Pathways for Energy Storage in the UK

8/9/2019 Pathways for Energy Storage in the UK

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Pathways forenergy storagein the UK


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AUTHORS

Peter TaylorUniversity of Leeds

Ronan BoltonUniversity of Leeds

Dave StoneUniversity of Sheffield

Xiao-Ping ZhangUniversity of Birmingham

Chris MartinUniversity of Leeds

Paul UphamUniversity of LeedsFinnish Environment Institute

CO-AUTHORS

Yongliang LiUniversity of Leeds

Richard PorterUniversity of Leeds

Eduardo Pereira BonvalletUniversity of Birmingham

Publication date

27 March 2012

Report no.

007

Publisher

The Centre for Low Carbon Futures 2012For citation and reprints, please contact the Centrefor Low Carbon Futures.

The report takes an integrated approach to examiningthe drivers and barriers to the development anddeployment of different forms of energy storagein the UK. It uses a number of scenarios for thedevelopment of the UK energy system to analyse thedifferent technologies and markets for energy storageand the likely timeframe for market development.

PATHWAYS FOR ENERGY STORAGE IN THE UK.PUBLISHED 2012.02


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CONTENTS

Foreword 04

Preface 06

Executive summary 07

1. Introduction 08

Storage in the current UK energy system 09

Future markets for electricityand heat storage 09

Factors impacting the future developmentof electricity and heat storage 11

2. Future developments in the UK energy system 12

Increase in variable renewableelectricity generation 12

Electrification of heat 16

Deployment of plug-in hybridand electric vehicles 16

Other changes 17

Conclusions 18

3. Technologies for storing electricity and heat 19

Electrical energy storage technologies 19

Thermal energy storage technologies 24

R&D efforts and needs 25

Conclusions 25

4. Electricity markets,regulation and related issues 26

Generation and Transmission 26

Distribution and the demand-side 31

Conclusions 33

5. Public attitudes to energy storage 34

Why public attitudes to new energytechnologies are important 34

Characteristics of public attitudesto energy technologies in general 34

Specific issues that may be relevantto energy storage 35

Conclusions 37

6. Alternative pathways for thedeployment of energy storage 38

User-led storage 39

Decentralised storage 39

Centralised storage 41

Conclusions 41

7. International developments in energy storage 42

China 42

European Union 43

Germany 44

Japan 45

South Korea 45

United States of America 46

Ireland 47

Denmark 47

8. Conclusions and recommendations 48

Glossary 50

References 52

Acknowledgements 55

Report no: 007

Publication date: 27 March 2012

PATHWAYS FOR ENERGY STORAGE IN THE UK.PUBLISHED 2012. 03


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FOREWORD

The UK has significant technology and policy gaps that needclosing if it is to deliver on the legislated 80% carbon reductionby 2050. The lack of suitable planned energy storage capability

is at the top of this list. The ability to store energy is a keycomponent to ensure national security of energy supply andallow credible implementation of renewable energy and to useavailable sources of heat.

Unlike coal, gas and petroleum, which are available in a physicalform, renewable supplies of energy (solar, wind, wave) arevirtual and often only available at a specific location andmoment in time. Renewable energy forms need to be capturedand stored to supply increasingly complex user demands.

This is a core requirement for our national resilience to anincreasing reliance on such variable energy sources. Recentlywe have become all too familiar with the dire consequences ofthe gap in our storage capacity most notably through theexample of wind power suppliers being paid not to generateand supply into the grid even when the wind is active!

Future scenarios indicate that energy storage is essential toreduce the burden on the national grid. The use of electric vehicles

and ground source pumps in domestic use will increase demandvery substantially and intolerably on our grid. Storage is not anoption but a necessity.

Key challenges for the UK are to:

understand what types of storage are needed, how muchand where it should be deployed in the energy system

develop a coherent policy approach to energy storage

stimulate governance and business models to enablerapid implementation.



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Technologically speaking, energy can be stored inmechanical, electrical or chemical devices and in theform of heat. All are probably needed, but in the UK other than pumped hydroelectric storage there

have been few examples at a significant scale. Theneed for flexibility in supply means that it is likely thatseveral different types of storage may be needed, sincesome can be switched on quickly (batteries) whereasothers require some time before providing an energysupply (heat, hydroelectric). The place of deployment ofdifferent technologies is likely to be at city, region, homeand personal/domestic device level. Very large-scalestorage capacity is likely to be associated with industrialoperations or at points of generation and distribution.The role of the distribution network and its flexibility isan essential component in the delivery and overall costand viability of any storage scheme. Clearly the point

of deployment affects the grid demand and methodsthrough which it may be controlled.

In 2010, the Royal Academy of Engineering initiateda series of workshops to explore these issuesin collaboration with the Chinese Academy ofSciences. The contrasting political settings, mix ofenergy supplies and storage technologies provideda stimulating set of comparisons between thetwo countries. These workshops1were pivotal instimulating a range of specialised activities in systemmodelling, comparison of demonstrator sites andcomparison of technological advances.

This report, Pathways for Energy Storage in theUK, is a further outcome from the workshops andaims to consider some of the key barriers and needsin a UK context. Crucially it sets the scene on arange of future developments to the energy system,in particular assumptions around enhanced useof renewables, greater use of electric and hybridvehicles, and moves towards electrification of heat.The report details the current status of electricalenergy storage devices and thermal storage devices.Scenarios for the future market and regulatorystructures for energy are painted along with likelyconsumer reaction to the deployment of various

types and scales of energy storage. The concludingdiscussion explores three pathways based ongovernance and business operations that may bedescribed as being wholly user-led; decentralisedand finally centralised.

