Storing Solar Power In Molten Salt

Solar power is a truly efficient source of energy, but it tends to fluctuate, and, as you might know, it turns off at night. One clever way to alleviate this intermittence is to store solar energy in the form of heat using molten salt. An aerospace company, Hamilton Sundstra, has created a venture called SolarReserve, and it plans to have its first molten salt solar power plant online by 2010.


(This picture is from eSolar, the solar thermal company Google is partnering with for its “RE Less Than C” program, but uses a similar setup as SolarReserve’s proposed plant design, with a central collection tower surrounded by heliostats.)

"The molten salt holds its heat very efficiently and for long periods of time," Dan Coulom a spokesman at Hamilton Sundstrand. Coulum said the company plans to build as many as 10 plants over the next 10 to 15 years, pulling in revenues of $1 billion over that time period.

With concentrated solar, a large number of motor-controlled mirrors track the sun and reflect the solar energy onto a tower receiver, which in turn heats a liquid that can be used to make steam. A steam turbine can then produce electricity.

"The molten salt, which is in a storage tank at the bottom of the tower, is run up through the receiver and heated to about 1,000 degrees Fahrenheit," said Coulom.

The company said using molten salt, a mixture of sodium and potassium nitrate, instead of water or oil, allows the heat to be stored for use on cloudy days or at night.

Via: Hamilton Sundstra Press Release via Cleantech

Comments

  1. Snoopy says

    I like to see that research is being put into this problem, but I can’t help but feel that the existing energy monopolies will put a stop to it. It’s just like the electric car–these startup companies want to develop their technology and then sell it to the big three, among others. Don’t they realize that those dirty bastards are in cahoots with the oil companies?
    It’s no good. The fat cats will kill us all.

  2. Snoopy says

    I like to see that research is being put into this problem, but I can’t help but feel that the existing energy monopolies will put a stop to it. It’s just like the electric car–these startup companies want to develop their technology and then sell it to the big three, among others. Don’t they realize that those dirty bastards are in cahoots with the oil companies?
    It’s no good. The fat cats will kill us all.
    And I don’t mean that people shouldn’t try–I only mean that it frustrates me greatly that these huge companies–infections, if you will–have so much sway over the fate of humanity.

  3. says

    i thought that the most efficient means storing large amounts of energy is to harness the calories at the state change? if they do employ this method then how do they move the solid salt around? for that matter i’d like to see the pump that is used to move 1000 degree molten salt around.

  4. EfficiencySeeker says

    All this solar power research might be for naught if the new safe nuclear light technology in a sheet of paper form factor turns out to be true!

  5. Joe Shabadu says

    Karl-

    My understanding is that the salt stays in a liquid state the entire time, and the energy storage is done through changing the heat of the liquid solution. Maybe this isn’t more efficient than changing the state, but it wouldn’t necessarily require a pump, as the difference in the temperature of the liquid would cause the hotter molecules in the solution to rise over the cooler molecules, causing circulation.

  6. Troye Welch says

    Karl et all,

    This is old news. (Specifically, over 20 years old) Google “Solar One”, “Solar Two” in Daggett CA. Thermodymanically, using the Carnot cycle (see http://en.wikipedia.org/wiki/Carnot_cycle) your efficiency depends on the temperature difference between your hot and cold bodies (the steam turbine is a heat engine, just like a steam engine of old). Soooo, since your cold side is usually a cooling tower, river, lake, ocean, etc, it’s pretty much fixed. You get efficiency by getting your hot side as hot as possible given your materials available. The potasium/sodium nitrate mix that is usually used in these “molten salt” is handled in stainless steel piping with stainless pumping and has a quite low (think water) viscosity when molten, I think. The solar two plant lost some (10%?) efficiency because they had to use electric resistance heating around the piping (I guess they never heard of good insulation) to keep the salts from “freezing” or undergoing phase change. These electrical parasitic losses would kick in at night or periods of cloud cover. In larger storage tanks, the ratio of the surface area to the volume decreases. The solar two team said their tank would lose something like 1% of it’s heat per *month*

    There’s a lot of info out there about power towers (Spain is actually the new leader here, sad to say). Also, I’m just a bit offended that the top graphic (quasi-rendering) is a blatant ripoff of the solar two project in Daggett (near Barstow) CA. Even the yellow crane at the top of the receiver is copied. (Oops! Better care photoshopping next time guys!!) The diagrams are all redrawn/regurgitated from what sunlabs. Eric Anderson, United Technologies, Solar Reserve, et all, should be ashamed for trying to pass this work off as original…

    the NREL is a good place to start for people looking into more research on this (http://www.nrel.gov/csp/) Note you can see the yellow crane at the top of the receiver at solar two. The array is de-focused; you can see the two focal spots in the air during the day to either side of the tower. Cheers!

