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EV WORLD EXCLUSIVE ARTICLE |
Conceptual illustration of future Ocean Thermal Energy Conversion plant by Ocean Power Plant. Such plants would generate electric power that could be used to make hydrogen and fresh water. Other potential ancillary activities could include aquaculture, deep sea mining and even rocket launch services.
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A trans-Pacific discussion with Dr. Hans Jurgen Krock, the founder of OCEES on the revival of Ocean Thermal Energy Conversion.
Open Access Article Originally Published: April 12, 2006
In the 1970s the concept of Ocean Thermal Energy Conversion or OTEC was proven technically feasible, but not economic. Oil and gas prices were just too low.
Now like a long-submerged submarine, OTEC is again resurfacing. With oil prices headed north of $60 a barrel, what wasn't economically practical just fifteen years ago is starting to look attractive again -- especially to original pioneers like Hans Jurgen Krock with the University of Hawaii .
Joining him is NREL's Terry Penney, himself an early OTEC researcher and proponent, with whom I was having dinner in Philadelphia a few weeks back. Appropriately, we were having seafood and the discussion gravitated, naturally enough, to making power from the difference between the warm surface waters of the tropics and the much colder waters 300 meters down. The concept has been around for more than a century, first being attempted off Cuba in the late 1920's. Unfortunately, a storm carried away the deep water pipe that was to bring up the cold water and the experiment never recovered.
Penney, who is a senior manager at NREL, worked on the Energy Department's original technology demonstration project in Hawaii, then moved on to SERI, which eventually became the National Renewable Energy Laboratory in Golden, Colorado.
The original research facility is still operating in Hawaii, but not on ocean thermal energy. Instead it uses electricity generated by Hawaiian Electric Company to draw up chilled seawater through a 55-inch diameter pipe. Using reverse osmosis, the operators purify the "ancient" water and bottle it for shipment to Japan and elsewhere. According to Dr. Krock, it is the islands' largest export dollar-wise. The facility also utilities the nutrient-rich waters to run an adjacent aquaculture operation, a vestige of the original 70s government program.
But the promise of using the ocean's unfathomable store of solar thermal energy has remained, until now, mostly an illusive dream for a handful of visionaries like Penney and Krock. Today, that's all changed.
"The economics have turned around completely," Krock told me via a voice-over-internet connection, "and in fact, it is now economically viable to look at this resource for power production and fresh water production."
Krock explained the basic concept of ocean thermal energy conversion, which works on the principle of a simple heat engine.
"You have a warm water reservoir, which is the surface of the ocean, the surface layer which is warm because the sun shines on it; and then you have the deep water, which is cold because the sunshine doesn't get down that far. The last time that water saw the light of day was in Antarctica or in the Arctic Ocean someplace and so you have this difference in temperature. In thermodynamic terms you can run a heat engine if you have a warm reservoir and a cold reservoir. And a heat engine is simply a very conventional system where you boil a working fluid and you run the working fluid through a turbine and the turbine is connected to a generator and you make electricity. After it runs through the turbine, it gets in touch with the cold water and it condenses back. So you have vapor production in the turbine and the condenser at the end. It's very simple conceptually and it simply uses the fact that heat flows to cold to run this engine."
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Reader Comments
10 comments so far...
17-Apr-2006
18350
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Mr. Harrison's point is quite convincing. The value of OTEC lies in its comprehensive package of benefits beside supplying energy. For energy production, please consider the fact that the ocean water pipe must reach great depth, hence incurring significant energy input in pumping losses through the length of the pipelines, in order to extract merely 3% of thermal efficiency. Anchoring these pipes at these depth means expensive robotic deep-sea machinery must be used, increasing the cost. Powerful ocean currents, storms and hurricanes, and large fish such as whale and sharks, submarines, etc can threaten the integrity of these deep sea pipes. Sea water is of course corrosive, so, then, protective coating must be applied. Just look at what corrosion has done to the Titanic after all these years. Will these pipes last over 50 years? I doubt it. The low temperature differential between hot and cold side means a lot, lot more heat-exchange surface area must be utilized, thus increase investment cost. Remember that heat conduction VARIES WITH THE SQUARE OF TEMPERATURE DIFFERENTIAL. Doubling the temperature and heat transfer increases four times. Plus, ammonia is expensive and very toxic if it should leak, so expensive safety provision must be in place in case of massive ammonia leak. Those aren't meant to damper anyone's enthusiasm about OTEC, a very creative and exciting idea,just that more government funded research must be needed before a conclusion of economic feasibility can be reached.
