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MIT Combines Carbon Foam and Graphite Flakes For Efficient Solar Steam Generati

timothy posted about 2 months ago | from the science-fiction-future-awaits dept.

Technology 110

rtoz (2530056) writes Researchers at MIT have developed a new spongelike material structure which can use 85% of incoming solar energy for converting water into steam. This spongelike structure has a layer of graphite flakes and an underlying carbon foam. This structure has many small pores. It can float on the water, and it will act as an insulator for preventing heat from escaping to the underlying liquid. As sunlight hits the structure, it creates a hotspot in the graphite layer, generating a pressure gradient that draws water up through the carbon foam. As water seeps into the graphite layer, the heat concentrated in the graphite turns the water into steam. This structure works much like a sponge. It is a significant improvement over recent approaches to solar-powered steam generation. And, this setup loses very little heat in the process, and can produce steam at relatively low solar intensity. If scaled up, this setup will not require complex, costly systems to highly concentrate sunlight.

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Sponge-like? (4, Funny)

ArcadeMan (2766669) | about 2 months ago | (#47507183)

SpongeBob Square Solarpanel?

Re:Sponge-like? (1)

richy freeway (623503) | about 2 months ago | (#47507495)

Spongebob Solarpants.

Re:Sponge-like? (1)

Anonymous Coward | about 2 months ago | (#47508239)


Re:Sponge-like? (1)

Ravaldy (2621787) | about 2 months ago | (#47510043)

The maturity level of the Slashdot crowd was just determined to be NIL. :)

Finally (1, Informative)

Triklyn (2455072) | about 2 months ago | (#47507205)

now here's a renewable i could get behind.

Re:Finally (3, Informative)

Mr D from 63 (3395377) | about 2 months ago | (#47507287)

“There is still a lot of research that can be done on implementing this in larger systems.”


“There is still a lot of research that MUST be done TO IMPLEMENT this in larger systems.”

Re:Finally (1)

i kan reed (749298) | about 2 months ago | (#47507425)

You forgot the most important part:

"And it may be impossible entirely"

Re:Finally (0)

Archangel Michael (180766) | about 2 months ago | (#47507517)

Do you realize that the #1 Greenhouse Gas is water vapor? []

Re:Finally (1)

Triklyn (2455072) | about 2 months ago | (#47507763)

:) was not aware, but i think you should propose a water sequestration program. it'll be real effective for you know... governing water loss from the oceans.

Re:Finally (2)

geekoid (135745) | about 2 months ago | (#47510369)

The most efficient way to do that is to reduce CO2 in the air.

Re:Finally (1)

Anonymous Coward | about 2 months ago | (#47508205)

If we take all of human's current power usage, rounded up to 20 TW, and applied that toward water vapor production, just using enthalpy of vaporization and no heating, we could produce ~300 gigatonnes of water vapor, which in five hundred years will catch up to the ~1400000 gigatonnes of water vapor evaporating from the oceans each year, assuming there is no mechanism for removing water vapor from the sky. Of course, if you put some of that energy into actually pumping the water vapor beyond the troposphere, there would be a bigger problem. Instead of using mechanical pumps though, it might be easier just to attach a carbon atom to the water, lose the oxygen, and then let it drift up on its own above the troposphere, where it react to form water again.

Re:Finally (0)

Anonymous Coward | about 2 months ago | (#47509161)

~300 gigatonnes of water at that! Every season is rainy season! :D

Re:Finally (1)

geekoid (135745) | about 2 months ago | (#47510355)

Did you know that's becasue of increased CO2?

Retarded (0)

Anonymous Coward | about 2 months ago | (#47516465)

Water vapor is not the #1 ghg, whatever that is, because of increased CO2. You should limit commenting on scientific matters until you get your head out of your ass.

Re: Retarded (1)

astar (203020) | about 2 months ago | (#47516937)


Algae (0)

Anonymous Coward | about 2 months ago | (#47507207)

Didn't RTMF... What happens when it gets all gunked up with algae?

