A 1 MW OTEC facility can produce up to 3500 cubic meters per day of potable water. The value added operational and marketing benefits of natural energy and self-sustainability are exploitable advantages. While the U.S. Department of Defense has carried out several studies to consider this alternative, there are hopes that an international funding organization, such as the World Bank or Asian Development Bank, will have the will to break from tradition to symbolically demonstrate the value of this sustainable option.
With water credit, it has been reported by PICHTR that a land-based 1 MW plant could be built to produce electricity at $0.25/kWh and 5 MW for about $0.10/kWh. A 50 MW floating closed cycle hybrid OTEC facility, with water sold at $3/1000 gallon, could produce electricity for $.06/kWh (1990 dollars). Appreciating that nothing much has been researched over the past two decades, and using 2008 dollars, this latter estimation should now be a bit more than 10 cents / kilowatt-hour, certainly of interest in Hawaii, when the residential rates are hovering in the range of 30 cents / kWh.
Can 100 MW and larger OTEC plantships someday produce hydrogen and other clean energy products? Studies are available detailing the production of hydrogen via water electrolysis on 50-400 MW OTEC platforms at costs low enough to manufacture on board and delivered to land-based users of ammonia and fertilizers to compete with conventional options. A 64 MW system could produce 8270 tons (one million GJ net heating value) of hydrogen per year.
A floating plantship can process 107 tons of coal per day (1.24kg/sec) to produce 47,400 tons of methanol annually, and because of the hydrogen from OTEC electrolysis, provide a 1:1.3 ratio of coal to methanol, whereas, typical plants today have a 1:0.6 ratio. There would also be the carbon sequestration benefit as mentioned earlier. Another variation, a renewable one, would use marine biomass as the feedstock to replace coal, for a large portion of the overall coal cost is just the delivery.
The rise of crude prices have now made OTEC electricity commercially competitive for sites using oil products to generate electricity. With water, carbon, and/or co-product credits, the promise increases for niche island applications today. In the mid term, as oil becomes even more expensive, OTEC hydrogen and other fuels and chemicals can become attractive substitutes to carbon fuels. In the very long term, the concept of artificial upwelling for broad scale marine development with concomitant environmental benefits looms large as a productive future.