Generating capacity and sustainable use of geothermal resources in Nevis

Abstract

Verification of the generating capacity and the sustainability of the geothermal resource on Nevis is important for the development of the country. The existence of numerous surface manifestations on the western side of the island led to studies and later exploratory work in 2007 by the West Indies Power Holding. The success of the exploratory work resulted in the proposed installation of an initial 10 MWe power plant and future expansion, first to 35 MWe to include the sister island of St. Kitts. Available field and downhole data indicate that a 210-260ºC high-temperature reservoir exists below a depth of approximately 600 m on the western side of the island. A volumetric resource assessment, incorporating parameter uncertainties by using a Monte Carlo approach, was applied and the results support the installation of the first phase of a 10 MWe plant. Under a very conservative analysis, the proven reservoir can supply 18-83 MWe for a period of 30 years. The results also imply that the expected 25 MWe addition of St. Kitts to the grid would not pose problems for the geothermal reservoir.

Adopting the concept that a sustainable production level E0 can be defined for every geothermal reservoir, the sustainability of the geothermal development based on a 100 year analysis supports a steady generation of 10 MWe. However, it is best to keep in mind that since no production has taken place to date, the value of E0 given in the report is not fixed and is likely to be higher, considering that recharge was not factored into the volumetric assessment. The analysis is, therefore, purely speculative and serves only as a guideline of the methods necessary to monitor the resource. It is clear that for the geothermal energy to become sustainable, this renewable source of energy must find a balance with the environment, and with economic and socio-political factors. Thus, if power plant extraction of heat and mass exceeds the rate of replenishment after years of development, then the production rate may need to be lowered to facilitate sustainability. This scenario is best avoided with proper monitoring and modelling of the reservoir.