The Speculist

One wonders what the large scale exploitation of this will do to the submarine currents that so impact the climate.

-Jim

Phil:

I love this part:

"Oney, who recently inked a deal with the Pentagon to build an OTEC power plant for a US naval base on the Indian Ocean island of Diego Garcia, envisions a day when floating OTEC platforms produce enough hydrogen to meet all of the world's energy needs."

The cold / hot differential -> electricity.

Electricity + salt water (I think salt water works better than fresh) = hyrogen and oxygen.

Wouldn't it be fairly simple to convert a deep water oil rig to this? Just pull the drill up out of the ocean floor and intake water at the bottom of the sea rather than oil from under the sea.

This could be the sort of thing to get the oil companies behind the hydrogen economy. They already have much of the infrastructure in place.

Very cool. This strikes me as a more doable system than the solar tower:

http://www.eurekalert.org/pub_releases/2004-02/uoc--msp022504.php

Jim --

I think we would have to be pumping a lot of water before it had an appreciable effect on the ocean currents. But that doesn't mean there isn't a risk. Likwise, wouldn't this approach slighly warm the oceans?

In a similar vein, I wonder how many windmills we would have to put up before they start changing the climate? I'm not sure how they would. Maybe creating enough drag that the jet stream starts to slow down. Or speed up?

In the end, I think we have to weigh the impact of competing methods of producing energy. Maybe the climate effects of cold-water pumping will be much more pronounced than those caused by burning fossil fuels. Then we have to look at other options -- nuclear, solar (which might also have some climate impact), near-zero-emissions burning of fossil fuels (until they run out), etc.

The bottom line is that we're going to get our energy from somewhere and we're going to need more and more of it.

If you're looking for the effects of OTEC, the first-order ones can be derived from first principles:

- Surface waters are cooled downcurrent of the outlet, and enriched in deep-water nutrients.
- The thermocline is driven downward.

The more OTEC units operating, the greater these effects.  Second-order effects might include increased phytoplankton growth and greater ocean productivity in the down-current area, like natural upwelling zones; whether this could be harvested usefully or not is an interesting question.

The big issue with OTEC is that the efficiency is very low and the capital investment is quite high.  It's been gracing the covers of magazines for at least two decades, maybe 3, but it's always been too expensive to go beyond the prototype stage.  It looks like you have to have close-to-ideal situations regarding nearby deep water, market for electricity, market for fresh water and market for cooling to make it pay.  Solar PV has far greater potential markets, because you can use it most anywhere; it also has about 8 times the actual efficiency and at least 30 times the potential efficiency (16-60% vs. 1-2%).

There are easier ways to make hydrogen, too.  Instead of going through turbines and whatnot, why not go straight from sunlight to hydrogen using green algae?  You might even be able to do it in floating bags in the ocean.

I think OTEC is a neat scheme, but it's too restricted to get far.