View source for Physics:Power-to-gas

{{Short description|Process to convert electric power into hydrogen or methane}}
 <!-- article is out of date and missing much of the past few years of advances in this field -->
'''Power-to-gas''' (often abbreviated '''P2G''') is a technology that uses electric power to produce a gaseous fuel.<ref name="BMVI2011">{{cite report |last1=Bünger | first1=U.  | last2=Landinger | first2=H.  | last3=Pschorr-Schoberer | first3=E.  | last4=Schmidt | first4=P. | last5=Weindorf | first5=W. | last6=Jöhrens | first6=J. | last7=Lambrecht | first7=U. |last8=Naumann | first8=K. |last9=Lischke | first9=A. |date=11 June 2014 |title=Power to gas in transport-Status quo and perspectives for development | url=https://www.bmvi.de/SharedDocs/EN/Documents/MKS/mks-studie-ptg-transport-status-quo-and-perspectives-for-development.pdf?__blob=publicationFile |publisher=Federal Ministry of Transport and Digital Infrastructure (BMVI), Germany |page= |accessdate=3 June 2021 |quote= }}</ref>  When using surplus power from wind generation, the concept is sometimes called '''windgas'''.{{Cn|date=April 2023|reason=needs cite that windgas is an English word not just German}}

Most P2G systems use [[Chemistry:Electrolysis|electrolysis]] to produce [[Chemistry:Hydrogen|hydrogen]]. The hydrogen can be used directly,<ref name="Eberle">{{cite journal |title=Fuel cell electric vehicles and hydrogen infrastructure: status 2012 |journal=Energy & Environmental Science |volume=5 |issue=10 |page=8780 |url=https://www.researchgate.net/publication/233987484 |last1=Eberle |first1=Ulrich |first2=Bernd |last2=Mueller |first3=Rittmar |last3=von Helmolt |access-date=2014-12-16 |doi=10.1039/C2EE22596D |year=2012 |archive-date=2014-02-09 |archive-url=https://web.archive.org/web/20140209172012/http://www.researchgate.net/publication/233987484_Fuel_cell_electric_vehicles_and_hydrogen_infrastructure_status_2012?ev=prf_pub |url-status=live }}</ref> or further steps (known as two-stage P2G systems) may convert the hydrogen into [[Chemistry:Syngas|syngas]], [[Chemistry:Methane|methane]],<ref name=NREL>{{cite report |url=http://www.nrel.gov/docs/fy13osti/51995.pdf |publisher=National Renewable Energy Laboratory |date=March 2013 |title=Blending hydrogen into natural gas pipeline networks: A review of key issues |last1=Melaina |first1=M. W. |last2=Antonia |first2=O. |last3=Penev |first3=M. |access-date=2022-12-24 |url-status=live |archive-url=https://web.archive.org/web/20221223190104/https://www.nrel.gov/docs/fy13osti/51995.pdf |archive-date=2022-12-23 |archive-format=pdf}}</ref> or LPG.<ref name=LPG>{{cite web | url=https://www.bpnews.com/index.php/publications/magazine/current-issue/830-u-s-is-world-s-largest-lpg-exporter-but-when-will-market-balance | title=BPN Butane – Propane news | access-date=10 April 2017 | archive-date=30 December 2017 | archive-url=https://web.archive.org/web/20171230230203/https://www.bpnews.com/index.php/publications/magazine/current-issue/830-u-s-is-world-s-largest-lpg-exporter-but-when-will-market-balance | url-status=live }}</ref> 
Single-stage P2G systems to produce methane also exist, such as [[Chemistry:Reversible solid oxide cell|reversible solid oxide cell]] (rSOC) technology.<ref name=cejournal201909>{{cite journal |vauthors=Mogensen MB, Chen M, Frandsen HL, Graves C, Hansen JB, Hansen KV, Hauch A, Jacobsen T, Jensen SH, Skafte TL, Sun X |title=Reversible solid-oxide cells for clean and sustainable energy |journal=Clean Energy |date=September 2019 |volume=3 |issue=3 |pages=175–201 |doi-access=free |doi=10.1093/ce/zkz023 |quote=over 100 times more solar photovoltaic energy than necessary is readily accessible and that practically available wind alone may deliver sufficient energy supply to the world. Due to the intermittency of these sources, effective and inexpensive energy-conversion and storage technology is needed. Motivation for the possible electrolysis application of reversible solid-oxide cells (RSOCs), including a comparison of power-to-fuel/fuel-to-power to other energy-conversion and storage technologies is presented.}}</ref>

The gas may be used as chemical feedstock, or converted back into electricity using conventional generators such as gas turbines.<ref name=EUturbines>{{cite web |title=EUTurbines |url=http://www.powertheeu.eu |website=www.poertheeu.eu |publisher=EUTurbines}}</ref> Power-to-gas allows energy from electricity to be stored and transported in the form of compressed gas, often using existing infrastructure for long-term transport and storage of [[Chemistry:Natural gas|natural gas]]. P2G is often considered the most promising technology for seasonal renewable energy storage.<ref>{{cite journal |last1=Andrews |first1=John |last2=Shabani |first2=Bahman |title=Re-envisioning the role of hydrogen in a sustainable energy economy |journal=International Journal of Hydrogen Energy |date=January 2012 |volume=37 |issue=2 |pages=1184–1203 |doi=10.1016/j.ijhydene.2011.09.137 }}</ref><ref>{{cite journal |last1=Staffell |first1=Iain |last2=Scamman |first2=Daniel |last3=Velazquez Abad |first3=Anthony |last4=Balcombe |first4=Paul |last5=Dodds |first5=Paul E. |last6=Ekins |first6=Paul |last7=Shah |first7=Nilay |last8=Ward |first8=Kate R. |title=The role of hydrogen and fuel cells in the global energy system |journal=Energy & Environmental Science |date=2019 |volume=12 |issue=2 |pages=463–491 |doi=10.1039/C8EE01157E|doi-access=free |hdl=10044/1/65315 |hdl-access=free }}</ref>

==Energy storage and transport==

Power-to-gas systems may be deployed as adjuncts to wind parks or solar power plants. The excess power or off-peak power generated by wind generators or solar arrays may then be used hours, days, or months later to produce electrical power for the [[Engineering:Electrical grid|electrical grid]]. In the case of Germany, before switching to [[Chemistry:Natural gas|natural gas]], the 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 GWh which is enough for several months of energy requirement. By comparison, the capacity of all German [[Engineering:Pumped-storage hydroelectricity|pumped-storage hydroelectricity]] plants amounts to only about 40 GWh.{{citation needed|date=July 2022}} 
Natural gas storage is a mature industry that has been in existence since Victorian times. The storage/retrieval power rate requirement in Germany is estimated at 16 GW in 2023, 80 GW in 2033 and 130 GW in 2050.<ref>{{cite report |date=December 2014 |title=Electricity storage in the German energy transition |url=https://www.agora-energiewende.de/fileadmin2/Projekte/2013/speicher-in-der-energiewende/Agora_Speicherstudie_EN_web.pdf |publisher=Agora Energiewende|access-date=2020-02-11}}</ref> The storage costs per kilowatt hour are estimated at €0.10 for hydrogen and €0.15 for methane.<ref>{{cite web |url=http://www.hi-tech-online.com/en/hitech-213/hifuture/windpower-to-hydrogen.html |title=Wind power to hydrogen |work=hi!tech |publisher=[[Company:Siemens|Siemens]] |access-date=2014-06-21 |archive-date=2014-07-14 |archive-url=https://web.archive.org/web/20140714220545/http://www.hi-tech-online.com/en/hitech-213/hifuture/windpower-to-hydrogen.html |url-status=live }}</ref>

The existing natural gas transport infrastructure conveys massive amounts of gas for long distances profitably using pipelines. It is now profitable to ship natural gas between continents using [[Engineering:LNG carrier|LNG carrier]]s. The transport of energy through a gas network is done with much less loss (<0.1%) than in an electrical transmission network (8%). This infrastructure can transport methane produced by P2G without modification. It is possible to use it for up to 20% hydrogen.<ref>{{Cite news |last=Millard |first=Rachel |date=2023-02-13 |title=Hydrogen to be pumped into main gas pipeline by 2025 |language=en-GB |work=The Telegraph |url=https://www.telegraph.co.uk/business/2023/02/13/hydrogen-pumped-main-gas-pipeline-2025/ |access-date=2023-04-30 |issn=0307-1235}}</ref> <ref>{{Cite web |title=Why is the hydrogen level set at a maximum of 20%? |url=https://hydeploy.co.uk/faqs/hydrogen-level-set-maximum-20/ |access-date=2023-04-30 |website=HyDeploy |language=en-GB}}</ref> The use of the existing natural gas pipelines for hydrogen was studied by the EU NaturalHy project<ref>{{cite web |url=http://issuu.com/exergia/docs/naturalhy_brochure?e=1774604/5468248 |title=Using the Existing Natural Gas System for Hydrogen |author=NaturalHY Project |publisher=EXERGIA |access-date=2014-06-21 |archive-date=2014-10-29 |archive-url=https://web.archive.org/web/20141029121012/http://issuu.com/exergia/docs/naturalhy_brochure?e=1774604%2F5468248 |url-status=live }}</ref> and the United States Department of Energy (DOE).<ref>[http://www.nrel.gov/docs/fy13osti/51995.pdf NREL - Blending hydrogen into natural gas pipeline networks A review of key issues]</ref> Blending technology is also used in [[Physics:HCNG|HCNG]].

