Power-to-Gas

As a power -to- gas (short PtG or P2G, German as: "Electrical energy to gas " ) is a chemical process is known in which some with downstream methanation under the use of electricity from renewable energy sources (RES ) produced by electrolysis of water, a fuel gas will. The gas thus generated is referred to as EE- gas. Depending on the type of renewable energy used, the gas is also called wind gas, solar gas or similar, depending on the chemical composition of the gas is used instead of the term "gas" and " methane " or " hydrogen " is used.

• 2.1 generation of electrical energy
• 2.2 Energy Transport
• 2.3 Heat
• 2.4 mobility
• 2.5 Power -to-liquid

• 3.1 Investments in Germany 3.1.1 MicroBEnergy plants in Schwandorf ( Oberpfalz)
• 3.1.2 Power -to- gas plants at STW 3.1.2.1 Test in the energy landscape Morbach
• 3.1.2.2 250 - kW system

• 3.1.3.1 Cooperation of Greenpeace Energy with Enertrag
• 3.1.3.2 Enertrag, TOTAL and Vattenfall

• 3.2.1 Supply of Utsira in Norway
• 3.2.2 Demonstration Plant in Foulum, Denmark
• 3.2.3 GRHYD - Demonstratonsprojekt in Dunkerque, France
• 3.2.4 Hybrid Aarmatt in Zuchwil, Switzerland

• 8.1 reports

Power -to- gas concept

One possible definition of power to gas is:

"The term ' power-to - gas represents a concept that is used in the excess current to flow via water electrolysis to produce hydrogen and in a second step using carbon dioxide when needed to convert (CO2) into synthetic methane. The storage for this methane and, to a certain volume fraction and the elemental hydrogen, the existing natural gas infrastructure, ie the gas system could be connected with the underground storage facilities used. "

So power-to - gas conversion refers to the energy generated from renewable electrical energy to chemical energy and storing it in the available gas network in the form of various gases. The basic concept, which is to take advantage of using wind energy electrolytically produced hydrogen as an energy carrier, it has been proposed the mid-19th century. An upheaval was the concept in the 20th century as a building block of the desired vision of a hydrogen economy or for the storage of electricity from renewable sources in the energy transition. Only since about the year 2009, the possibility is being discussed to produce methane instead of hydrogen.

The parastatal German Energy Agency ( dena) has the means of production of RES - gas since October 2011 specifically a strategy platform under the title Power to Gas.

In the online edition of Manager Magazin power-to - gas is referred to as a new technology, the model deceptively simple sword, because in 450.000 -kilometer-long gas lines and about 47 gas storage facilities in Germany already space for 23.5 billion cubic meters (m³) gas is, which is expected to increase by 2025 through expansions and new buildings to 32.5 billion cubic meters.

As a result of the energy transition more and more renewable generators are built. The fact that both conventional base load power plants can be throttled only to a certain degree, it can during times of high feed-in of wind and solar energy come to an oversupply of electricity, especially at low current demand. This energy is then ready priced. At the same time serves the integration of power-to - gas plants in the electric power supply systems of the relief of the cables and network stability, because power-to - gas plants can be used as a variable load. In the literature it is assumed that, as a renewable energy share of 40 % to a greater extent additional storage needed occasionally is the number called 70%.

EE- gas extraction

The methane gas produced synthetically is attributed due to its storage capability a special role in the field of renewable energies. As synthetic natural gas can be fed into the existing natural gas network, allowing for storage and transport of energy to the consumer and can therefore relieve the load electric power. Starting materials for the preparation of this EE- gas are water and carbon dioxide, which in times of surplus renewable energy, among others, to stabilize the grid by means of electrolysis of water into hydrogen and subsequently converted to methane via methanation.

Electrolysis

Hydrogen is produced by electrolysis of water and fed directly as possible into the gas network (which currently permissible upper limit for the concentration of hydrogen in the German natural gas grid is 5 percent by volume, in the city gas network about 50 % hydrogen were included) or temporarily stored in large tanks, such as salt caverns. The time required for electrolysis, electrical energy is generated by a wind turbine or solar cells.

For the production of hydrogen gas by electrolysis of water EE following chemical reaction takes place:

Two water molecules ( H2O) are split into two hydrogen molecules ( H2) and one oxygen molecule (O2).

