Select Committee on Innovation, Universities, Science and Skills Written Evidence

Memorandum 22

Submission from the British Geological Survey


  1.  The British Geological Survey (BGS) is a component body of the Natural Environment Research Council (NERC) and the UK's premier centre for earth science information and expertise. BGS welcomes the opportunity to contribute to this inquiry.

  2.  Evidence is provided on the current state of UK research and development on five renewable energy-generation technologies:.

    —  geothermal;

    —  hydrogen;

    —  underground storage of compressed air and hydrogen;

    —  tidal; and

    —  wave.


  3.  Geothermal electricity generation is mainly associated with volcanic regions of the world. However, a number of countries have demonstrated that geothermal resources can still be exploited in regions that do not have exceptionally high sub-surface temperatures. Temperatures increase with depth due to the small amount of heat conducted upwards from the deep earth. This results in the geothermal gradient, which has an average UK value of 26°C per km, but locally it can be in excess of 35°C per km. Evidence of these raised sub-surface temperatures is seen at Bath-Bristol and in the Peak District where hot springs discharge at the surface.

Investigation of the geothermal potential of the UK

  4.  In the late 1970s and early 80s the then UK Department of Energy funded a programme to assess the UK's geothermal resources. Deep sedimentary basins where porous, permeable rocks occur at depth were investigated as possible sources of hot water. The total heat-in-place was estimated to be in excess of 300 x 1018 Joules. Hot dry rock (HDR) technology was also examined as part of the geothermal programme. This involves drilling a deep well into crystalline rock, creating a permeable reservoir and pumping cold water, which becomes heated, to a production well. An experiment was conducted at Rosemanowes quarry on the Carnmenellis granite in Cornwall. Three wells were drilled to depths of over 2 km, but the programme came to an end because of the technical problems that needed to be overcome for HDR to have become a viable technology at that time.

Legacy of the geothermal programme

  5.  At Southampton, an exploration well was drilled as part of the geothermal programme and this was developed by the city council and a commercial partner to provide hot water to a district-heating scheme. The city centre scheme is an integrated energy scheme that incorporates geothermal energy and a gas fired Combined Heat and Power (CHP) plant. The scheme comprises 2 MW of thermal geothermal energy, 2 small CHP units, 8 MW of chilled water plant and a 5.7 MW dual fuel Wartsila CHP electric generator.

Developments in Continental Europe

  6.  In the UK research into the utilisation of our deeper geothermal resources ended with the termination of the Department of Energy's geothermal programme in the mid-1980s. However, other European countries with similar sub-surface temperatures to the UK continued their research and Germany, in particular, has encouraged renewable energy generation through legislation and grant funding. There are now a number of power generating geothermal schemes; of particular note are:

    —  At Unterhaching, near Munich in Germany, a 3.5 km deep borehole has tapped thermal water at a temperature of 122°C. This will be used to generate 3.7 MW of electricity and will provide a district-heating scheme with hot water (up to 41 MW(thermal)).

    —  Soultz-sous-Forts on the western edge of the Rhine Graben in north-east France is the site of the European Deep Geothermal Energy Programme pilot project. This is a Hot Dry Rock project where three boreholes have been drilled into crystalline rock to a depth of 5 km. Temperatures are around 200°C and the returned heated water will be used to drive a 6 MW electricity generating plant.

    —  In northern Germany, at Neustadt-Glewe, saline water is extracted from a sandstone aquifer at a depth of 2.3 km. The water is at a temperature of 98°C and has been used for over 10 years for a district-heating scheme. In 2003 a binary-cycle electricity generating plant was installed. This generates 400 kW of electricity, about half of which is used to power the plant and the remainder is fed into the local electricity network. At a temperature of 98°C, this is the lowest temperature in the world for the generation of geothermal electricity.

