3 inventory of energy storage technologies

8/13/2019 3 Inventory of Energy Storage Technologies

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3 Inventory of Energy Storage Technologies

This section outlines the key energy storage technologies that arecurrently available or projected to become more widely available.

There are a number of reports such as 'Outlook of Energy StorageTechnologies' (European Parliament 2008), IEA (2009) and Chenet al (2009) that provide detailed summaries of individual energystorage technology characteristics. As such the scope of thissection is to briefly summarise the current status of the individualtechnologies and their applicability to the Scottish electricitysector. A comparison of the different technologies is provided inFigure 3.1.1. The dashed lines indicate potential advances in thetechnology. A comparative assessment of the different

technologies is presented inAppendix 1. Following thiscomparison the most promising solutions to address increasingintermittent generation in Scotland have been highlighted andpresented in Section 6.4.

Figure 3.1.1: Typical storage capacity versus dischargetimes for energy storage technologies.
http://www.scotland.gov.uk/Publications/2010/10/28091356/11http://www.scotland.gov.uk/Publications/2010/10/28091356/11http://www.scotland.gov.uk/Publications/2010/10/28091356/11


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* SMES (Superconducting Magnetic Energy Storage)

As shown above in Figure 3.1.1 there is a wide range in the typesof storage technologies. These can be broadly defined into power

quality and energy management applications.

Energy Management: The conceptand practice of decoupling thegeneration of electricity frominstantaneous consumption.

Power Quality: The "quality" of

electrical power supplied toconsumers or the grid, typicallydefined by reference to issues such aslack of voltage fluctuations and lack ofharmonic distortions.

Energy management and power quality are two very different

problems that will both need to be addressed in a grid comprisingof an increasing proportion of intermittent generation. Thefollowing section reviews each of the technologies presented inFigure 3.1.1. This has been broken down into the followingtechnology headings:

Fluid storage Advanced Battery Systems

Mechanical Systems Electro-Magnetic Systems Hydrogen

3.1 Fluid Storage


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Pumped Hydro and Compressed Air Energy Storage ( CAES) arethe only two technologies that are currently commerciallyavailable above 100 MW per project.

3.1.1 Pumped Hydro

Technical summary: Pumped hydro-electric storage is the oldestand largest of all available energy storage technologies. Thetechnology consists of two reservoirs at different elevations witha store of water. Off peak electricity is used to pump water to theupper reservoir from which it can be discharged when required.Pumped hydro whilst being a mature technology is significantlyconstrained by the same geography and environmentalconsiderations that face the hydroelectric power sector.

Global status: Over 100 GW of pumped hydro generationcapacity is installed worldwide (Chen et al 2009).

Scottish context: In 2008 pumped hydro accounted for 2.2% or1,091 GWh of the total electricity generated in Scotland (ScottishGovernment, 2009). The key characteristics of Scotland's existingpumped storage stations are shown below:

Table 3.1.1 Scottish Pumped Storage Stations

Station Capacity

( MW)

Head

(m)

Response Time Energy

Stored (GWh)

Cruachan 400 396 2 mins fromstationary30 sec if spinning

8.8

Foyers 300 197 2 mins fromstationary

6.3


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The Scottish pumped hydro sector is continuing to develop.Scottish & Southern Energy ( SSE) have a number of plans forfurther installations totalling potentially 1.3 GW in capacity. SSE'sproposals include a 300-600 MW pumped storage station at

Balmacaan, 300-600 MW at Coire Glas and 72 MW at Sloy ( SSE2009).

In addition 2009 a further 100 MW of hydro capacity was addedat Glendoe. While this is not a pumped storage station, it isintended to operate as a fast response hydro. At present thisstation is not operational due to a rockfall in the main tunnel.Traditional pumped hydro will be one of the key technologiesrequired should energy storage demand increase in the future,

this is highlighted in section 6.4.

