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August 2012 Issue

Ocean Thermal Energy Conversion: A Commercialization Road Map
By Laurie Meyer

Ocean thermal energy conversion (OTEC) leverages a vast, untapped renewable reservoir of energy available in a broad area of the tropical oceans. OTEC is a standout renewable energy source in that it offers the potential to produce baseload, renewable power at a very large scale. However, despite this potential and major technological advances in the offshore industry, no commercial OTEC plants exist today, and an OTEC industry remains nascent.

The concept behind OTEC is straightforward: OTEC leverages the warm and cold temperature differential found in tropical waters to complete a power-producing cycle. But the energy density of that resource is low, so vast volumes of warm and cold seawater must be pumped through very large heat exchangers to produce commercially significant net power output.

Seawater pumps suitable for moving both warm and cold water in amounts necessary for commercial-scale energy output are massive and, therefore, must be optimized for efficiency. Packaging and layout of the warm and cold water pathways through the OTEC system must be designed in ways that minimize power losses as the water moves through the platform. Since the targeted cold water resource is typically found at water depths approaching 1 kilometer, an OTEC developer will be installing and operating these systems in the deepwater regime and in some cases far from shore and support infrastructure.

While the basic concept of OTEC has been around since 1881, the feasibility of a net-power-producing, ocean-based OTEC was not demonstrated until 1979 with the development and testing of Mini-OTEC off the Big Island of Hawaii by a consortium of companies led by Lockheed Martin Corp. (Bethesda, Maryland). Mini-OTEC produced 50 kilowatts of power, was not connected to a grid and only operated for about a three-month period. Nevertheless, it was considered a success given the relative immaturity of the offshore industry as a whole.

At that time, the offshore industry was just beginning to operate in the deepwater regime. Floating platforms and mooring systems were in the early stages of development and had not yet been proven through long-term operational deployment. Dynamic power cables capable of transmitting commercially significant amounts of power along the ocean were still being designed.

Additional OTEC-specific technology challenges included the need for a large-diameter cold water pipe solution at the length of 1 kilometer and capable of surviving a 20-to-30-year service life. There was also the need for affordable, high-performance heat exchangers optimized for OTEC cycle performance.

Despite being proven at the small scale of Mini-OTEC, and the resulting enthusiasm among renewable energy advocates of the day, dreams of commercializing OTEC took a major hit with the precipitous drop in oil prices during the mid-1980s. It has been only in the last five years, with the advent of a broader push for energy security and diversity coupled with mandates for significant levels of renewable-based generation capacity, that private companies and governments have once again begun to investigate how to make OTEC a commercially viable reality.

In the last 30 years, the offshore industry has moved beyond deepwater into ultradeepwater operations. Most of the non-OTEC-specific technologies required to build, install and operate an OTEC plant now exist as mature, commercially available solutions.

OTECís technology challenges have been helped along further with an increase in research and development attention from a variety of sources in the last five years, including industry, the Department of Energy and the U.S. Navy. The infusion of funds has spurred progress.

Research and development efforts in heat exchangers have focused on performance improvement, corrosion resistance and producibility. New designs are being tested in the lab, for example, at the National Energy Laboratory of Hawaii Authority, where Lockheed Martin has two units, with more planned.

Investments have also led to a design and process for building a low-cost, scalable composite cold water pipe in situ from an OTEC platform. This process and key elements of the composite tooling have been validated, and the challenging interfaces between the composite pipe and the steel platform structure have been successfully tackled. Plans are being finalized for full integration and demonstration of 4-meter-diameter pipe fabrication.

With component technology maturing, it is a promising time for OTEC. The moment has come to move from the research and development phase to a pilot operations phase that will integrate proven technologies and components to build a multimegawatt-scale OTEC system on an ocean platform.

The deployment and long-term operation of such a pilot plant that uses scalable technologies will result in lessons for achieving full-scale systems and driving down costs to make the technology commercially viable. This is the next step required for the true commercialization of OTEC because small-scale or land-based facilities, while good for demonstration purposes, will not yield the full knowledge needed to advance OTEC commercialization.

Like all industry breakthroughs, realizing OTECís potential will require investment and more government support. Developmental momentum must be capitalized on now so that OTEC becomes a renewable energy solution of today, instead of yet another challenge to be solved by future generations.



Laurie Meyer is chief engineer at Lockheed Martin Corp. and has planned and executed the companyís ocean thermal energy conversion (OTEC) research and development program for the last five years. She directed the multicompany design teams for the Naval Facilities Engineering Command OTEC Project Pilot Plant studies and key technology and hardware development, and coordinates ongoing technical activity.


2013:  JAN | FEB | MARCH | APRIL | MAY | JUNE | JULY | AUG | SEPT | OCT | NOV | DEC
2012:  JAN | FEB | MARCH | APRIL | MAY | JUNE | JULY | AUG | SEPT | OCT | NOV | DEC

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