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Power Technology

A Tower of Molten Salt Will Deliver Solar Power After Sunset ( 139

schwit1 sends this report from IEEE Spectrum: Solar power projects intended to turn solar heat into steam to generate electricity have struggled to compete amid tumbling prices for solar energy from solid-state photovoltaic (PV) panels. But the first commercial-scale implementation of an innovative solar thermal design could turn the tide. Engineered from the ground up to store some of its solar energy, the 110-megawatt plant is nearing completion in the Crescent Dunes near Tonopah, Nev. It aims to simultaneously produce the cheapest solar thermal power and to dispatch that power for up to 10 hours after the setting sun has idled photovoltaics. ... [The system] heats a molten mixture of nitrate salts that can be stored in insulated tanks and withdrawn on demand to run the plant’s steam generators and turbine when electricity is most valuable. ... Eliminating the heat exchange between oil and salts trims energy storage losses from about 7 percent to just 2 percent. The tower also heats its molten salt to 566 degrees C, whereas oil-based plants top out at 400 degrees C.
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A Tower of Molten Salt Will Deliver Solar Power After Sunset

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  • Downsides (Score:2, Interesting)

    by Elledan ( 582730 )
    Previously such thermal solar tower designs have caught a lot of flak for a number of reasons, including their ability to light passing birds on fire ('streamers'), their maintenance-intensive nature (lots of mirrors and associated electronics to clean and maintain), the risk of massive arrays of mirrors reflecting light for passing pilots, as well as their relatively low power density.

    The article reads more like a fluff PR piece instead of providing any credible reason for why we should get about yet ano
    • Especially since the plant is not up and proven yet. I am skeptical whenever I see "We are going to do this cool new thing that will change EVERYTHING!"
      • Re:Downsides (Score:5, Insightful)

        by Dutch Gun ( 899105 ) on Saturday October 24, 2015 @10:25AM (#50792999)

        In TFA they mention that there's a smaller-scale demonstration plant operational right now, so it's not like they're building this plant with no working experience. One would hope that the demonstration plant is operating well enough to have justified the construction of the larger one. In projects like this, scale often works to your economic advantage, so it makes sense to start building these things bigger.

        • by khallow ( 566160 )
          Glancing at Wikipedia, it appears they picked up a $737 million loan guarantee from the DoE to fund a 110 MW plant. So no economies of scale apparent.
          • Unless we know the final cost of the 20 MW plant vs the 110 MW plant, I'm not sure how you can come to that conclusion. The source of funding has nothing to do with the economy of scale, as much as I'd also prefer things like this to be privately funded. Operational costs vs power output, and the longevity of the plant will also play a significant role.

            We shouldn't have too long to wait to see if this is a great idea or a boondoggle. I'm not pretending to know enough either way to make a prediction.

            • by khallow ( 566160 )
              The 20 MW plant was just under half the cost [] (and a ludicrous $33/W). I instead based my conclusion on the price [] of the 110 MW station which at $975 million was almost $9/W. If you're not seeing vastly cheaper costs at that size a plant, then it's probably because the business plan is to sink the construction costs in other businesses you own rather than build anything of value. Thus, there is no incentive to create much less exploit economies of scale since that just reduces the take.
      • by Socguy ( 933973 )
        'If by cool new thing' you mean 'run for a few hours longer after dark.'

        I see no reason to doubt that refinements in design can squeeze out a few more hours of run-time.
    • Re:Downsides (Score:5, Interesting)

      by Gamasta ( 557555 ) on Saturday October 24, 2015 @10:40AM (#50793031)

      Besides the flaws you cite, molten salt has been previously used e.g. in the Andasol solar (thermal) power plant in Spain. []

      • The Andasol solar uses an HTF fluid circulating in the solar field []. This plant will use molten salt in the collector as well as in the storage medium. This is the big innovation of this new plant as it has higher temperatures and lower transfer loss. My concern is that pumping molten salt around is very different than pumping hot oil around. Oil does not solidify of the temperature drops If the salt solidifies in the tank it is no big deal. You just pump hot oil through the heat exchanger until the salt me

        • "How do you melt salt inside a pump and hundreds of feet of piping? "

          Electric heaters. That was solved 50 years ago.

          • Putting electric heaters inside a pump would make the pump more complex and therefore more expensive and prone to breakdown. See how the complexity of pumping molten salt around quickly rises?

            • Putting electric heaters inside a pump would make the pump more complex and therefore more expensive and prone to breakdown.

              Which is why you don't put the heater inside the pump. Instead, you use an ordinary pump and pipe, and simply run an off-the-shelf (cheap) heating wire alongside them. Then you wrap the whole thing in insulation.