Case Study: Pumped Hydropower in the EU

Historic growth of pumped hydro:Pumpedhydro is the largest energy storage technologyglobally with approximately 100 GW installedworldwide. Much of the EU growth in pumped

storage has taken place during the 1970s and1980s when approximately 7,500 MW and 14,000MW of pumped storage was installed respectively.This growth was driven by the need to addressenergy security following the 1970s oil crises andas peaking plants to compliment nuclear power.During the 1990s and 2000s a much lower figure

of around 2,000 MW was installed in each of thesedecades. Over the coming 8 years (up to 2018) areview by Deane et al (2010) identifiedapproximately 7,500 MW of pumped hydrototalling an investment of 6 million that is


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proposed. This figure only includes those plantsthat have completed the environmental impactassessment stage and therefore excludes the two

large schemes planned by SSE.

Accommodating increasing wind capacity:Thegraph below demonstrates the huge increase inwind power contribution to EU electricity. Thetrajectory of wind growth across the EU is growingrapidly. Considering this the EU pumped storage

generation has increased in comparison by a smallmargin.

Portugal has a number of similarities with Scotland

featuring a strong drive to renewable energy(potentially 45% in 2010, mainly from hydro thenwind) and increasing interconnection to itsneighbour of 3 GW by 2014 (in this case Spain).Portugal has the second highest planned capacity


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figure of pumped hydro with plans to upgrade orbuild new sites totalling 2000 MW. In 2010Portugal is expected to have 45% renewable with

hydro followed by wind the main contributors.Wind production in Portugal is poorly correlatedwith peak demand, the windiest periods occurringat night time and early morning (Deane et al2010). A Portuguese government programme 'The

National Programme of High Hydroelectric PotentialDams' reported that the ideal relationship between

pumping capacity and wind power was 1 MWpumped storage to 3.5 MW of wind power. Energiede Portugal ( EDP) who are building 4 new plantsstate that increasing wind penetration andinterconnection to Spain is adding value to pumpedhydro through energy storage and ancillaryservices.

Economics of pumped hydro:Reported costs forpumped hydro are extremely varied, the literaturereview found great inconsistency in cost ranges. Anumber of reasons exist for the range in cost;

Site suitability has a significant influence,

The installed power in relation to the energystorage capacity,

In addition there is also trend towardsextensions of existing projects and


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Repowering.

The reported capital costs for the proposed

pumped hydro schemes range from 470/kW-2170/kW and that (Deane et al 2010). Iberdrola,the worlds largest wind operator (and parentcompany of Scottish Power) state that pumpedhydro is the second best option to increasing windcapacity following conventional hydro. Iberdrola isseeking to increase its pumped hydro capacity but

reports that limited suitable sites are available.Even when suitable sites are identified the highinvestment cost means that developers are obligedto assume very high levels of risk. Despitehighlighting the economic barriers as being amajor constraint Iberdrola is developing 1,750 MWof pumped storage through to 2018 in Spain and

Portugal (Renewable Energy World, 2009).Public sector interventions:pumped hydrowhen sited in the correct location is economic.With increasing wind the value of pumped storageis set to increase. Across the EU new pumpedstorage opportunities are being identified by theutility companies. As such the only public sectorinterventions required are non-economic,specifically relating to approving relevant projectsthrough the planning/environmental phase. Itcould be argued that if deemed necessary,


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government loans could be one option to de-riskthe investment costs.

Other forms of pumped hydro

Seawater pumped hydro: this uses seawater as the operatingfluid and the open ocean as the lower reservoir. This allows agreater potential availability of suitable sites. Capital costs areestimated to be 15% higher than conventional pumped hydro dueto corrosion increasing the cost of the pump turbine. However theshort pipeline length can reduce pumping losses ( IEA, 2009).

Figure 3.1.2: Arial view of a 30 MW, 136m head seawaterpumped hydro plant in Japan.

Given Scotland's extensive coastline there may be potential for

this form of pumped hydro. The head for conventional pumpedhydro is typically several hundred metres. Hence while Scotlandhas a coastline with extensive areas of cliffs, there may bepotential for this form of pumped hydro at a limited number oflocations.


