIENT TECHNOLOGIES” is the new independent media platform for energy supply, efficiency improvement and alternative energy sources and storage. There is still a high potential to save energy in industry. Efficiency is not only important for the profitability of a company, it is also target-oriented and saves resources. The importance of efficiency, especially in energy production, the role played by hydrogen, industrial processes, resource and recycling management, how energy can be stored and much more can be found in the new GET.

Leading article However,

Leading article However, the latter is more combustible and highly viscous, which makes pumping difficult. Thus this storage medium is better suited for small units. Pre-filled cartridges can be used here. The disadvantage of these storage media is that waste heat is always produced centrally during storage, in a professional storage facility. This waste heat needs to be utilised, but magnesium hydride storage in the home cannot be realised. The electricity to electricity efficiency factor is similar for both. Thus one only needs to differentiate which method is a better fit for what process and application. We therefore have storage methods to help us realise a hydrogen society. Tools for change Electrolysis and fuel cells are at the core of the hydrogen society. Polymer exchange membrane (PEM) fuel cells are currently the most commonly used type. However, the solid oxide fuel cell appears to be the better technology for “home use”. It can be operated as both a fuel cell and an electrolysis cell. This means it can both produce hydrogen and turn it into electricity. Switching operating modes actually extends the service life of the unit. A very good efficiency factor combined with a high waste heat temperature is an advantage of this equipment technology. This waste heat can be used to separate the hydrogen from the LOHC (Fig. 1, winter mode, patented). If a home owner, for example, had such a unit, hydrogen could be produced at home (Fig. 1, summer mode). Photovoltaic energy could be used to produce hydrogen during the summer for storage in the LOHC. Electricity would then be available in winter from the LOHC with the help of the fuel cell. The corresponding hydrogenation unit is easy to build. What might such a hydrogen society look like? No doubt divided into small sections in many cases, with a decentralised infrastructure. However, the magnitude and location of the energy demand also has to be differentiated. Big industry Since the electricity supply for such enterprises works today, it will also work in the future. Where hydrogen is needed as a material for example, in the chemical industry ammonia imports are surely the most beneficial. The closer production is to the use of ammonia or hydrogen as a material, the more it benefits. The mechanical engineering industry on the other hand mainly needs electricity, with a large proportion surely produced by wind farms. Rooftop PV should nevertheless be installed in all industries, striving for a degree of self-sufficiency. Some of the electricity could come from nearby (PV) in the form of electricity, hydrogen or stored hydrogen, establishing some level of supply security. Part of the required process heat could be supplied through the delivery of electricity from private production to industry, where hydrogen is produced and stored to utilise the waste heat (electrolysis and hydrogenation). Then the LOHC could be supplied to private producers for electricity generation in winter (Fig. 1, left). Synergies between an industrial enterprise and its environment are therefore by all means conceivable. This would also cause the local population to better identify with the enterprise. Heat generation using pure oxygen (which will be in plentiful supply in the future) and SOFC winter mode SOFC summer mode Air used air waste heat (hot water) Waste heat: Hot water, cooking...? Fig. 1: SOFC fuel-electrolysis cells used to separate hydrogen from LOHC with direct subsequent electricity generation (winter mode) and to produce hydrogen (summer mode): A: Anode, E: Electrolyte, K: Cathode. (patented) 8 GREEN EFFICIENT TECHNOLOGIES 2022

Leading article combustible waste (sewage sludge, scrap wood...) is another option for the production of electricity and there fore hydrogen or also just heat during the winter. Heat pump technologies also exist that can deliver a supply temperature of up to 300 °C. This means that heat pumps are now an alternative for process technology as well. Decentralised small industry Small industry (SMEs) distributed across the country represents a key economic stability factor. Rooftop PV should be installed throughout in this sector as well. Small wind turbines may also be sensible depending on the building height. In summer, the electricity shortfall is made up by neighbours in the greater surrounding area. Depending on the product type and the process technology being used, the heat from hydrogen production and storage can be utilised or something has to be built to use the heat (in rural areas, for example, a distillery, bakery...). With regard to heat utilisation, the heat supply will not be sufficient in winter. The oxygen produced in summer could be stored in this case (easier to store than hydrogen). Heat could then be produced in winter using combustion processes with pure oxygen (at least 600° C hotter). Separating the hydrogen from the LOHC is another source to offset the electricity shortage in winter. A heat pump (see above) would also be a good solution here for supplemental heat. If heat energy is only needed for heating in winter, a heat pump could also be used to meet the entire heating demand. The electricity for this and the infrastructure could come from winter sunlight or from LOHC stored everywhere in summer. Synergies with the environment are conceivable here as well (nearby houses supply electricity to companies in summer and get back loaded LOHC in winter). This would almost certainly have a positive impact on coexistence. Residential buildings and areas Electrolysis and fuel cells form the core of such a supply (Fig. 1). While these are still very expensive right now, the SOFC technology (solid oxide) could be an initial step. The investment is halved since they can be operated as both a fuel cell (F) and an electrolysis cell (E). Once developed to series production readiness, the price will also be in an acceptable range. Switching from E to F and back has the advantage of extending the cell’s service life, further decreasing the cost. The efficiency factor from hydrogen to electricity is 60 % to 80 %. Waste heat is naturally produced, in the temperature range up to 1000 °C. Any temperature below 1000 °C can thus be reached when this is properly used, which covers domestic hot water, cooking and heating. However, the amount of energy is insufficient for the latter since we need at least three times as much heat energy as electricity. The SOFC technology could be used to produce electricity and hot water (winter) as well as hydrogen (summer). Heating does however require additional sources or measures. Improving the insulation of residential units would be the first step. Heating oil savings of at least 60 % could be obtained relatively easily here. A heat pump would be the next or possibly also the final step. A geothermal heat pump with a COP Reactor + EL SOFC Heat pump (co efficient of performance) greater than 6 is recommended here. This unit eliminates the noise of an air/air heat pump that is a nuisance for neighbours. Temperatures up to 80 °C are now possible with this technology, meaning normal radiators can also be supplied (Fig. 2). It is of course conceivable to obtain heat from a district heating network supplied, for example, by a waste water treatment plant energy centre. Energy storage in summer is straightforward. The F/E cell produces hydrogen that is stored. In winter, the waste heat from fuel cell operation is sufficient to separate the hydrogen from the LOHC and generate electricity. Self-sufficiency is therefore possible in principle. But what to do with the waste heat in summer? Hot water and swimming pool heating are obvious options. Still, there will be extra heat. The heat could be stored in a mobile heat storage unit (salt, sand...) and then sold to industrial enterprises. Cooperation with several neighbours would be sensible here. Examining the price in proportion to the size of an F/E cell shows that a system shared between 4 to 5 houses is sensible. Currently there are two manufacturers of such units for home use. Both have 10 KW units on the market or in the planning phase. The larger the community, the more readily heat can be sold. A PV system on every roof is the basis for all of this. Self-sufficiency is therefore possible for houses. Waste heat hot water (…cooking) hot water current waste heat heating summer/PV winter Fig. 2: Energy supply concept for residential buildings and areas, self-sufficient solution GREEN EFFICIENT TECHNOLOGIES 2022 9

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