=== Efficiency ===
In 2013, the round-trip efficiency of power-to-gas-storage was well below 50%, with the hydrogen path being able to reach a maximum efficiency of ~ 43% and methane of ~ 39% by using combined-cycle powerplants. If [[Physics:Cogeneration|cogeneration]] plants are used that produce both electricity and heat, efficiency can be above 60%, but is still less than pumped hydro or battery storage.<ref>Volker Quaschning, ''Regenerative Energiesysteme. Technologie - Berechnung - Simulation'', Hanser 2013, p 373.</ref> However, there is potential to increase the efficiency of power-to-gas storage. In 2015 a study published in Energy and Environmental Science found that by using [[Chemistry:Reversible solid oxide cell|reversible solid oxide cell]]s and recycling waste heat in the storage process, electricity-to-electricity round-trip efficiencies  exceeding 70% can be reached at low cost.<ref>{{cite journal | last1 = Jensen |display-authors=0  | year = 2015 | title = Large-scale electricity storage utilizing reversible solid oxide cells combined with underground storage of {{chem|C|O|2}} and {{chem|C|H|4}} | journal = Energy and Environmental Science | volume = 8 | issue = 8| pages = 2471–2479 | doi = 10.1039/c5ee01485a |s2cid=93334230 }}</ref> In addition, a 2018 study using pressurized reversible solid oxide cells and a similar methodology found that round-trip efficiencies (power-to-power) of up to 80% might be feasible.<ref>{{cite journal | last1 = Butera | first1 =Giacomo|display-authors=0  | year = 2019 | title = A novel system for large-scale storage of electricity as synthetic natural gas using reversible pressurized solid oxide cells | journal = Energy | volume = 166 | pages = 738–754 | doi = 10.1016/j.energy.2018.10.079 | s2cid =116315454| url =https://backend.orbit.dtu.dk/ws/files/157396142/1_s2.0_S0360544218320693_main.pdf}}</ref>

{| class="wikitable"
|-
|+ Overall [[Physics:Energy conversion efficiency|energy conversion efficiency]] by pathway and fuel<br/>using [[Physics:Electrolysis of water|electrolysis of water]], plus [[Chemistry:Methanation|methanation]] to produce methane<ref>(German) Fraunhofer -Energiewirtschaftliche und ökologische Bewertung eines Windgas-Angebotes, p. 18</ref>
! Fuel
! Efficiency
! Conditions
|-
! colspan=3  | Pathway: Electricity→Gas
|-
| Hydrogen || align=center | 54–72 % || rowspan="2" | 200 bar compression
|-
| Methane ([[Chemistry:Substitute natural gas|SNG]]) || align=center | 49–64 %
|-
| Hydrogen || align=center | 57–73 % || rowspan="2" | 80 bar compression (Natural gas pipeline)
|-
| Methane (SNG) || align=center | 50–64 %
|-
| Hydrogen || align=center | 64–77 % || rowspan="2" | without compression
|-
| Methane (SNG) || align=center | 51–65 %
|-
! colspan=3 | Pathway: Electricity→Gas→Electricity
|-
| Hydrogen || align=center | 34–44 % || rowspan="2" | 80 bar compression up to 60% back to electricity
|-
| Methane (SNG) || align=center | 30–38 %
|-
! colspan=3 | Pathway: Electricity→Gas→Electricity & heat {{small|([[Physics:Cogeneration|cogeneration]])}}
|-
| Hydrogen || align=center | 48–62 % || rowspan="2" | 80 bar compression and electricity/heat for 40/45 %
|-
| Methane (SNG) || align=center | 43–54 %
|-
|}

== Electrolysis technology ==
*Relative advantages and disadvantages of electrolysis technologies.<ref>{{cite web
 |url=https://www.gas-for-energy.com/fileadmin/G4E/pdf_Datein/gfe2_14_fb_Grond.pdf
 |title=Power-to-gas: Climbing the technology readiness ladder
 |last1=Grond
 |first1=Lukas
 |last2=Holstein
 |first2=Johan
 |date=February 2014
 |access-date=3 March 2020
 |archive-date=3 March 2020
 |archive-url=https://web.archive.org/web/20200303191026/https://www.gas-for-energy.com/fileadmin/G4E/pdf_Datein/gfe2_14_fb_Grond.pdf
 |url-status=live
 }}</ref>
{| class="wikitable"
|+ Alkaline Electrolysis
! Advantage !! Disadvantage
|-
| Commercial technology (high technology readiness level) || Limited cost reduction and efficiency improvement potential
|-
| Low investment electrolyser || High maintenance intensity
|-
| Large stack size || Modest reactivity, ramp rates and flexibility (minimal load 20%)
|-
| Extremely low hydrogen impurity (0.001%) || Stacks < 250&nbsp;kW require unusual AC/DC converters
|-
| &nbsp; || Corrosive electrolyte deteriorates when not operating nominally
|}

{| class="wikitable"
|+ Proton Exchange Membrane Electrolysis (PEME)
! Advantage !! Disadvantage
|-
| Reliable technology (no kinetics) and simple, compact design || High investment costs (noble metals, membrane)
|-
| Very fast response time || Limited lifetime of membranes
|-
| Cost reduction potential (modular design) || Requires high water purity
|}

{| class="wikitable"
|+ Solid Oxide Electrolysis Cell (SOEC)
! Advantage !! Disadvantage
|-
| Highest electrolysis efficiency || Very low technology readiness level (proof of concept)
|-
| Low capital costs || Poor lifetime because of high temperature and affected material stability
|-
| Possibilities for integration with chemical methanation (heat recycling) || Limited flexibility; constant load required
|}

== Power-to-hydrogen ==
All current P2G systems start by using electricity to [[Chemistry:Water splitting|split water]] into hydrogen and oxygen by means of electrolysis. In a "power-to-hydrogen" system, the resulting hydrogen is injected into the natural gas grid or is used in transport or industry rather than being used to produce another gas type.<ref name="Eberle" />

ITM Power won a tender in March 2013 for a Thüga Group project, to supply a 360&nbsp;kW self-pressurising [[Physics:High-pressure electrolysis|high-pressure electrolysis]] rapid response proton exchange membrane (PEM) electrolyser ''Rapid Response Electrolysis'' Power-to-Gas energy storage plant. The unit produces 125&nbsp;kg/day of hydrogen gas and incorporates [[Company:AEG (German company)|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.&nbsp;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.<ref>{{Cite web | url=http://www.itm-power.com/news-item/first-sale-of-power-to-gas-plant-in-germany/ | title=First Sale of 'Power-to-Gas' Plant in Germany – | access-date=2013-05-17 | archive-date=2013-05-02 | archive-url=https://web.archive.org/web/20130502063959/http://www.itm-power.com/news-item/first-sale-of-power-to-gas-plant-in-germany/ | url-status=live }}</ref> 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.<ref>[http://www.fuelcelltoday.com/news-events/news-archive/2013/july/ground-broken-at-itm-power-power-to-gas-pilot-plant-in-frankfurt Ground broken at ITM Power power-to-gas pilot plant in Frankfurt] {{webarchive|url=https://web.archive.org/web/20131111103354/http://www.fuelcelltoday.com/news-events/news-archive/2013/july/ground-broken-at-itm-power-power-to-gas-pilot-plant-in-frankfurt |date=2013-11-11 }}</ref>

[[File:Power to Gas HGas.jpg|thumb|upright=1.15|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 [[Chemistry:Hydrogen|hydrogen]] and thus in one hour can feed 3,000 cubic meters of hydrogen-enriched natural gas into the network.<ref>{{Cite web | url=http://www.itm-power.com/news-item/injection-of-hydrogen-into-the-german-gas-distribution-grid/ | title=Injection of Hydrogen into the German Gas Distribution Grid – | access-date=2013-12-05 | archive-date=2014-03-08 | archive-url=https://web.archive.org/web/20140308041637/http://www.itm-power.com/news-item/injection-of-hydrogen-into-the-german-gas-distribution-grid/ | url-status=live }}</ref>