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A potential application would be to located seawater pumpedhydro in conjunction with offshore wind or wave and tidalinstallations. This application would entail:

Location of seawater pumped hydro at the landfall for cablesfrom offshore wind, wave or tidal generation.

Operation of the seawater pumped hydro to average out thepeaks and troughs of offshore generation.

Net output from the offshore generation would be lessvariable.

Less investment required for transmission capacity toaccommodate the offshore generation.

The concept would be suited to offshore generation projectslocated adjacent to shore lines with a cliff line over 100 metres.From the recent Crown Estate licensing rounds, the Beatrice andMoray Firth projects may have some potential as the landfall forthe cables could be in the area of cliffs south of Dunbeath.

There is discussion currently underway in Ireland looking at theconcept of several large seawater pumped hydro plants. Theconcept being promoted by Spirit of Ireland is looking to flood upto 5 large glacial valleys that meet the sea on the west coast ofIreland. As reported by the Irish Times discussions are underwaywith the Department of Communications, Energy and NaturalResources. Spirit of Ireland have estimated that each site wouldbe in the order of 750-1000 MW. Installing 2-3 of these plantstogether with increasing wind power would allow Ireland tobecome energy independent, installing further sites would allowexport to the UK grid (Sprit of Ireland and Irish Times, 2010).

Adjustable speed pumped hydro:the rotational speed of theturbo impeller and the pumping head determine the input of thepump turbine and hence the pump output. When operating at acertain pumping head a single speed motor cannot vary the inputand hence the pump output is also fixed. An adjustable-speedturbine can in contrast vary the input and thereby enable it to


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follow the variable generation output from wind, wave and tidalgeneration. A number of adjustable speed pump hydro systemsare in use in Japan, with output over 300 MW ( IEA, 2009).

Underground pumped hydro:The lower reservoir is comprisedof artificial underground tunnels. The upper reservoir could be anatural lake or the sea meaning these tunnels are filled withfreshwater and seawater respectively depending upon thelocation. This design expands plant location choice as well asminimising ecological impacts.

The capital costs of creating the lower reservoir are likely besignificant. Hence the scale of the project will need to be large toprovide sufficient income to balance the large capital cost.Studies in Japan were on a 2,000 MW scheme. Alternatively useof existing underground chambers (abandoned coal mines etc.)would reduce costs.

Figure 3.1.3 (left): schematic of a underground pumpedhydro plant (Source IEA, 2009).


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Pumped Storage-summary

Storage

Capacity

/kWcapaci

ty

Power

rating

Efficiency

Technology

status

Technology

lifetime

20years

3.1.2 Compressed Air Energy Storage ( CAES)

Technical summary: CAES is a technology that uses energystorage as a means to improve the efficiency of a gas fired powergeneration. CAES works by storing a volume of compressed air inan underground cavern. It is essentially a variation of a combinedcycle gas turbine ( CCGT) power plant.

The key features of CAES are listed below:

Grid electricity is used to compress air. Compressed air is stored in large impervious caverns (e.g.

salt caverns) at pressures of 45 to 70 bar.

Compressed air is recovered and used as combustion air fora CCGT.

Waste heat is recovered and heats the recoveredcompressed air.

The compressed air improves the efficiency of the CCGT andallows up to a 60% reduction in gas consumption compared to aconventional CCGT. The schematic diagram below gives anindication of a CAES layout.


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Figure 3.1.2: Schematic diagram of CAES (Source: Chen etal 2009, originally McDowall 2004)

A weakness of conventional CAES is the efficiency of thecompression process. Compressed air contains heat and this isremoved prior to storage, reducing efficiency. Several alternativedesigns have been considered which recover the heat in thecompressed air.

Power charge

Power discharge

Because this is a fossil fuel generation, the commercial operationof CAES will depend on the price of gas vs. the wholesale price ofelectricity.


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CAES units can be operational within about 14 minutes. Unlikeother storage technologies, the use of natural gas means thatadditional CO 2is produced by this form of storage technology. Inprinciple, CAES could be combined with Carbon Capture and

Storage ( CCS), with additional capital and operational costs.

