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 natureAs 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 spaceThe 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 powerWhile 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 methaneHighly 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 infrastructureThanks 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 initiativeThe 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 qualityThe 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.

Background: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.

Image: BioPower2Gas demonstration plant

(1) PEM electrolyzer (400 kW) by Schmack Carbotech,

Viessmann Group

(2) Biological methanation, separate pressure tank

(3) Process container: pumps, tanks, gas analysis system,

temperature regulating system

(4) Control container: controls, measurement and control

technology

3

1

2

4

March 2015