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
Steve W. says:
August 4, 2010 at 11:02 am
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.
Spot on. I fail to understand the fascination of placing machinery in the most corrosive environment the planet has to offer. Ask any boat owner about maintenance – that’s why they’re called boats – Break Out Another Thousand.
Tidal, wave and offshore wind may be attractive from the planning point of view but as a potential shareholder (electricity customer), I am horrified when I think of the maintenance costs. After a number of years these begin to look like the usual portrayal of the CO2 graph.
“and the solar cell gurus want to put their 20% conversion efficiency solar cells”
Last I checked an affordable 20% efficient solar cell is still a wet dream. Seems I recall 14% in modestly expensive thin film is about as good as it gets and have an expected service life of 20 years or so. Advances in manufacturing and economy of scale are hoped to halve the price in tens years or so and then make some economic sense in large installations.
Keep in mind distribution costs are sky high for power coming from a remote desert and you have significant transmission losses. For a home installation with net metering where distribution is already taken care of it’s looking practical or can easily be made practical with some modest advances in economy of scale in the hardware. Displacing a significant amount of transportation fuel with electricity is still a pipe dream due to, among other things, no grid anywhere near able to carry the additional load. We get big brownouts now all over the country during periods of peak demand. No way it can move more juice without serious expansion. Just imagine how much everyone is going to love more high tension transmission lines going over their homes and schools and way more substations filled with big buzzing transformers.
Besides corrosion, one of the early problems NELHA had was that the pipes are so big they provided space for their own ecosystems.
The environmentalists had to figure out how to kill many innocent sea critters just to keep the water flowing.
Two pipes with venturi foot valve. Called a jet pump. Water goes down one pipe and suction generated by a venturi brings a greater volume up the other pipe. No electrical lines or underwater motors involved. Rather common method in water wells and surface water pumping.
The pipes, per se, aren’t the problem. They have to be well insulated pipes to preserve as much temperature differential as possible. Nobody usually cares about temperature change in normal well pump operations.
Let’s not confuse thermal efficiency with economic efficiency. If I can build a process that ends up producing power at a levelized cost of $0.05/kWh over a 20 year period, I build the thing regardless of its Carnot efficiency, which in and of itself is a contextless number.
Let’s compare two fairly well known scenarios. A coal fired power plant and a natural gas in combined cycle plant. The capital to build a 100MW plant is less for the natural gas plant and the efficiency of the natural gas plant is considerably higher, yet the cheaper power will always be from coal. Why? Fuel costs. If you looked straight at efficiency here, you would wrongly come to the conclusion that natural gas power is cheaper.
Using the 20% efficiency of solar cells is also a bit of red herring. It’s not the efficiency that does in the economic feasibility of a solar cell. It’s not even the land costs. It’s the capital tied up in solar cells collecting a low energy density source (sunlight). If you don’t believe me, think about this. A 1 KW system requires roughly 1 m^2 of space and costs $6K. That means to fill an acre with solar cells where only 50% of the land is occupied by the cells, it would cost $2.4 million dollars. That dwarfs the tens of thousand you are paying for the land. Even if you got 55% efficiency (in the natural gas combined cycle realm), it barely makes economic sense without subsidies.
So what’s the biggest difference between the low energy density source (the ocean) and the other low energy density source (the sun)? You can control how much water flows through your energy production system. With the sun, it is what it is. So long as you can economically generate energy beyond the parasitic load of pumping the water, thermal efficiency matters not. In this case the metric that matters will be $/KW capacity installed (net of parasitic load.), not the thermal efficiency. Efficiency, while interesting, can never tell the whole story on its own.
BTW… I did not mean to suggest with my previous post that $0.05/kWh was what this power would cost. I only used that number to demonstrate that I cared more about the levelized cost of producing the power than the actual efficiency in producing it. I have no actual knowledge as to what it would cost to build a large scale OTEC plant.
Why ITER is a boondoggle. Billions of dollars, and ITER won’t achieve break-even even if successful.
Polywell and Dense Plasma Focus Fusion have a chance, and they aren’t massive money sinks to find out. Polywell is adequately funded, and Focus Fusion has raised enough money privately to see if it’s workable.
Note that only the aneutronic proton-Boron fuel cycle can really be called “clean”, unless you’re willing to disregard the neutron irradiated reactor parts.
Friends:
Several here have commented that this is not new. But the article and the comments miss some important points. The Hawaiian OTEC process does have economic potential but only in a very few geographical locations.