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.<ref>{{Cite press release |title=E.ON inaugurates power-to-gas unit in Falkenhagen in eastern Germany |date=2013-08-28 |url= http://www.eon.com/en/media/news/press-releases/2013/8/28/eon-inaugurates-power-to-gas-unit-in-falkenhagen-in-eastern-germany.html |archive-url=https://web.archive.org/web/20130911034244/http://www.eon.com/en/media/news/press-releases/2013/8/28/eon-inaugurates-power-to-gas-unit-in-falkenhagen-in-eastern-germany.html |archive-date=2013-09-11 |url-status=dead |website=e·on}}</ref> The plant uses wind power and [[Company:Hydrogenics|Hydrogenics]]<ref>{{Cite web |url=http://www.cbc.ca/news/business/hydrogenics-and-enbridge-to-develop-utility-scale-energy-storage-1.1286432 |title=Hydrogenics and Enbridge to develop utility-scale energy storage |access-date=2013-11-11 |archive-date=2013-11-11 |archive-url=https://web.archive.org/web/20131111123135/http://www.cbc.ca/news/business/hydrogenics-and-enbridge-to-develop-utility-scale-energy-storage-1.1286432 |url-status=live }}</ref> 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&nbsp;kW power-to-gas project has been started in [[Place:Hamburg|Hamburg]]/Reitbrook district<ref>{{Cite web |url=http://renewables.seenews.com/news/e-on-hanse-starts-construction-of-power-to-gas-facility-in-hamburg-361477 |title=E.on Hanse starts construction of power-to-gas facility in Hamburg |access-date=2013-11-19 |archive-date=2014-03-15 |archive-url=https://web.archive.org/web/20140315171957/http://renewables.seenews.com/news/e-on-hanse-starts-construction-of-power-to-gas-facility-in-hamburg-361477 |url-status=live }}</ref> and is expected to open in 2015.<ref>{{Cite web |url=http://www.eon.com/en/media/news/press-releases/2014/9/1/eon-power-to-gas-pilot-unit-falkenhagen.html |title=E.ON power-to-gas pilot unit in Falkenhagen first year of operation |access-date=2014-11-10 |archive-date=2014-11-11 |archive-url=https://web.archive.org/web/20141111010255/http://www.eon.com/en/media/news/press-releases/2014/9/1/eon-power-to-gas-pilot-unit-falkenhagen.html |url-status=live }}</ref>

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 [[Earth:Internal combustion engine|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.<ref>{{cite news|title=German wind park with 1 MW Hydrogenics electrolyser for Power-to-Gas energy storage|url=http://www.renewableenergyfocus.com/view/35124/german-wind-park-with-1-mw-hydrogenics-electrolyser-for-power-to-gas-energy-storage/|access-date=21 July 2017|work=Renewable Energy Focus|date=17 October 2013|archive-date=1 June 2017|archive-url=https://web.archive.org/web/20170601103007/http://www.renewableenergyfocus.com/view/35124/german-wind-park-with-1-mw-hydrogenics-electrolyser-for-power-to-gas-energy-storage/|url-status=live}}</ref> The electrolyser produces 210 Nm<sup>3</sup>/h of hydrogen and is operated by RH2-WKA.<ref>{{Cite web |url=http://www.rh2-wka.de/ |title=RH2-WKA |access-date=2013-11-11 |archive-date=2013-11-24 |archive-url=https://web.archive.org/web/20131124030058/http://www.rh2-wka.de/ |url-status=live }}</ref>

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.<ref>{{Cite web |url=http://www.fuelcelltoday.com/news-events/news-archive/2012/july/ingrid-project-to-launch-12-mw-electrolyser-with-1-ton-of-storage-for-smart-grid-balancing-in-italy |title=INGRID Project to Launch 1.2 MW Electrolyser with 1 Ton of Storage for Smart Grid Balancing in Italy |access-date=2013-11-11 |archive-date=2013-11-11 |archive-url=https://web.archive.org/web/20131111111934/http://www.fuelcelltoday.com/news-events/news-archive/2012/july/ingrid-project-to-launch-12-mw-electrolyser-with-1-ton-of-storage-for-smart-grid-balancing-in-italy |url-status=live }}</ref> The hydrogen is used for grid balancing, transport, industry, and injection into the gas network.<ref>{{Cite web |url=http://www.hydrogenics.com/docs/default-source/pdf/renewable-projects-references---grid-balancing-and-ptg.pdf?sfvrsn=0 |title=Grid balancing, Power to Gas (PtG) |access-date=2013-11-11 |archive-date=2013-11-11 |archive-url=https://web.archive.org/web/20131111112937/http://www.hydrogenics.com/docs/default-source/pdf/renewable-projects-references---grid-balancing-and-ptg.pdf?sfvrsn=0 |url-status=live }}</ref>

The surplus energy from the 12 MW Prenzlau Windpark in Brandenburg, Germany<ref>[http://www.thewindpower.net/windfarm_en_6309_prenzlau.php Prenzlau Windpark (Germany)]</ref> will be injected into the gas grid from 2014 on.

The 6 MW Energiepark Mainz<ref>[http://www.energiepark-mainz.de/ Energiepark Mainz]</ref> from Stadtwerke Mainz, RheinMain University of Applied Sciences,  Linde and [[Company:Siemens|Siemens]] in [[Place:Mainz|Mainz]] (Germany) will open in 2015.

Power to gas and other [[Engineering:Energy storage|energy storage]] schemes to store and utilize [[Engineering:Renewable energy|renewable energy]] are part of Germany's [[Earth:Energiewende|Energiewende]] (energy transition program).<ref name=Nature41013>{{cite news|title=Renewable power: Germany's energy gamble: An ambitious plan to slash greenhouse-gas emissions must clear some high technical and economic hurdles.|url=http://www.nature.com/news/renewable-power-germany-s-energy-gamble-1.12755|access-date=April 10, 2013|newspaper=Nature|date=April 10, 2013|first=Quirin|last=Schiermeier|archive-date=April 13, 2013|archive-url=https://web.archive.org/web/20130413065727/http://www.nature.com/news/renewable-power-germany-s-energy-gamble-1.12755|url-status=live}}</ref>

In France, the MINERVE demonstrator of AFUL Chantrerie (Federation of Local Utilities Association) aims to promote the development of energy solutions for the future with elected representatives, companies and more generally civil society. It aims to experiment with various reactors and catalysts. The synthetic methane produced by the MINERVE demonstrator (0.6 Nm<sup>3</sup> / h of CH<sub>4</sub>) is recovered as CNG fuel, which is used in the boilers of the AFUL Chantrerie boiler plant. The installation was designed and built by the French SME Top Industrie, with the support of Leaf. In November 2017 it achieved the predicted performance, 93.3% of CH<sub>4</sub>. This project was supported by the ADEME and the ERDF-Pays de la Loire Region, as well as by several other partners: Conseil départemental de Loire -Atlantic, Engie-Cofely, GRDF, GRTGaz, Nantes-Metropolis, Sydela and Sydev.<ref>{{cite journal|title=Un démonstrateur Power to gas en service à Nantes|url=https://www.lemoniteur.fr/article/un-demonstrateur-power-to-gas-en-service-a-nantes-35321848|journal=Lemoniteur.fr|language=fr|date=2018|access-date=9 February 2018}}.</ref>

A full scale 1GW electrolyzer operated by EWE and Tree Energy Solutions is planned at the gas terminal in Wilhelmshaven, Germany. The first 500 MW is expected to begin operation in 2028. Wilhelmshaven can accommodate a second plant, bringing total potential capacity to 2GW.<ref>{{cite web|title=TES and EWE to Build 500MW Electrolyser at Wilhelmshaven Green Energy Hub|url=https://www.ewe.com/en/media-center/press-releases/2022/11/tes-and-ewe-to-build-500mw-electrolyser-at-wilhelmshaven-green-energy-hub-ewe-ag|date=25 November 2022|access-date=20 December 2022}}.</ref>

=== Grid injection without compression ===

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.
<ref>{{Cite web | url=http://www.energie-und-wende.de/no_cache/service/presse/presseinformationen/presseinformationen-detail/article/pressemitteilung-41.html | title=Energiewende & Dekarbonisierung Archive | access-date=2013-12-05 | archive-date=2013-12-05 | archive-url=https://archive.today/20131205102006/http://www.energie-und-wende.de/no_cache/service/presse/presseinformationen/presseinformationen-detail/article/pressemitteilung-41.html | url-status=live }}</ref>

== Power-to-methane ==
[[File:Methanation of CO2.png|thumb|upright=1.6|Methanation of CO<sub>2</sub> by electrolytically obtained hydrogen]]
A power-to-methane system combines hydrogen from a power-to-hydrogen system with carbon dioxide to produce methane<ref>{{Cite web |url=http://www.dnv.com/binaries/DNV%20KEMA%20(2013)%20-%20Systems%20Analyses%20Power%20to%20Gas%20-%20Technology%20Review_tcm4-567461.pdf |title=DNV-Kema Systems analyses power to gas |access-date=2014-08-21 |archive-url=https://web.archive.org/web/20150124021520/http://www.dnv.com/binaries/DNV%20KEMA%20(2013)%20-%20Systems%20Analyses%20Power%20to%20Gas%20-%20Technology%20Review_tcm4-567461.pdf |archive-date=2015-01-24 |url-status=dead }}</ref> (see [[Chemistry:Natural gas|natural gas]]) using a [[Chemistry:Methanation|methanation]] reaction such as the [[Chemistry:Sabatier reaction|Sabatier reaction]] or biological methanation resulting in an extra energy conversion loss of 8%,{{citation needed|date=May 2018}} the methane may then be fed into the natural gas grid if the purity requirement is reached.<ref name="p2m">{{cite journal|last1=Ghaib|first1=Karim|last2=Ben-Fares|first2=Fatima-Zahrae|title=Power-to-Methane: A state-of-the-art review|journal=Renewable and Sustainable Energy Reviews|date=2018|volume=81|pages=433–446|doi=10.1016/j.rser.2017.08.004|url=http://docdroid.net/IfMKlA3/power-to-methane.pdf|access-date=1 May 2018}}</ref>

