Energy Storage and Management Study

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3 Inventory of Energy Storage Technologies

This section outlines the key energy storage technologies that are currently available or projected to become more widely available. There are a number of reports such as 'Outlook of Energy Storage Technologies' (European Parliament 2008), IEA (2009) and Chen et al (2009) that provide detailed summaries of individual energy storage technology characteristics. As such the scope of this section is to briefly summarise the current status of the individual technologies and their applicability to the Scottish electricity sector. A comparison of the different technologies is provided in Figure 3.1.1. The dashed lines indicate potential advances in the technology. A comparative assessment of the different technologies is presented in Appendix 1. Following this comparison the most promising solutions to address increasing intermittent generation in Scotland have been highlighted and presented in Section 6.4.

Figure 3.1.1: Typical storage capacity versus discharge times for energy storage technologies.

Figure 3.1.1: Typical storage capacity versus discharge times for energy storage technologies.

* SMES (Superconducting Magnetic Energy Storage)

As shown above in Figure 3.1.1 there is a wide range in the types of storage technologies. These can be broadly defined into power quality and energy management applications.

Energy Management: The concept and practice of decoupling the generation of electricity from instantaneous consumption.

Power Quality: The "quality" of electrical power supplied to consumers or the grid, typically defined by reference to issues such as lack of voltage fluctuations and lack of harmonic distortions.

Energy management and power quality are two very different problems that will both need to be addressed in a grid comprising of an increasing proportion of intermittent generation. The following section reviews each of the technologies presented in Figure 3.1.1. This has been broken down into the following technology headings:

  • Fluid storage
  • Advanced Battery Systems
  • Mechanical Systems
  • Electro-Magnetic Systems
  • Hydrogen

3.1 Fluid Storage

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

3.1.1 Pumped Hydro

Technical summary: Pumped hydro-electric storage is the oldest and largest of all available energy storage technologies. The technology consists of two reservoirs at different elevations with a store of water. Off peak electricity is used to pump water to the upper reservoir from which it can be discharged when required. Pumped hydro whilst being a mature technology is significantly constrained by the same geography and environmental considerations that face the hydroelectric power sector.

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

Scottish context: In 2008 pumped hydro accounted for 2.2% or 1,091 GWh of the total electricity generated in Scotland (Scottish Government, 2009). The key characteristics of Scotland's existing pumped 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 from stationary
30 sec if spinning

8.8

Foyers

300

197

2 mins from stationary

6.3

The Scottish pumped hydro sector is continuing to develop. Scottish & Southern Energy ( SSE) have a number of plans for further installations totalling potentially 1.3 GW in capacity. SSE's proposals include a 300-600 MW pumped storage station at Balmacaan, 300-600 MW at Coire Glas and 72 MW at Sloy ( SSE 2009).

In addition 2009 a further 100 MW of hydro capacity was added at Glendoe. While this is not a pumped storage station, it is intended to operate as a fast response hydro. At present this station is not operational due to a rockfall in the main tunnel. Traditional pumped hydro will be one of the key technologies required 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: Pumped hydro is the largest energy storage technology globally with approximately 100 GW installed worldwide. Much of the EU growth in pumped storage has taken place during the 1970s and 1980s when approximately 7,500 MW and 14,000 MW of pumped storage was installed respectively. This growth was driven by the need to address energy security following the 1970s oil crises and as 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 these decades. Over the coming 8 years (up to 2018) a review by Deane et al (2010) identified approximately 7,500 MW of pumped hydro totalling an investment of €6 million that is proposed. This figure only includes those plants that have completed the environmental impact assessment stage and therefore excludes the two large schemes planned by SSE.

