The oceans contain an immense amount of heat, and OTEC can turn some of it into electricity. The problem is how much infrastructure it takes to extract each useful megawatt.
It is good that as a public writer you are bringing out the salient but largely unknown spoken truths about OTEC. We applaud your in-depth review and analysis of the reports that you have cited. You have identified correctly specific mechanical and cost issues.
We figured these fundamental facts out about ocean thermal energy in the 1960’s, long before the coined “OTEC”, came into the public eye. But, as individual engineers, a small company, and considered “inventors” we were largely ignored. We have tackled all these mechanical and cost issues you have identified, as well as others you have not publicly mentioned.
Without going into specifics about all comparative dimensions and flows in this note a rough comparison with the information you have presented as for instance the figure of 25 m^3/kwhr of water flow for a 100 MW net plant. Our own engineering using various innovations shows a total water flow of about 14 m^3/kwhr. Obviously, our cold-water pipe is smaller than the 10 m pipe you identify for a 100 MW net plant. Our comparative parasitic losses are considerably less than are commonly calculated and which you have correctly mentioned. All the improvements lead to a reduction in use of materials per kw and thus lower costs for a complete plant and installation.
It is interesting today, however, how several countries and organizations, are slowly coming to know our name and are seeking out from us, privately, why we are different and able to provide more specific engineering and explanation and justification than others can provide.
We agree that “OTEC still has a plausible niche” and hope to demonstrate this in the near future.
We appreciate your honest observations. Thank you.
fully agree - build a mini-demonstration plant (100kw - 1 MW) in an atoll state where it would make an enormous difference. Hawaii doesnt work because its US - the expectation of how much energy you need for wellbeing is unrealistic. But Kiribati, Tuvalu, Marshall islands - this can be an absolute game changer. 10MW doesn't need anywhere near 10m pipe diameter and would more than meet all the electricity needed for Majuro Atoll
And it's also a tiny fraction of global energy requirements that has to compete with cheap solar and batteries. Tiny fractional energy markets really aren't a market.
No, its isnt a market - which is why it hasnt been developed. BUT, it would be a game-changer for those micro-economies and cultures at the cutting edge of a deepening climate crisis - which is more than sufficient reason to pursue it. They are currently paying $0.5/unit for diesel generated electricity. So - its a no-brainer
My analysis was based on the October 2 Ckeantecnica article which was abridged, therefore I didn't see the detailed cold water intake was a separate 235 m3/s, with 705 m3/s being the total cold and hot water draw.
Obviously pushing that seawater at 3 m/s is vastly different than 9 m/s. Since the pressure drop is proportional to the velocity SQUARED, the corrected values are 3.6 kPa in commercial steel, 4.5 kPa in smooth concrete. The required power is a mere 1 MW in steel, 1.25 MW in concrete.
Apologies for the confusion. Nevertheless my environmental concerns, especially oxygenation, remain at the corrected flow rates.
Was there an environmental study of the effect of discharging cold, significantly less oxygenated water?
Is the discharge water returned 1km down requiring additional pumping, or is it dumped overboard?
If the later, how long could a 100 MW plant operate before 700 cubic meters per second of cold water degrades the local surface water environment, and is that devastation exponential as the size of the plant increases to the 1,500 MW of the Oahu grid? Even for the 300 MW of Maui County or Kauai's grids there has to be an effect if 2100 m^3/s of 5°C water is surface discharged and locals notice their surfing is becoming cold.
Independent of land based or offshore as illustrated, the deep, cold water's oxygen level is 80% less than surface oxygenation according to the Station ALOHA Hawaii Ocean Time Series. Therefore how big a cloud of marine life suffocation would exist given the above surface discharges of Oahu or Maui?
Assuming the above demands a return discharge, the velocity of 700 m^3/s in a 10m diameter pipe is 9 m/s. Pushed through a commercial steel pipe with 0.045 mm of surface roughness by an 85% efficient turbine is 30 kPa pressure difference (40 kPa in smooth concrete with 0.3mm roughness) requiring 25 MW to push it back down (33 MW in a concrete pipe.) This drops the net output to 75 MW in steel pipe, 67 MW in concrete for an offshore plant as illustrated.
If the plant is onshore with 5 km of pipe, the discharge pumping power of 125 MW exceeds the generation.
Finally, is the 100 MW output the net power after the same 25-33 MW required alone to pump the water straight up 1km, not including pumping it through the valves and heat exchanger?
I don't see the viability, I however appreciate the thought experiment.
Sincerely,
Hector E. Joules
B.S. Mechanical Engineering, Rensselaer Polytechnic Institute
I'm sure there were environmental studies, but that wasn't my focus and I haven't looked for them.
The water is discharged subsurface, presumably downstream of intake. This technology would require a place with decent currents and some care in outflow, but while the volumes of water are staggering to contemplate, they are literally a drop in the bucket compared to oceans.
To your point (with corrected math in the other comment), yes, parasitic load for pumping is the Achilles heel of the technology. Even at the low speed with the large pipe, it eats a third of the total electricity. Higher speed and it eats it all. Net power of 100 MW takes a lot more than 100 MW.
And your point about viability is apt. There's a reason why there are a lot of studies and as far as I can tell exactly one small working test site. And there's a reason why in my decarbonization study of Hawai'i I have lots of cold water cooling of urban centers and no OTEC.
Decent article. That's why all the Sankey diagrams I create (and I've done a lot of them) have rejected energy as the LLNL ones do, something that far too few contain. I make it very clear that the rejected energy is an opportunity.
If you haven't seen the LLN diagrams, it's likely worth looking at them.
It is good that as a public writer you are bringing out the salient but largely unknown spoken truths about OTEC. We applaud your in-depth review and analysis of the reports that you have cited. You have identified correctly specific mechanical and cost issues.
