Session: 14-01-01: Small Maritime Nations

Paper Number: 104431

104431 - Ocean Thermal Energy Conversion and Sustainable Island Nations: The Case Study of the Island of Nauru 

Pacific Island Countries and Territories often lack natural resources and rely on importing diesel for energy production, which threatens the energy security. Furthermore, their remoteness and limited land resources are also limiting factors for food production, posing an obstacle to agriculture and aquaculture practices. Lastly, the water sector is also at risk, as rainfall water is still a widely utilized water source and there are challenges regarding water pollution and lack of freshwater sources. The energy, food and water sectors have been facing challenges that could be further exacerbated by adverse climate effects, such as droughts, ocean acidification, and rising sea levels.

Ocean Thermal Energy Conversion (OTEC) is a clean source of energy that operates on the principles of temperature difference for energy generation, using warm water from the surface and cold deep-sea water; The most important aspect of OTEC is the deep-sea water that is extracted from the ocean at depths larger than 500m. This water has essential properties, including a high presence of nutrients, minerals, and a lack of bacteria. Deep-sea water can be used for coral conservation, mineral water production, greenhouse cooling, fishery fertilization, food processing, among other options.

 Nauru has the ideal conditions for ocean thermal energy – it is situated in the Western Equatorial region, where surface temperature is higher, it has steep bathymetry profiles near the island, and it is also possible to achieve a high temperature difference at 700m depth. Thus, Nauru is a suitable candidate for OTEC and its potential has been analyzed during this study using Regional Modelling Ocean System (ROMS). Our goal was to quantify the thermal energy resources, identify potential obstacles, and find suitable areas for OTEC. For the methodology, ROMS runs were divided into two separate parts; First, HYCOM data was used to create a 3km model resolution of the Nauru domain. Then, a 1km model resolution was created using boundary conditions from the 3km model.

Through the outputs of our high-resolution model we were able to quantify temperature difference at several depths, exergy, and annual energy production for ocean thermal energy. At 700m depth, temperature difference values within the 23 – 23.4֯C range can be expected, showing that it is possible to achieve a high-temperature difference at 700m near Nauru. If we consider an efficiency of 30% for ocean thermal energy production, the output energy can vary between 1095 and 1185 kW. To estimate the annual energy production (AEP) we set the annual operating hours variable to 7000 h/year and the AEP would vary between 7665000 and 8295000 kWh/year. These numbers represent roughly 21% of the total energy delivered to the grid in 2020 and would be a huge contributor to the local energy production.

We have found that Nauru is a potential candidate for OTEC and could benefit from a multi-purpose plant, which would not only increase the energy production but also the water production. The deep-sea water extracted during the process will be a key factor to expanding the agriculture and aquaculture sectors, while also preserving the local corals.

Presenting Author: Jessica Posterari University of Tokyo

Presenting Author Biography: PhD student at the University of Tokyo researching Ocean Thermal Energy Conversion in the context of sustainable development in the Pacific Island Countries.

Authors:

Jessica Posterari University of Tokyo
Takuji Waseda University of Tokyo
Keiji Kiyomatsu Freelancer