The Role Of Geothermal In Reaching Future Electricity Targets For The UK Stevie Spencer 24 th February 2005

What Is Geothermal? “It’s source is the earth’s internal heat, which originates mainly from the decay of long-lived radioactive elements” Boyle, 2003 This is most useful where close to the surface and easily accessible. For the process to be successful the resource must also be close to a large water supply.

What Is Geothermal? Its reliable! Continuous regardless of the time of day, weather or season. “Geothermal energy is the most extensively used renewable energy worldwide apart from hydropower.” In 2000 “the electrical energy produced was roughly 50,000 GWh per year” Hurter, 2003

How Much Resource Is Available In The UK? A definition of a geothermal resource is “that part of the accessible resource base that could be extracted economically and legally at some specified time in the future” Muffler, 1978 Therefore my projections for the future are an expansion of… 0 MW

Hot Dry Rock (HDR) Two boreholes are drilled. Water is pumped down one of the boreholes. Passes through natural fissures in the hot dry rock. Returns to the surface as superheated water or steam though the second borehole. This can then be used in steam turbines to generated electricity.

Problems With Hot Dry Rock No commercial HDR schemes in existence anywhere in the world. In the UK it would be necessary to drill to depths of 6km. Overall efficiency of conversion is just 3% Local rivers in areas such as Cornwall have insufficient flow rates to support a HDR scheme. Sensitive to unknown deep geology. Department of Energy 1994

Problems With Hot Dry Rock Such a scheme would be very expensive and the electricity generated would not be at a completive price. High risk investment because success is dependant upon geological characteristics and therefore will not be in the interest of the private sector. In July 1993 the closure of the Cornwall HDR program was announced. Department of Energy 1994

Geothermal Aquifers This method uses one borehole. Geothermal aquifers extract the heat from natural ground waters. These are drilled and passed though a heat exchanger at the surface. If the temperature is above 150°C it can be used to generate electricity, below this, as a source of hot water.

What Does This Mean For The UK? The UK has very few sources above 60°C. Larne, Cleethorpes, Marchwood and Southampton are all possible sites

The Southampton Scheme Southampton has developed a scheme using a temperature of 72°C. The project was abandoned by the department of energy but taken up by Southampton City Council and Utilicom. It is a large CHP scheme with district heating for 20 of the city’s major consumers including the local hospital. One fifth of the systems heat input is from the geothermal, the rest from fossil fuels.

The Problems The resource must coincide with the demand as it is not feasible to transport the hot fluids. Uncertainty about the lifetime and productivity of the project due to individual geology characteristics affecting water flow. Care would be required regarding the disposal of the water Many locations need a second borehole to dispose of the fluids (making them environmentally and economically unattractive)

The Problems Disturbance of laying district heating mains in already urban areas. Market penetration may be difficult as it is required to be integrated into the design of local housing. Again a high degree of risk is involved, which is unattractive to private investors.

So To Conclude… Although there are a small number of potential locations they are currently uneconomical. Developments of the HDR may begin to occur by the middle of the century. Heat pumps are often included within the Geothermal banner, but are not. Instead they used energy from the sun trapped in the surface layer of ground and should be classed as an energy conservation measure.

References And Further Reading Boyle G., 2003, Energy Systems and Sustainability – Power for a sustainable future, Oxford University Press Boyle G., 2002, Renewable Energy – Power for a sustainable future, Oxford University Press Department of Energy, 1994, Paper 62 Hurtler S., Schellschmidt R., 2003, Atlas of geothermal resources in Europe, Geothermics, p