Ocean heat may be used to generate electricity

The power required depends on the diameter of the pipe and can be quite negligible as the losses are only due to friction along the pipe. The water is not really pumped "up" it is pumped "through" 1 km. Essentially the pressure at 1 km depth is equivalent to the head needed to pump water from -1km to the surface. Another way of looking at it is that at the bottom of the 1 km pipe you have 100 bar of pressure from the 1 km of seatwre over your head to push the water in the pipe.
On land however the situation is quite different. if you pump water up a 1 km pipe, there is no surrounding pressure at the base of the pipe to push the water through the pipe.
Other expalnations are rather mathematical I'm afraid.

Exactly the question that came to my mind as I read the article. The writer does not say how much power would be required to pump seawater up a one kilometer pipe and how it compares with the final output. Would the science correspondent care to enlighten us?

A wonderful idea at first glance that doesn't survive 10 minutes computation, has never deterred the hucksters from hype. Let's take 2 minutes to debunk most of it here.

The efficiency of any heat engine has an upper limit. Assuming a 20 degree temperature differential at 25 degrees for the hot side of a heat engine cycle yields a theoretical maximum efficiency of 8.4%. That's before flow loss/turbine/generation/transmission losses, so actual efficiency can't get much above 5-6%.

The process thus requires roughly moving 15,000 liters of water per second per megawatt. So a 100 MW plant will move 1.5 million liters per second of 20 degrees colder water to the surface. Imagine the havoc that much cold water will have on the local ecosystem, not to mention the local weather.

And that's just one 100 MW plant. The world generates over 20 TW hours of electricity per year, or roughly 25 million times this 100 MW example.

An article in Scientific American some 35+ years ago hyped this idea predicting that the US could get as much as 10% of its electricity from the Atlantic Ocean. Alas, running their numbers showed that they used the entire Gulf Stream flow lowered by 1 degree celsius to generate that power. Somehow, I don't think Ireland or UK would smile on a dewy eyed US plan that lowered their local water temperature by so much as a fraction of a degree.

Hey, maybe we've found the solution to global warming! Just build a few million of these things, and the ocean surface will cool by enough to stop the Gulf Stream in its tracks, and put us into an ice age.

More likely, the relentless Carnot equation will yet again overcome even the most ardent hype, and this idea will die the same death it did 30 years ago.

Marine architecture with salt water, ocean tides, storms and intense sun insures nothing last more than a few years and then only with painstaking effort. Rust begins after the first day.
Wave energy turbines, floating windfarms, ocean platforms are battered and aged prematurely. It might as well be a sea of acid. Barnacles and algae will gum up any exposed surface. Sea bird poop is corrosive. Hurricane season brings its own challenges.

There are very few environment more hostile to complex engineering designs than an ocean shore. Turbine engineers from university labs cannot fathom the depths of deviousness of a rip tide or violence of a wave break. That is the real world.

If it is as durable as a river stone it might make it. Otherwise it is metal spaghetti after the first winter.

Though the first plant was in the west, it was Japan who truly pioneered it. India learned from Japan, and recently Lockheed consulted India for their plant.

Efficiency is indeed low, but if the plant could last a few decades, its worth the effort as the fuel doesn't run out. Given that offshore oil rigs survive for a long time (digging up filthy corrosive oil),
OTEC plants can potentially last long enough.

I would still favour wave and tidal energy converters as they require much lower capital, are already as competitive as offshore wind(economically), and will be easier to maintain.

The small temperature difference dooms OTEC to efficiencies on the order of 4%. Hardly encouraging.

I'm skeptical about this alt energy option. Like previously stated, it seems like a lot of capital to invest in infrastructure that will soon succumb to the harsh conditions of the ocean. Also, with high storm intensity from hurricanes in areas such as the Caribbean, would the facilities be able to stand the test?

As a marine ecologist, I cannot help but wonder how this form of energy would impact the local ecosystems. Cold waters from the deep can be quite different in chemical composition than at the surface. Would the cold water be released at the surface? Or pumped back down to deeper water? If released at the surface, it could potentially induce phytoplankton blooms that normally do not occur in those areas.

I agree that OTEC is a fantasy for all but the most remote applications; one must assume a fossil fuel cost of roughly 5 times the current rate per BTU to make $10M per MW installed work out even Stephen over 20 years, even discounting operation and maint costs, which will be huge. However, I disagree with PSH's calculations; I come up with 23 thousand (NOT 25 million) of these giant drinking straws needed to produce the 20 THOUSAND Tera-watt Hours needed to power the whole world. As a matter of scale, a 1 GW plant is a typical large power plant and there are perhaps 4 thousand plants on this scale operating in the world, some as baseline and some as peaking plants. I recommend Brian Hayes' excellent book on infrastructure for those interested.