Research and development in the UK

  7.  The UK currently has no on-going research or development into geothermal electricity generation. However, we can gain from the experiences of others in Europe and North America and with central government finance we could build on the investigations of the 1970s and 80s. There are a number of potential programmes that could be researched:

  8.  Further explore the potential of deep UK aquifers to produce hot water for district-heating schemes and assess the latest binary-cycle generation technologies that may enable such schemes to be self-sustaining and carbon neutral.

  9.  Consider the instigation of another hot dry rock project situated on a suitable radiothermal granite that can take advantage of the technological developments pioneered at other HDR sites.

  10.  Investigate the geothermal potential of the North Sea where many oilfields are coming to the end of their productive lives. These fields have been thoroughly explored and the infrastructure for the extraction of deep, hot brines is already in place. Some of these fields have sub-surface temperatures in excess of 100°C and so electricity generation, especially using binary-cycle technology should be possible. It is unclear, given the high running costs of rigs in deep water, if electricity generation could be economical. However, some rigs could be retained to become multi-purpose platforms for the sequestration of carbon dioxide, as hubs for wind turbines and for geothermal electricity generation.

Iceland as an external supplier of geothermal electricity to the UK

  11.  Iceland is a volcanic region that is near to becoming self-sufficient in electricity generated from its geothermal resources. A research project, entitled "Iceland Deep Drilling Project", is aiming to drill deep boreholes ( into super critical geothermal reservoirs where temperatures are likely to be 400° to 600°C. It is envisioned that these super critical resources could increase power generation ten fold. The UK could import the surplus of Icelandic green electricity through a cable interconnector and thus increase the diversity of UK energy suppliers. As the UK stands to benefit we could offer our expertise in some aspects of the project in order to assist in its realisation.


  12.  Hydrogen is regarded as having great potential for use as a versatile and major energy carrier, being complementary to electricity, and with the potential to replace fossil fuels in what is referred to as a future Hydrogen Economy. It is, however, presently used mostly as chemical feedstock in the petrochemical industry, and in food, electronics and metallurgical processing industries.

  13.  Currently the bulk of hydrogen is made from natural gas, but there may be potential to explore for naturally-occurring hydrogen overseas and in the oceans. Little research has been conducted so far. Sustainably produced hydrogen should be the basis of a low carbon economy, delivering a reduction in emissions of the greenhouse carbon dioxide (CO2) and other atmospheric pollutants, with the associated benefit of security of supply. The use of hydrogen as a fuel and energy carrier will require an infrastructure for safe and cost-effective hydrogen transport and storage. A "green" Hydrogen Economy should include the production of hydrogen and electricity generated fully from sustainable, renewable sources, such as on Unst, NW Scotland. A variety of process technologies can be used, including chemical, biological, electrolytic, photolytic and thermo-chemical.

  14.  There are industrial parks using hydrogen to power buildings, local buses and converted cars on Teesside and the island of Unst, NW Scotland. On Teesside, hydrogen obtained from industrial processes, once obtained, is already stored underground in salt caverns.

Underground storage of compressed air and hydrogen

  15.  Most renewable energy is from wind power which is, of course, dependent on prevailing weather conditions and cannot directly be varied to meet diurnal or seasonal variation in demand. Energy storage, in the form of underground compressed air energy and hydrogen, could help to minimise the temporal mismatch between supply and demand by storing energy produced at times of low demand as compressed air and converting it back to electricity at times of peak demand.

Compressed air storage (CAS) and compressed air energy storage (CAES)

  16.  The potential exists for CAS and CAES of electricity generated from renewable sources such as wind or tidal energy. Electricity is not usually stored as such, but is converted to other forms such as gravitational, pneumatic, kinetic potential (CAS, CAES and hydroelectric facilities), magnetic or chemical energy. Alongside pumped-hydroelectric, CAES is currently the only other commercially available (and economic) technology relying on geological storage and the cheapest, most abundant substances (ie elevated water or compressed air), capable of providing the requirement of very large system energy storage deliverability. However, the scale and location-specific nature of energy storage in natural formations renders it of limited benefit to small scale, local distributed networks and renewable energy generation sites.