Re:Algae (1)

ArcadeMan (2766669) | about 2 months ago | (#47507247)

You get solar-powered ice cream.

Re:Algae (2)

Applehu Akbar (2968043) | about 2 months ago | (#47507553)

Ben 'n Jerry's flavor name: Solargreen
Baskin-Robbins: Peanut Algae
Dreyer's: Verde Vivacious

Re:Algae (2)

Immerman (2627577) | about 2 months ago | (#47507297)

If its boiling water I suspect it won't get too gunked up, except possibly for the bottom-most layers I suppose.

Re:Algae (2)

Immerman (2627577) | about 2 months ago | (#47507339)

Also - bleach. Doesn't take much to render water unfit for life, and if you're capturing the steam (presumably under pressure) then you're likely dealing with a closed-loop system, with the carbon absorbing virtually all of the sunlight vital to algae growth.

Re:Algae (2)

Mr D from 63 (3395377) | about 2 months ago | (#47507367)

Only if you are boiling pure water, otherwise you will likely get mineral deposits and such rather quickly.

Chemistry (1)

dbIII (701233) | about 2 months ago | (#47507497)

Only if the conditions are right for them to come out of solution and stick. Graphite crucibles are used to melt steel, and even that doesn't stick very well once it solidifies.

Re:Algae (1)

gl4ss (559668) | about 2 months ago | (#47509015)

well after the first run through the loop it's not going to get any more..

pssh. you would think that slashdotters would release that steam has been used quite a while and even getting the purified water is the least of the problems with implementing the plant.

Re:Algae (2)

Mr D from 63 (3395377) | about 2 months ago | (#47509325)

Water in a typical closed steam system is managed with various chemicals, and not simply pure water. That is because even with pure water, you will always get some interaction with the system elements and oxygen or whatever gases are present. Methods for managing that have been optimized for large steam plants. Who knows what would "get into the water" even in a closed system with this material and whatever others are required.

I wouldn't assume you can produce high pressure steam with any velocity through this foam. It appears very fragile, and would probably get torn apart by even a low flow approach. If true, that makes a direct closed system approach unlikely. If not true, it still would appear to require a huge exposure area to produce any usable output, which presents significant flow management and collection problems.

So, not all slashdotters are as lost on the matter as you may suppose.

Re:Algae (2)

Mr D from 63 (3395377) | about 2 months ago | (#47507361)

Didn't RTMF... What happens when it gets all gunked up with algae?

It seems fouling would be a big problem in an open system. If you had a closed system, sandwiched the material under a glass plate and circulated pure water or some other fluid in a closed system, with a heat transfer means on a bottom plate, then maybe that would make a usable system. But that would also reduce efficiency by some amount.

Re:Algae (1)

HiThere (15173) | about 2 months ago | (#47511897)

Hun? Reduce the efficiency? If you run the steam through some system to extract most of the energy, one of the outputs is going to be hot water, which you can feed back into the system as water that's already been preheated.

Re:Algae (1)

Mr D from 63 (3395377) | about 2 months ago | (#47512067)

Heat transfer in any system has an efficiency loss associated with it. If you have a primary heat system and transfer that energy to a secondary steam system, you will lose energy in the process. Part of that lost energy is not only direct heat loss from the slowed heat transfer rates, but also in the additional energy required circulate through the heat exchanger, which depends on a lot of fluid passing over a larger surface area.

De-salination? (5, Interesting)

Squidlips (1206004) | about 2 months ago | (#47507237)

Could it be used for de-salination

Re:De-salination? (1)

Mr D from 63 (3395377) | about 2 months ago | (#47507301)

Possibly, but there is no indication if this material will see fouling or depositing from such a process.

Re:De-salination? (4, Funny)

ArcadeMan (2766669) | about 2 months ago | (#47507331)

Faster CPUs, better solar panels, radiation shielding and drinkable water for all the world.