Methanation

Alternatively, the hydrogen can be converted into methane gas along with carbon dioxide, which can be up to 100% fed into the gas grid or stored in gas storage.

For the production of methane gas EE following reaction takes place:

It describes the released during this exothermic reaction enthalpy. The reaction takes place in two partial reactions:

In the first part of the reaction produced by electrolysis, hydrogen (H2) reacts initially in an inverse water -gas shift reaction with carbon dioxide ( CO2) to carbon monoxide (CO ) and water ( H2O). In the second part of the reaction, the carbon monoxide formed in the first step react with more hydrogen to methane (CH4) and water again. In this second part of the reaction is a variant of the Fischer- Tropsch synthesis. Because the process is exothermic, heat is produced. Use of this waste heat to increase the efficiency is explored.

Possible Kohlenstoffdioxidquellen are fired with fossil and biomass fuel power plants, biogas plants, industrial processes, and direct deposition from the ambient air. Also, sewage treatment plants offer themselves due to synergy effects. However, two composite effects arise from the combination with a biogas plant. Firstly, the entry point can be shared in the natural gas grid, on the other hand contains raw biogas in addition to methane as the main constituent significant amounts of CO2. The latter would have to be removed before feeding, as well as in the production of biomethane as biofuels. This step can be saved by methanation. The already existing methane does not interfere, but rather traces of hydrogen sulfide, which must be separated for this use, such as activated carbon. Oxidative processes such as flue gas desulfurization would be inappropriate because the necessary air entry would reduce the income.

While hydrogen as a renewable gas only requires the electrolysis, the most methods for EE- gas production in the form of methane run from chemically and require a high pressure, high temperature, CO2 concentration and purity. There is also the possibility of the synthesis of methane in bioreactors using archaea perform. Due to the high selectivity of the microorganisms can be methanated and at lower concentrations. A new, still in development, exploiting Knitting procedure laid methanation in the fermenter of a biogas plant that leverage the existing microorganisms. The excess amounts of CO2 arise because the microorganisms find too little hydrogen. When hydrogen is produced by electrolysis directly in the fermenter generated, so a methane yield of up to 95 percent can be achieved and the waste heat can be also used.

Hydrogen feed versus methanation

In the implementation of power-to - gas in the art, various problems are discussed.

According to the gas grid operator Ontras hydrogen can damage the wires and make expensive upgrades necessary in the gas at high concentrations. Affordable it would be for gas network operators, converted it after the addition of carbon dioxide to accept as methane. However, the recovery of CO2 from air or industrial sources is still too expensive to be profitable. Absorb one ton of CO2 cost up to 500 euros.

The adverse corrosion effects occur mainly in unskilled or low-alloy steels. The steels according to DIN EN 10208-2, which are nowadays generally used in gas pipeline construction, are less affected, as evidenced on the basis of several studies.

The Federal Network Agency is of the opinion that both the hydrogen have priority at the level of the transmission networks as well as the methanation at the level of gas distribution a future. For a too high hydrogen concentrations speak at the current infrastructure is not only possible material damage to gas pipelines, compressors and other gas handling equipment, but also security issues to avoid an oxyhydrogen reaction.

On the other hand, there are already in the Ruhr area for decades over a 240-kilometer hydrogen network. Worldwide, there were in 2010 more than a thousand kilometers of water fuel lines. Air Liquide operates twelve pipeline network with a total length of 1200 km.

Furthermore, it is debatable how quickly the Einspeisegrenzen (now directly a maximum of 5 % hydrogen content ) can be achieved. In the methanation in turn consumes extra energy, which is why you currently emanating from an energy loss during the reconversion 50-67 percent. These are the consulting firm A.T. Kearney that a resulting EE gas price of 80 euros per megawatt hour would be three times as high as that of conventional natural gas.

Entry points for EE- gas

EE- gas can be fed in principle at any point into the gas grid. Since entry points require an appropriate infrastructure for the measurement of the injected amount of gas, for example, offer a feed in the area of existing or newly created gas supply buildings, to which said among other things, gas stations, gas power plants, hybrid power plants, combined heat and power plants, compressor stations, or even the Gasometer gas tank count as entry points. Also, a link to the feed with existing biogas plants is generally feasible.

