This seems like an interesting idea, the feasibility may drop with scale though.
College Park, MD (August 3, 2010) — Researchers at the University of Hawaii at Manoa say that the Leeward side of Hawaiian Islands may be ideal for future ocean-based renewable energy plants that would use seawater from the oceans’ depths to drive massive heat engines and produce steady amounts of renewable energy.
The technology, referred to as Ocean Thermal Energy Conversion (OTEC), is described in the Journal of Renewable and Sustainable Energy, which is published by the American Institute of Physics (AIP).
It involves placing a heat engine between warm water collected at the ocean’s surface and cold water pumped from the deep ocean. Like a ball rolling downhill, heat flows from the warm reservoir to the cool one. The greater the temperature difference, the stronger the flow of heat that can be used to do useful work such as spinning a turbine and generating electricity.
The history of OTEC dates back more than a half century. However, the technology has never taken off — largely because of the relatively low cost of oil and other fossil fuels. But if there are any places on Earth where large OTEC facilities would be most cost competitive, it is where the ocean temperature differentials are the greatest.
Analyzing data from the National Oceanic and Atmospheric Administration’s National Oceanographic Data Center, the University of Hawaii’s Gérard Nihous says that the warm-cold temperature differential is about one degree Celsius greater on the leeward (western) side of the Hawaiian Islands than that on the windward (eastern) side.
This small difference translates to 15 percent more power for an OTEC plant, says Nihous, whose theoretical work focuses on driving down cost and increasing efficiency of future facilities, the biggest hurdles to bringing the technology to the mainstream.
“Testing that was done in the 1980s clearly demonstrates the feasibility of this technology,” he says. “Now it’s just a matter of paying for it.”
More information in the project, see: http://hinmrec.hnei.hawaii.edu/ongoing-projects/otec-thermal-resource/
The article, “Mapping available Ocean Thermal Energy Conversion resources around the main Hawaiian Islands with state-of-the-art tools” by Gérard C. Nihous will appear in the Journal of Renewable and Sustainable Energy. See: http://jrse.aip.org/jrsebh/v2/i4/p043104_s1
chris y says:
August 4, 2010 at 8:21 am
You misread the caption. The temperatures are not sea surface, they are the difference between near-surface and 1000m. If the surface temp is 300 kelvins, and the 20 kelvins less at 1000m, then your equation is (300-280)/300, or some 6.6%.
Note also you’re moving water 1000m, not hundreds of Km!
I’ve long thought one could do well with air conditioning by running a coolant loop up the side of someplace like Mt. Washington. Cool it at the top to ambient air temp (20-30F cooler than at the base), use as cooling at the bottom, perhaps augmented with a heat pump, circulate warm coolant uphill. I don’t know the fluid drag formulae, but if you could circulate the coolant just by thermal expansion and gravity, so much the better!
if the warm water was available on the seabed there MIGHT be something to all of this. but i’d like to call attention to the law of conservation of energy. unless someone changed the rules recently the amount of energy required to move the water MUST be greater than the energy produced
Wouldn’t it be better to get all the energy saved in that dreamland CO2 heat piggy bank in the tropical atmosphere of the recent fallen angel Al Baby?
Jeff says:
this is beyond old news … studied this in the ’70′s at the Naval Academy … it just doesn’t scale up to real power …
I worked on this in 1975 a few miles from the US Naval Academy, and yes, Hawaii was the best location. In addition to Jeff’s comments about scalability, a fatal problem was the marine fouling of the enormous heat exchangers. It used low pressure anhydrous ammonia as the working fluid. Of course the capital investment only makes sense if Obama can carry out his campaign promise of making electricity prices “skyrocket”.
Why not making a big, big, transparent crystal box, fill it with heat absorbing CO2 and utilize that “gigantic” source of energy?
It could power a big, big, diapers’ factory to cover the increasing market of bedwetters.
In the end it’s all about Watts!
Great idea, but limited scope to change the global energy profile, even if a large scale system worked. There are simply not enough places on land with deep water close by.
Fusion is the only practical approach to achieving cheap, clean energy. It is a travesty that governments around the world are not putting more money and effort into this.
re Rick Werme- “You misread the caption. The temperatures are not sea surface, they are the difference between near-surface and 1000m. ”
Yep, thanks for pointing out my error. It looks like delta T = 24 C max, and assume T0=4 C = 277K, so as Steve Kirkpatrick points out, the efficiency is maximum 6.7%. But then, increasing the delta T by 1 C only improves the efficiency to maximum 7%, a 5% improvement and a smaller increase than 15% that the article claims.
“Note also you’re moving water 1000m, not hundreds of Km!”
It needs to be lifted vertically by 1000 m, through a pipe having frictional losses. The energy needed for this cannot be dismissed compared to the energy produced by the heat engine.