A core message is that energy storage encompassesa rich and varied range of technologies, involvingboth electricity and heat, which can be applied atthe micro, meso and macro-scale and can provide

benefits across the energy value chain. However, wecurrently have a poor understanding of these benefits,which often can be spread across different actors inthe energy system. There is a risk that this lack ofunderstanding, coupled with market and regulatoryarrangements that may not always recognise thesystem benefits of storage, could lead to wrongsolutions or sub-optimal solutions being adopted. Anexample of this might be over-reliance on assumedbenefits from smart metering and use of so-calledsmart grids using a myriad of technological metersand devices under sophisticated computer control.

Alongside the conclusions, the report providesa commentary on the state of advancementinternationally similarities can be seen but in somecases storage has been aligned as part of largerscale hybrid solutions (e.g. alongside solar projects).

It is hoped this report will further stimulate detailedand more rapid considerations of options for energystorage suited for the UK needs, which can beaccompanied and stimulated by policies that resultin truly optimal national solutions. This review groupmakes specific recommendations for moving towardssuch an integrated energy system.

Richard A Williams OBE FREng FTSERoyal Academy of Engineering, London


1. The Future of Energy Storage Technologies and Policy,Royal Academy of Engineering (London) and Chinese Academyof Sciences (Beijing), 2012.


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EXECUTIVE SUMMARY

The United Kingdom has made acommitment to reduce greenhouse gasemissions by at least 80% below base

year levels by 2050. A system of carbonbudgets have been introduced whichprovide legally binding limits on theamount of emissions that may beproduced in successive five-yearperiods, beginning in 2008. The fourthcarbon budget, covering the period202327, was set in law in June 2011and requires emissions to be reduced

by 50% below 1990 levels.Meeting these greenhouse reductiontargets will require significant changesto the way that energy is produced andused. These changes will include ahuge increase in the use of renewableenergy, a substantial increase in theuse of electricity to provide heat andtransport and sustained improvements

in energy efficiency.

These developments are likely to pose significantchallenges for the energy system in matchingsupply and demand, and so create opportunities forthe deployment of additional electricity and heat

storage. The opportunities will exist across a rangeof applications and scales from macro, centralisedstorage to micro and meso-scale decentralisedstorage and for storage durations from secondsthrough to months.

However, storage is not the only solution to meetingthese challenges. Back-up fossil generation capacity,interconnectors and flexible demand, amongst others,can also play a role. The most appropriate contributionfrom energy storage is currently poorly understood andwill be impacted by a wide range of technical, economic,market, regulatory and social factors.

This report uses an integrated systems approach toassess the role of energy storage, taking into accountthe range of factors that can impact its deployment. Itfinds that, despite being under-represented in manyexisting scenarios on decarbonisation, energy storagecould be crucial in helping achieve a cost effective,low carbon energy system by improving theutilisation of generation assets, avoiding investmentrequired in transmission and distribution networksand reducing investment in back up generation.There is also emerging evidence that decentralisedstorage options, including heat storage located on thedistribution network or in peoples homes, could offer

most value to the energy system.The report identifies many different technologies forheat or electrical storage at different stages of maturityand with a wide range of characteristics. It is unlikelythat a single solution will emerge in the future giventhe wide variations in possible applications. Furtherresearch is therefore needed into both technologies thatcan offer long-term large scale storage solutions andthose that can provide fast response. Decentralisedelectrical and heat storage technologies are also worthinvestigating further. Energy storage also currentlyfaces a number of regulatory and market barriers.

While energy storage can provide significant systembenefits, it is often too expensive for any discretepart of the value chain to realise a sufficient returnon investment. New regulatory and business modelswill therefore be needed to exploit its potential. Publicattitudes towards energy storage could be crucial indetermining its role in the energy system, but to datelittle or no work has been undertaken in this area.Empirical studies are needed to understand the ways inwhich customers engage with different energy storagetechnologies and how this might influence their uptake.

Given these findings, there is an urgent need for along-term vision for storage that is consistent with

developments in the wider energy system. This mightbest be achieved through a UK roadmap for energystorage that brings together relevant stakeholders,including government, researchers, business,regulators and representatives from civil society.



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1: INTRODUCTION

The UK has ambitious goals for greenhouse gas reduction overthe period to 2050 that will require the rapid decarbonisation ofits energy system. Until recently, little attention had been given

to the role of energy storage in helping to achieve these goals.However, in summer 2011, the Energy Research Partnership (ERP)released a report highlighting that energy storage could have animportant role to play in helping to facilitate a low-carbon energytransition, but that it currently faces a number of technical andmarket/regulatory challenges (ERP, 2011). Participants at a UKEnergy Research Centre workshop held earlier in 2011 concludedthat examining the potential of energy storage should involve aholistic approach, requiring system-wide studies and joined-up

thinking that recognise both the interdisciplinary nature of manyof the issues relating to storage and how these can be consideredsufficiently comprehensively (UKERC, 2011). The Royal Academy ofEngineering and the Chinese Academy of Sciences also heldworkshops on energy storage during 2011 to highlight key strategicneeds for research and identify areas for bilateral co-operation.