Storage capacity of the German natural gas network

Of great importance in the use of renewable gas is allocated in an existing natural gas network the possibility of storing the hydrogen and methane gas.

According to the Fraunhofer Institute for Wind Energy and Energy System Technology ( IWES ) Germany needed in 2050, when according to the Federal Government 80 % of the power to come from renewable sources to balance seasonal fluctuations in wind and solar power, storage capacities of 30 terawatt hours ( TWh). In contrast, the storage capacity of natural gas storage in the German natural gas grid is specified by the Fraunhofer IWES with over 200 TWh in April 2010, which corresponds to a consumption of several months.

The German pumped storage power plants have a capacity of 0.04 TWh and are designed for a service life of several hours. Although pumped storage power plants have a much higher efficiency (between 70 % and 85 %), the efficiency is determined also by the considerable investments and land use. The installed capacity is being expanded, but in Germany can not get in the magnitude of the storage capacity of the gas network due to topographic as well as political reasons. Great potential for storage exists, however, in Northern Europe. In Norway, for example, there usable for storage hydroelectric reservoirs with a potential storage capacity of approximately 84 TWh in Sweden of about 34 TWh. This storage capacity is of a similar size as the storage capacity of the German gas network.

Of RES-E gas

For hydrogen and methane, different possibilities offer. Because natural gas is made up predominantly of methane, natural gas can be replaced in many cases by methane from power-to - gas plants. The power-to - gas technology can therefore be used for many applications and thus connects markets for electricity, heat and mobility together. The efficiency is dependent on hydrogen feed of the use of the gas, the energy required for compression as well as the length of the transmission lines.

Generation of electrical energy

The chemical energy from renewable gas can be converted into electrical energy when needed. It can be converted back into different types of gas-fired power plants and combined heat and power plants. If EE gas is used for energy storage, then the efficiency of current is to flow between 30 % and 44 %. If EE- gas converted back into combined heat and power plants, overall efficiencies can be reached from 43% to 62 %. A recent analysis shows that it is possible to achieve an efficiency of about 70% in a transport of 500 kilometers in the gas network in power generation. The electrolysis with the auxiliary equipment is responsible for 23.7 percent of the losses, transformer and rectifier cause about 5 percent. This is almost the same efficiency as a pump storage power plant ( 72% ). The hydrogen must still be methanized fall again in losses to 14.2 percent.

Energy transport

With EE- gas very high performance can be transported. Large natural gas pipelines can transport rates from 70 GWth, a high voltage transmission line consisting of a 380 kV double system, however, only about 3.5 GWel.

As natural gas today can EE- gas are used for the provision of heat, for example, for cooking and heating. If the admixed hydrogen is used in a boiler to generate heat, an efficiency of 69 % is achieved.

Mobility

EE- gas can be used in fuel cell vehicles or for driving gas vehicles with internal combustion engine. An important application of EE- gas in the form of renewable hydrogen may be the mobility in the form of fuel for fuel cell vehicles. This is explained by the following reasons:

• The production of renewable hydrogen takes place in times of high energy supply from wind and solar energy with the aim of herauszutransferieren energy from the electrical system: under stay A return of this energy into the electrical system is connected with high losses and should or bottleneck times ( too little electricity supply ) are reserved.
• The use of renewable hydrogen in mobility achieved with about 50% of the highest efficiency and the best economic effect - the latter especially because fuel cell vehicles only about 10-20 kWh of energy (about 0.35 to 0.7 kg of hydrogen ) to 100 km need. While vehicles with internal combustion engines require about 50-150 kWh of primary energy per 100 km, consume fuel cell vehicles also taking into account the conversion losses to hydrogen only about 30 kWh primary wind or solar electricity. With the use of wind power to the value of about 0.10 € / kWh wind hydrogen prices of about 8 € / kg can be achieved, which corresponds to about 0.27 € / kWh. Thus fuel costs 8-16 € per 100 km can be achieved, which is comparable to today's cost.
• While oil is becoming scarcer and more expensive, the price of wind and solar power continue to fall steadily.

Power -to-liquid

In the professional world now also the term Power to Liquid was ( German as: "Electrical energy to liquid") introduced. Unlike power-to - gas the different power- to-liquid technologies have the production of liquid fuels as a target.

