The need for energy storage
The Department of Enterprise, Trade and Investment (DETI) is responsible for energy in Northern Ireland and recently published the Strategic Energy Framework 2010 (SEF 2010) outlining energy policy going forward to 2020. This identified four key energy goals of building competitive markets, ensuring security of supply, enhancing sustainability and developing Northern Ireland’s energy infrastructure.
Energy storage has a primary role to play helping to ensure security of supply but also has the potential to enhance sustainability.
Northern Ireland is heavily dependent on imported fossil fuels to meet its energy requirements in the power, heating and transport sectors. Although the SEF 2010 sets a target of producing 40% of Northern Ireland’s power from renewable energy sources by 2020, and there are proposals to meet 10% of heating needs by the same year, this strategy still assumes that fossil fuels will make up the greater part of Northern Ireland’s energy mix for years to come.
The SEF 2010 recognises the vulnerability of the energy network in Northern Ireland and across the whole island of Ireland to interruptions in the supply of imported gas, oil or coal. Although primarily developed by the private sector as a means of making profits from the price fluctuations in the wholesale gas market, underground gas storage has the potential to establish strategic reserves of gas that would reduce the impact of short term interruptions to the supplies of imported gas.
Compressed air energy storage (CAES)
Compressed air energy storage (CAES) is a technology whereby excess electricity (produced at times of low demand) can be used to compress air which is pumped into underground storage facilities. This compressed air can then be released to the surface to generate electricity when demand is high. CAES may be particularly useful when used in conjunction with wind power generation where the peaks of electricity supply and demand may not coincide
Worldwide use of underground gas storage and CAES
Gas and other forms of energy can be stored underground in a range of manufactured or engineered geological environments. These include depleted oil or gas fields, aquifers, salt caverns, lined rock caverns and abandoned mines.
In particular, salt caverns provide potentially secure environments for the containment of materials that do not cause dissolution of salt, such as natural gas. Salt caverns have been used to store liquefied petroleum gas (LPG) for many years but an increasing number of natural gas stores have been developed worldwide in the last 50 years. Although there have been several high profile disasters in the USA these have resulted in improved designs and this type of gas storage has a much better safety record than similar surface facilities.
The caverns are developed by drilling a well into a salt dome or bedded salt sequence and then leaching out the salt by the controlled circulation of water down into the salt and back up to the surface as a brine solution. In this way the shape and size of the cavern can be accurately controlled and matched to the depth and thickness of the salt and the maximum operating pressure.
Thick halite deposits, found both onshore in Northern Ireland and immediately offshore in the North Channel, offer potential for salt cavern storage facilities. The salt deposits occur as bedded deposits with minor halokinesis (geological movement of salt) forming salt swells rather than pillows or domes so that the height of any cavern may be restricted by bed thickness. Pure salt beds tend to be thin (approximately 100-250 metres maximum thickness) compared to those used elsewhere and the presence of significant insoluble impurities and minor intrusive dolerite dykes or sills may reduce their suitability.
The Larne and Carrickfergus area of County Antrim is the only part of the whole island where thick salt beds occur. Elsewhere in the UK parts of Cheshire, Lancashire, Teesside, Humberside and Dorset have similar, or thicker, developments of salt beds and gas storage facilities are either in construction, or are already in operation.
GSNI and BGS scientists carried out a review of the geological storage potential of Northern Ireland on behalf of DETI and this report is available for download.
Further investigations into the potential of Permian and Triassic salt beds for underground energy storage has been undertaken both by the private sector and by the Northern Ireland Government.
BGS obtained funding from the Research and Demonstration Programme within DETI’s Energy and Renewable Energy Fund (EREF) and later under the Chancellor’s Innovation Fund to carry out further studies of the energy storage potential of the salt beds onshore and offshore Northern Ireland.
These included a major study of the offshore salt bed potential, to complement the private sector studies into the salt beds in Larne Lough and the onshore Larne area.
The results of this study which included new seismic reflection and multibeam sidescan sonar data acquisition are available for download below: