Ocean Thermal Energy Conversion plant

[leilanidude]

If a system cannot compete on price why would the PUC force the consumer to pay extra? We already have geothermal which not only can compete on price, but gets rid of diesel generators. Solar and wind don't really count since they do not provide a steady base load (and they cost too much as well).

[kalakoa]

If a system cannot compete on price why would the PUC force the consumer to pay extra?

Mistakenly assumes PUC is pro-consumer.

We already have geothermal which not only can compete on price, but gets rid of diesel generators.

Somehow the diesels are still running and electricity is still expensive.

Solar and wind don't really count since they do not provide a steady base load

Wrong end of the problem: the concept of "base load" needs to be revised.

[MarkP]

quote:

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Originally posted by VancouverIslander

At least this kind of technology could replace dirty energy sources like diesel generators while cooling ocean surface temperatures. From an environment standpoint, it's a win/win.

Just call me Mike

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NPDES permits are required. Such permits prohibit polluting the ocean in various ways, one of which is temperature pollution. The water would have to be put back where it would not significantly alter the temperature of the local water. Now in my opinion, there are lots worse things than for example converting the Ala Wai canal in Waikiki from a stagnant overheated drainage ditch into a cool flowing current of clean seawater, as would happen if all the hotels and condos lining it used deep ocean water for air conditioning and disposed of the "used" water into the canal. However, there are lots of other situations where delicate sea life could be harmed by making the ocean environment either hotter or colder. I don't know if the argument could be made that you are cooling surface waters down to what they should/used to be, but there would be lots of red tape involved.

[PunaMauka2]

I seem to recall first hearing about this concept as a student back at UHH. I believe it was in an Environmental Science class. I seem to remember that at the time the process wasn't quite efficient enough to be feasible.

I find this very exciting. Clean and simple concept. With the ocean essentially acting as one big mega-huge solar battery, an indefinitely reliable and relatively unchanging source of energy which I assume would likely be available to harness from all our islands.

[PunaMauka2]

In regard to the potential environmental concerns raised above, according to the U.S. Department of Energy, that chilled water byproduct could actually be an asset. It could be used to generate air conditioning, support chilled-soil agriculture, support aquaculture of cold-water delicacies, and ...in an open or hybrid system... will produce fresh water from seawater.



http://energy.gov/eere/energybasics/arti...ion-basics

from above link:


"Complementary Technologies

OTEC has potential benefits beyond power production. For example, spent cold seawater from an OTEC plant can chill fresh water in a heat exchanger or flow directly into a cooling system. Simple systems of this type have air-conditioned buildings at the Natural Energy Laboratory for several years.

OTEC technology also supports chilled-soil agriculture. When cold seawater flows through underground pipes, it chills the surrounding soil. The temperature difference between plant roots in the cool soil and plant leaves in the warm air allows many plants that evolved in temperate climates to be grown in the subtropics. The Natural Energy Laboratory maintains a demonstration garden near its OTEC plant with more than 100 fruits and vegetables, many of which would not normally survive in Hawaii.

Aquaculture is perhaps the most well-known byproduct of OTEC. Cold-water delicacies, such as salmon and lobster, thrive in the nutrient-rich, deep seawater culled from the OTEC process. Microalgae such as Spirulina, a health food supplement, also can be cultivated in the deep-ocean water.

Finally, an advantage of open or hybrid-cycle OTEC plants is the production of fresh water from seawater. Theoretically, an OTEC plant that generates 2 megawatts of net electricity could produce about 14,118.3 cubic feet (4,300 cubic meters) of desalinated water each day.



Environmental and Economic Challenges

In general, careful site selection is key to keeping the environmental effects of OTEC minimal. OTEC experts believe that appropriate spacing of plants throughout tropical oceans can nearly eliminate any potential negative effects on ocean temperatures and marine life.

OTEC power plants require substantial capital investment upfront. OTEC researchers believe private sector firms probably will be unwilling to make the enormous initial investment required to build large-scale plants until the price of fossil fuels increases dramatically or national governments provide financial incentives. Another factor hindering the commercialization of OTEC is that there are only a few hundred land-based sites in the tropics where deep-ocean water is close enough to shore to make OTEC plants feasible."

