Molten Salt-Based Solar Power Plant

rcastro0 writes "Hamilton Sundstrand, a division of United Technologies, announced today that it will start to commercialize a new type of solar power plant. A new company called SolarReserve will be created to provide heat-resistant pumps and other equipment, as well as the expertise in handling and storing salt that has been heated to more than 1,050 degrees Fahrenheit. According to venture capitalist Vinod Khosla 'Three percent of the land area of Morocco could support all of the electricity for Western Europe.' Molten Salt storage is already used in Nevada's Solar One power plant. Is this the post-hydrocarbon world finally knocking?"

Pretty light on detail

[AshtangiMan (684031)]

Don't current adsorption chillers use solar heat/ molten salt? A pretty week summary but perhaps someone out there knows how this works . . .

Re:Pretty light on detail

[jcaldwel (935913)]

I'm with you, I wanted more info. I found a page with a little more technical information about how this works: http://www-stud.fht-esslingen.de/projects/alt_energy/sol_thermal/powertower.html [fht-esslingen.de]

Re:Pretty light on detail

[modecx (130548)]

Metals can be a great conductor alright, but most aren't all that great at storing heat, especially compared to water, which has every metal beat to a margin greater than 5:1. At any rate, you misunderstand the purpose of the molten salt. It's there to move heat alright, but not entirely through heat conduction. Heat conduction is far too slow a process be used in a multi megawatt power plant. The molten salt is there because it's pumpable, so that it can quickly gather up a bunch of energy from the reflectors, and just as quickly dump it through conduction when the heat is used to make steam. Water is king, in terms of storing heat, unfortunately it turns to gas at a relatively low temperature. Fortunately, it can be stored under pressure, unfortunately the pressure goes up very much at very high temperatures, which makes containing it more expensive, more dangerous and generally harder to do.

Heat engines also require a big temperature gradient to do work at high efficiency, which makes using steam directly a harder proposal. Molten salt is well understood in used as a coolant in some types of nuclear reactors, and it works well for this purpose, and that's why it's used.

Re:Pretty light on detail

[falconwolf (725481)]

The molten salt is there because it's pumpable, so that it can quickly gather up a bunch of energy from the reflectors, and just as quickly dump it through conduction when the heat is used to make steam. Water is king, in terms of storing heat, unfortunately it turns to gas at a relatively low temperature.

However in cases like the Nevada Solar One power plant, it's oil that is circulated through tubes and is heated. Then the heated oil goes through a heat exchanger where the heat is transfered to water which spins the turbines. Only if the heat can't be used right away will the heat be transfered to the salt, which stores the heat for later use.

Falcon

Re:Pretty light on detail

[ibbey (27873)]

I suspect that this is the difference between this latest invention and the the current tech, though it's certainly not clear from the article. The January '08 issue of Scientific American covers this topic, and they say that one of the breakthroughs needed for molten salt solar is to be able to directly use the molten salt as the transfer fluid. The article doesn't go into a lot of detail on this topic, but here's the quote:

Engineers are also investigating how to us molten salt itself as the heat-transfer fluid, reducing heat losses as well as capital costs. Salt is corrosive, however, so more resilient piping systems are needed.

The article is available online [sciam.com], and I highly recommend anyone interested in solar check it out. They outline a plan that could provide 69% of the countries electricity & 35% of it's total energy from solar by 2050.

Re:Pretty light on detail

[ibbey (27873)]

Thanks for your input. Some quick googling suggests that the current state-of-the-art hydrogen conversion is approaching 75% efficiency (See http://www.qsinano.com/white_papers/2006_09_15.pdf [qsinano.com], note this is lab efficiency, not truly applied yet). Assuming that the efficiency continues to improve, I would expect that that value will rise notably by 2020 and beyond. When you factor in the NG used, transmission losses, etc., compressed air is only about 80% efficient (see post 101 [sciam.com] of the SciAm discussion), so it would seem that hydrogen might be feasible as a replacement in the not terribly distant future.

Since there would also be lost efficiency going the other way (hydrogen > electricity), it probably isn't a very good sole storage solution, but it would seem to be a good solution to burn hydrogen in place of the NG. That would obviously result in further reduced efficiency, but would remove any Co2 from the equation. I'm not a chemist, physicist, or really any other -ist, but it seems like there is at least some potential there.

Re:Pretty light on detail

[Mark_MF-WN (678030)]

The larger the plant gets, the more inefficient it gets.

Actually, this the exact opposite of reality. Larger plants are vastly more efficient. Otherwise, all of the world's power would be provided by trillions of 500 milliwatt plants rather than thousands of 500 megawatt plants.