The Pacific Institute in Hawaii perfected the technology for economic power from OTEC in the 1990s, but most of the product from their system is cold water (from deep ocean) with some (very small amount of ) electricity as a by-product. Using this cold water as a coolant for air conditionig would be cheeper than electricity for air conditioning (air conditioning is a major user of electricity in warm climates) .
The system is only useable in locations with direct access to deep ocean (e.g. Hawaii and parts of the coast of India).
So, the Hawaiian OTEC system could be very economic as a source of air conditioning and as a soil coolant for horticulture but only in the few places with direct access to deep ocean.
Hence, in common with most other renewables, it has a potential niche market but lacks potential for use to displace the bulk of fossil fuel usage.
Richard
Just as a sciencey aside for home experimenters small air and water venturis for generating vacuums are less than $20. The water venturi is fast at drawing a vacuum and any old household tapwater source 30psi or more has enough pressure to drive them. The water venturi’s best vacuum is limited by the vaporization temperature of the water source. One you have a hard enough vacuum to hit vaporization point you’re sucking steam not water and have reached the limit. The colder the water source the better the vacuum. Air venturi’s have no such limit and will draw a substantially harder vacuum but they need a lot of air at 90psi or better. A small shop compressor with 2-3hp motor and 10 gallon air tank can’t keep up for long but will evacuate vessels up to a gallon or so in one or two minutes. The water venturi’s can be had from scientific supply houses. The air venturi’s are most economical purchased from hardware stores and are designed to evacuate water from air conditioner freon pumps & lines.
One nifty little thing I made out of a couple rubber corks, copper tube, a water venturi, a hot air blow dryer (small handheld for drying hair), two wine bottles (one full of wine), and an ice bath. Basically connect the two bottles through the tube & corks and put the vacuum source on the empty bottle. Hot air gently heats the bottle filled with wine, alcohol vaporizes and passes into second bottle which is in the ice bath. First bottle is turned into non-alcoholic wine and second bottle ends up 100+ proof grape brandy that will burn nicely for flaming drinks, deserts, and so forth. Very low heat is the key to good flavor. The wine never gets above room temperature. The hot air dryer just replaces the latent heat of vaporization being carried away as the alcohol evaporates. By keeping the temperature low none of the heat sensitive taste & aroma components in the wine or the brandy are disturbed. Start to finish is about 10 minutes for a liter of wine. Whole setup costs about $25 in parts and a couple hours to make. Beer & wine homebrew stores have the right rubber corks (one with a single hole and one with two holes). Home Depot has everything else.
“”” Dave Springer says:
August 4, 2010 at 12:51 pm
“and the solar cell gurus want to put their 20% conversion efficiency solar cells”
Last I checked an affordable 20% efficient solar cell is still a wet dream. Seems I recall 14% in modestly expensive thin film is about as good as it gets and have an expected service life of 20 years or so. Advances in manufacturing and economy of scale are hoped to halve the price in tens years or so and then make some economic sense in large installations. “””
Well Dave, I hear you Mate; I have some actual product literature ( commercially available panels) from Sun Power Syatems and they claim 22% efficiency.
Now they don’t say whether that is an actual final assembled panel as installed operating solar to AC grid efficiency or whether it is Air Mass zero or one measured or what. They are so far as I know purely silicon cells; and likely not so-called Blue cells, since that would not seem to be useful for Air Mass one applications.
I could almost buy that efficiency for a bare cell under lab ideal air mass zero conditions; but like you I am skeptical of such operational efficiency claims. There’s no reason teo expect a 20 year life limit. Like all semi-conductor devices they will have infant mortality failures; but with proper QA, they could easily exceed 20 years life.
Fred Singer’s comment on the 30,000 squ mile thing was: “Who is going to clean 30,000 square miles of solar cells every now and then ?”
Such a farm would have to fenced and patrolled by armed guards after removal of ALL human inhabitants; since it would be too much of a vandal/terrorist target.
TJ Rodgers is nobody’s fool, and if anyone is going to have success in the solar cell business; Sunpower is a most likely candidate. Other schemes, which I won’t mention to save them and their “investors” including us poor sap taxpayers from embarrassment, have never made a dime, and aren’t going to make a dime, even after they run through their taxpayer funded loans.
Stanford University announced just this week, a possible breakthrough that could make some solar cell farms viable.
The big problem with PV cells is that they only convert a certain fraction of the solar spectrum because of their band-gap; and Silicon is the only economically viable choice. The rest of the solar spectrum and photon energy over the bandgap just becomes waste heat which raises the cell temperature; which drops the cell Voltage and lowers the efficiency.
