Power-to-gas plant put into operation
Key technology to enter sustainable energy era
Methane produced in a biological process using surplus electricity from renewable sources such as wind and the sun is being fed into the natural gas grid for the first time at Viessmann's company headquarters in Allendorf (Eder), Germany. The first system of this type in the world went into operation in early March. Over the past few weeks, the necessary technology, equal in size to three shipping containers, was integrated into the existing biomethane plant in Allendorf (Eder). Approval has already been given to expand the system, so that it can generate and process around 400 cubic meters of hydrogen per hour (Nm³/h).
Storage process imitates nature
As the use of wind and solar energy becomes more widespread, increasingly larger quantities of surplus electricity which cannot be fed into the power grid will be produced at times when there is a great deal of wind or sunshine. On the flip side, there may also be a shortfall in supplies when there is little sun or wind as conventional power stations are being dismantled for the sustainable energy era. Developing energy storage systems is thus one of the greatest challenges of the sustainable energy era. One interesting approach is the power-to-gas technology which is now being used at Viessmann. This process can be used to produce hydrogen from surplus wind and solar electricity using electrolysis of water. This hydrogen is then either used directly or mixed with carbon dioxide from a biogas system and converted into methane gas using a microbiological process.
Generation and consumption separated in time and space
The gas network in Germany has a storage capacity of several months thanks to its pipelines and underground chambers. The fuel can thus be stored for a long time and used to supply heat or to power natural gas vehicles as a climate-friendly fuel source, irrespective of where the electricity was actually generated. It is precisely this long-term storage capacity which makes power-to-gas different from other storage technologies such as batteries, pump storage systems, or power-to-heat, which mainly provide economic energy storage over a few days only.
Optimum versatility in absorbing wind and solar power
While existing power-to-gas projects have been using a chemical-catalytic approach to methanation, the Viessmann Group company MicrobEnergy has developed a new microbiological process, which now works on a large scale. This process combines hydrogen from an external source with the carbon dioxide generated during fermentation in a biogas plant and converts them into methane using a microbiological method. A PEM electrolyzer built by Carbotech, another Viessmann company, is used to produce hydrogen. Biological methanation impresses due to its optimum flexibility, making it eminently suitable to absorb fluctuating quantities of energy produced by wind or solar power.
Micro-organisms produce methane
Highly specialized microorganisms perform the actual methanation. They absorb the carbon dioxide and the hydrogen in liquid form through their cell walls, 'digesting' and converting them into methane. The only thing left over after this process is water.
Reduced costs thanks to use of existing infrastructure
Thanks to the use of existing biogas and sewer gas plants, the investment costs for power-to-gas plants can be reduced significantly since transformers, electricity mains connections, and gas network connections are often already installed.
Funding as part of BioPower2Gas initiative
The plant has been set up in Allendorf (Eder) as a demonstration power-to-gas plant as part of the BioPower2Gas subsidy program. The main goals of the project are testing the electrolyzer and biological methanation with regard to stability for the long and short term, integrating the system fully into the biomethane plant, achieving a stable gas quality capable of being fed into the network and demonstrating process-safe, dynamic operation. The project also aims to test control energy operation and operation with varying input gas qualities (CO2, moisture content, temperature, cycles and seasonal differences). Conformance of the synthetic methane produced with bio-fuel market requirements is also being established during cost accounting, verification, and certification procedures, so that this storage gas can be marketed.
Test results: excellent gas quality
The MicrobEnergy demonstration plant had been in operation at the Schwandorf sewage works until the end of December 2014. The test results revealed excellent product gas quality of more than 98 % methane content with a stable production volume and a very low proportion of hydrogen at 2 %.
After the plant was relocated to the Allendorf site, the hydrogen produced there has been methanated using the tested biological process and fed into the natural gas grid via the existing biogas feed-in system since early March 2015. The CO2 required is either taken from the gas processing plant or raw biogas is used directly with the CO2 that it contains. In this case, the power-to-gas process is also regarded as an upgrading technology for raw biogas supplied from biogas and sewage plants.
The BioPower2Gas (www.biopower2gas.de) research project funded by the German Federal Ministry for Economic Affairs and Energy brings partners together who are tasked with expanding flexible power generation capacities from renewable energies. These partners are the technology developer MicrobEnergy GmbH, a Viessmann Group subsidiary, network operator EnergieNetz Mitte GmbH, utilities company EAM EnergiePlus GmbH, part of the EAM Group, engineering consultants CUBE Engineering GmbH, and research body IdE Institut dezentrale Energietechnologien GmbH (project coordinator). The bioenergy village of Jühnde an associated partner of the project. The research is funded as part of the German Federal Ministry for Economic Affairs and Energy's Bio-mass energy use program with scientific support provided by the DBFZ (Deutsches Biomasseforschungszentrum), the German biomass research center.