View source for Power-to-X

{{Short description|Storing surplus electricity production in chemical form}}
{{Use dmy dates|date=April 2016}}
[[File:Transformation in joining up sectors.jpg|thumb|Transformation in joining up sectors]]
'''Power-to-X''' (also '''P2X''' and '''P2Y''') are [[electricity]] [[energy transformation|conversion]], [[energy storage]], and reconversion pathways from surplus [[renewable energy]].<ref name="acatech-2016">{{cite book | editor1 = acatech
 | editor2 = Lepoldina | editor3 = Akademienunion | year = 2016 | title = Flexibility concepts for the German power supply in 2050 : ensuring stability in the age of renewable energies | publisher = [[acatech]] — National Academy of Science and Engineering | place = Berlin, Germany | isbn = 978-3-8047-3549-1 | url = http://www.acatech.de/fileadmin/user_upload/Baumstruktur_nach_Website/Acatech/root/de/Publikationen/Kooperationspublikationen/ESYS_Position_Paper_Flexibility_concepts.pdf
 | access-date = 2016-06-10 | archive-url = https://web.archive.org/web/20161006041130/http://www.acatech.de/fileadmin/user_upload/Baumstruktur_nach_Website/Acatech/root/de/Publikationen/Kooperationspublikationen/ESYS_Position_Paper_Flexibility_concepts.pdf
 | archive-date = 6 October 2016 | url-status = dead }}</ref><ref name="lund-etal-2015">{{cite journal | first1 = Peter D | last1 = Lund | first2 = Juuso | last2 = Lindgren | first3 = Jani | last3 = Mikkola | first4 = Jyri | last4 = Salpakari | title = Review of energy system flexibility measures to enable high levels of variable renewable electricity | date = 2015 | journal = [[Renewable and Sustainable Energy Reviews]] | volume = 45 | pages = 785–807 | doi = 10.1016/j.rser.2015.01.057| url = https://research.aalto.fi/files/6557604/lund_et_al_review.pdf }}</ref> 
Power-to-X conversion technologies allow for the decoupling of power from the electricity sector for use in other sectors (such as transport or chemicals), possibly using power that has been provided by additional investments in generation.<ref name="acatech-2016"/> The term is widely used in [[Germany]] and may have originated there.

The '''X''' in the terminology can refer to one of the following: power-to-[[ammonia]], power-to-[[feedstock|chemicals]], [[Electrofuel|power-to-fuel]],<ref>{{Cite web|last=Trakimavicius|first=Lukas|date=December 2023|title=Mission Net-Zero: Charting the Path for E-fuels in the Military|url=https://www.enseccoe.org/publications/mission-net-zero-charting-the-path-for-e-fuels-in-the-military/|publisher=NATO Energy Security Centre of Excellence}}</ref> [[power-to-gas]] (power-to-hydrogen, power-to-methane) power-to-liquid ([[synthetic fuel]]), power to food,<ref>{{Cite journal|last1=Sillman|first1=J.|last2=Uusitalo|first2=V.|last3=Ruuskanen|first3=V.|last4=Ojala|first4=L.|last5=Kahiluoto|first5=H.|last6=Soukka|first6=R.|last7=Ahola|first7=J.|date=2020-11-01|title=A life cycle environmental sustainability analysis of microbial protein production via power-to-food approaches|journal=The International Journal of Life Cycle Assessment|language=en|volume=25|issue=11|pages=2190–2203|doi=10.1007/s11367-020-01771-3|issn=1614-7502|doi-access=free}}</ref> [[power-to-heat]]. Electric vehicle charging, space heating and cooling, and water heating can be shifted in time to match generation, forms of [[demand response]] that can be called power-to-mobility and power-to-[[thermal energy|heat]].

Collectively power-to-X schemes which use surplus power fall under the heading of flexibility measures and are particularly useful in energy systems with high shares of renewable generation and/or with strong [[Low-carbon economy|decarbonization]] targets.<ref name="acatech-2016"/><ref name="lund-etal-2015"/> A large number of pathways and technologies are encompassed by the term. In 2016 the German government funded a €30{{nbsp}}million first-phase research project into power-to-X options.<ref name="rwth-2016">{{cite press release | author = <!-- staff writer, no by-line --> | title = Power-to-X: entering the energy transition with Kopernikus | date = 5 April 2016 | publisher = RWTH Aachen | location = Aachen, Germany | url = https://www.rwth-aachen.de/go/id/kvyv/lidx/1 | access-date = 2016-06-09}}</ref>