Think about it -- these plants have to store heat; heat is proportional to mass, which scales as cube of diameter. Meanwhile, they lose heat at a rate that is proportional to surface area, which scales as the square of diameter. You need only the most basic math skills to see that this results in VASTLY better efficiency at larger sizes.

But, no, I'm sure you're much smarter than... you know... the actual engineers and physicists who designed this plant. Or the people who built any of the nuclear plants that pump liquid salt to transfer heat. Those silly people, they've probably never even HEARD of using oil to store heat!

Solar panels and cells are expensive to produce, and the process uses tremendous amounts of energy. After all, it requires producing perfectly pure silicon, not a trivial task. And a huge amount of waste is produced in the process.

That's not to dismiss solar cells -- but we need to explore every avenue. And at the large scales where power plants become commercially viable, heat engines rule. Coal and gas-fired reactors, as well as nuclear plants, they're all just big heat engines. Heat engines have over two centuries of engineering research and development behind them. And Semiconductors just can't be produced in large enough quantities cheaply enough (yet).

Not that new...

[zippthorne (748122)]

This kind of thing has been suggested for use in high-power spacecraft, and it's not necessarily sodium salt that's the storage mechanism.

I don't see why you'd lose much efficiency. You'd chose a salt that was molten over the operating range, and no matter what, you cannot exceed the temperature limitations of the other materials you've built the thing from, so that's your design temp. Because of the T(t) smoothing effects, you'd be able to run the generator at maximum efficiency for most of the time. Thus, you can size your machinery to the average capacity rather than the peak available solar input. Not spooling the generator up and down as the sun waxes and wanes is great for efficiency.

For instance, you might pick a salt that has a liquid-solid transition just below your desired T_hot, ensuring even temperature until all the salt solidifies. This has the added benefit that, depending on the expansion characteristics of the salt in question, you have a number of ways to evaluate the remaining generating capacity.

With good insulation, and a fixed installation can be made arbitrarily well insulated, you would lose a lot less energy than storage in batteries, and it scales very well: the larger the installation, the thinner the needed insulation is relative to the total volume.

The main loss would be radiation from the absorption patch. Presumably you'd mitigate this by having some kind of louver or hatch that you could close to insulate that during the night and overcast days. You could also take advantage of the much lower-than-the-sun temperatures, and use a covering that is transparent to visible light, but reflective to lower frequency light. Although there would still be a fair bit of radiation in the visible at reasonably efficient temperatures.

Nuclear's the future.

[urcreepyneighbor (1171755)]

Is this be the post-hydrocarbon world finally knocking?

A "post-hydrocarbon world" has been available for a long time - nuclear. She's been knocking for so long that her hand is sore.

While I would love to believe some form of solar power would meet the world's needs, it simply isn't feasible with current technology.

We'll probably have wormholes, sexbots and universal prosperity before solar can meet the demand. :)

Re:

[Smordnys s'regrepsA (1160895)]

Ah, but didn't you hear [slashdot.org], the sexbots will meet the demand!

Re:

[B3ryllium (571199)]

With apologies to The Tick ... Fission is a harsh mistress.

Nuclear is not the future..

[cybrthng (22291)]

The energy cost with refining, processing, storing and disposing of nuclear materials makes solar look like a bargain. Nuclear fanatics seem to forget the process it takes from digging up something that is one of the rarest elements on our planet and then disposing of such elements when we are done.

Re:Nuclear is not the future..

[Entropius (188861)]

What are you smoking?

It requires an absolutely tiny amount of uranium to run a nuclear plant, compared to the 10,000 tons/day that a 1GW coal plant uses. Uranium is rare, but you don't actually need that much *of* it. 95% of the fuel used in fission plants can be reprocessed. Coal producers are chopping off the tops of entire *mountains* in Appalachia;

"Disposal" isn't as big a problem as it's made out to be; reprocessing reduces the amount of waste produced tremendously, and storing a little waste for a time is a whole lot better than *not* storing it and dumping it into the atmosphere, as we're doing with coal.

There are other forms of power generation than nuclear, but at the moment it is the only proven, scalable, clean, and economical alternative to fossil fuels for power generation. Perhaps solar-thermal (as in this article) or geothermal or tidal power or some sort of wind power can be used to carry a lot of the load, but nuclear power is available now, and the only thing lacking is the political will to implement it.

France had that political will, and now they have the cheapest power and the cleanest air in Europe.

Re:Nuclear is not the future..

[linzeal (197905)]

It is not just that they are chopping whole mountains off it is that there are 1000's Coal Fires [wikipedia.org] in mines underground that are adding anything from 1-5% of the worlds Co2.

Re:Nuclear is not the future..

[falconwolf (725481)]

"Disposal" isn't as big a problem as it's made out to be; reprocessing reduces the amount of waste produced tremendously, and storing a little waste for a time is a whole lot better than *not* storing it and dumping it into the atmosphere, as we're doing with coal.

The French, who have come the farthest in reprocessing, are finding out it's not as simple to reprocess as many would have you believe. IEEE's magazine "Spectrum" has a good article on this: "Nuclear Wasteland" [ieee.org]. However another /.er brought up the Candu [wikipedia.org] reactor in Canada a few weeks ago. I don't know much about it so I can't say whether there are any problems with the design or waste, or whether its economically feasible. However nuclear power isn't really needed, not in the US. The Rocky Mountains [nrel.gov] alone contain enough potential wind power to supply the 48 continuous states with electricity. Add OR, CA, AZ, NM, and Texas along with some offshore sites from Cape Cod to the Mid Atlantic and much more can be generated by wind. Also many megawatts of potential power goes up smoke stacks daily as Waste Heat [enn.com]. Combining wind, solar power, cogeneration or waste heat recovery [csiro.au] and conservation negates the need for nuclear power. The alternative power sources, both listed above and others, have a distinct advantage over nuclear power, while it can take years and years for a nuclear power plant to be constructed and brought online, these others can be added immediately. Wind generators and solar PVs can be made from raw material and brought online in months, and can be sited closer to many of the placed where the energy is needed. Besides PVs on roofs a farmer in the Adirondack Mountains [adirondackwind.com] in New York can provide electricity to NYC. The farmer would then have a second source of income.

Falcon

Re:Nuclear is not the future..

[AJWM (19027)]

so you need a lot of high quality ore to get fuel in an expensive and energy intensive process (eg. heat a heavy metal all the way to a gas and centrifuge it).

Um, no. You only need to do that if you're planning on building bombs. (And anyway, gas centrifuges don't heat the uranium to a gas but chemically convert it to uranium hexafluoride before centrifuging.)

There are plenty of reactor designs that run on unenriched uranium, including most of the nuclear power plants in Canada (CANDU) and places to where Canada has sold reactors.

Re:Nuclear is not the future..

[dbIII (701233)]

As an engineer with a background in power generation (but ten years out of touch and most of the nuclear power plant guys I worked with were Russian and Indonesian) I'd say what we'll be using in the future as in the past is a mix of a lot of things depending on what is easiest in specific locations. There are solar thermal baseload designs that usually run on the principle of having a big heat reservoir (in this case molten metal salts) to run stuff around the clock but they all have to be large so there is resistance to building them. Your average thermal plant can run for quite a while after you stop shoving in fuel because there is so much steam in the system so this is expanding on the idea (ie. being able to give you a full nights worth of steam after the power is cut). What most people miss is that the real problem in electicity generation is covering the peaks - and they almost always happen in daylight anyway.

This is going to take years and it's a matter of people seeing a lot of solar hot water collecters on rooftops before governments decide it is a safe bet to go for large solar power projects - I think industry on it's own will hit exactly the same problem the nuclear power advocates have. For really big thermal plants they want government money because they can't get commerical finance. Electricity is heavily regulated in most places anyway so it usually takes government involvment to just get a foot in the door. This sometimes involves convincing relatively old people who did not have the benefit of finishing high school of the merits of a project - hence the delay until solar thermal (eg. hot water) comes into the personal experience of the people regulating things.

Re:Nuclear's the future.

[jcaldwel (935913)]

While I would love to believe some form of solar power would meet the world's needs, it simply isn't feasible with current technology.

Much of the argument against solar is one of economics, but a company called Nanosolar has recently produced solar panels making energy more cheaply than coal. [grist.org] "Current Technology" is a moving target.

Re:Yes, Solar is great...

[MrKaos (858439)]

Nuclear is ideal for providing base-load power (30-40% of peak capacity), suplemented by Solar, Wind and Tidal power.

Geothermal is ideal for providing base-load power (30-40% of peak capacity), suplemented by Solar, Wind and Tidal power.

Fixed that for ya, Mr AC.

post hydrocarbon already here

[thule (9041)]

" Is this be the post-hydrocarbon world finally knocking?".....

It was here 50 years ago with nuclear power. Thankfully, it's finally getting attention again.

Re:post hydrocarbon already here

[BlueParrot (965239)]

On a related note, nuclear engineers were using molten salts decades ago, and even developed a special corrosion resistant alloy, Hastelloy-N, to deal with the corrosion problems. However, the molten salt system turned out to be more expensive than water based technology, thou this may change if thermochemical production of hydrogen kicks of.

Essentially, proponents of solar power usually like to fantasize about theoretical advances in solar technology, while simultaneously refusing to recognise advances in nuclear technology. As an example, electric cars are usually touted as being CO2 neutral "if the electricity comes from renewables". It is outright obvious that this remains true with nuclear as well, but that is scary and hence rarely mentioned. Similarily advances in electric storage is usually touted as a means of allowing solar to be used for baseload, but rarely is it pointed out that the same tech coudl allow nuclear to deliver peak-energy at increased efficiency by running the plant at its maximum output even when demand is low.

 

A few notes and questions

[stomv (80392)]

1. Nuclear power is not carbon neutral. Uranium is mined, and nobody is running mining equipment on biodiesel, nor are they transporting it to power plants using biodiesel, ethanol, or even renewable generated electricity on electric locomotives. To be sure, the amount of carbon is extremely low per kWh of electricity generated, but very small > 0, even for very small cases of very small.

2. As you know, nuclear proponents continually ignore the major immediate problem with nuclear power -- waste storage. Nobody wants more glass-encased nuclear waste in their neighborhood, and presently nobody wants some other neighborhood's nuclear waste being transported through their neighborhood. The nuclear industry has got to find technical and political solutions to these problems before society will embrace nuclear as a green solution. I'm not arguing that burning coal or oil is safer or cleaner than nuclear, just that any change to a status quo requires more than a slight or obscured imbalance, which is how the public currently perceives the status quo.

3. What is Hubbart's Peak for uranium? I have no idea, but it surely must have one.

4. Which nations have substantial amounts of useful uranium? What would the balance of power be if those nations became the new Saudi Arabia of energy?

5. Solar off-peak is simply not a problem, not for a long time. Peak demand is highly correlated with sunshine in most of the world -- solar could serve quite effectively as the peaking plant, relying on other types of generation for base load. Electric storage is just not a major issue for solar -- it might become one for wind but it wouldn't be that hard to operate other green energy plants in a negative correlation to wind, ie burn woodchips when the wind isn't blowing, but not when the wind is blowing.

6. That said, plug in cars might change that formulation substantially, since most people would plug in their cars at night thereby adding demand off-peak [and off-sun]. If/when that happens, much of (5) becomes moot and there'd be some shifting of nighttime use [industrial, it's cheaper] to daytime and there'd be encouragement for folks to charge during the day [plug in jacks at car parks] to help keep demand during the day higher, when production due to solar is higher.

7. Ultimately, this doesn't matter. Solar production in the US is well less than 1%. Even at 10% there won't be a necessary substantial change in infrastructures or demand shaping. So, until then, more of every kind of renewable electricity generation is better, and none of it will create challenges. And, of course, nuclear may or may not be greenish, but it is not renewable.

Re:A few notes and questions

[Rei (128717)]

3. A long, long way away when you consider seawater extraction, and even further with breeders, incl. thorium. Sure, it's quite expensive in comparison to mining, but the cost of fuel isn't the real cost in nuclear power -- it's paying for your reactor construction and decomission that kills you.

4. Ignoring seawater? Australia by far, at 24% of known reserves. Other significant sources include Kazakhstan, Canada, South Africa, Namibia, Brazil, Russia, the US, and Uzbekistan.

Re:A few notes and questions

[radl33t (900691)]

A commonly employed tactic, you have just narrowed your scope such that you can criticize nuclear energy. 2. Not a problem. More people would understand this if fear hadn't reigned and nuclear research didn't take a nose dive decades ago. 3. Also not an imaginary problem. Proper (well documented) reactor design will eliminate this concern. IT would be a done deal if we maintained the nuke program from the 60s through today. Even existing tech would allow us to burn other elements, which are more plentiful than uranium. On second thought, why aren't you concerned with Hubbert's Peak for the sun or the universe? The timescales of these peaks are not really of a concern same as those for uranium, unless you really think you can plan for 100+ generations out. 4. There is enough unused "waste" sitting around for thousands of years. Plenty hiding around down under too. 5. Actually the lack of off-peak energy is a massive problem, mostly for economic reasons. IT is probably the single largest cost barrier for both wind and solar, which typically enjoy moderate to peak output less than 20% of the time. In other words, to reach cost parity with coal they actually need to be 5 times cheaper. 6. Ultimately it doesn't matter? Um, yes of course if you are so narrowly focused that you don't consider things like economies and social welfare. Why isn't nuclear renewable? Just as renewable as our sun if you ask me. p.s. pv isn't carbon neutral either p.s.s. Life is destructive. take it or leave it. Don't kid yourself. Nuclear energy is at least as good an option as solar or wind for decades. At least until fancy PV arrives at 100s of GW of annual production. But then again theres no difference between fear of nuclear energy and whatever other boogieman is out there.

Re:A few notes and questions

[sholden (12227)]

1. Solar cells are made from silicon, which carried in trucks and hence not carbon neutral. Every power source is not carbon neutral since it has manufactured components that were transported at some point. Of course once you have plentiful power from the nuke plants you might change that...

2. It'd be mighty expensive but you could just mix it back with the non-uranium rock you dug out and put it back where you found it... A lot of that waste also isn't waste, it's fissionable material that politically isn't used (because doing so gives you plutonium easily used in weapons).

3. In 20 years we'd run out if we just used uranium in nuke plants for all our electricity. Again allow breeding to plutonium and it turns into 2000 years...

4. The top 5 known recoverable uranium holders are: Australia, Khazakhstan, Canada, USA, South Africa - they make up about 2/3rds of the total. From a Western world perspective, that's a much nicer set then the oil top 5: Saudi Arabia, Canada, Iran, Iraq, Kuwait...

 

Re:A few notes and questions

[sploxx (622853)]

1. Solar cells are made from silicon, which carried in trucks and hence not carbon neutral. Every power source is not carbon neutral since it has manufactured components that were transported at some point. Of course once you have plentiful power from the nuke plants you might change that...

And to further elaborate on this: There is this concept called Energy Returned on Energy Invested [wikipedia.org]. (And even more refined indicators).

I have heard this flawed argument against nuclear power so often that it is not really funny anymore.

Re:A few notes and questions

[Bender0x7D1 (536254)]

I would encourage you to read up on nuclear power - while a lot of what you are saying is true, it really doesn't capture the reality of the situation.

1. No, nuclear, by itself, is not carbon neutral. However, neither is any other alternative energy. However, when you have the extra electrical power, you can construct "factories" that will scrub the carbon dioxide out of the atmosphere. Now, we might not have the political will to carry it out, but nuclear alone is still way better than what we have now.

2. Fast breeder reactors can run on our current nuclear waste and the waste from those reactors doesn't last nearly as long. So we get to reduce the amount of waste and what's left doesn't last as long. The reason we don't use them is that reprocessing can create weapons-grade plutonium. Again, this is a political issue instead of a technological one.

3. With today's "wasteful" reactors using Uranium-235 it is estimated between 80 and 300 years. If we use breeder reactors so we can use U-238 and Thorium, it can be billions of years at current energy levels.

4. If necessary, fuel can be extracted from sea water making it a moot point.

5. There is also a peak in the evening when everyone turns on lights and TVs. Also, winter means a lot less sunlight in many populated areas so more demand for lighting and heating.

6. Moving power around might help, but there are just too many hours when power is needed and solar isn't available. Also, cloudy days affect production and can't be planned around. Limiting solar farms to areas with minimal cloud cover means increased losses from transport.

7. Nuclear doesn't have to be renewable if we have a few billion years, (or even a few million), years available. If we can assume a technology level that can protect us from extinction due to an asteroid or comet in that time period, we can assume a technology level that can mine the moon, mars or asteroids for more nuclear material.

While nuclear has its problems, they are really political instead of technological. I really hope we get past our fears of nuclear power so we have a chance of keeping our planet habitable for humans.

Waste salt

[Threni (635302)]

I hope they don't start dumping waste salt in the oceans...

I am be

[mi (197448)]

Is this be the post-hydrocarbon world finally knocking?

Slashdot editors are be the worst ever...

vinod is late to the game

[WindBourne (631190)]

There are a number of companies doing this. One is looking to work in conjunction with POwer plants esp Nukes. The waste heat can actually kick the salts up a bit, and then solar pushes is that much higher. The nice thing is that this can be used on really hot days as a means of cooling off the waste heat from the nuke prior to putting in streams. Where this might get really interesting is to combine with geo-thermal power. The same sets of solar concentrators can be used to kick up heated water/steam from the ground and make the generators more efficient. During the daytime, the generators can run at full tilt, while at night, when it is just geo-thermal, then generators run at less efficient speeds.

I know this is somewhat OT

[MichaelCrawford (610140)]

Nuclear reactors can be made smaller and more efficient if they use liquid sodium for cooling. I think this may be because they can run at a higher temperature, which is more harmonious with the laws of thermodynamics.

