HPS inaugurates home with solar hydrogen storage system
In Schöneiche, a suburb east of Berlin, the first self-sufficient hydrogen house is starting practical testing. A solar year-round storage tank should cover the demand for the modern timber house. The goal of the FlexEhome research project is to show how a home can be self-sufficient with electricity and heat if it is suitably well insulated. In the scope of this project, the participants are also testing grid-serving services.
The photovoltaic system of the brand new single-family home in the street Schillerstraße was deliberately designed to be very large with a total output of almost 30 kilowatts – so it can generate a solar energy surplus for the production of clean hydrogen. Currently, most buildings with photovoltaic systems and batteries produce too much electricity in the summer, however, not enough in the winter months. So far, there is no seasonal storage.
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In a practical test, the FlexEhome research project will now demonstrate that it can be done differently: Electricity should only be released into the grid or taken out when it is also useful for the grid. This is possible due to a significantly larger storage capacity compared to batteries and the production of hydrogen, which can be stored for longer periods of time. Thanks to this flexibility, grid stability is improved and the need for expansion of the decentralised distribution grids is minimised. In this way, the residents of such a building contribute to power grid stability and supply security.
“In the future, such decentralised flexibilities will be indispensable for the success of the energy transition,” emphasised Zeyad Abul-Ella, head and founder of Home Power Solutions (HPS), at the ceremonial presentation of this solar hydrogen house. An essential component of the project is the long-term storage picea from HPS, which stores the surplus electricity from the solar system in the summer in the form of hydrogen by means of electrolysis. In winter, the green gas is converted back into electricity and heat via the fuel cell.
AEM electrolyser from Enapter
The hydrogen is produced by an AEM electrolyser 2.0 from the German-Italian manufacturer Enapter. The module can start and ramp up relatively quickly. The battery storage is a German-made lead-gel accumulator with a net capacity of 20 kWh. Lead – although a toxic heavy metal – has the advantage that there is already a well-established recycling system – especially for starter batteries from motor vehicles.
Civil engineer Abul-Ella developed the complete system of electrolyser, fuel cell, hydrogen tank as well as lead storage and ventilation unit himself almost ten years ago. However, the picea system is not cheap, costing 120,000 Euro for the full system. Nevertheless, sales of the so-called all-season power storage units have increased strongly in recent months. More than a hundred units are already in operation, and more than 500 have been ordered.
The Berlin-based company can hardly keep up with the orders. The waiting time is currently about twelve months. The production of HPS is therefore to be expanded further. Also because of projects such as FlexEhome: Participating partners are, for example, the heat pump manufacturer Vaillant, the timber house builder Albert Haus and the Technical University of Berlin.
Solar facing to the east-west and south
In order to smooth out the solar harvest from the roof already during production, the majority of the photovoltaic modules with 27.4 kilowatts were installed as a roof-integrated solution facing east-west. In addition, seven modules with a total of 2.4 kilowatts are located on the balcony railing facing to the south. Both together reduce the PV midday peak by 30 percent (see Fig. 2) – and therefore extend the runtime of the electrolyser by four hours per day in summer. “This increases the hydrogen yield by as much as 40 percent,” says Daniel Wolf from HPS. The engineer is the network coordinator of this innovative project.
The electrolyser with a total of four bundles of pressurised gas cylinders, each with an electrical output of 300 kWh (see Fig. 3), is located in a timber house on the north side of the detached house to store the H2 gas from the summer months for the winter months. According to the calculations of Daniel Wolf, the hydrogen storage tank would be completely full again by July. The space heating demand of the almost 150-square-metre home is around 40 percent below that of a KfW55 house. This high insulation standard is also necessary so that the house can supply itself with electricity and heat all year round. This is the key and the basis for full green supply.