The Stanford scheme appears to deposit a spectrally selective reflective layer on top of the silicon to reflect almost all of the spectrum outside what the silicon can directly convert to electricity; so that greatly reduces cell heating adn keeps the efficiency up.
But the panels now become efficient reflectors of the remainder of the soalr spectrum; so they can be oriented to reflect the sunlight on to a central tower and run a thermal collector steam turbine system. They claim they can reach 1100 deg (probably F).
So this would work for the major plant concept; but even there they have a new problem.
Those steam turbine plants require that almost ALL of the panels be tilted off the normal to the sun direction; since they must focus on an off-axis central collector. They all need to be steered through the day, which is a complication and control expense; given that the thing needs to withstand a 100 year storm; not to mention sand storms; but the off-axis Optics means that an even larger surface area of solar cells must be constructed, since only the are projected on the sun dirtection is collecting.
They claim they can get about 60% total solar to electric power conversion efficiency from this combined PV/Thermal collector.
But it is not your home rooftop solution.
Oh, even cooler thing about the wine vaporizer described above is that once you have an initial vacuum in the empty wine bottle you no longer need the vacuum source running so it only uses a few gallons of tap water in the process. The volume of liquid alcohol coming out of the first bottle is exactly the volume the condenses in the ice bath bottle so, no net change in volume spells no net loss of initial vacuum. The connections are super easy to get vacuum tight. The vacuum pressure sucks the corks down into the bottles and compresses the rubber against the copper tubes – loosely set corks self-seal on their own recognizance.
I love tinkering!
Thanks for keeping this blog accessible for scientifically unsophisticated layman like me. I found this blog in July 2008 when I realized the the Sun was weaker working outside on my market gardens.
I love this beautiful graphic. I grew up in Hawaii and always wondered why the North Shore beaches where colder than the Leeward beaches of Honolulu. I am very interested in understanding how the inner earth transmits heat to oceans and the impact this has for understanding and predicting climate. The recent gravitational variation map was sensational but unsure if it is useful in the measure of heat transfer from the mantle to the oceans. Is it possible this mesure will be useful in predicting future La Nina and El Nino months before they happen? Is it known to what degree the inner Earth heats it’s oceans. Do we know if there is a relationship between the Sun’s magnetic dynamic and the dynamics happening with in the inner earth that would explain changes ocean heating, regional variations in gravity, volcanism and earthquakes?
“”” L. Bowser says:
August 4, 2010 at 1:28 pm
BTW… I did not mean to suggest with my previous post that $0.05/kWh was what this power would cost. I only used that number to demonstrate that I cared more about the levelized cost of producing the power than the actual efficiency in producing it. I have no actual knowledge as to what it would cost to build a large scale OTEC plant. “””
Well then you care about something that is entirely of no consequence.
The problerm of alternative energy schemes is NOT ECONOMIC ! If it WAS economic, then it could be solved with the stroke of a pen; as I have described elsewhere; simply place a tax of $1,000,000 per barrel equivalent on fossil fuels; and Voilla ! instantly your renewables are economically viable; whether they are 50 cents per Watt or $50 per Watt (peak power level); or $500 per Watt for that matter.
But the problem is NOT economic; it is TECHNOLOGICAL. There are no alternative renewable energy schemes that are competitive technologically with fossil fuels; if they existed, they would already be in widespread use; and no amount of Governmental duck shoving could render them uneconomical.
The fundamental real cost of any enterprise is the sum total of all of the energies it takes to arrive at the finished product.
When our ancestors already had free clean green renewable energy; it proved to be so energy intensive to get at; that it had a hard time maintaining even their puny numbers at the time. They spent nearly every waking hour clambering around in fig trees picking figs to get their free clean green renewable energy.
It wasn’t till they discovered stored chemical energy, and the means of accessing it through fire, that they were able to sustain themsleves, and grow their numbers and enrich their societies.
Renewables didn’t work back then; and they won’t work today either.
Yes they are renewable; but the are simply too diffusely dispersed; and they renew far too slowly for our needs.
Yes I plan to stick around till the oil runs; out just to watch the green weenies squirm when they run into the cold reality of their folly.
L. Bowser- Interesting comments in comparing gas with coal.
“In this case the metric that matters will be $/KW capacity installed (net of parasitic load.), not the thermal efficiency. Efficiency, while interesting, can never tell the whole story on its own.”
Agreed. What I find useful with the Carnot efficiency calculation is that it gives a starting point to calculate whether the energy needed to run the parasitic losses (moving water up 1000 m through a lossy pipe, thermal losses along the way, losses in the engine) will exceed the energy generated by the temperature differential that finally arrives at the heat engine. If you start with a low efficiency, the losses need to be really small to even break even. I have serious doubts it will generate enough energy to move the column of water.
