
New saltwater electrical generation could power submarines or medical devices - jonbaer
https://spectrum.ieee.org/energywise/green-tech/geothermal-and-tidal/a-saltwater-river-runs-through-it
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leoedin
The power generation potential given is in units which make it almost useless.
A kWh is a unit of energy, converted into a frame of reference more useful
than the joule. Saying that a device can generate 2 kWh doesn't really tell
you much - it could generate that in 10 seconds (good) or 10 years (bad).

I think the quoted figure was meant to be in kW - a unit of power, which is a
much more useful piece of information. I looked at the original paper (here:
[https://arxiv.org/pdf/1907.13170.pdf](https://arxiv.org/pdf/1907.13170.pdf))
but couldn't find any reference to the 2kWh quoted from the researchers.

If the suggestion is correct, and a 10mx10m panel can generate 2kW, then
there's some really interesting potential applications. History has shown that
the path towards robust technology is normally by making things solid state -
vacuum tubes to transistors, solar collectors to solar panels, even
helicopters to drones all benefited from a huge decrease in mechanical
complexity.

~~~
thaumaturgy
It might be a nice add-on for desal plants, which already have plenty of waste
saltwater getting pumped around.

Someday.

~~~
imglorp
I think that's the key right there: motion of the water. There's no free lunch
here; it's not a battery.

Maybe a good application would be throwing the whole rig into the surf, or a
salty tidal stream, where you get the induced current from lunar power.

~~~
ihaveajob
Your comment made me go on a total tangent considering whether the Moon with
eventually fall on us if we harvest enough tidal energy due to gravitational
drag. But interestingly enough, the opposite is true, tidal drag is actually
moving the moon further away from us, and slowing down the Earth's spinning.

~~~
Gracana
That didn't make sense to me, so I looked it up and found there's a good
wikipedia article about it (which you probably read as well.) It's too much
for me to explain poorly in an HN comment, so I'll just link it for anyone
who's also scratching their head:
[https://en.wikipedia.org/wiki/Tidal_acceleration#Effects_of_...](https://en.wikipedia.org/wiki/Tidal_acceleration#Effects_of_Moon's_gravity)

~~~
ihaveajob
The key point to me was that since earth is spinning about 28 times faster
than the moon rotates around us, the drag force equalizes the frequencies by
making earth spin slower, and the moon rotate faster, thus further away from
us. Eventually they'd be in equilibrium, spinning in lockstep.

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regularfry
Submarines sound like a stretch to me - the motion of the water past the hull
would be driven by the main engine, so it would just be reclaiming some of
that energy (and inducing drag into the bargain). Where I _can_ see it
potentially working is on Slocum gliders, where the main motive force comes
from gravity. Whether you'd get enough watts off the available surface area to
be worth the added drag, though... different question.

~~~
eloff
I think the idea is to run the process in reverse - run an electrical current
through the metal to push against the ions in the water. No idea how practical
it would be.

~~~
masklinn
Not very, at 2kW per 100sqm of material, covering an attack sub in this
material would give you the power of a compact car's motor: approximated to a
cylinder 12m by 110, USS Seawolf has a lateral surface of under 4200sqm, 42
panes, 84kW.

The 2018-2019 Kia Soul EV has a 81.4kW engine.

~~~
clort
I see you've posted this approximate figure and its comparison to a car three
times already, but the Kia figure is irrelevant. The relevant comparision is
the required power to push the USS Seawolf forward and what speed can you get
with 84kW? I myself can push a 6500Kg boat although not as fast as the built-
in 10kW engine, admittedly.

Don't forget that it is a sub and silent running is likely way more valuable
than fast running (nobody is saying they can't have two methods of propulsion)