Global Status: Two major plants in operation, Hundorf,Germany at 290 MW and McIntosh, Alabama, USA with 110 MW,with these both being commissioned by 1991. At present, there issignificant interest in this technology in the USA with severallocations being considered. The largest is the Iowa Stored EnergyPark at 2,700 MW. This is being developed in conjunction with alarge wind farm. Excess wind generation will supply the electricity

for the air compression. At this stage the plant is estimated tocome online in 2011 although delays have been experienced todate and construction has yet to start.

Scottish context:There are no sites developed in Scotland atpresent. One site is currently being considered in NorthernIreland (Energy Saving Trust, 2009). CAES faces a similar issueto pumped hydro in terms of its geographical constraints. Asuitable storage cavern is dependent upon rock mines, saltcaverns, aquifers or depleted gas fields. The British GeologicalSurvey ( BGS) was consulted as part of this study regarding thesuitability of sites in Scotland. This clarified that Scotland ,unlikeparts of England, has no natural salt caverns. Other possibleoptions are abandoned coal mines below a certain depth, hardrock caverns or deep aquifers. Other gases, such as LPG arestored in chalk caverns in Humberside. The BGS believes thatthere could be merits to investigating the suitability of deeperabandoned coal mines particularly in the Central Belt of Scotland.Interest in CAES is developing in Scotland and a compressed airfor renewables event was held in February 2010 at EdinburghUniversity. A summary of the discussions from this event can befound inAppendix 2of this report.

CAES summary
http://www.scotland.gov.uk/Publications/2010/10/28091356/12http://www.scotland.gov.uk/Publications/2010/10/28091356/12http://www.scotland.gov.uk/Publications/2010/10/28091356/12http://www.scotland.gov.uk/Publications/2010/10/28091356/12


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Storage

Capaci

ty

/kWcapaci

ty

Power

ratin

g

Efficiency

Technology

status

Technology

lifetime

100-1,000MWh

500-600

5-300MW

70-79% Mature 20-40years

3.1.3 Cryogenic Energy Storage

Technical summary: A cryogenic liquid (e.g. liquid nitrogen orliquid air) is generated by off-peak power. At times of peakdemand ambient temperature is used superheat the cryogenthereby boiling the liquid and forming a high pressure gas. Theheated cryogen is then used to generate electricity. The systemcan also provide refrigeration and cooling.

Global Status: This is new technology and as such is largelybeing explored in the academic area (Chen et al 2009). There areno installed full scale examples at the time of writing.

Scottish context: A UK based company, Highview PowerStorage are currently developing a 500kW, 2 MWh prototype tobe installed near London which is due to be tested this year. Fullscale commercial deployment at 3 MW size is planned for 2012(Highview Power Storage, 2010). As stated above under theglobal status this is a developing sector primarily beinginvestigated by academia, in the UK Leeds University are the only

research institute actively involved in this area.

Figure 3.1.3 Schematic of Highview cryogen storage device(Source: Highview Power Storage, 2010)


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Cryogenic storage summary

Storage

Capacity

/kWcapaci

ty

Power

rating

Efficiency

Technology

status

Technology

lifetime

10-100MWh

250-500

500kW-10

MW

40-50% Prototypetesting

phase

20-40years

3.2 Advanced battery systems

3.2.1 Flow Battery


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Technical Summary: Flow batteries function through the storeand release of energy via a reversible electrochemical reactionbetween two electrolytes. There are several types of flow batterywith varying electroactive species; Vanadium redox battery (

VRB), zinc bromine battery (ZnBr), Polysulphide bromide battery( PSB) and cerium zinc being the most common. VRB appears tobe the most advanced with the key benefits being full dischargeand recharge without reducing the life expectancy.

Global status:There are several VRB systems installed asbackup solutions often in remote areas. In Kenya a small 5kWsolution has been installed by a telecoms company and beenrunning successfully (Winafrique, 2009). At the larger end of the

scale in Sapporo, Japan a 4 MW system (6 MW pulse) has beenrunning since 2005 with over 14,000 cycles completed (Holzman,2007). In general progress appears to have stagnated over thelast couple of years, with no significant installations taking placeon the back of earlier good promise.