ZSW (Center for Solar Energy and Hydrogen Research) and SolarFuel GmbH (now ETOGAS GmbH) realized a demonstration project with 250&nbsp;kW electrical input power in Stuttgart, Germany.<ref>{{cite news |url=https://www.reuters.com/article/us-tennet-thyssengas-powertogas/german-network-companies-join-up-to-build-power-to-gas-plant-idUSKCN1MQ25R |title=German network companies join up to build power-to-gas plant |access-date=17 October 2018 |newspaper=Reuters |date=2018-10-16 |archive-date=16 October 2018 |archive-url=https://web.archive.org/web/20181016224110/https://www.reuters.com/article/us-tennet-thyssengas-powertogas/german-network-companies-join-up-to-build-power-to-gas-plant-idUSKCN1MQ25R |url-status=live }}</ref> The plant was put into operation on October 30, 2012.<ref>{{cite web |url=http://www.zsw-bw.de/infoportal/presseinformationen/presse-detail/weltweit-groesste-power-to-gas-anlage-zur-methan-erzeugung-geht-in-betrieb.html |title=Weltweit größte Power-to-Gas-Anlage zur Methan-Erzeugung geht in Betrieb |website=ZSW-BW.de |language=de |access-date=2017-12-01 |url-status=dead |archive-url=https://web.archive.org/web/20121107140857/http://www.zsw-bw.de/infoportal/presseinformationen/presse-detail/weltweit-groesste-power-to-gas-anlage-zur-methan-erzeugung-geht-in-betrieb.html |archive-date=2012-11-07 }}</ref>

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 CO<sub>2</sub> from a waste-[[Physics:Biogas|biogas]] plant and [[Engineering:Variable renewable energy|intermittent renewable power]] to produce synthetic natural gas (SNG) which is directly fed into the local gas grid (which is operated by EWE).<ref>{{Cite web |url=http://www.audi.com/content/com/brand/en/vorsprung_durch_technik/content/2013/10/energy-turnaround-in-the-tank.html |title=Energy turnaround in the tank |website=Audi.com |access-date=2014-06-03 |archive-url=https://web.archive.org/web/20140606235918/http://www.audi.com/content/com/brand/en/vorsprung_durch_technik/content/2013/10/energy-turnaround-in-the-tank.html |archive-date=2014-06-06 |url-status=dead }}</ref> The plant is part of the Audi e-fuels program. The produced synthetic natural gas, named Audi e-gas, enables CO<sub>2</sub>-neutral mobility with standard CNG vehicles. Currently it is available to customers of Audi's first CNG car, the Audi A3 g-tron.<ref>{{Cite web | url=http://www.audi.com/corporate/en/corporate-responsibility/we-live-responsibility/product/audi-e-gas-new-fuel.html | title=Company | website=Audi.com | access-date=2014-06-04 | archive-date=2014-06-06 | archive-url=https://web.archive.org/web/20140606230322/http://www.audi.com/corporate/en/corporate-responsibility/we-live-responsibility/product/audi-e-gas-new-fuel.html | url-status=live }}</ref>

[[File:Helmeth_PtG_Anlage.jpg|thumb|upright=1.15|HELMETH Power-to-Gas Prototype]]
In April 2014 the [[Social:European Union|European Union]]'s co-financed and from the KIT coordinated<ref>{{cite web | url=http://vbt.ebi.kit.edu/index.pl/en/proj_steckb/HELMETH | title=Engler-Bunte-Institute Division of Combustion Technology - Project HELMETH | access-date=2014-10-31}}</ref> HELMETH<ref>{{cite web | url=http://www.helmeth.eu/ | title=Project homepage - HELMETH | access-date=2014-10-31}}</ref> (Integrated '''H'''igh-Temperature '''EL'''ectrolysis and '''METH'''anation for Effective Power to Gas Conversion) research project started.<ref>{{cite web | url=http://www.kit.edu/kit/english/pi_2014_14950.php | title=Karlsruhe Institute of Technology - Press Release 044/2014 | access-date=2014-10-31}}</ref> 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 CO<sub>2</sub>-methanation. 
Through the thermal integration of exothermal methanation and steam generation for the high temperature steam electrolysis  conversion efficiency > 85% ([[Physics:Heat of combustion|higher heating value]] of produced methane per used electrical energy) are theoretically possible. The process consists of a pressurized high-temperature steam [[Physics:Electrolysis of water|electrolysis]] and a pressurized CO<sub>2</sub>-methanation module. 
The project was completed in 2017 and achieved an efficiency of 76% for the prototype with an indicated growth potential of 80% for industrial scale plants.<ref>{{cite web |url=https://www.kit.edu/kit/pi_2018_009_power-to-gas-mit-hohem-wirkungsgrad.php |title=Karlsruhe Institute of Technology - Press Release 009/2018 |access-date=2018-02-21}}</ref> The operating conditions of the CO<sub>2</sub>-methanation are a gas pressure of 10 - 30 bar, a [[Chemistry:Substitute natural gas|SNG]] production of 1 - 5.4 m<sup>3</sup>/h (NTP) and a [[Chemistry:Conversion|reactant conversion]] that produces SNG with H<sub>2</sub> < 2 vol.-% resp. CH<sub>4</sub> > 97 vol.-%.<ref>{{cite web |url=http://www.helmeth.eu/ |title=Project homepage - HELMETH | access-date=2018-02-21}}</ref> Thus, the generated substitute natural gas can be injected in the entire German natural gas network without limitations.<ref name="DIN EN 16723-2">[https://www.beuth.de/de/norm/din-en-16723-2/265820994 DIN EN 16723-2:2017-10 - Erdgas und Biomethan zur Verwendung im Transportwesen und Biomethan zur Einspeisung ins Erdgasnetz]</ref> As a cooling medium for the exothermic reaction boiling water is used at up to 300&nbsp;°C, which corresponds to a [[Physics:Vapour pressure of water|water vapour pressure]] of about 87 bar. The SOEC works with a pressure of up to 15 bar, steam conversions of up to 90% and generates one [[Physics:Standard cubic meter|standard cubic meter]] of hydrogen from 3.37 [[Kilowatt hour|kWh]] of electricity as feed for the methanation.

The technological maturity of Power to Gas is evaluated in the European 27 partner project STORE&GO, which has started in March 2016 with a runtime of four years.<ref>{{cite web | url=http://www.dvgw.de/en/english-pages/dvgw/news-details/meldung/21697/liste/29071/link//9fdb2cfb8c7bd1d3c7811603a2bcd6d3/ | title=Deutscher Verein des Gas und Wasserfaches e.V.: Press release - Project Store&Go | access-date=2016-12-12 | archive-url=https://web.archive.org/web/20160801042942/http://www.dvgw.de/en/english-pages/dvgw/news-details/meldung/21697/liste/29071/link//9fdb2cfb8c7bd1d3c7811603a2bcd6d3/ | archive-date=2016-08-01 | url-status=dead }}</ref> Three different technological concepts are demonstrated in three different European countries (Falkenhagen/{{wipe|Germany}}, [[Place:Solothurn|Solothurn]]/{{wipe|Switzerland}}, Troia/Italy). The technologies involved include biological and chemical [[Chemistry:Methanation|methanation]], [[Earth:Direct air capture|direct capture of CO<sub>2</sub>]] from atmosphere, liquefaction of the synthesized methane to bio-[[Chemistry:Liquefied natural gas|LNG]], and direct injection into the gas grid. The overall goal of the project is to assess those technologies and various usage paths under technical,<ref>{{cite web | url=http://www.wattdor4all.ch/projects/storego-erdgasnetz-als-riesen-batterie/ | title=Watt d'Or 4 all: "Store&Go" – Erdgasnetz als Riesen-Batterie | access-date=2016-12-12 | url-status=dead | archive-url=https://web.archive.org/web/20170221014103/http://www.wattdor4all.ch/projects/storego-erdgasnetz-als-riesen-batterie/ | archive-date=2017-02-21 }}</ref> economic,<ref>{{cite web | url=http://www.energieinstitut-linz.at/v2/portfolio-item/store-and-go/ | title=Store&Go, Innovative large-scale energy STORagE technologies AND Power-to-Gas concepts after Optimisation | access-date=2016-12-12 | archive-date=2016-11-24 | archive-url=https://web.archive.org/web/20161124034202/http://www.energieinstitut-linz.at/v2/portfolio-item/store-and-go/ | url-status=live }}</ref>
and legal <ref>{{cite web | url=http://www.rug.nl/rechten/recht-en-samenleving/projecten/het-juridische-effect-van-innovatieve-energieconversie-en-_opslag | title=Het juridische effect van innovatieve energieconversie en –opslag | access-date=2016-12-12}}</ref> aspects to identify business cases on the short and on the long term.  The project is co-funded by the [[Social:European Union|European Union]]'s Horizon 2020 research and innovation programme (18 million euro) and the Swiss government (6 million euro), with another 4 million euro coming from participating industrial partners.<ref>{{cite web | url=http://www.storeandgo.info/ | title=Project homepage - STORE&GO| access-date=2016-12-12}}</ref> The coordinator of the overall project is the research center of the 
[[Physics:Deutscher Verein des Gas- und Wasserfaches|DVGW]]<ref>{{cite web | url=http://www.dvgw-ebi.de/download/Press_Release_Store-Go-Kick-Off_16-03-16.pdf | title=Deutscher Verein des Gas und Wasserfaches e.V.: Press release - Innovative 28 million E project STORE&GO started to show large scale energy storage by Power-to-Gas is already possible today | access-date=2016-12-12}}</ref> located at the KIT.