== Power-to-fuel ==
{{Main|Power-to-gas}}
Surplus electric power can be converted to gas [[fuel]] energy for storage and reconversion.<ref name="sternberg-etal-2015">{{cite journal | last1 = Sternberg | first1 = André | last2 = Bardow | first2 = André | title = Power-to-What? — Environmental assessment of energy storage systems | year = 2015 | journal = [[Energy and Environmental Science]] | volume = 8 | issue = 2 | pages = 389–400 | doi = 10.1039/c4ee03051f}}</ref><ref name="agora-2014">{{cite book | author = Agora Energiewende | title = Electricity storage in the German energy transition : analysis of the storage required in the power market, ancillary services market and the distribution grid | year = 2014 | publisher = [[Agora Energiewende]] | place = Berlin, Germany | url = https://www.agora-energiewende.de/fileadmin2/Projekte/2013/speicher-in-der-energiewende/Agora_Speicherstudie_EN_web.pdf | access-date = 2018-12-30}}</ref><ref name="sterner-etal-2014">{{cite book | first1 = Michael | last1 = Sterner | first2 = Fabian | last2 = Eckert | first3 = Martin | last3 = Thema | display-authors = etal | title = Langzeitspeicher in der Energiewende — Präsentation | trans-title = Long-term storage in the ''Energiewende'' — Presentation | year = 2014 | publisher = Forschungsstelle für Energienetze und Energiespeicher (FENES), OTH Regensburg
 | place = Regensburg, Germany | url = http://www.bmwi.de/BMWi/Redaktion/PDF/S-T/speicherkonferenz-michael-sterner-langzeitspeicher-energiewende | access-date = 2016-05-09}}</ref><ref name="ausfelder-etal-2016">{{cite book | first1 = Florian | last1 = Ausfelder | first2 = Christian | last2 = Beilmann | first3 = Sigmar | last3 = Bräuninger | first4 = Reinhold | last4 = Elsen | first5 = Erik | last5 = Hauptmeier | first6 = Angelika | last6 = Heinzel | first7 = Renate | last7 = Hoer | first8 = Wolfram | last8 = Koch | first9 = Falko | last9 = Mahlendorf | first10 = Anja | last10 = Metzelthin | first11 = Martin | last11 = Reuter | first12 = Sebastian | last12 = Schiebahn | first13 = Ekkehard | last13 = Schwab | first14 = Ferdi | last14 = Schüth | first15 = Detlef | last15 = Stolten | first16 = Gisa | last16 = Teßmer | first17 = Kurt | last17 = Wagemann
 | first18 = Karl-Friedrich | last18 = Ziegahn | title = Energy storage systems: the contribution of chemistry — Position paper | date = May 2016 | publisher = Koordinierungskreis Chemische Energieforschung (Joint Working Group on Chemical Energy Research) | place = Germany | isbn = 978-3-89746-183-3 | url = http://www.dgmk.de/DBG_PP_Energiespeicher_2015_A4_engl.pdf
 | access-date = 2016-06-09}}</ref> 
Direct current [[electrolysis of water]] (efficiency 80–85% at best) can be used to produce [[hydrogen]] which can, in turn, be converted to [[methane]] (CH<sub>4</sub>) via [[methanation]].<ref name=sternberg-etal-2015/><ref name="pagliaro-and-konstandopoulos-2012">
<!-- url: http://pubs.rsc.org/en/content/ebook/978-1-84973-195-9#!divbookcontent -->
{{cite book|title=Solar Hydrogen: Fuel of the Future|last1=Pagliaro|first1=Mario|last2=Konstandopoulos|first2=Athanasios G|date=15 June 2012|publisher=RSC Publishing|isbn=978-1-84973-195-9|location=Cambridge, United Kingdom|doi=10.1039/9781849733175|s2cid=241910312 }}
</ref> Another possibility is converting the hydrogen, along with CO<sub>2</sub> to methanol.<ref>[https://www.chemicals-technology.com/projects/george-olah-renewable-methanol-plant-iceland/ George Olah's renewable methanol plant]</ref> Both these fuels can be stored and used to produce electricity again, hours to months later. 

