Known as the “Emerald Isle” of the Caribbean due to historical ties with the Irish, Montserrat is poised to become one of the world’s few metaphorically “green” and sustainable islands. The same geological forces unleashed by the Soufrière Hills volcano are being harnessed to power the island’s electricity grid from a geothermal source.
Geothermal energy, the productive use of the vast quantity of thermal energy within the Earth’s crust, is one of the few renewable, low-carbon emission energy sources that can consistently generate power 24-hours a day, irrespective of the season. Its primary limitation is not weather but location, as it can only be exploited in places with specific geology, where some of the Earth’s intense inner heat reaches close enough to the surface to be of use. Montserrat’s geology is suitable for geothermal use: hot molten magma rises to shallow depths, driven by the forces of regional plate tectonics. The heat from this magma warms the surrounding rocks, providing a heat source that can be tapped if it can be brought back to the surface. Rainwater and seawater are natural aids to this process as they penetrate through cracks and pores in the rocks to several kilometres beneath the island, absorbing heat from the magma heated rocks. Once heated, the hot fluid rises buoyantly to shallower levels where it can be tapped by drilling geothermal wells. As the ascending fluid boils, it produces pressurised steam which rotates turbines to generate electricity.
The high cost of drilling wells (a single well can cost several million US dollars) coupled with the potential risk of drilling an unproductive well are the principle reasons that geothermal potential has not been fully exploited. To increase the likelihood of drilling a productive well, the project to exploit geothermal power on Montserrat used an array of technologies, such as magnetotellurics and seismic tomography to more clearly understand the rocks beneath the surface.
Magnetotellurics uses naturally occurring signals from lightning storms and charged particles ejected from the sun to penetrate below ground. Seismic tomography uses the responses of elastic waves created by carefully generated explosions to generate images of the rocks. Aided by researchers at the UWI-Seismic Research Centre and the University of Auckland these techniques were used to create the subsurface maps (Figure 1) that have successfully guided Montserrat’s geothermal drilling programme.
Between March and September of 2013 the Iceland Drilling Company drilled Montserrat’s first two geothermal wells, to depths of 2,300 and 2,900 metres, striking temperatures of over 260°C. A third well started in September 2016 has also encountered high temperatures but the well needs to be thoroughly cleaned before it can be completed. Test results from the first two wells indicate that they could generate more electrical power than is currently needed by the island’s reduced population of around 5,000 inhabitants. Once completed, the geothermal power station will free the island from its current reliance on expensive diesel-powered generators for its electricity – currently among the most expensive electricity in the world.
The MVO along with its managing agency The University of the West Indies Seismic Research Centre is closely monitoring earthquake activity and ground deformation that might be associated with the geothermal reservoir as well as, actively carrying out research on the geology and geophysics of the various sites. In addition to helping to secure funding for the taking of core samples during the drilling of well MON#3, MVO Director Roderick Stewart sits on the Geothermal Steering Committee which oversees the project.
Montserrat is not the only nation in the region with geothermal aspirations. Many of the islands of the Lesser Antilles have similar geological settings and therefore geothermal potential. The French island of Guadeloupe, with 15MW of installed capacity, is the only Caribbean island that currently uses geothermal energy for electricity. However, in the last few years, there have been geothermal initiatives on other island nations including St Kitts and Nevis, St. Vincent and Grenada. A European Union funded project in Dominica has also resulted in several promising exploratory wells.
Geoscientists have recognised the geothermal potential of the region for many decades. But it is only in the past few years that the promise of a cheap, local energy source that can free the region from volatile oil prices has caught the imagination of regional governments and agencies.