But the US Navy refused to build any sodium-cooled submarine reactors. Finally a Congressional committee hauled Admiral Rickover in to a hearing to testify as to why he wasn't making better use of taxpayer's money.

To which he replied "This is what happens when sodium gets wet," and he threw a chunk of sodium into some water.

Re:

[MBCook (132727)]

There WAS a liquid sodium reactor in the US. The seals in the cooling system seals started to fail leading to severe consequences. See Wikipeida [wikipedia.org].

Re:I know this is somewhat OT

[BlueParrot (965239)]

To which he replied "This is what happens when sodium gets wet," and he threw a chunk of sodium into some water.

Care to guess what happens when 300 C warm and radioactive water goes from 15 mega pascal to neutral pressure within a fraction of a second after a coolant pipe bursts? No matter if it is sodium or water primary coolant leaking is a Bad Thing (tm) , and sodium has the advantage that you don't have to keep it under pressure, thus reducing the chance of a leak greatly.

In addition sodium is practically non-corrosive to steal, while boric-acid spiked water at 300 C is quite agressive. Sodium also has a much better heat conductivity than water, so the reactor won't melt down if the primary cooling pumps fail ( natural convection of the coolant is enough to cool the spent fuel once the chain reaction has stopped, as it will do due to thermal expansion of the fuel rods ).

Having said this, my favourite candidate for coolant is molten-lead. Like sodium you don't have to pressurise it, it doesn't react with water or air, it won't boil even if you overheat teh ractor so much that the steel melts, and it is an excellent radiation shield against gamma-radiation. Main issue is corrosion, but 20+ years of research has produced alloys that are very stable in molten lead, so you could expect comercial plants using it within a deacde or two.

Re:I know this is somewhat OT

[Rob Riggs (6418)]

You admit that it's somewhat OT, but did you also know it's mostly BS?

Two competing concepts for cooling nuclear submarine reactors were available, cooling by pressurized water and by liquid metal. Rickover wanted to try both of them, so he arranged with Westinghouse in 1949 to investigate the pressurized water approach, and with General Electric in 1950 to pursue a liquid sodium approach.

Rickover's faith in nuclear submarines was vindicated in January 1955, when the USS Nautilus reported that it was underway entirely with nuclear power. The Nautilus employed the pressurized water method of reactor cooling. The Navy's second nuclear submarine, USS Seawolf, was powered by a reactor using liquid sodium.

http://www.u-s-history.com/pages/h1857.html

Article reads like a business deal.

[Kuukai (865890)]

If you're more interested in the technology, try looking at this [news.com]. It doesn't work "like a hydroelectric plant." (spinning a turbine doesn't = "hydroelectric") It simply uses an array of mirrors to aim sunlight at salt and heat it. The molten salt can then be used to steam water and turn a turbine, or saved for later.

Still limited by Carnot efficiency

[compumike (454538)]

Any system that does a thermal -> mechanical conversion is limited by the Carnot efficiency [wikipedia.org]. This system would be limited by the temperatures of the hot side (sun's heating of the salt, balanced with losses from the pipes) and the cold side (presumably atmosphere or a cold river). In contrast, a solar cell directly rectifies electromagnetic field energy (light), so it doesn't obey the Carnot limit. That's why for a system like the one in this article, there's a need to push the operating hot-side temperature up as much as possible.

--
Educational microcontroller kits for the digital generation. [nerdkits.com]

Re:Still limited by Carnot efficiency

[Rei (128717)]

Huh? Have you compared what people were paying for solar cells back in the 70s to what they are now? And even today's prices are inflated by manufacturing shortages (the market isn't stable). If manufacturing actually met demand, we'd be paying about $3/W today, not $4.80/W. And this ignores CIGS production like NanoSolar's that's just now coming online. NanoSolar claims $1/W would still be profitable for them. The other CIGS manufacturers also (quite reasonably) anticipate very low production costs. Sure, indium is rare (about as common as silver), but you only need a tiny amount of it.

As for the necessity of high efficiency, it's not neccessary. Even if just a small fraction of the world's urban area was paved with inefficient solar cells, it'd still power the world. I don't care to repeat this calculation yet again (I do it about once a month it seems), but look up China's total urban area (just China's) and do the math with 10% efficient cells (less than NanoSolar's) at, say, 20% coverage and an average 100W/m^2, then compare that to the entire world's electricity demand.