=== Storage and reconversion of power-to-fuel ===

Hydrogen and methane can be used as downstream [[fuel]]s, fed into the [[natural gas]] grid, or used to make [[synthetic fuel]].<ref name="koenig-etal-2014">{{cite conference | last1 = König | first1 = Daniel Helmut | last2 = Baucks | first2 = Nadine | last3 = Kraaij | first3 = Gerard | last4 = Wörner | first4 = Antje | title = Entwicklung und Bewertung von Verfahrenskonzepten zur Speicherung von fluktuierenden erneuerbaren Energien in flüssigen Kohlenwasserstoffen | trans-title = Development and evaluation of process concepts for storing fluctuating renewable energy in liquid hydrocarbons | book-title = Jahrestreffen der ProcessNet-Fachgruppe Energieverfahrenstechnik | date = 18–19 February 2014 | place = Karlsruhe, Germany
 | url = http://elib.dlr.de/88355 | access-date = 2016-05-09}}</ref><ref name="foit-etal-2016">{{cite journal | last1 = Foit | first1 = Severin | last2 = Eichel | first2 = Rüdiger-A | last3 = Vinke | first3 = Izaak C | last4 = de Haart | first4 = Lambertus GJ | title = Power-to-Syngas – an enabling technology for the transition of the energy system? Production of tailored synfuels and chemicals using renewably generated electricity | date = 1 October 2016 | journal = Angewandte Chemie International Edition | volume = 56 | issue = 20 | pages = 5402–5411 | doi = 10.1002/anie.201607552 | issn = 1521-3773 | pmid=27714905}}</ref> Alternatively they can be used as a chemical [[feedstock]], as can [[ammonia]] ({{NH3}}).

Reconversion technologies include [[Gas turbine#Industrial gas turbines for power generation|gas turbines]], [[combined cycle plant]]s, [[reciprocating engine]]s and [[fuel cell]]s. 
Power-to-power refers to the round-trip reconversion efficiency.<ref name=sternberg-etal-2015/> For hydrogen storage, the round-trip efficiency remains limited at 35–50%.<ref name="lund-etal-2015"/> Electrolysis is expensive and power-to-gas processes need substantial full-load hours to be economic.<ref name=acatech-2016/> 
However, while round-trip conversion efficiency of power-to-power is lower than with batteries and electrolysis can be expensive, storage of the fuels themselves is quite inexpensive.{{cn|date=April 2022}} This means that large amounts of energy can be stored for long periods of time with power-to-power, which is ideal for seasonal storage. This could be particularly useful for systems with high [[variable renewable energy]] penetration, since many areas have significant seasonal variability of solar, wind, and [[run-of-the-river]]-hydroelectric generation.

=== Batteries ===

Despite it also being based fundamentally on [[electrolytic]] chemical reactions, [[battery storage]] is not normally considered a power-to-fuel concept.

== Power-to-heat ==

The purpose of power-to-heat systems is to utilize excess electricity generated by renewable energy sources which would otherwise be wasted. Depending on the context, the power-to-heat can either be stored as heat, or delivered as heat to meet a need.<ref name="bloess-etal-2018">
{{cite journal
 | last1 = Bloess | first1 = Andreas
 | last2 = Schill | first2 = Wolf-Peter
 | last3 = Zerrahn | first3 = Alexander
 | title = Power-to-heat for renewable energy integration: a review of technologies, modeling approaches, and flexibility potentials
 | date = 15 February 2018
 | journal = Applied Energy
 | volume = 212
 | pages = 1611–1626
 | doi = 10.1016/j.apenergy.2017.12.073
 | issn = 0306-2619
| doi-access = free
 | hdl = 10419/200120
 | hdl-access = free
 }}  {{open access}}
</ref>

=== Heating systems ===
In contrast to simple electric heating systems such as night storage heating which covers the complete heating requirements, power-to-heat systems are hybrid systems, which additionally have traditional heating systems using chemical fuels like wood or natural gas.<ref>{{Cite book|title=Energiespeicher – Bedarf, Technologien, Integration.|last=Sterner, Stadler|first=Michael, Ingo|year=2014|location=Berlin and Heidelberg}}</ref>{{rp|124}} When there are excess energy the heat production can result from electric energy otherwise the traditional heating system will be used. In order to increase flexibility power-to-heat systems are often coupled with heat accumulators. The power supply occurs for the most part in the local and district heating networks. Power-to-heat systems are also able to supply buildings or industrial systems with heat.<ref>{{Cite journal|last=Schweiger|first=Gerald|date=2017|title=The potential of power-to-heat in Swedish district heating systems.|doi=10.1016/j.energy.2017.02.075|journal=Energy|volume=137|pages=661–669}}</ref>