  17.  The efficiency of conversion and re-conversion between electricity and the stored energy form of each system ultimately governs the viability of any scheme, but is maximised by generating electricity from storage to meet demand peaks and gain maximum revenue.


  18.  With CAS, compressed air is stored in conventional high-pressure gas cylinders or pressure vessels (generally above ground). Current technological and cost limitations of manufacturing such pressure vessels on the scales required for efficient CAES plants mean that CAS is generally too small to be considered for CAES schemes. Above ground storage systems only become competitive with large underground storage facilities when capacities are limited to short durations of perhaps 3-5 hours supply, which is very small for CAES storage.


  19.  Hydroelectric power plants have, for many years, been used to store excess off peak (night-time and weekends) power and provide increased peak time output. CAES facilities likewise provide the potential to store energy and could be used alongside, for example, wind turbines. Though instances of this technology are not numerous, it is likely that compressed air energy storage will assume a greater importance as energy markets change with time. To date, CAES has been found to be too inefficient and costly for wide spread commercial use by the wind industry, due largely to the energy losses resulting from the requirement to turn two rotational devices—the air turbine and then the generator motor.

  20.  The technological concept of CAES is more than 30 years old with the first CAES facility commissioned in Germany in 1978 using caverns created in the Huntorf salt dome near Hamburg for storage. A second plant near McIntosh in Alabama, USA, was constructed in 1991, and utilises caverns constructed in the McIntosh salt dome. In 2001, approval was granted to develop a CAES plant in an old limestone mine 670 metres (2,200 feet) below ground at Norton, Ohio. Commercial operation was estimated to begin in 2003 and to be fully operational by 2008. Research into CAES is ongoing around the world, with plans to construct a number of CAES plants that will utilise aquifers and former mines. Italy has operated a small 25 MW CAES research facility based on aquifer storage, whilst Israel has conducted research in to building a 3x100 MW CAES facility using hard rock aquifers.

  21.  The basic concept is that during the storage phase, electrical energy (from eg wind energy or excess output of power plants) is used to compress air, which is stored under pressure underground. Storage can be in porous rocks or in large voids, such as salt caverns. Storage volumes required to make CAES plants economic are large, hence above ground facilities are not practicable due to prohibitive costs. The stored air is held until the demand on the grid for energy is such that the compressed air is released through a turbine (it may also be mixed with gas) and connected generator, generating power (electricity) through a generator.

  22.  A CAES power plant is therefore, a combination of compressed air storage and a modified gas turbine power plant. Technical issues surround the heat generated during compression of air, but these are lessening.

  23.  Gaelectric Developments Ltd was awarded a licence in Northern Ireland during 2006 to assess suitability of Triassic halite for compressed air storage. This would represent an important development as there are only two other operational sites in the world. However, there is no Government involvement and development would probably be heavily dependent on German technical expertise.

Future technologies/developments

  24.  In 2003, it was planned to build the Iowa stored energy plant, which would be the first plant to use wind energy, as well as off-peak electricity to compress the air and store it in an underground aquifer. The proposal included building a wind farm, however, following further investigations, the geology may not be as favourable as was originally thought.

  25.  Early in 2005, a Canadian company indicated that it was working on developing a system that will allow wind energy producers to store energy in the form of compressed air in underground steel tanks or pipes, and release it through a special generator to create electricity when it is needed. The wind energy storage system will make use of a Magnetic Piston Generator (MPG), which permits the generation of electricity through conventional wind turbine means when the wind is blowing as well as simultaneously compressing and storing compressed air in a storage facility for release through the MPG when the wind turbine cuts out due to lack of wind.

Public perception of CAES

  26.  Recent planning applications for Underground Gas Storage facilities in England have attracted considerable public opposition. Public safety concerns have been raised by reports of serious but isolated incidents where stored gas has escaped from caverns, particularly in the USA. Such public fears and reluctance to accept underground energy storage options could be important when considering and planning for the renewables sector, eg storage of hydrogen.

