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Physical Storage

The heat management developed in the WOMBAT research project: When the Audi e-gas plant runs, it supplies the hygienisation and amine scrubbing systems in the biogas plant with heat. This therefore considerably increases the overall efficiency of the Power-to-Gas/biogas plant.

World's first industrial power-to-gas plant

In the WOMBAT project, researchers are pursuing the idea of combining

the electricity and gas network. The intention is to utilise surplus

electricity from renewable sources for generating hydrogen. This is

synthesised with carbon dioxide in biogas plants to form methane, which

is the main component of natural gas. This makes it possible to utilise

the complex infrastructure for the gas industry, ranging from the

transport to the storage.

Project status Project completed
Typical system size Energy Capacity of natural gas grid
Typical system size Output 6 MW
Volumetric energy density Identical to natural gas grid
Efficiency AC/VN CH4 54% +/- 3%
Service life of the system > 20 years
Typical discharge time 30 seconds
Typical period between storage and withdrawal Variable due to high amount of gas power stations in the grid
Example application areas Adjustable at will (power conversion at any place in the grid)
Project duration Supply of synthetic methane from excess power for mobility purposes. Use of the PtG plant for control power.

Based on the world's first functional power-to-gas plant, which combines an electricity and gas grid by way of electrolysis and methanation, the WOMBAT project (the name stemming from the German acronym for efficiency optimization, methanation and biogas plant technology) seeks to demonstrate ways of making the technology generally cost-effective and achieving ecological optimization throughout the energy/mobility system. These include technical optimization of the combined plant operations, systemic analysis of the feed-back to the grids and in the mobility sector, as well as establishing practicable marketing channels for the stored energy on the revenue side.
The PtG pilot plant in Werlte, as the world's first industrial-scale (> 5 MW) application of the technology, offers a unique opportunity to obtain findings from live operation of such a plant

  • With three 2 MW electrolysers, the Audi e-gas plant is one of the largest Power-to-Gas sites in the world © AUDI AG
  • Graphic showing the Power-to-Gas plant © Audi AG
  • The alkaline electrolyser is manufactured by the McPhy Energy company © AUDI AG
  • The core of the Audi e-gas plant: The methanation unit where the hydrogen and carbon dioxide react to form methane © AUDI AG
  • The amine scrubber in the EWE biogas plant separates CO2 from the raw biogas, thus ensuring injection-capable biomethane, and now also supplies CO2 to the methanation unit in the Audi e-gas plant. © AUDI AG


A key area of the focus is on the targeted synergies with the biomethane plant operated by project partner EWE.  The project aims to investigate the extent to which the efficiency of a combined biomethane/PtG plant can be enhanced by specific heat management as opposed to stand-alone operation of the two plants. This approach appears promising because while the PtG plant has a variety of heat sources (electrolyzer, methanation unit) the biomethane plant has a number of heat sinks (hygienization of waste, fermenter heating, CO2 separation). It appears sensible to exchange the heat volumes. This does, however, pose some special challenges because the PtG plant only runs intermittently whereas the biomethane plant has a continuous heat demand.

Most of the stored synthetic methane shall be used as fuel for CNG-powered vehicles. The project aims to identify means of optimizing both the revenues from renewable methane and the costs of bringing it to market in the transport sector. This will reveal ways in which PtG plants can be operated cost-effectively within a market economy before they actually become an essential element of a reliable energy supply, so enabling them to be developed further.


The optimization of the combined biomethane/PtG plant will be comprehensively monitored and documented. In doing so, a technical concept will be devised incorporating a series of measuring points by which material and energy flows can be recorded and analyzed at short time intervals throughout the project period. In view of the different operating strategies to be implemented and analyzed under varying conditions dependent on the situation in the power grid, the weather etc., the PtG plant requires increased supervision by experts. The objective is an optimization in terms of various criteria (power grid stabilization, reduction of non-usable electricity volumes, cost-effectiveness, overall ecological sustainability of the combined PtG/biogas plant, stability of electrolysis/methanation), so that ultimately practicable and stable control algorithms can be developed, enabling the plant to run largely on an automated basis.

Focus on economic viability

PtG plants will only be capable of delivering the required system service if overall cost-effectiveness can be achieved, thereby opening up the possibility of the technology being spread further based on investment. Consequently, a particular focus of the project is on analyzing and optimizing the factors having a major influence on costs and revenues.

Regular operation starting 2013

In May 2011 the decision was made, in conjunction with plant builder SolarFuel, to construct an industrial power-to-gas plant adjacent to an existing biomethane plant operated by power company EWE in the Emsland region of northern Germany. The idea was to obtain the CO2 required for methanation from the biogas plant.

The power-to-gas plant was in the regular operation until the end of 2013. Basic preparatory work has been started in relation to heat management monitoring, electricity sourcing, as well as life-cycle analysis and e-gas logistics.
This year other measures will include optimization of the biomethane plant aimed at ensuring improved supply to the e-gas plant of highly concentrated carbon dioxide. The commissioning of the e-gas plant during the summer will enable data to be collected from the monitoring installations and subsequently allow the first technical optimization measures to be initiated for combined operation of the two plants. The plans for 2014 and subsequent years then include ecological and economic optimization of the operations of both plants, particularly against the background of the availability of substrates for the biogas plant and the concrete grid situation (electricity and gas) at the Werlte location.

Supported by: The Federal Government on the basis of a decision by the German Bundestag


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Research funding

The information system EnArgus provides information on research funding, including on this project (German only).