Power to gas

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Power to gas (often abbreviated P2G) is a technology that converts electrical power to a gas fuel.[1] There are currently three methods in use; all use electricity to split water into hydrogen and oxygen by means of electrolysis.

In the first method, the resulting hydrogen is injected into the natural gas grid or is used in transport or industry.[2] The second method is to combine the hydrogen with carbon dioxide and convert the two gases to methane (see natural gas) using a methanation reaction such as the Sabatier reaction, or biological methanation resulting in an extra energy conversion loss of 8%. The methane may then be fed into the natural gas grid. The third method uses the output gas of a wood gas generator or a biogas plant, after the biogas upgrader is mixed with the produced hydrogen from the electrolyzer, to upgrade the quality of the biogas.

Impurities, such as carbon dioxide, water, hydrogen sulfide, and particulates, must be removed from the biogas if the gas is used for pipeline storage to prevent damage.[3]

Storage function[edit]

Power-to-gas systems may be deployed as adjuncts to wind parks or solar-electric generation. The excess power or off-peak power generated by wind generators or solar arrays may then be used at a later time for load balancing in the energy grid. Before switching to natural gas, the German gas networks were operated using towngas, which for 50-60 % consisted of hydrogen. The storage capacity of the German natural gas network is more than 200,000 GW·h which is enough for several months of energy requirement. By comparison, the capacity of all German pumped storage power plants amounts to only about 40 GW·h. The storage requirement in Germany is estimated at 16GW in 2023, 80GW in 2033 and 130GW in 2050.[4] The transport of energy through a gas network is done with much less loss (<0.1%) than in a power network (8%). The storage costs per kilowatt hour are estimated at €0.10 for hydrogen and €0.15 for methane.[5] The use of the existing natural gas pipelines for hydrogen was studied by the EU NaturalHy project[6] and US DOE.[7] The blending technology is also used in HCNG.


Efficiency by method
(ggf. Methanisation of Biogas)[8]
Method Efficiency Remarks
Electricity → Gas
Hydrogen 54–72 % 200 bar compression
Methane (SNG) 49–64 %
Hydrogen 57–73 % 80 bar compression
(Natural gas pipeline)
Methane (SNG) 50–64 %
Hydrogen 64–77 % Without compression
Methane (SNG) 51–65 %
Electricity → Gas → Electricity
Hydrogen 34–44 % 80 bar compression
up to 60% back to electricity
Methane (SNG) 30–38 %
Electricity → Gas → Electricity & heat (cogeneration)
Hydrogen 48–62 % 80 bar compression and
electricity/heat for 40/45 %
Methane (SNG) 43–54 %

Power to gas: hydrogen[edit]

In this method, electricity is used to split water into hydrogen and oxygen by means of electrolysis. The resulting hydrogen is injected into the natural gas grid or is used in transport or industry.[2]

ITM Power won a tender in March 2013 for a Thüga Group project, to supply a 360 kW self-pressurising high pressure electrolysis rapid response PEM electrolyser Rapid Response Electrolysis Power-to-Gas energy storage plant. The unit produces 125 kg/day of hydrogen gas and incorporates AEG power electronics. It will be situated at a Mainova AG site in the Schielestraße, Frankfurt in the state of Hessen. The operational data will be shared by the whole Thüga group – the largest network of energy companies in Germany with around 100 municipal utility members. The project partners include: badenova AG & Co. kg, Erdgas Mittelsachsen GmbH, Energieversorgung Mittelrhein GmbH, erdgas schwaben GmbH, Gasversorgung Westerwald GmbH, Mainova Aktiengesellschaft, Stadtwerke Ansbach GmbH, Stadtwerke Bad Hersfeld GmbH, Thüga Energienetze GmbH, WEMAG AG, e-rp GmbH, ESWE Versorgungs AG with Thüga Aktiengesellschaft as project coordinator. Scientific partners will participate in the operational phase.[9] It can produce 60 cubic metres of hydrogen per hour and feed 3,000 cubic metres of natural gas enriched with hydrogen into the grid per hour. An expansion of the pilot plant is planned from 2016, facilitating the full conversion of the hydrogen produced into methane to be directly injected into the natural gas grid.[10]

Units like ITM Power's HGas generates hydrogen to be directly injected into the gas network as Power to Gas

In December 2013, ITM Power, Mainova, and NRM Netzdienste Rhein-Main GmbH began injecting hydrogen into the German gas distribution network using ITM Power HGas, which is a rapid response proton exchange membrane electrolyser plant. The power consumption of the electrolyser is 315 kilowatts. It produces about 60 cubic meters per hour of hydrogen and thus in one hour can feed 3,000 cubic meters of hydrogen-enriched natural gas into the network.[11]