But the long-term storage of electricity should also pay off economically in the future – through trading on the electricity market. Because there are very high exchange electricity prices every now and then, as on some days in December 2022, when it was the equivalent of 60 ct/kWh. On the other hand, there is the extreme of negative electricity prices, such as at the beginning of June 2021, when minus 5 ct/kWh was requested. This is where the H2 storage of HPS, which has reserves at all times, could pay off, says Daniel Wolf.
The (TU) Technical University of Berlin monitors all energy flows
The hydrogen is turned back into electricity and heat in a combined heat and power generation plant, where waste heat is also used. In combination with a heat pump, this ensures a year-round supply of the house with self-generated solar power. The interaction with the heat pump in particular will be investigated in greater detail through this project in the coming months.
Soon, a family of four will be living in the project house for rent. They will pay a lower rent compared to the local area, but will have to allow professional visitors and technicians access to the technical room from time to time by appointment. In order to document the full supply and a grid-serving feed-in, over the next few months the TU Berlin will also monitor all energy flows in the house in detail.
The researchers will continue to support the project until at least the end of 2024. In addition to the energy balances, they also look at the CO2 emissions. “In the end, we want to assess whether a building like this is worthwhile for climate protection,” says Alexander Studniorz from the TU Berlin. The scientists are conducting a life cycle analysis for this purpose. The scientist’s assumption is that it is the temporal shift in electricity consumption that will have a positive impact on the CO2 balance. This is because, unlike in homes with a PV system and a battery storage system, no additional grey electricity needs to be drawn from the grid on a cold winter night when many fossil-fuel power plants are in operation. “The seasonal buffer in particular, in combination with the heat pump, therefore guarantees low CO2 emissions all year round,” predicts the TU researcher.
Biomass – an underestimated source of green hydrogen
Researchers want to produce hydrogen from regional wood waste in the future. Green waste and sewage sludge can help produce green hydrogen for the energy and transport transition. If chipboard or MDF panels are used, they must first be freed from adhesives. Then, however, the regenerative energy carrier can be used by local businesses and energy suppliers. Biogenic hydrogen would have the potential to cover the energy needs of the industrial and heavy transport sectors – a real wild card for the energy transition.
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A climate-neutral circular economy based on wood would have many advantages, in the Black Forest region (Schwarzwald) for example, where wood is the most important economic good. During its processing into furniture and building materials or during the demolition of buildings, considerable amounts of wood scrap accumulates. The disposal usually costs even more money. Up to now, waste wood and scraps have generally been utilized in wood-burning systems for energy.
As early as the summer of 2021, the region in southern Germany has been pursuing a new path: Out of the wood waste is to emerge green hydrogen. “Following a bioeconomic approach, with the aid of biotechnological processes, we want to produce climate-neutral biohydrogen as well as additionally usable substances, such as carotenoids or proteins, from waste wood and wood scraps,” says Ursula Schließmann. She works at the Fraunhofer Institute for Interfacial Engineering and Biotechnology (Fraunhofer IGB) and coordinates the joint project H2Wood – BlackForest.
By using scrap wood, CO2 can be saved in two ways. On the one hand, renewable biohydrogen can substitute existing fossil fuels. On the other hand, scrap and waste wood will provide not only hydrogen. Through the new biotechnological approach, the energy recovery of the wood waste is combined with a material utilization. “The CO2 released from the wood is bound in the form of carbon-based co-products,” explains Schließmann, “This way, it is fed back into the natural carbon cycle.”
So far, however, no plant yet exists that produces biohydrogen on a large scale. At Fraunhofer IGB, the processes required for this are now being prepared and investigated, before they are implemented in the pilot plant at the digital engineering center Campus Schwarzwald in Freudenstadt.
The German education ministry (BMBF) is funding the project in the Schwarzwald until mid-2024 with around 12 million euros. Partners of the project are, in addition to Fraunhofer IGB, also the Fraunhofer Institute for Manufacturing Engineering and Automation (Fraunhofer IPA), the research center IFF of Universität Stuttgart (Institut für industrielle Fertigung und Fabrikbetrieb) and Campus Schwarzwald.
