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from the seawater-is-more-than-just-salty-water dept.
There are many ways to generate electricity—batteries, solar panels, wind turbines, and hydroelectric dams, to name a few examples... and now, there's rust.
New research conducted by scientists at Caltech and Northwestern University shows that thin films of rust—iron oxide—can generate electricity when saltwater flows over them. These films represent an entirely new way of generating electricity and could be used to develop new forms of sustainable power production.
Interactions between metal compounds and saltwater often generate electricity, but this is usually the result of a chemical reaction in which one or more compounds are converted to new compounds. Reactions like these are what is at work inside batteries.
In contrast, the phenomenon discovered by Tom Miller, Caltech professor of chemistry, and Franz Geiger, Dow Professor of Chemistry at Northwestern, does not involve chemical reactions, but rather converts the kinetic energy of flowing saltwater into electricity.
https://phys.org/news/2019-07-ultra-thin-layers-rust-electricity.html
More information: Mavis D. Boamah et al. Energy conversion via metal nanolayers, Proceedings of the National Academy of Sciences (2019). DOI: 10.1073/pnas.1906601116
(Score: 3, Insightful) by JoeMerchant on Wednesday July 31 2019, @07:40PM (14 children)
10 square meters is ~108 square feet, a little over a 10'x10' plate. That's a lot of iron, and a lot of flowing saltwater, granted for a lot of power, but imagining this being implemented on a houseboat (someplace that has ready access to flowing saltwater), the friction generated by that plate in the water - even without an electrical generation load - would make it more efficient to just run a fuel powered generator rather than trying to tow this thing in the water to make the same power.
Then we get into questions of lifetime: how long does a rusty plate last in a saltwater environment?
🌻🌻 [google.com]
(Score: 2) by deimtee on Wednesday July 31 2019, @07:54PM (1 child)
They don't give a required speed, but there are places where the tidal flow can reach several knots. If the speed is low enough and it can handle pulsed power, it might even be an efficient way to recover wave energy.
If you cough while drinking cheap red wine it really cleans out your sinuses.
(Score: 2) by JoeMerchant on Wednesday July 31 2019, @11:15PM
Tidal flows are a good source, still questionable how much energy is required to create, install and decommission the plate vs how much energy it produces in its useful lifetime.
🌻🌻 [google.com]
(Score: 2) by Immerman on Thursday August 01 2019, @03:21AM (2 children)
>That's a lot of iron,
Not really, they use vapor deposition to create a layer of iron oxide 10nm thick. 10m^2*10nm = 0.1 mm^3 of iron oxide - or basically nothing. Of course they don't mention what the substrate is, but even if it's iron it could presumably be a thin foil laminated to something light and rigid.
(Score: 2) by JoeMerchant on Thursday August 01 2019, @02:41PM (1 child)
Iron isn't the greatest electrical conductor, on something with a span of 10's of feet I'd expect significant losses if they're using thin iron as the wires. I'd expect bigger problems if they're trying to get bonding between iron oxide and something like copper or aluminum.
🌻🌻 [google.com]
(Score: 2) by Immerman on Thursday August 01 2019, @07:34PM
Even a thin iron foil is actually a decent conductor when 10 feet wide - resistance is proportional to the cross-sectional area, and being 10 feet wide really helps with that. It'll need to be almost 6x thicker than a copper foil to get the same conductance, but it's hundreds of times cheaper, so it'd probably still be an obvious choice.
(Score: 2) by RS3 on Thursday August 01 2019, @03:28AM (1 child)
You just invented perpetual motion! Connect the rusty plate battery to a propeller motor! Voilà!! Cruise around the world!
And you answered your own question- you'll get extra power because the saltwater will, what, make the plate clean? No no no, it will rust MORE, and you'll generate MORE POWER!!
(Score: 0) by Anonymous Coward on Thursday August 01 2019, @10:33PM
imagine a hydrodam with a rusty impeller: it makes soo much energy it can pump more water up then used down! soon all ocean will be dry!
(Score: 0) by Anonymous Coward on Thursday August 01 2019, @09:09AM (6 children)
The article has been corrected to say that you will get "a few kilowatt-hours" which gives no information whatsoever about the power generated by this thing, because kilowatt-hours is a unit of energy and power is a rate of energy output over time... and the time is not specified (so I suppose it must be the total produced over the lifetime of the device?)
And "a few kilowatt-hours" is not very much energy at all.
(Score: 2) by JoeMerchant on Thursday August 01 2019, @02:43PM (4 children)
I can buy a kWH for about $0.11 at retail, seems like a 10'x10' plate of anything is going to cost many multiples of $0.11 just to get it placed in a saltwater environment, even if the material it is made of is free.
🌻🌻 [google.com]
(Score: 2) by Immerman on Thursday August 01 2019, @07:41PM (3 children)
That's the difference between buying power, and buying generating capacity. Hint - the coal plant you're probably buying most of your power from cost a LOT more than 10 cents per kilowatt to build.
Buy 1kWh of power, and it's keep your 1kW load running for one hour, and then you have to buy another kWh.
Buy 1kW of generating capacity and (assuming it runs 24/7 with no fuel consumption) it'll run your 1kW load indefinitely, producing about 9000 kWh per year
(Score: 2) by JoeMerchant on Thursday August 01 2019, @09:19PM (2 children)
This circles back to the question posed earlier: are they telling what the generating capacity is, or are they actually quoting the total generating capacity of the device over its lifetime (as the units implied...)
One would hope they just flubbed the units in the usual fashion and they really meant generating capacity (in kW) instead of total lifetime generating capacity (in kWh).
🌻🌻 [google.com]
(Score: 2) by Immerman on Friday August 02 2019, @03:05AM (1 child)
I'm not paying to skim the paper, and the top several results from Google all have the exact same quote:
>"For perspective, plates having an area of 10 square meters each would generate a few kilowatts per hour -- enough for a standard U.S. home" Miller said.
Heck, they might all be republishing the exact same press release - I just searched for "watts"
I'm confident it was a units flub. Though I've heard that in the power industry (and perhaps researchers?), where "kWh" is the "normal" unit to be discussing, and is often shortened to just "kW" when speaking, in which case "kW/h" would in fact be the correct way to converse about instantaneous power - doubly so since it's pretty much a nonsense unit so that it won't confuse anyone (except outsiders, but how often do you talk to them about your work?)
At any rate, lets get to the meat of the claim: assume that Miller at least knows what they're talking about, and that "enough for a standard U.S. home" is correct. The average U.S. home consumes about 10,000kWh per year, or an average of a bit over 1 kW-hour per hour. Of course peak load will be a few times higher than that. So "a few kW hours per hour" would in fact provide for the average U.S. home, with a generous window for individual variability (or leaving out the batteries), and is almost certainly what he meant actually.
So this technology could supposedly produce a few hundred watts per square meter, which would put it roughly on par with solar panels in terms of peak generating potential per unit area. And I would presume this could be "stacked" in all sorts of interesting ways - how much surface area is in a car's radiator? If it could be made cheaply enough this might be a huge boon to seaside communities. Of course there is the question of how it actually stacks up to other forms of wave and tidal power. The lack of moving parts would seem to be a huge boon, but that's an awful lot of delicate surface area to keep clean and undamaged
(Score: 2) by hendrikboom on Friday August 02 2019, @11:52AM
Love the unit! It's probably what the original article needed in the first place!
(Score: 2) by Immerman on Thursday August 01 2019, @07:36PM
They say that it's "enough to power a house", so presumably that's per-day, or *maybe* per-hour (though that would be a heck of a high-power house)