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1、The future of home heatingThe roles of heat pumps and hydrogen An Energy Futures Lab Briefing PaperAmy TraskDr Richard HannaDr Aidan RhodesThe future of home heating The roles of heat pumps and hydrogen 2Reviewers:Rob Gross UK Energy Research CentreRichard Lowes Regulatory Assistance ProjectNixon Su

2、nny Imperial College LondonAcknowledgmentsThis Energy Futures Lab Briefing Paper has been prepared by researchers from Imperial College London working independently via Imperial Consultants.The paper preparation was supported by the MCS Charitable Foundation,an independent UK-wide charity with a mis

3、sion to accelerate the widespread adoption of renewable energy and low carbon technologies.The Foundation oversees the Microgeneration Certification Scheme(MCS),which defines,maintains,and improves quality standards for renewable energy at buildings scale.https:/www.mcscharitablefoundation.org/Energ

4、y Futures Lab is one of seven Global Institutes at Imperial College London.The institute was established to address global energy challenges by identifying and leading new opportunities to serve industry,government and society at large through high quality research,evidence and advocacy for positive

5、 change.The institute aims to promote energy innovation and advance systemic solutions for a sustainable energy future by bringing together the science,engineering and policy expertise at Imperial and fostering collaboration with a wide variety of external partners.The Energy Futures Lab Briefing Pa

6、pers are periodic reports aimed at all stakeholders in the energy sector.They bring together expertise from across Imperial College London to provide clarity on a wide range of energy topics.For more information visit:http:/www.imperial.ac.uk/energy-futures-labJanuary 2022 Energy Futures LabLIST OF

7、ACRONYMS4EXECUTIVE SUMMARY51INTRODUCTION81.1Aim and approach102TECHNOLOGIES AND SUPPLY112.1Heat pumps112.1.1Types of heat pumps112.1.2How heat pumps work122.1.3Efficiency of a heat pump&cost of installation132.1.4UK heat pump market and international comparison142.1.5Carbon intensity152.2Hydrogen152

8、.2.1The case for low-carbon hydrogen152.2.2Production methods152.2.3Hydrogen production in the UK and industrial clusters162.2.4Hydrogen trials in the UK182.2.5Carbon intensity182.3Summary193DISTRIBUTION AND DEMAND203.1Heat pumps203.1.1Supply chain203.2Hydrogen213.2.1Transmission&distribution213.2.2

9、End-use233.3Summary234BARRIERS TO IMPLEMENTATION244.1General barriers to heat pump and hydrogen heating deployment244.1.1Building energy efficiency244.1.2Industry skills and training244.1.3Public awareness254.2Heat pumps254.2.1Financial barriers to uptake254.2.2Consumer preferences,installation&main

10、tenance264.2.3The power grid274.3Hydrogen274.3.1Hydrogen supply274.3.2Storage274.3.3Household costs284.3.4Safety concerns294.3.5Cost-competitiveness304.3.6Blue hydrogen304.3.7Green hydrogen314.4Scenario comparisons314.4.1Systems-based approach314.4.2Household scale324.5Key barriers that will need ad

11、dressing in the next ten years344.5.1General344.5.2Heat pumps344.5.3Hydrogen355POLICY SUPPORT AND REGULATION365.1Heat pumps365.1.1Subsidising upfront and ongoing costs365.1.2Technological innovation,cost reduction and industry growth405.1.3Regulation,standards andcertification schemes425.1.4Consumer

12、 engagement,behaviour change and smart heat425.1.5Policies to manage electricity demand and impact on the power grid from heat pumps435.2Hydrogen445.2.1General445.2.2Blue hydrogen465.2.3Green hydrogen465.2.4Is heat decarbonisation in buildings the best use of hydrogen?465.3Heat pumps and hydrogen as

13、 complementary technologies475.4Key policies and regulations over the next ten years485.4.1Heat pumps485.4.2Hydrogen496SUMMARY AND RECOMMENDATIONS506.1Summary of findings506.2Policy recommendations51REFERENCES53Table of ContentsThe future of home heating The roles of heat pumps and hydrogen 4 List o

14、f AcronymsList of Acronyms ASHP Air-source Heat PumpBEIS Department for Business,Energy and Industrial StrategyCCC Climate Change CommitteeCCS Carbon Capture and StorageCCUS Carbon Capture Utilisation and Storage CHP Combined Heat and PowerCO2 Carbon DioxideCoP Coefficient of PerformanceDACCS Direct

15、 Air Carbon Capture and StorageEFV Excess Flow ValveEHPA European Heat Pump AssociationEPC Energy Performance CertificateEU European UnionGSHP Ground-source Heat PumpGW GigawattGWh Gigawatt-hourGWP Global Warming PotentialH2 HydrogenHaaS Heat as a ServiceHHP Hybrid Heat PumpHP Heat pumpIMRP Iron Mai

16、ns Replacement ProgrammekgCO2e Kilograms of carbon dioxide equivalentkgCO2e per kWh Kilograms of carbon dioxide equivalent per kilowatt-hour of thermal energykgCO2e per kg H2 Kilograms of carbon dioxide equivalent per kg of hydrogenkW KilowattkWh Kilowatt-hourMCS Microgeneration Certification Scheme

17、MtCO2 Megatonnes(Million tonnes)of Carbon Capture and StorageMW MegawattMWh Megawatt-hourNO2 Nitrogen DioxideRHI Renewable Heat IncentiveSMR Steam Methane ReformationSPF Seasonal Performance FactorUK United KingdomExecutive SummaryExecutive Summary In this Briefing Paper,the prospects for the future

18、 of home heating are analysed with specific reference to heat pumps and hydrogen heating.The report is based on extensive literature surrounding the topic of decarbonisation of the heat sector in the UK and will discuss the various advantages,challenges,and technicalities surrounding the two technol

19、ogies.The evidence gathered and discussed culminates in a set of recommendations that prioritise key areas that require addressing over the course of the next decade.Heat PumpsHeat pumps are a well-established technology that are powered by electricity to transfer heat from external sources(e.g.,air

20、,ground,water)to provide warmth and hot water to a building.Whilst efficient,with a low carbon footprint when powered by renewable electricity,they have had a limited roll-out in the UK to date and make up less than 1%of installed heat capacity(BSRIA,2017).Imminent action is necessary to develop the

21、 market and reduce costs for low-carbon heating(BEIS,2021f,p.11).The Government has set a target for 600,000 heat pumps to be installed annually by 2028 (HM Government 2020),with the Climate Change Committee estimating that nearly 19 million heat pumps may need to be installed by 2050 to achieve net

22、 zero(CCC,2019c,p.84).Meeting this demand should be feasible,with transferrable skills and learnings from complementary technologies(e.g.boilers and air conditioners)enabling the manufacturing base to increase.However,consumer awareness of heat pumps is low and they are currently expensive to instal

23、l.The UK governments Heat and Buildings Strategy sets ambitions,through collaboration with industry,to lower heat pump installation costs by at least 25%50%by 2025,and to lower purchase prices and running costs to close to parity with gas boilers by 2030(BEIS,2021f).This will require a coordinated a

24、pproach to technological innovation and consumer engagement and policies to expand the UK supply chain for heat pumps(see Policy and regulations section below).HydrogenRepurposing the natural gas grid with hydrogen would mean no CO2 emissions at the point of use(as with heat pumps).However,combustio

25、n of hydrogen can result in emissions of nitrogen oxides(NOx)air pollutants this would need to be carefully regulated through an emissions standard for hydrogen appliances.Hydrogen is predominantly derived from fossil fuels in energy intensive production processes.This means that for a hydrogen grid

26、 to be a viable strategy for net zero,its production needs to be low-carbon.The UK has endorsed a twin track approach with regards to this,focussing on steam methane reformation with carbon capture(blue hydrogen)or electrolysis powered by renewables(green hydrogen)(BEIS,2021f,p.68).The differences b

27、etween hydrogen and natural gas mean that to deliver hydrogen safely into homes,certain sections of the gas grid would need to be retrofitted.Whilst a large proportion of iron pipelines are already being replaced through the Iron Mains Replacement Programme,there remains steel pipework that would ne

28、ed to be replaced if the transmission pipeline is repurposed.Within houses the use of hydrogen heating could be a more familiar experience to consumers,bearing similarities to the use of natural gas heating systems.However,there are several obstacles to overcome before this would be feasible.Propert

29、ies in areas converted for heating via a hydrogen grid would be subject to a certain level of disruption resulting from home surveys,any required updates of existing natural gas pipework and the conversion or installation of appliances suitable for use with hydrogen.The future of home heating The ro

30、les of heat pumps and hydrogen 6Barriers to ImplementationRegardless of which heating technologies dominate in domestic settings in the future,there will be some common barriers to uptake faced by each option.With the UK having one of the least thermally efficient building stocks in Europe(ACE,2015)

31、,the demanding timescales necessary to meet net zero,and a low public awareness of alternative heating technologies(BEIS,2021f),improving energy efficiency,recruiting employees and upskilling existing workforces,as well as improving public awareness,are necessary measures moving forward.For heat pum

32、ps specifically,in the next decade some of the most pressing barriers relate to the installation process.For example,high upfront costs mean they are several times more expensive than a gas boiler,there is a lack of qualified installers,they may require oversized or thicker radiators to be installed

33、 alongside them,and typically require more space than modern gas combi boilers.Furthermore,if a large share of UK homes are fitted with heat pumps,the power grid will need reinforcement to manage total and peak electricity demand;smart,flexible operation of heat pumps could help to smooth peaks of d

34、emand and reduce some need for physical reinforcement.A hydrogen heating scenario would face its own set of issues as there are currently very limited sources of low-carbon hydrogen.Although there are plans in place for 5 GW of low-carbon hydrogen by 2030(HM Government,2020),this is destined for ind

35、ustry as the harder to decarbonise sectors will take priority.There are also a number of safety concerns related to hydrogen use,which will need addressing before its widescale adoption can take place.Storage facilities to cope with periods of high demand will also need to be established.Green hydro

36、gen,in particular,is not currently cost competitive and a limited carbon capture roll-out means that blue hydrogen is not yet feasible on a commercial level.Policy and regulationsThe Boiler Upgrade Scheme,a three-year,450 million scheme that will support the installation of approximately 90,000 heat

37、 pumps,is the most recent grant support mechanism announced by the Government to increase the deployment of heat pumps in the UK(BEIS,2021f).However,given the limited success of previous schemes it may not be enough to stimulate market growth to the levels required,with affordability being noted as

38、a key barrier to heat pump uptake.Technological innovation,cost reduction and local job creation could be boosted by government support to expand the UK heat pump market and domestic supply chain.This could include the establishment of a national,dedicated test centre for the development and perform

39、ance monitoring of heat pumps,and incentives for complementary manufacturers to shift production from established fossil fuel heating technologies to heat pumps.The Government has recently published a consultation on a proposed market-based mechanism for low-carbon heat which could oblige fossil fue

40、l boiler manufacturers to progressively increase their sales of heat pumps relative to gas and oil boiler sales.The creation of a heat pump council,which brings together national and local government,regulators,industry,and civil society could prove important in taking a coordinated approach to deve