Remove adhesives and varnishes
The first step and prerequisite for biotechnological conversion is a pretreatment. Because wood waste like particleboard or MDF contains adhesives such as resins and phenols or even varnishes. These chemical components would have to be removed, because only then could bacteria and microalgae do their work, the researcher explained. In addition, the wood must be broken down into its building blocks so that the obtained cellulose can be split into individual sugar molecules, which in turn serve as food for the H2-producing microorganisms.
For the biotechnological conversion of the wood sugar, Fraunhofer IGB is relying on a fermentation process with bacteria, which metabolize the various sugars into CO2, organic acids and ethanol. The metabolic products of the bacteria serve as nutrients for the microalgae. These synthesize carotenoids or proteins as co-products and also release hydrogen in the process.
The idea that green hydrogen has the potential to meet the energy needs of the industrial and heavy transport sector of a region is supported by the current study by Fraunhofer IPA “Industrielle Wasserstoff-Hubs in Baden-Württemberg” (industrial hydrogen hubs in the German state of Baden-Württemberg). Its conclusion: Decentralized hydrogen production and use pays off if distribution centers, known as hubs in neo-German, are strategically placed and connected in the right way. Electrolyzers in these hubs would then be operated with green electricity. To keep transport costs low, the centers must be close to the consumers. Another criterion: The industry at the site must have a need for process heat, high-temperature processes and hydrogen gas, for nitrogen fertilizer production for example.”
“Ideal locations are near busy roads with truck depots where H2 refueling stations can be set up” says Jürgen Henke from Fraunhofer IPA. With the help of the location criteria, the research team was able to identify suitable sites in Baden-Württemberg. Particularly in the metropolitan regions Rhein-Neckar Karlsruhe. Computer simulations made at Fraunhofer IPA show that 30 percent of fossil energy can be replaced with regionally produced green hydrogen within ten years – and that’s if only building on free state-owned spaces.
Project: Hydrogen from plant waste
Along with wood, green waste is a largely untapped resource. Around 4.6 million tonnes was collected in the brown garbage bins of German residents alone in the previous year, according to the national environmental agency (Umweltbundesamt). Added to the waste from public parks, gardens, agriculture, food production, sewage sludge and cafeteria leftovers – all in all, a good 15 million tonnes.
The majority ends up in composting facilities or is incinerated to generate heat and electricity. “But the green waste is much too good for that,” stressed Johannes Full, head of the sustainable development of biointelligent technologies group at Fraunhofer IPA, “it would be more pragmatic to generate hydrogen from it and to capture the resulting CO2, store it or use it in the long term.”
How that works Fraunhofer IPA is demonstrating at a business from the metal industry. There, waste from fruit and wine growers in the surrounding area, cardboard and waste wood as well as cafeteria waste can be converted into hydrogen. This is then used directly in the metal processing. To do this, the fruit scraps and cafeteria waste are first fermented with the help of bacteria in dark containers, thus generating H2 and CO2. Then, the fermented mass is brewed in a biogas plant to make methane.
Light flashes decompose banana peels
At the technical university TH Lausanne in Switzerland as well, a team of researchers, led by Hubert Girault, is converting biomass into hydrogen – by means of photopyrolysis. In a reactor is a xenon flash lamp that emits high-energy light. The team has tried it with banana peels, gnawed corn cobs, orange peels, coffee bean skins and coconut shells. These were first dried at 105 °C for 24 hours and then milled.
The researchers put the powder into the reactor at ambient pressure. Then, the xenon lamp sends flashes into the biomass, which turns into hydrogen and biochar. The process is complete after only a few milliseconds. From every kilogram of biomass are obtained about 100 liters of hydrogen and 330 grams of biochar. That corresponds to about one third of the mass of the dried banana peels started with.