=== Microbial methanation ===

The biological methanation combines both processes, the [[Chemistry:Electrolysis|electrolysis]] of water to form [[Chemistry:Hydrogen|hydrogen]] and the subsequent CO<sub>2</sub> reduction to [[Chemistry:Methane|methane]] using this [[Chemistry:Hydrogen|hydrogen]]. During this process, methane forming microorganisms (methanogenic [[Biology:Archaea|archaea]] or methanogens) release [[Biology:Enzymes|enzymes]] that reduce the [[Chemistry:Overpotential|overpotential]] of a non-catalytic [[Physics:Electrode|electrode]] (the [[Physics:Cathode|cathode]]) so that it can produce [[Chemistry:Hydrogen|hydrogen]].<ref>{{cite journal | title=Deutzmann, J. S.; Sahin, M.; Spormann, A. M., Extracellular enzymes facilitate electron uptake in biocorrosion and bioelectrosynthesis| journal=mBio| volume=6| issue=2| doi=10.1128/mBio.00496-15| pmid=25900658| pmc=4453541| year=2015| last1=Deutzmann| first1=Jörg S.| last2=Sahin| first2=Merve| last3=Spormann| first3=Alfred M.}}</ref><ref>{{cite journal | last1 = Yates | first1 = Matthew D. | last2 = Siegert | first2 = Michael | last3 = Logan | first3 = Bruce E. | year = 2014 | title =  Hydrogen evolution catalyzed by viable and non-viable cells on biocathodes | doi=10.1016/j.ijhydene.2014.08.015 | volume=39 | issue = 30 | journal = [[Physics:International Journal of Hydrogen Energy|International Journal of Hydrogen Energy]] | pages=16841–16851}}</ref> This microbial power-to-gas reaction occurs at ambient conditions, i.e. room temperature and pH 7, at efficiencies that routinely reach 80-100%.<ref>{{cite journal | title=  Electrosynthesis of commodity chemicals by an autotrophic microbial community.|journal= Appl. Environ. Microbiol. |year=2012|volume= 78|issue=23|pages= 8412–8420 |doi=10.1128/aem.02401-12| pmid=  23001672|pmc=3497389| last1=  Marshall| first1=  C. W.| last2=  Ross| first2=  D. E.| last3=  Fichot| first3=  E. B.| last4=  Norman| first4=  R. S.| last5=  May| first5=  H. D.|bibcode= 2012ApEnM..78.8412M }}</ref><ref>{{cite journal | last1 = Siegert | first1 = Michael | last2 = Yates | first2 = Matthew D. | last3 = Call | first3 = Douglas F. | last4 = Zhu | first4 = Xiuping | last5 = Spormann | first5 = Alfred | last6 = Logan | first6 = Bruce E. |year = 2014 | title= Comparison of Nonprecious Metal Cathode Materials for Methane Production by Electromethanogenesis| doi=10.1021/sc400520x |pmid = 24741468| pmc = 3982937 | volume=2 | issue = 4 | journal = ACS Sustainable Chemistry & Engineering | pages=910–917}}</ref> However, methane is formed more slowly than in the Sabatier reaction due to the lower temperatures. A direct conversion of CO<sub>2</sub> to [[Chemistry:Methane|methane]] has also been postulated, circumventing the need for [[Chemistry:Hydrogen|hydrogen]] production.<ref>{{cite journal | title= Direct biological conversion of electric current into methane by electromethanogenesis. | doi=10.1021/es803531g | pmid=19544913 | volume=43 | issue=10 | journal=Environmental Science | pages=3953–3958| bibcode=2009EnST...43.3953C | last1=Cheng | first1=Shaoan | last2=Xing | first2=Defeng | last3=Call | first3=Douglas F. | last4=Logan | first4=Bruce E. | year=2009 }}</ref>
Microorganisms involved in the microbial power-to-gas reaction are typically members of the order ''[[Biology:Methanobacteriales|Methanobacteriales]]''. [[Biology:Genus|Genera]] that were shown to catalyze this reaction are ''[[Biology:Methanobacterium|Methanobacterium]]'',<ref>{{cite journal | last1 = Beese-Vasbender | first1 = Pascal F. | last2 = Grote | first2 = Jan-Philipp | last3 = Garrelfs | first3 = Julia | last4 = Stratmann | first4 = Martin | last5 = Mayrhofer | first5 = Karl J.J. | year = 2015 | title = Selective microbial electrosynthesis of methane by a pure culture of a marine lithoautotrophic archaeon. | journal = Bioelectrochemistry | volume = 102 | pages = 50–5 | doi = 10.1016/j.bioelechem.2014.11.004 | pmid = 25486337 }}</ref><ref>{{cite journal | last1 = Siegert | first1 = Michael | last2 = Yates | first2 = Matthew D. | last3 = Spormann | first3 = Alfred M. | last4 = Logan | first4 = Bruce E. | year = 2015 | title = ''Methanobacterium'' dominates biocathodic archaeal communities in methanogenic microbial electrolysis cells. | journal = ACS Sustainable Chemistry & Engineering | volume = 3 | issue = 7| page = 1668−1676 | doi = 10.1021/acssuschemeng.5b00367 | doi-access = free }}</ref> ''[[Biology:Methanobrevibacter|Methanobrevibacter]]'',<ref>{{cite journal | last1 = Siegert | first1 = Michael | last2 = Li | first2 = Xiu-Fen | last3 = Yates | first3 = Matthew D. | last4 = Logan | first4 = Bruce E. | year = 2015 | title = The presence of hydrogenotrophic methanogens in the inoculum improves methane gas production in microbial electrolysis cells. | journal = Frontiers in Microbiology | volume = 5 | page = 778 | doi = 10.3389/fmicb.2014.00778 | pmid = 25642216 | pmc = 4295556 | doi-access = free }}</ref> and ''[[Biology:Methanothermobacter|Methanothermobacter]]'' ([[Earth:Thermophile|thermophile]]).<ref>{{cite journal | last1 = Sato | first1 = Kozo | last2 = Kawaguchi | first2 = Hideo | last3 = Kobayashi | first3 = Hajime | year = 2013 | title = Bio-electrochemical conversion of carbon dioxide to methane in geological storage reservoirs. | journal = Energy Conversion and Management | volume = 66 | page = 343 | doi = 10.1016/j.enconman.2012.12.008 }}</ref>

===LPG production===
Methane can be used to produce LPG by synthesising SNG with partial reverse [[Chemistry:Hydrogenation|hydrogenation]] at high pressure and low temperature. LPG in turn can be converted into alkylate which is a premium [[Chemistry:Gasoline|gasoline]] blending stock because it has exceptional antiknock properties and gives clean burning.<ref name=LPG/>