The purpose of this report is to examine key drivers and barriersto the development and deployment of electricity and heat energystorage in the UK and to identify further work necessary tounderstand and facilitate its appropriate role within a low-carbonenergy system. It does this by bringing a whole systemsunderstanding of the factors that impact energy storage andintegrating these different perspectives in a number of pathwaysfor storage to identify the likely timeframe over which the marketcould develop.



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STORAGE IN THE CURRENT UK ENERGY SYSTEM

When the term energy storage is used, most peoplethink about the storage of electricity or perhaps heatand, indeed, storage of energy in these themes is themain focus of this report. However, it is important toremember that most of the energy storage capacityin the current UK energy system is provided by stocksof fossil fuels. One estimate puts the electricity thatcould be generated from UK stocks of coal and gasdestined for the power sector at around 30 000 GWhand 7 000 GWh respectively (Wilson, 2010).

These fossil fuel stocks are far greater than thestorage available within the electricity systemitself. Bulk storage of electricity is currently largelyprovided by pumped hydroelectric plants connectedto the transmission system. There are four major

schemes in the UK, all now more than 30 years old,with an installed capacity of 2.7 GW and a volume of27.6 GWh. There are also a few smaller electricitystorage facilities (mostly demonstration projectsinvolving different types of battery) connected to thedistribution system in various parts of the country.

Heat storage is largely distributed and mostly at anindividual building scale. Almost 14m households in theUK have a hot water cylinder (CLG, 2009), givinga maximum combined storage capacity of around80 GWh2. However, the volume of this kind of hot waterstorage is on the decline as 80% of sales of new gas

boilers are of the combi variety that do not require ahot water tank (Royal Academy of Engineering, 2012). Anumber of district heating schemes in the UK also havehot water storage associated with them. Oneof the largest is in Pimlico in London, consisting of a3.4 MWthcombined heat and power (CHP) plant and anaccumulator that can store 2,500m3of water at just lessthan boiling point. The other major form of heat storageis electrical storage heaters. These use off-peakelectricity to store heat (in high density bricks), which isreleased throughout the course of the day. Around 1.6mdwellings in the UK (mostly flats) have storage heatersas their primary heating system (BRE, 2007).

FUTURE MARKETS FORELECTRICITY AND HEAT STORAGE

Electricity and heat storage can play an enabling rolein any energy system, facilitating the matching ofsupply and demand at intervals from seconds throughminutes, hours and days by their ability to time-shiftboth supply and demand. One of the major benefits ofstorage is that it can improve the utilisation of otherenergy assets, so potentially enhancing the overalltechnical and economic efficiency of the system (ifthe overall system efficiency gain is greater than theefficiency loss in the storage itself).

In the future there are likely to be a number ofdevelopments that could pose challenges for theenergy system in matching supply and demand and socreate opportunities for the deployment of additional

electricity and heat storage. These opportunities willpotentially exist across a range of applications andscales from macro, centralised storage to micro andmeso-scale decentralised storage and for storagedurations from seconds through to months. Some ofthe most important challenges and possible storagesolutions are summarised in Table 1.1. However,storage is not the only solution to meeting thesechallenges. Back-up fossil generation capacity,interconnectors and flexible demand, amongst others,can also play a role.


2. Assuming an average sized tank is 100 litres and holds waterheated to 50oC.


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TIMESCALE CHALLENGE POTENTIAL STORAGE SOLUTION

SECONDS Some renewable generationintroduces harmonics and affects

power supply quality.

Very fast response/low volumeelectricity storage associated with

generation, transmissionor distribution.

MINUTES Rapid ramping in responseto changing supply from windgeneration affecting power frequencycharacteristics.

Relatively fast response electricitystorage associated with generation,transmission or distribution.

HOURS Daily peak for electricity is greaterto meet demand for heat and/orrecharging of electric vehicles.

High-power bulk electricity storage tomeet peaks in electricity. Distributedelectrical battery storage to smoothout charging peaks. Household levelheat storage in tanks or integrated intothe building fabric.

HOURS DAYS Variability of wind generation needsback-up supply or demand response.

Increased use of electricity forheat causes increased variabilityin daily and weekly demand.

Large-scale or decentralisedelectricity storage to back-upwind generation.

Heat storage at community orbuilding level, use of CHP withstorage to act as a buffer betweenelectricity and heat.

MONTHS Increased use of electricity forheat leads to strong seasonaldemand profile.

Large scale inter-seasonal heatstorage associated with combinedheat and power and district heatingschemes or use of novel materials toprovide longer duration heat storage

in buildings.


Table 1.1 Future challenges to the UK energy system that could be addressed by energy storage.Source: Adapted from ERP (2011)


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ENERGY STORAGEElectricity/Heat

Public attitudes

Characteristics of

the wider energysystem

Institutions and

business models

Technology

development

Market

structure andregulation

Time2012 2050

FACTORS IMPACTING THE FUTURE DEVELOPMENTOF ELECTRICITY AND HEAT STORAGE

The extent to which the market for electricity and heatstorage will develop in the UK is dependent on a widerange of technical, economic, regulatory and socialfactors (Figure 1.1).