Scottish Context: Some research on flow batteries isprogressing in the UK, the Technology Strategy Board arecurrently funding two flow battery projects. Scottish Power areinvolved in one of the projects entitled 'Development of RedoxFlow Battery for Utility Energy Storage', this is being led by ESDLtd. A second project looking a redox flow batteries is led by C-Tec Innovation Ltd. Both of these projects are small scale trialsbut intend to be developed to a larger scale if successful. Plurion,based in Fife are developing flow battery technology. Their flowbattery is based upon cerium-zinc electrolyte. Plurion arecurrently working on developing a 1 MWh device.

SSE are also involved in the flow battery sector having acquired a

minority stake in Premium Power, an American developer of zincbromide flow batteries. SSE have since installed and successfullycommissioned a 100kW (150kWh) demonstration flow batterywhich is being tested at its Nairn substation. This installation isbeing used to examine wind balancing and energy arbitragebased upon trial data. ( SSE, 2009b).


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In Ireland, a Vanadium Redox battery was planned in associationwith the second phase of the Sorne wind farm. This was due tobe a 2 MW x 6 hour system supplied by VRB Power Systems. Thisproject is unlikely to proceed and VRB filed for insolvency late in

2008. The assets of VRB Power were acquired by a Chinese basedcompany Prudent Energy in early 2009. They have now taken onthe VRB technology and are looking at new opportunities. Flowbatteries have been identified in the technology review as beingone of the technologies that has potential in either energystorage or power quality applications. This is discussed in section6.4.

Flow Battery Summary

Storage

Capacity

/kWcapaci

ty

Power

rating

Efficiency

Technology

status

Technology

lifetime

1-10MWh

1000+

5kW-4

MW

80-90% Immature, a few

examplesworldwide

14,000+cycles

3.2.2 Sodium sulphur (NaS) Battery

Technical summary: NaS batteries are the most advanced type ofhigh temperature battery and consist of liquid sulphur and liquidsodium separated by a solid beta alumina ceramic electrolyte.The battery operating temperature is between 300-350C. Themajor drawback of the technology is the high operatingtemperature which uses some of the battery's stored energy.

Global Status: NGK insulators Ltd state that there has been over300 MW installed, a significant proportion of these are in Japan.


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One large installation of 8 MW is at the Hitachi parts plant inJapan. NGK have recently installed a 34 MW battery inconjunction with a 51 MW wind farm at Rokkasho, Japan, thisbecame the largest wind and storage scheme in Japan (Smart

Grid News, 2009).

Scottish context: there are limited applications in Europe, withno known examples in Scotland or the UK. Enercon in Germanyhave installed a NaS system in conjunction with a 6 MW windturbine. Younicos in Germany are also testing a NGK 1 MW NaSbattery at their site in Berlin, They are feeding in real time solarPV and wind data from Graciosa in the Azores to mimic therequirements of the island and using the battery for storing

excess production or providing supply at times of low generation(Price 2010).

NaS Battery summary

Storage

Capacity

/kWcapaci

ty

Power

rating

Efficiency

Technology

status

Technology

lifetime

1-34MWh

1000-2000

50kW-34

MW

80-90% Immature, a few

examplesworldwide

2500cycles

3.2.3 Lithium Battery

Technical summary: Lithium batteries are electrochemical cellsand similar to other advanced battery systems. The mainadvantages they offer are the high energy density and almost100% efficiency. However, to date the main obstacle to overcomehas been the cost especially for larger batteries. There are also


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some safety considerations to address relating to igniting orexploding through short circuiting.

Global status: Main application is in the portable battery sector

where lithium batteries command over 50% of the small portabledevices market. At the larger scale the developments themaximum size in development is around 100kW. Li-ion batteriesrequire cobalt as a material with three countries (Congo, Zambiaand Australia) accounting for 56% of production. Future depositsare concentrated in Congo, a politically unstable country ( IEA,2009).

