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Hot Granite In The NE Has Geothermal Potential

Scotland’s first geothermal power station could be built near Aberdeen

Aberdeen’s fabled  granite bedrock could become the North-East’s newest energy source. Scientists believe that suitably high temperatures exist several miles underground in the so-called ‘Energetica’ development corridoor between Aberdeen and Peterhead, and also in other locations near Inverurie and Stonehaven.

Geothermal power station in IcelandNormally the temperature four miles underground would be about 150deg C, but granite holds the heat longer. According to geologists this may be accounted for by radioactive minerals within granite giving  off heat as they decay. This means that temperatures as high as 210deg C could be found at these depths – and of course the North-East has the drilling technology available locally  to reach this hot rock.
 
A major study is now being set up, funded by Scottish Enterprise, to look into the possibility of building a test plant somewhere  between Aberdeen and Peterhead. The geothermal power plant would be part of the Energetica project, which is  designed to help consolidate  Aberdeen City and Aberdeenshire’s position  as a global energy hub by creating a 30-mile corridor between Aberdeen and Peterhead which will be home to  energy technology companies, housing and leisure facilities.   
 
Energetica project director Sara Budge said:

“As part of our quest to make Energetica a world-class, all-energy destination, we are exploring various avenues for generating renewable energy in the corridor which stretches north from the Bridge of Don up to Peterhead and west to Aberdeen Airport.
 
“Geothermal is one source we are considering. We have just issued a tender to appoint an appropriate organisation to undertake a feasibility study into the potential for geothermal heat generation within Energetica but also in other locations across Aberdeenshire.”

LINKS

Scotland’s Geothermal Energy Potential 

Energetica

 

Scotland’s Geothermal Energy Potential

The Potential for Exploiting Geothermal Energy in Scotland

(This article is written by Dr Ed Stephens, Senior Lecturer at the University of St. Andrews, and reproduced with his kind permission)

BACKGROUND

Effectively limitless quantities of geothermal energy are contained within the Earth’s crust. If this energy could be could be accessed and exploited at economic cost all current demands for heat and power could be supplied by one of the cleanest available sources of renewable energy. This goal is beginning to be realised but full exploitation of this resource in Scotland is some way off.

This website explores the possibility that Scotland, with its highly varied geology, has the potential to exploit geothermal energy as a sustainable and near-zero carbon source of heat and power. A multi-billion dollar geothermal industry has grown from nothing in Australia in less than a decade. Germany, with similar geothermal potential to Scotland, has more geothermal projects are under development than anywhere else in Europe. It has made leadership in geothermal energy a strategic objective and is rapidly developing expertise and new technologies for local implementation and export. There are opportunities for Scotland to join the leaders in developing geothermal energy by applying its advanced drilling technologies and utilising the geological and engineering skills of its petroleum industry.

SCOTLAND’S RENEWABLE ENERGY TARGETS

Scotland’s target of deriving 100% of its energy from renewable sources by 2020 is among the most ambitious in the world. Scotland’s 2009 Renewables Action Plan identifies bioenergy, hydro power, hydrogen, offshore and onshore wind, and marine energy as the main foci for development, and the Action Plan makes no mention of geothermal energy, nor indeed does the National Conversation debate on the political context for the future of energy in Scotland. This is not surprising as historically the contribution of geothermal energy to Scotland’s energy needs has been negligible and until recently no evidence has been advanced that it may play any greater role in the future. Indeed the Royal Society of Edinburgh’s report on Energy in Scotland (2006) deemed the nation’s geology to be unsuitable for geothermal energy. This web site presents several lines of new evidence to suggest that it might be timely to revisit that conclusion.

DIVERSITY OF GEOTHERMAL ENERGY SOURCES IN SCOTLAND

Although we have no active volcanoes in Scotland we do have a rich diversity of geological formations, some of which may host useful geothermal resources. Shallow ground sources of heat such as soils, ponds, shallow boreholes etc. extracted using heat pumps are not considered here, although the uptake of this simple but effective technology in the UK has been very limited compared with most EU countries with similar climates, and greater roll-out could make a very significant contribution to meeting targets for renewable heat.

This site focuses on deeper and larger sources of geothermal energy in the form of heat contained in hot rocks at depth, hot waters trapped in sedimentary aquifers or co-produced at rigs while oil is extracted, and water in disused coalmines. Each is examined from a Scottish perspective, and the brief summaries below are linked to more detailed descriptions on other pages of Dr. Stephens’ website.

1. HOT FRACTURED ROCKS (HFR)

All rocks get hotter with depth and there is now intensive research into artificially stimulating fractures to create permeable pathways to access this heat in large volumes of rock at >200°C, typically at depths of 4-5 kilometres in the crust. In such hot fractured rock (HFR) or hot dry rock (HDR) systems cold water is pumped along fractures at depth and recovered as steam which is then passed through a conventional steam turbine for power generation. Such systems, generically termed Enhanced (or Engineered) Geothermal Systems (EGS), extract heat originally generated in rock by radioactive decay and accumulated over millions of years. Almost invariably the rocks are granitic and some bodies of granite in the east of Scotland appear to be good candidates for EGS. Evidence is presented to show that this resource may be much more promising for EGS than previously thought.  More information …..

