

Power from the sea

Second time around…

Ocean heat may be used to generate electricity

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Dear Sir
And about to use the natural solar energy on inhabited Deserts? Perhaps in the future thousands of square kilometers on Surface’s Deserts will be covered by Black Body Sun heat absorbing material.
By the way the State of California is mainly a Desert .Even that, it is the richest US State!
Oceans ( natural water) must be untouchable , if our civilization wishes to survive Ecological deep damage already being done , besides of geological and artificial temperature changes on the Planet in a near future .

Sid 34

Would I invest $10000 so I could run my kettle for free, probably not. But I am sure the US military will spend that.









$1 billion for a first generation 100MW plant would be bloody amazing!

Ballpark: imagine it runs at 80% of its annual generating capacity (some downtime for maintenance and such). Imagine we are depreciating it over 20 years. Imagine we are paying 2% real interest (2% above inflation) for our capital. Imagine we are selling the power wholesale at 12.5 cents/ kWh (that's only 30% above the current wholesale US average - which will rise after the shale gas boom).

Then we our total capital cost (20 year bonds) would be $1.49 billion, and total revenue would be $1.55 billion.

The subsidies necessary will be modest, and these numbers would certainly make sense already for naval bases and pacific islands. If costs come down with the next generation, scale economies and outsourcing to China, then this could provide a significant share of world energy (if the numbers really did bare out in practice, this would be much more promising than wind or solar).

A renewable source with massive potential. This and other energy research need far more government investment - time to slash electric car subsidies for the rich, stop mass (government subsidized) installation of noncompetitive solar panels and cut corn ethanol subsidies!

It is right for the government to fund development of new technology (especially in strategic areas like energy), but it is very wrong for the government to subsidize the consumption of rich people.

shaun39 in reply to shaun39

And more importantly, if you could cut capital costs from $1 billion to $200 million for a 100MW plant...

It could yield a 6% real return on capital (6% above inflation) depreciated over 10 years, allowing for $10 million/ year in maintenance costs, and providing $0.06/ kWh wholesale (same as natural gas) running at 80% of annual generating capacity.

If the first generation really does turn out to be $1 billion, and if mass production/ outsourcing could cut initial costs by 80%, this would be enormously profitable. Deep sea ports would be the sites of aluminium smelters and steel works (convenient for shipping to boot).

This ain't so crazy as some people seem to think. This could be really cheap energy - well worth investing in pilot schemes, and well worth localized damage to marine ecosystems (hell, at least it would reduce the rate of ocean acidification!).


Scaling up an OTEC plant to 100MW is the WORST thing to do with it. These plants are more useful in the 1-5MW range, where they can be used as baseload plant for remote islands which would otherwise have to use diesel engine/turbine generators at much lower efficiency (30-35% at partial load) than the conventional CCGT (50% plus) in the mainland.
By the way, low efficiency of OTEC plant is almost irrelevant at small scale, because the heat source is free. Same low efficiency applies to most natural energy sources such as wind turbines and photovoltaic cells...


Solitaire first shipped with Windows 3.0 in 1990 so the first nine years of the OTEC permit office must have been very dreary indeed


@professional rationalist

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


Staggering numbers either way.




spandas in reply to PSH

@professional rationalist

Thank you for debunking this fantasy. I wish that Economist would get proper reality check before running this kind of "thumbs up' stories. On the other hand, the quality of tech reporting in cyber security and computing in general is even worse - I gave up trying to responde to all that nonsense.

shaun39 in reply to PSH


The world doesn't consume energy at an average rate of 20TW!

Rather, the world consumes 18 trillion kWh / year (18*10^9 kWh).
(https://www.cia.gov/library/publications/the-world-factbook/fields/2042.... , see entry for "world")

There are 24*365.25 = 8765 hours in the average year. So the world consumes energy at a rate of (18*10^9 ) / ( 8.77*10^3) = 2.05 * 10^6 kW.

That's 2.05 TW, or roughly the equivalent of 20,000 separate 100MW plants running at full capacity.

20TW really would be insane - the last doubling of world electricity consumption took 28 years. Even if the growth rate doubled (crazily bullish), we wouldn't see 20TW before 2065.

But such talk is trivia; the world economy is a big thing, and this won't impact on the viability or attractiveness of test plants (though it has implications for the potential regarding scale economies).

Fergus MacPhellimy in reply to PSH

Furthermore, accelerating 1.5 * 10^6 kg of water to 20 m/s would require 3*10^8W. Where did this figure of 1.5*10^6 l/s come from?

Also the cold water will be denser than the surface water, so extra energy will be needed to lift it.


Uh oh.
But still better than some.
Coal? How do you replace a mountain?
Fracked natural gas? How do you fix a polluted aquifer?
PV Solar? What about during the night time?