Scottish context: Scotland has a number of companies in thelithium battery market. Axeon in Dundee produce lithiumbatteries for electric vehicles, motive power and power tools.ABSL in Thurso develop and manufacture specialist lithiumbatteries for military, space and other applications. A relevant UKexample that has potential transferability to Scotland is a trial byEDF Energy Networks at Martham substation in the East ofEngland. In an area of high wind penetration they aredemonstrating a SAFT Li-ion battery to provide 600k VAautomatic voltage control (Price 2010).

Lithium batteries summary

Storage

Capacity

/kWcapaci

ty

Power

rating

Efficiency

Technology

status

Technology

lifetime

1-10MWh 1000-3000 0-100kW

99% Matureportablemarket

10,000cycles

3.2.1 Other Battery Types


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The following batteries, metal air, lead acid, nickel and supercapacitors have been included in the technology inventoryhowever their potential for application as energy storagetechnologies in Scotland is somewhat limited. With the exception

of super-capacitors the other batteries are all maturetechnologies that have limited technology lifetime (in terms ofdischarge cycles) and contain toxic materials. The review hasfound no significant evidence of these technologies being furtherdeveloped globally or within Scotland and therefore providingsignificant as yet unknown technological advances are madethese technologies can be discounted from addressing theintermittency challenge in Scotland. Super-capacitors have greatfuture potential but it appears that they are largely developing

into a niche market focussed upon transport applications.

3.2.2 Metal air battery

Technical summary: Metal air batteries use metal as the fuel andair as the oxidant. They are very compact and one of the leastexpensive batteries, however they offer limited recharge potentialwith efficiency lying around 50%. The cost should be viewed withcaution as the lifetime of the batteries will be much shorter thanother options.

Metal air batteries are unlikely to be a viable technology optionfor Scotland to consider in addressing the intermittency issue.

Metal air battery summary

Storage

Capacity

/kWcapaci

ty

Power

rating

Efficiency

Technology

status

Technology

lifetime

0.1-1MWh

100-250

1-10k

40-50% Mature 100-300cycles


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W

3.2.3 Lead Acid Batteries

Technical summary: This is the oldest and most widely usedrechargeable electrochemical device. They are electrochemicalcells within which a lead and sulphuric acid reaction takes place.

Global status: There are a few large scale commercial examplesof lead-acid batteries, notably a 8.5 MWh installation in Berlin andthe world's largest 40 MWh, 10 MW (for 4 hours) system inChino, California.

Scottish context: Limited future applicability, Lead-acidbatteries niche market is more focussed upon power quality, UPSand spinning reserve applications. The poor technology lifetimethrough limited number of discharge cycles means that onsustainability grounds it will probably be unsuitable.

Lead-acid batteries summary

Storage

Capacity

/kWcapaci

ty

Power

rating

Efficiency

Technology

status

Technology

lifetime

40MWh

250-500

10MW

70-90% Mature 500-1000cycles

3.2.4 Nickel battery

Technical summary: There are various different Nickel batteriesavailable with Nickel-Cadmium (Ni-Cd) being the most common.They perform a mediocre number of discharge cycles incomparison to other batteries.


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Global status: One large application, a 27 MW plant inFairbanks, Alaska. This can supply power for 15 minutes and actsas a stabilisation system to the local grid in the event of a powerfailure

Scottish context: Cadmium used in Ni-Cd batteries is highlytoxic and EU legislation means that Nickel Metal Hydride (Ni- MH)has essentially superseded this technology. Barriers thereforeexist for future development.

Nickel Battery summary

Storag

eCapaci

ty

/kW

capacity

Pow

erratin

g

Efficien

cy

Technolo

gystatus

Technolo

gylifetime

1-10MWh

500-750

1-27MW

80-90% Few largescale

examples

worldwide

2000-2500

cycles

3.2.5 Super-capacitors

Technical summary: Super capacitors utilise a simple approachwith which to store energy this being within an electric fieldbetween two charged plates. They can be charged and dischargedvery quickly, i.e. split seconds. Super capacitors modify the abovesystem with a greater electrode surface area, liquid electrolyte

and polymer membrane. Super-capacitors are suited to powerquality (or short term storage) due to their high energydissipation.

