Ocean thermal energy conversion

Georges Claude à l'Institut 1926

Ocean Thermal Energy Conversion (OTEC) is a process that uses the temperature difference between cooler deep and warmer shallow or surface seawaters to run a heat engine and produce useful work, usually in the form of electricity. OTEC can operate with a very high capacity factor and so can operate in base load mode.

Overview

The concept of OTEC originates from the 19th century, with significant advancements and research occurring in the 20th and 21st centuries. The principle behind OTEC is simple: warm surface water is used to boil a working fluid, which has a low boiling point, in a heat exchanger. This produces vapor, which drives a turbine attached to an electric generator. The vapor is then cooled using cold water pumped from the deeper layers of the ocean, condenses back into a liquid, and is recycled through the system.

Types of OTEC Systems

There are three main types of OTEC systems: closed-cycle, open-cycle, and hybrid systems.

• Closed-Cycle OTEC uses a working fluid that is vaporized and condensed in a completely closed loop. The most commonly used fluids are ammonia or a mixture of ammonia and water because of their favorable thermodynamic properties.
• Open-Cycle OTEC operates by boiling seawater under low pressure, making it turn into steam, which then drives a turbine. After passing through the turbine, the steam is condensed into fresh water.
• Hybrid OTEC combines both closed and open-cycle processes.

Benefits

OTEC offers several benefits, including the production of renewable energy, minimal environmental impact, and the potential for co-products like desalinated water. It is particularly attractive for tropical island nations where energy costs are high and water is scarce.

Challenges

Despite its potential, OTEC faces several challenges. The initial capital costs are high, and the technology requires a significant temperature difference between surface and deep water, limiting its applicability to tropical regions. There are also environmental concerns, including the potential for affecting marine ecosystems through the discharge of large volumes of deep cold seawater.

Current Status and Future Prospects

As of now, several pilot projects and studies are exploring the viability of OTEC. The technology has not yet been implemented on a large scale, but it holds promise as a sustainable energy source, especially for island nations with limited access to other renewable resources.

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