Obstacles to getting Ocean Thermal to market
OTEC came very close to being reality during the first oil crunch, more than a quarter century ago. The project was a largely commercial deal with modest federal support, but with very strong support at the state level (Hawaii.) With no concern for climate change at that time (except the few like Roger Revelle smart enough to see it coming) OTEC almost took off. We clearly need to learn from that scenario -- why didn't it fly then? what is different now? Why have other technologies for ocean power extraction which were non-existent in the 1970s moved ahead while OTEC remained stagnant.
Some of the obstacles are obvious:
1) OTEC has to be constructed as one very large facility, compared to say a wind or wave power extraction farm which could in principle be built up one small unit at a time.
2) OTEC needs a large thermal gradient (deep water and near-tropics warm surface water) within reasonable transmission line distance to large markets for electricity. This severely limits practical locations within the US.
3) Floating OTEC would operate in a risky environment (warm surface water means hurricanes.) Big Oil & Gas has learned how to manage this risk, but at costs which OTEC might not be able to afford. Profit margins in the electric power industry are nothing like those of Big Oil & Gas.
If OTEC came as close as it did in the last century, what can we learn from looking back?
1) The Hawaiian plant was to built on shore because the steep island slopes allowed
for cold water piping to be laid on the bottom or even drilled as a tunnel.
2) No long transmission lines
3) Greatly reduced risk of storm damage
4) Existing electric power cost were very high because of the necessity for importing oil.
OTEC is the only ocean power technology able to provide base power (continuous, dependable, constant level.) This sets it apart from ocean winds, waves and tidal currents. This feature alone should have moved it up the scale of desirability. In many ways, OTEC resembles onshore nuclear power more than the other ocean renewables. Perhaps it needs federal subsidizing to get it going, just as nuclear did.
I would be interested in other people's take on why it hasn't happened, or -- more importantly -- what to do to make it happen.
Dick Seymour, SIO
Some of the obstacles are obvious:
1) OTEC has to be constructed as one very large facility, compared to say a wind or wave power extraction farm which could in principle be built up one small unit at a time.
2) OTEC needs a large thermal gradient (deep water and near-tropics warm surface water) within reasonable transmission line distance to large markets for electricity. This severely limits practical locations within the US.
3) Floating OTEC would operate in a risky environment (warm surface water means hurricanes.) Big Oil & Gas has learned how to manage this risk, but at costs which OTEC might not be able to afford. Profit margins in the electric power industry are nothing like those of Big Oil & Gas.
If OTEC came as close as it did in the last century, what can we learn from looking back?
1) The Hawaiian plant was to built on shore because the steep island slopes allowed
for cold water piping to be laid on the bottom or even drilled as a tunnel.
2) No long transmission lines
3) Greatly reduced risk of storm damage
4) Existing electric power cost were very high because of the necessity for importing oil.
OTEC is the only ocean power technology able to provide base power (continuous, dependable, constant level.) This sets it apart from ocean winds, waves and tidal currents. This feature alone should have moved it up the scale of desirability. In many ways, OTEC resembles onshore nuclear power more than the other ocean renewables. Perhaps it needs federal subsidizing to get it going, just as nuclear did.
I would be interested in other people's take on why it hasn't happened, or -- more importantly -- what to do to make it happen.
Dick Seymour, SIO
Tags: ocean energy, ocean thermal, otec
Replies to This Discussion
-
Permalink Reply by Tom Swift on -
Hi Dick, Why OTEC hasn't happened? It's the basic technology that is the problem! High temperatures expand a liquid into a high pressure vapor, which pushes a turbine like a fan, spinning an electric generator. The expanded vapor gets cooled and it condenses back to a low pressure liquid.
Some of that electricity is used to RUN A PUMP, which must overpower the high pressure steam in the boiler in order to pump the cooled condensed low pressure liquid back into the hot high pressure evaporator, where it all started. THERE'S THE PROBLEM: THAT PUMP. If we didn't need the pump, then we'd get to keep all that electricity.