Global Status:Growing rapidly in the automotive sector,deployed in systems such as regenerative braking which can


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reduce overall emissions. They are generally used in short termstorage applications.

Super-capacitors summary

Storage

Capacity

/kWcapaci

ty

Power

rating

Efficiency

Technology

status

Technology

lifetime

>0.1MWh

500-750

0-300k

W

90-95% Developing in

transportapplicatio

ns

50,000+cycles

3.3 Mechanical Systems

3.3.1 Flywheels

Technical summary: There have been recent technical advancesin flywheel technology which itself is mature. Flywheels representstored mechanical energy in the form of kinetic energy from ahigh speed spinning wheel. Modern flywheels comprise of arotating cylinder featuring magnetically levitated bearings andoperating in a low pressure environment to reduce air friction.The high rotation speeds of in excess of 20,000 rpm can releaseenergy for up to 30 minutes.

Global status: Modern flywheels as described above areprimarily being developed by a number of companies one leadingplayer being Beacon Power Corp. They have recently attracted a$43 million conditional loan and a subsequent $24 million smartgrid stimulus grant from the US Department of Energy (BeaconPower Corp, 2010). They are installing a 20 MW system near New


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York which will earn revenue by providing grid frequencyregulation, further plants are planned across the US. In Japan,the Okinawa Electric Company and Toshiba have developed andinstalled a 23 MW system to provide frequency regulation.

Operating since 1996 the system has contributed to goodfrequency control on a small grid in a situation on a small gridwhere frequency control is very sensitive ( IEA, 2009).

Scottish context: Would have potential applications to supportshort term frequency fluctuations from wind farms which couldenable a greater availability and improve grid stability. Thereview found that there is limited if any work on advancedflywheels in Scotland or the UK.

Flywheel summary

Storage

Capacity

/kWcapaci

ty

Power

rating

Efficiency

Technology

status

Technology

lifetime

0.1-10MWh 500-750 0-20MW 80-90% Immature, fewplantsunder

construction

20,000+cycles

3.4 Electro Magnetic Systems

3.4.1 Superconducting Magnetic Energy Storage ( SMES)

Technical summary: SMES stores electrical energy in a magneticfield within a cooled superconducting coil. This coil is cooled tobeyond its super conducting temperature (-269C). At these


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temperatures limited electrical resistance mean high efficienciesof up to 97% can be achieved. The present maximum size is 10MW but the estimated theoretical potential is 2000 MW (ImperialCollege, 2003).

Global status: There are several examples of SMES worldwideas a power quality application, as it has the ability to dischargepower rapidly. Over 100 MW has been installed worldwide (Chenet al 2009). At the larger scale the projected development of aload levelling 100 MWh system could be completed during 2020-30. In the decade 2030-40 it is projected that a 1 GWh classsystem for daily load levelling could be available ( IEA, 2009).

Scottish context: in its current form SMES is useful as a powerquality application to industrial users. Potential developments atthe large end of the scale would have potential. Should largescale SMES be developed the magnetic field at this scale maycause local environmental issues. As seen from the global statusprojections this could be a highly useful technology in the futurebut probably not for at least another 30-40 years due to thesignificant scientific advances required.

SMES summary

Storage

Capacity

/kWcapac

ity

Powerrating

Efficiency

Technology

status

Technology

lifetime

1-10

MWh

250-

500

1-10

MW(potenti

allyhundred

s of


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MW) ons

3.5 Hydrogen for energy storage

Technical summary: Hydrogen production from electricity will bethrough the electrolysis of water using surplus electricity. Thehydrogen can then be reconverted to electricity through the useof a fuel cell. The main issue with using hydrogen as an energystorage mechanism is that it has only been demonstrated at smallscale to date.

Due to the energy efficiency of the electrolysis - hydrogen - fuel

cell conversion, hydrogen technologies will require significant costreductions to occur before large scale deployment is undertaken(Pew Centre, 2009).