Some of the most important include:

the wider development of the UK energy system,which may provide opportunities for the servicesthat storage provides, but may also encouragecompeting solutions;

research and development into electricity andheat and storage technologies, which may resultin more or less favourable trends in the cost andperformance of existing storage options, as well as

providing new alternatives;

developments in the structure of heat andelectricity markets in the UK, which may encouragestorage as a solution or present barriers;

developments in the organisational structuresof actors in the electricity markets that mayencourage or hinder new business modelspromoting energy storage;

public attitudes and behaviours, which mayfind different scales and technologies for storagemore or less acceptable and more or less easyto integrate into lifestyles.

THE FOLLOWING SECTIONS IN THE REPORTCONSIDER THESE ISSUES IN MORE DETAIL,BEFORE INTEGRATING THEIR FINDINGS IN A

RANGE OF POSSIBLE PATHWAYS FOR THEDEPLOYMENT OF ENERGY STORAGE IN THE UK.


Figure 1.1 Factors impacting the deployment of energy storage in the UK.


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2: FUTURE DEVELOPMENTSIN THE UK ENERGY SYSTEM

The Climate Change Act establisheda legally binding target to reduce theUKs greenhouse gas emissions by at

least 80% below base year levels by2050 (Great Britain, Climate ChangeAct 2008)3.

To achieve sustained emissionsreductions towards this target, the Actintroduced a system of carbon budgetswhich provide legally binding limits onthe amount of emissions that may beproduced in successive five-year

periods, beginning in 2008. The fourthcarbon budget, covering the period202327, was set in law in June 2011and requires emissions to be reducedby 50% below 1990 levels.

Meeting these targets will require massive changesin the way that the UK supplies and uses energy.Scenarios produced by the Government in its CarbonPlan (Box 2.1) show that the share of fossil fuel use in

the primary fuel mix will fall from around 90% todayto between 13% and 43% by 2050. In contrast, theshare of renewable energy will increase to between36% and 46% from a level of less than 4% today.Even by 2030 the energy mix could look quitedifferent, with fossil fuels accounting for less thantwo-thirds of the primary fuel mix and renewablesfor more than a quarter. A second major trend is thegreater use of electricity particularly to provideheat and transport. The proportion of electricity intotal final demand is currently around 18%, but underthe Carbon Plan scenarios this share increases tobetween 25% and 31% by 2030 and between 33% and

44% by 2050. All scenarios also show a substantialincrease in energy efficiency.

Much of the storage capability of the energy systemis currently provided by fossil fuels. However, withthe share of these declining and a much greater useof renewable energy as a primary energy carrierand electricity as a secondary carrier, there islikely to be a greater emphasis on the potential fordirectly storing electricity and heat. The precise rolethat energy storage will play will be impacted bydevelopments right across the energy system.Some of the most important are discussed below.

INCREASE IN VARIABLERENEWABLE ELECTRICITY GENERATION

The share of electricity generation from variablerenewables (taken in this report to include onshore andoffshore wind, photovoltaics and tidal and wave power)increases rapidly from less than 5% today to between15% and 26% by 2020 depending on the scenario (Figure2.2). All Carbon Plan scenarios then show the share ofvariable renewables peaking between the years 2030and 2040 at between 19% and 64%. This corresponds toan installed capacity of 28 GW to 91 GW.

After 2030, the absolute amount of electricitygeneration from variable renewables stabilises or fallsslightly in all scenarios except the high renewablesvariant, as the role of nuclear and thermal plant withcarbon capture and storage (CCS) becomes moreimportant. By 2050 the variable renewable shares aretherefore somewhat lower than their peak values atbetween 11% and 61% (corresponding to an installedcapacity of 20 GW to 106 GW). This potentially implies asignificant increase in the need for additional reserveand response capacity over the period from 2020 to2030, in addition to the extra 3 GW that already havebeen identified by National Grid for the period to 2020(National Grid, 2011a).


3. Greenhouse gas emissions reduction achieved outside the UKcan count towards the target.


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Core MARKAL

Higher CSS:

More bioenergy

Higher nuclear:

Less energy efficiency

Higher renewables:

More energy efficiency

Step-change inbehaviour change,renewable technologycosts and storage

No game-changingtechnology costbreakthrough

in power

Step-changein technology,in power andindustry applications

AS PART OF ITS CARBON PLAN (DECC 2011A),THE GOVERNMENT PRESENTS FOUR ALTERNATIVESCENARIOS TO 2050 IN ORDER TO UNDERSTANDTHE POTENTIAL ROLE OF DIFFERENT SUPPLY AND

END-USE TECHNOLOGIES OVER THE NEXT 40 YEARS.THERE ARE MANY THOUSANDS OF PLAUSIBLEPATHWAY COMBINATIONS WHICH COULD BEPOSSIBLE AND THE GOVERNMENT NOTES THATTHE ELECTRICITY GENERATION MIXES, DEGREEOF ELECTRIFICATION AND LEVELS OF DEMANDREDUCTION SHOWN IN THESE FUTURES SHOULDNOT BE SEEN AS THE ONLY LIKELY OR AVAILABLECOMBINATIONS.

HOWEVER, THE SCENARIOS PROVIDE A USEFULINDICATION OF THE SCALE, PACE AND DIRECTIONOF CHANGE TO THE UK ENERGY SYSTEM OVER THE

NEXT 40 YEARS.