As for what potential efficiency we're capable of, it's actually looking up. But not for CIGS -- for more conventional semiconductor cells, which aren't likely to be cheap enough to panel the world. We're up to a staggering 42.8% now (Honsberg and Barnett) -- and the record keeps growing at a rather surprising clip. And there's more potential for that number to keep growing up to 60-70% or so. There are three technologies pushing this -- the ability to get multiple electrons out of a single photon, the use of integrated beam splitters so that different parts of the cell can be optmized to specific parts of the solar spectrum, and the use of phosphor coatings that can be excited to release photons in a desired energy range. These technologies may not end up running our grid, but they'll be running our satellites, our malibu lights, our self-illuminated highway signs, and so forth.

Back to the initial topic: Just to drive home the point as to how much photovoltaic prices have been dropping, let's put in some historical price points (in non-inflation-adjusted dollars):

1956: Bell solar cell: $300/W .
Early 1970s: Bergman's improvements lowers the price from then $100/W to $20/W

Specifically [unu.edu] (in 1994 dollars):
1976: ~$51
1977: ~$38
1978: ~$27
1979: ~$21
1980: ~$18
1981: ~$15
1982: ~$14
1983: ~$11
1984: ~$11
1985: ~$10
1986: ~$9
1987: ~$8
1988: ~$8
1989: ~$8
1990: ~$8
1991: ~$7
1992: ~$7
1993: ~$6
1994: ~$6

In non-inflation-adjusted dollars, solar prices were at a minimum in the early '00s (~4$/W, if I recall correctly), and rose up until this summer due to supply shortages, when they started to go down again. And with the CIGS companies, the prices can be expected to go down a lot over the next several years. Anyways, I really don't see how anyone can look at the numbers and act like solar hasn't been advancing by leaps and bounds since it was first turned from a laboratory curiosity into a commercial product in the '50s.

Might be better with smart power...

[tempest69 (572798)]

The concept is this.. The power company auctions off power in real time to devices which automatically bid for "cheap energy blocks" The cheap energy blocks never exceed the price of standard energy. This allows the power company to adjust load based on production from non-predictable sources. So when a windfarm starts going crazy with power, the air conditioner in your house can go full steam for quarter price. As the number of smart devices increases, the prices can auction to higher values. As smart devices get more vogue, we can rely on sporadic power generation more and more. Right now, the power companies predict usage, with little control, with smart energy, they can tune usage much more efficiently.

The concept of storing the energy as thermal is fine, but reducing the amount of energy swaps is going to be the more efficient way to use the power. The efficiency that they can store energy and re-convert it is going to determine how low a cheap power block can sell for.

Anyway, just a crazy rant.. enjoy,

Storm

Nothing new here. See Solar Two Mojave

[John Sokol (109591)]

I will just dump a mess of links from an old E-mail I did on this some time ago. It's all good stuff, Solar two in Mojave was also molten salt based. I knew someone who bought it after it failed and got to explore it before it was partly dismantled.

---------

Solar two was a flat mirror array.

Search google image search with
            "solar two" Mojave

http://maps.google.com/maps?f=q&hl=en&geocode=&q=yermo,+ca&ie=UTF8&ll=34.871919,-116.83416&spn=0.005915,0.010042&t=h&z=17&om=1 [google.com]

Take the link above and zoom out, just below and to the right is a Parabolic glass mirrors plant

http://en.wikipedia.org/wiki/Solar_Two [wikipedia.org]

http://www.powerfromthesun.net/Chapter10/Chapter10new.htm [powerfromthesun.net]

http://en.wikipedia.org/wiki/Image:Solar_Two_2003.jpg [wikipedia.org]

http://en.wikipedia.org/wiki/Image:Solar_Two_Heliostat.jpg [wikipedia.org]

http://theothersolar.com/?m=200702 [theothersolar.com]

http://www.commondreams.org/headlines06/1101-10.htm [commondreams.org]

http://www.global-greenhouse-warming.com/solar-central-power-towers.html [global-gre...arming.com]

http://www.ldeo.columbia.edu/edu/dees/U4735/projections/pitman/solar.elec.jpg [columbia.edu]

http://fixedreference.org/2006-Wikipedia-CD-Selection/wp/s/Solar_power.htm [fixedreference.org]
(search for "Solar two")

http://www.reia-nm.org/HTML_Docs/Solar_Thermal_Electrical.html [reia-nm.org]

http://greatgreengadgets.com/gadgets/category/solar/ [greatgreengadgets.com]

http://www.answers.com/topic/solar-thermal-energy [answers.com]

http://blogs.business2.com/greenwombat/2006/week44/index.html [business2.com]

Excellent page on many technologies - Sorry it's in Spanish.
      http://g3nergy.blogspot.com/2006_11_01_archive.html [blogspot.com]
      Search for "Australia to Build 154 MW Solar Energy Plant"
      This one is identical in design to the one in the Mojave Dessert here.