On August 28, 2013, E.ON Hanse, Solvicore, and Swissgas inaugurated a commercial power-to-gas unit in Falkenhagen, Germany. The unit, which has a capacity of two megawatts, can produce 360 cubic meters of hydrogen per hour.[12] The plant uses wind power and Hydrogenics[13] electrolysis equipment to transform water into hydrogen, which is then injected into the existing regional natural gas transmission system. Swissgas, which represents over 100 local natural gas utilities, is a partner in the project with a 20 percent capital stake and an agreement to purchase a portion of the gas produced. A second 800 kW power-to-gas project has been started in Hamburg/Reitbrook district[14] and is expected to open in 2015.[15]

In August 2013, a 140 MW wind park in Grapzow, Mecklenburg-Vorpommern ,owned by E.ON received an electrolyser. The hydrogen produced can be used in an internal combustion engine or can be injected into the local gas grid. The hydrogen compression and storage system stores up to 27 MWh of energy and increases the overall efficiency of the wind park by tapping into wind energy that otherwise would be wasted.[16] The electrolyser produces 210 Nm3/h of hydrogen and is operated by RH2-WKA.[17]

The GRHYD project (2013-2020) of GDF SUEZ and Areva in France started in 2012 for injecting hydrogen into the natural gas network of 200 houses.[18]

The INGRID project started in 2013 in Apulia, Italy. It is a four-year project with 39 MWh storage and a 1.2 MW electrolyser for smart grid monitoring and control.[19] The hydrogen is used for grid balancing, transport, industry, and injection into the gas network.[20]

The surplus energy from the 12 MW Prenzlau Windpark in Brandenburg, Germany[21] will be injected into the gas grid from 2014 on.

The 6 MW Energiepark Mainz[22] from Stadtwerke Mainz, RheinMain University of Applied Sciences, Linde and Siemens in Mainz (Germany) will open in 2015.

Power to gas and other energy storage schemes to store and utilize renewable energy are part of Germany's Energiewende (energy transition program).[23]

H2 injection without compression[edit]

The core of the system is a proton exchange membrane (PEM) electrolyser. The electrolyser converts electrical energy into chemical energy, which in turn facilitates the storage of electricity. A gas mixing plant ensures that the proportion of hydrogen in the natural gas stream does not exceed two per cent by volume, the technically permissible maximum value when a natural gas filling station is situated in the local distribution network. The electrolyser supplies the hydrogen-methane mixture at the same pressure as the gas distribution network, namely 3.5 bar. [24]

Power to gas: methane[edit]

The Power to Gas Methane method is to combine hydrogen from an electrolyzer with carbon dioxide and convert the two gases to methane[25] (see natural gas) using a methanation reaction such as the Sabatier reaction or biological methanation resulting in an extra energy conversion loss of 8%, the methane may then be fed into the natural gas grid if the purity requirement is reached.

ZSW (Center for Solar Energy and Hydrogen Research) and SolarFuel GmbH (now ETOGAS GmbH) realized a demonstration project with 250 kW electrical input power in Stuttgart, Germany. The plant was put into operation on October 30, 2012.[26]

The first industry-scale Power-to-Methane plant was realized by ETOGAS for Audi AG in Werlte, Germany. The plant with 6 MW electrical input power is using CO2 from a waste-biogas plant and intermittent renewable power to produce synthetic natural gas (SNG) which is directly fed into the local gas grid (which is operated by EWE).[27] The plant is part of the Audi e-fuels program. The produced synthetic natural gas, named Audi e-gas, enables CO2-neutral mobility with standard CNG vehicles. Currently it is available to customers of Audi's first CNG car, the Audi A3 g-tron.[28]

In April 2014 the European Union’s co-financed and from the KIT coordinated[29] HELMETH[30] (Integrated High-Temperature ELectrolysis and METHanation for Effective Power to Gas Conversion) research project started.[31] The objective of the project is the proof of concept of a highly efficient Power-to-Gas technology by thermally integrating high temperature electrolysis (SOEC technology) with CO2-methanation. Through the thermal integration of exothermal methanation and steam generation for the high temperature steam electrolysis a conversion efficiency > 85% is expected (higher heating value of produced methane per used electrical energy). The process consists of a pressurized high-temperature steam electrolysis and a pressurized CO2-methanation module which are planned to be coupled in 2016. A methane output of approximately 30 kW (higher heating value) is targeted.

Biogas upgrade[edit]

In the third method the carbon dioxide in the output of a wood gas generator or a biogas plant after the biogas upgrader is mixed with the produced hydrogen from the electrolyzer to produce methane. The free heat coming from the electrolyzer is used to cut heating costs in the biogas plant. The impurities carbon dioxide, water, hydrogen sulfide, and particulates must be removed from the biogas if the gas is used for pipeline storage to prevent damage.