Planned and realized power-to - gas plants

Investment in Germany

An overview of the power- to- gas demonstration plants in Germany is a card issued by the DVGW with as of August 2013.

MicroBEnergy plants in Schwandorf ( Oberpfalz)

In Schwandorf / Oberpfalz has taken MicrobEnergy GmbH in February 2013 a research facility in operation, part of the Viessmann Group Company, in which a microbiological process for the methanation of hydrogen is employed. From the generated in the electrolyzer 21.3 m3 of hydrogen per hour caused an average of 5.3 m3 / h of methane. A second MIcrobEnergy plant located since July 2013 under construction. At the location of the wastewater treatment plant Schwandorf - Wackersdorf an electrolyzer produces 30 m3 / hydrogen, which are converted into a 1300 cubic meter digester microbiologically in 7.5 m3 / h of methane. The project partner is beside the purpose association wastewater treatment plant Schwandorf the Research Centre for Energy Networks and energy storage ( Fenes ) of the Technical University of Regensburg.

Power -to- gas plants at STW

A first pilot plant with a capacity of 25 kW for the production of methane after the power-to - gas process was established in November 2009 in Stuttgart at the Centre for Solar Energy and Hydrogen Research Baden- Württemberg ( STW ) with the participation of the Fraunhofer Institute for Wind energy and Energy System technology (IWES ) and the company SolarFuel (now ETOGAS GmbH) put into operation. The basic technical development was carried out by the research institutes and STW IWES. As CO2 source is ambient air, the efficiency of the plant is 40%.

Test in the energy landscape Morbach

In March 2011, the 25 - kW wind gas system of Juwi and SolarFuel in the energy landscape Morbach in the Hunsrück has been installed and tested for a few weeks. This test combined a wind gas plant, a wind farm and a biogas plant. When converting electricity into methane, the system achieves an efficiency of over 60 percent.

250 kW system

In October 2012 came with a 250 kW power ten times as large - at the time the world's largest power-to - gas plant - in the operation.

Hybrid power plant of Enertrag

The company Enertrag operates a pilot plant, a Gone to normal operation in March 2012 hybrid power plant in the north of Uckermark Prenzlau (Brandenburg ), which uses hydrogen as a temporary storage. Is fed the plant, which first went into operation in October 2011, of a total of three wind turbines, each with two megawatts. The performance of the electrolyzer is 500 kW at 75 % efficiency.

Cooperation of Greenpeace Energy with Enertrag

The utility Greenpeace Energy offered since October 1, 2011, a wind -gas conveying tariff, which in supply of conventional natural gas, a delivery fee of 0.4 euro cents per kilowatt hour for wind gas equipment contains, and is currently subsidized by 6,000 customers. Since Greenpeace Energy has no electrolyzer, the company signed in January 2012, a purchase agreement for the purchase of hydrogen by the company Enertrag. After contract problems and starting difficulties, the supply of " wind gas " into the gas grid should be done by the Enertrag pilot plant in Uckermark now from 2014.

Plans for setting up your own Greenpeace plant for the production of wind gas were initially rejected unanimously by the Board in late 2012. Background are the current full compensation or the EEG compensation for non infeeding wind peak load current, which makes at least from an economic perspective for energy producers do not wind gas plants absolutely necessary and the wind gas - concept run against. But Greenpeace Energy plans to build its own electrolysis system for 2015.

Enertrag, TOTAL and Vattenfall

The same Enertrag plant also serves the TOTAL Germany as a supplier of a wind - hydrogen filling station in the heath street in central Berlin, which since 18 April 2012 as part of the hydrogen project, Clean Energy Partnership ( CEP), first 50 and by the end of the current year 2012 according to the Federal Wind Energy Association then will supply 100 fuel cell vehicles with hydrogen. Furthermore, the system is also part of a collaboration between Enertrag, TOTAL and Vattenfall Europe Innovation GmbH on renewable energy.

Audi -Power -to- gas plant in Werlte

On behalf of Audi AG ETOGAS GmbH in Werlte built next to an existing biogas plant an industrial pilot plant for the conversion of renewable electricity surpluses in renewable natural gas, called by Audi " e-gas ". This also regenerative CO2 from a supplied by MT biomethane biogas upgrading plant is used for methanation addition to hydrogen produced from renewable sources. The 6 -megawatt plant will produce 1.4 million cubic meters of natural gas in standard quality per year. The plant was inaugurated on 25 June 2013, and is in the fall of 2013 [ deprecated] have completed their trial run.