The young Swiss company H2Valais now wants to employ this process on a large scale. The photopyrolysis, however, is competing with the hydrothermal gasification of biomass that startups like SCW Systems in the Netherlands and TreaTech in Switzerland are using. In this, wet biomass is subjected to a pressure of 250 to 350 bar and a temperature of 400 to 700 °C. Under these conditions, methane and hydrogen are formed within a few hours. This shows once again: There are a diversity of approaches for obtaining H2 from biomass. This potential for the energy transition should be unlocked sooner than later.
Containerized unit turns pellets into pure H2
The joint project BiDroGen is likewise realizing the goal of converting wood into hydrogen. The companies BtX Energy and A.H.T. Syngas Technology is getting 630,800 euros of funding for it from the German economy ministry. The project aims to develop to market maturity a compact container solution for the decentralized production of hydrogen from pelletized wood waste.
The basis is the already existing gasifier technology from BtX to separate pure hydrogen from mixed gases. The goal is to accordingly maximize the hydrogen content of the wood gas produced from the pellets through innovative catalysts, to guarantee the gas purity for downstream processes and to enable separation of H2 from the product gas stream. This is how very pure hydrogen is to be obtained from pelletized scrap wood. One kilogram of pure hydrogen can be obtained from 12 to 15 kg of wood, depending on the gas quality. That corresponds to an efficiency of over 50 percent.
The mobile container solution would then provide decentralized green hydrogen. For application, the company sees great potential particularly in rural areas. For the clean transport transition, it could be a very useful card in the deck, as municipalities could procure hydrogen-powered vehicles right away, even if there is no hydrogen refueling station in the region yet.
Filling and emptying large tanks for hydrogen transportation is a highly complex process. To ensure these activities are safe, they have to be carried out within permitted pressure and temperature windows. A global energy corporation undertook analyses and thermodynamic modeling for its vessels and asked the fuel cell technology center ZBT to validate the results in a series of physical tests.
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Hydrogen refueling stations that are used to fill up fuel cell electric vehicles or FCEVs need to either produce the required hydrogen on site themselves or have it delivered via various distribution pathways. One way of conveying hydrogen to a filling station is by high-capacity trailers that are fitted with several high-pressure tanks for transporting gaseous hydrogen.
It must be ensured that these tanks meet the permitted temperature and pressure ranges while they are being both filled and discharged and that their operation is, above all, safe. To make certain this is the case, an international energy company devised analyses and thermodynamic modeling for the filling and discharging processes of its custom hydrogen trailer for type IV composite cylinders.
Experimental investigations
ZBT was commissioned to carry out physical tests on an individual tank to validate these analyses. The 2-cubic-meter (70-cubic-foot) trailer tank, which has an operating pressure of over 500 bar and a hydrogen storage capacity of around 70 kilograms, was tested successfully at the center’s testing area in Duisburg, Germany. The type IV tank, made from composite materials, is 6 meters (20 feet) long, has a diameter of approximately 80 centimeters (31 inches) and weighs just over one metric ton. The experimental investigations involved both filling and discharging under varying operating parameters.
The examined tank was produced especially for these series of tests, having been fitted with a range of thermocouples on and in the carbon fiber matrix. The multitude of measuring points provided information about the heating behavior during fill-up and the cooling behavior when the tank was emptied.
Expansion under pressure
The tank was additionally fitted with strain sensors for the investigations. The aim was to assess the axial and radial expansion in relation to pressure in order to check the design for the placement and arrangement of storage cylinders on the trailer. Tank expansion was predominantly identified along the axial plane. Radial expansion was minimal.
A recirculation system was installed in the hydrogen testing area so that hydrogen consumption could be kept as low as possible during the investigations. Thanks to this system, most of the hydrogen could be returned following each test to its original storage vessel in the testing area and thereby avoid unnecessarily high emissions of hydrogen into the atmosphere.
Test series
For the filling tests, the various operating parameters comprised the precooling temperature of the incoming hydrogen, the starting pressure of the tank and the filling speed. Here the focus was not on filling the tank at the usual controlled pressure ramping rates but on filling at a constant mass flow rate.