2014-Avedøre wastewater Services in Avedøre, Kopenhagen (Denmark) is adding a 1 MW electrolyzer plant to upgrade the anaerobic digestion biogas from sewage sludge.[32] The produced hydrogen is used with the carbon dioxide from the biogas in a Sabatier reaction to produce methane. Electrochaea[33] is testing another project outside P2G BioCat with biocatalytic methanation. The company uses an adapted strain of the thermophilic methanogen Methanothermobacter thermautotrophicus and has demonstrated its technology at laboratory-scale in an industrial environment.[34] A pre-commercial demonstration project with a 10,000-liter reactor vessel was executed between January and November 2013 in Foulum, Denmark.[35]

In 2016 Torrgas, Siemens, Stedin, Gasunie, A.Hak, Hanzehogeschool/EnTranCe and Energy Valley intent to open a 12 MW Power to Gas facility in Delfzijl (The Netherlands) where biogas from Torrgas (biocoal) will be upgraded with hydrogen from electrolysis and delivered to nearby industrial consumers.[36]

See also[edit]


  1. ^ DLR-Power to gas in transport-Status quo and perspectives for development
  2. ^ a b Eberle, Ulrich; Mueller, Bernd; von Helmolt, Rittmar. "Fuel cell electric vehicles and hydrogen infrastructure: status 2012". Energy & Environmental Science. Retrieved 2014-12-16. 
  3. ^ NREL 2013: Blending hydrogen into natural gas pipeline networks: A review of key issues
  4. ^ Electricity storage in the German energy transition
  5. ^ "Wind power to hydrogen". hi!tech. Siemens. Retrieved 2014-06-21. 
  6. ^ NaturalHY Project. "Using the Existing Natural Gas System for Hydrogen". EXERGIA. Retrieved 2014-06-21. 
  7. ^ NREL - Blending hydrogen into natural gas pipeline networks A review of key issues
  8. ^ (German) Fraunhofer -Energiewirtschaftliche und ökologische Bewertung eines Windgas-Angebotes, p. 18
  9. ^ http://www.itm-power.com/news-item/first-sale-of-power-to-gas-plant-in-germany/
  10. ^ Ground broken at ITM Power power-to-gas pilot plant in Frankfurt
  11. ^ http://www.itm-power.com/news-item/injection-of-hydrogen-into-the-german-gas-distribution-grid/
  12. ^ http://www.eon.com/en/media/news/press-releases/2013/8/28/eon-inaugurates-power-to-gas-unit-in-falkenhagen-in-eastern-germany.html
  13. ^ Hydrogenics and Enbridge to develop utility-scale energy storage
  14. ^ E.on Hanse starts construction of power-to-gas facility in Hamburg
  15. ^ E.ON power-to-gas pilot unit in Falkenhagen first year of operation
  16. ^ German wind park with 1 MW Hydrogenics electrolyser for power-to-gas energy storage
  17. ^ RH2-WKA
  18. ^ The GRHYD demonstration project
  19. ^ INGRID Project to Launch 1.2 MW Electrolyser with 1 Ton of Storage for Smart Grid Balancing in Italy
  20. ^ Grid balancing, Power to Gas (PtG)
  21. ^ Prenzlau Windpark (Germany)
  22. ^ Energiepark Mainz
  23. ^ Quirin Schiermeier (April 10, 2013). "Renewable power: Germany’s energy gamble: An ambitious plan to slash greenhouse-gas emissions must clear some high technical and economic hurdles.". Nature. Retrieved April 10, 2013. 
  24. ^ [1]
  25. ^ DNV-Kema Systems analyses power to gas
  26. ^ http://www.zsw-bw.de/infoportal/presseinformationen/presse-detail/weltweit-groesste-power-to-gas-anlage-zur-methan-erzeugung-geht-in-betrieb.html
  27. ^ http://www.audi.com/content/com/brand/en/vorsprung_durch_technik/content/2013/10/energy-turnaround-in-the-tank.html
  28. ^ http://www.audi.com/corporate/en/corporate-responsibility/we-live-responsibility/product/audi-e-gas-new-fuel.html
  29. ^ "Engler-Bunte-Institute Division of Combustion Technology - Project HELMETH". Retrieved 2014-10-31. 
  30. ^ "Project homepage - HELMETH". Retrieved 2014-10-31. 
  31. ^ "Karlsruhe Institute of Technology - Press Release 044/2014". Retrieved 2014-10-31. 
  32. ^ Excess wind power is turned into green gas in Avedøre
  33. ^ Electrochaea
  34. ^ http://www.hindawi.com/journals/archaea/2013/157529/
  35. ^ http://www.electrochaea.com/technology.html
  36. ^ Power-to-Gas plant for Delfzijl

Further reading[edit]

External links[edit]