Thermal Energy Seas, an energy of unknown future!

Renewable energies except solar electric or thermal (seeforums dedicated below): wind turbines, energy from the sea, hydraulic and hydroelectricity, biomass, biogas, deep geothermal energy ...
Christophe
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by Christophe » 21/02/08, 15:43

Last edited by Christophe the 26 / 02 / 15, 18: 35, 1 edited once.
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by Christophe » 21/02/08, 15:46

Remundo wrote:But still, for mass energy, it is really thermodynamic solar that is relevant.


Well, ETM is thermodynamic solar ... but indirect and that works, moreover, 24/24! And if the water is heated by an underwater volcano it becomes indirect deep geothermal energy :)

I am wrong? :?:
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by rescwood » 21/02/08, 16:32

I am not sure that the efficiency of a Stirling engine or of a solar concentrator plant is significantly higher than that of an ETM plant. And even less the economically conceivable production capacity.

ETM is always available in huge quantities. The oceans are immense heat reservoirs whose reasonable exploitation would make it possible to register in a logic of sustainable development. Potential resources are renewable, permanently available, accessible, and of the same order of magnitude as the needs to be covered. Technologies exist and are just waiting to be developed on an industrial scale. Obviously, this kind of investment is surely not as profitable in the short term as gray energy technologies .... One day perhaps.
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by Remundo » 22/02/08, 22:55

Hello everyone,

rescwood wrote:I am not sure that the efficiency of a Stirling engine or of a solar concentrator plant is significantly higher than that of an ETM plant. And even less the economically conceivable production capacity.

Well if you do a little Carnot only on cycles ... with a cold source comparable to 273 K

1-273 / 1000 = 70% mechanical / thermal efficiency in thermodynamic solar (1000 K hot spring

1- 273/373 = 25% for the ETM, and again, I left a deltaT of 100 ° C, nice!

Just 3 times more yield ...

In addition, as you say Christophe, the ETM is indirect solar, I would even say indirect indirect : Cheesy: by comparison with the water cycle or the biomass ... So it's peanut next to the direct capture of solar radiation.

But like I said, everything renewable is good to take :P

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by rescwood » 23/02/08, 09:49

1-273 / 1000 = 70% mechanical / thermal efficiency in thermodynamic solar (1000 K hot spring


If we take a solar concentrator, what fraction of the solar radiation transforms it into heat at 1000 ° K (727 ° C)?
A cylindro-parabolic collector can go up to 833 ° K but with an efficiency of 50% (Solar heat / heat). These yields drop with higher temperatures. In the oceans, the solar radiation that enters the water is transformed into heat. This heat is partially dissipated by the surface wind, and by the convection currents created by the temperature differences in oceanic water masses ... In terms of radiation / heat transformation efficiency, the comparison seems to me to be much less trench.
In terms of heat / mechanical energy transformation efficiency, it is true that an ETM plant is not very efficient 7 to 8% of thermal energy is transformed into mechanical energy.
In practical terms, a solar concentrator plant measures in m2 of collector, an ETM plant in pump capacity.
"Economically" speaking, it seems to me that an ETM plant capable of exploiting a resource available in large quantities 24 hours a day and in a limited space of energy captured over hundreds (if not thousands) of km24, deserves reflection. ..

In addition, as you say Christophe, the ETM is indirect solar, I would even say indirect indirect by comparison with the water cycle or biomass ... So it's peanut next to the capture direct from solar radiation.


ETM is "direct capture of solar radiation", at low temperature, of course, but with a good yield (certainly greater than 50% in tropical regions).
Biomass only converts 1 to 2% of solar radiation.
As for the water cycle: Evaporation 2257Kj / Kg returned to the atmosphere during precipitation, the transport of steam is provided by the wind (also due to solar radiation) ... If we take stock of the energy solar brought into play compared to what can be recovered mechanically in a hydraulic system, I suspect that the "yield" will not be really famous ... and certainly much lower than the 7-8% of an ETM plant, not to mention that the resource available in ETM is much higher than in hydraulics.
I remain convinced that the direct exploitation of the heat stored in the oceans is a potential (and partial) solution to our energy needs consistent with a sustainable and economically sustainable development (as our "friends" from across the Atlantic say).
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by Remundo » 23/02/08, 12:31

Your comments are relevant.

but 50% x 70% = 35%

For the sea, there is a minimum of 10% reflection at the air / water interface.

