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?"

Comments

Pretty light on detail

[AshtangiMan]

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]

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

Re:Pretty light on detail

[modecx]

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]

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]

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, 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

[Mark_MF-WN]

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).

Article reads like a business deal.

[Kuukai]

If you're more interested in the technology, try looking at this. 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]

Any system that does a thermal -> mechanical conversion is limited by the Carnot efficiency. 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.

Re:Still limited by Carnot efficiency

[Rei]

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 (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.

Nothing new here. See Solar Two Mojave

[John Sokol]

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

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

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

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

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

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

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

http://www.global-greenhouse-warming.com/solar-central-power-towers.html

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

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

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

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

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

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

Excellent page on many technologies - Sorry it's in Spanish.
      http://g3nergy.blogspot.com/2006_11_01_archive.html
      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/ Abandoned Solar Power Plant

Re:I know this is somewhat OT

[BlueParrot]

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.

salt - water heat exchanger: tricky

[smellsofbikes]

Here 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, only a little larger than hydrogen -- and can diffuse into metals, weakening them and creating leaks.

Re:I know this is somewhat OT

[Rob Riggs]

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

Re:A few notes and questions

[sholden]

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:Nuclear's the future.

[jcaldwel]

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. "Current Technology" is a moving target.

Re:Nuclear is not the future..

[AJWM]

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.