41、loping the heat pump market through consumer engagement and quality assurance via the recommended national test centre for heat pumps.With the increasing amounts of heat pump installations expected in the next decade,demand management policies are required to limit the impact on peak electricity dem

42、and and maintain a balanced grid.In the coming decade there are a number of government planned initiatives that aim to support a low-carbon hydrogen economy and try to overcome the associated barriers of its Executive SummaryExecutive Summarydeployment.A 240 million Net Zero Hydrogen Fund has been s

43、et up as a co-investment into the hydrogen economy and a hydrogen business model will be outlined to try to improve the cost-competitiveness of low-carbon hydrogen,which will soon be defined by standards to monitor lifecycle emissions.Hydrogen trials on a neighbourhood scale are due to begin in the

44、next few years and can provide a safety case for the use of the gas.Meanwhile a decision on whether or not to blend the current gas grid with a proportion of hydrogen to reduce emissions and potentially provide a smoother route to a 100%hydrogen gas grid is expected in 2023(HM Government,2020;BEIS,2

45、021f).The government plans to make a strategic decision in 2026 about the role of hydrogen in heating buildings,based on evidence from local trials and research and development(BEIS,2021f).It is important to consider how hydrogen could be used in(and whether it should be prioritised for)harder to el

46、ectrify sectors(e.g.,industry and shipping).With respect to its potential application in building heat decarbonisation,we find that hydrogen would be best placed strategically in industrial clusters or as a(hydrogen boiler)component in hybrid heat pump systems.Strategic placement of hydrogen facilit

47、ies near industrial clusters,where the demand for it is already in place will likely aid development of low-carbon hydrogen.In this way,regions within proximity to clusters could transition away from natural gas to hydrogen heating in homes if hydrogen trials prove it as a viable and safe option.Our

48、 recommendations related to the future of home heating are as follows:Energy levies should be moved away from electricity and transitioned over to more carbon intensive fuels;Support the development of UK heat pump manufacturing through policy support and incentives for UK-based manufacturers of com

49、plementary technologies(e.g.gas boilers,air conditioners)to shift or diversify production to heat pumps;Long-term grants(of at least 10 years)are recommended to increase revenue certainty in the heat pump industry;Introduction of green financing schemes and products for domestic renewables and energ

50、y efficiency measures;Establishment of a heat pump council comprising members from national and local government,regulators,industry,and civil society to help coordinate consumer engagement with heat pump deployment;Investment in a national research,testing and training facility for heat pumps to mo

51、nitor and develop the technology further;The utilisation of hybrid heat pumps is proposed to take advantage of time-of-use price differences and engage users through Heat-as-a-Service business models;Utilisation of low-carbon hydrogen strategically in hard to electrify sectors such as industry and s

52、hipping is recommended;Low-carbon hydrogen should be clearly defined and standards will need to be in place if the market is to be developed for heat decarbonisation in buildings (The government have recently completed a consultation which aims to create a low-carbon hydrogen standard);Support the d

53、evelopment of electrolysers in the UK to improve the cost-effectiveness of green hydrogen;Focus on the deployment of solutions currently available such as energy efficiency,electrification through heat pumps and heat networks.The future of home heating The roles of heat pumps and hydrogen 8While ren

54、ewable technologies are rapidly evolving and dropping in price to provide a cost-effective way to decarbonise the power sector,the heating sector,which is responsible for approximately 23%of UK emissions,is forecast to be more difficult to decarbonise(BEIS,2018).Heating demand in the UK,as well as a

55、ccounting for 60 80%of final demand in residential and commercial properties(Staffell et al.,2019),varies both daily and seasonally,with evening demand considerably higher than midday demand and winter demand many times higher than summer demand.This requires a flexible solution,which until now has

56、been met by fossil fuels with the UK mostly supplied by natural gas.In addition,domestic heat is largely decentralised,with heat generation in nearly all cases in the UK occurring at the point-of-use.The UK is more dependent on gas central heating than many other European nations(Fig.1)-since the mi

57、d-1970s,most UK households have generated heat via individual natural gas boilers feeding a hot-water delivery system.This technology has the advantages of being widely understood,quick to deliver heat,efficient(with a modern condensing boiler),flexible,and has historically benefitted from low gas p

58、rices until recent energy price spikes(Fernndez Alvarez and Molnar,2021).However,natural gas is difficult to decarbonise,and the UKs net zero commitments will necessitate a shift from gas boilers to low-carbon heating systems.Other methods of domestic heating used in the UK include heat pumps,electr

59、ic resistance heaters and storage heaters,limited deployment of local heat networks and off-gas-grid oil heating.Currently,less than half a million UK homes utilise low-carbon heating,not counting wood-fired stoves or open fires(Green Alliance,2020).There are several technologies which could play an

60、 important role in the decarbonisation of domestic heat,including heat networks,biogas,heat pumps and hydrogen.This Briefing Paper investigates the challenge of decarbonising domestic heat in the UK,focusing on two leading technology candidates that have recently been the focus of considerable debat

61、e heat pumps and hydrogen heating.In so doing,we recognise that energy demand reduction and the deployment of heat networks are also likely to play a significant role in the transition to low-carbon heat(CCC,2020).However,these options are not considered as part of the scope of this report,except wh

62、ere relevant to heat pump or hydrogen heating deployment.Heat pumps are electrically driven and work by transferring heat from the outside of a property to the inside via a transfer medium.This arrangement is considerably more efficient than the direct conversion of electrical energy to heat in an e

63、lectric radiator or heater,as each unit of electricity consumed can bring typically between 35 units of heat into the property.They can be powered by low-carbon electricity,greatly reducing the carbon intensity from natural gas heating.Heat pumps are commercially available in the UK,though uptake is

64、 still very limited,with around 265,000 units installed as of 2020(EHPA,2021c).Hydrogen heating in the UK could largely utilise the existing gas grid to deliver hydrogen to domestic properties on the gas grid.The grid would need to be upgraded in order to deliver hydrogen,including the replacement o

65、f steel distribution pipes with plastic.There would also be additional challenges and disruption,since each property would need to be surveyed prior In order to mitigate the dangerous effects of climate change and keep global temperature rises below 1.5 C,it is vitally important to embark on far-rea

66、ching,ambitious efforts to decarbonise the UKs economy and infrastructure.1.Introduction 1.Introduction1.Introductionto conversion,existing pipework upgraded if necessary and new appliances installed (or existing appliances converted for use with hydrogen)(Frazer-Nash,2018).Once installed,hydrogen b

67、oilers would heat hot water and transfer it to radiators in much the same way as gas boilers.This is argued to require little change in consumer behaviour and may be perceived by householders as a more equivalent technology to gas boilers compared to a heat pump(Williams et al.,2018).Hydrogen can be

68、 generated by electrolysis,which when paired with low-carbon generation is known as green hydrogen,or by conversion of fossil fuels,which currently has substantial associated carbon emissions.Figure 1:Diversity of fuel shares for residential and non-residential heating in selected countries.Gross&Ha

69、nna(2019)based on data obtained with permissions of Vivid Economics and the Department for Business,Energy and Industrial Strategy Natural gas Coal Oil products Biofuels and waste District heating Electricity OtherNetherlandsItalyBelgiumUSGermanyFranceSpainPolandPortugalLatviaGreeceSwedenUKHungaryCa

70、nadaCzech RepublicCroatiaIrelandAustriaNew ZealandDenmarkLithuaniaEstoniaNorwayFinlandFuel share for residential and non-residential heating demand(%)0201040608070503090100The future of home heating The roles of heat pumps and hydrogen 101.1 Aim and approachThe aim of this Briefing Paper is to discu

71、ss heat pumps and hydrogen heating and their prospects for development and uptake in the UK over the next decade,based on a thorough review of existing literature.It will consider the supply-and demand-side characteristics of the two technologies,advantages and challenges facing them and the feasibi

72、lity of uptake over the next decade.Each option is also considered in terms of what will need to be prioritised over the next ten years in order to help meet the UKs 2050 net zero target.The evidence has been gathered using a narrative review1 of academic and grey literature drawn from the Science D

73、irect and Google Scholar databases.The study also updates relevant information based on previous systematic reviews carried out by the authors on international heat decarbonisation policies(Hanna et al.,2016;Sahni et al.,2017).We also draw upon recent work carried out by the authors focused on heat

74、system change and smart heat in the UK(Gross and Hanna,2019;Carmichael et al.,2020).Finally,we have engaged with selected experts either through inviting comments on the draft Briefing Paper or through holding discussion meetings.The Briefing Paper is divided into five sections.Section 2 provides a

75、primer of the two technologies,discusses their current market conditions,and covers some environmental implications they may have.Section 3 focuses on the demand-side,showcasing the mid-and down-stream aspects of the technologies and how they would work in a domestic household.Section 4 explains the

76、 barriers to implementation,exploring the challenges that each technology faces in adoption over the next decade.Section 5 proposes policy recommendations and support to overcome these barriers.1.Introduction1 Narrative reviews provide a general overview of literature related to a particular researc

77、h topic,and the search method,inclusion of studies and interpretation of the studies reviewed relies upon the judgement and expertise of the authors.Systematic reviews typically set out a clearly defined research question or hypothesis and the search method and inclusion of studies are based on pred

78、efined protocols/search criteria(Baethge et al.,2019;Pae,2015).2.Technologies and supply2.1 Heat Pumps2.1.1 Types of heat pumpsIn a domestic setting,a heat pump(HP)can be installed as a low-carbon means to provide space and water heating.Some HPs also offer cooling in the form of reversible air-to-a

79、ir pumps.They are powered by electricity and allow for the efficient transfer of heat from an external source(air,ground,or water)into a building.Table 1 gives an overview of the most common types of HPs,classified by their heat source and how it is distributed e.g.,an air-to-water heat pump uses am

80、bient air as a heat source and transfers heat into a building via the central heating system either in radiators or underfloor heating.A HP that uses water as a heat transfer medium (as in a central heating system)is also referred to as a hydronic HP.Heat pump systems can consist of a single exterio

81、r unit(monobloc)or be a split system.Split systems feature two units(one indoor,one outdoor)that can be situated up to 30 meters apart,connected via internal pipework that commonly uses hydrofluorocarbons and therefore require the installer to have a specific F-gas qualification.However,the exterior

82、 unit in a monobloc system houses the entire refrigeration cycle,and as such no F-gas qualification is required for its installation.In the UK,air-to-water monoblocs made up 69%of the heat pump market in 2019(BEIS,2020a,p.13).The way in which heat pumps or hydrogen-based appliances can or could deli

83、ver space and water heating to households varies greatly.This section will introduce the two technologies at hand,discussing their uses,current market conditions in the UK,and environmental implications,forming the basis of the ongoing discussion around decarbonisation of domestic heating.2.Technolo

84、gies and supplyHeat sourceOutputNameAcronymAirHot air via fanAir-to-airASHPRadiators/Underfloor heatingAir-to-waterGroundHot air via fanGround-to-airGSHPRadiators/Underfloor heatingGround-to-waterWater*Hot air via fanWater-to-airWSHPRadiators/Underfloor heatingWater-to-water*Water source HPs are fur

