The huge energy reservoir in the tropical ocean available via the OTEC process will require a transportable form of that energy to allow access by the demand centers in the Temperate Zone. The most attractive and versatile transportable energy form is hydrogen. There are several natural synergies between OTEC and hydrogen, especially liquid hydrogen (LH₂).

TECHNICAL AND ECONOMIC DEVELOPMENTS

     Since the time of the Lockheed proposal, in the early 1980's, there have been several technical improvements and economic developments that make an OTEC system that provides hydrogen even more attractive. These include:

• The development and installation of several Kalina Cycle^® plants. The Kalina Cycle^® with its ammonia/water working fluid improves the efficiency of power production above that of the power cycle using pure ammonia as the working fluid. Kalina Cycle^® plants are now proven technology.

• The development and installation of offshore oil production platforms in waters deeper than 3000 feet. In the tropical ocean these platforms could be used for OTEC hydrogen production. This technology, although developed for oil, is directly applicable to form the base of an OTEC hydrogen plant.

• The optimization of the hydrogen production system by electrolysis of water with a high KOH concentration. This improved the efficiency of electrolysis from about 70% to about 85%, a significant improvement.

• The optimization of the production of liquid hydrogen (LH₂) using several steps. The steps include compression and cooling followed by further cooling with liquid nitrogen; counter cooling heat exchange with very cold gaseous hydrogen followed by liquefaction through a Joule-Thompson valve. George Claude who also was the first to install an open-cycle OTEC plant (in Cuba) first developed an earlier version of this process.

• The development of LH₂ transport and storage systems. Currently, LH₂ is transported via barge from Louisiana to Florida for use by the space shuttle. LH₂ is also regularly transported via tanker trucks on the Autobahn in Germany and used by experimental vehicle fleets which fill up at LH₂ stations.

• The development of a full-scale system to use LH₂ for transportation in fuel cell powered vehicles in Iceland. In this case geothermal power plants produce the electricity (instead of OTEC plants). A car company (Daimler-Chrysler), an energy company (Dutch Shell), and a local Icelandic development company teamed up to put this system into place.

     Considering this recent technological history it can be stated that the development of OTEC hydrogen requires no technological breakthrough. Working facilities have proved every aspect of a modern OTEC system.

     Present economic conditions are also favorable for the development of OTEC hydrogen. Interest rates are at a 40 year low and competing oil prices are relatively high ($29 per barrel as of this writing, September 15, 2002).

OTEC HYDROGEN SYNERGIES

     There are a number of advantages to combining an offshore OTEC platform with a hydrogen production and liquefying process. These include:

• Full and efficient utilization can be made of the investment in production capacity because OTEC is available 24 hours per day, and 365 days per year. This is in contrast to most renewable energy systems such as wind, waves, tide, direct solar and photovoltaics. In addition, OTEC systems cannot exhaust the resource at the location where they are installed – in contrast with oil, natural gas, geothermal or even hydroelectric (the reservoir eventually silts up).

• The efficient production of hydrogen by electrolysis requires very pure water for the KOH solution. A small part of the OTEC process can be used to produce this pure water from the surface seawater.

• Liquefying hydrogen by the Claude process requires an efficient heat sink to minimize process energy. The cold seawater that is used in the OTEC process provides this efficient heat sink.

• Ocean Tankers most efficiently transport liquid hydrogen. The offshore OTEC hydrogen plant is already located on the transport medium and therefore would result in the lowest cost for transport to market. From a global perspective, ocean transport distances of OTEC derived LH₂ are much shorter than our present system of oil transport from the Middle East around Africa to North America or Europe or from the Middle East around India and the Malay Peninsula to Japan.

     All elements of the technology required to economically produce LH₂ using OTEC exist. No significant technical barriers remain. The successful development of a global hydrogen economy will undoubtedly have to involve the largest renewable energy resource in the world – the tropical ocean.