“I’ve long thought one could do well with air conditioning by running a coolant loop up the side of someplace like Mt. Washington.”
Same problem- energy needed to move cooling fluid, compared to energy use avoided by relying on low ambient temperature at the top of the mountain.
geez. their water is warmer than our air temperatures.
Take into account the energy needed to pump all that water around,
Bingo! Unless the heat differential is HUGE, I doubt this will be cost effective.
And here’s a thought…. If it’s heat you want? Hell, we’re talking about Hawaii…. Volcanoes anyone????
Note: There is a reason why Geothermal has never taken off. My understanding from my days as a geology student is that the steam produced by geothermal vents tends to be very corrosive, which both eats away at critical components, and mineral rich, which also deposits on those components, sulfur being the obvious example.
Steve Fitzpatrick says: “…So the best thermal efficiency (extracted energy compared to energy moved from the hot to the cold reservoir) is about 1 – (277/301) = ~8%. Take into account the energy needed to pump all that water around, and the inevitable less-than-theoretical efficiency of any real Carnot engine, plus the losses in conversion of mechanical energy to electricity, and it becomes clear that this whole enterprise is unlikely to be economically useful….”
Spoilsport.
This seems to be a rather complex way to do things. Especially on a volcanic island with active volcanos (one of which is the most active on the planet.)
If extracting power from Kilauea is too difficult Mauna Kea is dormant and snow capped.
So the temperature difference available is at least 100C, far more than you could get from water out of the Pacific.
Also suitable geothermal power will enable electricity generation using conventional steam turbines. To keep the AGW lot happy it can even be declared “carbon neutral” 🙂
I’m sure there’s some tipping point or other involved with sucking heat out of the oceans.
It’s a boondoggle. At one point, Natural Energy Laboratory of Hawaii was using the cool deep water to cool soil to grow strawberries on the hot coast, although the world’s finest land for growing strawberries already existed a few miles inland (and upland) at Waimea.
If it weren’t for Sen. Dan Inouye, this joke would never have come into being, and when he leaves the Senate, it will go back to being what it used to be, a shelf of hot, bare lava rock.
I visited the http://www.nelha.org/ site on the big island on vacation about 3 years ago (that IS why you go on vacation, right?). The site just provides and disposes of the ocean water. They have a couple of large pipes going down deep, and several at intermediate depths. They lease space to tenants that wish to make use of the water. They had an algea grower, a bottled water company (yes, they take the very pure deep ocean water, filter out the salt and sell it for big bucks), and someone experimenting with concentrated solar power when I was there. They talked about having a bid from someone to put in a power plant.
They have a very nice (million dollar) visitors building that is covered with solar cells and cooled by the deep ocean water. They have regular talks there for visitors (call first).
The docent giving the talk said some interesting things:
1. This is salt water, so it really eats up whatever machinery you put in place. The test plant of years ago rotted out pretty fast.
2. You have to build BIG to get any real power out of it. ($$$)
3. The geothermal power being generated down in Puna has a lot of potential (I think far more). http://www.punageothermalventure.com/
4. They don’t release the deep, mineral-rich water to the surface. That would change the costal echosystem, so the re-release the water at various depths, depending on it’s final temperature.
I’m as big a curmudgeon about “sustainable” energy as anyone, but I’ve always been fascinated by OTEC. As one commenter noted, it can produce saleable byproducts such as fresh water along with electricity. One ingenious scheme floated a few decades ago was to produce ammonia on OTEC barges, with the low-pressure, heat differential turbine providing the electrical power. But the ultimate price competitor for electricity production is always going to be coal, and it’s hard to see how any sustainable source will ever be able to beat it.
“”” chris y says:
August 4, 2010 at 8:21 am
A Carnot engine is the best that you can do in terms of classical heat engine efficiency. “””
HOORAY !!!
Finally somebody sane does some real scientific thinking.
Chris why don’t you ask those dummies for a piece of their research grant ?
Unless somebody imagines that sea water can actually “focus” solar energy; as in compact it into a smaller space than it arrived in; we can presume that the input to this heat engine is less than 1 kWatt/m^2; then throw in your Carnot efficiency on top of that and you have a real fizzer as far as fireworks go.
SPACE COSTS MONEY !! EFFICIENCY IS EVERYTHING !!
Chris the same pestilence (Carnot Efficiency) plagues the wind energy idea. A wind generator is a gas tubine engine; with air being the working fluid, and the sun being the source of “heat” energy to raise the kinetic energy of the working fluid, and its Temperature to feed to the output turbine wheel (propellor) to convert it to shaft horsepower and thence to electricity by way of a conventional alternator or other generator. The working fluid comes in over a vast space from some solar heated hot place; often over the ocean, and the cooler exhaust gas must be discarded to some vast cooler exhaust space.
