I suspect the rate at which you can burn seaweed is far less than that of alcohol/petrol etc.

Therefore you _may_ release more energy, but if it doesn't burn quickly enough you aren't going to have any compression and so no power.

But this is a solar-powered system.

It is a way of using the surface of the sea as farmland for producing biomass.

Some carbon (and other stuff) takes a temporary role in the storage mechanism, and after you've used up the ethanol you made, the world is more or less where it was before you farmed the seaweed. (how more or less is obviously an important and complex thing)

Certainly worth considering if it means we don't muck about making fuel on the proper farmland that we need for making food.

@Richard Ball

All energy on Earth is in some way directly or indirectly solar powered. All wind, wave, bio, hydro, ground heat, and fossil fuel comes from the Sun (some may argue that wave power may be driven by tidal forces, but the energy derived is effectively potential energy left over from when the moon was captured, as a result of gravity maintained by the gravity wells in the solar system, the largest of which is the Sun's)

Even nuclear and geothermal power relies on processes long ago that were caused by the Sun (accretion during the formation of the solar system).

You may possibly claim that the heavy fissionable elements are actually left over from the Big-Bang or supernovae, I suppose. If we ever get hydrogen fusion reactors, that would be the first energy source that has nothing to do with the Sun.

Anyway, it's all Entropy.

@Ru

I like the idea of floating farms, although the energy that falls on the surface of the deep oceans is used by free-floating plankton at the base of the food hierarchy, and also produces the warm water and water vapour that conditions the weather systems. Capture the energy, cool the oceans, and starve the animals in the deep.

As people like Robert Heinlein and others before him said, There Ain't No Such Thing As A Free Lunch!

"free-floating plankton", etc

That's not an unreasonable point. However, I'd contend that the required surface area (which was quoted at 3% of the world's *coastal* waters) is absolutely miniscule in the context of the total area of deep ocean. Shading enough of the ocean to kill off that much phytoplankton seems like an absolutely epic engineering project; it would be easier to build photovoltaic farms in the sahara and set up HVDC lines to Europe, or build orbital solar power systems with microwave receivers on earth, etc.

Sir

"You may possibly claim that the heavy fissionable elements are actually left over from the Big-Bang or supernovae, I suppose. If we ever get hydrogen fusion reactors, that would be the first energy source that has nothing to do with the Sun."

You could at least try and be consistent. According to your ultimate logic, anything that we build on Earth comes from the Sun. True, but not really helpful.

@Runcible - OK, obvious contradiction.

Comes of going back after writing a post and adding to it and clicking submit without re-reading it properly. Yes, heavy elements were pre-solar, but pretty much everything else is some form of solar energy. Still not helpful for the discussion, though.

My apologies.

@Ru

I though nucleosynthesys during the Big-Bang went further. Wikipedia suggests that it went no further than beryllium. I was obviously wrong. OK, just supernovae.

I Am (obviously) Not An Astrophysicist either!

Pathetic fallacy

"If it exists in our ecosystem, it's because it has a purpose."

Nothing in the ecosystem has a purpose unless and until we assign it one. "Purpose" is an intentional attribute; it's a concept that a thinking being ascribes to a perception. Purposes don't exist in nature.

We often use "purpose" as a gloss for "function" or "operation" (eg "the purpose of the mitochondria..."), but that's not the sense in which you're using it there. Claiming a biological entity has a purpose, a role it's meant to fulfill, is the pathetic fallacy - imposing human motivation on the natural world.

Everything in the ecosystem gets *used*, eventually, either for the potential energy in its chemical bonds, or as raw material for forming new complex structures (which in turn will eventually be broken down again for that bound energy, ad infinitum). But that's not the same as having a purpose.

Any human action has some effect on the ecosystem. Mostly these are negligible, and even when they aren't, they generally affect a relatively small segment - a few species, for example. This is often regrettable for any number of reasons, such as reducing aspects of biodiversity that we find pleasant, or that might be useful to us; or, depending on your philosophical stance, simply for ethical reasons. But the biosphere is very robust (which is not really surprising, given the thermodynamics and chemical makeup of the planet's surface). So there's little to be gained by making some sweeping generalization of widespread doom, because it's implausible. What's more likely is that something specific and important to a significant group of people will be affected - say, shellfish food production.

oops

Fuck me, I'm glad I never tried to point that one out :)