Graphite. Is there anything it can't do?

Re:De-salination? (4, Funny)

dotancohen (1015143) | about 2 months ago | (#47507605)

Faster CPUs, better solar panels, radiation shielding and drinkable water for all the world.

Graphite. Is there anything it can't do?

Frankly, silicone still has a purpose that graphite doesn't fulfil.

Re:De-salination? (1)

x4nder (3738723) | about 2 months ago | (#47516475)

Titillating response. Ba dum psh.

Re:De-salination? (1)

gstoddart (321705) | about 2 months ago | (#47507665)

Graphite. Is there anything it can't do?

Breast implants?

Re:De-salination? (1)

GNious (953874) | about 2 months ago | (#47507719)

I see no reason why not ... might not be optimal, but technically you can implant anything into breasts.

Re:De-salination? (0)

Anonymous Coward | about 2 months ago | (#47508767)

I know I have...

Re:De-salination? (1)

Triklyn (2455072) | about 2 months ago | (#47507779)

can it... love?

Re:De-salination? (1)

rogerrabit (2885897) | about 2 months ago | (#47508037)

You're mixing up graphite with graphene.

Re:De-salination? (1)

FatdogHaiku (978357) | about 2 months ago | (#47508521)

You're mixing up graphite with graphene.

My God Man, you've just invented graphitene!
To The Patent Office!

Re:De-salination? (0)

Anonymous Coward | about 2 months ago | (#47507333)

Desalination was my first thought as well. The press release does mention it, though only in general terms:

"Steam is important for desalination, hygiene systems, and sterilization," says Ghasemi, who led the development of the structure. "Especially in remote areas where the sun is the only source of energy, if you can generate steam with solar energy, it would be very useful."

Re:De-salination? (2)

aaronb1138 (2035478) | about 2 months ago | (#47507365)

This is exactly what I was thinking about. I am betting all along the Middle East and African coastlines this would be a killer technology to both drive steam turbines and produce potable water concurrently. I would bet the issue would be salts and other particulates clogging the water passages though. Might work as a final stage distillation in a plant that is completely solar powered though.

The other issue for using it as an electric (or rather mechanical) generation source is the fact that it needs direct sunlight in the "boiler" or pressurized section which is tricky. This would definitely necessitate a different structure of solar farm + turbine than currently in use. Most of the more successful solar thermal electricity generation schemes have worked precisely because they plug into existing electricity generation turbine infrastructure.

Re:De-salination? (2)

Mr D from 63 (3395377) | about 2 months ago | (#47507511)

This foam looks pretty fragile to me. I would guess with any flow rate approaching what would be required to run a steam turbine, the foam would be torn apart. I think that is one reason the researchers didn't point this out as a likely use.

Re:De-salination? (3, Insightful)

Immerman (2627577) | about 2 months ago | (#47507401)

Oh, now *there's* an idea. I suspect you'd have issues using saltwater though - when the water is boiled the salt would be left behind within the foam. In a closed-loop system that might not be an issue as the distilled water would be reintroduced to the reservoir preventing excessive concentration of salts, but otherwise you'd almost certainly end up with salt crystals completely coating the foam, Which would either render it immediately ineffective or eventually build up to such a level that it dies as a solid block of salt with an embedded carbon lattice.

Of course desalination isn't cheap, so it might be cost-effective to replace the foam regularly. You might even be able to rinse the crystals away with filtered seawater in order to reuse the foam.

Re:De-salination? (4, Insightful)

Chris Mattern (191822) | about 2 months ago | (#47507689)

You wouldn't boil the saltwater in foam, genius. Use properly prepared and recycled water as a heat transfer fluid and use that heat to distill seawater in tanks built for that process.