Any sturctures in the way of the working fluid intake; or the exhaust fluid outflow, will create turbulence and spoil the flow pattern and turbine blade efficiency.
So if you think that a simple wind turbine just takes up a quarter acre or so; you are in need of a serious attitude adjustment.
And this Hawaii boon doggle is the same darn thing.
Yes there’s a vast amount of energy in the system. Don’t people ever consider how much of that energy is available to recovery.
I was reading down to see if anyone at all had caught the Carnot Trap; because I was going to post it; if you hadn’t already Chris.
“…one degree Celsius greater on the leeward (western) side of the Hawaiian Islands than that on the windward (eastern) side.
This small difference translates to 15 percent more power for an OTEC plant…”
___
Would someone please explain to me how this could be physically possible.
Was Carnot truly wrong for all these years?
Interesting. Drawbacks include corrosive effects of seawater, similar to why geothermal is so hard and expensive. Assuming more efficient engineering and materials in the 21st century another reason OTEC might actually be a good idea in this particular instance and actually economical is the very high price of oil, etc. in Hawaii. These schemes are best tried out where the cost of energy is highest.
from OP:
This is one of those instances where 15% of almost zero is still almost zero. It needs a lot more heat differential than the ocean can provide except perhaps from thermal vents. Heat engines have been of interest to many inventors for nearly 200 years and counting since Carnot came up with the Carnot Heat Cycle. Every conceivable way of extracting power from small temperature differentials less than about 250F has been tried and found greatly wanting.
The source of cooling water is nice if they use solar to heat the water up to 500 degrees or more to run steam turbines but that’s about it. A small scale (large but not commercially large) experimental site is still struggling to attain modest efficiency in a Stirling engine in a SW US desert where they have relatively little problem getting nice fat temperature differentials from solar heated hot water.
“”” chris y says:
August 4, 2010 at 10:26 am
re Rick Werme- “You misread the caption. The temperatures are not sea surface, they are the difference between near-surface and 1000m. ”
Yep, thanks for pointing out my error. It looks like delta T = 24 C max, and assume T0=4 C = 277K, so as Steve Kirkpatrick points out, the efficiency is maximum 6.7%. But then, increasing the delta T by 1 C only improves the efficiency to maximum 7%, a 5% improvement and a smaller increase than 15% that the article claims. “””
The numbers were wrong (I never even bothered to read them) but your conclusion Chris was correct.
Carnot inneficiency kills this idea.
Anybody who thinks a 6-7 % efficiency is viable just hasn’t ever bought any real estate.
A serious large scale PV solar project proposed for the Desert SouthWest “wastelands” of the USA in Jan 2008 issue of Scientific American took up just 30,000 square miles for soalr cells; that’s 19.2 million acres; which just coincidently is the exact size of the entire arctic National Wild life Refuge.
So the Evil Fossil Fuel Barons wanted to drill on 2400 acres of ANWR for their filthy petroleum; about the size of The Great Mall of America Shopping Center in San Jose CA ; and the solar cell gurus want to put their 20% conversion efficiency solar cells over the whole 19.2 million acres near the four corners region; plus another 10l.24 million acres for a solar steam farm of mirrors.
Now comes the Polynesian Luau with its 6-7% Carnot efficiency.
Now who was it that claimed that this machine even achieves anything near Carnot efficiency, with whatever heat engine cycle they are planning to run; so I would discount that 6-7%
Now how about the heat losses fromt that column of water that they are planning on raising 1000 metres. How do they propose to thermally insulate all that 1 km of pipe to stop losing what little energy they have .
And probably my tax dollars went into this silliness.
Yes by all means give some private investors permission to build the darn thing and reap their just rewards; but don’t ask me to invest in their company.
Wouldn’t the work needed to bring the warm and cold water together negate the energy derived from allowing them to exchange heat?
Wait till they find out the realities of engineering: the ocean is a corrosive, fickle biatch that likes to tear anything Man makes apart. Trying to keep something together long enough to make it pay off is NOT EASY.
…..but hey for the greenies it’s easy to just make up stuff that never works in the real world….
What about all of those lovely Hydrogen and Deuterium atoms, swimming around, not doing any work.
Marshal T Savage’s “The Millennial Project:colonizing the galaxy in eight easy steps” outlines using OTECs on a massive scale. He mentions that water having neutral buoyancy only needs to overcome the difference in density so pumping massive quantities up a vertical pipe is not as difficult as may seem (unless you find a 12m diameter pipe going down 1000m difficult!) He naturally picked equatorial locations to maximize delta T. His best delta T location was Sri Lanka if I recall.
“The Millennial Project” would certainly appeal to many WUWT readers though, a fun blend of engineering and speculation. A good read on a cold winter’s evening!