[MarkP]

I have to be open here as I am not up on the latest details but I think there is ample room for misunderstanding. I don't think that there is much wiggle room to overlap uses. Air conditioning typically employs chilled water with a low temperature in the mid 40's and a high in the mid 50's. Above that the air is not cooled sufficiently to properly condense and control humidity in the conditioned space. That's a delta T of about 10 degrees F. Chilling water into the mid 30's and employing a larger delta T of 20 degrees F works great and is sometimes done but it gets disproportionately more expensive to "make" chilled water that cold, so the 10 degree spread represents sort of a sweet spot in terms of cost. The deep ocean water we are talking about is in the mid 30's so it represents a great fit, but when you are done cooling a building with it there won't be much cold left in it in a way that is useful for further chilling or power generation.

Generating power is a whole 'nuther story. The 40 degree spread from mid 30's to mid 70's is abysmally low to drive any sort of heat engine. It is a huge challenge to generate power using the whole delta T. Hoping to use spent water to chill buildings is like hoping to tow a 5th wheel RV with a prius. There might be some application for chilling garden soil.

I think that by "byproduct" they mean that they installed the pipe already and since they are really not doing too much OTEC with the water, it is available to use for other things.

[MarkP]

I have to be open here as I am not up on the latest details but I think there is ample room for misunderstanding. I don't think that there is much wiggle room to overlap uses. Air conditioning typically employs chilled water with a low temperature in the mid 40's and a high in the mid 50's. Above that the air is not cooled sufficiently to properly condense and control humidity in the conditioned space. That's a delta T of about 10 degrees F. Chilling water into the mid 30's and employing a larger delta T of 20 degrees F works great and is sometimes done but it gets disproportionately more expensive to "make" chilled water that cold, so the 10 degree spread represents sort of a sweet spot in terms of cost. The deep ocean water we are talking about is in the mid 30's so it represents a great fit, but when you are done cooling a building with it there won't be much cold left in it in a way that is useful for further chilling or power generation.

Generating power is a whole 'nuther story. The 40 degree spread from mid 30's to mid 70's is abysmally low to drive any sort of heat engine. It is a huge challenge to generate power using the whole delta T. Hoping to use spent water to chill buildings is like hoping to tow a 5th wheel RV with a prius. There might be some application for chilling garden soil.

I think that by "byproduct" they mean that they installed the pipe already and since they are really not doing too much OTEC with the water, it is available to use for other things.

[PunaMauka2]

"OTEC has potential benefits beyond power production. For example, spent cold seawater from an OTEC plant can chill fresh water in a heat exchanger or flow directly into a cooling system. Simple systems of this type have air-conditioned buildings at the Natural Energy Laboratory for several years."

- U.S. Department of Energy


Are they lying?

Main thing is that there are a number of potential uses for leftover chilled water.

[leilanidude]

They aren't lying. There is currently a large project in Honolulu to provide cold water for dozens of high rise towers chillers.

[MarkP]

I probably shouldn't have sounded so sure of myself, but the challenges I mentioned are valid, and human nature is such that it is very easy to oversell something like this. True, chilled water at 55 degrees F is still colder than ambient but there are reasons why they don't cool buildings with 65 degree water. The humidity control would be terrible. You could pre-cool outside ambient make-up air from 80 deg to 70 deg using 65 deg water and that is worth something but that means installing an additional chilled water loop and air handler for the higher temperature system. There is lots of stuff that seems worth doing on paper but typically isn't done because it is a pain and has a marginal payback. Open cycle OTEC has been the holy grail for decades because it would produce desalinated water. Total win/win if they can ever get it to work economically. So far they haven't so cut me some slack for pointing that out. A quick google check shows abalone like about 65 degrees F so that could work really well for wringing the last use out of the water after cooling a building but I don't see it happening in Waikiki.

I continue to defend my assertion that lots of what you read on the internet is overly-hyped bull.