First Approval in Principle for floating renewable energy plant

Class society ABS has issued its first Approval in Principle (AIP) for a new concept renewable energy design in which a moored spar uses ammonia in a closed-cycle process to produce electrical power for a commercial utility grid. Unlike wind, tidal or solar power the advanced design for this Ocean Thermal Energy Conversion (OTEC) system can deliver constant output 24 hours a day.

Developed by OTEC International (OTI) LLC of Baltimore, Maryland, the approach converts liquid ammonia into gas in a heat exchanger using warm ocean surface water. The ammonia gas then drives turbines that turn generators to produce electricity which is then exported through a submarine power cable to a land-based utility company. The ammonia is condensed back into a liquid phase using cold ocean water pumped from below the water’s surface and the process begins again. The process is based upon the well-established thermodynamic Rankine cycle.

Key elements evaluated by ABS include: spar hull sizing for the deep draft spar design; energy conversion equipment located in the spar; handling and storage of hazardous materials; deepwater mooring system; cold water pipe conduit suspended from the base of the spar; construction and attachment of the cold water pipe conduit; and power transmission cable with its securing, anchoring and suspension arrangements. ABS reviewed the design for an extended 30-year facility on-station life.

ABS has issued Approval in Principle for both the 25MW and 100MW designs; OTI could be eligible for ABS’ class notation A1, Floating Offshore Installation (FOI) Spar, SFA(30).