We figured these fundamental facts out about ocean thermal energy in the 1960’s, long before the coined “OTEC”, came into the public eye. But, as individual engineers, a small company, and considered “inventors” we were largely ignored. We have tackled all these mechanical and cost issues you have identified, as well as others you have not publicly mentioned.
Without going into specifics about all comparative dimensions and flows in this note a rough comparison with the information you have presented as for instance the figure of 25 m^3/kwhr of water flow for a 100 MW net plant. Our own engineering using various innovations shows a total water flow of about 14 m^3/kwhr. Obviously, our cold-water pipe is smaller than the 10 m pipe you identify for a 100 MW net plant. Our comparative parasitic losses are considerably less than are commonly calculated and which you have correctly mentioned. All the improvements lead to a reduction in use of materials per kw and thus lower costs for a complete plant and installation.
It is interesting today, however, how several countries and organizations, are slowly coming to know our name and are seeking out from us, privately, why we are different and able to provide more specific engineering and explanation and justification than others can provide.
We agree that “OTEC still has a plausible niche” and hope to demonstrate this in the near future.
We appreciate your honest observations. Thank you.
fully agree - build a mini-demonstration plant (100kw - 1 MW) in an atoll state where it would make an enormous difference. Hawaii doesnt work because its US - the expectation of how much energy you need for wellbeing is unrealistic. But Kiribati, Tuvalu, Marshall islands - this can be an absolute game changer. 10MW doesn't need anywhere near 10m pipe diameter and would more than meet all the electricity needed for Majuro Atoll
And it's also a tiny fraction of global energy requirements that has to compete with cheap solar and batteries. Tiny fractional energy markets really aren't a market.
No, its isnt a market - which is why it hasnt been developed. BUT, it would be a game-changer for those micro-economies and cultures at the cutting edge of a deepening climate crisis - which is more than sufficient reason to pursue it. They are currently paying $0.5/unit for diesel generated electricity. So - its a no-brainer
My analysis was based on the October 2 Ckeantecnica article which was abridged, therefore I didn't see the detailed cold water intake was a separate 235 m3/s, with 705 m3/s being the total cold and hot water draw.
Obviously pushing that seawater at 3 m/s is vastly different than 9 m/s. Since the pressure drop is proportional to the velocity SQUARED, the corrected values are 3.6 kPa in commercial steel, 4.5 kPa in smooth concrete. The required power is a mere 1 MW in steel, 1.25 MW in concrete.
Apologies for the confusion. Nevertheless my environmental concerns, especially oxygenation, remain at the corrected flow rates.
Was there an environmental study of the effect of discharging cold, significantly less oxygenated water?
Is the discharge water returned 1km down requiring additional pumping, or is it dumped overboard?
If the later, how long could a 100 MW plant operate before 700 cubic meters per second of cold water degrades the local surface water environment, and is that devastation exponential as the size of the plant increases to the 1,500 MW of the Oahu grid? Even for the 300 MW of Maui County or Kauai's grids there has to be an effect if 2100 m^3/s of 5°C water is surface discharged and locals notice their surfing is becoming cold.
Independent of land based or offshore as illustrated, the deep, cold water's oxygen level is 80% less than surface oxygenation according to the Station ALOHA Hawaii Ocean Time Series. Therefore how big a cloud of marine life suffocation would exist given the above surface discharges of Oahu or Maui?
Assuming the above demands a return discharge, the velocity of 700 m^3/s in a 10m diameter pipe is 9 m/s. Pushed through a commercial steel pipe with 0.045 mm of surface roughness by an 85% efficient turbine is 30 kPa pressure difference (40 kPa in smooth concrete with 0.3mm roughness) requiring 25 MW to push it back down (33 MW in a concrete pipe.) This drops the net output to 75 MW in steel pipe, 67 MW in concrete for an offshore plant as illustrated.
If the plant is onshore with 5 km of pipe, the discharge pumping power of 125 MW exceeds the generation.
Finally, is the 100 MW output the net power after the same 25-33 MW required alone to pump the water straight up 1km, not including pumping it through the valves and heat exchanger?
I don't see the viability, I however appreciate the thought experiment.
Sincerely,
Hector E. Joules
B.S. Mechanical Engineering, Rensselaer Polytechnic Institute
I'm sure there were environmental studies, but that wasn't my focus and I haven't looked for them.
The water is discharged subsurface, presumably downstream of intake. This technology would require a place with decent currents and some care in outflow, but while the volumes of water are staggering to contemplate, they are literally a drop in the bucket compared to oceans.
To your point (with corrected math in the other comment), yes, parasitic load for pumping is the Achilles heel of the technology. Even at the low speed with the large pipe, it eats a third of the total electricity. Higher speed and it eats it all. Net power of 100 MW takes a lot more than 100 MW.
And your point about viability is apt. There's a reason why there are a lot of studies and as far as I can tell exactly one small working test site. And there's a reason why in my decarbonization study of Hawai'i I have lots of cold water cooling of urban centers and no OTEC.
Thanks. I am glad I found your substack via CleanTechnica and look forward to perusing your posts. I don’t intend to sound anti-renewable, but I am a realist. https://hectorejoules.substack.com/p/its-the-radiator-stupid for example.
Decent article. That's why all the Sankey diagrams I create (and I've done a lot of them) have rejected energy as the LLNL ones do, something that far too few contain. I make it very clear that the rejected energy is an opportunity.
If you haven't seen the LLN diagrams, it's likely worth looking at them.
https://flowcharts.llnl.gov/
Thanks. I’m well aware of Sankey, and in hindsight, I have no idea why I didn’t include one!