All OTEC are not the same. Why some engineers like to make things more complicated, why I do not know, but there is a much simpler way.
Two-phase flow of water (vapor to liquid) has the energy to do all the things desired from an OTEC process, and it does it in the most efficient way. A waterfall in the ocean to produce hydroelectricity! Mist Lift OTEC, is a "near" perpetual pumping machine, by way of two-phase flow of water, to pump deep ocean water for the purpose of electrical power generation and desalinization for drinking water.
What has been holding OTEC back all these years? It is the complications and low efficiencies and cost! A lot of water has to be pumped, I mean a LOT! These huge and power consuming pumps require lots of energy to operate besides their maintenance. Then there is the HUGE and expensive heat exchangers needed in the closed cycle approach. This keeps a lot of mechanical engineers employed, trying to design them to do the job and once done require lots of maintenance to keep them working. Are all these experts going to be around to maintain this complication? Where I live, the island of Saipan, they can not even keep diesel generators running. Getting replacement parts is a time consuming process also. It is costing $0.40 kWh for electricity on our island and we need drinking water too.
We all know that large OTEC plants are not suited for land base, due to the sizes needed to convert this thermal energy difference. They are going to need to be 'floating' plants. With the present approach to OTEC these floating or grazing plants are very expensive to build and man. Then they face the forces of nature. Ships sink! The Mist Lift OTEC 'hull' is mostly BELOW the surface of the water, thus making it less susceptible to bad weather and it does not need much personnel to operate. Concrete has a proven record to last in the ocean. Steel ships need a lot of care to last as long as concrete ones. The concrete hull is cheaper to build too. The cost of its fabrication will go down with volume of 'hulls' needed. So, let us see, mist generator, concrete hull, typical hydroelectric generator and vacuum pump. Simple! Very few moving parts or devises to maintain. Simplicity is beauty.
Two Stage Mist Lift OTEC also requires that LESS cold water to be brought up thus making the deep cold water pipe to be smaller for a same size power plant by other OTEC approaches. Also Two Stage Mist Lift OTEC comes very close to the theoretical maximum efficiency possible. So let us recap:
• No power hungry circulation pumps needed thus giving more NET electricity
• No huge and expensive heat exchanger needed (Closed cycle)
• No huge steam turbine (Open cycle)
• Less deep cold water needed to be brought up from the deep
• Less personnel to operate with less expertise
• Less susceptible to weather forces
• Less cost to build
Since this Mist Lift OTEC approach was presented to the OTEC community over 30 years ago, right at the end of funding by the US DOE, it has sat on the shelf. In these 30 years other OTEC approaches have moved at a snails pace with little forward movement. Yes, Saga University has built around 11 "pilot" plants of which none of them have been able to come to market. They are too complicated and they missed the mark. Yes, their efforts can be made useful in other areas (land based) but when it comes to doing all the 'hype' of what OTEC is possible of doing, they just have not made it happen. Mist Lift OTEC can do it!!