Accommodating increasing wind capacity: The graph below demonstrates the huge increase in wind power contribution to EU electricity. The trajectory of wind growth across the EU is growing rapidly. Considering this the EU pumped storage generation has increased in comparison by a small margin.

the huge increase in wind power contribution to EU electricity

Portugal has a number of similarities with Scotland featuring a strong drive to renewable energy (potentially 45% in 2010, mainly from hydro then wind) and increasing interconnection to its neighbour of 3 GW by 2014 (in this case Spain). Portugal has the second highest planned capacity figure of pumped hydro with plans to upgrade or build new sites totalling 2000 MW. In 2010 Portugal is expected to have 45% renewable with hydro followed by wind the main contributors. Wind production in Portugal is poorly correlated with peak demand, the windiest periods occurring at night time and early morning (Deane et al 2010). A Portuguese government programme 'The National Programme of High Hydroelectric Potential Dams' reported that the ideal relationship between pumping capacity and wind power was 1 MW pumped storage to 3.5 MW of wind power. Energie de Portugal ( EDP) who are building 4 new plants state that increasing wind penetration and interconnection to Spain is adding value to pumped hydro through energy storage and ancillary services.

Economics of pumped hydro: Reported costs for pumped hydro are extremely varied, the literature review found great inconsistency in cost ranges. A number of reasons exist for the range in cost;

  • Site suitability has a significant influence,
  • The installed power in relation to the energy storage capacity,
  • In addition there is also trend towards extensions of existing projects and
  • 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 parent company of Scottish Power) state that pumped hydro is the second best option to increasing wind capacity following conventional hydro. Iberdrola is seeking to increase its pumped hydro capacity but reports that limited suitable sites are available. Even when suitable sites are identified the high investment cost means that developers are obliged to assume very high levels of risk. Despite highlighting the economic barriers as being a major constraint Iberdrola is developing 1,750 MW of pumped storage through to 2018 in Spain and Portugal (Renewable Energy World, 2009).

Public sector interventions: pumped hydro when sited in the correct location is economic. With increasing wind the value of pumped storage is set to increase. Across the EU new pumped storage opportunities are being identified by the utility companies. As such the only public sector interventions required are non-economic, specifically relating to approving relevant projects through the planning/environmental phase. It could be argued that if deemed necessary, government loans could be one option to de-risk the investment costs.

Other forms of pumped hydro

Seawater pumped hydro: this uses seawater as the operating fluid and the open ocean as the lower reservoir. This allows a greater potential availability of suitable sites. Capital costs are estimated to be 15% higher than conventional pumped hydro due to corrosion increasing the cost of the pump turbine. However the short pipeline length can reduce pumping losses ( IEA, 2009).

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

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

Given Scotland's extensive coastline there may be potential for this form of pumped hydro. The head for conventional pumped hydro is typically several hundred metres. Hence while Scotland has a coastline with extensive areas of cliffs, there may be potential for this form of pumped hydro at a limited number of locations.

A potential application would be to located seawater pumped hydro in conjunction with offshore wind or wave and tidal installations. This application would entail:

  • Location of seawater pumped hydro at the landfall for cables from offshore wind, wave or tidal generation.
  • Operation of the seawater pumped hydro to average out the peaks and troughs of offshore generation.
  • Net output from the offshore generation would be less variable.
  • Less investment required for transmission capacity to accommodate the offshore generation.

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

There is discussion currently underway in Ireland looking at the concept of several large seawater pumped hydro plants. The concept being promoted by Spirit of Ireland is looking to flood up to 5 large glacial valleys that meet the sea on the west coast of Ireland. As reported by the Irish Times discussions are underway with the Department of Communications, Energy and Natural Resources. Spirit of Ireland have estimated that each site would be in the order of 750-1000 MW. Installing 2-3 of these plants together with increasing wind power would allow Ireland to become energy independent, installing further sites would allow export to the UK grid (Sprit of Ireland and Irish Times, 2010).

Adjustable speed pumped hydro: the rotational speed of the turbo impeller and the pumping head determine the input of the pump turbine and hence the pump output. When operating at a certain pumping head a single speed motor cannot vary the input and hence the pump output is also fixed. An adjustable-speed turbine can in contrast vary the input and thereby enable it to follow the variable generation output from wind, wave and tidal generation. A number of adjustable speed pump hydro systems are in use in Japan, with output over 300 MW ( IEA, 2009).