The starting point for the scenarios is the outputsfrom the core run of the cost-optimising model,MARKAL, which was produced as part of theDepartment of Energy and Climate Changes

analysis to support the setting of the fourthcarbon budget. Alongside this, the Governmenthas developed three further futures thatattempt to stress test the results of the core runby recognising that it is not possible to predictaccurately trends in the development, cost andpublic acceptability of different technologies inevery sector of the economy.

Future Higher renewables, more energyefficiency assumes a major reduction in the costof renewable generation alongside innovationsthat facilitate a large expansion in electricitystorage capacity. It is consistent with a worldwhere high fossil fuel prices or global politicalcommitment to tackling climate change drivesmajor investment and innovation in renewables.

Future Higher CCS, more bioenergyassumesthe successful deployment of CCS technology atcommercial scale and its use in power generationand industry, supported by significant natural gasimports, driven by changes such as a reductionin fossil fuel prices as a result of large-scaleexploitation of shale gas reserves. It also assumeslow and plentiful sustainable bioenergy resources.

Future Higher nuclear, less energy efficiencyis a future that is more cautious about innovationin newer technologies. CCS does not becomecommercially viable. Innovation in offshorewind and solar does not produce major costreductions. Lack of innovation in solid wallinsulation results in low public acceptabilityof energy efficiency measures.


Figure 2.1: Energy Futures to 2050.Source: DECC (2011a)

Box 2.1: Long-term scenarios in the UK Carbon Plan.


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0%

10%

20%

30%

40%

50%

60%

70%

2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050

HIGHER RENEWABLES, MORE ENERGY EFFICIENCY HIGHER CCS, MORE BIOENERGY

Core MARKALHIGHER NUCLEAR, LESS ENERGY EFFICIENCY

SHAREOFTOTALELECTRICITYGENERATION

0%

20%

40%

60%

80%

100%

2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050



SHAREOFHO

USEHOLDS


Figure 2.3: Share of households using electricity as their main heating source.

Figure 2.2: Share of electricity generation from variable renewables.


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2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050



0%

10%

20%

30%

40%

50%

60%

70%

80%

SHAR

EOFTOTALCARPASSENGERKILOMETR

ES

2000 2005 2010 2015 2020 2025 2030 2035 2040 2045 2050



0%

10%

20%

30%

40%

50%

60%

SHAREOFTOTALCARPA

SSENGERKILOMETRES


Source: based on data from the DECC Excel 2050 Calculator(www.decc.gov.uk/en/content/cms/tackling/2050/2050.aspx)

Figure 2.5: Share of PHEVs in meeting passenger car demand.

Figure 2.4: Share of EVs in meeting passenger car demand.


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ELECTRIFICATION OF HEAT

The trends in the electrification of household heatingshow a small decline to 2015, as existing electricalheating systems are retired, followed by a sustainedincrease in all scenarios driven by the deploymentof both air and ground source heat pumps. By 2020,the share of households with electric heating rangesbetween 13% and 20% and this proportion growssteadily over the next 30 years under all scenarios.By 2030, between 18% and 33% of households haveelectric heating and this grows to between 48% and100% by 2050, depending on the scenario.

The implications for this trend in terms of peakelectricity demand could be very significant. As anillustration, if 10 million homes (around 40% of thetotal) replaced their gas boilers with air source heat

pumps, each with a 5 kWepeak load, this wouldhave the potential to create up to 50 GW of additionalelectricity demand (Speirs, 2010). Furthermore, thepeaks in heating demand could coincide with theexisting morning and evening peaks in electricitydemand. Combining heat pumps with thermal storagecould facilitate a different mode of operation, enablingsignificant use of off-peak electricity.

Analysis for the Climate Change Committeesuggested that a 2,500 litre hot water accumulatorcoupled with a 9 kWthheat pump would allowbetween 70% to 90% of heat demand to be during

off-peak hours on an Economy 10 tariff (NERA andAEA Technology, 2010). However, the Royal Academyof Engineering have noted that well insulated hotwater tanks or underground inter-seasonal thermalstores will be simpler to provide on a communitybasis given the small (and reducing) size of mostUK homes (Royal Academy of Engineering, 2012).

DEPLOYMENT OF PLUG-INHYBRID AND ELECTRIC VEHICLES

Another important future demand for electricity islikely to come from the deployment of plug-in hybridvehicles (PHEV) and all-electric vehicles (EVs).All the scenarios show that, in the period to 2040,it is likely PHEVs will be the most important batteryvehicle technology. In 2025 PHEVs account for 13%to 23% of all passenger-kilometres travelled by car,rising to between 32% and 38% by 2040.

After 2040, the share of PHEVs stabilises or startsto decline in all scenarios except the CCS variant. Incontrast, the share of EVs increases significantly from2020 onwards in all scenarios except the CCS variant,meeting between 38% and 80% of total passengercar demand in 2050 across the other three scenarios.

Thus, across all four scenarios, the combined shareof EVs and PHEVs increases from between 15% to32% in 2025 to between 63% and 80% in 2050. Againthe impact on electricity demand could be significant.For instance, if the entire population of light/mediumsize vehicles was converted to electricity, the totaldaily energy requirement would amount to around150 GWh (Strbac, 2010).

