Memorandum 22
Submission from the British Geological
Survey
EXECUTIVE SUMMARY
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:.
— underground storage of compressed
air and hydrogen;
GEOTHERMAL
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
(3.5.km) 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.
HYDROGEN
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.
CAS
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.
CAES
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.
TIDAL
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.
WAVE
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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