Global Status: This is new technology which is beingdemonstrated at the pilot / demonstration scale. Work is beingundertaken internationally with projects being demonstrated inNorway (Utsira); Canada (Ramea) (Oprisan 2007) and severalprojects currently being undertaken in the UK (the HARI projectin Loughborough, the Yorkshire hydrogen project and severalScottish projects (see next section)). To our knowledge there arecurrently no large scale demonstration projects with research anddevelopment focussing on hydrogen storage and the integrationof hydrogen with renewable energy. Integration demonstrationprojects are small scale and typically utilising less than 100kW ofinstalled wind capacity. However the International Energy Agencyhas commissioned Task 24: Wind Energy and HydrogenIntegration to investigate hydrogen storage as a means ofintegrating wind energy.

In relation to storage, research and development is focussing onimprovements in liquid storage and storage as a compressed gas.Research is also investigating solid state storage in a variety ofmaterials including chemical and metal hydrides and activatedcarbon.


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In addition to hydrogen's ability to act as an energy store for gridbalancing purposes, it is being viewed as a long term transportfuel solution. It is this use that has attracted most attention todate.

Scottish context: Scotland has at least six projects currently inoperation (or close to operational) that are generating hydrogenfrom renewable energy with a view to storing and re-use at alater stage. The use of hydrogen as an energy store depends onthe circumstances, and for each project is listed below:

Berwickshire Housing Association h-5 ecohome generateshydrogen through a 4.5kW electrolyser from surplus windand solar electricity generated on site. This hydrogen is thenreconverted to electricity through a 5kW fuel cell(Berwickshire Ltd, 2009).

The PURE Energy Centre generates hydrogen from on-sitewind which is then used as either a transport fuel in a fuelcell/ battery hybrid vehicle or reconverted to electricitythrough a fuel cell ( PURE, 2010).

The Hydrogen Office is incorporating a store for 30kg ofhydrogen under pressure. The hydrogen will be generated

from surplus electricity from an on-site wind turbine andreconverted to electricity through a fuel cell (The HydrogenOffice, 2010)

H2 SEED hydrogen is being produced by the electrolysis ofwater operated by electricity from the anaerobic digestion ofmunicipal waste. The hydrogen is stored in pressurised "K"type cylinders and is being used for road transport.

Lews Castle College generation of hydrogen from on-sitewind turbines. The hydrogen is being stored in "K" typecylinders for use in the college's hydrogen laboratory.

Wind Hydrogen Limited ( WHL) have proposed developing a48 MW wind farm and a 5 MW hydrogen generation schemein Ayrshire. The hydrogen generation plan gained outline


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planning consent in 2009, however the wind farm wasrefused outline planning consent.

The projects at the Berwickshire Housing Association, H2 SEED

and Lews Castle College were supported by funding from theScottish Government through the Renewable Hydrogen and FuelCell Support Scheme which operated between December 2006and March 2008.

Whilst hydrogen has great future potential as a technology atpresent the economics are unfavourable. Many of the proposedprojects in Scotland have been planned and discussed for manyyears. The situation of WHL highlights the barriers in thehydrogen storage sector that are currently being experienced.That large scale projects at Hunterston and Shetlands were beingplanned for at least 5 years suggests that significant economicbarriers exist.

The Technology Strategy Board have announced that they will belaunching a competition for funding in the fuel cell and hydrogenarea during 2010. This will provide 7 million of governmentfunding to 15 projects in the stationary power and transportmarkets under the Fuel Cells and Hydrogen Demonstrator

Programme (Energie Bulletin, 2010).

Hence there will be further opportunities to develop hydrogendemonstration projects similar to the small scale pilots anddemonstrations that have already taken place in Scotland.Significant know-how and lessons were learnt in the earlierdemonstrations. Hence a further round of projects could capitaliseon this and establish in more detail the role of hydrogen as anenergy storage technology for the island and small communities

that are common in Western and Highland Scotland.

3 inventory of energy storage technologies

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