Underground pumped hydro: The lower reservoir is comprised of artificial underground tunnels. The upper reservoir could be a natural lake or the sea meaning these tunnels are filled with freshwater and seawater respectively depending upon the location. This design expands plant location choice as well as minimising ecological impacts.

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

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

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

Pumped Storage-summary

Storage Capacity

£/kW capacity

Power rating

Efficiency

Technology status

Technology lifetime

<1,000 MWh

£500-2,000

100-5,000 MW

70-79%

Mature

> 20 years

3.1.2 Compressed Air Energy Storage ( CAES)

Technical summary: CAES is a technology that uses energy storage as a means to improve the efficiency of a gas fired power generation. CAES works by storing a volume of compressed air in an underground cavern. It is essentially a variation of a combined cycle 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 for a CCGT.
  • Waste heat is recovered and heats the recovered compressed air.

The compressed air improves the efficiency of the CCGT and allows up to a 60% reduction in gas consumption compared to a conventional CCGT. The schematic diagram below gives an indication of a CAES layout.

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

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

A weakness of conventional CAES is the efficiency of the compression process. Compressed air contains heat and this is removed prior to storage, reducing efficiency. Several alternative designs have been considered which recover the heat in the compressed air.

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

CAES units can be operational within about 14 minutes. Unlike other storage technologies, the use of natural gas means that additional CO 2 is produced by this form of storage technology. In principle, 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 is significant interest in this technology in the USA with several locations being considered. The largest is the Iowa Stored Energy Park at 2,700 MW. This is being developed in conjunction with a large wind farm. Excess wind generation will supply the electricity for the air compression. At this stage the plant is estimated to come online in 2011 although delays have been experienced to date and construction has yet to start.

Scottish context: There are no sites developed in Scotland at present. One site is currently being considered in Northern Ireland (Energy Saving Trust, 2009). CAES faces a similar issue to pumped hydro in terms of its geographical constraints. A suitable storage cavern is dependent upon rock mines, salt caverns, aquifers or depleted gas fields. The British Geological Survey ( BGS) was consulted as part of this study regarding the suitability of sites in Scotland. This clarified that Scotland ,unlike parts of England, has no natural salt caverns. Other possible options are abandoned coal mines below a certain depth, hard rock caverns or deep aquifers. Other gases, such as LPG are stored in chalk caverns in Humberside. The BGS believes that there could be merits to investigating the suitability of deeper abandoned coal mines particularly in the Central Belt of Scotland. Interest in CAES is developing in Scotland and a compressed air for renewables event was held in February 2010 at Edinburgh University. A summary of the discussions from this event can be found in Appendix 2 of this report.

CAES summary

Storage Capacity

£/kW capacity

Power rating

Efficiency

Technology status

Technology lifetime

100-1,000 MWh

£500-600

5-300 MW

70-79%

Mature

20-40 years

3.1.3 Cryogenic Energy Storage

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

Global Status: This is new technology and as such is largely being explored in the academic area (Chen et al 2009). There are no installed full scale examples at the time of writing.

Scottish context: A UK based company, Highview Power Storage are currently developing a 500kW, 2 MWh prototype to be installed near London which is due to be tested this year. Full scale commercial deployment at 3 MW size is planned for 2012 (Highview Power Storage, 2010). As stated above under the global status this is a developing sector primarily being investigated 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)

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

Cryogenic storage summary

Storage Capacity

£/kW capacity

Power rating

Efficiency

Technology status

Technology lifetime

10-100 MWh

£250-500

500kW-10 MW

40-50%

Prototype testing phase

20-40 years

3.2 Advanced battery systems

3.2.1 Flow Battery

Technical Summary: Flow batteries function through the store and release of energy via a reversible electrochemical reaction between two electrolytes. There are several types of flow battery with varying electroactive species; Vanadium redox battery ( VRB), zinc bromine battery (ZnBr), Polysulphide bromide battery ( PSB) and cerium zinc being the most common. VRB appears to be the most advanced with the key benefits being full discharge and recharge without reducing the life expectancy.