That said, I admire the sort of thumbnail calculations native to the Engineer that can combine money, time and thermodynamics into a coherent package. It is sad that such basic math is rarely undertaken and too-often ignored, as the ethanol idiocy shows us.

Some perspective on a 1.5 million liters per second flow rate. This is about
twice the Thames River
5% of Niagara Falls
3.5 times the Colorado River
(average flow).

if its ever up and running, then some save-the-world environmentalists will find a computer model that shows that changing the huge ocean's "delicate" temperature balance will result in catastrophe. the ensuing battle to save the earth will keep the environmentalists funded for decades, and maybe make for some more movies like "2012".

Efficiency doesn't matter when the fuel is free.

$1billion for 100MW? $1billion for 1km? Surely they can do better than that?

@professional rationalist

My mistake:
20 TW = 20x10^12 watts
100 MW = 1x10^8 watts

If the plants ran continuously, then you would need 20x10^4, or 200,000 of these to generate 20 TW. No plant runs 100% of the time, so allowing for around 1/4 downtime, you get roughly 250,000 plants, not 25 million.

Staggering numbers either way.

Also, 1.5 million liters of water through a 10 meter diameter pipe is just about 20 meters per second, or 72 kph (roughly 45 mph). Clearly, whoever came up with this design hasn't tried controlling water moving at this speed, much less a 1 km column of it weighing over 1.5 million metric tons. Serious water hammer this.

Setting aside the cavitation and control aspects, the losses would be considerable, even if you could keep the barnacles off, so my 5-6% efficiency should be reduced. Maybe we need 350-400,000 of these things now.

Me, I'd just like to see them put the brakes on that much 70 kph water without blowing the entire thing to smithereens.

$10/Watt?
Uh oh.
But still better than some.
Nuclear power gets mighty expensive if you include the 100,000 year security costs.
Coal? How do you replace a mountain?
Fracked natural gas? How do you fix a polluted aquifer?
Stirling Solar? Infinia's concentrating dish solar Stirling came in around $20/Watt. SES went under.
PV Solar? What about during the night time?
Wind? What about when it isn't windy and what about all those birds?
Oil? Just how many wars are we prepared to fight and how many beaches to clean up?

Maybe OTEC is the answer.
Solar preheating could improve the efficiency.
With low operating temperatures, why use metal?
Make it a contest and I'm sure a cold water pipe with the correct specs could be constructed for far less.
Of course, there's the ocean thermal and salinity pollution that would have to be addressed but that seems mild compared to Fukishima fission products in the ocean or a dead Gulf of Mexico or acid rain or natural gas fizzing from water faucets.

OTEC is the energy solution millions have been waiting for. The Caribbean is paying massive costs to import fossil fuels to aging power plants, and the populations still deals with blackouts from plants that can't handle the demand. OTEC has been proven for decades and is now ready to go commercial. The Bahamas are starting a trend for the rest of the world to follow. Clean energy plus clean water is an equation millions of people can benefit from. For more on the deal in the Bahamas and to keep up to date on more OTEC news visit the On Project.

http://www.theonproject.org/2011/the-bahamas-sign-memorandum-of-understa...

More energy lunacy. Would you spend a billion dollars to grow a million dollars worth of potatoes? What is it about energy that inhibits rational thought? The world is accessing a huge new supply of natural gas - use it.

Wow. You drank the Kool-Aid, cup and all, didn't you? As Robert North pointed out, 100 megawatts is next-to-nothing as far as energy generation goes, and having to spend a billion dollars to get that 100 MW is downright ridiculous.

Energy generation is about getting the most oomph per dollar spent, and this concept is an interesting science fair project, but not a practical solution to anything at this point.

After a tour of the facility in Hawaii it occurs to me that the real value is for aquaculture. Essentially the net power gain from a 20 c temperature difference is so low that it seems more likely to provide power for an aqua culture facility.

Deep ocean water is high in nutrients for phytoplankton and is cold so popular cold water species can be grown in the nutrient rich cold water. This is working well in Hawaii where, as I understand it, they raise lobster to sell to asia (and locally I presume).

The plant is not free,even free fuel does not help if the plant has to be so huge it never recovers the cost.

Would it not be simpler to utilise this "free" water pressure to turn a turbine and produce electricity in this way?