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Hot rods – drilling deep for energy in Cornwall; the KTN view

Posted on 06/11/2018

Drilling has begun in Cornwall by Geothermal Engineering to extract geothermal heat from the granite rocks.

Two wells will be drilled over the next seven months almost three miles deep into the rock near Redruth.  The temperature at that level is up to 200C; cold water will be pumped down to the hot rocks and then brought back to the surface as heated water.  Steam from that heated water drives turbines, produces electricity and can potentially power up to 3,000 homes.

Cornwall sits on top of granite and the heat-producing properties of the rock makes it ideal for extracting geothermal energy.  This looks like the ideal renewable, clean energy.  But is it one of the answers to the UK’s energy problems?  Jenni McDonnell, KTN’s Knowledge Transfer Manager for Thermal Energy Systems, commented: “If the extraction is managed properly the heat produced should continue indefinitely as it is a renewable and baseload source of energy.  It is also, once the site is generating power, emission free as they can use some of the power for operations on site.”

But she sounded a note of caution.  “This type of deep geothermal system can have problems with scaling which can lead to operations being suspended.  In other parts of the world a closed binary system is used to mitigate this issue, using a working fluid within a closed system which absorbs the heat underground and then transfers the heat at the surface using heat exchangers. This has the added advantage of leaving potentially harmful minerals in the ground.”

Jenni’s final query was around the underground reservoir that needs to be created to allow cold water to be pumped in and hot water to be pumped out.  For this to work, there needs to be a fracture system between the wells to allow the water to flow.  Jenni said: “They may need to employ hydraulic fracturing to improve the permeability of the reservoir between the injection well and production well. If this is the case there may be public objections to the fracking as we have seen with shale gas.”

So, whilst geothermal energy could provide some energy for Cornwall, it’s not without its issues.  Jenni is a fan of the process but commented: “Although this type of renewable energy has always been a personal favourite of mine it’s expensive to deploy in the UK because the high grade heat resource is not near the surface and drilling through hard rocks to the depths required to reach the high grade heat is expensive.  However once the drilling is complete and the system is established it is a great source of renewable energy.”

You can read more about the BBC’s take on the Cornwall story here and more about deep thermal drilling on the Renewable Energy Association’s site here.