===Power to food===
The synthetic methane generated from electricity can also be used for generating protein rich feed for cattle, poultry and fish economically by cultivating ''[[Biology:Methylococcus capsulatus|Methylococcus capsulatus]]'' bacteria culture with tiny land and water footprint.<ref>{{Cite web |url=https://www.ntva.no/wp-content/uploads/2014/01/04-huslid.pdf |title=BioProtein Production |access-date=31 January 2018 |archive-url=https://web.archive.org/web/20170510151825/http://www.ntva.no/wp-content/uploads/2014/01/04-huslid.pdf |archive-date=10 May 2017 |url-status=dead }}</ref><ref>{{Cite web |url=https://www.newscientist.com/article/2112298-food-made-from-natural-gas-will-soon-feed-farm-animals-and-us/ |title=Food made from natural gas will soon feed farm animals – and us |access-date=31 January 2018 |archive-date=12 December 2019 |archive-url=https://web.archive.org/web/20191212070800/https://www.newscientist.com/article/2112298-food-made-from-natural-gas-will-soon-feed-farm-animals-and-us/ |url-status=live }}</ref><ref>{{Cite web |url=https://www.cargill.com/2016/new-venture-selects-cargill-tennessee-to-produce-feedkind |title=New venture selects Cargill's Tennessee site to produce Calysta FeedKind Protein |access-date=31 January 2018 |archive-date=30 December 2019 |archive-url=https://web.archive.org/web/20191230182858/https://www.cargill.com/2016/new-venture-selects-cargill-tennessee-to-produce-feedkind |url-status=live }}</ref>{{Request quotation|date=April 2023|reason=if it is economical why is it not done?}}The carbon dioxide gas produced as by-product from these plants can be  recycled in the generation of synthetic methane (SNG). Similarly, oxygen gas produced as by product from the electrolysis of water and the [[Chemistry:Methanation|methanation]]  process can be consumed in the cultivation of bacteria culture. With these integrated plants, the abundant renewable solar and wind power potential can be converted into high value food products without any water pollution or [[Chemistry:Greenhouse gas|greenhouse gas]] (GHG) emissions.<ref>{{cite web |url=https://www.carbontrust.com/media/672719/calysta-feedkind.pdf |title=Assessment of environmental impact of FeedKind protein |access-date=20 June 2017 |archive-url=https://web.archive.org/web/20190802163726/https://www.carbontrust.com/media/672719/calysta-feedkind.pdf |archive-date=2 August 2019 |url-status=dead }}</ref>

== Biogas-upgrading to biomethane ==

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.<ref name=NREL/>

2014-Avedøre wastewater Services in Avedøre, Kopenhagen (Denmark) is adding a 1 MW electrolyzer plant to upgrade the [[Physics:Anaerobic digestion|anaerobic digestion]] biogas from sewage sludge.<ref>{{Cite web |url=http://energinet.dk/EN/FORSKNING/Nyheder/Sider/Overskydende-vindkraft-bliver-til-groen-gas-i-Avedoere.aspx |title=Excess wind power is turned into green gas in Avedøre |access-date=2014-05-30 |archive-url=https://web.archive.org/web/20140531090937/http://energinet.dk/EN/FORSKNING/Nyheder/Sider/Overskydende-vindkraft-bliver-til-groen-gas-i-Avedoere.aspx |archive-date=2014-05-31 |url-status=dead }}</ref> The produced hydrogen is used with the carbon dioxide from the biogas in a Sabatier reaction to produce methane. Electrochaea<ref>{{Cite web |url=http://www.electrochaea.com/ |title=Electrochaea |access-date=2014-01-12 |archive-date=2014-01-12 |archive-url=https://web.archive.org/web/20140112170243/http://www.electrochaea.com/ |url-status=live }}</ref> 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.<ref>{{Cite journal | title=A Single-Culture Bioprocess of Methanothermobacter thermautotrophicus to Upgrade Digester Biogas by {{chem|C|O|2}}-to-{{chem|C|H|4}} Conversion with {{chem|H|2}} |last1=Martin|first1=Matthew R.|last2=Fornero|first2=Jeffrey J.|last3=Stark|first3=Rebecca|last4=Mets|first4=Laurens|last5=Angenent|first5=Largus T.|journal=Archaea|volume=2013| pages=157529 |year=2013|id=Article ID 157529|doi=10.1155/2013/157529| pmid=24194675 | pmc=3806361 |doi-access=free }}</ref> A pre-commercial demonstration project with a 10,000-liter reactor vessel was executed between January and November 2013 in Foulum, Denmark.<ref>{{cite web |url=http://www.electrochaea.com/technology.html |title=Power-to-Gas Energy Storage - Technology Description |website=Electrochaea.com |access-date=2014-01-12 |url-status=dead |archive-url=https://web.archive.org/web/20140112171007/http://www.electrochaea.com/technology.html |archive-date=2014-01-12 }}</ref>

In 2016 Torrgas, [[Company:Siemens|Siemens]], Stedin, [[Company:Gasunie|Gasunie]], A.Hak, Hanzehogeschool/EnTranCe and Energy Valley intend to open a 12 MW Power to Gas facility in Delfzijl (The Netherlands) where biogas from Torrgas ([[Chemistry:Torrefaction|biocoal]]) will be upgraded with hydrogen from electrolysis and delivered to nearby industrial consumers.<ref>{{Cite web |url=http://www.nvnom.com/homepage/power-gas-plant-delfzijl/ |title=Power-to-Gas plant for Delfzijl |access-date=2014-05-30 |archive-date=2014-05-31 |archive-url=https://web.archive.org/web/20140531090450/http://www.nvnom.com/homepage/power-gas-plant-delfzijl/ |url-status=live }}</ref>

== Power-to-syngas==
{{image frame|caption=Power-to-syngas process|pos=top
|content=
{{chart/start}}
{{chart|border=1|boxstyle=background:#66FF66; |RED  | | | | | |BLUE |RED=Water|BLUE=CO<sub>2</sub>}}
{{chart| |'|-|-|.| | | | |!| }}
{{chart|border=3|boxstyle=background:yellow; | | | | |CLEAR| | |!| |CLEAR=Electrolysis of Water}}
{{chart| |,|-|-|'|!| | | |!| }}
{{chart|border=1|RED  | |GREEN| | |!| |RED=Oxygen|GREEN=Hydrogen}}
{{chart| | | | ||!|,|-|-|'| }}
{{chart|border=3|boxstyle=background:yellow; | | | | |CLEAR| | | | |CLEAR=Conversion Reactor}}
{{chart| |,|-|-|'|!|'|-|-|.| }}
{{chart|border=1|RED  | |GREEN| |BLUE |RED=Water|GREEN=Hydrogen|BLUE=CO}}
{{chart/end}}
}}
[[Chemistry:Syngas|Syngas]] is a mixture of hydrogen and carbon monoxide. It has been used since Victorian times, when it was produced from coal and known as "towngas". A power-to-syngas system uses hydrogen from a power-to-hydrogen system to produce syngas.
*1st step: Electrolysis of Water (SOEC) −water is split into hydrogen and oxygen.
*2nd step: Conversion Reactor ([[Chemistry:Water-gas shift reaction#Reverse water-gas shift|RWGSR]]) −hydrogen and carbon dioxide are inputs to the Conversion Reactor that outputs hydrogen, carbon monoxide, and water. 3H<sub>2</sub> + CO<sub>2</sub>  → (2H<sub>2</sub> + CO)<sup>syngas</sup> + H<sub>2</sub>O
*[[Chemistry:Syngas|Syngas]] is used to produce synfuels.
[[File:Indirect conversion synthetic fuels processes.jpg|thumbnail|left|upright=2.5|Power-to-syngas [[Chemistry:Raw material|feedstock]] is the same as feedstock derived from other sources.]]
{{clear left}}