Also, I don't know anything about this USS Seawolf - is it a nuclear sub? IIRC
the problem with them is that the pumps cooling the atomic core can't be shut
down, meaning there is always detectable sound. Would a hose with this
material on the inside be able to pump cooling water silently? Don't forget
that the 'pump' in that case could be almost the entire length of the sub..

~~~
masklinn
> I see you've posted this approximate figure and its comparison to a car
> three times already, but the Kia figure is irrelevant.

It's very relevant as it gives a sense of scale of the issue and how little
power is actually produced.

> The relevant comparision is the required power to push the USS Seawolf
> forward and what speed can you get with 84kW

Since you're apparently checking all my comments you've likely seen Gotland's
2x75kW AIP gives it a top speed of 5kn. These 85kW would be a smidge above
half that on a submarine about 6 times the weight. The relationship is
probably somewhat non-linear but I'd say the result would be around "geriatric
pacing".

> Don't forget that it is a sub and silent running is likely way more valuable
> than fast running (nobody is saying they can't have two methods of
> propulsion)

You could get about the same effect by just shutting down propulsion entirely.

> Also, I don't know anything about this USS Seawolf - is it a nuclear sub?
> IIRC the problem with them is that the pumps cooling the atomic core can't
> be shut down, meaning there is always detectable sound.

That doesn't seem to have any relevance to my point that this tech doesn't
seem able to actually provide propulsion for a sub'.

> Would a hose with this material on the inside be able to pump cooling water
> silently? Don't forget that the 'pump' in that case could be almost the
> entire length of the sub..

You do realise there's other shit in a sub than just reactor cooling systems
right?

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driverdan
> We’ve got a device that works, and we’ve got a number of ways we can run it.
> But we have not, for example, yet lit up a lightbulb.

IEEE is really hurting their image with these poorly written clickbait
headlines. While an interesting idea if it can't even produce enough power for
a lightbulb it's not going t obe powering submarines or medical devices
anytime soon.

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kryogen1c
>10-meter-by-10-meter

>as much as 2-5 kilowatt-hours of electrical power

>could power submarines

Not really. I don't know about non-nuclear subs, but this is several orders of
magnitude too low to be space effective for use on subs. I cant find any
official public info, but suffice it to say subs run closer to 2MWs than 2KWs

~~~
SamBam
I believe the submarine use-case is supposed to be the other way around:

> and even (running the process in reverse) a silent propulsion system for
> boats or submarines.

So the submarine would have on-board power generation that powers this, not
that this would provide the power to the submarine.

~~~
masklinn
> and even (running the process in reverse) a silent propulsion system for
> boats or submarines.

10x10m for 2kW is 2kW per 100sqm.

That's pretty much nothing, propulsion-wise. A seawolf-sized sub (108m long
and 12m wide) covered in this material would produce about 85kW. That's around
the powertrain of a modern compact / city car: the nissan leaf's motor is
80kW.

~~~
SamBam
> would produce about 85kW

It's not _meant_ to produce energy in this case. That's what I'm saying.

~~~
masklinn
It would convert electrical energy to mechanical, acting like an engine (and
drivetrain).

An 85kW engine.

Which is — as I noted — about what you'd find on a compact EV (that's about
115hp).

~~~
ska
Or for another point of reference, about what a fast-ish medium sized
motorcycle of around 400lb/180kg produces.

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colechristensen
Bad title, it could be used to generate power when it is fixed and there is a
source of moving water (tides, fixed implanted medical devices) or generate
force for something moving through water (submarine), but not both at the same
time.

Moving water generates electrical currents, this is a pretty standard physics
demonstration and how lightning works. This is perhaps a novel way of
utilizing that property with thin conductive films.

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gibolt
This sounds like a quite promising generation method. They quote 10x10 meter
area with 100 layers as potentially generating 2-5 kwh.

It fails to mention if water flow can be continuous or has to be droplets and
flow speed/salt content required for that generation.

Running in reverse to generate propulsion is also mentioned. Covering a
submarine and just moving a thin layer of water out of the way to move forward
is a super interesting application.

~~~
clort
Also, they are worried about slime build up. but in the case of using that as
a motor rather than generator, I wonder if that would be an issue at all, or
if once activated it would just push the slime off..?

~~~
gibolt
It is a fun thought. Probably far less efficient and slower than current
propulsion, but no moving parts is a big plus.

Small drones that patrol the ocean for long times would be a cool application.
Move a bit until the batteries are nearly depleted, float around to recharge,
and then resume moving.

~~~
stevenhubertron
Silent operation is always a big plus for subs that want to stay hidden.

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Areading314
kWh are units of energy, not power. This method is of no interest if it takes
years to generate those kwh!

Also those films will rust completely off the slide in a matter of hours.

Edit in the case of iron, a 20nm film would fully corrode in about 20 min
using a corrosion rate of 0.55mm/y

~~~
t0mbstone
"Energy is the total amount of work done, and power is how fast you can do it.
In other words, power is energy per unit of time. Power is watts. Energy is
watt-hours."

~~~
agumonkey
energy is total change, power is change over time

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ummonk
How is running this in reverse different from a magnetohydrodynamic drive?

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t0mbstone
So the trick would be to get a vat of salt water with these sheets in them,
then set up an electric pump to circulate the salt water across the sheets.
Power the electric pump using the generated electricity and... tada! Free
energy! :D

~~~
outworlder
Right. Reductio at perpetuum mobile proves this idea doesn't work.

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pitaj
Reminds me of two works of science fiction:

20,000 Leagues Under the Sea

and

Red October