85、ther divided into open-and closed-loop options.Closed loop systems use refrigerant,similar to a ground source heat pump.Open loop,however,abstracts water from a river,or aquifer and circulates this around the system in place of refrigerant,discarding used water upstream once a cycle is complete.Tabl

86、e 1 Types of heat pumps The future of home heating The roles of heat pumps and hydrogen 122.Technologies and supplyAnother option that combines a fossil-fuelled boiler and HP is a Hybrid Heat Pump(HHP).This combination is a lower carbon option than a single conventional boiler and can optimise opera

87、tional costs and energy efficiency,with carbon emissions that can fluctuate dependent on the heat source.2.1.2 How heat pumps workHeat pumps work through a series of heat transfers,with the aim of providing warmth to an indoor space and hot water.The process used is similar to a refrigeration unit i

88、n reverse.Figure 2 gives a simplified version of how a hydronic (e.g.air-to-water)HP works(BEIS,2020a).The contained refrigerant has a lower temperature than the external environment,so heat transfers from the surrounding environment(air,ground,or water)to the refrigerant in the pipe.The refrigerant

89、 is compressed into a superheated,high temperature and high-pressure vapour by the compressor using energy from the electricity grid.This increases the refrigerant to a useful temperature.In a hydronic heat pump,a plate heat exchanger is used to transfer heat from the refrigerant into the central he

90、ating system.Water returning from the heating system inside the building enters the plate heat exchanger.Here heat from the superheated refrigerant is absorbed by the water,which then leaves the heat exchanger at a higher temperature.Water leaves the heat exchanger and enters the building to be used

91、 for heating and hot water.Having transferred much of its heat,the refrigerant is cooler and in liquid phase.It then enters an expansion valve,which will further decrease its temperature.The refrigerant is now at a low pressure and temperature and exists as a liquid/vapour mix to repeat the cycle.Fi

92、gure 2:Simplified diagram of how a hydronic heat pump functions11234567CompressorExpansionValve265473Plate Heat ExchangerHeat PumpCentral Heating System2.Technologies and supplyIn Figure 2,an air output HP such as air-to-air HP would connect to a fan at point 3,expelling warm vapour and subsequently

93、 cooling down the refrigerant before passing through an expansion valve.2.1.3 Efficiency of a heat pump&cost of installationThe efficiency of a heat pump is measured by its Coefficient of Performance(CoP).The CoP indicates the amount of heat produced per unit of electricity consumed.The higher the C

94、oP,the more efficient the heat pump.As an example,a CoP of 4 suggests that for every 1 kWh of electricity used to power a heat pump,4 kWh of heat is output.The average CoP of a heat pump is called the Seasonal Performance Factor(SPF)and reflects the technologys efficiency over the course of the year

95、 and may also include other elements of the heating system such as circulation pumps.This measure is commonly used as a HPs efficiency varies across different seasons,as external temperatures impact how much heat is transferred from the surrounding environment to the refrigerant.For example,a warmer

96、 external temperature would mean the compressor does not need to work as hard to reach a desired temperature,increasing its efficiency(Kensa Heat Pumps,2014).Table 2 details the Theoretical CoP,SPF,Observed SPF and respective installation costs for some of the most common heat pumps in the UK.As the

97、 most common brands in the UK,theoretical CoP is the reported efficiency by Mitsubishi and Kensa for a range of their air and ground source heat pumps,respectively.The average climate SPFs reported in brackets in the second column are provided by the European Heat Pump Association and are comparable

98、 to the observed SPFs.The observed measurements are taken from a sample of 700 heat pumps installed under the Renewable Heat Premium Payment Scheme in the UK,and were calculated with data collected between 31st October 2013 to 31st March 2015.The distinction between these two values is made as there

99、 are a number of variables that influence just how efficient a HP is.For instance,the position and orientation of an air-to-air HP in relation to a building as well as the quality of installation impact its efficiency,resulting in the lower observed CoPs(Hong-Wen et al.,2020).Heat sourceTheoretical

100、CoP1,2(SPF)3Observed SPF4Cost of Installation5Air-to-water2.5 2.8(2.6)2.458,750 21,550Air-to-air2.5 2.8(2.6)2.452,400 8,800Ground-to-water3.5 4.5(3.2)2.8213,200 27,350Table 2 Heat pump efficiency and expected cost of installation Notes to Table 2 1.Source:Mitsubishi Electric(2020)2.Source:Kensa Heat

101、 Pumps(2021)3.Source:EHPA(2021c)4.Source:Lowe et al.(2017)5.Source:Myers et al.(2018)The future of home heating The roles of heat pumps and hydrogen 14 2.Technologies and supply2.1.4 UK heat pump market and international comparisonAs of 2020 there were 265,000 heat pump installations in the UK(EHPA,

102、2021c),with 87%of these estimated to be air source heat pumps,9%ground and water source HPs combined,and 4%HHPs(BEIS,2020a,p.10 11;de Best,2021).When considered alongside the 26 million fossil-fuelled boilers present in the UK,this means the HP market is marginal,making up less than 1%of installed h

103、eat capacity(BSRIA,2017).The majority of these heat pumps are hydronic and so rely on radiators and/or underfloor heating to provide warmth(EHPA,2021b).Their popularity within the UK is partly driven by convenience and climate as most heating in the UK is already provided through radiators in line w

104、ith hydronic systems and there is little demand for air-conditioning within homes(BEIS,2020a,p.11).Across Europe,the Nordic countries,Estonia,Switzerland and France have the most developed markets,normalised by heat pumps installed per 1000 households in 2018(Figure 3).While these leading countries

105、range from 8%to more than 50%of heat pumps installed in homes,the UK has the second lowest installation stock of the countries shown at less than 1%of households.One factor that has benefitted the speed of heat pump deployment in France and northern Europe is the acceptance of electricity as an ener

106、gy source for domestic heating(Nowak,2018).In these countries,a large part of their energy supply is provided by direct electric heaters,so the switch to heat pumps saves on final energy,emissions,and cost.Although Italy has a large gas grid,heat pump deployment increased after the introduction of a

107、 special tariff in 2014.Despite the tariff no longer accepting new applications,summertime weather conditions means reversible air-to-air heat pumps remain popular(Pieve and Trinchieri,2019).Figure 3:Number of installed heat pumps per 1000 households in different European countries(2018)Notes to Fig

108、ure 3 1.The chart data is sourced from EHPA(2021c).2.The column values are rounded to 0 decimal places.NorwayFinlandDenmarkFranceItalySpainCzech RepublicBelgiumIrelandSlovakiaHungarySwedenEstoniaSwitzwerlandAustriaPortugalGermanyLithuaniaNetherlandsPolandUnited KingdomNumber of installed heat pumps

109、per 1000 households in different European countries(2018)0200100400600500300517389332284139988078744038262222171714118712.Technologies and supply2.1.5 Carbon intensityCompared to a natural gas boiler,the carbon emissions per unit of useful energy delivered are much lower.A lifecycle assessment condu

110、cted by Sevindik et al.(2021)took into consideration the manufacturing,transportation,assembly,installation,maintenance,use,and disposal of an ASHP,GSHP,and natural gas boiler to compare the difference in carbon intensities of the two technologies.They found that per kWh of thermal energy generated

111、for domestic heating,0.11 kgCO2e and 0.1 kgCO2e are produced by an air and ground source heat pump,respectively.On the other hand,the carbon intensity of a natural gas boiler was found to be 0.24 kgCO2e per kWh of thermal energy.These figures are based on the electricity mix of the UK in 2018,with a

112、ssumed CoPs of 2.8(ASHP)and 3.4(GSHP).Overall,lifetime emissions(assumed to be over 20 years for both technologies)were 96.2 tCO2e for a natural gas boiler compared to 42.3 tCO2e and 38.8 tCO2e for an ASHP and GSHP,respectively.2.2 Hydrogen 2.2.1 The case for low-carbon hydrogen When combusted,hydro

113、gen does not emit any CO2(although it can result in emissions of NOx air pollutants see section 4.3.4)and,as a versatile energy carrier that can be used in a range of sectors,several countries have outlined hydrogen strategies to address the growing need to decarbonise(COAG Energy Council,2019;USDOE

114、,2020a;BEIS 2021l).With regards to domestic heating,its application could be similar to that of natural gas,with homes converting to hydrogen boilers and appliances,suiting the UKs extensive gas grid and consumption habits.However,despite being the most abundant element in the universe,there are ext

115、remely limited natural sources of pure hydrogen.As a result,it is not easily extracted for commercial use and instead requires energy intensive production processes(see Box 1),the most common method being steam methane reformation(SMR)using natural gas.At an international level,approximately 97%of h

116、ydrogen production relies on fossil fuels,resulting in 830 million tonnes of CO2 being emitted per year,the equivalent of the UK and Indonesias annual CO2 emissions combined(IEA,2019,p.17;Jaganmohan,2021).Alternative production methods that are both widely deployable and suitable for a net zero tran

117、sition are therefore required.These could include the electrolysis of water using low-carbon electricity or SMR combined with carbon capture and storage(CCS).2.2.2 Production methods2.2.2.1 Blue HydrogenBlue hydrogen is the production of hydrogen from fossil fuels but with the resultant CO2 prevente

118、d from reaching the atmosphere through use of CCS technology.It has the advantage of relying on existing technologies that are widely deployed and already used to produce hydrogen for industry e.g.,gasification and SMR.However,CCS has not been deployed at the scales envisaged and the amount of CO2 c

119、aptured throughout the process is dependent on the type and source of the fossil fuel used.Currently,hydrogen facilities coupled with CCS capture only 50 60%of plantwide CO2 emissions,but demonstration plants have recorded capture rates above 90%(USDEO,2020b;Bauer et al.,2021),however no such facili

120、ties currently exist in the UK.2.2.2.2 Green HydrogenDespite electrolysis predating lab scale SMR(grey hydrogen),the reduced cost of hydrocarbons led SMR to develop into the dominant hydrogen supply method with hydrogen production from electrolysis currently limited to demonstration projects(Gielen,

121、Taibi The future of home heating The roles of heat pumps and hydrogen 16and Miranda,2019;OMalley and Sunny,2021).Within the UK data suggests that it currently makes up less than 1%of hydrogen capacity(Fuel Cells and Hydrogen Observatory,2021).Theoretically,green hydrogen could be a strong candidate

122、for net zero,given its low emissions profile,however,it faces several barriers to its large scale adoption in domestic heating from the scale of required renewables deployment to cost competitiveness(see Section 4).2.2.2.3 Turquoise HydrogenMethane pyrolysis has been suggested as a timely alternativ

123、e to grey hydrogen produced through SMR.As it is more environmentally friendly than grey hydrogen and less energy intensive than green hydrogen,it could become a valuable source of low-carbon hydrogen(Snchez-Bastardo et al.,2020,p.1589).The process is,however,still in the experimental phase and unli

124、kely to be commercialised in the next decade.2.2.3 Hydrogen production in the UK and industrial clustersWithin the UK,it is estimated that the current hydrogen production capacity is between 3 5 GW(Sunny et al.,2020),the majority of which is produced via SMR and used within industries such as oil re