And I just read your full story above; L. Bowser so let me ask you. WHAT ON EARTH DO YOU IMAGINE CAUSES THOSE UNECONOMICAL COSTS YOU ARE TALKING ABOUT ??
If I can double the efficiency of a solar cell, I can halve the area needed to produce acertain amount of electricity. Many people believe that if you halve the land area you need for a project that you will about halve the cost of the installation. Fancy that; isn’t that radical that you can impact the cost of an enterprise by increasing the efficiency of that enterprise.
The very mention of your “subsidy” indicates you don’t have the foggiest idea what is driving the system.
A $1 taxpayer subsidy for your renewable energy plant requires roughly a $2.86 taxable profit (35% Corporate Income Tax Rate) from private enterprise businesses. The long term average profitability of all corporations and small businesses is something like 4%; so on average they have to do $25 worth of taxable enterprise to make a $1 profit; or about $71 to make the $2.86 profit to subsidize your scam with a $1 subsidy.
If you think that efficiency doesn’t matter and cost is paramount; then L. I have the perfect solution for you.
How about ZERO cost for your renewable energy; for as large a power plant as you want to build.
You tell me what your favorite renewable energy scheme is; and how big a plant you would like (how many GigaWatt’s peak generating capacity).
Now I will build you that plant and give it to you for free; ZERO capital cost. Now you can run your free factory accessing the free clean green renewable energy so your costs are, and always will be ZERO !
Oh there is one small thing I would like you to do for me; before you start selling your free clean green renewable energy at a totally sinful profit margin.
Using the free energy output from your plant that I gave you for free; along with all of the natural resources in the universe in their natural state; wherever they are; Please construct for me, a duplicate of the plant I gave you.
After you have built me a duplicate copy of my gift to you; using only the energy it provides you with; then you may hang up your shingle and open up for business; and make yourself filthy rich.
I believe you can get filthy rich; if you choose for me to gift you, a modern Fission Nuclear Power Plant.
Sans Fossil Fuels, I am not ware of any other way to get rich.
Martin Brumby says:
August 4, 2010 at 9:33 am
“[…] …Greenies and amateur bunny huggers won’t hear of the idea. […]”
ROTFLOL! As opposed to professional bunny huggers!?!?
I think the professionals are paid by NGOs. (And just think of the questions during the job interview for that position…)
Thanks, Mr. Brumby! First time I’ve seen that phrase on here and it’s ripping good.
chris y says:
August 4, 2010 at 10:26 am
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.
____________________________________________________________
No, you are completely wrong, as the hydraulic pressure term is cancels out, you are left with the head loss term and the v^2/2g term via the Bernoulli Equation, both of which can be made negligently small by making the intake riser pipe sufficiently large.
You are not lifting water 1000 meters, as there is ambient ocean water outside the pump/OTEC plant at the same elevation of the ocean water inside the pump.
BTW, I did graduate research work on the OTEC concept in the late 70’s, and even published a paper in the peer reviewed Hydraulics journal of the ASCE.
It is my opinion that OTEC is not as promising a technology as wind, or solar, or geothermal. It may not even be as promising a technology as wave energy extraction, which I also don’t consider as promising a technology as solar, or wind, or geothermal.
@Dave Springer,
Your wine vaporizer sounds very much like the sea water vaporizer I describe above. Yours produces distilled alcohol, the one I describe above would produce distilled water plus power.
What? Engineeing programs always have a component of engineering economics. Engineers have to propose realistic projects after all, and cost effectiveness is a large component of that.
The cost estimates I have seen for OTEC lie between $10,000-$20,000 per kW installed capacity which makes it “only” about 5-10 times more expensive than wind power, which is itself about 6 times more expensive than a coal-fired plant. Installed capital cost is not the only factor involved in determining the cost of delivered energy, but it is a dominating factor, especially as someone has pointed out here, the replacement time for equipment could be very short.
As Chris and others have pointed out, maximum possible efficiency is around 6%, and the feasible efficiency might be as much as 80% of maximum considering that pumps and turbines are pretty efficient (wind turbines achieve about 86% of the betz limit when operated at optimum wind speed). The resulting 4-5% efficiency of OTEC simply runs the cost per kW outta’ sight.
chris y:
At August 4, 2010 at 2:19 pm you say:
“What I find useful with the Carnot efficiency calculation is that it gives a starting point to calculate whether the energy needed to run the parasitic losses (moving water up 1000 m through a lossy pipe, thermal losses along the way, losses in the engine) will exceed the energy generated by the temperature differential that finally arrives at the heat engine. If you start with a low efficiency, the losses need to be really small to even break even. I have serious doubts it will generate enough energy to move the column of water.”