Re:De-salination? (1)

Immerman (2627577) | about 2 months ago | (#47508269)


Of course then you're no longer using the foam for desalination, as I interpreted the question, but only indirectly as a replacement for some other heat source. If this foam (plus the sealed, transparent, insulated tanks containing it and the water) can truly be produced more cheaply than an energy-equivalent solar concentrator then that could indeed be a viable option. It seems like it would be a *lot* less fault tolerant than a sheet of polished metal bent into a parabolic trough on a stationary mount though. Maybe it's not quite as efficient, but I would want to see the 40-year amortized cost comparison before I believed that this foam technique is substantially cheaper.

Re:De-salination? (1)

trout007 (975317) | about 2 months ago | (#47507903)

But you could burn away the carbon and have an unlimited supply of sea salt.

Re:De-salination? (1)

Lord Lemur (993283) | about 2 months ago | (#47510085)

Or have a closed loop exchange heat with an open loop, depending on the relative tempratures. If you have a liquid that significantly exceeds the boiling point of water in the closed loop there should be enough room to operate. Your going to loose effiency, there is a ton of Sun and open area in many dry places.

Re:De-salination? (2)

Ronin Developer (67677) | about 2 months ago | (#47507677)

They speak of micropores in the sponge material. This would likely foul with particulate in the water. The water in the system would need to be fairly pure to start.

That being said, if it is an efficient steam generator, perhaps, it could be used to provide the heat source for desalination systems such as what are used onboard navy ships for the production of fresh water?

Re:De-salination? (1)

HiThere (15173) | about 2 months ago | (#47511931)

Not directly. If you fed salt water into the system is would get blocked up with salt crystals. Indirectly, yes. The output is steam, and you could use that to heat the salt water to the point where it started rapidly evaporating. (You'd want to recycle the "working fluid" water, so you don't just bubble it through the salt water, but instead you use the salt water to cool the steam until it condenses and then feed it back into the heater.)

The next generation of MIT? (3, Insightful)

damn_registrars (1103043) | about 2 months ago | (#47507241)

I hadn't previously heard of this MIT' before. I hope we see good things from them.

Re:The next generation of MIT? (3, Funny)

ArcadeMan (2766669) | about 2 months ago | (#47507303)

It's MIT Prime, a.k.a. MIT: The Next Generation.

The next generation of MIT? (1)

Black.Shuck (704538) | about 2 months ago | (#47507555)

There's another MIT headline further down the front-page: "MIT's Ted Postol Presents More Evidence On Iron Dome Failures"

I'm guessing timothy copy-pasted that headline then deleted everything except the first few characters, but forgot to zap the apostrophe. All to save himself the arduous task of typing "MIT".

Well, I'm just speculating, of course.

Re:The next generation of MIT? (2)

damn_registrars (1103043) | about 2 months ago | (#47508529)

Are you suggesting that Timothy (or any slashdot "editor") uses a keyboard? I thought those were too old-fashioned for them and they did all their entry using 12th-generation iPad femtos with tactile inputs that are derived from Minority Report

That's amazing (0)

Anonymous Coward | about 2 months ago | (#47507311)

I have this thing called a lens that uses 100% of incoming solar energy to burn things. Where's my grant?

But (1)

rossdee (243626) | about 2 months ago | (#47507319)

You've still got to convert that steam into electricity, presumably with a turbine. so what is the overall efficiency?
And do you get bits of graphite and carbon foam gumming up your turbine?

Re:But (2)

jehan60188 (2535020) | about 2 months ago | (#47507377)

that's what I came to post.
the inefficiencies of steam-powered power-plants are in the moving parts of the rankine cycle. this device helps create the steam (one of the four major parts of the rankine cycle), but we can't harness it to do work.

Re:But (1)

pr0fessor (1940368) | about 2 months ago | (#47507461)

I was imagining a great big terrarium.