  7. Juan Adame says

    Well this is a kind of pointless technology. Its not even moving forward, it would be expensive to build a facililty using it, as molten salt, ie chlorides are highly corrosive at those temperatures. Stainless steel? not for long, Chloride stress corrosion cracking and causitc shock would pretty much murder steam tubes if not the piping hauling it around. It would be incredibly hard to maintain anykind of Ph control… yeah the whole thing is a night mare.
    But way to go. keep on turning out mediocre improvements to outdated methods.
    Ever stop to wonder if the cranes on top of the solar towers had a practical application there, and where therefore somewhat standard? Just a thought.

  8. Juan Adame says

    Well this is a kind of pointless technology. Its not even moving forward, it would be expensive to build a facililty using it, as molten salt, ie chlorides are highly corrosive at those temperatures. Stainless steel? not for long, Chloride stress corrosion cracking and causitc shock would pretty much murder steam tubes if not the piping hauling it around. It would be incredibly hard to maintain anykind of Ph control… yeah the whole thing is a night mare.
    But way to go. keep on turning out mediocre improvements to outdated methods.
    Ever stop to wonder if the cranes on top of the solar towers had a practical application there, and were therefore somewhat standard? Just a thought.

  9. says

    It is interesting to compare the cost of converting solar power to electricity with solar cells and then using sodium sulphur batteries to store the electricity in the sunless periods. Has there been any feasibility studies to compare costs.

  10. Troye Welch says

    Juan Adame,

    No one said anything about chlorides. It is nitrates we’re talking about. The stainless steel held up fine (trouble with some valves, but nothing major) and there are multi-hundred page reports compiled and years of data on all of this.

    Also, I wouldn’t call it outdated… Google Ausra, Brightsource, and eSolar. These are all modern-day companies doing the same thing. They may or may not use molten salt as a thermal storage medium, but they all recognize the concept.

    Also, if you actually looked at the photos above and the original photos of Solar 1, you would see that the towers in their entirety are identical, not just the crane. At least eSolar’s conceptual drawings are their own. The graphic at the top of the page is a blatant photoshop composite of a much older system than they would have you believe.

    Salt was chosen because it was cheap and because the best oils (synthetic/silicone based such as Therminol) will only go up to 400 degrees or so. (see my previous comments on thermodynamic efficiency)

    Way to double post. Got any more thoughts?

  11. James says

    Troye,

    You seem to know quitet a bit about the molten salt technology and the application of stainless steel. I am assuming you are referring to the use of stainless steel for a containment vessel for the hot salt. What are the exact specifications for the stainless steel type, and the thickness of the vessel you recommend? And are you confident that the metal will hold up without having to worry about corrosion (for a long time)? Can you tell me which technical report you are talking about? I would like to read it. You can also reach me at my email address: cybergenic_systems@yahoo.com

  12. James says

    Does anyone have any comment about using copper instead of stainless steel for transporting and/or holding the molten nitrate salt? Will it be too corrosive for the copper?

  13. Uncle B says

    It is perhaps, time for humanity to follow the more natural cycles and turn off at night too! We have been driven in America by an unnatural vulture capitalism, akin to slavery, and it is now time for democracy to surpass corporate living and stop the madness! Check with your doctor! Before the industrial revolution and the vulture capitalistic mad dash for ROI, we were agrarian, and slept nights! To return to a more natural cycle will improve our health and possibly our war-like attitudes will be softened! Perhaps, trying to force the sun to work night-shift is part of the same drive for ROI that has lead to the American capital rush towards the Beijing, Shanghai and Hong Kong stock markets, leaving Americans short on money and deserting the American dollar altogether! Is this a greed driven obsession of the paper, a corporate world, driving America in the wrong direction at many junctures? Do we need “Corrective” laws added to the basic corporate and business laws to compensate for the human factor, the environmental factor? Forcing the sun seems such and extreme measure! To mold mother nature against her will one more time? And force humans into more waking hours ?

  14. Joe says

    The ancient “Solar One”, “Solar Two” in Daggett, CA. originated from a company that is now under the UTC umbrella, just like Hamilton Sundstrand, SolarReserve, Pratt Whitney Rocketdyne, etc.

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