Hydrogen Storage

  27.  Hydrogen storage becomes an issue if generation exceeds requirements locally. On Unst, any geological storage would have to be in rock caverns, but this is not yet envisaged. Further potential for storage might be in porous strata (aquifers or depleted oil/gasfields), perhaps with the use of water curtains to maintain the pressure on the formation and prevent outward migration of the stored hydrogen away from the injection site (footprint).

Storage media

  28.  Two basic types of storage facility exist for the storage of renewable energies: salt caverns and lined rock caverns (LRC).

  29.  Underground salt caverns provide potentially secure environments for the containment of materials that do not cause dissolution of salt. Salt cavern storage is based on proven technology and is used throughout Europe and North America and offers options for the storage of liquid (oil, LPG and LNG), natural gas, hydrogen and compressed air. Stable salt caverns are fashioned by solution mining, which involves the injection of water under carefully controlled conditions to create uniform shapes and prevent subsidence. A borehole is drilled into the halite beds and then completed with two or three casings. Fresh or saltwater is injected, which dissolves the salt, producing brine that is pumped up a central casing for subsequent disposal or use (as a chemical feedstock, for example).

  30.  England and Northern Ireland possess major salt deposits and potential to develop salt cavern storage onshore exists in the UK in a number of areas. The salt deposits are of two different ages, being Permian in the NE of England and Triassic in the NW, Cheshire Basin, Worcester, Somerset and Wessex areas. Gas storage facilities already exist in the Triassic salts of Cheshire Basin (Hole House) and Permian salts in NE England (Atwick/Hornsea and Billingham on Teesside) and there are a number of other sites in England currently under development or at the application stages, including those in the Triassic halites of Cheshire (Byley and Holford), Lancashire (Wyre/Preesall) and Dorset (Isle of Portland area). Further facilities are planned in the Permian salt deposits near Aldborough and the currently operational site at Atwick (Hornsea). The onshore salt deposits extend offshore in a number of areas, such as the East Irish Sea and Southern North Sea, where they are generally thicker and could provide nearshore options for development of caverns associated with offshore windfarms.

  31.  LRC provides storage capacities in countries/regions where crystalline and metamorphic strata form the majority of rocks at outcrop and where there is a lack of other suitable geological formations (such as salt deposits or sandstone reservoir rocks) to provide underground storage facilities. The LRC concept has been successfully tested at two sites in Sweden. The main principle relies on a rock mass (primarily, crystalline rock) serving as a pressure vessel in containing stored gas or air at high pressures (15—25 MPa). The caverns are lined with reinforced concrete and thin carbon steel liners, the latter acting as an impermeable barrier to the gas/air. They can be cycled many times per year and thus provide high deliverability.

  32.  Other forms of storage may be possible, such as in porous rocks (aquifers, depleted oil/gasfields) but the two types above are likely to be of more immediate relevance in the UK context.


  33.  BGS has developed seabed drilling technology for site investigation work in areas with high tidal currents and a successful project was recently completed offshore Orkney. The BGS seabed mapping programme collects new data and integrates this with existing third party data to produce better understanding of the seabed, seabed sediments, and sediment movement. These data are critical to understanding the impacts of tidal stream and barrage developments. The data underpins site investigation and is a key contribution to the information required to underpin marine spatial planning. It is directly relevant to marine developments, including all marine renewables, extraction of aggregates and environmental and conservation issues. BGS has recently undertaken mapping surveys in the East English Channel, the Bristol Channel, the Forth, the Clyde, and near Ullapool. BGS works closely with other marine organisations, including CEFAS, JNCC and the devolved conservation agencies, SAMS and the DTI strategic environment assessment programme. BGS has several joint PhD projects on marine geohazards (landslides and tsunamis) and geodiversity and marine habitats.


  34.  The BGS geological mapping programme is directly relevant to site investigation, and research is currently in progress studying sandbanks, their historical evolution and movement and potential for future movement.

July 2007

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