Global status: There are several VRB systems installed as backup solutions often in remote areas. In Kenya a small 5kW solution has been installed by a telecoms company and been running successfully (Winafrique, 2009). At the larger end of the scale in Sapporo, Japan a 4 MW system (6 MW pulse) has been running since 2005 with over 14,000 cycles completed (Holzman, 2007). In general progress appears to have stagnated over the last couple of years, with no significant installations taking place on the back of earlier good promise.

Scottish Context: Some research on flow batteries is progressing in the UK, the Technology Strategy Board are currently funding two flow battery projects. Scottish Power are involved in one of the projects entitled 'Development of Redox Flow Battery for Utility Energy Storage', this is being led by ESD Ltd. A second project looking a redox flow batteries is led by C-Tec Innovation Ltd. Both of these projects are small scale trials but intend to be developed to a larger scale if successful. Plurion, based in Fife are developing flow battery technology. Their flow battery is based upon cerium-zinc electrolyte. Plurion are currently 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 zinc bromide flow batteries. SSE have since installed and successfully commissioned a 100kW (150kWh) demonstration flow battery which is being tested at its Nairn substation. This installation is being used to examine wind balancing and energy arbitrage based upon trial data. ( SSE, 2009b).

In Ireland, a Vanadium Redox battery was planned in association with the second phase of the Sorne wind farm. This was due to be a 2 MW x 6 hour system supplied by VRB Power Systems. This project is unlikely to proceed and VRB filed for insolvency late in 2008. The assets of VRB Power were acquired by a Chinese based company Prudent Energy in early 2009. They have now taken on the VRB technology and are looking at new opportunities. Flow batteries have been identified in the technology review as being one of the technologies that has potential in either energy storage or power quality applications. This is discussed in section 6.4.

Flow Battery Summary

Storage Capacity

£/kW capacity

Power rating

Efficiency

Technology status

Technology lifetime

1-10 MWh

£1000+

5kW-4 MW

80-90%

Immature, a few examples worldwide

14,000+ cycles

3.2.2 Sodium sulphur (NaS) Battery

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

Global Status: NGK insulators Ltd state that there has been over 300 MW installed, a significant proportion of these are in Japan. One large installation of 8 MW is at the Hitachi parts plant in Japan. NGK have recently installed a 34 MW battery in conjunction with a 51 MW wind farm at Rokkasho, Japan, this became the largest wind and storage scheme in Japan (Smart Grid News, 2009).

Scottish context: there are limited applications in Europe, with no known examples in Scotland or the UK. Enercon in Germany have installed a NaS system in conjunction with a 6 MW wind turbine. Younicos in Germany are also testing a NGK 1 MW NaS battery at their site in Berlin, They are feeding in real time solar PV and wind data from Graciosa in the Azores to mimic the requirements 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

£/kW capacity

Power rating

Efficiency

Technology status

Technology lifetime

1-34 MWh

£1000-£2000

50kW-34 MW

80-90%

Immature, a few examples worldwide

2500 cycles

3.2.3 Lithium Battery

Technical summary: Lithium batteries are electrochemical cells and similar to other advanced battery systems. The main advantages they offer are the high energy density and almost 100% efficiency. However, to date the main obstacle to overcome has been the cost especially for larger batteries. There are also some safety considerations to address relating to igniting or exploding through short circuiting.

Global status: Main application is in the portable battery sector where lithium batteries command over 50% of the small portable devices market. At the larger scale the developments the maximum size in development is around 100kW. Li-ion batteries require cobalt as a material with three countries (Congo, Zambia and Australia) accounting for 56% of production. Future deposits are concentrated in Congo, a politically unstable country ( IEA, 2009).

Scottish context: Scotland has a number of companies in the lithium battery market. Axeon in Dundee produce lithium batteries for electric vehicles, motive power and power tools. ABSL in Thurso develop and manufacture specialist lithium batteries for military, space and other applications. A relevant UK example that has potential transferability to Scotland is a trial by EDF Energy Networks at Martham substation in the East of England. In an area of high wind penetration they are demonstrating a SAFT Li-ion battery to provide 600k VA automatic voltage control (Price 2010).

