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Harnessing Energy from Ocean Thermal Layers

11/19/2015 12:15 PM

Has anyone watched this video?

http://techxplore.com/news/2015-08-celebrating-hawaii-ocean-thermal-energy.htm

I watched this, but one question was NEVER answered. You know,.....the question about the 800 lb gorilla in the room........Namely, ......How much energy is required to pump that much sea water that high into the air, and from hundreds of feet deep in the ocean???

Any one have thoughts on this besides me? Any one else view this with skepticism besides me?

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#1

Re: Harnessing energy from ocean thermal layers

11/19/2015 1:01 PM

Here's a link that works:

http://techxplore.com/news/2015-08-celebrating-hawaii-ocean-thermal-energy.html

Monsieur Carnot still limits the amount of energy you can get from a small temperature difference, and like you said, you still have the overhead of pumping, etc. I suspect in the present political climate, economics may take a back seat to politics.

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#2
In reply to #1

Re: Harnessing energy from ocean thermal layers

11/19/2015 1:21 PM

Thanks for the assist!

My thoughts exactly.........

But.....a great project for using up any "over generation" of electrical power! ......like, when we have too much power from all the green solar and wind generators out there....

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#13
In reply to #1

Re: Harnessing energy from ocean thermal layers

11/20/2015 4:21 AM

It makes me wonder whether these people know what they're talking about when I see "....will provide power for 120 homes per year". Will it do 240 homes next year and 360 the year after? It's a bit like knots per hour and kW per sec that you occasioally see.

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#3

Re: Harnessing energy from ocean thermal layers

11/19/2015 1:27 PM

...and then the temperatures equalize, and the Gulf Stream stops...

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#4

Re: Harnessing Energy from Ocean Thermal Layers

11/19/2015 2:16 PM

"This plant provides a much-needed test bed to commercialize ocean thermal energy conversion technology and bolster innovation

That about says it all.

It will be interesting to see if it works economically as the alternative power generation for small islands previously running diesel generators and with limited land for solar and unsuitability for wind and sea turbines has been a logistical and environmental problem.

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#5

Re: Harnessing Energy from Ocean Thermal Layers

11/19/2015 3:39 PM

Perhaps we should bring all the coal-fired power plants back on line.....and use that power to pump the sea water, so we could generate green power for coastal/island locations!

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#6
In reply to #5

Re: Harnessing Energy from Ocean Thermal Layers

11/19/2015 3:51 PM

You joke, but where do you think the power comes from to make all those 'green' silicon solar panels manufactured overseas.

NIMBY works just as well for the eco green movement.

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#7
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Re: Harnessing Energy from Ocean Thermal Layers

11/19/2015 4:06 PM

You need to re-read my post! You missed my point ENTIRELY!

I was merely alluding to the fact that many power plants have been shut down due to the perceived evil nature of burning coal. They are sitting idle. (Yet, California still buys power from coal-fired plants in Arizona/Nevada/Utah!)

A previous poster also pointed out the fallacy of this ocean technology....without knowing it! He stated that some islands don't have the room for wind/solar energy, so a technology that uses more energy than it produces would be a good fit for them....such as this scheme for harnessing energy from the ocean's thermal layers.

I am the one here who is pointing out my skepticism with this idea. It takes A LOT of power to pump sea water in large quantities..... hundreds of feet up!

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#8
In reply to #7

Re: Harnessing Energy from Ocean Thermal Layers

11/19/2015 4:08 PM

Silly me.....

I re-read YOUR post just now. You got what I said. My bad!!

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#9
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Re: Harnessing Energy from Ocean Thermal Layers

11/19/2015 4:10 PM

Perhaps I just need to go back to work on my project here.......

Every once in a while, have to re-train my focus here...

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#12
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Re: Harnessing Energy from Ocean Thermal Layers

11/20/2015 1:09 AM

Better reread the process, the water is not being pumped, it is being circulated, and so acts like a siphon. What needs to be overcome is the friction of the loop and the change in density, once at the highpoint gravity pulls it back down to the bottom, it's not being discharged at a higher elevation which would require much more power.

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#14
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Re: Harnessing Energy from Ocean Thermal Layers

11/20/2015 9:39 AM

I think YOU had better re-read the process!! Those pump symbols for the process (as shown in the video) are not "syphon symbols"!! ...And, how are you EVER going to syphon cold water from ocean depths, and return it much warmer, and to a much higher level, by syphoning???!!!

In order to syphon, you must transfer the liquid from a HIGHER to a LOWER level......not the other way around!! (Moving MASSIVE AMOUNTS of cold water hundreds of feet laterally, then lifting it hundreds of feet vertically)

Last I looked, water doesn't stretch too well!!! Syphoning doesn't even work when transferring from one level to the same level..... (Transferring MASSIVE AMOUNTS of warm seawater laterally, then lifting it hundreds of feet vertically)

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#15
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Re: Harnessing Energy from Ocean Thermal Layers

11/20/2015 11:25 AM

In reality, the only pumping loss is due to the piping and heat exchanger tubing flow friction. The elevation change is mostly balanced since the downward flow acts to siphon the upflow. If you look at the loop system in its entirety you will see that there is no hydraulic head differential below the water surface. The only hydraulic head differential is the height differential between the top of the tower loop and 28 feed above the water level. If they stop the pumps then they simply create a 28 ft head differential vacuum at the top of the tower.