Re:But (2)

brambus (3457531) | about 2 months ago | (#47507547)

> the inefficiencies of steam-powered power-plants are in the moving parts of the rankine cycle

No, the inefficiencies of the Rankine cycle come from fundamental laws of thermodynamics and are inherent to all heat engines.

Re:But (0)

Anonymous Coward | about 2 months ago | (#47507727)

No. Thermodynamics stipulates the maximum theoretical efficiency of an engine (no engine can be more efficient than a Carnot engine) based on the temperature difference between input and output but otherwise the efficiency of the engine is dictated by the shape of the particular thermodynamic cycle.

Re:But (2)

pavon (30274) | about 2 months ago | (#47507691)

The quickest numbers I could find [] say that at the scales of large power-plants, the generator is very efficient, but the turbine not so much, around 50%. This would put the system as a whole at around 40% efficency sunlight -> electricity. That's competitive with the best solar voltaic systems tested in the lab, and 50-100% better than practical systems on the market. Assuming their system really does scale up to power plant sizes, of course.

Re:But (1)

LoRdTAW (99712) | about 2 months ago | (#47508001)

I would worry more about condensation of the cool steam in the turbine itself. The only way this would be good for a turbine is if the steam can be further heated via a solar super heater.

This is why power plant boilers have a superheater which passes the steam from the boilers steam drum through a heat exchanger in the hot exhaust stream of the boiler. This brings the steam temperature up well past the boiling point of water and prevents steam from condensing in the turbine. Imagine a turbine spinning at 3600 RPM (for a 2 pole 60Hz alternator) in which droplets of water form and begin to collide with the blades. All you need is one blade to fail from getting pummeled with water and it's game over for the turbine. The steam is condensed once it exits the turbine exhaust which creates a vacuum effect which increases the turbines efficiency, you pull steam through it. The steam is condensed using cooling towers, water cooled heat exchangers or fed to a district heating system and customers pay to do some of the condensing (and maintain the infrastructure while increasing efficiency).

Re:But (1)

LWATCDR (28044) | about 2 months ago | (#47508877)

Simple, low.
The greater the heat differential the greater the efficiency. To use low temperature aka low pressure would require massive turbines. BTW temperature and pressure in a gas are very related. So much so that you can almost treat them as the same thing.

Re:But (1)

geekoid (135745) | about 2 months ago | (#47510405)

It needs 1/10 the solar energy then previous methods.
That means mirror don't have to be as precise, uses less area, cheaper, can make smaller plants.
I still don't know what data centers aren't put in sunny area and power from Industrial Solar Thermal.

Re:But (1)

spitzak (4019) | about 2 months ago | (#47511273)

I don't think it produces 10x as much steam for a given amount of solar energy. What it does is produce steam at a solar intensity 1/10 of the level at which other things produce steam (the other thing is producing zero steam at the temperature this one is producing steam at).

I think the real result is you need the same amount of reflector as for other schemes, however it can concentrate the solar energy on an area 10 times as large, which may be much less expensive (due to it not requiring as much accuracy, and because the receiver is nowhere near as hot).

Re:But (1)

Required Snark (1702878) | about 2 months ago | (#47515701)

A turbine is the wrong technology. I think that this would work better with a Sterling Engine [] . The steam temperature is (obviously) 100C, and the cold side could either be ambient air temperature or water.

The Sterling crank output could drive a generator, and there are some existing Sterling designs that use the linear motion of the pistons as magnets with a coil for electrical generation. The boiling water is a closed loop that is the hot side of the Sterling engine.

This lends itself to a modular design where the water boiling and Sterling power generation are a sealed unit, and you get more power (and protection against single points of failure) by replicating the module. The major limitation of this system is that it only works during daylight hours. Even so, if it has high enough efficiency and low enough manufacturing cost it could be useful for environments without extensive electrical grid infrastructure.

details (4, Informative)

Anonymous Coward | about 2 months ago | (#47507325)

They found they were able to convert 85 percent of solar energy into steam at a solar intensity 10 times that of a typical sunny day.

