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Deep geothermal energy
Geothermal energy could supply 20% of UK electricity from around 9.5GW of installed capacity, according to a report by consultants Sinclair Knight Mertz (SKM) for the Renewable Energy Association (REA). Geothermal projects with a 25 year lifetime could also, it claims, support 100GW of heat generating capacity, meeting all UK space heating needs.
There have been some pioneering geothermal heat projects in the UK before, including the aquifer project in Southampton, but the new ‘enhanced geothermal’ technology involves drilling deep wells to access higher temperatures for electricity production. So you are not limited just to aquifer sites, and the deep geothermal resource is widely spread around the UK, with ‘hotspots’ in Cornwall, Weardale, Lake District, E. Yorkshire, Lincolnshire, Cheshire, Worcester, Dorset, Hampshire, N Ireland & Scotland - see below.
Cluff Geothermal’s summary of the UK resource:
Cornwall and the South West HEAT: 13,000 MWth POWER: 4,000 MWe
The North East HEAT: 9,000 MWth POWER: 4,000 MWe
The Lake District HEAT: 8,000 MWth POWER: 2,300 MWe
Wessex Basin HEAT: 33,000 MWth
Cheshire Basin HEAT: 14,000 MWth
East of England* HEAT: 12,000 MWth
Worcester Basin* HEAT: 6,700 MWth
Larne Basin HEAT: 1,000 MWth
*With heat pump.
However, the REA says, despite this significant potential, the UK support is only about half that in Germany and Switzerland. As a result of support in Germany, the deep geothermal industry now employs 6,000 people and has attracted €4 bn of investment. The REA comments ‘We don’t want to be left out of a global industry which is estimated to be worth £30 bn by 2020.’ Although some pioneering ‘hot dry rock’ work was done in Cornwall between 1976 and 1991, it was halted, and the UK government’s current commitment is relatively limited, although there are some projects underway. EGS Energy is developing a 3MWe demonstration geothermal project on a site at the Eden Project near St Austell in Cornwall. It was awarded £2m via the Deep Geothermal Challenge Fund. www.egs-energy.com. Geothermal Engineering Ltd. is planning a plant near Redruth, with a well reaching 4.5km below ground level to access rocks at temperatures of around 200°C. This will provide up to 55 MW of renewable heat and 10 MW of electricity. It was awarded £1.45m in funding by DECC in Dec 2009. www.geothermalengineering.co.uk.
Three geothermal energy projects run by Keele University, Newcastle and Durham University and Cofely District Energy in Southampton are sharing £1.1m from the Government’s Deep Geothermal Challenge Fund’s second round.
Once running, geothermal electricity generation projects are eligible for support under the governments Renewables Obligation scheme, earning Renewable Obligation Certificates (ROCs), but the REA notes that the UK industry ‘has been shocked by initial proposals to freeze support for deep geothermal power at 2 ROCs, a level too low to stimulate domestic investment’. It adds ‘Deep geothermal power is a new technology in the UK and it requires similar support to wave and tidal in its initial development phase.’
The REA claims that the increase in costs associated with raising support for geothermal power to match levels proposed for wave and tidal will be less than £11 million per annum. It says that the support needs for deep geothermal heat are within a similar range to other renewable heat technologies. The REA estimates the additional annual cost of increasing the level of RHI for deep geothermal heat will be £1.3 million.
SKM’s report states that ‘risk reduction support is the most critical in developing a cost effective large utilisation of the geothermal resources in the UK. This is particularly needed to enable the early development of sedimentary aquifers for direct heat use as this offers the potential for the most significant and early contribution to meeting the UK commitments to the EU’s Renewable Energy Directive.’
It claims that a Feed in Tariff level of approximately 300 £/MWh for electrical generation and combined heat and power projects is required to develop these geothermal projects in the UK. This is approx equal to five Renewable Obligation Certificates (ROCs) /MWh. For heat only projects a Renewable Heat Incentive of 30 to 70 £/MWh is needed.
SKM concludes that, with the implementation of its recommended support mechanisms, ‘it should be possible for geothermal energy to provide the UK with a cumulative benefit of 5,000 Giga Watt hours (GWh) of electricity and 32,000 GWh heat by 2030.’
Globally there is over 10GW of geothermal electricity generation capacity in place and much more heat supply capacity. The USA is in the lead, with over 120 new projects under development, at least 5GW, but Germany and Japan now taking geothermal increasingly seriously. Iceland is also a leading user of geothermal energy. Enthusiasts argue that if you go deep enough the power available is almost unlimited, although there are environmental (and cost) limitations. Some early systems vent gasses from underground, which can lead to contamination (e.g. from SO2), but modern closed-loop systems re-inject the extracted water. In some cases, drilling deep wells and opening out heat capturing fractures, can also trigger micro quakes, in much the same way as shale gas fraking, And geothermal energy is not strictly renewable - the local heat gradient will be exhausted after few decades, so new wells in new locations will have to be dug, while the heat gradient at the original site recovers. The ultimate source of the energy is of course nuclear isotope decay deep in the earth’s core, so geothermal is actually ‘natural nuclear power’ and to that extent is replenished. Since, during the wells lifetime, energy can be produced continually, geothermal is a firm source, which could be used to back up variable renewable sources, especially if operated in combined heat and power mode.
*You don’t always have to dig deep to get heat. Excess heat from steel plants could be used feed the already well developed District Heating network in Sheffield, which generates 21MW of electricity and 60MW of heat, providing an extra 20MW of heat. www.theengineer.co.uk/sectors/energy-and-environment/ news/excess-heat-from-steel-plants-could-be-used-to-heat-sheffield/1012592.article#ixzz1v2CLgn9q
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