Lithium batteries summary

Storage Capacity

£/kW capacity

Power rating

Efficiency

Technology status

Technology lifetime

1-10 MWh

£1000-£3000

0-100kW

99%

Mature portable market

10,000 cycles

3.2.1 Other Battery Types

The following batteries, metal air, lead acid, nickel and super capacitors have been included in the technology inventory however their potential for application as energy storage technologies in Scotland is somewhat limited. With the exception of super-capacitors the other batteries are all mature technologies that have limited technology lifetime (in terms of discharge cycles) and contain toxic materials. The review has found no significant evidence of these technologies being further developed globally or within Scotland and therefore providing significant as yet unknown technological advances are made these technologies can be discounted from addressing the intermittency challenge in Scotland. Super-capacitors have great future 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 and air as the oxidant. They are very compact and one of the least expensive batteries, however they offer limited recharge potential with efficiency lying around 50%. The cost should be viewed with caution as the lifetime of the batteries will be much shorter than other options.

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

Metal air battery summary

Storage Capacity

£/kW capacity

Power rating

Efficiency

Technology status

Technology lifetime

0.1-1 MWh

£100-£250

1-10kW

40-50%

Mature

100-300 cycles

3.2.3 Lead Acid Batteries

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

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

Scottish context: Limited future applicability, Lead-acid batteries niche market is more focussed upon power quality, UPS and spinning reserve applications. The poor technology lifetime through limited number of discharge cycles means that on sustainability grounds it will probably be unsuitable.

Lead-acid batteries summary

Storage Capacity

£/kW capacity

Power rating

Efficiency

Technology status

Technology lifetime

40 MWh

£250-500

10 MW

70-90%

Mature

500-1000 cycles

3.2.4 Nickel battery

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

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

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

Nickel Battery summary

Storage Capacity

£/kW capacity

Power rating

Efficiency

Technology status

Technology lifetime

1-10 MWh

£500-750

1-27 MW

80-90%

Few large scale examples worldwide

2000-2500 cycles

3.2.5 Super-capacitors

Technical summary: Super capacitors utilise a simple approach with which to store energy this being within an electric field between two charged plates. They can be charged and discharged very quickly, i.e. split seconds. Super capacitors modify the above system with a greater electrode surface area, liquid electrolyte and polymer membrane. Super-capacitors are suited to power quality (or short term storage) due to their high energy dissipation.

Global Status: Growing rapidly in the automotive sector, deployed in systems such as regenerative braking which can reduce overall emissions. They are generally used in short term storage applications.

Super-capacitors summary

Storage Capacity

£/kW capacity

Power rating

Efficiency

Technology status

Technology lifetime

>0.1 MWh

£500-750

0-300kW

90-95%

Developing in transport applications

50,000+ cycles

3.3 Mechanical Systems

3.3.1 Flywheels

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

Global status: Modern flywheels as described above are primarily being developed by a number of companies one leading player being Beacon Power Corp. They have recently attracted a $43 million conditional loan and a subsequent $24 million smart grid stimulus grant from the US Department of Energy (Beacon Power Corp, 2010). They are installing a 20 MW system near New York which will earn revenue by providing grid frequency regulation, further plants are planned across the US. In Japan, the Okinawa Electric Company and Toshiba have developed and installed a 23 MW system to provide frequency regulation. Operating since 1996 the system has contributed to good frequency control on a small grid in a situation on a small grid where frequency control is very sensitive ( IEA, 2009).

Scottish context: Would have potential applications to support short term frequency fluctuations from wind farms which could enable a greater availability and improve grid stability. The review found that there is limited if any work on advanced flywheels in Scotland or the UK.

Flywheel summary

Storage Capacity

£/kW capacity

Power rating

Efficiency

Technology status

Technology lifetime

0.1-10 MWh

£500-750

0-20 MW

80-90%

Immature, few plants under 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 magnetic field within a cooled superconducting coil. This coil is cooled to beyond its super conducting temperature (-269°C). At these temperatures limited electrical resistance mean high efficiencies of up to 97% can be achieved. The present maximum size is 10 MW but the estimated theoretical potential is 2000 MW (Imperial College, 2003).

