Changing the Game - Enhanced OTEC System Design

Abstract

Ocean Thermal Energy Conversion, better known as OTEC is a base load power source that runs on the temperature difference between warm surface water and cold depths. Generally, the accepted minimum temperature difference is 18°C, with a minimum surface water temperature of 25°C. The maximum possible thermal efficiency of these systems is 3% to 7% and requires massive flows of seawater. The concept was first developed in the 1890's but has struggled since then, with every commercial scale system to date suffering failures on the cold water riser due to required pipe diameter (up to 14m being considered) and the required water depth to reach the cold waters, usually taken as greater than 1000 meters. This paper presents the thermodynamic analysis of an Enhanced OTEC system that will allow for an order of magnitude reduction in the size of the down risers. This enhancement should both improve the performance of the OTEC system and reduce the cost, bringing the Levelized Cost of Energy on par with Offshore Wind. Using computer modeling the new system is compared to a conventional system's performance. A comparison using a thermodynamics and energy balance, outputs of the models are used to confirm that the increase in power and a reduction required riser size are possible. The new system provides significant improvements in terms of performance, while adding some mechanical complexity, in the form of a second closed fluid loop. The Enhanced OTEC system (E-OTEC) will bring this century old technology into the 21st century as a leading source of clean energy. It is unlike any existing OTEC system.