Multi-Use Ocean Thermal Energy Conversion (OTEC) Platforms

Abstract

Ocean Thermal Energy Conversion (OTEC) generates power from a heat exchange process using the temperature differential between warm tropical surface water and cold deep ocean water and is a unique marine energy technology with a long history of development on- and offshore. With the ability to generate power 24 hours a day, OTEC can provide a more significant baseline power potential than any other offshore renewable technology. Pathways to wide-spread OTEC production indicate the potential to bring its levelized cost of energy (LCOE) down to levels that rival solar and wind energy on land.

OTEC is a low efficiency heat exchange process (as compared to other thermal engines) that requires the pumping of extremely large quantities of seawater from depth and a plant with a sizable footprint, resulting in high capital costs for OTEC projects. These capital requirements have prevented OTEC from becoming established as a commercial energy source to date, with commercial scale development of the first OTEC plants ranging from 500M USD to 800M USD. OTEC’s use of seawater and large infrastructure allow for additional value streams that could help to reduce the cost of power generation and provide much needed services and products in the tropical islands and coastal regions where the process is viable.

Pacific Northwest National Laboratory (PNNL) and their partners explored the potential for incorporating other value streams with OTEC, assessed the tradeoffs of adding those additional products or services including seawater air conditioning, desalination, supporting aquaculture, critical mineral extraction, and generating efuels. The project sought to determine which combinations of uses are feasible for end users. A series of use cases were developed to examine the potential uses and tradeoffs.

The project focused around a theoretical OTEC plant placed at the site of the existing 100kW onshore OTEC plant at the National Energy Laboratory of Hawaii Administration (NELHA)’s Hawaii Ocean Science & Technology Park (HOST Park), located north of Kona, Hawaii, USA. The multiple uses of OTEC water were examined by conducting an OTEC resource assessment around Kona; exploring design considerations for OTEC and additional uses; examining environmental effects and modeling the cold water return water; engaging with the community to educate and gather input; and considering tradeoffs among multiple uses. This paper will report on the outcomes.