The possible impacts of PHEVs and EVs on themarket for energy storage are complex. On the onehand, greater electrical energy storage may beneeded at a household level to buffer the demand

from recharging vehicles. For example, a battery unitlocated in the garage could be trickle-charged usingoff-peak electricity and then used to provide morerapid charging as needed to the vehicle. On the otherhand, PHEVs and EVs could themselves be used as asource of electrical storage through the use of smartcharging and vehicle-to-grid (V2G) technology.



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OTHER CHANGES

Other potential changes to the UK energy system

could positively or negatively impact on the amountand type of storage required. These include:

Cost and degree of flexibility of fossil-fuelledback-up generation.Currently most large-scalereserve and response functions on the electricitygrid are provided by flexible fossil fuel generation,including open cycle gas turbines, combined cycle gasturbines and steam-cycle coal plant. All the CarbonPlan scenarios show that the amount of fossil-fuelledelectricity generation will decline substantially in thefuture with shares of between 2% and 54% by 2050.Much of the generation that remains will be combined

with CCS.The extent to which any remaining fossil fuel plantswill continue to play a role in providing reserve andresponse functions and so limit opportunities forstorage may depend on a combination of factors.These include the flexibility of large-scale fossil fuelplants when using CCS and the economic viabilityand environmental acceptability (in terms of CO 2emissions) of smaller, dedicated fossil fuel backup plants (without CCS) operating at very low loadfactors (dependent on both investment and operating,mostly fuel, costs).

Deployment of CHP and district heating.While mostof the scenarios in UK Carbon Plan anticipate thatelectricity (heat pumps) will become the dominantenergy source for heating in households, the CCSvariant shows a substantial increase in communityscale CHP. By 2030 19% of households have thisas their major heating source, rising to 39% by2050. Other studies have concluded that CHP anddistrict heating could have an enhanced role in adecarbonised energy system (e.g. Speirs, 2010;Rhodes, 2012). While a greater penetration of CHP anddistrict heating may lower the demand for electric

heating and associated storage at the household level,it could itself be combined with larger scale hot wateraccumulators or other storage devices.

Uptake of space cooling.Energy demand for spacecooling has been growing since the 1970s, largelyas result of its use in the service and commercialsectors. It is only relatively recently that airconditioning has started to penetrate households.For domestic cooling, the Carbon Plan scenariosrange in assumptions between no additional domesticair conditioning used over the period to 2050 relativeto today, and two-thirds of households having air

conditioning by 2050. In the case of commercialbuildings, the assumptions span 40% of non-domesticfloor space being air-conditioned in 2050, to achievinga 90% reduction in cooling demand compared with anaverage air conditioned building within the existing

stock in 2007. Increased demand for cooling couldcreate additional demands for storage that can handleboth heating and cooling, such as the integration ofphase change materials into the fabric of buildings.

Level of interconnection with other countries.Currently, the UK is connected to France via a2GW DC line, the 1 GW BritNed connector to theNetherlands and a 0.5 GW link from Scotlandto Ireland. There are plans to build furtherinterconnectors with other countries includingIreland, Belgium, Norway and France (DECC, 2010).Most of the scenarios in the Carbon Plan foreseethe level of interconnection increasing to 8 GW in2025 and to 10 GW by 2050. However, for therenewables variant the capacities are 15 GW and30 GW respectively. Interconnection could provide an

alternative to storage in some cases but it could alsogenerate additional storage demands, for instance inthe case that it was economically viable to store off-peak electricity imported from continental Europe.

Degree of demand-side flexibility.The ability to flexdemand (i.e. by shifting load from one time period toanother) could play a major role in matching supplyand demand. In the case of electricity demand, suchflexibility could be facilitated by the roll-out of smartmetering. For heat demand, building level storage couldhave an important role to play. In principle, a wide rangeof electrical appliances could be involved in providingflexible demand. In the Carbon Plan scenarios, thefocus is on the role that PHEVs and EVs could play.This could involve short-term periods of flexibility, forexample short-term variations in the pattern of demandfor overnight charging as well as longer-term flexibility,facilitated by higher car battery capacity, which couldinvolve flexibility in charging patterns over a week. Inaddition, PHEVs could run solely using their internalcombustion engine, hence reducing electricity demandfrom recharging the battery.

Under the Carbon Plan scenarios, the share of all EVsthat have shiftable demand capacity ranges between

25% and 75%, with figures for the share of PHEVsvarying between 30% and 90%. In addition, someflexibility in space and water heating is assumed; withup to 12 hours for space heating in a well-insulatedhome and between 12 and 24 hours for water heating.Modelling work has indicated that optimising demandresponse can result in massively improved utilisationof generation and network capacity, and significantlyreduced network investment, even for very low levelsof penetration of electric vehicles and heat pumps(Strbac, 2010).