2. HOT SEDIMENTARY AQUIFERS (HSA)

Groundwater is extracted from shallow aquifers in Scotland principally for agricultural purposes. Where these aquifers reach depths of >2 kilometres they may contain useful and exploitable heat, as demonstrated by the successful combined heat and power plant in Southampton city centre where water at 76°C has been extracted continuously since the 1980s from a 1.8 km deep borehole into an aquifer below the city. There are probably rock formations 2-3 km deep in the Midland Valley of Scotland that have aquifer geothermal fluids close to 100°C and depending on location, temperature, flow rates as well as other factors these may well be capable of providing heat, and possibly power, to the Central Belt.  More information …..

3. OIL-GEOTHERMAL CO-PRODUCTION (OGCP)

Typically 10-20 barrels of hot water are recovered with each barrel of oil extracted. This hydrothermal fluid is normally discarded but on-rig experiments currently being conducted in the USA are converting this energy into electrical power even when the fluid is not hot enough to produce steam. Although still at the development stage it is conceivable that far offshore in the North Sea such co-produced energy could be used to power rigs, thus saving significant emissions from diesel power units, whereas closer to shore in the Inner Moray Firth it might even be practical to feed excess power into the grid. The technology is being developed as bolt-on modules easily retrofitted to rigs.  More information …..

4. MINEWATERS IN DISUSED COLLIERIES

The Central Belt of Scotland has many flooded coal mines and water in some of the deeper reaches the can approach 40°C. These minewaters contain a potentially useable thermal resource, indeed many have to be pumped for environmental protection and the heat is presently discarded. The resource within Scotland’s disused collieries has been calculated at 300 MWth although not all this could be realised as demand is not always located close to the mines. An independent survey [1] suggests that up to 3% of Scotland’s total heat requirements could come from this source, i.e. approximately a quarter (27%) of the 2020 renewable heat target. While other factors would reduce this figure given that only 1.4% of heat demand is currently met from renewable sources it would be timely to reinvestigate minewaters as a source of renewable heat in some coal mining districts of the Central Belt. More information …..

SEASONAL THERMAL ENERGY STORAGE (STES)

These pages are concerned primarily with exploiting heat resources in rocks, however the same geological conditions, particularly aquifers, can also be used to store excess heat until it is required. Conventional power generators and industrial processes often produce large quantities of excess hot water that in summer could be pumped into aquifers or disused mines and stored until it can be recovered for use in winter. STES is an established technology. In the Netherlands around 700 systems are currently using aquifers to store waste heat in the summer, principally to support office and domestic heating in winter, and some 50-100 new STES systems are added each year. Deep coal mines may also be useful in this context.

WHAT ROLE COULD GEOTHERMAL ENERGY PLAY IN SCOTLAND?

Even if we only exploit the easily accessible resources that have already been identified, i.e. the heat available in disused collieries within the Central Belt, up to a quarter of the 2020 renewable heat target could be met. At the other end of the spectrum if we locate some hot granites buried a few kilometres under our sedimentary basins and efficiently exploit their heat then there is potential for generating 10s-100s MWe, possibly even GWe of baseload power. In this event geothermal energy might rival wind power in contributing to renewables targets, but with the advantage of supporting baseload independent of weather conditions. Almost inevitably the future will lie somewhere between these scenarios.

Geothermal systems are generally non-polluting, carbon-free and long-term energy resources. Their physical and environmental footprints are small and are unlikely to impact negatively on important but environmentally sensitive industries such as tourism. Similarly, storage of waste heat in aquifers beneath the Central Belt could contribute to emissions targets.

The Australian experience of geothermal energy has been remarkably positive. A new industry has been stimulated by technological developments and the creation of new economic activity in the pursuit of greener energy. In just a few years several tens of new companies (including many start-ups) have become involved in applying the EGS and HSA concepts and exporting their technologies beyond Australia. Many of the key skills for developing geothermal energy already exist within Scotland’s petroleum industry, for example modelling heat flow and thermal histories of basins, geophysical and structural characterisation of deep geology, and drilling & reservoir engineering technologies.

Scotland is committed to developing wind and marine sources of energy where the resource is clearly immense, and to gaining leadership in related technologies. Notwithstanding, Scotland has an opportunity to join the leaders in geothermal energy while also using the available resource to meet its renewables targets. These aims need not be mutually exclusive.

A WAY FORWARD

It is argued here and on the linked pages that Scotland’s geology has a high potential for hosting significant reserves of geothermal energy. The types of geological setting most favourable for exploitation are reasonably well known but no specific location in Scotland has yet been identified. A programme of research is required to identify the best locations in relation to the local heat and power demands and infrastructure. Particularly important is a more complete characterisation of Scotland’s continental crust down to 5 kilometres, especially in the Midland Valley. Such characterisation is within the capability of Scotland’s academic and research institutions and a collaborative study could contribute significantly to aspirations for new energy sources and environmental protection. Examples include geothermal energy; storage of heat, natural gas and fluids in aquifers; CO2 storage; buried hydrocarbon resources such as coal bed methane, coal for gasification, and oil shales; and the disposal of hazardous materials.

POSTSCRIPT

Scotland’s 19th century wealth was based on power provided by its vast reserves of coal, while North Sea oil significantly bolstered the national economy through the latter part of the 20th century. In the 21st century Scotland’s geology and technological skills may once again bring economic benefits, in part through geothermal energy, but this time in providing solutions rather than causing environmental problems.

Recent investment in large scale geothermal projects by the USA, Germany and Australia means that major engineering advances can be anticipated, bringing down the capital costs and associated risks [MIT report]. As a small country already substantially committed to wind and marine energy Scotland may be unable to participate in making these engineering advances, but it should at least place itself in a position of readiness by establishing what its resources are, and where they are located.

Ed Stephens
University of St Andrews
June 2011