125、fineries.The UKs strategy for decarbonisation within industry plans to utilise low-carbon hydrogen in industrial clusters(HM Government,2021).These are places where there has been coordinated effort across industries to co-locate,allowing them to benefit from shared decarbonisation infrastructure an

126、d reduced costs related to carbon abatement.Certain attributes suit the placement of hydrogen production in industrial clusters,for example,high demands for hydrogen in surrounding locations as well as access to underground storage(Sunny et al.,2020).In the case of blue hydrogen,geological storage f

127、or CO2 also provides convenience(ibid.),whilst green hydrogen production may suit locations close to renewables hubs.In its industrial decarbonisation strategy,the government sets out plans to create four low-carbon industrial clusters by 2030,and at least one net zero cluster by 2040(HM Government,

128、2021,p.86).In order for these industrial clusters(and blue hydrogen production within them)to be low-carbon,the governments strategy requires that CCUS would be operational in two industrial clusters by the mid-2020s,demonstrated at scale through the 2020s and that approximately 3 MtCO2 of industry

129、emissions would be captured per year by 2030(Ibid.).Currently,around 40 MtCO2 is captured by operational CCUS facilities globally(see section 4.3.6.2),however there are not yet any operational facilities in the UK.Recently,BP announced plans to construct the UKs largest blue hydrogen production faci

130、lity in Teeside(BP,2021).The project aims to produce 1 GW of blue hydrogen by 2030;one-fifth of the UKs Ten Point plan ambition.The location is complementary to the existing hydrogen storage and distribution capabilities present in the area as well as being near North Sea storage sites and pipe corr

131、idors(ibid.).The industrial cluster approach the UK is taking towards hard to decarbonise sectors may be able to assist in the roll-out of hydrogen in domestic heating through the strategic placement of hydrogen fuelled homes.One such example of this is the H21 North of England project,currently in

132、planning,which could use blue hydrogen produced by Equinor transmitted via a gas distribution network to industrial,commercial and domestic appliances(Sadler et al.,2018,p.6).2.Technologies and supply BOX 1:Colours of Hydrogen Hydrogen is often referred to by colours,which indicate its production me

133、thod see Figure 4.Green Hydrogen Electrolysis is a process that uses electricity to split water into hydrogen and oxygen.When renewable electricity is used the result is“green”hydrogen.Green hydrogen is often favoured as a future alternative to grey hydrogen,given the lower carbon emissions produced

134、(see below).Grey Hydrogen Natural gas can be split into hydrogen,carbon monoxide,and carbon dioxide through a process called steam methane reformation.Most the worlds hydrogen is currently“grey”having been produced through this method.However,the carbon dioxide by-product in this process is released

135、 into the atmosphere,contributing to emissions.Black/Brown Hydrogen Syngas(hydrogen,carbon monoxide,carbon dioxide)is produced in a process called gasification using coal as a feedstock.Hydrogen can be isolated from the syngas mixture and dependent on the type of coal used,lignite or bituminous,is k

136、nown as brown or black hydrogen,respectively.Blue Hydrogen The process to make blue hydrogen is similar to grey(and black/brown)hydrogen,only the carbon dioxide produced alongside the hydrogen in SMR or gasification is captured and then stored.This mitigates against the carbon dioxide emissions from

137、 grey hydrogen,although there are still upstream emissions produced by methane leakage.Turquoise Hydrogen Although also reliant on natural gas as a feedstock,the process ascribed to turquoise hydrogen does not produce carbon dioxide gas,when powered with renewable electricity.Rather,methane pyrolysi

138、s produces carbon in a solid form,which can be used in other applications and avoids the need for CCS.Pink&Yellow Hydrogen These terms often refer to hydrogen production through electrolysis but specify the power source as nuclear(pink)or solar(yellow).2.Technologies and supplyFigure 4:Hydrogen prod

139、uction method by colour.Based on Edwardes-Evans et al.(2020)and National Grid(2022)Black/BrownBlueGreyTurquoiseGreenCO2CO2CO2Coal+Steam+OxygenNatural Gas+Steam Natural Gas+Renewable Electricity Water+Renewable Electricity Hydrogen+Carbon DioxideHydrogen+Carbon DioxideHydrogen+CarbonHydrogen+OxygenHy

140、drogenGasificationCarbon Capture&Storage+O2+Black/Brown HydrogenGrey HydrogenTurquoise HydrogenGreen HydrogenBlue Hydrogen+Steam Methane ReformationPyrolysisElectrolysis+H2O(Solid)The future of home heating The roles of heat pumps and hydrogen 182.2.4 Hydrogen trials in the UKHydrogen blends have al

141、ready been trialled at Keele University,where the private gas network was blended with 20%hydrogen.The trial“HyDeploy”was completed in March 2021,with plans to expand to a public network in North-East England(HyDeploy,2021).The UK Government has outlined its ambitions to support full hydrogen heatin

142、g trials in local neighbourhoods by 2023 through the use of hydrogen boilers in homes,and in larger villages by 2025,building up to a pilot hydrogen town by the end of the decade(HM Government,2020,p.10 11).H100 in Fife,Scotland will aim to supply 300 homes with hydrogen heating using a new network

143、alongside the existing gas infrastructure,over the course of four years(SGN,2021).2.2.5 Carbon intensity2.2.5.1 Grey hydrogenWith the production of grey hydrogen,direct CO2 emissions from SMR were found to be the largest source of emissions in a lifecycle assessment conducted by Antonini et al.(2020

144、),accountable for more than six times the emissions attributed to the natural gas supply chain.Overall,it is estimated that the amount of CO2 produced per kilogram of grey hydrogen ranges from 8.9 12.9 kgCO2e(Bhandari,Trudewind and Zapp,2014).2.2.5.2 Blue hydrogen With CCS,dependent on the capture r

145、ate and method used,expected carbon emissions fall to 3.4 kgCO2e per kg of H2(Mehmeti et al.,2018,p.9),however,the potential impact blue hydrogen may have is disputed.Although the majority of literature available on the subject reports blue hydrogen having a lower emissions intensity when compared t

146、o grey(Sunny,Mac Dowell and Shah,2020;Barrett and Gallo Cassarino,2021;Bauer et al.,2021)the figures can differ dependent on the assumptions applied e.g.methane emissions rate of the natural gas supply chain,the efficiency of the carbon removal,and global warming potential(GWP)metric (Bauer et al.,2

147、021).In their central assumption,Barrett and Cassarino(2021)determine that blue hydrogen would have a 71 81%emission reduction compared to burning natural gas over a 100-year time horizon and 61 79%reduction on a 20-year time horizon.The difference between these values is attributed to the relativel

148、y short atmospheric presence of methane so the GWP used over a longer time horizon is smaller.One example that found blue hydrogen to have a higher impact than burning natural gas is Howarth&Jacobson(2021).On a 20-year timescale,they report that the carbon emissions produced from blue hydrogen were

149、only 9 12%less than for grey and fugitive methane emissions were higher.Overall,the greenhouse gas footprint of blue hydrogen was estimated to be 20%greater than burning natural gas(ibid.).Given the uncertainty surrounding its impact,therefore,blue hydrogen needs to be carefully regulated to ensure

150、it is net zero compliant.The government has recently consulted over options for an emissions standard which defines low carbon hydrogen,including a method to calculate greenhouse gas emissions from hydrogen production,and a greenhouse gas emissions threshold to assess different low carbon hydrogen p

151、roduction pathways(BEIS,2021c).2.2.5.3 Green hydrogenElectrolytic hydrogen is only as clean as the electricity it uses.MacDowell et al.(2021),detail that for electrolytic hydrogen to be less carbon intensive than SMR combined with CCS,the carbon intensity of the grid should at least be within the ra

152、nge of 30 140 kgCO2/MWh,with the UKs 2020 average being at 181 kgCO2/MWh.When reliant on wind energy the carbon intensity of green hydrogen is reported as being between 0.97 2.21 kgCO2e per kg H2(Bhandari,Trudewind and Zapp,2014 p.159;Mehmeti et al.,2018,p.10).Whilst dramatically 2.Technologies and

153、supply2.Technologies and supplylower figures compared to grey hydrogen,it is still worth noting that these figures are not net zero aligned and would require further abatement still.2.3 SummaryThis section has explored the current conditions surrounding heat pump deployment and hydrogen roll-out in

154、the UK.Heat pumps offer low-carbon alternatives to natural gas boilers.Air and ground source heat pumps have been found to produce 0.11 kgCO2e and 0.1 kgCO2e per kWh of thermal energy respectively,in comparison to a carbon intensity of 0.24 kgCO2e per kWh of thermal energy for natural gas boilers.Th

155、ese intensities are based on the UK electricity mix in 2018 and assume CoPs of 2.8(ASHPs)and 3.4(GSHPs).Within the UK,air-to-water heat pumps occupy 69%of the heat pump market,however,less than 1%of the UKs domestic heat capacity is currently provided by heat pumps.Hydrogen capacity is estimated to

156、be around 3 5 GW in the UK,the majority of which is used in industrial processes.Most hydrogen production currently relies on the extraction and reformation of fossil fuels and as such low-carbon alternatives are required when assessing its compatibility with net zero.Blue hydrogen,combining fossil

157、fuelled hydrogen production with CCS,alongside green hydrogen,which is produced through renewably powered electrolysis,are two options that could offer an alternative solution.Green hydrogen from wind-powered electrolysis has been estimated to produce 0.97 2.21 kgCO2e per kg of H2,compared to 3.4 kg

158、CO2e per kg H2 for blue hydrogen and 8.9 12.9 kgCO2e per kg H2 for grey hydrogen.However,the carbon intensity of blue hydrogen is disputed and can vary considerably based on various factors such as the methane emissions rate from natural gas,the availability and efficiency of CCS,and the global warm

159、ing potential metric used.Both blue and green hydrogen require technological development and upscaling to provide the amount of hydrogen capacity required for domestic heating,with limited infrastructure in place to complement their roll-out.The future of home heating The roles of heat pumps and hyd

160、rogen 203.1 Heat Pumps3.1.1 Supply ChainIn the UK,approximately 85%of residential buildings(23 million)are connected to the gas grid(CCC,2016).The annual deployment of at least 600,000 HP systems by 2028 is thought to be necessary to keep the UK on track to reach net zero and by 2050 the CCC estimat

161、e that nearly 19 million HPs will need to be installed in their“Further Ambition”scenario(CCC,2019c,p.84).Imminent action is necessary to develop the market and reduce costs for low-carbon heating options(BEIS,2021f,p.11).Currently,the UK heat pump market is relatively small(see 2.1.4)with only a fe

162、w UK-based manufacturers,meaning that most stock is imported from abroad.As HPs are expected to play a large part in the decarbonisation of domestic heating,understanding the potential growth of the UKs manufacturing supply chain could help optimise their roll-out(BEIS,2020a,p.9).Whilst achieving 19

163、 million installed HPs by 2050 will prove challenging,the support of well-established industries that offer similar components and transferable skills could help with deployment.3.1.1.1 Meeting demandAccording to interviews conducted by BEIS with HP manufacturers,achieving 19 million installed HPs i

164、n the UK by 2050 is unlikely to cause a manufacturing issue,with high confidence in their ability to increase supply by 25 30%year-on-year,for the next 15 years.This would mean an annual installation rate of 1,149,000 HPs by 2030,in line with the CCC recommendations(BEIS,2020a,p.84).The confidence o

165、f manufacturers to achieve this level of roll-out is due to several reasons(BEIS,2020a).Firstly,HPs are a mature technology,having been produced on a large scale outside of the UK for many years.They already have well-established supply chains in place through which most HP components(except compres

166、sors)are sourced from outside of the UK,with low manufacturing demand not enough to support component manufacturing.However,existing UK based HP manufacturers have seen increases in local businesses sourcing components with increasing demand for HPs.These local supply chains could develop as require

167、d to meet the UKs growth in demand providing it is cost-effective to do so.Further to this,manufacturers of technologies that rely on similar materials and components(e.g.boilers,air conditioners,fridges)could switch to heat pump manufacturing if viable.As other countries markets have grown and This

168、 section will consider how a heat pump or hydrogen strategy could evolve to meet the growing demands for low-carbon domestic heating and what this may mean for end users.Despite the current heat pump market being relatively small in the UK,manufacturers are confident that this can develop at a succe

169、ssful rate,given that heat pumps are a mature technology and widely deployed in countries outside of the UK.Wider heat pump adoption by households would require thorough installation practices and sufficient consumer acceptance due to their fundamental differences to gas boilers.These points are ela

170、borated on in Sections 4 and 5.The consumer experience of hydrogen boilers may be relatively similar to that of gas boiler end users connected to the grid,however its delivery is more complex with the need to upscale production,supply chains,and storage,and repurposing the gas grid bringing its own

171、complexities.3.Distribution and demand 3.Distribution and demand3.Distribution and demanddeveloped,production capacity has not limited the supply chain,with accurate forecasting being an important factor in enabling the market to meet demand(BEIS,2020a,p.84).3.1.1.2 Establishing UK based manufacture

172、rs The boiler industry is well-established in the UK with 55%of demand being met through domestic based manufacturing(BSRIA,2021).Whilst boilers may differ technologically to heat pumps,they are constructed of similar materials and the industry offers complementary skills to HP production.Air condit

173、ioning(AC)systems also use similar materials to HPs,with some European manufacturers utilising the same facilities for AC and HPs production.In the UK,three main companies occupy two-thirds of the air-to-water heat pump market(69%market share in 2019):Mitsubishi 31 35%;Daikin 16 20%;and Samsung 11 1

174、5%(BEIS,2020a p.12 13).Of those three companies,Mitsubishi is the only one to have their heat pumps manufactured within the UK,alongside Global Energy Systems and Big Magic Thermodynamic Box,whose shares in the UK market lie below 1%(ibid.).Recently,Vaillant,whose market share lies between 1 5%,anno

175、unced plans to expand their boiler manufacturing site in Derby to produce air-to-water heat pumps,starting in 2022(Vaillant,2021).The UK ground source heat pump market is even more concentrated,with two companies sharing two-thirds of sales:Kensa 41 45%;and NIBE 16 20%;producing their heat pumps in

176、the UK and Sweden,respectively(BEIS,2020a p.13).Across both technologies,68%are imported into the UK whilst 32%are produced in the UK(BEIS,2020a p.53).According to the European Heat Pump Association(EHPA)the 265,000 installed heat pumps in the UK has helped support 2,000 jobs in 2020 required for th

177、eir production,installation and maintenance(EHPA 2021a).Looking forward,the anticipated increase in UK based manufacturing could help support 10,000 new jobs(BEIS,2021f).There are only 1,100 certified heat pump installation companies in the UK(ibid.).It is estimated that an additional 12,400 heat pu

178、mp installers will be required by 2025 and 50,200 by 2030 to support the growing market(HPA,2020).To achieve this,there will need to be a level of encouragement aimed at gas engineers,electricians and those with relevant and transferable skills to retrain(BEIS,2021f,p.56).3.2 Hydrogen3.2.1 Transmiss

179、ion&DistributionThe UK has an extensive gas network composed of transmission,distribution,and service pipelines covering approximately 7,600 km,280,000 km,and 255,000 km,respectively(Dodds and Demoullin,2013).Transmission networks supply high-pressure natural gas from import terminals to regional di

180、stribution networks,which gradually lower the pressure at reduction stations,so it is suitable for delivery to end users via short service pipelines.The pipeline material differs dependent on its age and use;post-1970 polyethylene was used in distribution pipelines,whereas prior to this steel and ir

181、on were favoured for transmission and distribution,and copper for service pipelines.3.2.1.1 Suitability for hydrogen delivery Ensuring the gas grid is safe and suitable for hydrogen delivery is fundamental for a national conversion,however,given the differences between the two gases this would not b

182、e a straightforward transition.Factors influencing the ability of the current gas network to facilitate hydrogen delivery include the material,pressure,age,and condition of the pipework(Haeseldonckx and Dhaeseleer,2007).As the pressure increases,embrittlement is more likely to occur in hydrogen pipe

183、lines constructed of high-strength steel,which is problematic for the integrity of high-pressure transmission and distribution segments,and may require their replacement(Dodds and Demoullin,2013).The future of home heating The roles of heat pumps and hydrogen 22Polyethylene,used in distribution and

184、service pipelines since the 1970s,should be suitable for the distribution of hydrogen.This material has been used in the Iron Mains Replacement Programme(IMRP),which began in 2002 and aims to replace most iron pipelines within 30 metres of homes within 30 years.The service was started due to societa

185、l concern of the safety of cast iron pipelines,and once complete will leave limited iron pipework on the distribution system.As polyethylene is more porous to hydrogen,however,leakage may increase in transitioning away from natural gas.Studies have however shown this figure to be incremental(0.001%o

186、f average annual volume)and not enough to present a safety hazard(Haeseldonckx and Dhaeseleer,2007;Dodds and Demoullin,2013).3.2.1.2 Cost of conversion The cost of converting the grid will depend on the existing infrastructure,how much of it requires replacing or upgrading,and the cost of replacing

187、each component.Although the IMRP,with an expected completion date of 2032,will continue regardless of a hydrogen conversion,research commissioned by BEIS estimates that following the completion date 5%of iron and 100%of steel pipework will still need to be replaced across the gas grid(Element Energy

188、,2018,p.77 82).Further to this,certain components such as gas meters and detectors may require replacement to ensure compatibility,which come with associated labour costs.In their base case evaluation of cost,Element Energy estimate a capital expenditure of 22.2 bn to make the grid suitable for hydr

189、ogen distribution(ibid.),with the largest expected costs arising from the replacement of domestic gas meters and their labour and installation costs(7 bn combined).With an estimated 23 million consumers connected to the gas grid(CCC,2016),the conversion of the gas grid would amount to approximately

190、960 per household.There are,however,many uncertainties around this estimate,which revolve around the lack of understanding as to whether all gas meters would require replacement and just how much of the existing infrastructure is suitable for hydrogen after the IMRP.3.Distribution and demandPipeline

191、 TypeComponentPressure (bar)Length (km)CompositionPre-1970sPost-1970sTransmissionTransmission70 947,600High-strength SteelDistributionHigh Pressure7 3012,000High-strength SteelIntermediate Pressure2 75,000SteelHD polyethyleneMedium Pressure0.075 230,000IronMD polyethyleneLow Pressure 0.075233,000Iro

192、nMD polyethyleneServiceBuilding Connections 0.075255,000CopperMD polyethyleneTable 3 UK Gas Network Overview.Based on Dodds and Demoullin(2013)3.2.2 End-useOn the consumer side of the hydrogen conversion,appliances,and the way they are used,will require some adjustment.Hydrogen levels in the HyDeplo

193、y trial(see 2.2.4)were limited to 20%when blended with natural gas for three main reasons:This level was deemed unlikely to increase the risks associated with the use of natural gas for consumers or members of the public by the Health and Safety Laboratory in the UK(Hodges et al.,2015);Consumers are

194、 not affected from a supply or demand standpoint with this blend composition(HyDeploy,2017);All gas appliances manufactured after 1996 are operational at a 23%hydrogen mix(HyDeploy,2017).In order to increase this 20%blend to 100%hydrogen for a given area,a property-by-property conversion would be re

195、quired.Frazer-Nash(2018)note that,“a switchover will require multiple visits to collect information and undoubtedly result in some physical disruption to the property”(Ibid.,p.24).Householders might need to be offered incentives by way of compensation for this disruption(Frazer-Nash,2018).This proce

196、ss would comprise of initial house surveys,note any necessary pre-conversion preparations,assess the condition of existing pipework and upgrade it if required,and take an inventory of gas appliances.Hydrogen boilers and appliances(discussed in Section 4.3.3)will be required for the domestic use of h

197、ydrogen,which may appeal more to consumers given the similarities they would bear to gas appliances(Williams et al.,2018).3.2.2.1 Delivery of conversionIn the UK,the Gas Safe Register would be well placed to oversee the conversion.In 2018,it consisted of over 130,000 individual engineers from 74,000

198、 employers,of which 80%are qualified to work with natural gas within residences.The size and success of a hydrogen roll-out could be dependent on upskilling current operatives and establishing a conversion workforce.Frazer-Nash Consultancy estimate that with no growth in the existing Gas Safe engine

199、ers work force,conversion could take up to 16 years,but with a dedicated team of 100,000 the necessary residential conversions could,in theory,be complete within 4 years indicating the importance of a specialised task force(Frazer-Nash,2018,p.4).3.3 Summary The UK heat pump market is relatively smal

200、l,however,manufacturers are confident in their ability to increase heat pump deployment to suit the growing need for low-carbon domestic heating options.This is aided by complementary technologies that are established and utilise similar components e.g.,boilers and air-conditioners.From an end-use p

201、erspective,heat pumps are likely to be experienced as a new technology to many homeowners and will require adjustments to how they are used in comparison to familiar heating technologies such as boilers(discussed further in Section 4).The extensive gas grid in place could be repurposed for the wide-

202、scale deployment of hydrogen.The Iron Mains Replacement Programme(currently underway and due to finish in 2032)will mean that a large part of the distribution system will be suitable for hydrogen,however,once complete there will still be a need to replace steel pipelines if the transmission pipeline

203、 is repurposed.A transition to 100%hydrogen in a given area would involve some level of disruption to householders in preparing existing properties for the conversion.Post-installation,consumers are nevertheless likely to experience the use of a hydrogen boiler as a relatively familiar technology,gi

204、ven the similarities it would bear to gas boiler heating systems currently widespread in the UK.3.Distribution and demandThe future of home heating The roles of heat pumps and hydrogen 244.Barriers to Implementation4.1 General barriers to heat pump and hydrogen heating deployment4.1.1 Building energ

205、y efficiencyThe UK has one of the oldest and least thermally efficient building stocks in Europe(ACE,2015)and improving this building energy efficiency will help to reduce carbon emissions from heating no matter which mix of heat sources and technologies are deployed(Rosenow and Lowes,2020).Doing so

206、 will also help to insulate the UK against disruptive events such as the current energy price spikes(Hannon and Clarke,2021).While the energy efficiency of homes has improved in the UK over the last decade,still only 40%of dwellings are in Energy Performance Certificate(EPC)bands A to C(MHCLG,2021).

