New Power Plant Produces Both Energy & Fresh Water

joshmccormack writes "An article in Sunday's New York Times (Free Reg, mah peeps) tells of how Japanese scientists have found a way to make fresh water and energy from temperature differences in ocean water. This may change the rules of what land is considered habitable, and the value of energy." Fascinating stuff, next step is rumored to be beer and power.

Comments

Thermodynamic law

[very]

Temperature difference in sea.
the temperature difference is enough to liquify certain gasses, and then expand it again.

Just like the refrigerating unit.

Not to mention the increase of pressure water gets deeper.

Before we get carried away

[jandersen]

- it's worth thinking about the environmental impact. Since the industrial revolution we've kept saying that 'of course pollution is no problem' - first we created smog in the cities, then we filled the seas and rivers with shit, now we have global warming etc etc. So lets just stop briefly before we plunge into this one, OK?

This affects not only the athmosphere by releasing ammonia (which is only a minor problem), but also the temperature balance in the ocean. Things such as the major ocean currents are driven by differences in salinity and temperature of the water. The big currents control at least part of our climate - eg. if the Gulf Stream were to shut down (which some think it might all too easily do if the polar ice cap melts), we will probably have a new ice age

And before you start jeering and making stupid jokes about it, remember that only 30 years ago the idea that human pollution could affect our athmosphere and the seas, was regarded as utter nonsense and hysteria.

Re:Before we get carried away

[freestyle-fiend]

I'd mod you up if I could, but instead I'll disagree with you.

One of the effects of fossil fuel use is CO2 production. How fast we use our (assuming nobody else wants them) fossil fuels effects not only how quickly we have to find an alternative, but also CO2 concentrations in the intervening time.

If we burn all of our fossil fuels this year, then air quality would worsen dramatically. I think you are right that in the long term it will make very little difference. However, if this is the case, it also seems likely that burning fossil fuel very gradually will have little environmental impact (as the environment will compensate or adapt). Therefore, it would be preferable to slow fossil fuel use.

Also there is the option of not using fossil fuels at all. If alternatives (with sufficient power) are possible, then why not stop burning fossil fuels now? What if the best alternatives that we can think of also pollute? We could burn ethanol and wood, both of which are renewable, but which also release CO2 when burned. Then we must also reduce fuel consumption, as we do not have the answer that you give: that the fuel will be used up (and its damage done) eventually.

few coastal OTEC locations

[wfmcwalter]

Last time I read the OTEC literature (which, I admit, was a couple of years ago) the prevailing thought was that there were only a handful of places on earth where a coastal OTEC would be viable. You needed to have a location with a large temperature difference between the water at different depths, and have the relief of the seafloor be sufficiently steep that you didn't have to trail pipes out tens of miles in order to harness this differential. Hence there being only a few steep'n'tropical locations, like the Hawaiian one.

When I was about ten I read one of those cool-science-futures-for-kids magazines, which showed a floating OTEC with a vertical downpipe - that makes more sense, as it doesn't rely on rare coastal relief. I believe Bruce Sterling's novel Islands in the Net also had similar floating OTECs. Perhaps building such a device of the necessary scale (you have to pump a lot of water around, after all) just isn't economic?

Even if you do get mass OTEC production working, its quite debateable if it's really such a good idea. It's a lot of effort (money, materials, time) devoted to something that doesn't generate a terribly impressive amount of energy, and by its very nature it both warms the deep water and cools the surface water, which will have localised environmental consequences.

I despair that everyone is concentrating on renewable resources while so many people (particularly in hot western US states) live in essentially uninsulated houses with single glazed windows. Biomas, geothermal, wind, solar, and ocean generation are all expensive and uncertain - tripleglazed solarglass windows and super-thick wall insulation are available fairly cheaply right now, are guaranteed to pay for themselves way before a windmill, an OTEC, or even a biomass plant. Yet still we're paying to air condition the sky.

Save the Plankton!

[sssmashy]

More studies are needed, but the real environmental problem with OTEC is not ammonia, nor is it the temperature balance of the ocean. Ammonia would only be released by accident, and even then it wouldn't be much of a problem.

Temperature balance is regulated because hot and cold streams of water leaving the OTEC are mixed, and then discharged by pumping it to a depth of about 60m, where the water temperature is about equal to the discharge temperature.

The real environmental issue is the fact that 99% of the seawater going through the plant is discharged back to the ocean (rather than being evaporated to fresh water). This means that huge volumes of water - thousands of gallons per second - most be pumped to generate a relatively small amount of electricity. The problem is that for every gallon of seawater that passes through, most of the plankton, algae and other tiny sea creatures who live in that gallon don't survive the amazing journey. A 10 MW island OTEC plant would inevitably destroy thousands of tons of biomass at the bottom rung of the local food chain.