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Bill1939's avatar

Has anyone seen this article on generating energy from seawater?

Asked by Bill1939 (5812 points ) April 21st, 2014

The US Navy has proven the concept of generating energy from seawater. See

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10 Answers

Adirondackwannabe's avatar

@Bill1939 The link isn’t working.

FireMadeFlesh's avatar

@Adirondackwannabe Works here.

The concept is, as far as I understand it, only really applicable in the military context. In keeping with the laws of thermodynamics, there is a net energy loss involved in the process, so it won’t solve our climate change problems. What it will do is still quite incredible though. Aircraft carriers won’t have to be resupplied as often, meaning merchant navy crews make less trips and take on less risk. Planes will never be grounded due to fuel issues, meaning they can still operate if oil producing nations refuse supply for whatever reason. BUT this only works with nuclear power, as diesel power combined with the net energy loss means energy being taken away from the ship itself.

CWOTUS's avatar

Yes, and it’s interesting, but for now only for military applications, I’m sure. Because of the physical constraint of “conservation of energy”, the process as described won’t give us “free energy from seawater”, but it’s a way to shrink the logistical tail of fuel tankers having to visit (nuclear) aircraft carriers at sea to transfer jet fuel. (This will only be a workable solution on nukes, since they alone have the capability to produce the needed electrical power to run the process, without themselves needing resupply of fuel to run their generators.)

From that standpoint, when implemented in a “production” environment, this could introduce significant strategic and tactical advantages. But you won’t be filling your car’s gas tank with “sea gas” any time soon.

funkdaddy's avatar

Are you guys saying you find this process to be more intensive than the process fossil fuels go through to reach gas stations?

Imagine there were vast oceans of surface oil and how much easier, cheaper, and less damaging that would make the whole process of petroleum refinement.

Once the process is done, you have a liquid fuel in both cases.

Other than the fact that the infrastructure doesn’t already exist from decades of heavy investment, what makes this less promising than fossil fuels?

FireMadeFlesh's avatar

@funkdaddy I’m not sure what you mean by intensive, but the limiting factor here is the net energy loss. Oil extraction and refinement into petroleum does not have this issue, as it is not producing petroleum as such. It is separating the petroleum component from crude oil. This seawater method is a true production of petroleum, and so it loses energy throughout the process.

To make it possible in a commercial context, we would need to have huge amounts of redundant non-fossil fuel energy in the power grid. There would need to be nuclear, solar, or geothermal power stations dedicated to the production of seawater based petroleum. But of course this isn’t economically viable.

I think a far more attractive commercial green option would be to have dedicated solar power stations converting seawater into pure hydrogen, to be used in hydrogen fuel cell vehicles. While this may sound similar to the option I’ve just written off as not viable, the real world efficiency is at least 2–3 times greater.

funkdaddy's avatar

And that scenario would be almost inexhaustible, work with existing technologies, would seem to have a positive effect on the chemistry of the seas, reduce pollution over existing fuels, and move away from concentrating power to those in oil rich areas. Just about every box on the wish list.

I guess my point is, why would this be limited to military applications when huge industries run on liquid fuels currently?

CWOTUS's avatar

The point that @FireMadeFlesh is trying to make, @funkdaddy, and which it’s not clear whether you get or not, is that this is a negative-return proposition. It costs more energy to create the liquid fuel from seawater than the liquid fuel will return to us. For its military applications, or for various other situations where “cost is not the driving factor”, that’s not an insurmountable handicap. But for those industries that you mention that run on liquid fuels (primarily road transportation, civilian shipping and aircraft operation, home heating in some parts of the world), “cost of fuel” is all-important. Cost is the primary driver for those industries and applications.

Cost is still “important” for military applications, but it’s not the most important issue there. Military strategy and tactics are not bound by simple “dollars and cents” cost constraints. The primary issue there is “ready supply”, and if a ship (with nuclear-generated electricity in abundance) can produce the power needed to run the process and produce the necessary fuel in adequate supply, then that potentially eliminates the need for another ship (which may have to traverse a long way over sometimes hostile ocean routes, through ambush points, etc. – and using additional crews to man and defend), then that’s worth the added cost. Eliminating the long supply line for that one item – liquid fuel – could enable the aircraft carrier to carry more weapons and food for the crew, for example, and reduce even further the logistical train that has to follow to resupply. It can be a huge strategic advantage and worth a very high cost in dollars.

This is also why fuel cells were developed for the manned space program. Again, the cost of running the fuel cell is exorbitantly expensive to use on Earth where liquid fuels are still more cost-effective, but in space liquid fuels (burning oxygen) are not the best way to produce power. So for that application as well, cost is not the primary driver.

In addition to all that, of course, we really don’t know from that article what the net effect on the ocean water really is. It may not be a very environmentally friendly process at all. Finally, with the current use of fracking technology making formerly “exhausted” oil fields in the USA once again viable producers, this country is on its way to potentially becoming a net exporter of petroleum once again.

FireMadeFlesh's avatar

Completely agree with @CWOTUS.

funkdaddy's avatar

Every method we have of energy transfer is a net loss. Every single one.

Burning organics is a horrible way of getting energy. We do it because they are easily portable, have the greatest history, the greatest infrastructure, we understand how they work, and are cool with the tradeoffs they provide.

But if this method transfers other forms of energy back into a combustible liquid fuel, that’s useful right now in a number of fields. Not because it’s overly efficient, but because it piggybacks on the existing infrastructure and bias with the important advantage of not needing an input of a limited and expensive resource (fossil fuels).

It’s man made gas.

——-

Put in someone else’s words from the comments

To me, it’s more that it shows potential to be an alternative to fossil fuels that makes it, if not newsworthy, then worthy of being on a watch list. It’s not that we put more energy in to convert the fuel than what we get out; that’s always been the case with pretty much everything (albeit, solar panel manufacturing has come a very long way).

It’s not fusion by any means, but if it continues like this, it could be along the same scales as gasoline. If that is the case, then we need to look at benefits like getting CO2 out of the oceans to help with climate change (even if it’s just a little bit), and giving the US less reason to fund military ops in the Middle East. Because those are also benefits that could help offset the cost of manufacturing the fuel.

AND

It’s not relevant that it takes more energy to make this fuel than the energy the fuel produces. What they are proposing is efficient and dense storage of energy not a primary source of energy. Similar to a battery but with much more power. A gallon of gas holds much more energy that a lithium battery of the same size.

FireMadeFlesh's avatar

@funkdaddy I see your point. Yes, all energy transfer has a net loss involved. To be honest I don’t have the data at my disposal to determine to any degree of exactness the resulting fuel price, if this process were to be scaled up to match the required output. But I don’t see it being within the reach of the masses.

I would love to be proven wrong about the assertions I made above. I am a petrol-head, so if we could power our cars from clean petrol, that would be incredible.

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