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DEVELOPMENT ELECTRICAL ENERGY STORAGE HEAT ENERGY STORAGE

MORE VARIABLE RENEWABLEENERGY

Positive for all scales and for bothpower and energy storage

Could be positive if used withcombined heat and power as a bufferbetween electricity and heat

ELECTRIFICATION OF HEAT Could be positive particularly atmacro and meso-scale (systemoperator and distribution networkoperators managing demand)

Positive at micro-scale (combinedwith heat pumps), but less so atmeso-scale (less market for DH)

PHEVS AND EVS Uncertain could provide additionalopportunities or compete for someservices

Little impact

LOW COST AND FLEXIBLE FOSSILFUEL GENERATION

Negative for macro-level reserveand response functions

Negative for macro-scale inter-seasonal storage

INCREASED CHP AND DISTRICTHEATING

Negative for meso and micro-scalestorage

Positive for macro and meso-scalestorage, but negative for micro-storage at household level (unlesscombined with micro-CHP)

INCREASED DEMAND FOR SPACECOOLING

Positive if can help smooth demand Positive for systems that combineheating and cooling

GREATER INTERCONNECTION Uncertain depending on relativeelectricity prices

Little impact

INCREASED DEMAND-SIDEFLEXIBILITY

Generally negative althoughopportunities to contribute toincreased flexibility at household

level

May contribute to increased flexibility

CONCLUSIONS

The direction of future developments in the UK energysystem will have a profound impact on the marketsfor both electricity and heat storage. While there aremany scenarios for the future, the majority show adramatic fall in the use of fossil fuels and growingdependence on both renewable energy and the use ofelectricity. These trends are likely to pose additionalchallenges in terms of matching supply and demandfor energy, since the existing fossil fuel storagecapacity of the energy system will be much reduced.The role for both heat and electricity storage istherefore likely to increase.

However, the extent of the market for storage andthe precise applications needed are much moreuncertain. Some trends, such as an increase inthe amount of generation from variable renewable

energy and greater electrification of heat, are likelyto increase the market for storage. Others, such asgreater demand flexibility, may provide competitionand squeeze storage out of certain applications.Other changes, such as the impact of EVs andgreater interconnection are much more uncertain.A summary of these factors is provided in Table 2.1


Table 2.1: The impacts of selected energy system developments on the market for energy storage.


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3: TECHNOLOGIES FOR STORINGELECTRICITY AND HEAT

ELECTRICAL ENERGY STORAGE TECHNOLOGIES

There are a wide range of different technologies4that can be used for electrical energy storage (EES),which can be grouped according to the physical orchemical principle employed:

MECHANICAL: PUMPED HYDROELECTRICSTORAGE (PHS), COMPRESSED AIR ENERGYSTORAGE (CAES), FLYWHEEL;

ELECTROCHEMICAL: BATTERIES (INCLUDINGNICKEL, LITHIUM-ION, LEAD-ACID, METAL-AIRAND SODIUM-SULPHUR CHEMISTRIES), FLOWBATTERIES, FUEL CELLS;

ELECTRICAL: SUPERCONDUCTING MAGNETICENERGY STORAGE (SMES), ELECTRIC-DOUBLELAYER CAPACITORS (SUPERCAPACITORS); AND

THERMAL: CRYOGENIC ENERGY STORAGE (CES).

PHSis the most established form of large-scaleenergy storage, accounting for over 99% of globalEES capacity. Water is pumped from a lowerreservoir to a higher reservoir when there is asurplus of electricity. This can then be releasedthrough a turbine to generate electricity at timesof peak demand.

CAESis the only other commercially availabletechnology for providing large EES. It works by usingelectricity to compress air and store it in large caverns.At a later time, the air is then expanded through aconventional gas turbine unit connected to a generatorto produce electricity. Only two schemes have beencommissioned to date, in Germany and the US.

There are a number of different types of batterysystem being considered for energy storage, includinglead-acid, sodium-sulphur, lithium-ion, nickel-basedand metal-air designs. Lead-acid batteries are themost mature rechargeable battery, and are low-costand rugged. However, they tend to have limited cycle

life and so are not ideal for energy management.Sodium-sulphur battery systems are commerciallyavailable, with a number of systems in Japan, the USand Europe, including a 1 MW system on Shetland.However, there have been some concerns expressedover safety following a fire in Japan in October 2011.Lithium-ion batteries are widely used in portableelectronic equipment and there are a number oflarge-scale demonstration projects aimed at utilityfrequency regulation and fast response applications,including at Hemsby in Norfolk.

There are many different technologiesthat can provide heat or electricalstorage. Each technology has its own

particular characteristics and likelymarket application. The technologiesare currently at different stages ofmaturity but, in many cases, futuredevelopments in both cost andperformance will be vital in determiningwhether they are taken up by themarket. This section briefly reviewssome of the most promising electricity

and heat storage technologies for a widerange of applications and identifies keyresearch and development needs.


4. Further details and full references for each of the technologiescan be found in the technology factsheets available at:www.lowcarbonfutures.org/projects/energy-systems/energy-storage


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Currently, Li-ion batteries are high cost and thereare a number of emerging challenges that willneed to be addressed for the technology to be fullycommercialised at large-scale. Nickel-cadmium

batteries are the only other type of battery to bewidely demonstrated at utility-scale, but cost is asignificant issue. Other nickel chemistries have notyet reached large-scale implementation, althoughthere is interest in nickel metal hydride systems.Metal-air batteries have the potential to attain veryhigh specific energy densities, but so far are at theresearch and early demonstration phase.

Flow batteriesoperate differently from batterysystems the chemical reaction takes place in areaction chamber, with the electrolytes stored inexternal tanks. Unlike a battery system, energy andpower in a flow cell are independent of each other,so it is easier to develop modular systems that canbe expanded as required. There are currently anumber of electro-chemistries at different stagesof development and deployment including the use ofvanadium and zinc bromine.

