OTEC - Ocean Thermal Energy Conversion
Perhaps the single-most important technology in the entire Aquarius phase and linchpin of Marshal Savage’s scheme for improving environment, civilization, and socioeconomic conditions on Earth, OTEC or Ocean Thermal Energy Conversion is the essential reason for the existence of the marine colony –or to be more specific, the purpose of the marine colony is to integrate OTEC with the full spectrum of industries fully exploiting its potential.
OTEC is an old, simple, well understood, and well-proven renewable energy technology that has remained largely under developed today owing to the remote nature of the marine locations and large minimum system scales it requires. OTEC functions basically like any solar-dynamic power system employing Rankine cycle systems –such as large solar-dynamic plants based on vast solar mirror collector arrays and a thermal fluid. The difference with OTEC is that the solar collector is the ocean itself, the system running on the difference in temperature between warm surface seawater and cold deep seawater. Thus the effective solar collection area of an OTEC plant covers many thousands of square kilometers, making OTEC plants the largest solar energy systems possible on Earth and potentially the most economical.
But, of course, an OTEC only functions best in locations where the difference in temperature between surface and deep seawater is consistently great and this has severely limited the deployment of OTEC plants to a small number of near-Equatorial coastal locations with steep nearby undersea landscapes that allow close-by access to depths below 2500 feet. Such locations are few and remote and, though dozens of experimental OTEC plants have been built since its invention –well demonstrating its functionality and potential– very little attention has been given to this technology both in the mainstream media and by environmentalists and renewable energy proponents. OTEC shares an essential logistical problem all forms of renewable energy technology share; the optimal locations for renewable energy production tend to be far removed from the locations where most people live owing to the fact that generations of reliance on fossil fuels, with their great portability, has allowed people to live and build communities in places that are not entirely practical. Other renewable energy technologies have dealt with this issue through scalability.
Though their function may not be as optimal as in their ideal size and locations, systems like photovoltaics and wind turbines can be reduced in size and deployed in many more locations at that reduced scale. This allowed the deployment of these technologies on a personal level, making renewable energy use a personal decision and establishing grassroots support for the technology. OTEC cannot be scaled to such small sizes nor can it function outside of its optimal near-equatorial zones with easy deep-ocean access. Thus this most powerful of all known solar energy technologies has languished despite its proven ability. OTEC has needed new means of packaging and globally distributing its energy production, allowing OTEC plants to follow more of an oil industry paradigm than a municipal power model.
This is a radical idea for proponents of renewable energy who, having long faced resistance by the large corporate/government establishments, have relied on the concept of personal/individual energy autonomy through small systems as the basis of social support for the technology’s advancement. In effect, proponents of renewable energy have been dealing with the resistance of The Powers The Be to this more rational technology by essentially trying to use that very technology to deconstruct the centralized energy infrastructures that created that compulsively resistant centralized economic/political power in the first place. Problem is, reduced to small scales and non-optimal locations these technologies just haven’t performed that well. They were too costly, too limited, demanded too much skill and knowledge on the part of their users, and consequently too much change in lifestyle for most of the population. Indeed, the Off-Grid movement has long encouraged a suburban diaspora based on the premise of seeking personal energy independence, thus inadvertently damaging the very environment it purports to be protecting! Thus all renewable energy has struggled, waiting for the technology of small scale systems to achieve some breakthrough point in cost-performance that has yet to arrive –though in recent years is looking more imminent thanks as much to the unfolding failure of the fossil fuel infrastructure as to actual technology improvements.