Posted by: Roger Pham
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12-Apr-2006
17849
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If the Navy is being engaged then this is a serious venture. So why isn't OTEC in the news more? 2008 isn't that far away and if that is a real launch date then this thing has to be under construction to make that date. Is it really that startegic that our government is keeping it under the radar? OK, if EV World gets shut down then we know we have a conspiracy theory ripe for the picking! ; >
Posted by: Serafino Carri
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12-Apr-2006
17862
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Sounds interesting. Cost-effectiveness, however, is another issue. Needing a large-scale pilot research facility before all cost calculations can be figured out. However, Mr. Krock's statement that "...the resource that we are tapping into, the ocean thermal heat storage... is the only resource large enough to be able to replace oil" is somewhat biased. At only 3%thermal efficiency, due to the low thermal gradient, it is no match for solar thermal energy or concentrated PV at 30% efficiency, or TEN Times more efficient. The higher the thermal efficiency (heat to electricity conversion efficiency) the less investment in hardware and facility expenditure required to generate a given amount of electrical power. To be fair, OTEC has an advantage over solar and wind in that the power generated is continous and not intermittent, BUT, TOO BAD, OTEC facilities are to be located in middle of the ocean where it would be impractical to transmit electrical power to the end-user. If OTEC is to be used to generate hydrogen at 1/4 to 1/3 the overall efficiency of direct electrical power utilization, and the hydrogen is to be liquefied to be shipped on land, then Solar and Wind intermittency disadvantage in comparison to OTEC would be a moot point. Furthermore,one must factor in a 3-4 fold more expensive in OTEC's hydrogen energy when converting back to electricity in comparison to solar and wind electricity. Good luck, Mr. Krock! (good thing your name is spelled with a K instead of a C, he he :)
Posted by: Roger Pham
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12-Apr-2006
17878
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I agree with Roger's comments about economic viability. Some commentators have suggested that the geothermal energy available at the vast mid-ocean ridges could be used because 1000 degrees celcius rocks lie close to zero degree seawater. That huge temperature difference could drive Stirling engines to produce electricity. But what to do with the electricity? Giant battery ships sailing between coastal cities and the ocean ridge? Liquified hydrogen transport to coastal cities? These ideas are likely to fail on economic grounds. Slap heavy energy security and greenhouse gas emission taxes on fossil fuels and then we will see investment money pour into alternative energy schemes. I don't see OTEC being a starter except in places like the Hawaiian Islands where deep water is close to land.
Posted by: Shane Wilson
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12-Apr-2006
17884
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The BIG difference here guys is that this renewable energy source is available 24-7 unlike solar (5 hrs a day) or wind (?). I agree that energy conversion factor is low compared to concentrated solar, but according to the original study that killed the project in the 1980s, oil had to get to $30 a barrel before this would be economical. It just hit shy of $70 today. Also, neither wind nor solar can create desalinated water -- another huge environmental problem looming ahead -- or make aquaculture possible. I'd say those three will make this viable in a energy-short, water-starved, hungry world.
Posted by: Bill Moore
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13-Apr-2006
17903
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I see your points, Bill. Certainly, OTEC has other important functions aside energy generation in our future over-populated world. Perhaps other money-making functions of OTEC beside energy generation will help make it an economically feasible investment. Quite a creative and ingenious idea. Not a substitute for solar, wind and biomass energy, though. Perhaps an additional source of energy in coastal region with access to deep ocean.