CESis a newly developed EES technology. Off-peakelectricity is used to liquefy air or nitrogen, which isthen stored in cryogenic tanks. Ambient or other heatcan then be used to superheat the cryogen, boilingthe liquid and forming a high pressure gas to drive aturbine to produce electricity. CES is at an early stageof commercialisation, with a 500 kW project in the UK.

Flywheelsystems consist of a motor/generatorattached to a rotor of large mass. When electricalenergy is to be stored the motor accelerates theflywheel and the energy is then recovered byswitching the operating mode so that the flywheeldrives the generator. The use of flywheel energystorage systems on a grid scale are a recentdevelopment, with a number of demonstrationprojects around the world. Their main advantage isthe very fast response times, making them suitablefor voltage and frequency stabilisation, while theypossess relatively low energy capacities.

SMESstores energy in a superconducting coilin the form of a magnetic field. SMES have fastresponse, but can only store energy for a few hours.It is therefore most suited for grid stabilisation

applications. Micro-SMES devices (smaller than30 MW) are commercially available and there area number of larger SMES demonstration projectsaround the world.

Supercapacitors consist of two metal electrodescoated with a high surface area type of activatedcarbon and separated by a thin porous insulator.They can store or deliver energy at a very high ratebut have limited capacity compared to batteries.Traditionally they have been used to complementbattery storage systems, to increase the overallpower density. Standalone supercapacitor systemsare still at an early demonstration phase.

Hydrogen storage andfuel cellsare promisingtechnologies and the subject of significant researcheffort. The system differs from a normal EEStechnology since it uses two different processes forthe cycle of energy storage, production and use.An electrolyser unit separates water into oxygenand hydrogen using electricity. The hydrogen isthen stored in high pressure tanks, or other formsof storage. Electricity is then produced from thestored hydrogen using an electrochemical devicecalled a fuel cell.

Suitability of EES technologiesfor different applications

An ideal EES would be cheap, have high cycleefficiency, high energy and power density and along lifetime, while being environmentally benign.A combination of these six attributes does notyet exist in a single solution, but instead differentEES systems are more or less suited to differentapplication ranges. Historically, most EES systemshave been targeted towards bulk/centralisedstorage and have been used to provide storage overrelatively long durations (such as PHS) or have beenused for fast response (e.g. flywheels). However,there is an increasingly strong argument for theuse of decentralised, or distributed, storage that isembedded within the distribution network, or formsan integral part of a buildings electrical system.An example of this would be the deployment ofsmall battery packs in houses alongside roofmounted solar panel installations.



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TECH

NOLOGY

TYPICAL

RATED

CAPACITY

(MW)

NOMINAL

DURATION

CYCLE

EFFICIENCY

(%)

EN

ERGY

CO

ST($/

KW

H)

POWER

CAPACITY

COST($/

KW)

TYPICALLIFE

(YEARS)

TECHNOLOGY

MATURITY

USUAL/

ANTICIPA

TEDSCALE

PUMPED

HYDR

OELECTRIC

STOR

AGE

100-5000

1-

24+hrs

70-87

5-100

600-2000

30-60

Mature&

Commercial

Largegrid

COMPRESSEDAIR

ENER

GYSTORAGE

50-300

1-

24+hrs

70-89

2-120

400-1150

20-40

Commercial

Largegrid

CRYO

GEN-BASED

ENER

GYSTORAGE

10-200

1-

12+hrs

40-90+

26

0-530

900-2000

20-40+

Early

commercial

Grid/EV/

CommercialUPS

FLYW

HEEL

0.4-20

1

-15mins

80-95

10

00-

14

000

250-25000

15-20

Demo/Early

commercial

Smallgrid/House/EV

HYDR

OGEN

STOR

AGEANDFUEL

CELL

0-50

Seconds-24+

hrs

20-85

6-725

1500-

10000+

5-20

Demo

Grid/House/EV/

CommercialUPS

Flow

0.03-3

Seconds-10h

65-85

15

0-1000

600-2500

5-30+

(200-1200

0

cycles)

Research/

Earlydemo

Grid/House/EV/

CommercialUPS

Lithium

1-100

0.15-1hrs

75-90

60

0-3800

400-1600

5-15

(4000-100

,000

cycles)

Demo

Grid/House/EV/

CommercialUPS

Metal-Air

0.01-50

Seconds-5hrs

~75

10

-340

100-1700

(100-1000

0

cycles)

Research/

Earlydemo

Grid/House/EV/

CommercialUPS

Sodium-

Sulphur

0.05-34

Seconds-8hrs

75-90

30

0-500

350-3000

5-15

(2500-4500

cycles)

Commercial

Grid/House/EV/

CommercialUPS

Nickel

0-40

Seconds-hrs

60-90

80

0-1500

400-2400

10-20

(1500-300

0

cycles)

Early

commercial

Grid/House/EV/

CommercialUPS

Lead-Acid

0-40

Seconds-10hrs

63-90

20

0-400

50-600

5-20

(200-1000

cycles)

Mature&

Commercial

Grid/House/EV/

CommercialUPS

SUPE

RCONDUCTING

MAGNETICENERGY

STOR

AGE

0.1-10

M

illiseconds-

se

conds

90-97+

10

00-

10

000

200-350

20-30

Early

commercial

Smallgrid/

CommercialUPS

SUPE

RCAPACITOR

0-10

M

illiseconds

-1

hr

Pathways for Energy Storage in the UK

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