207、In order to achieve net zero by 2050,the Climate Change Committee estimates that building insulation will need to be improved in 15 million homes,and draught proofing installed in a further 8 million dwellings(CCC,2020).This will require wide-scale and consistent home refurbishments over the next fe

208、w decades.4.1.2 Industry skills and trainingThe current UK skills base in heating and energy efficiency industries needs to be scaled up significantly to support a transition to low-carbon heating.To improve the building fabric energy efficiency of the entire UK building stock,it has been estimated

209、that a trained workforce of 230,000 would be required by 2030,implying a need to train 12,000 workers every year until 2025,and 30,000 workers annually between 2025 and 2030(Green Jobs Taskforce,2021;Oswald et al.,2021).1.7 million new gas boilers are installed in the UK each year,maintained by appr

210、oximately 130,000 gas safe engineers(Green Jobs Taskforce,2021;BEIS,2021f).As noted in Section 3.1,there are currently only around 1,100 heat pump installation companies registered to the Microgeneration Certification Scheme(BEIS,2021f),while the governments Ten Point Plan sets an ambition to instal

211、l 600,000 heat pumps annually by 2028(HM Government,2020).The government aims to have four industrial clusters utilising hydrogen production operational by 2030,with an objective that at least one cluster would achieve net zero by 2040,requiring effective deployment of CCUS(ibid.).The demanding time

212、scales targeted to establish these clusters suggests that recruitment and training of the Whilst the discussion has so far orientated around how a heat pump or hydrogen-based strategy could theoretically be made possible,the present section will analyse some of the main barriers regarding their impl

213、ementation.Heat pumps main concerns revolve around high upfront costs to homeowners,consumer preferences,and the challenge full scale electrification may bring to the power grid.Hydrogen,however,faces issues in scaling up production of a relatively nascent technology;in creating demand,becoming cost

214、-competitive,and uncertainties regarding safety.In this section,we first consider several general barriers to uptake which apply to both technologies,including poor building energy efficiency and low consumer awareness of low-carbon and alternative heating options.We then discuss specific barriers i

215、n relation to heat pumps and hydrogen in turn.The section ends with a review of literature that compares the two from a cost perspective on both a system-wide and household level.4.Barriers to Implementation 4.Barriers to Implementationrequisite labour will be challenging,although there may be some

216、scope to utilise transferable skills in the current oil and gas sector workforce(Green Jobs Taskforce,2021).4.1.3 Public awarenessA challenge for consumer engagement in the UK is that there is a relatively low public awareness of low-carbon or alternative heating technologies(BEIS,2021f)including he

217、at pumps and hydrogen boilers.For example,a survey of 2,000 consumers carried out by the Energy Systems Catapult(2020)revealed that only around half of respondents were aware of low-carbon heating.Many thought that converting to low-carbon heat technologies would be difficult or expensive,and only a

218、round half realised that gas boilers contribute to climate change(Energy Systems Catapult,2020).In a separate survey with around 1,000 respondents living in households connected to the gas grid,42 per cent of respondents had never heard of ASHPs or GSHPs,while approximately half had not heard of hyd

219、rogen boilers(Williams et al.,2018).4.2 Heat Pumps4.2.1 Financial Barriers to UptakeAt present,heat pumps are a small market segment in the UK,comprising around 1%of installed heating systems.Compared to the mature boiler market,they are substantially more expensive to install.Running costs are high

220、er than they need to be due to greater policy costs on electricity than gas prices(see Section 5.1.2).Analysis for BEIS conducted by Myers et al.(2018,p.911)and presented in Table 2(section 2.1.3)estimate that air-to-water heat pumps start at around 9k to install,based on the size of the property an

221、d the amount of retrofitting required.Ground-to-water heat pumps are estimated to start from 13k,once again based on property size and required retrofitting.Air-to-air heat pumps are the cheapest installation option,ranging from 2.4k for a one-bedroom flat to 8.8k for a four-bedroom house.In compari

222、son,costs for replacing gas boilers range from 2.2 6.2k depending on the size of boiler and ancillary work required on the controls and heating distribution system(Myers et al.,2018,p.7).The installation costs of hybrid heat pumps,where the heat pump acts in concert with a gas boiler,may reflect the

223、 costs of each separate technology as most installers will consider these as two separate installations.Similarly,servicing and maintenance costs may effectively be doubled.In a survey of public attitudes in which around 4,000 people in the UK participated(BEIS,2021a),55%of respondents stated that t

224、hey would only replace their current heating system when it breaks down or starts to deteriorate.An additional one in five(19%)would however consider replacing their heating system while still operational.Similarly,in a primary research study of around 2,900 household owner-occupiers in Great Britai

225、n,Ipsos MORI&EST(2013)found that most replacements were prompted either by heating system breakdown(30%),anticipated breakdown as homeowners heating systems near the end of their life(14%),a need for frequent repairs(14%),or the system no longer operating effectively(9%).There is a risk therefore th

226、at many consumers will go for a quick and familiar replacement as the performance of their current heating system starts to decline towards the end of its lifespan,or following a break down.Research undertaken in 2015 by Clarke(2018)suggested that consumers at that time had a tipping point of approx

227、imately 3k for low-carbon heating installation,above which they would not pay.The cost for even a simple air-to-water heat pump installation is substantially over this price,meaning that a cost reduction or subsidy will be required to upscale this technology.The future of home heating The roles of h

228、eat pumps and hydrogen 264.Barriers to Implementation4.2.2 Consumer Preferences,Installation&MaintenanceHeat pump installation requires several steps to provide efficient heating within a home.An on-site survey is carried out to assess the energy efficiency of the home as well as the location and si

229、ze requirement of the outdoor unit,heat distribution method(e.g.,underfloor heating,radiators),installation level,and more.Several alterations may be necessary in the event of a heat pump being installed,such as the addition of a hot water tank,buffer tank,insulation upgrades,and radiator and pipewo

230、rk replacements.If a ground source heat pump is being installed this will also require groundwork to place subterranean pipes.If homeowners want to take advantage of government support mechanisms to fund their installation,such as the Renewable Heat Incentive(RHI),then the installation of the HP mus

231、t be carried out by a MCS approved installer.However,there is currently no certification required by law for the installation of a heat pump if it is privately funded.Once installed,day to day use differs between heat pumps and boilers;whereas boilers can be turned on and off and react quickly to a

232、desired change in temperature,heat pumps are designed to run for longer periods of time at a continuous pace.This is due to the difference in temperature reached by the two systems.In the case of space heating,heat pumps deliver heat between 35 60C,which is comparably lower than a conventional fossi

233、l fuelled boiler,capable of reaching temperatures over 80C(BEIS,2021d,p.6).The contrast in temperature is the reason why heat pumps suit the instalment of larger radiators and work better with underfloor heating;both options having larger surface areas to emit heat.Retrofitting an existing property

234、to effectively utilise a heat pump instead of gas central heating,therefore may entail a certain level of disruption.Replacement of radiators and upgrading of insulation measures will therefore be needed in addition to the heat pump installation itself in many homes.However,improved insulation measu

235、res will be required in any case for many properties to meet UK net zero targets.Well-insulated homes will allow for more efficient retention of lower-temperature heat,increasing the efficiency of heat pumps substantially.Newbuild houses will require little or no modification for heat pump installat

236、ion due to improved insulation building regulations.Siting and competent installation of heat pumps is critically important to maximise their efficiency.Poor siting of outdoor units can decrease efficiency substantially,leading to greater running costs and poor customer satisfaction.Installations ma

237、y also require substantial modification to the heat distribution system in some homes and installation of a hot water tank if one does not already exist.There are fewer qualified installers for heat pumps than for gas boilers,meaning labour costs may be higher and installers more difficult for custo

238、mers to find.The UK also has a current shortage of F-gas qualified installation engineers of around 50,000(BEIS,2020a,p.18),who are required to install split air-source heat pump units.If the UK is expected to see a large increase of heat pump installations,upskilling of engineers will need to be a

239、priority.Heat pumps require annual servicing to ensure they are running at peak efficiency(US DOE,2021).Dirty filters as well as larger blockages can drastically reduce performance.Hybrid heating systems that combine an electrically driven heat pump and a fossil fuelled boiler may have the potential

240、 to offer convenience whilst limiting emissions.Running the heat pump component on a continual basis with thermal storage offers greater emission reductions compared to a gas boiler with 55%of annual emissions being saved,and based on 2016 prices could reduce installation costs by 450 2,800 compared

241、 to a standalone heat pump for a typical semi-detached house in the UK(Element Energy,2017).4.2.3 The Power GridAlthough heat pumps can supply on average about 2.54 kW of heat per kW of electricity used,heat pumps draw considerable amounts of power from the electricity supply.The average household u

242、ses approximately 12,000 kWh of heat energy per year,which with a heat pump CoP of 3 would require 4,000 kWh of electrical energy for a heat pump to supply.This will place a significant extra load on the power grid both in total across the year and at times of peak demand.The majority of the UKs hea

243、t demand occurs between November and February,with daily peaks occurring in the morning and evening.Research funded by BEIS estimates a 20%penetration of heat pumps will create a 14%increase on peak winter evening GB electricity demand an increase of approximately 7.5 GW(Love et al.,2017).A morning

244、electricity demand peak will also begin to form.Heat pumps naturally spread their load more than gas boilers due to their method of operation,meaning that the peaks are less defined than the equivalent gas demand.However,this will still require reinforcement of local distribution networks.Methods of

245、 spreading the heat demand across the day,including thermal storage and smart controls,could help defer some physical reinforcement(ibid.)4.3 Hydrogen4.3.1 Hydrogen supply In the UK Hydrogen Strategy,the government expects the demand for hydrogen in domestic heating to be relatively low in 2030;belo

246、w 1,000 GWh(BEIS,2021l,p.62).With total annual domestic gas consumption in the UK in 2019/20 being 325,183 GWh this would have represented around 0.3%of demand in 2020(BEIS,2020b,p.19).This approximation increases dramatically over the course of the proceeding five years,with the demand range expect

247、ed to be between 0 45,000 GWh by 2035(BEIS,2021h,p.15).This would require over 5 GW of hydrogen deployment specifically for domestic heating,to meet the upper estimation of 45,000 GWh by 2035.Further,despite such a high aspiration,the Energy Networks Association(ENA)foresee the 5 GW outlined in the

248、UKs Ten Point Plan needing to be increased to 10 GW by 2030(ENA,2020,p.11).This is also a sentiment advanced by the UK Hydrogen&Fuel Cell Association who claim the 5 GW is“lacking in ambition”(UKHFA,2021,p.10).With the current UK capacity of hydrogen estimated to be between 3 5 GW,a current target o

249、f 5 GW of low-carbon hydrogen for industry in 2030(HM Government,2020;Sunny et al.,2020),and no operational blue hydrogen facilities,it is uncertain as to where this supply will come from.Regardless,the two most likely candidates,blue and green hydrogen,face their own sets of challenges before wide-