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

Scottish context: in its current form SMES is useful as a power quality application to industrial users. Potential developments at the large end of the scale would have potential. Should large scale SMES be developed the magnetic field at this scale may cause local environmental issues. As seen from the global status projections this could be a highly useful technology in the future but probably not for at least another 30-40 years due to the significant scientific advances required.

SMES summary

Storage Capacity

£/kW capacity

Power rating

Efficiency

Technology status

Technology lifetime

1-10 MWh

£250-500

1-10 MW (potentially hundreds of MW)

<90%

Immature, few power quality applications

100,000+ cycles

3.5 Hydrogen for energy storage

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

Due to the energy efficiency of the electrolysis - hydrogen - fuel cell conversion, hydrogen technologies will require significant cost reductions to occur before large scale deployment is undertaken (Pew Centre, 2009).

Global Status: This is new technology which is being demonstrated at the pilot / demonstration scale. Work is being undertaken internationally with projects being demonstrated in Norway (Utsira); Canada (Ramea) (Oprisan 2007) and several projects currently being undertaken in the UK (the HARI project in Loughborough, the Yorkshire hydrogen project and several Scottish projects (see next section)). To our knowledge there are currently no large scale demonstration projects with research and development focussing on hydrogen storage and the integration of hydrogen with renewable energy. Integration demonstration projects are small scale and typically utilising less than 100kW of installed wind capacity. However the International Energy Agency has commissioned Task 24: Wind Energy and Hydrogen Integration to investigate hydrogen storage as a means of integrating wind energy.

In relation to storage, research and development is focussing on improvements in liquid storage and storage as a compressed gas. Research is also investigating solid state storage in a variety of materials including chemical and metal hydrides and activated carbon.

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

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

  • Berwickshire Housing Association h-5 ecohome generates hydrogen through a 4.5kW electrolyser from surplus wind and solar electricity generated on site. This hydrogen is then reconverted to electricity through a 5kW fuel cell (Berwickshire Ltd, 2009).
  • The PURE Energy Centre generates hydrogen from on-site wind which is then used as either a transport fuel in a fuel cell/ battery hybrid vehicle or reconverted to electricity through a fuel cell ( PURE, 2010).
  • The Hydrogen Office is incorporating a store for 30kg of hydrogen under pressure. The hydrogen will be generated from surplus electricity from an on-site wind turbine and reconverted to electricity through a fuel cell (The Hydrogen Office, 2010)
  • H2 SEED hydrogen is being produced by the electrolysis of water operated by electricity from the anaerobic digestion of municipal 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-site wind turbines. The hydrogen is being stored in "K" type cylinders for use in the college's hydrogen laboratory.
  • Wind Hydrogen Limited ( WHL) have proposed developing a 48 MW wind farm and a 5 MW hydrogen generation scheme in Ayrshire. The hydrogen generation plan gained outline planning consent in 2009, however the wind farm was refused outline planning consent.

The projects at the Berwickshire Housing Association, H2 SEED and Lews Castle College were supported by funding from the Scottish Government through the Renewable Hydrogen and Fuel Cell Support Scheme which operated between December 2006 and March 2008.

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

The Technology Strategy Board have announced that they will be launching a competition for funding in the fuel cell and hydrogen area during 2010. This will provide £7 million of government funding to 15 projects in the stationary power and transport markets under the Fuel Cells and Hydrogen Demonstrator Programme (Energie Bulletin, 2010).

Hence there will be further opportunities to develop hydrogen demonstration projects similar to the small scale pilots and demonstrations that have already taken place in Scotland. Significant know-how and lessons were learnt in the earlier demonstrations. Hence a further round of projects could capitalise on this and establish in more detail the role of hydrogen as an energy storage technology for the island and small communities that are common in Western and Highland Scotland.

Hydrogen Summary

Storage Capacity

£/kW capacity

Power rating

Efficiency

Technology status

Technology lifetime

1-10 MWh

£1000-£2000

5kW-5 MW

40%

Small scale examples

1000+ cycles