Re:details (1)

jehan60188 (2535020) | about 2 months ago | (#47507391)

i didn't get this sentence when i first read it, but now it makes sense.
basically you'd need a magnifying glass on top of this thing.

Re:details (1)

dbIII (701233) | about 2 months ago | (#47507521)

That's already done with some of the more expensive photovoltaics.

Re:details (0)

Anonymous Coward | about 2 months ago | (#47513621)

I wondered why 'hot spot' was in the summary and this explains it. This suggests this iteration of material is intended for use in concentrated solar installations where the sun is focused using mirrors. Typically the current working fluid of these is some form of salt, which then needs to go through a heat exchanger to generate steam to then drive a turbine. It would seem this technology aims to take out the salt requirement to simplify the process.

costly concentration (4, Insightful)

Immerman (2627577) | about 2 months ago | (#47507327)

> if scaled up, this setup will not require complex, costly systems to highly concentrate sunlight.

So, mirrors are costly now - does that imply that this carbon foam stuff is cheaper to produce than a sheet of polished stainless steel? If so that *is* promising.

Re:costly concentration (0)

Anonymous Coward | about 2 months ago | (#47507443)

The main issue I see with that is.

Now you have a field that generates steam, do you also have a plan on how to collect it?

Seems easier to replace the top of a current solar tower and see if efficiency is increased.

Re:costly concentration (1)

Immerman (2627577) | about 2 months ago | (#47507573)

It would have to be a sealed system, obviously - steam doesn't do you much good unless it's under pressure (though I suppose you could use it as a heat source for an external combustion engine). And for decent efficiency you'd need either insanely well-insulated steam pipes, and/or to have the turbines quite near the generation. Considering how simple/cheap a steam turbine can be I wouldn't be all that surprised if every "covered swimming pool" had it's own turbine on one side

I suspect combining it with serious solar concentration would be a problem though - graphite flakes are basically powdered coal after all, get it hot enough and "fwoosh".

Re:costly concentration (0)

Anonymous Coward | about 2 months ago | (#47508965)

Steam doesn't need to be under pressure to drive an engine. You get the pressure differential when you condense it back to water. So simple steam engines work at low negative pressure, not positive pressure.

Re:costly concentration (0)

Anonymous Coward | about 2 months ago | (#47507819)

You Luddite, when they come for you with 3D printed carbon nano foam, will you still be so glib?

Re:costly concentration (1)

Immerman (2627577) | about 2 months ago | (#47508161)

Umm, I don't think Luddite is the term you're looking for. Maybe it has an antonym that would be more fitting?

Re:costly concentration (1)

pr0fessor (1940368) | about 2 months ago | (#47508189)

I was looking a cds the other day and found that printed cardboard sleeves were a few cents more expensive than the cheap slim line plastic cases with a paper insert. I wasn't expecting that so who knows it might be cheaper.

Re:costly concentration (1)

tomhath (637240) | about 2 months ago | (#47508685)

This process still requires some mirrors; it starts to work at about 10x maximum solar light. But that's still a couple of orders of magnitude better than any other system using mirrors.

Re:costly concentration (1)

MozeeToby (1163751) | about 2 months ago | (#47509109)

Mirrors are cheap. Water to wash a few hundred acres worth of mirrors is relatively expensive. Especially in the middle of the desert where we like to park solar installations.

Re:costly concentration (1)

Immerman (2627577) | about 2 months ago | (#47512203)

And what makes you think it would be any more water-efficient to wash the glass/plastic covering an equal area of foam-solar reactors?

Re:costly concentration (1)

TubeSteak (669689) | about 2 months ago | (#47510615)

So, mirrors are costly now -

Mirrors are cheap, it's the several acres of tracking mechanisms which the mirrors are mounted to that are expensive.

The idea is, if the steam generator requires less concentrated light, you can save money on the solar tracking mechanisms, which lowers the final cost of each solar array.