250、scale deployment(see subsections 4.3.6&4.3.7).4.3.2 StorageStorage facilities are required to support the gas grid system during intra-day and inter-seasonal periods of high demand.As hydrogen has a very low volumetric energy density,large volumes of space are required for storage.It is possible to

251、increase its storage density so that a smaller volume of space is required,but this would require energy input or hydrogen binding materials.There is currently limited research into the wide-scale storage of hydrogen beyond underground storage.The ways in which hydrogen is stored can be divided into

252、 three main categories:1)physical storage,2)adsorption,3)chemical storage(Andersson and Grnkvist,2019).Currently,physical storage of hydrogen in salt caverns is the only wide-scale method implemented,an example of which can be found in Teesside in the UK.This method requires minimal construction,has

253、 low leakage rates,is relatively quick to inject and withdraw hydrogen,and has reduced levels of contamination.Centralised storage sites like this would allow for large volumes of 4.Barriers to ImplementationThe future of home heating The roles of heat pumps and hydrogen 28hydrogen to be accumulated

254、 during periods of low demand(summer)for use during peak seasonal heat demand(winter).However,this option is restricted by geological conditions,with only specific regions in the UK being able to cater to this form of storage e.g.,Teesside,Cheshire Basin and East Yorkshire.Safety risks with the stor

255、age of hydrogen in salt caverns would also need to be managed:these include the potential release of toxic chemicals due to bacterial metabolism converting hydrogen to methane;and given hydrogens low ignition temperature and wide flammability range,leakages could lead to fire or an explosion in conf

256、ined spaces in particular(Portarapillo and Di Benedetto,2021).Aside from physical storage,adsorption and chemical storage are still being actively investigated as alternatives,given the geographical restraints presented by underground options.However,the uncertainties surrounding these replacements(

257、such as reactor designs and heat supply for dehydrogenation)make it challenging to consider these options accurately from an economic standpoint and draw comparisons(Andersson and Grnkvist,2019).4.3.3 Household costs 4.3.3.1 Internal pipework As well as the transmission and distribution system,domes

258、tic pipework may also require replacement to adjust to hydrogen conversion,which could increase the cost of conversion if large amounts of work are necessary.Work prepared for BEIS,indicates how the inaccessibility of domestic pipework could present a significant barrier in the conversion to hydroge

259、n(Frazer-Nash,2018,p.3 4).This is because natural gas pipes are often enclosed in concrete or otherwise isolated,which would make it challenging to inspect or replace them if necessary.Prior to deployment,gas tightness tests will be required to examine the integrity of internal pipework.This process

260、 requires home surveys taking approximately 1 2 hours per property and would require the gas supply to be cut for 10 20 minutes(Frazer-Nash,2018).The cost of these pre-conversion tasks is less certain as there are a variety of materials used for domestic pipework(copper,steel,polyethylene)and hydrog

261、en presents a different range of safety hazards,but estimates range from 100 to 500 per property(Sadler et al.,2016;Element Energy,2018).4.3.3.2 Hydrogen boilers For nationwide use,the roll-out of a hydrogen-based grid would be in combination with the use of hydrogen-ready boilers in domestic settin

262、gs.Manufacturers such as Baxi and Worcester-Bosch have developed prototypes of these boilers based on a conventional gas boiler.As hydrogen has a higher flame speed and is colourless when combusted,a hydrogen-ready boiler has alterations to its ignition system and flame detection.The cost of replaci

263、ng a natural gas-fired boiler with a hydrogen gas-fired boiler would be alike,as the process and components are similar.For the boiler unit itself,estimates currently average 850 1,000,increasing up to 2,500,the latter assuming only 10,000 boilers are commissioned(Sadler et al.,2016,p.146;Element En

264、ergy,2018,p.89).These estimates are comparable to the price of a natural gas combi or system boiler which are within the range of 850 1100(ibid.).4.3.3.3 Hydrogen appliancesAlthough appliances manufactured since 1996 can operate with a 23%hydrogen blend,to function entirely on hydrogen gas would req

265、uire adaptations or replacement.For example,a natural gas-fired hob would not be suitable for use with hydrogen given that its invisible flame would mean the consumer would not be able to use the appliance safely,discussed in 4.3.4.The deployment of dual fuel technologies that can function on both n

266、atural gas and hydrogen may aid the transition,limiting the time and effort required to carry out 4.Barriers to Implementationthe conversion.Including house visits,labour,and appliance changeovers the H21 project estimated approximately 840 per household(Sadler et al.,2016,p.145).Overall,with the in

267、clusion of labour and overheads the H21 project estimates an overall cost of 3,078 per property in making the pipework,boilers,appliances,and homes safe for hydrogen usage(Sadler et al.,2016,p.147).This cost is similar to that of the conversion from town gas to natural gas on the Isle of Man in 2010

268、 at 3,500 per property.It is,however,important to note that the forecast expected cost of 3,078 would only be made possible through mass manufacturing and deployment of hydrogen appliances.4.3.4 Safety concernsHydrogen and natural gas have different properties,which affect the way they can be handle

269、d safely.Hydrogen is non-toxic and produces no carbon monoxide when combusted meaning that there is no risk of carbon monoxide poisoning associated with its use.Furthermore,as it is lighter than air,when there is a leak it dissipates at a faster rate.However,it burns with an invisible flame,leaks at

270、 a rate approximately three times greater than natural gas,and has a lower ignition energy,which are factors that may complicate its uptake in domestic settings.Regarding flame detection,whilst the use of colourants has been suggested as a possible solution(Frazer-Nash,2018),investigations by the Hy

271、4Heat program concluded that adding colourant into the network or internal pipework should not be carried out.This is due to use of a colourant potentially impacting the integrity of the pipework and the safety of the end-use appliances,among additional operational complexities.Instead,thermochromic

272、 materials are suggested as a means of indicating an appliance is on(similar to electric hobs)and UV and temperature detection for use in boilers(Hy4Heat&BEIS,2021a,p.68 71).With regards to leakages and ignition,a risk assessment carried out under the Hy4Heat programme determined that with the use o

273、f two Excess Flow Valves(EFVs)the assumed risk of a hydrogen conversion in a domestic setting was no greater than the current natural gas setup in place.An EFV would limit the flow rate to the service pipe of the building,with one of the recommended valves being placed upstream of the meter installa

274、tion,and the other located within the smart meter installation(Hy4Heat&BEIS,2021b).When hydrogen is combusted in pure oxygen the only product is water vapour(H2O),however,except for some specialist applications,hydrogen combustion will take place in the presence of air.As hydrogen burns with a very

275、hot flame the resultant reaction can produce nitrogen oxide(NO)as a by-product,which reacts in the atmosphere to form nitrogen dioxide(NO2).NO2 is a globally regulated air pollutant that is harmful to health(Lewis,2021)and experiments conducted by Cellek&Pinarbai(2018)found that the number of point

276、NOx emissions produced by a hydrogen boiler compared to a natural gas boiler can be up to six times higher.Lewis(2021)comments on the challenge of balancing thermal efficiency and NOx emissions,with an emphasis placed on the importance of developing of new emissions standards for hydrogen appliances

277、 in relation to NOx pollutants to mitigate the effects of hydrogen combustion.Further recommended safety measures for a community trial require the compliance of regulations and standards currently in place for natural gas(hydrogen appliances must include flame failure devices and comply with PAS444

278、4,which are guidelines specific to hydrogen-fired gas appliances),adequate ventilation in properties,the inspection of internal pipework,the inclusion of odorants in the gas mix,and hydrogen detection alarms(Hy4Heat&BEIS,2021b,p.23 24).4.Barriers to ImplementationThe future of home heating The roles

279、 of heat pumps and hydrogen 304.3.5 Cost-competitiveness Fossil fuel-based hydrogen production is a mature technology with well-established supply chains,which means that current low-carbon alternatives are not cost competitive.Moreover,as a derivative of natural gas,blue hydrogen is naturally more

280、costly without incentives toward abatement.In their hydrogen strategy,the European Commission estimated various costs associated with hydrogen production methods as shown in Table 4(European Commission,2020,p.4).This price differential favours fossil fuel-based production and therefore gives little

281、incentive to procure low-carbon hydrogen,especially green,without an associated cost for CO2 emissions.As the development of large-scale,low-cost hydrogen production is an important precondition to its success(Maclean et al.,2016),looking at ways to reduce its levelised cost is necessary.4.3.6 Blue

282、Hydrogen 4.3.6.1 Net zero alignmentWhilst blue hydrogen is based on the familiar production of fossil fuel-based techniques such as steam methane reformation(SMR),carbon capture and storage(CCS)is a vital step in the process that could make blue hydrogen a low-carbon alternative.CCS aims to capture

283、CO2 from large sources of production,such as power generation,or directly from the atmosphere(DACCS).Once captured the CO2 requires transportation to a storage facility and injection into geological formations for its permanent sequestration.Although it is suggested that blue hydrogen may help incre

284、ase demand for low-carbon hydrogen,and in that way increase the market available to green hydrogen(Bauer et al.,2021;UKFCA,2021),blue hydrogen is not aligned with net zero ambitions.Natural gas leakages upstream and carbon capture inefficiencies mean that whilst in theory it could capture a vast maj

285、ority of emissions,its actual environmental impact is disputed(Howarth and Jacobson,2021).Standards and regulations that carefully monitor operational and supply chain emissions should therefore be put in place for strategies that rely on it as a solution.4.3.6.2 Carbon capture and storageIn 2021 th

286、ere were 27 operational,commercial CCS facilities globally and a further four facilities under construction,capturing a combined 40 MtCO2 per year(Global CCS Institute,2021).Natural gas processing facilities were responsible for the large majority of this captured CO2,whilst hydrogen production was

287、the source of 3.3 MtCO2 captured in 2020(IEA,2020a).An additional 102 CCS facilities were in various stages of development in 2021,with potential to capture a further combined 108 MtCO2 per year(Global CCS Institute,2021).Despite CCUS deployment tripling in the last decade,it has fallen short of cap

288、acity expectations in that it lags behind other clean energy technologies.For example,40 MtCO2 is just 13%of the IEAs roadmap for CCUS developed in 2009,which stated that 100 large-scale CCUS projects,capturing 300 MtCO2/yr by 2020 would be required to meet climate goals(IEA,2009,p.22).In the IEAs l

289、atest roadmap to achieve net zero emissions 4.Barriers to ImplementationHydrogen Production MethodCost per kg H22Fossil fuel-based1.29(1.50)Fossil fuel-based with CCS1.72(2.00)Renewable2.15 4.73(2.5 5.5)Table 4 Estimated cost of per kg of hydrogen by production method 2 Converted from Euros:GBP with

290、 1:0.86(IEA,2021),global CCUS capacity would need to be rapidly scaled up to 1.6 GtCO2/yr by 2030 and 7.6 GtCO2/yr by 2050.CCS faces numerous barriers in its own right that have hindered its deployment,such as insufficient value placed on emissions,interdependency of the value chain on other industr