=== Initiatives ===
Other initiatives to create syngas from carbon dioxide and water may use different [[Chemistry:Water splitting|water splitting]] methods.
*[[Engineering:Concentrated solar power|CSP]]
**2004 Sunshine-to-Petrol —[[Organization:Sandia National Laboratories|Sandia National Laboratories]].<ref>{{cite web|title=Sunshine to Petrol|url=http://energy.sandia.gov/energy/renewable-energy/solar-energy/sunshine-to-petrol/|website=Sandia National Laboratories|publisher=United States Department of Energy (DOE)|access-date=15 May 2015}}</ref><ref>[http://energy.sandia.gov/wp-content/gallery/uploads/S2P_SAND2009-5796P.pdf SNL: Sunshine to Petrol - Solar Recycling of Carbon Dioxide into Hydrocarbon Fuels]</ref><ref>{{cite web|title=Sandia and Sunshine-to-Petrol: Renewable Drop-in Transportation Fuels|url=https://www.fbo.gov/index?s=opportunity&mode=form&id=698e254d2c8fea2fc478add76d2aac1c&tab=core&_cview=0|website=Federal Business Opportunities|publisher=U.S. Federal Government|access-date=15 May 2015|date=Oct 29, 2013}}</ref><ref>{{cite web|last1=Biello|first1=David|title=Reverse Combustion: Can CO2 Be Turned Back into Fuel?|url=http://www.scientificamerican.com/article/turning-carbon-dioxide-back-into-fuel/|website=Scientific American - Energy & Sustainability|access-date=17 May 2015|date=September 23, 2010|archive-date=16 May 2015|archive-url=https://web.archive.org/web/20150516091656/http://www.scientificamerican.com/article/turning-carbon-dioxide-back-into-fuel/|url-status=live}}</ref><ref>{{cite web|last1=Lavelle|first1=Marianne|title=Carbon Recycling: Mining the Air for Fuel|url=http://news.nationalgeographic.com/news/energy/2011/08/110811-turning-carbon-emissions-into-fuel/|website=National Geographic - News|publisher=National Geographic Society|access-date=19 May 2015|date=August 11, 2011|archive-date=20 May 2015|archive-url=https://web.archive.org/web/20150520020840/http://news.nationalgeographic.com/news/energy/2011/08/110811-turning-carbon-emissions-into-fuel/|url-status=dead}}</ref>
**2013 {{Proper name|NewCO2Fuels}} —{{Proper name|New CO2 Fuels Ltd}} ([[ISO 3166-2:IL|IL]]) and Weizmann Institute of Science.<ref>{{cite web|title=Bright Way to Convert Greenhouse Gas to Biofuel|url=http://web.weizmann.org.uk/2012/12/18/bright-way-to-convert-greenhouse-gas-to-biofuel/|website=Weizmann UK|publisher=Weizmann UK. Registered Charity No. 232666|access-date=19 May 2015|date=18 December 2012}} </ref><ref>{{cite web|title={{chem|C|O|2}} and {{chem|H|2|O}} Dissociation Process|url=http://www.newco2fuels.co.il/technology/1/process|website=NCF - Technology Process|publisher=New CO2 Fuels Ltd|access-date=19 May 2015}}</ref><ref>{{cite web|url=http://www.newco2fuels.co.il/files/files/NCF%20Newsletter%20Issue01%20Sept%202012.pdf|title=Newsletter NewCO2Fuels, Issue 1|date=September 2012}}</ref><ref>{{Cite web |url=http://www.asx.com.au/asxpdf/20130411/pdf/42f6524n3tpxs3.pdf |title=From challenge to opportunity New {{chem|C|O|2}} Fuels: An Introduction... |access-date=2015-05-30 |archive-date=2015-05-30 |archive-url=https://web.archive.org/web/20150530074508/http://www.asx.com.au/asxpdf/20130411/pdf/42f6524n3tpxs3.pdf |url-status=live }}</ref>
**2014 Solar-Jet Fuels —Consortium partners [[Organization:ETH Zurich|ETH]], SHELL, [[Organization:German Aerospace Center|DLR]], Bauhaus Luftfahrt, ARTTIC.<ref>{{cite web|title=SOLAR-JET Project|url=http://www.solar-jet.aero/page/about-solar-jet/objectives.php|website=SOLAR-JET|publisher=SOLAR-JET Project Office: ARTTIC|access-date=15 May 2015|archive-date=18 May 2015|archive-url=https://web.archive.org/web/20150518080031/http://www.solar-jet.aero/page/about-solar-jet/objectives.php|url-status=dead}}</ref><ref>{{cite web|title=Sunlight to jet fuel|url=https://www.ethz.ch/en/news-and-events/eth-news/news/2014/04/sunlight-to-jet-fuel.html|website=The ETH Zurich|publisher=Eidgenössische Technische Hochschule Zürich|access-date=15 May 2015|archive-date=10 September 2014|archive-url=https://web.archive.org/web/20140910032329/https://www.ethz.ch/en/news-and-events/eth-news/news/2014/04/sunlight-to-jet-fuel.html|url-status=live}}</ref><ref>{{cite web|last1=Alexander|first1=Meg|title="Solar" jet fuel created from water and carbon dioxide|url=http://www.gizmag.com/sunlight-carbon-dioxide-jet-fuel/31872/|website=Gizmag|publisher=Gizmag|access-date=15 May 2015|date=May 1, 2014|archive-date=18 May 2015|archive-url=https://web.archive.org/web/20150518080134/http://www.gizmag.com/sunlight-carbon-dioxide-jet-fuel/31872/|url-status=live}}</ref><ref>{{cite web|title=SOLARJET demonstrates full process for thermochemical production of renewable jet fuel from H2O & CO2|url=http://www.greencarcongress.com/2015/04/20150428-solarjet.html|website=Green Car Congress|publisher=BioAge Group, LLC|access-date=15 May 2015|date=28 April 2015|archive-date=18 May 2015|archive-url=https://web.archive.org/web/20150518090314/http://www.greencarcongress.com/2015/04/20150428-solarjet.html|url-status=live}}</ref><ref>{{cite web|title=Aldo Steinfeld - Solar Syngas|url=https://b60099084-dev-blakely-dot-google-solveforx.appspot.com/moonshots/aldo-steinfeld-solar-syngas|website=Solve For <X>|publisher=Google Inc.}}{{dead link|date=March 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{Cite web |url=http://www.psi.ch/lst/BooksEN/MRS_Bulletin_-_Energy_Quarterly,_Vol_38,_2013.pdf |title=Brewing fuels in a solar furnace |access-date=2015-05-30 |archive-date=2015-05-19 |archive-url=https://web.archive.org/web/20150519120146/http://www.psi.ch/lst/BooksEN/MRS_Bulletin_-_Energy_Quarterly,_Vol_38,_2013.pdf |url-status=live }}</ref>
*[[Physics:High-temperature electrolysis|HTE]] / [[Chemistry:Alkaline water electrolysis|Alkaline water electrolysis]]
**2004 Syntrolysis Fuels —[[Organization:Idaho National Laboratory|Idaho National Laboratory]] and Ceramatec, Inc. (US).<ref>{{Cite web |url=http://www4vip.inl.gov/factsheets/docs/syntrolysis.pdf |title=Syntrolysis, Synthetic Fuels from Carbon Dioxide, Electricity and Steam |access-date=2015-05-30 |archive-url=https://web.archive.org/web/20150521021039/http://www4vip.inl.gov/factsheets/docs/syntrolysis.pdf |archive-date=2015-05-21 |url-status=dead }}</ref><ref>{{cite web|title=Synthetic Fuel (syntrolysis) |url=http://www.thoughtware.tv/test/show/2274|website=Thoughtware.TV|publisher=Thoughtware.TV|access-date=20 May 2015|date=June 17, 2008}}</ref><ref>{{cite conference |last1=Stoots |first1=C.M. |last2=O'Brien |first2=J.T. |last3=Hartvigsen |first3=J. |title=Carbon Neutral Production of Syngas via High Temperature Electrolytic Reduction of Steam and {{chem|C|O|2}} |book-title=ASME 2007 International Mechanical Engineering Congress and Exposition |date=2007 |volume=15: Sustainable Products and Processes |pages=185–194 |doi=10.1115/IMECE2007-43667 |isbn=978-0-7918-4309-3 |conference=2007 ASME International Mechanical Engineering Congress and Exposition, November 11–15, 2007, Seattle, Washington, USA |url= http://www5vip.inl.gov/technicalpublications/Documents/3867730.pdf |access-date=May 30, 2015 |archive-url= https://web.archive.org/web/20150521013659/http://www5vip.inl.gov/technicalpublications/Documents/3867730.pdf |archive-date=May 21, 2015 |url-status=dead}}</ref><ref>[http://www.hydrogen.energy.gov/pdfs/review04/3_nhi_overview_henderson.pdf Nuclear Hydrogen Initiative Overview]</ref><ref>[https://www.iaea.org/About/Policy/GC/GC57/GC57InfDocuments/English/gc57inf-2-att1_en.pdf Nuclear Hydrogen Production Technology]</ref><ref>[http://www.topsoe.com/sites/default/files/topsoe_scot_electrolysis_synthetic_fuel_production.pdf Electrolysis For Synthetic Fuel Production] {{webarchive|url=https://web.archive.org/web/20150530075842/http://www.topsoe.com/sites/default/files/topsoe_scot_electrolysis_synthetic_fuel_production.pdf |date=2015-05-30 }}</ref>
**2008 WindFuels —Doty Energy (US).<ref>{{cite web|title=The WindFuels Primer - Basic Explanation for the Non-scientist|url=http://dotyenergy.com/Introduction/primer.htm|website=Doty Energy|publisher=Doty Energy|access-date=16 May 2015|archive-date=16 May 2015|archive-url=https://web.archive.org/web/20150516234209/http://www.dotyenergy.com/Introduction/primer.htm|url-status=live}}</ref><ref>{{Cite web |url=http://dotyenergy.com/PDFs/Doty-WindFuels-WP.pdf |title=Securing Our Energy Future by Efficiently Recycling {{chem|C|O|2}} into Transportation Fuels |access-date=2015-05-30 |archive-date=2016-03-04 |archive-url=https://web.archive.org/web/20160304091950/http://dotyenergy.com/PDFs/Doty-WindFuels-WP.pdf |url-status=live }}</ref>
**2012 Air Fuel Synthesis —Air Fuel Synthesis Ltd (UK).<ref>{{cite web|title=The AFS Process - turning air into a sustainable fuel|url=http://www.airfuelsynthesis.com/technology/technical-review.html|website=Air Fuel Synthesis - Technical Review|publisher=Air Fuel Synthesis Limited|access-date=19 May 2015|archive-url=https://web.archive.org/web/20150403145733/http://www.airfuelsynthesis.com/technology/technical-review.html|archive-date=3 April 2015|url-status=dead}}</ref><ref>[http://www.airfuelsynthesis.com/images/stories/pdfs/demonstrator%20unit.pdf Case Study: AFS demonstrator unit]{{Dead link|date=May 2020 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{cite web |title=Cars Fueled by Air?|url=http://www.planetforward.org/tv-segments/cars-fueled-by-air |website=PlanetForward.org|publisher=Planet Forward|access-date=20 May 2015}}</ref><ref>{{cite web |last1=Rapier |first1=Robert |title=Investors Beware of Fuel from Thin Air |url=http://www.investingdaily.com/15833/investors-beware-of-fuel-from-thin-air/ |website=Investing Daily |access-date=17 May 2015 |date=October 31, 2012 |archive-date=18 May 2015 |archive-url=https://web.archive.org/web/20150518223943/http://www.investingdaily.com/15833/investors-beware-of-fuel-from-thin-air/ |url-status=live }}</ref><ref>{{cite report |first1=K.R. |last1=Williams |first2=N. |last2=van Lookeren Campagne |title=Synthetic Fuels From Atmospheric Carbon Dioxide |url= https://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/16_4_BOSTON_04-72_0017.pdf |archive-url=https://web.archive.org/web/20130304160544/https://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/16_4_BOSTON_04-72_0017.pdf |archive-date=2013-03-04 |url-status=dead}}</ref> Air Fuel Synthesis Ltd have become insolvent.<ref>{{cite web |title=Air Fuel Synthesis Limited |url=https://www.thegazette.co.uk/notice/2496487 |website=www.thegazette.co.uk |publisher=The Gazette |access-date=19 October 2018}}</ref>
**2013 Green Feed —[[Organization:Ben-Gurion University of the Negev|BGU]] and Israel Strategic Alternative Energy Foundation (I-SAEF).<ref>{{cite web|title=BGU Researchers invent Green Alternative to Crude Oil |url= http://in.bgu.ac.il/en/Pages/news/oil_greenalternative.aspx|website=Ben-Gurion University of the Negev|publisher=Ben-Gurion University of the Negev|access-date=17 May 2015|date=13 November 2013}}</ref><ref>{{cite web |title=Recent Success Story: Converting carbon dioxide, a damaging greenhouse gas, into fuel that may be used for transportation|url=http://www.i-saef.org/early-success.html|website=I-SAEF|publisher=Israel Strategic Alternative Energy Foundation|access-date=15 May 2015}}</ref><ref>{{cite web|title=BGU Researchers Develop New Type of Crude Oil Using Carbon Dioxide and Hydrogen|url=http://www.bgustudyabroad.org/media-center/news-releases/bgu-crude-oil.html |website=American Associates (Ben-Gurion University of the Negev)|publisher=American Associates (AABGU)|access-date=15 May 2015|url-status=dead |archive-url= https://web.archive.org/web/20150518102319/http://www.bgustudyabroad.org/media-center/news-releases/bgu-crude-oil.html|archive-date=18 May 2015}}</ref><ref>{{cite web|title=BGU researchers developing more efficient process for hydrogenation of CO2 to synthetic crude|url=http://www.greencarcongress.com/2013/11/20131121-bgu.html|website=Green Car Congress|publisher=BioAge Group, LLC|access-date=15 May 2015|date=21 November 2013|archive-date=4 August 2015|archive-url=https://web.archive.org/web/20150804053042/http://www.greencarcongress.com/2013/11/20131121-bgu.html|url-status=live}}</ref>
**2014 [[Chemistry:E-diesel|E-diesel]] —Sunfire, a clean technology company and [[Company:Audi|Audi]].<ref>{{cite web|title=Fuel of the future: Research facility in Dresden produces first batch of Audi e-diesel|url=https://www.audi-mediaservices.com/publish/ms/content/en/public/pressemitteilungen/2015/04/21/fuel_of_the_future.html|website=Audi MediaServices - Press release|publisher=AUDI AG.|access-date=23 May 2015|location=Ingolstadt/Berlin|date=2015-04-21|archive-date=19 May 2015|archive-url=https://web.archive.org/web/20150519052201/https://www.audi-mediaservices.com/publish/ms/content/en/public/pressemitteilungen/2015/04/21/fuel_of_the_future.html|url-status=live}}</ref><ref>{{cite web|last1=Rapier|first1=Robert|title=Is Audi's Carbon-Neutral Diesel a Game-Changer?|url=http://www.energytrendsinsider.com/2015/04/30/is-audis-carbon-neutral-diesel-a-game-changer/|website=Energy Trends Insider|publisher=Energy Trends Insider|access-date=15 May 2015|archive-date=18 May 2015|archive-url=https://web.archive.org/web/20150518095920/http://www.energytrendsinsider.com/2015/04/30/is-audis-carbon-neutral-diesel-a-game-changer/|url-status=live}}</ref><ref>{{cite web|last1=Novella|first1=Steven|title=Apr 28 2015 Audi's E-Diesel|url=http://theness.com/neurologicablog/index.php/audis-e-diesel/|website=The NeuroLogicaBlog - Technology|publisher=Steven Novella, MD|access-date=24 May 2015|date=28 April 2015|archive-date=30 May 2015|archive-url=https://web.archive.org/web/20150530073305/http://theness.com/neurologicablog/index.php/audis-e-diesel/|url-status=live}}</ref>

