Power-to-Gas for Homeowners

Demonstration system with switchboard, © Exytron

Reusing carbon dioxide over and again in a closed process would be an optimal solution for protecting our environment. A demonstration system doing exactly what is needed has been running in one of Exytron’s showrooms at Rostock Port since September 2015. About 50 meters or 164 feet away from the wharf at the Unterwarnow, the river flowing through the old part of this Hanseatic city, you will find the headquarters of a young business that won the Start-up GreenTec Award at the end of April last year. But what was more important than the EUR 10,000 endowment which came with the prize was the attention Exytron received – for itself and the catalytic process it developed in-house, the patented SmartEnergyTechnology.

The first commercial power-to-gas system by Exytron is ready and waiting to be delivered to Alzey. The small city has a population of around 18,000 and is located 50 kilometers (31 miles) to the northwest of Mannheim, Germany. The building permit for the row house complex in the state of Rhineland-Palatinate had already been submitted in November 2015. Plans are to supply partially off-grid and almost emission-free energy to all in all 37 residential units. That was the clear-cut requirement set by the principal contractor, Deutsche Reihenhaus. The temporary delay is the result of an improper inspection of the former Deutsche Bahn premises, which will make an environmental site assessment necessary. In the meantime, the winter is causing another months-long postponement of civil engineering work. “Our energy supply system has been ready for delivery since 2016; we’re basically waiting for the go-ahead,” said Klaus Schirmer, sales and project manager of 2013-founded Exytron.

Based on current planning, the project is scheduled for completion in spring 2017. By then, the 37 residential units are thought to be supplied by eco-power as well as heat energy through a district heating grid. However, the focus of this pilot project has not been on economic feasibility. The main issue was CO2-neutral living. An Exytron simulation showed a 99.3 percent reduction in carbon dioxide emissions compared to similar residential developments. Almost emission-free living seems possible.

The heart of the supply system is its mechanical room, which has the size of around three-and-a-half car garages. It contains the electrolyzer, methane reformers, condensing boilers, CHP plant, hot water storage and central control unit. This room will supply the houses with electricity and with heat from a district heating system. Remote monitoring makes it possible to check whether everything is running smoothly.

The alkaline electrolyzer has a capacity of 40 kilowatts. It primarily uses power sourced from a PV system (125 kW). Additionally, eco-friendly electricity is bought off the grid, as the solar energy is not enough to provide heat and power to the entire residential complex. This makes the project partially grid-independent.

Designated a biogas system

“Right now, we are taking advantage of the regulations in place, which term our methanization system a biogas plant,” Schirmer said. Having their plant designated a biogas production facility means they benefit from cheaper grid power for electrolysis and methanization, as there will be no electricity tax or grid fees added. This reduces power prices to between 10 and 11 euro cents.

The system’s USP is its CO2-free output. The CHP part and the gas boiler have been modified to separate the environmentally harmful gas from the other exhaust fumes. Afterward, the captured carbon dioxide can be used to produce methane by using a catalyst. “The recovery is what differentiates this plant from common methanization systems. It’s the reason you can use the power-to-gas plant at any location, meaning decentralized, and provide businesses with heat directly at their facilities,” the project manager said.

Waste heat recovery improves system performance

In contrast to conventional power-to-gas processes, the focus is not on the production and storage of methane. The system that Exytron designed prioritizes heat transmission through methane synthesis, and most of the energy is used on-site. “It increases the system’s overall efficiency compared to centralized power-to-gas systems, which don’t use this heat or only a small part of it,” Schirmer said.

The process was developed in close collaboration with the Rostock-based Leibniz Institute for Catalysis, one of the biggest publicly funded organizations to research catalysis for industrial purposes in Europe. What’s special about this concept is the focus on thermal energy created through converting hydrogen into methane. The exothermic reaction produces the best results between 300 and 400 °C and the research team of Professor Matthias Beller has optimized the catalytic process to produce as much usable heat as possible – at least, enough to heat a building.

“We were successful in expanding the heat range. Catalysis is done in an environment in which we can make efficient use of the generated heat,” Andreas Martin summed up the research findings. The project participants tested a variety of catalysts, pipe sizes and carrier materials (see box). The aim was to use a “packed bed” to have heat released across the largest possible surface, i.e., to avoid heat being concentrated in a certain “hot spot” only.

How to get to 80 percent efficiency

The production output of hydrogen and synthetic natural gas fluctuates because the control unit provides different fuel quantities based on individual calculations of current and forecast demand. The system can create up to 10 Nm³ of hydrogen and 2.5 Nm³ of synthesis gas per hour.

Excess eco-power will first be used to split water into hydrogen and oxygen inside the electrolyzer. With the help of a catalyst specifically designed for this task by the Rostock-based Leibniz Institute, hydrogen will be directly converted into methane by adding CO2 (Sabatier reaction) stored in a natural gas tank. If required, the methane can be burned and the subsequently released CO2 fed again into the closed process and reused for methanization. The modified combustion process does not release any nitrous gases, which could harm the environment.

“Our plant has no steady system or utilization efficiency; both will fluctuate based on the mode of operation, consumption and energy sources,” Schirmer explained. Simulations show efficiency values ranging between 70 and 80 percent. They could still be improved by increasing the heat transfer from pumps and compressors, but that would not make much sense economically right now, he explained, as 80 percent efficiency was enough. In a decentralized system, the overall design of energy supply was more important than efficiency, he said.

There is still more R&D work to be done before intelligent controls can be used for the entire system, something that is still a novelty and technically challenging. It requires the consideration of many parameters (energy supply, storage and energy input). Differing consumption values, weather patterns and forecast figures play their part too. Exytron intends to learn from the pilot project in Alzey what it can to enhance the productivity and manageability of the system.

No added costs

This all will be of little concern to the users living in the residential units. They pay no extra charges, but – as per Schirmer – less than the cheapest price for electricity they can find on online portal Verivox. Heat is said to cost around EUR 1.30 per square meter and month. After all, power-to-gas systems for homeowners must remain economically feasible once subsidies run out. Schirmer knows that: “It is what we strive for.” He added that the technology’s possible scaling in quantity and size could already reveal a notable cost-cutting potential throughout the next projects.

“The system is technologically mature,” Schirmer said. “The biggest challenges domestically are the many regulations governing energy supply. Right now, we are primarily planning projects for larger residential units and apartment complexes or blocks.” In the German state of Bavaria, negotiations are taking place about building a power plant equipped with Exytron’s technology. Implementing the project would create the world’s biggest power-to-gas system.

Schirmer said that businesses from many industries had shown interest in the new technology: From lodgings to owners of single-family homes and multi-family buildings who want more grid independence and customers who have no or only limited access to the grid, such as in remote areas in Africa and Central Asia – or on certain islands, where power is still being produced by diesel generators. Even across Germany, there is still much untapped potential: As many as 19.3 percent of the around 40 million households use natural gas for heating.

The EUR 2.4 million project Chemical Energy Storage for Decentralized Supply was subsidized by the economy ministry of the German state of Mecklenburg-Vorpommern through the European Regional Development Fund.

Author: Niels Hendrik Petersen

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