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#16
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Re: Harnessing Energy from Ocean Thermal Layers

11/20/2015 11:55 AM

"The only hydraulic head differential is the height differential between the top of the tower loop and 28 feed above the water level."

We must have some engineers that learned math from a Common Core school.....

As I look at the model, it says they are drawing cold water from a depth of 3000 feet. Mixed water return to 330 feet. .....and you say there is only a 28 foot difference???

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#17
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Re: Harnessing Energy from Ocean Thermal Layers

11/20/2015 1:34 PM

I guess the PhD engineer who wrote this OTEC paper from the Marine Technology Society didn't go to the same Common Core school that you went to, seems he agrees with JAlberts and me:

"... The power required to pump seawater is determined accounting for the pipe-fluid frictional losses and in the case of the cold seawater for the density head, i.e., gravitational energy due to the differences in density between the heavier (colder) water inside the pipe and the surrounding water column. The seawater temperature rise, due to frictional losses, is negligible for the designs presented herein..."

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#19
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Re: Harnessing Energy from Ocean Thermal Layers

11/20/2015 2:43 PM

Not sure where the 28ft came from. I would assume the whole thing is submerged so there is no actual lifting of water. That's what the picture on the OTEC paper looks like. A pump is needed to circulate, but it only sees head difference due to the difference in temperature hence water density. Density difference between 5 and 25┬░C is about 3%, and assuming the temperature outside the cold water pipe varies continuously over the depth, over a depth 1000m ΔH comes to ~ 1.5 mm water. For a flow 1 m3/s that needs a hydraulic power 150 watt. I'd expect friction losses to be much higher than 1.5mm, and then there's pump efficiency.

The theoretical Carnot efficiency is 1 - (5 + 273)/(25 + 273) = 6.7%. OTEC says something about 3% in practice. On that basis I make power from 1m3/s about 2500kW which sounds rather high, maybe I've gone wrong somewhere.

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#18
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Re: Harnessing Energy from Ocean Thermal Layers

11/20/2015 1:50 PM

Pump heads are based on the surface levels of the source and destination, not on the depths. Except for friction due to pipe length, the 3000 foot depth is irrelevant.

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#20
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Re: Harnessing Energy from Ocean Thermal Layers

11/20/2015 5:19 PM

What is it that you cannot see that prevents you from realizing that the length of the pipes below the water surface has nothing to do with the water head at the surface.

If I stick a pipe 1 foot below the surface of the water and another pipe 30 mile below the surface of the water the water level at the top of both pipes is going to be the same.

As for the 28 ft head of vacuum at the top of the loop, since the atmospheric pressure at sea level is 14.7 psig and sea water pressure is approximately .5 psi/foot of depth, the maximum water column height in a sealed top tube that can be supported by atmospheric pressure is approximately 28 feet. (For reference, do a web search on "water barometers")

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#21
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Re: Harnessing Energy from Ocean Thermal Layers

11/21/2015 6:44 AM

I guessed the 28ft was related to the approx maximum water head sustained by atmospheric pressure, but I don't see the relevance. If the whole thing is submerged there is no negative pressure (the 2nd picture in Rixter's link #1 shows a tall structure, but I believe that is in the secondary circuit).

If there is a pipe loop coming above the surface it doesn't alter the pump head, as you say, but some priming arrangement is needed. But it needn't be 28ft above, and the vacuum at the top of the loop = the height at that point. Moreover, the vacuum is the same whether or not the pump is running. 28ft is about the maximum possible height for the loop.

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#10

Re: Harnessing Energy from Ocean Thermal Layers

11/19/2015 7:22 PM

At $41,000.00 USD per house, this will be a hard sell.

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#11
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Re: Harnessing Energy from Ocean Thermal Layers

11/19/2015 7:38 PM

You just have to know a good subsidy engineer who can milk government programs for all they're worth. Then you can become a gentrified welfare queen.

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#22

Re: Harnessing Energy from Ocean Thermal Layers

11/21/2015 10:35 AM

Definitely an alternative life style proposal to limit each household to an average of 846 watts per household (104kW/125 households)

My microwave needs 1450 watts to operate.

so it might not work if the consumer is load-average-limited.

I suppose the consumer will have to sell/buy/trade kW credits - I use my neighbor Jim's kW allocation while he's at work so I can use my microwave.

I can imagine the social regulations to accompany power rationing on this scale:
- Microwave only from 11PM to 5AM
- No dishwashers, washing machines or refrigerators (inductive motor loads)
- No laser printers
- Vintage tube Hi-Fi's by permit only with restricted hours

In fact, the monitoring/rationing scheme will require a full time staff 6 (site manager, ass't mgr, electrician, shift supv, monitor tech, security guard) which requires a total contingent of 22 personnel to cover 24-7 shift work.

Of course, their little compound will be allocated 20kW of the entire production for the needs of any newspeak bureaucracy: lunch room: freezer, refrigerator, microwave and convection heat electric oven, uniform washing machine and dryer, and 10kW of floodlights illuminating the razor wire topped fencing (a designated high priority homeland security function - utility generation protection).

Does this portend the return of the iceman?

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