Geothermal energy often crops-up in social media comments and radio phone-ins about renewable energy sources that may be suitable for the Isle of Man. But what are the pros and cons?

What is geothermal energy?

It’s energy that comes in the form of heat from underground due to the immense temperatures at the earth’s core.

Those temperatures heat rocks near the surface which can be used to heat water which can ultimately be used to drive turbines to generate electricity.

In places such as Iceland where there’s an abundant and easily accessible source of geothermal energy it is a source of renewable energy that has an advantage over wind and solar power because it’s constant (i.e. unlike the wind and sun which varies with the weather).

Geothermal energy is also used in Cornwall where unique geological characteristics and environmental benefits.

Why is it not a good choice for the Isle of Man?

It’s an area’s unique geological characteristics – in particular underground temperatures – that are critical to where it’s a suitable and viable option.

If you look at a geological heat map of the British Isles you will see that Cornwall is in a relative ‘hot spot’ while most other areas, including the Isle of Man, are much cooler.

In areas where geothermal is most suitable it’s because the ground is so hot that water can be piped from boreholes relatively close to the surface, and used to form steam which drives turbines that generate electricity.

In other areas there are ‘aquifers’ which are types of porous rocks which contain natural fractures that allow access to hot water at a depth of a few kilometres, which again means it’s accessible as a viable source of heat energy.

But here in the island at the depths required to access geothermal energy there are Manx slate and granite rocks which are impermeable – so artificial fractures would need to be created, and that involves a process called ‘fracking’ that’s not only technically and financially challenging, but also controversial because of the impact it can have on communities.

This blog by the Isle of Man Government’s net-zero team goes into great detail about the technical explanation – but, in short, the Island’s geology is simply not suited to geothermal. Bearing in mind that there are other sources of renewable energy which are much more suited to the Island from a practical, technical and cost perspective – it makes little sense to pursue geothermal ahead of wind or solar power projects.

Globally, geothermal does have a lot of potential, especially as scientific understanding and technology evolves. But right now, and for the foreseeable future, the overwhelming balance of expert opinion says it is not a viable option for the Isle of Man.