Posted by: Roger Pham
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13-Apr-2006
17903
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I see your points, Bill. Certainly, OTEC has other important functions aside energy generation in our future over-populated world. Perhaps other money-making functions of OTEC beside energy generation will help make it an economically feasible investment. Quite a creative and ingenious idea. Not a substitute for solar, wind and biomass energy, though. Perhaps an additional source of energy in coastal region with access to deep ocean.
Posted by: Roger Pham
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18-Apr-2006
18365
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Shane Wilson's arguments about desalination seem to hmmm... hold water. The combination of steam and photovoltaic power and direct heating with concentrating mirrors is a natural for producing fresh water, and it's effectiveness can be multiplied with multiple effect evaporators (unless reverse osmosis is more efficient?). What could be a better "integrator" than a reservoir of fresh water, thereby possibly perfectly utilizing the available sunlight.
As for the idea that power generation is a vastly greater need than water desalination, I'm not so sure. There have been rumblings once again that dropping water tables threaten to remove the water supplies we and many other areas of the world rely on for food (irrigation, about 70% of fresh water use) and for cities. Places like the Sahara desert and Australia have an ideal combination of intense sunlight and vast open areas which irrigation could conceivably be made to be sustainable, given a large fresh water supply (and some good design to avoid the pitfalls of irrigation).
Posted by: Kevin Hill
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13-Apr-2006
17944
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Bill wrote: neither wind nor solar can create desalinated water.
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I disagree. A distillation apparatus + a parabolic reflector + sunlight + seawater = freshwater. There are small-scale solar stills advertised on the internet. Thermal solar desalination is a much simpler process than thermal-solar based electricity generation because the thermal energy can be directly used to boil off fresh water from salty water, while electricity generation requires the added complexity of turbines, Stirling engines, dynamos, transformers and the like. Also, intermittent sunlight means intermittent fresh water generation which is more tolerable than intermittent supply of voltage and current to a grid. One of the major problems with solar generated electricity is to match supply with demand. Storing electricity with giant batteries, pumped hydro, compressed air, and flywheels is very expensive. Storing fresh water only requires a reservoir or a tank. So variability of sunlight is not a major problem for solar desalination. Similarly, wind energy could be used to generate desalinated water. Mechanical energy from a wind turbine could be used to drive a pump to provide the water pressure required to desalinate using a reverse osmosis membrane. Again variability of wind will be less of an issue for desalination than for electricity generation. Reverse osmosis equipment is very simple. I've used it for years to provide deionized water for laboratory purposes. One can even buy little hand pump reverse osmosis devices for hikers and campers. Even water pressure from wave energy is being investigated for reverse osmosis desalination (http://www.ausindustry.gov.au/content/content.cfm?ObjectID=F5E76F06-9E1F-469A-9BF1E8925657209B&L3Keyword=plant). Much more research funding has been provided for electricity generation by solar, wind, and wave energy sources, than research funding for desalination by these sources. This is to be expected because the world's electricity generation requirements are vastly greater than the desalination requirements. Renewable energy electricity generation attracts subsidies from many governments. Most governments aren't even aware of the possibilities of renewable energy use for desalination.
Posted by: Shane Wilson
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16-Apr-2006
18215
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OTEC thermal efficiency is low at 3% but the materials used are also not exotic. No expensive silicon, gallium etc. needed. OTEC operates at low pressures and temperatures and thus machinery, if properly marinized should be very long lived. I am willing to bet that properly maintained OTEC machinery will last well over 50 years.
OTEC is also 24/7 energy which means any capital cost for OTEC should be divided by about 3 to get the equivalent competitive cost for wind solar etc. plus the marinization and electricity transmission costs. It also supplies fresh water, can possibly produce fish and other proteins etc.
For tropical maritime areas, it is possibly their biggest resource working nicely alongside wind, distributed solar, geothermal etc. and killing the nuclear people's arguments that only they can scale to meet the challenge.
Posted by: SHeldon Harrison
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