Power-to-heat involves contributing to the heat sector, either by [[resistance heating]] or via a [[heat pump]]. Resistance heaters have unity efficiency, and the corresponding [[coefficient of performance]] (COP) of heat pumps is 2–5.<ref name=sternberg-etal-2015/> Back-up immersion heating of both [[domestic hot water]] and [[district heating]] offers a cheap way of using surplus renewable energy and will often displace [[carbon-intensive]] fossil fuels for the task.<ref name="acatech-2016"/> Large-scale heat pumps in district heating systems with thermal energy storage are an especially attractive option for power-to-heat: they offer exceptionally high efficiency for balancing excess wind and solar power, and they can be profitable investments.<ref name="zakeri-etal-2016">{{cite journal
 | last1 = Zakeri| first1 = Behnam | last2 = Rinne| first2 = Samuli | last3 = Syri | first3 = Sanna | title = Wind integration into energy systems with a high share of nuclear power – what are the compromises? | date = 31 March 2015 | journal = Energies | volume = 8 | issue = 4 | pages = 2493–2527 | doi = 10.3390/en8042493 | doi-access=free | issn = 1996-1073}}</ref><ref name="salpakari-etal-2016">{{cite journal | last1 = Salpakari | first1 = Jyri | last2 = Mikkola | first2 = Jani | last3 = Lund | first3 = Peter D | title = Improved flexibility with large-scale variable renewable power in cities through optimal demand side management and power-to-heat conversion | date = 2016 | journal = Energy Conversion and Management | doi = 10.1016/j.enconman.2016.08.041 | issn = 0196-8904 | volume=126 | pages=649–661| url = https://aaltodoc.aalto.fi/handle/123456789/24304 }}</ref>

=== Heat storage systems ===

{{Main|Thermal battery}}

== Other forms of power-to-X ==

Power-to-mobility refers to the charging of [[battery electric vehicle]]s (BEV). Given the expected uptake of EVs, dedicated dispatch will be required. As vehicles are idle for most of the time, shifting the charging time can offer considerable flexibility: the charging window is a relatively long 8–12{{nbsp}}hours, whereas the charging duration is around 90{{nbsp}}minutes.<ref name="lund-etal-2015"/> The EV batteries can also be discharged to the grid to make them work as electricity storage devices, but this causes additional wear to the battery.<ref name="lund-etal-2015"/>

== Impact ==

According to the German concept of sector coupling interconnecting all the energy-using sectors will require the digitalisation and automation of numerous processes to synchronise supply and demand.<ref>{{Cite web|url=https://www.cleanenergywire.org/factsheets/sector-coupling-shaping-integrated-renewable-power-system|title=Sector coupling – Shaping an integrated renewable energy system|date=2018-04-18|website=Clean Energy Wire|language=en|access-date=2019-03-06}}</ref>

A 2023 study examined to role that power{{nbhyph}}to{{nbhyph}}X could play in a highly{{nbhyph}}renewable future energy system for [[Japan]].  The P2X technologies considered include [[electrolysis of water|water electrolysis]], [[methanation]], [[Fischer–Tropsch process|Fischer–Tropsch synthesis]], and [[Haber process|Haber–Bosch synthesis]] and the study used [[linear programming]] to determine least{{nbhyph}}cost system structure and operation.  Results indicate that these various P2X technologies can effectively shift electricity loads and reduce [[curtailment (electricity)|curtailment]] by 80% or more.<ref name="onodera-etal-2023">
{{cite journal
 | last1 = Onodera | first1 = Hiroaki
 | last2 = Delage | first2 = Rémi
 | last3 = Nakata | first3 = Toshihiko
 | title = Systematic effects of flexible power-to-X operation in a renewable energy system: a case study from Japan
 | date = 1 October 2023
 | journal = Energy Conversion and Management:{{nbsp}}X
 | volume = 20
 | pages = 100416
 | doi = 10.1016/j.ecmx.2023.100416
 | issn = 2590-1745
 | url = https://www.sciencedirect.com/science/article/pii/S2590174523000727/pdfft
 | access-date = 2023-09-01
| doi-access = free
 }}  {{open access}}
</ref>

== See also ==
* [[Grid energy storage]]
* [[Flywheel]]

== References ==
{{reflist}}

{{Electricity grid modernization|state=expanded}}
{{Electricity generation}}

[[Category:Energy policy]]
[[Category:Energy policy of Germany]]
[[Category:Energy storage]]
[[Category:Power engineering]]