After that goes well, 90% absorption.

BUT the delta T is ridiculous ... 25 ° C, not much more ...

So (1-273 / 298) x 0,9 = 0,08 = 8%

In reality, the imperfections mean that the 2 yields are lower.

And again ... this requires heat exchangers of a considerable size, at these delaT, the thermal inertia is large ...

The current thermodynamic solar has approximately 30% of output of the sun to the starting electrical network. Between 3 and 4 times more than the ETM, with sensors of reasonable size.

But ETM has its place in a renewable energy mix! I don't denigrate her :D

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by rescwood » 23/02/08, 14:18

Found on:
http://www.otecnews.org/articles/vega/02_tech_limitations.html
It has been determined that approximately 4 m3 s-1 of warm seawater and 2 m3 s-1 of cold seawater (ratio of 2: 1), with a nominal temperature difference of 20 ° C, are required per MW of exportable or net electricity (net = gross - inhouse usage).


Either to produce an electric MW in open circuit ETM in sea water, 4m3 / s of "hot" water (25 ° C) and 2m3 / s of cold water (5 ° C)

To produce 1MW electric in thermodynamic solar: over 24 hours, output 0.15 (the sun shines 12 hours a day on average). Considering a radiation of 2KW / m2, it would be necessary: ​​1000/2 * 0.15 = 3333.33 m2 of sensor-concentrators.

From a technical and economic point of view which deposit is the most exploitable?

And again ... this requires heat exchangers of a considerable size, at these delaT, the thermal inertia is large ...


In ETM open circuit in sea water, no exchanger for evaporation, hot water is sprayed ("flash vaporization"), we can imagine the same process for condensation unless we want to recover fresh water .

If a closed circuit is used under NH3, for example, well-sized plate heat exchangers, exchange surfaces and above all passage speeds, guarantee efficient and rapid heat exchange.

I am not "focused" on ETM but if I had a few million € to invest in renewable energies, it is a path that I would consider very seriously.
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by Remundo » 23/02/08, 17:13

Well yes but are we talking about efficiency or energy produced?

In both cases, I give the advantage to solar.

But ETM defends itself by increasing data rates, that's for sure :D

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by rescwood » 23/02/08, 19:49

A bit of both, indeed ... I got carried away by the word "relevant" :| ...

Remundo wrote:Yes, it's interesting indeed,

any renewable source must be exploited.

But still, for mass energy, it is really thermodynamic solar that is relevant.

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In my humble opinion, a diffuse energy like solar energy cannot be exploited "en masse" given the necessary investments in m2 of installations. On the other hand, the ETM, solar energy accumulated in the tropical oceanic masses could lend itself to a "mass" production, the investments in € / KWelectric being lower since a single plant can exploit the energy accumulated over several hundred km2.
In short, "econologically" speaking: thermodynamic solar for localized production, ETM for larger scale production.

One thing remains certain is that all renewable energies have their origin in solar radiation and therefore direct use of it will always have a better energy conversion efficiency than any indirect use. The problem is that this radiation is not very "dense", 1 to 2.5 KW / m2, compared to fossil fuels and / or from biomass, 10KW / L for fuel oil, 4.5 / kg for wood, ... several hundred thousand years to "harvest" fuel oil, 10 m2 and 1 year for 1Kg of wood ... ETM, MW of renewable solar energy that can be exploited at one point, like a solar power plant with hundreds of km2 of inexpensive but "low yield", "low yield" sensors largely offset by "low" investment and operating costs.

I heat myself with wood and I do it myself, with my little hands, a chainsaw, a hammer, a few corners and my trailer. Of course it would take me much less time and energy if I had a crawler harvester, a tractor equipped with a sawing and splitting machine as well as a conveyor belt to load a trailer of several m3. But I don't care, the wood, I have it for free and, for my needs the energy and the time I spend are largely rewarded by the soft heat which reigns in my humble abode when the icy breeze of our mountains blows. from Luxie. :D
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by Remundo » 23/02/08, 23:23

Yes, we could already supply the whole planet with photovoltaic solar energy with a few hundred km ² in the deserts (not very big on a country scale, I would remind you that France has 551 km ²).

Thermodynamic solar is of course more efficient and progress is expected in this area ...

But maybe this is also valid for the ETM :!: :D

Bravo for your ecological gesture of making your wood. And at the same time, it's sport :P

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