The US Naval Research Laboratory (NRL) is designing a power-to-liquids system using the Fischer-Tropsch Process to create fuel on board a ship at sea,<ref>{{cite web|title=How the United States Navy Plans to Turn Seawater into Jet Fuel|url=http://www.altenergy.org/new_energy/seawater-into-jet-fuel.html |website=Alternative Energy|publisher=altenergy.org|access-date=8 May 2015}}</ref> with the base products carbon dioxide (CO<sub>2</sub>) and water (H<sub>2</sub>O) being derived from sea water via "An Electrochemical Module Configuration For The Continuous Acidification Of Alkaline Water Sources And Recovery Of CO<sub>2</sub> With Continuous Hydrogen Gas Production".<ref>{{cite web|title=Patent: US 20140238869 A1|url=http://www.google.com/patents/US20140238869?cl=en|website=Google Patents|access-date=8 May 2015|archive-date=18 May 2015|archive-url=https://web.archive.org/web/20150518171911/http://www.google.com/patents/US20140238869?cl=en|url-status=live}}</ref><ref>The total carbon content of the world's oceans is roughly 38,000 GtC. Over 95% of this carbon is in the form of dissolved bicarbonate ion (HCO<sub>3</sub> <sup>−</sup>). {{cite book |last=Cline |first=William |date=1992 |title=The Economics of Global Warming |publisher=Institute for International Economics |location=Washington D.C. |quote=The dissolved bicarbonate and carbonate of the ocean is essentially bound CO<sub>2</sub> and the sum of these species along with gaseous CO<sub>2</sub>, shown in the following equation, represents the total carbon dioxide concentration [CO<sub>2</sub>]<sub>T</sub>, of the world's oceans. Σ[CO<sub>2</sub>]<sub>T</sub>=[CO<sub>2</sub>(g)]<sub>l</sub>+[HCO<sub>3</sub> <sup>−</sup>]+[CO<sub>3</sub> <sup>2−</sup>]}}{{vn|date=July 2020|reason=Unsure which (if any) is a quote from the book. The first may be original research or a note.}}
</ref>

== See also ==

* [[Earth:Carbon-neutral fuel|Carbon-neutral fuel]]
* [[Biology:Electromethanogenesis|Electromethanogenesis]]
* [[Chemistry:Electrofuel|Electrofuel]] 
* [[Biology:Electrohydrogenesis|Electrohydrogenesis]]
* [[Engineering:Grid energy storage|Grid energy storage]]
* [[Physics:Hydrogen economy|Hydrogen economy]]
* [[Chemistry:Methanation|Methanation]]
* List of energy storage power plants
* [[Engineering:Power-to-X|Power-to-X]]
* [[Biology:Renewable natural gas|Renewable natural gas]]
* [[Physics:Timeline of hydrogen technologies|Timeline of hydrogen technologies]]

== Notes ==

{{reflist|30em}}

== Further reading ==

* {{cite journal | last1 = Götz | first1 = Manuel | last2 = Lefebvre | first2 = Jonathan | last3 = Mörs | first3 = Friedemann | last4 = McDaniel Koch | first4 = Amy | last5 = Graf | first5 = Frank | last6 = Bajohr | first6 = Siegfried | last7 = Reimert | first7 = Rainer | last8 = Kolb | first8 = Thomas | year = 2016 | title = Renewable Power-to-Gas: A technological and economic review | journal = Renewable Energy | volume = 85 | pages = 1371–1390 | doi = 10.1016/j.renene.2015.07.066 | doi-access = free }}
* Méziane Boudellal. "Power-to-Gas. Renewable Hydrogen Economy for the Energy Transition". Second edition. 249 pages. English edition. Editor: de Gruyter, March 2023. https://www.degruyter.com/document/doi/10.1515/9783110781892/html

== External links ==
* [https://youtube.com/watch?v=xMU_ipvHb7A Three minute explainer video] by the Institute for Energy Technology (2016)
*[https://web.archive.org/web/20130414232837/http://www.zsw-bw.de/en/the-zsw.html Zentrum für Sonnenenergie-und Wasserstoff-Forschung (ZSW) Baden-Württemberg]

[[Category:Energy storage]]
[[Category:Energy conversion]]

{{Sourceattribution|Power-to-gas}}