Re:costly concentration (1)

Immerman (2627577) | about 2 months ago | (#47512457)

I had more in mind a simple solar-trough design -admittedly less efficient than a tracking mechanism per unit area, but much less to go wrong. And if you have people go out a few times a year to adjust the orientation for seasonal variances you can still capture much of the energy you would from a tracking system. For desert situations where the environment is harsh and the land is essentially useless for anything else it can make a lot of sense.

unedited summary (1)

estitabarnak (654060) | about 2 months ago | (#47507335)

I don't normally bitch about editing on summaries but, good heavens, does anyone even read this shit? The same "85% of solar energy..." line is used twice. The final line begins with "i-e" which means "that is," but it doesn't reference anything relevant to scaling. What's the appropriate tag here? !sensical? !edited? !proofed?

I'm probably just burning through karma here, but I like to think that if it's a "legitimate" rage, that the body had a way of rejecting the negative effects.

Re:unedited summary (1)

jheath314 (916607) | about 2 months ago | (#47507491)

The downmods are just slashdot's way of shutting that whole thing down.

We're lucky! (1, Funny)

Charliemopps (1157495) | about 2 months ago | (#47507393)

Made of carbon? Damn! We're lucky we've been producing all this carbon with our cars or we'd never have a chance to solve this climate change problem!

could even use lightning? (0)

Anonymous Coward | about 2 months ago | (#47507411)

almost any juice just don't call it water powered?

No concentrators. Really? (3, Interesting)

necro81 (917438) | about 2 months ago | (#47507447)

The summary states "if scaled up, this setup will not require complex, costly systems to highly concentrate sunlight". But the video itself says that all of their testing was done with light at 10x normal solar intensity. In other words - you still need concentrated sunlight, you won't be able to set this beaker out in the bright sunshine and expect it to start boiling. The authors contrast it with solar power towers that concentrate sunlight to 100x or 1000x, but it still sounds like you'd need concentration of some sort.

Re:No concentrators. Really? (1)

Mr D from 63 (3395377) | about 2 months ago | (#47507477)

If there were a viable system, you would still likely WANT to use mirrors just because they are low cost and make better use of the higher cost heat transfer elements.

Re:No concentrators. Really? (1)

Daniel Hoffmann (2902427) | about 2 months ago | (#47509173)

I thought the mirrors in solar-powered towers were specially made for reflection (and thus more expensive) and had huge problems with keeping them clean. Don't quote me on this though.

Re:No concentrators. Really? (1)

dbIII (701233) | about 2 months ago | (#47507543)

"if scaled up, this setup will not require complex, costly systems to highly concentrate sunlight"

A parabolic mirror trough is an example of something that is not complex or costly.

Re:No concentrators. Really? (0)

Anonymous Coward | about 2 months ago | (#47507915)

Assuming you can get the sun to sit still.

true of all solar electric (1)

raymorris (2726007) | about 2 months ago | (#47508123)

That's an assumption made by all solar-electric systems, though, that the sun is directly overhead when you need power. The other 21 hours a day, you use another source of power.

Re:true of all solar electric (1)

geekoid (135745) | about 2 months ago | (#47510421)

No it isn't.

Well, you COULD flood most of the country (1)

raymorris (2726007) | about 2 months ago | (#47510761)

Let me guess, you want to store the energy of the midday sun, maybe by pumping water uphill from 10:00-2:00, then running it back down through turbines the rest of the day. Sounds great, right?

Hoover dam provides 0.1% of US energy needs. So we need 1,000 reservoirs the size of Hoover Dam / Lake Meade, with dams across 1,0000 large canyons. The dam is powered by the 248 square mile reservoir pushing against it, the 248 square miles it flooded up the canyon. So 1,000 of those is 248,000 square miles. You need depth of course - you're not going to get any power sending water down a 12 inch incline. To get an idea of what we need, we're working with Lake Meade-sized reservoirs, so 582 feet deep. Do you think we're going to be able to flood 248,000 square miles 582 feet deep? Really? That's what pumped storage requires in order to make solar a primary energy source.