Taking a page from the likes of Buckminster Fuller, Marshal Savage realized that the key to successful implementation of renewable energy rested in its logistics more than its particular technological performance. While OTEC is the Earth’s best means of exploiting solar energy it can’t scale greatly or work outside of its ideal marine locations. Thus it is those logistics that link OTEC inevitably with marine colonization as a means of hosting the industrial infrastructure needed to link this single-greatest reserve of solar energy to the globe. Full exploitation of the sea’s renewable energy potential means freeing OTEC from dependence upon a few providentially optimal coastal locations. But while OTEC ships are certainly possible, they lack the scale needed to implement any better means of power distribution than short distance undersea cables. A larger OTEC ship might also be fashioned to store and transport the energy it gathers, but the distances to northern industrial communities means such vessels will spend more of their time in transit than in actual OTEC operation, radically impacting their efficiency. Such a strategy would only be practical for the OTEC ship functioning as a fuel station on the transit routes of ships it fuels.
While the marine colony community of Aquarius will most certainly seek advances in undersea cable technology to enable increasing line distances with decreasing losses, near-term no existing submarine power cable technology can effectively link a fleet of OTEC ships spanning the Equator with the rest of the world, thus limiting their use to just about as many locations as coastal OTEC's are limited to. To overcome this the OTEC must be complemented with facilities for the continuous packaging and distribution of energy in a more practical portable form; hydrogen or other energy packaging mediums. This requires not only plants and large volume storage for this conversion but also a shipping infrastructure that can deliver these energy products to the rest of the world. Thus we see that OTEC is NOT simply a way to provide power for a marine colony and produce a little export income. The marine colony is the key to the implementation of OTEC as a global energy source. The marine colony would exist for the sake of OTEC, which is ultimately only able to fully realize its potential in that context.
Savage also realized that there are many other side-benefits of OTEC that also require a marine colony to host their facilities. In operation, OTECs function like miniature upwelling zones bringing up nutrient-rich deep seawater and discharging it after its use as a heat-sink is complete, much like natural upwelling zones which are responsible for many of the world’s greatest coastal fisheries. In fact, this actually gives OTECs great potential as a carbon sequestration method because salps (an algaevore that excretes carbon at great depths) and algae growth would both be much increased at the outer perimeter of this upwelling plume –a phenomenon already being exploited for this purpose using solar-powered floating seawater pump stations. By using this huge volume of discharge water as the source nutrient supply of a poly-species network of mariculture founded on algeaculture, extremely vast industrial mariculture systems could be developed producing vast quantities of food with no overhead in feed stock and minimal environmental impact. Proportional to the scale of OTEC power production, such mariculture facilities could easily become a major source of food on the global scale –which, of course, needs shipping facilities to distribute it just as the packaged energy does. Given full-scale deployment over the Aquarius phase, such marine colony food production could easily become one of the single-greatest food sources on the entire planet, thus this, in combination with the encouraged conversion of global energy reliance to renewable energy, has become a key factor in Savage’s original plan for using the Aquarius phase as a means of ameliorating much of the socioeconomic strife world-wide, creating a global sociopolitical climate more amenable to human progress and the advance to concerted space development.
Thus we can see how OTEC has the potential to be one of the most significant technologies in the entire 21st century. A world-transforming technology if appropriately and fully implemented in concert with marine colonization. For centuries people have fantasized about living on the sea but there has never truly be an entirely practical reason for that. But with OTEC we have reasons so practical –so vital– they may determine the very survival of human civilization and its ability to expand into space.
Types of OTECs
There are typically three forms of OTEC system in development today; open cycle, closed cycle, and hybrids. A fourth type, passive cycle, remains in more speculative development.
The preferred form in Marshal Savage’s plan, open cycle OTECs rely on low-pressure steam extracted from warm water itself to drive low-pressure turbines to generate power. This is achieved by using a partial vacuum in a warm water evaporator chamber (initiated by vacuum pumps but largely sustained by later-stage condensation) which causes the water to boil to steam and drive a turbine before being condensed to distilled water through heat exchange with cold deep seawater. This deep seawater is brought to the surface in a long (2500-5000 feet) pipe typically representing the single largest and most expensive component of the OTEC plant. The warmed deep seawater is finally mixed with discharge water from the evaporation station and ejected at a depth below the level of warm water intake. (and/or diverted as a nutrient source for mariculture/algaeculture and chill water for air conditioning, cold-bed agriculture, and industrial refrigeration) The condensed distilled water is discharged as potable water for domestic and industrial uses. Vaporizing warm seawater also produced some discharge gasses –particularly ammonia which is removed and collected in a ‘degassing’ stage and condensed for output as another industrial by-product. As you might imagine, a large scale open-cycle OTEC, such as the 100-megawatt plants Savage envisioned, would produce huge volumes of both distilled and chilled nutrient-rich salt water. Estimates suggest just under 2000 cubic meters of chilled water and over 5 cubic meters of distilled water per second! A typical colony may employ 6-8 such OTEC plants. Indeed, the inhabitants of an Aquarian colony can expect to enjoy a generous supply of fresh water for their domestic needs and a verdant garden living environment thanks to such copious water production.
