Variation of Power Output From an OTEC Power Plant Based on Longterm Sea Surface Temperature Data Analysis

Abstract

Though natural resources are abundantly available for utilization of renewable energy sources, many Pacific Island countries continue to rely on fossil fuels. The use of fossil fuels is known to significantly contribute to climate change. Heavy reliance on fossil fuels also hinders the economic development of most of the Pacific Island Countries. To overcome these issues, the energy sector in Fiji is aiming to generate 100% of the required energy using renewables by 2036. One of the viable options which can contribute to this goal is Ocean Thermal Energy Conversion (OTEC) power. The standard OTEC cycle is a modified Carnot cycle and has low efficiency due to the small temperature difference it works with. In this work, we carried out resource assessment around Fiji to identify potential locations where an OTEC power plant can be installed as well as the conceptual design of a 1 MW net power OTEC plant and the variations in power output due to change in surface seawater temperatures (SSTs). Seawater temperature data (in-situ) between 2012–2022 for three locations were obtained and their seasonal, monthly, and diurnal variations were analysed to study the variation of power generation potential. The analysis shows that during the summer season (November to April), a higher temperature difference is available which results in higher power output and efficiency compared to the winter season. The maximum monthly average temperature difference between the surface and the deep sea (4°C) was recorded for March 2022 with a difference of 25.7°C in Suva. The winter month of August in 2015, had the minimum average temperature difference of 20.1°C in Beqa. The maximum surface temperature recorded during the measurement period was nearly 30.5°C (Suva). The analysis of diurnal variation of hourly averaged temperature showed an interesting trend of essentially constant temperature round the clock with the maximum recorded at 4 am. The net power was calculated for the 3 locations for seasonal, monthly and hourly variations. The net power that was estimated to be 1.15 MW for the maximum monthly average temperature, was reduced by about 63% for the minimum. Similarly, the gross power ranged between 1.7 to 2.4 MW for the temperature range. The net power loss increased from 5% to 16% for a drop in 0.5°C in SST from 30°C to 24°C.