| Abstract |
It is recognized by virtually every credible organization such the IEA, MIT, IGA etc that the EGS resource might be extensive in regions with appropriate igneous basement, yet it appears that in some instances the assessment of the potential of EGS is being manipulated and degraded to suit political agendas. The data used to quantify EGS potential are much the same regardless of who is making the assessment. Ideally, then, the estimated resource should in principle be relative constant across different assessments, with perhaps minor variation. Additionally, there appears to be misunderstanding between resource and reserve. To quantify the reserve in EGS is going to be difficult as there is no specific boundary similar to that in mineral or hydrocarbon reserve where the resource is locked up in a set boundary. For EGS, the igneous rock could be very extensive and a possible reserve would be the boundary of where the EGS reservoir could be economically created. It is of great concern to see how estimates of EGS resource and reserve vary from one organization’s assessment to another. Take an example of the various studies carried out in the UK. • A study in 1976 estimated that EGS in southwest England could yield the equivalent energy to 8000 million tonnes of coal (ie about 60,000 TWh). Converted into electricity with an efficiency of l0%, this represented a resource of about 5000 TWh(e). • A strategic review undertaken by ETSU in 1982 indicated that the EGS electricity resource might be between 2500 and 60,000 TWh(e) for depths down to 8 or 9 km in the UK. • In 1984, ETSU estimated that the UK geothermal EGS resource could provide 20,000 to 130,000 TWh(e), with a ‘technical potential’ for electricity generation of up to 25 TWh/y (10% of the contemporary UK electricity demand) for about 800 years. • In 1992, MacDonald assessed that with the low thermal gradients that exist in the UK, it was unlikely that EGS would provide an energy source with a wide application. Unless there was a significant technological break-through in an area that cannot currently be foreseen, the costs of generating electricity from EGS in the UK would likely remain uncompetitive with conventional methods by a large margin. • In 2011, Ove Arup & Partners Ltd reviewed the potential for geothermal in the UK based on cost estimates and economic constraints. That review concluded that energy produced by deep geothermal methods is a viable energy source in Cornwall. • Sinclair Knight Merz made a report for the REA in 2012 and concluded that, using today’s technology alone, EGS could provide 9.5 GW of base load renewable electricity and 100 GW of heat for the UK. That equates to 20% of the UK annual average electricity generation capacity. • Atkins wrote a report on geothermal for the DECC in 2013. The report stated that as geothermal power plants do not exist in the UK, no reserves could be defined by the Australian code. The report concluded that the potential for geothermal power was currently difficult to quantify, but tentatively 1 to 1.5 GWe might be argued in the longer term (2050) for the UK as a whole. This equates to 3-4% of current average UK electricity demand (or 1.0 – 1.7% of current UK generating capacity). These wide variations in estimating the EGS resource should be a concern for the geothermal industry in general as potential investors and governments are disillusioned by the lack of sound quantification of the resource. A mechanism needs to be established whereby hydrothermal and EGS resources can be comparatively quantified based on a specific internationally recognized criteria. |