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

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.

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: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: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: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: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.