The same cycle is used in high temperature coal burning plants as in low temperature OTEC plants. But the thermodynamic payoffs are much different. High temperature steam expands one or two thousand times the original volume of the liquid that it came from. But OTEC plants operate at the temperature of the ocean, 80 or 90 degrees. Not 1200 degrees. The OTEC expansion is miniscule compared to the high temperature processes. And ORC's have even less expansion.
Since the vapor in OTEC doesn't expand nearly as much as in cycles operating at conventional temperatures, it takes more liquid to be vaporized to run the turbine. And all that extra liquid will need to be pumped back into the boiler, after it gets vaporized and then condensed. It's a lot more work for the PUMP. And that means that more electricity needs to be generated and sent to the pump. And that means the entire OTEC plant must be built bigger to make up for all the electricity that it's got to devote to simply perpetuating the cycle. So the OTEC plant gets bigger and more expensive in comparison to the conventional high temperature power plant. It is more expensive, not competitive with the power utility. It doesn't make a profit. It looses money unless it can sell enough heat to the fish-farm, or distilled water to the Japanese, and continue to qualify for federal and state subsidies. I'm guessing all OTEC looses money.
Now, it would make sense if we didn't need to power that pump. The electricity that we'd save would constitute the majority of the net output of the power plant.
I've built five or six power plants that eliminate that pump. Based on an independent study by SATOP, a NASA funded organization of scientists, my power cycle is at least 15% more efficient in the temperature range for OTEC. My guess (since I haven't tried OTEC yet) is that my cycle might be the only hope of ever using OTEC successfully.
You can see my cycle, pictures, an animation, and pick up a lot of info on my web site MATTER AND ENERGY DOT COM
http://matterandenergy.com
-
Permalink Reply by Paul on -
Carnot Efficiency = (Thi-Tlo)/Thi or 1- (Tlo/Thi)
Temperatures *MUST* be in absolute units K or R
For OTEC tropical & polar the temps are: Thi = 35C = 308K, Tlo = 4C = 277K therefore the theoretical efficiency of a perfect Carnot engine would be 31/308 = 10.06%
If we analyze the enthalpy in the water using 1.0 J/g-K we see that we could have 35k * 10.06% = 3.5J/g Thus for each kW of power the system would have to flow ~ 0.285 g/sec or ~4.5 gal/min.
A reasonable sized OTEC say 100MW would require the pumping of no less than 450,000 gallons per minute. It's not about the water, it's about the pump!
And those numbers are for *thermodynamically perfect* equipment, which simply does not exist. I'm not against the technology, I just hope that folks will realize that it simply isn't practical yet... *YET*
Years ago the steel industry scoffed at 20-25% Fe Taconite ores as being too poor to mine. Today Most virgin iron comes from, guess what! "Inferior" taconite. Hmmm... Someday OTEC might be important.
-
Permalink Reply by Russ H. Robinson on -
Aloha Richard,
I live on the Big Island of Hawaii, and have been concerned with the high cost of motor fuel, and electricity. Which leads to the high price of food and water on this island.
So please answer a couple of questions for me.
Q #1. There’s an “urban rumor going around that says that early OTEC demonstrations failed because the problem of plant growth in the plumbing could not be over come. Is there any truth to this?
Q#2. What if scaled up to economically competitive OTEC plants were coupled to hydrogen producing facilities, along with wind, wave, and solar “farms”. The hydrogen could then be transported to generating facilities connected to load centers by existing grids.
Q#3. Has anyone ever suggested doing for the renewable energy business what Rockefeller did for the oil business, I.e. form an integrated renewable energy company?
I’ll bet that ARAMCO and the Dubai petrobanks would be leaders in the field once the concept was proven.
Russ Robinson
Featured Discussion
Twitter Feed
© 2009 Created by PickensPlan
Badges | Community Guidelines | Report an Issue | Privacy | Terms of Service
