Go anywhere in the United Kingdom, drill down a thousand or two metres and you have temperatures hot enough to boil water. And if you can get that hot water to the surface you can use it to generate electricity or heat buildings. The British Geological Survey has conducted research into the geothermal characteristics of the U.K. and can provide much useful information for developers wishing to exploit this resource. For example, they have produced a 3D map of subterranean Glasgow. This data has been interpreted from records of 50 000 boreholes in the Glasgow area, coupled with details of mines dating back to 1839 and brought together with other data to produce the 3D model. This 3D model, including mine layouts can be used to predict where all the hot spots are.
An assessment of the potential for geothermal energy in the U.K. was carried out by Sinclair Knight Merz (SKM), a global consultancy firm with extensive experience in geothermal energy with numerous projects in about twenty countries. Their study indicated that U.K.has the potential to produce 100 gigawatts of geothermal power with the possibility of accessing up to 4% by 2030.
There are two principal methods of geothermal energy extraction. The simplest being direct injection of water down one borehole where it filters through the rock being heated on the way to a second borehole which recovers the water under pressure to the surface. This may be assisted by a process similar to fracking where the injection under pressure opens the natural fractures in the rock so water can pass though. This method is used where the water returns at a temperature of around 150ºC (or more) as steam and passes through a turbine to produce power.
Where the geology is only at around 100ºC the hot water is brought to the surface where it is passed through a heat transfer system to heat a refrigerant like liquid which has a low boiling point. The refrigerant vapourises and this vapour is used to drive the electrical turbine, cooling back into a liquid as it does so which is reused. This method is called a Binary Geothermal System.
At shallower depths the temperatures are not so high however these level are still ideal for HVAC applications.
Cornwall is reported as having the hottest geology in the U.K. and so is the site of several geothermal projects. Most notable amongst them is the Eden Projects proposal, in conjunction with Cornwall-based EGS Energy, to install a 3-4MW geothermal power plant on the Eden Project site. It is proposed that this project will supply all the power needs of the Eden project as well sufficient additional power to supply up to 4000 homes. In the Midlands GT Energy has signed a Memorandum of Understanding with E.ON UK to develop five new deep-geothermal projects around Manchester.
Several other projects have received Government funding in recent years, such as;
- United Downs near Redruth, Cornwall – £1.475m in 2009
- Eden Project near St Austell, Cornwall – £2.011m in 2009
- Southampton City Centre – £200,000 in 2010.
- Eastgate in Weardale, County Durham – £461,000 in 2009
- Science Central site, Newcastle City Centre – £400,000 in 2010
Deep geothermal power is not without its difficulties. Injecting water under pressure is not unlike fracking and does cause further fracturing of the geology which raises concerns about the effects of the process on groundwater for domestic purposes. Though the injected water does not contain chemicals as used in oil or gas fracking, it is not well understood exactly what effect this process has on the geology.
Of course the best geothermal comes from the hottest ground and that means drilling deeper, but, the further one drills the greater the problems with the drilling process. Steel become more brittle at higher temperatures and the process of drilling more expensive the deeper you go. At some point the expenses returns outweigh the returns, at least in the shorter term. Very deep wells may not produce the ROI expected by investors in the time frame investors like to work with.
Be that as it may, geothermal does provide an new horizon for development in the future. The Department of Energy and Climate Change (DECC) in their 2050 Pathways predict that geothermal could supply 35TWh, or 10% of the U.K’s annual electricity demand.
Geothermal potential is definitely there, let’s start using it.
(Image courtesy of Raya Group Australia.)