291、ies,and lack of viable business models(Global CCS Institute,2020,p.25;Sunny,Mac Dowell and Shah,2020).Wang et al.(2021)found that 43%of CCUS projects announced in the last 30 years have been cancelled or postponed,and concluded that most CCUS projects are high-risk and low-return with respect to dir

292、ect economic outputs,and heavily dependent on public funding in the absence of high carbon prices.Without CCS,methane-derived hydrogen is not low-carbon and its current lack of deployment is concerning for strategies that may depend on its success.4.3.7 Green HydrogenWith high production costs and h

293、igh energy losses,green hydrogen has multiple barriers to overcome before it is seen as a viable alternative to grey hydrogen and can be widely deployed.The major expenditure in green hydrogen production is the cost of renewable electricity required to operate electrolysers,followed by the cost of t

294、he electrolyser facilities themselves(IRENA 2020b).In 2019,the average renewable energy plant would have produced green hydrogen at a cost that was two to three times more expensive than grey hydrogen(IRENA,2020a).This could result in high end-user costs and,as it needs to be cost competitive with b

295、oth fossil fuels and different shades of hydrogen,poses an issue for the success of green hydrogen.Conversely,a recent analysis by Longden et al.(2022)suggests that green hydrogen production could become cheaper than blue hydrogen in the near future,due to greater potential to reduce costs through s

296、caling up and deployment of renewables and electrolysers in comparison to fossil fuel production with CCS.The production of green hydrogen incurs a 30 35%loss in energy through the process of electrolysis,which means higher levels of renewable generators are required to produce hydrogen than if elec

297、tricity is used directly.It is estimated that the amount of offshore wind farm capacity required to replace gas boilers with green hydrogen in the UK is 30 times more than currently deployed(Phillips and Fischer,2021).This brings questions as to whether renewables will be able to develop at the pace

298、 required to support increasing electrification and green hydrogen development(IRENA,2020a).4.4 Scenario comparisonsThe following subsections will draw on relevant literature to compare how hydrogen and heat pump pathways are expected to fare in 2050 in relation to cost.Whilst a whole systems-based

299、model reveals similar costings for each strategy,at a household level there is a higher differential between the two.4.4.1 Systems-based approachThe Climate Change Committees(CCC)report on“Hydrogen in a low-carbon economy”estimates that the overall system costs associated with full electrification o

300、r full hydrogen pathway would not differ significantly in 2050(CCC,2018).This includes scenarios where the gas grid has limited or benign use,meaning that the sunken costs associated with having a decommissioned gas grid does not make a hydrogen pathway more affordable.The findings presented are bas

301、ed on analysis carried out by Strbac et al.(2018),who assessed three potential pathways;full hydrogen conversion,full electrification,and a hybrid scenario with the majority of heating demand covered by electricity and the use of biomethane or low-carbon hydrogen for peak periods.Different decarboni

302、sation scenarios and their associated costs were also predicted,namely,0 MtCO2/yr,10 MtCO2/yr,and 30 MtCO2/yr.4.Barriers to ImplementationThe future of home heating The roles of heat pumps and hydrogen 32Across the different decarbonisation scenarios,hybrid pathways were predicted to have the lowest

303、 system cost per year in 2050,followed by full electrification and then full hydrogen strategies.Whilst all three were similar in cost at 30 MtCO2/yr,ranging from 81.6 bn/yr 89.6 bn/yr,the cost differential between electrification and hydrogen pathways increased significantly in a net zero strategy,

304、with a full electric and hydrogen system costing 92.2 bn/yr and 121.7 bn/yr,respectively.The reason for this increase being attributed to the need for green hydrogen and high renewable investment as opposed to blue hydrogen,which is not compatible with net zero unless carbon capture rates were to ev

305、olve to 100%(Strbac et al.,2018).4.4.2 Household scaleAlthough extremely useful to analyse whole system costs of different strategies,how these costs may be allocated across the economy also needs consideration.The International Council on Clean Transportation(ICCT)carried out a household level cost

306、 analysis of seven different low-carbon domestic heating options3(Baldino et al.,2020).The assessment aimed to project the costs and carbon intensity related to each for a UK homeowner in 2050.4.4.2.1 AssumptionsWith regards to the hydrogen pathways the following assumptions were made.By 2050,the SM

307、R and CCS process will use renewable electricity,and it is further assumed that some of the hydrogen produced would be used in place of natural gas as a process fuel.Upstream leakage rates are between 0.5%2%for the production and transport of natural gas and CCS capture rates range between 70 90%.In

308、 scenarios with high hydrogen demand,the cost of replacing steel pipelines in the UK and charge for their use is incorporated into the model.There are short term storage fees,but seasonal storage cost is not accounted for.In the hybrid scenario using blue hydrogen,a median value of carbon intensity

309、was multiplied by the percentage of heat demand expected to be covered by hydrogen to determine the overall carbon intensity.This value was estimated to be 21%and is further reasoned by Baldino et al.(Baldino et al.,2020).To reflect a lower hydrogen demand in this scenario it is assumed that trucks

310、would instead be used for the transportation of liquified hydrogen.With regards to heat pump scenarios,the CoP of the heat pumps were assumed to be 3.19.Across all scenarios,renewable electricity from wind or solar is assumed to have zero-carbon intensity and similarly for the production of electrol

311、ytic hydrogen.Emissions regarding the manufacturing of the heating technologies were also not accounted for.4.4.2.2 ResultsTheir findings are presented in Figure 5 which demonstrates that the lowest cost option are household heat pumps,followed by hybrid heat pump variations.Carbon intensities are d

312、enoted with triangles and demonstrate the significance of relying on blue hydrogen boilers.The natural gas comparator is given as a reference for carbon intensity.Renewable electricity and natural gas prices were the main drivers behind the heating scenarios,and as there is a high level of uncertain

313、ty that comes with predicting energy prices in 2050,a sensitivity analysis was carried out.This determined that even if renewables were 50%more expensive,and natural gas 50%cheaper than predicted a heat pump would still be the most cost beneficial option.Further,for a boiler with green hydrogen to b

314、e cost competitive with blue,either renewables would have to be 50%lower in cost,or natural gas 50%more expensive(Baldino et al.,2020).4.Changes in Electricity Use at Household Scale 3 Heating technologies analysed were:fuel cells,hydrogen boilers,hybrid heat pumps,and heat pumps.Each hydrogen optio

315、n was also assessed with both green and blue options.4.Changes in Electricity Use at Household Scale Natural gas comparator(Carbon Intensity)Annual household cost(/year)Carbon intensity(gCO2e/MJ)001000Fuel cell with electrolysis hydrogenFuel cell with steam methane reforming+carbon capture and stora

316、ge(SMR+CCS)hydrogenBoiler with electrolysis hydrogenBoiler with SMR+CCS hydrogenHybrid heat pump:Electrolysis hydrogenHybrid heat SMR+CCS hydrogenHeat pump20003000400050006000700080001020304050607080Figure 5:Cost comparison and carbon intensities of different decarbonisation pathways for households

317、in the UK.Image courtesy of Baldino et al.(2020)The future of home heating The roles of heat pumps and hydrogen 344.Changes in Electricity Use at Household Scale 4.5 Key barriers that will need addressing in the next ten years 4.5.1 General There is an urgent need to improve thermal efficiency of UK

318、 buildings,both as a means to reduce heating demand and to optimise performance of heat pumps or hydrogen boilers.There are currently significant shortages of skilled workers in heat pump installation and maintenance,and gas installers do not currently possess requisite skills for installation of hy

319、drogen boilers.Low-carbon or alternative heating systems remain unfamiliar and poorly understood amongst the general public.4.5.2 Heat pumps Installation and up-front purchase costs of heat pumps are currently a key barrier to uptake.For example,the cost of installing an air-to-water heat pump syste

320、m is typically around four times the cost of replacing a gas boiler.Heat pumps require competent specification and installation to maximise their performance and efficiency;the current lack of qualified installers is a priority area for action.Low-temperature heat pump systems need to be fitted in c

321、onjunction with adequate home insulation and may also require oversized or thicker radiators to be installed.Heat pumps are typically comprised of several separate components and therefore have greater space requirements than gas combi boilers,which is a constraint to uptake in certain residential a

322、partment types in particular.If a large share of UK homes is fitted with heat pumps,this will have a significant impact on total and peak electricity demand.While heat demand from heat pumps is more distributed across different parts of the day compared to gas boilers,there will still be a need for

323、grid reinforcement of local distribution networks.4.Changes in Electricity Use at Household Scale 4.5.3 Hydrogen The ability to meet demand could be a significant barrier in hydrogens household use as there are very limited sources at present.Furthermore,its use in sectors that are harder to decarbo

324、nise will likely take priority.If hydrogen is to be used within residences,ensuring it is safe to do so is paramount.This will be an area of priority in the coming years,aided by further hydrogen trials.Storage facilities would be required to cope with periods of high heating demand.There is current

325、ly limited research into wide-scale hydrogen storage beyond underground storage.Safety risks with hydrogen storage in salt caverns would need to be managed.At present,low-carbon hydrogen is not cost competitive,which poses a barrier to its deployment.Green hydrogen is currently more expensive to pro

326、duce than blue hydrogen but may have more potential to experience cost reductions from scaling up and deployment of renewables and electrolysers compared to fossil fuel production with CCS.CCS infrastructure has not been deployed on the scale that was anticipated.Without CCS,hydrogen derived from me

327、thane cannot be low-carbon.Greater capacity of renewable generation will be required to produce green hydrogen than if electricity is used directly placing additional demands upon electrification.The future of home heating The roles of heat pumps and hydrogen 365.Policy support and regulation5.1 Hea

328、t PumpsIn general,there is a low uptake of heat pumps in the UK,with approximately 265,000 heat pump installations nationwide as of 2020(EHPA,2021c),representing around 1%of installed heating systems.Less than 500,000 homes utilise low-carbon heating(Rosenow and Lowes,2020).By way of comparison,Fran

329、ce has an installed stock of 3.1 million heat pumps,Sweden 2 million and Germany 1.1 million(EHPA,2021c).To meet the UKs net zero emissions target,by 2050 heat pumps may need to be installed in 17 to 19 million homes,with an additional 5 million homes connected to low-carbon heat networks(CCC,2019a)

330、.5.1.1 Subsidising upfront and ongoing costs As discussed in Section 4,the upfront costs of heat pumps remain well above consumers general willingness to pay for alternative heating.It is important therefore that there are financial support mechanisms in place to help the roll-out of heat pumps nati

331、onwide.An international review of low-carbon heat policies revealed that European countries that have deployed heat pumps more extensively than in the UK have generally implemented grants covering part of the purchase cost(Hanna et al.,2016;Sahni et al.,2017).These grants have frequently included mi

332、nimum requirements for the performance of heat pumps(typically using the seasonal performance factor).In the UK,financial incentives have been available from time to time but not on a continual basis and have supported either the upfront or ongoing costs of the technology.Previously available,active

333、,and proposed subsidies supporting heat pump installation or resulting heat use in homes are summarised in Table 5.In this section,we consider polices and regulations which could help to address existing barriers to both heat pump and hydrogen deployment and resolve current inadequacies with policy implementation.5.Policy support and regulationNotes to Table 5 1.The Heat and Buildings Strategy sta