http://ludb.clui.org/ex/i/CA4965/ [clui.org] Abandoned Solar Power Plant

O&M Expense

[sphealey (2855)]

Molten salt heat exchange technology isn't new, and has been tried in various forms of electric generating plant for at least 25 years to my memory (and probably a lot longer - they tried a lot of odd stuff in the 1920s and 1950s). The think to keep an eye on is projected operating and maintenance expenses over the long term. Molten salt is nasty stuff and does a lot of damage to everything it touches. Major components such as pumps have to be considered replacement rather than repair items for example. So the O&M cost projections are critical.

sPh

and without subsidies!

[MrKaos (858439)]

I'm wondering if this is result of carbon taxes becoming inevitable. It would seem to me that some companies are positioning themselves to take advantage of funding and tax breaks that hopefully will become available in a carbon trading world. Even if the project can only address peak power demands it's certainly appears capable of offsetting a large amount of carbon production during peak energy demand times.

If this is project is feasible and is what can be achieved without subsidies I wonder what solar energy projects (and indeed other alternative energy projects) can be created with funding.

salt - water heat exchanger: tricky

[smellsofbikes (890263)]

Here [legitreviews.com] is a shorter, and in my opinion, more informative summary. They're heating up sodium chloride salt, then using that to produce steam from water, which drives turbines. That's nice, because molten salt is fairly nasty stuff to work with.
Anything has its chemical activity rise exponentially with temperature (the Arrhenius equation) so as things get hotter, they get more chemically aggressive. Molten glass will dissolve bricks and mortar. Molten sodium and chlorine ions are even nastier -- a sodium ion is a very small object [chemguide.co.uk], only a little larger than hydrogen -- and can diffuse into metals, weakening them and creating leaks.

Re:Electricity for the masses.

[Rob Riggs (6418)]

On a more serious note, 3% of Moroccos land mass could provide power for ALL of Western Europe? Can I ask what possible reason there could be beyond corruption and greed for this NOT to be used? Somehow I think that this kind of technology, no matter the initial cost, would be an absolute boon and can see no reason why it shouldn't be adopted.

Well, according to the article it is being used and will be used more in the future. The issue is that it takes time, money and a lot of land (3% of Morocco [cia.gov] may seem small (446,300 km^2 * .03 = 13389 km^2), but it's larger than some European countries (think countries that start with the letter "L") and about 1/3 of the size of the Netherlands.

It may take Hamilton Sundstrand and others quite a few years to ramp up production to the point where they can consider converting even 100 km^2 of land over to solar energy production.

Re:Electricity for the masses.

[vijayiyer (728590)]

Except that you can't easily get electricity from Morocco to Europe. Transmission of electricity isn't lossless or free.

Re:

[WaltBusterkeys (1156557)]

Don't forget transmission costs--even if Morocco produced enough power for western Europe, the power would still be in Africa instead of Europe. Long-distance power lines are expensive, vulnerable to failure, and lose (at best) 10% of power transmitted. There's water between Europe and Africa, meaning that they'd either have to string really big lines across Gibralter or run a giant copper cable. Going underground through cable is expensive and leads to larger power losses because you can't run the same

Re:

[MachineShedFred (621896)]

While I'm sure your post was in joking fashion, Rocketdyne was the company who made the five F-1 motors in the first stage of the Saturn V.

I know, I know... why ruin jokes with facts! Why, indeed - I'm an ass. That's why!

Re:

[UbuntuDupe (970646)]

I'm more more surprised that no one has yet made a grammar comment with a mocking pirate theme, like,

"Arrr, I think this be post-hydriecarba world knockin on 'r door, matey! It be a danger too, since less global waaaarmin means less 'f us!"

Re:sun renewable?

[rustalot42684 (1055008)]

I got in trouble for that in grade 5 when I pointed out that the sun would eventually die out. I was told "Well, it's not going to die out in our lifetimes". I replied with "So are oil and gas renewable resources if they aren't depleted before we die?". The teacher put on my report card " ... seems to have trouble distinguishing between renewable and non-renewable resources."

Re:sun renewable?

[Dorceon (928997)]

I guess the relevant terms should be exhaustable vs. non-exhaustable. Using sunlight for power doesn't change when the sun will die. Using fossil fuels for power changes when the fossil fuels will run out.

Re:

[Bryansix (761547)]

British people are totally backwards. For proof look at their use of "Fanny Fun" to refer to straight sex between a man and a woman. The only Poofters are the ridiculous people who use such a word.