E.ON plant in Falk Hagen ( Brandenburg)

In Falk Hagen in the Brandenburg Prignitz the energy company E.ON has first fed into the natural gas network in June 2013 during a test run of a pilot plant from wind generated hydrogen. A total of approximately 160 cubic meters of hydrogen were in the one hour test period and fed. This E.on has the entire process chain practically implemented by the current capture to supply the hydrogen for the first time with success.

End of August 2013, the pilot plant was put into operation. According E.on the plant by means of alkali electrolysis produces about 360 standard cubic meters of hydrogen per hour.

WIND-projekt - turbine will Werder / Kessin

WIND-projekt built the wind farm Werder / Kessin an electrolysis plant with 1000 kW planned performance.

Demonstration plant Thüga Group

At the Frankfurt location Thüga group has taken a power- to- gas demonstration plants in operation on 11.26.2013. 60 m³ hydrogen are produced per hour for a proton exchange membrane ( PEM). A special feature of the system is the supply of hydrogen in the local natural gas distribution network.

Further plans for power-to - gas plants

Other users individual the power-to - gas technology is the sunfire GmbH.

In the energy park to be built by 2015 Mainz an electrolyzer with a capacity of 6 MW. The research project will, inter alia, funded by the Federal Ministry of Economics. Participants include the Hochschule Rhein Main as well as the companies Siemens, Linde and Stadtwerke Mainz.

According to Manager Magazin also Enercon and some municipal utilities interested in the power-to - gas technology. The argument that in the meantime interest also gas suppliers for the technology, including the retrograde gas demand for heating is given due to improved insulation of buildings.

Plants outside Germany

Supply of Utsira in Norway

Since 2004 the Norwegian island of Utsira wind turbines as well as a storage system is supplied consisting of electrolyzer, accumulator, fuel cell and hydrogen turbine with power.

Demonstration plant in Foulum, Denmark

The University of Aarhus, the power station of Zurich ( ewz ) City, natural gas Zurich and other Danish and German actors committed to building a demonstration plant in the Danish Foulum.

GRHYD - Demonstratonsprojekt in Dunkerque, France

An industry consortium, consisting among other things of GDF Suez and Areva, plans in Dunkirk for a gas station for a liquid fuel with up to 20% hydrogen content, on the other hand, the introduction of hydrogen in the gas distribution network.

Hybrid Aarmatt in Zuchwil, Switzerland

The regional energy planning in Solothurn Zuchwil (Canton Solothurn ) is a " Hybrid " to put into operation, which is to connect the electricity, gas and heating networks with each other. The first stage of this hybrid plant consisting of a 6- MW gas-fired central heating system with two 5.5 - MWh heat storage, a 0.7 MW cogeneration plant, a 300 - kWe electrolyzer and a hydrogen storage be commissioned in late 2014. In a further stage along with two other, larger CHP and an additional heat storage, a methanation and a 300 -kW compressed air storage is to be integrated into the hybrid plant.

Legal Requirements in Germany

If power-to - gas plants run on electricity from renewable energy sources, renewable gas falls within the definition of " gas storage " according to § 3 No. 9a EEG ( Renewable Energy Act ) and " Biogas" according to § 3 No. 10c energy Act ( energy Act ).

In recent times, it is discussed whether this applies in addition to the Renewable Energy Sources Act ( EEG), for more than ten years and the so-called Gas Network Access Ordinance ( GasNZV ), which ensures the feeding of biogas and renewable gas by the network operator, an additional " law is needed to promote the integration of gas " to promote appropriate technologies using special subsidies.

Criticism

As long as natural gas is extensively used to provide process heat and hot water, is the simultaneous production of RES - gas is a waste of energy as electricity for heating purposes has an efficiency of nearly 100% and thus more natural gas can be saved by direct heating with electricity, can be generated as EE- gas with the same amount of electricity.

Is disputed also whether any sufficient carbon dioxide from biogenic and industrial processes is a large-scale application of Methanisierungstechnologie available.

Basically limited by the high conversion losses - - high cost of synthetically produced methane criticized Besides are.