The discharging tests were in turn carried out at constant pressure ramping rates. This led to interesting results in relation to the temperature behavior of the gas both in the tank as well as in the gas flow coming from the tank.
The figures show examples of graphical analyses for a filling and discharging operation. Both representations show the measured tank pressure and the measured values of various embedded thermocouples during the test.
Parameters for safe operation identified
Assessment of the measured values revealed that safe and efficient operation is possible within the given temperature and pressure ranges. Variation of the filling parameters did not produce a configuration resulting in a state close to the thresholds. In any case, the temperature reached of the exiting gas as the tank discharged was under -40 °C, which in turn led to meeting the shutdown thresholds that were defined to protect downstream assemblies.
It was observed that the tank cooled down considerably even when discharged at low mass flow rates, evident from the temperature of the exiting gas. The tests were conducted at ambient temperatures of around 10 °C to 15 °C and gave rise to significant restrictions on maximum discharging speeds in some cases, particularly for the discharging of such tanks in colder environmental conditions.
Authors: Alexander Kvasnicka, a.kvasnicka@zbt.de , Christian Spitta, c.spitta@zbt.de, Lukas Willmeroth, l.willmeroth@zbt.de All from Zentrum für BrennstoffzellenTechnik GmbH (ZBT), Duisburg, Germany
ZBT
ZBT is one of Europe’s leading research organizations for fuel cells, hydrogen technologies and energy storage. It is a sought-after R&D partner for top-level European and German research and industry projects, specializing in automotive applications, distribution, storage and stationary energy conversion. The around 170 staff members at ZBT have access to extensive technical resources that include production and testing facilities, chemical labs and high-tech analytics.
Shipping is responsible for roughly 3 percent of all carbon dioxide emissions around the globe. The International Maritime Organization or IMO therefore set itself the goal of at least halving this figure by the year 2050, relative to a 2008 baseline. Due to the high power requirements and the large distances traveled by ships, fully electric solutions are only possible in isolated cases. Hydrogen and its derivatives are therefore attracting increasing interest from the maritime industry because of their potential to greatly reduce ship emissions. The challenge in this sector is, firstly, how to store the hydrogen on board safely in a minimal amount of space and, secondly, how to engineer the overall energy system to meet various requirements while optimizing its control.
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The Hitzler Werft shipyard in Lauenburg, Germany, is currently building the Coriolis research vessel for the Helmholtz-Zentrum Hereon research center in Geesthacht. The ship will be fitted with a diesel electric power system in addition to batteries and a hydrogen system. The latter was designed by Hereon together with the DLR Institute of Maritime Energy Systems and the engineering consultancy Technolog in Hamburg.
Hydrogen system lab on board
The hydrogen system lab – H2SL – is designed to be a hydrogen system that is spread across the vessel. The main components are a metal hydride tank, which was developed by Hereon, and a low-temperature proton exchange membrane (PEM) fuel cell. Accompanying these are various pieces of peripheral equipment, such as a bunker station for hydrogen, a tank connection space at the metal hydride tank and two vent masts.
For a comparably small vessel such as the Coriolis, whose length is just under 30 meters (100 feet), extremely careful consideration is needed when arranging the components. One of the reasons for this is because there are no binding regulations yet that govern the use of hydrogen on board.
The definition of hazardous zones and the distances that need to be maintained between ventilation facilities come from the IGF Code, which regulates the handling of low-flashpoint fuels in shipping and has been primarily used for liquefied natural gas up until now. The code does not yet take into account the special properties of hydrogen, for instance its much higher volatility compared with LNG. Among other things, this evident in the size and shape of the hazardous zones (see the spherical hazardous zones around the vents and air inlets). Work on the IGF Code is currently ongoing to extend its scope to include the use of hydrogen.