Please see my comment at August 4, 2010 at 1:37 pm .
The Hawaiian OTEC system lifts water up one tube, uses it as a coolant (for air conditioning or soil cooling in horticulture), then returns the water via another tube. Once started, the energy required for the lifting is not great because the mass of rising water equals the mass of falling water and only the ‘friction’ of the water in the pipes has to be overcome.
More problematic is the energy required to pump the water around the small-bore pipes used for the cooling. And the only energy used by the system is provided by the temperature difference between the cold water from depth and the warm near-surface water. Furthermore, the energy extraction transfers heat from the warm water to the cold water, and if the cold water is warmed too much then it loses its usefulness. These factors provide a limit to the area that can be supplied with the cold water for cooling.
But the Pacific Institute in Hawaii built and demonstrated a full-scale working system in the 1990s (I saw it working and I wrote an article about it).
However, the fact that the system works and is cost-effective does not mean much because, as I said,
“The system is only useable in locations with direct access to deep ocean (e.g. Hawaii and parts of the coast of India).
So, the Hawaiian OTEC system could be very economic as a source of air conditioning and as a soil coolant for horticulture but only in the few places with direct access to deep ocean.
Hence, in common with most other renewables, it has a potential niche market but lacks potential for use to displace the bulk of fossil fuel usage.”
Richard
http://www.lockheedmartin.com/products/OTEC/index.html
Lockheed Martin has been dabbling for a while in OTEC SINCE THE 1970’s.
For carnot – at low temp differences you will be very lucky to get even 30% of the carnot eff. A 2% overall efficiency would be impressive. Think on that – 50GW of heat transfer for 1GW of power.
Hawaii has a 4000m tall strato volcano that is a better resource, with temps that are (depending on lapse rate) 30-40°C cooler at the top than at sea level, and on land where it is easy to work. A 2-3km tall radio-mast type tower on top of the mountain with some nice big heat exchangers at top and a hydrogen loop running down to sea level through a gas turbine would get perhaps 10% overall efficiency with a 60°C temperature differential. It would also make one hell of a tourist attraction.
Ingenious solution to a non-existant problem.
I was the Lead Operating Engineer on board the Ocean Energy Converter, an old WWII T2 tanker that was the platform for OTEC-1 off of Keahole point in Hawaii in 1980. It was operated for the Department of Energy by Rockwell International, my employer at the time. I started and ran the plant for most of its operating life, less than a year. The operating fluid was Ammonia. The system did not generate electrical power, instead it just flashed the Ammonia across a drag valve on the way to the condenser. Electrical output was estimated (modeled) at about 1 Megawatt. The system did operate well within its design parameters. We had a 2000 foot long cold water pipe that was three, five foot diameter polypropylene pipes bound together to supply the condenser. A ten foot diameter warm surface water pipe for the evaporator supply and 150 foot long, fifteen foot diameter fabric tube to handle the combined water discharge. The subsurface discharge was an environmental necessity because the discharge water might disrupt the lives of the surface fish (God forbid!). Total water pump horsepower was around 15000 hp, about 10 Mwt! for a modeled net output of minus nine MWt, not bad for an alternate energy project. /sarc
The next step in the project was to be the 400 MWt. near commercial plant. Construction highlights would be slip forming a 100 foot diameter concrete cold water pipe, two thousand feet down into the ocean from the platform. Plus the invention of a 100 mile long submersible extension cord so we could plug the thing into the grid. We would also need enough pump power to handle about one fourth of the average annual Mississippi River flow. We inquired discreetly to the manufactures of the largest water pumps on earth if they could provide something like this and their response was to ask what we were smoking and could they have some?
After a year, sanity (and I guess Ronald Reagan) prevailed, we pulled the plug on the experiment, gave most of the equipment to the State of Hawaii, declared victory and went home.
The efficiency of this type of engine is so low that it require equipment of unbelievable size. Even though it was a high point of my career, it saddens me to think this very poorly thought out idea could possibly be making a comeback.
Dave Springer says:
August 4, 2010 at 1:52 pm
Just as a sciencey aside for home experimenters…
A retired air conditioning engineer in Greenfield NH (Sanford Farms) used something similar to make the most incredible tasting blueberry jam. The jam was “cooked” at low temperatures and ended up tasting just like fresh blueberries…. drool