Maybe OTEC is the answer.
Solar preheating could improve the efficiency.
With low operating temperatures, why use metal?

Professional Rationalist




twice the Thames River
5% of Niagara Falls
3.5 times the Colorado River
(average flow).











Fergus MacPhellimy in reply to PSH

Deep ocean water contains a lot more dissolved CO2 than surface water because of the greater pressure. I have read that natural upwelling releases significant amounts of carbon dioxide into the atmosphere, but I have not yet found out how much.

Can anyone estimate how much carbon dioxide would be released, and how would this compare with, say, burning natural gas?

Fergus MacPhellimy in reply to PSH

Are you sure of your figures? I suspect you have misplace a decimal point somewhere.

Give an efficiency of 5% means that for every Joule of electricity generated 20 Joules of heat must be transferred to the cold water. Assuming a specific heat capacity of 4.2kJ/kg raising the temperature by just over 2K will sink about 10kJ. So each kJ generated requires 2l of water. So 1MJ requires 2000l of water, or 1MW requires 2000l/s.











OTEC plants can potentially last long enough.


Anjin-San in reply to rvsmaverick

Thank you for referring to the pioneering work by the University of Saga, whose design was used in the OTEC test vessel "Shakti Saga" that have conducted test power generation in the Indian Ocean.

Peter Sellers


ZeFox in reply to Peter Sellers

Other expalnations are rather mathematical I'm afraid.

ZeFox in reply to Peter Sellers

Unfortunately your proposal would not work in practice. Essentially for every 10m extra water depth, the isostatic pressure rises by 1 Bar. (isostatic = compressing a volume uniformly from all directions in space). To turn the 100Bar pressure at -1km into work you would need to channel the pressurised water from -1km through a turbine to wherever there is zero water pressure and that would be at the surface. The energy needed to do that is more than the energy you would get. Nature's way of saying there is no such thing as a free lunch. Just theoretically, another way would be to find an underwater cavern at -1km free of water containing air at 1 Bar, but that would fill up at some point with all the water coming through the turbine and then then the turbine would stop.
As to the efficiency, as said by the previous poster, it is limited by the temperature difference acc. to Carnot equation which gives the upper theoretical limit . According to this equation, effciency n = (Temp hot side - Temp cold side) / Temp. hot side. Put all the temperatures in degrees Kelvin (= Temp.in degrees Celcius + 273.15) and you get:
(298.15-278.15)/298.15 = 0.067 or 6.7 %. (number in % = number x 100) Then you have to subtract from this ideal efficiency figure the losses mentioned by previous poster. Losses in the heat exchangers, pipe friction, turbine etc. which are yet to be determined and validated by the proponents.
One other point. The power P available at 100% efficiency in the water temperature difference is calculated acc.
P = rho x A x V x Cp x DT
rho = 1000 kg/m3 water density
A = section of 10 m tube = 78.5 m2
V = water velocity in m/s
Cp = water thermal capacity = 4000 J/kg
DT = temperature difference
This is for 100% efficiency. If you apply the efficiency factor n found above you cannot get P but at most you get nxP acc.:
n x P = n x rho x A x V x Cp x DT
This calculated power taking into account only the Carnot efficiency has to reach the target of 100 MW or 100'000'000 W, lets call it Pt
Pt = n x P = n x rho x A x V x Cp x DT
You want to get the velocity V
V = Pt / (n x rho x A x Cp x DT)
V = 100'000'000 / (0.067 x 1000 x 78.5 x 4000 x 20) = 0.23 m/s
This seems quite a reasonable figure which would not cause too much friction. The speed is inversely proportional to efficiency. So if half the efficiency of 6.7% gets eaten up by the system you would need to double the velocity, to about 0.45 m/s or 1.7 km/h. However...the devil is in the detail.
It is highly likely the proponents have run through the figures in fare greater detail. As long as there are enough kilowatts produced per $ invested it may be worth it but it seems to hinge on the price of the 1 km pipe. If that alone costs 1 billion dollars, added to all the other costs it may prove too much for the 100 MW net production. What is needed is a demonstration plant to weed out all the detail problems and a better idea for the pipe than standard concrete/steel construction from the offshore oil industry. Then you can get an idea of the real costs. Engineering is about paying attention to detail.

ZeFox in reply to chocerady

Sorry the previous post should have been in reply to chocerady in chocerady who asked:
Would it not be simpler to utilise this "free" water pressure to turn a turbine and produce electricity in this way?

spandas in reply to ZeFox

@ ZeFox

"To turn the 100Bar pressure at -1km into work you would need to channel the pressurized water from -1km through a turbine to wherever there is zero water pressure and that would be at the surface."

You kind of give the right answer but for a completely wrong reasons. Please, please pick up any school book on Archimedes law and see your error!!! Until than, do pity on some of us who actually studied and taught physics and stop posting nonsense.




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