The tank system, consisting of an actual metal hydride tank and the mandatory inertable tank connection space, will be built on a 5-foot container base plate and have around half the height. In addition to the weight of the metal hydride itself, the overall weight is made up of the steel tank shells, pipework and, in particular, the pressure vessel of the tank connection space. The overall system volume of around 4 cubic meters (140 cubic feet) and an overall system weight of 5 metric tons mean that the tank system stores approximately 30 kilograms of hydrogen.
This allows the fuel cell to supply the ship with roughly 500 kilowatt-hours of green energy. That said, this can only happen if the bunkering of green hydrogen is actually possible and permitted – a challenge in itself, as initial exploratory talks with port authorities and hydrogen producers have shown.
Prior to the shipyard tender, the energy requirement for craft propulsion was ascertained at SVA Potsdam using a model test and subsequently scaled up. The shape of the Coriolis is optimized for operation at low speed as this matches the primary operating profile of inshore journeys (see fig. 3).
Due to the low power requirement for creep speed, the fuel cell, which will have a rated electrical power of around 100 kilowatts, can be used in combination with the battery for numerous monitoring activities and in the other operating states of the Coriolis e.g., during layovers, without having to switch on a diesel engine. As well as the propulsion system, the electrical consumers on board also need to be supplied, although these only require a fraction of the power needed for propulsion.
Metal hydride tanks
From Hereon’s perspective, the following properties make metal hydride or MH tanks attractive for a range of maritime applications:
Moderate loading pressures of well under 100 bar at operating temperatures below 100 °C
Cold start of a MH tank possible in principle even at temperatures below 0 °C (Hereon EP 3 843 190)
By the very nature of MH tanks, the hydrogen is chemically bound meaning the tanks cannot suddenly release large quantities of hydrogen, which is a significant on-board safety advantage.
The low loading pressures allow a flexible structural form which makes it easy to adapt to the shape of the ship à saves space. Today’s pressurized hydrogen tanks take up a lot of room, especially on small vessels, which reduces valuable cargo space.
The high weight can even be advantageous in certain applications, e.g., for sailing ships where it can be used instead of the obligatory “deadweight” ballast for stability.
Research in the H2SL
Hereon and DLR are working together to investigate which types of ship are best suited to the combination of a low-temperature fuel cell and a metal hydride tank for the propulsion system. The goal of the two research institutes is to create a guiding principle that enables the Coriolis energy system concept to be adapted and integrated easily into other ships and types of craft.
The H2SL offers many more opportunities to pursue innovative research approaches in addition to facilitating zero-emission operation. Hereon and DLR are planning an intensive program of research using the power system and are expecting to gain valuable knowledge and real-time data on relevant research issues. This will be made possible by running the H2SL in a real maritime environment with the option to access operating data remotely online and immediately adjust the control parameters. The effects of these changes will then be the subject of further study.
DLR will develop a digital twin of the hydrogen energy system based on the operating data in order to produce a continuous record of the system status, optimize the system control and derive feedback for the operation.
What’s more, the information should allow operational strategies to be developed for the Coriolis’ hybrid energy system. The variation in energy sources, i.e., battery, fuel cell and combustion engine, creates a high degree of flexibility with regard to operation in a wide range of energy consumption scenarios. The goal is to achieve an optimal balance in relation to fuel consumption and operating costs through intelligent load sharing for a wide variety of traveling and loading states.
A benefit of carrying out this kind of investigative work on a research vessel is that strategies developed from theoretical principles can be transferred directly to the energy management system, allowing them to be swiftly validated during operation.
Hybrid energy systems are being built into ships with increasing frequency. The knowledge gained from sailing the Coriolis will supply valuable information in future that can also be transferred to other types of craft and thus contribute toward reducing emissions in the maritime sector.
The energy source of the future is hydrogen. It can be produced from renewables and used as a raw material or an energy source in multiple industries. The biggest challenge industrial companies face with hydrogen is also key to implementing energy systems integration in general.
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