Open-cycle OTECs, however, are one of the more complex forms of OTEC system and tend not to be as efficient. In order to function at much lower pressures, turbines of enormous size but low mass are required, making for a much bulkier system design while parasitic energy loses from various forms of pumps are much greater than other systems. Because the secondary uses of OTEC by-products tend to be something of a ‘hard sell’ to typically simple-minded financial executives, OTEC developers have tended to favor closed-cycle systems offering a better energy yield at the cost of outputting fresh water.
Closed cycle OTECs rely on a separate thermal fluid medium supporting higher vapor pressures at lower temperatures, thus allowing the OTEC to be designed with more compact turbines. Operating otherwise the same as an open-cycle OTEC, heat exchangers mediate the thermal exchange between warm and cold water sides of the system and there is no production of distilled water or other by-products. This results in about a third higher electricity yield and a much more compact plant overall but at the cost of these valuable by-products.
As their name implies, hybrid OTECs combine characteristics of both open and closed cycle systems, usually in order to tap into some of the by-product potential of open-cycle systems while retaining the compactness and higher efficiencies of closed-cycle systems. This is usually achieved by deploying ‘parasitic’ sub-systems with an essentially closed-cycle system that perform degassing for ammonia extraction and steam desalination for water production.
Passive-cycle OTECs are a largely unexplored area offering the potential for greater compactness and freer system scalability than has been traditional with the other types of plants. These are either closed-cycle or solid-state systems which communicate thermal exchange along the length of a structure between the surface and cold deep water. A good example would be the Liquid Armature Dynamo or magnetohydrodynamic generator. This system would use a closed loop tube running between surface and deep sea passive heat exchangers to setup a continuous thermosiphon cycle in a working fluid consisting of a magnetodynamic mixture or suspension such as the ‘ferrofluids’ used in exotic audio speakers. The continuously moving fluid would function like the armature in a dynamo, passing through field coils along the length of the tubing loop in which direct current electricity is generated. Other concepts have been based on the generation of a self-perpetuating vortex within an open tube that is driven as a thermosiphon, energy being extracted in the walls of the tube itself through pezioelectric membranes that respond to the perpetually cycling pressure waves traveling along the thermal vortex. Such technologies would, of course, sacrifice all the valuable by-products of the open-cycle process but offer such radical simplification of OTEC systems –and hence a reduction in their cost and improvement in output power yield– that they make for very compelling alternatives.
Other Information Sources
- What is Ocean Thermal Energy Conversion?
- Wikipedia:Ocean thermal energy conversion
- OTEC News - Clean Energy, Water and Food
- Pneumatically Stabilized Platforms - PSP
- Sea Towers
- Aquarian Digital Infrastructure
- Cold Water Radiant Cooling
- Large Area Cast Acrylic Structures
- Polyspecies Mariculture
- Free-Range Fish Farming
- Terra Preta
- Cold-Bed Agriculture
- Small Space Animal Husbandry
- Tidal/Wave/Current Systems
- Algae-Based Biofuel Systems
- Vanadium Redox Systems
- Hydride Storage Systems
- Next-Generation Hydrogen Storage
- Alternative Hydrolizer Systems
- Supercritical Water Oxidation
- Plasma Waste Conversion