Of course, you can't really build a 600 foot high dam all the way around the states you decide to flood. Leaks would be guaranteed, and it would cost quadrillons of dollars. What you'd actually have would be shallower reservoirs that were larger. If you could find 1,000 appropriate places to dam where the water could be 100 feet deep, you'd only need the surface area to be 248,000 X 6 = 1.49 million square miles. That's cool, that's just half of the continental US that has to completely covered in nothing but reservoirs.

Got another theory you want to try, and we can do the math to see how it actually works?

Re:Well, you COULD flood most of the country (1)

spitzak (4019) | about 2 months ago | (#47511297)

Hoover dam does not use the entire contents of Lake Mead in one day, stupid.

Re:No concentrators. Really? (0)

Anonymous Coward | about 2 months ago | (#47508283)

10x... so, a simple parabolic trough?

Vague, poorly constrained phrases like "complex, costly systems" are infuriating. Depending on the context and how one wishes to portray it, a parabolic trough concentrator with sun tracking might be either simplicity personified, or complicated and high maintainence... "complex and costly" relative to fucking WHAT? A nuclear reactor? A PV cell that you literally sit down in the sunlight and walk away?

Re:No concentrators. Really? (1)

cp5i6 (544080) | about 2 months ago | (#47509049)

see fresnel lenses

Very far from practical application (2)

brambus (3457531) | about 2 months ago | (#47507619)

This is all neat, but it's very far from practical application. What they've created is essentially just a very dark lump of porous carbon that can draw in water and exchange heat with it. Interesting, but not revolutionary by any means. Most important questions still remain:
  • What's the production cost of this material?
  • What are the scaling properties? (Presumably, since we're talking about surface heating here, pretty limited.)
  • What's the longevity of the material under non-stop usage?
  • What's the steam outlet temperature and pressure from a system like this? If it's 100C and ~1atm, then just install solar PV or CSP.

Re:Very far from practical application (1)

kanweg (771128) | about 2 months ago | (#47508431)

"Interesting, but not revolutionary by any means."

To the contrary, it is fucking brilliant.
1) Instead of having to heat up bulk of water (like what you do if you use a boiler), they only heat up the water that is actually going to be converted into steam. So, the start-up time is greatly improved.
2) The steam generated passes through the foam up, where the foam is even hotter. The steam gets heated to a higher temperature, making it more useful to generate power. Another way of looking at the foam, is recognising that it flows in counter current with the heat source, just exactly what you want if you want to transfer heat in the best way.

And the questions you pose? They're more of the engineering type. The direction is determined by the above principle.

As an aside: Instead of water you can use another liquid, such as hexane or something. Reaching high pressures with that should not be a problem.


Re:Very far from practical application (1)

brambus (3457531) | about 2 months ago | (#47510449)

1) You're confusing your home water heating with a power steam generator. 2) Exactly, the foam is nothing but a heat exchanger. What exactly does this do that a heat exchanger doesn't? Look, fundamentally what they've got here is just a highly porous black body. They use the blackness to absorb lots of solar radiation energy and use its porousness to transfer heat to a working fluid. Neat, but not really such a revolution. As for hexane as a working fluid: not sure a highly flammable gas with a flash point of -26C being moved through a gas turbine under high temperature and pressure is such a great idea. There's probably a reason why we tend to use inert working fluids in these things.

Generati? (1)

Bill, Shooter of Bul (629286) | about 2 months ago | (#47507697)

What, can't be bothered to review the headline before posting, Tim?

Re: Generati? (1)

Jade_Wayfarer (1741180) | about 2 months ago | (#47507795)

That's not a typo, they are just some long-lost cousins of Illuminati. More green-oriented, I presume.
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