              See how the complexity of pumping molten salt around quickly rises?

              No, but I have seen how factories that have to do so do it. It's not a problem.

    • Re:Downsides (Score:5, Insightful)

      by Socguy ( 933973 ) on Saturday October 24, 2015 @10:57AM (#50793089)
      If this company thinks they can operate this plant, I see no reason to stop them.

      I see no reason why you keep mentioning birds like it's some sort of game changer. In Canada between 16-42 million birds are killed each year through collisions with buildings. Should we stop building houses? [] North America wide that number may rise as high at 1 billion. [] Not to mention that you conveniently left out the death toll on all animals from pollution/habitat loss from the fossil fuel generators which far exceeds the numbers of 'streamers' that these plants will generate.

      Improvements on all fronts, should not be abandoned because those improvements are not perfect.
      • by 0123456 ( 636235 )

        Indeed. Massacring birds is the new Green.

        • by dave420 ( 699308 )
          So in your perverted mind "kill fewer birds" = "massacre the birds". Energy sources like this kill fewer birds than the habitat devastation and pollution caused by the energy sources they replace. This really isn't difficult to understand...
      • The issue with birds is not a simple matter of using averages over an entire country. Solar plants like this are situated in desert conditions where bird populations are very low to start with. It is not valid to equate the impact of loosing some birds in a high bird population area with losing the same number of birds in a low bird population area. The problem with these collectors is that the brightness attracts insects. The insects attract songbirds. The songbirds attract raptors. Losing 1000 songbirds f

        • Solar plants like this are situated in desert conditions where bird populations are very low to start with. It is not valid to equate the impact of loosing some birds in a high bird population area with losing the same number of birds in a low bird population area.

          It's also not valid to equate the number of bird fatalities in areas with high bird population area with the number of bird fatalities in ares with a low bird population.

          Besides, since it's a power plant and in the middle of a desert, can't you j

          • rig strobo lights or loudspeakers or something to drive away whatever birds wander near?

            Airports have been trying to drive birds away and have had little success. If jet engine noises wont drive birds away then neither will loudspeakers. Birds get acclimatized to situations.

    • by Kohath ( 38547 )

      And natural gas is super cheap.

      The combination of cheap gas and people who care about animals more than humans will prevent these from being built in the US. In more sensible countries with more expensive gas, these should be a good way to generate reliable power.

    • So, if you work there, there's always roast chicken in the canteen?
  • by Rei ( 128717 ) on Saturday October 24, 2015 @10:14AM (#50792983) Homepage

    ... and many more will, this is an old design, already in use.

    Personally my favorite solar thermal concept is the compact linear fresnel reflector. They're much more dense (land area used per unit power generated) than pretty much all other solar tracking methods. Also, they only require single-axis tracking in long linear rows - but unlike other single-axis tracking methods like parabolic troughs, you don't need a receiver (heat pipe) running through the middle of every reflector; a reflector is *just* a reflector. The alternation of directions in which light gets reflected reduces blocking between reflectors, and thus increases how close you can space them. And the high density means less distance for the hot water to flow, and thus less heat loss, further increasing the power generation per unit area.

  • by davecb ( 6526 ) <> on Saturday October 24, 2015 @10:30AM (#50793007) Homepage Journal

    My cottage is quite close, the project is described at []

    This approach is low-cost, and used in Brazil among other places: []

    • pumped storage is only of use for peak smoothing and generally only has enough capacity for a couple of hours' operation per day.

  • What could possibly go wrong?
    • Not much. It cannot go critical. If it leaks and dumps all the stuff on the ground, oh well, Scrap it up and haul it away. It won't poison water tables or irradiate anyone.

      Worst it could is burn someone unlucky enough to get too close to it when hot.

  • Excellent! (Score:4, Interesting)

    by blindseer ( 891256 ) <> on Saturday October 24, 2015 @01:35PM (#50793575)

    I like seeing things like this. I'm not excited about the solar power aspect, I actually think that is a fool's errand. I'm excited about seeing people research molten salt power transfer systems and high temperature power generation.

    One big problem holding up research in molten salt fission reactors is that the power generation systems it relies upon for much of its efficiency gains have not been tested fully. If we can prove to the powers that be, like the US Department of Energy, that we can handle molten salts safely then we can get that much closer to getting a molten salt reactor built.

    Looking into how these concentrated solar power plants work I had to ask myself, what do they do when the sun doesn't shine enough to keep the salt molten? They claim ten hours of storage capability, that might get them through the night I suppose. What if the morning sun is obstructed by clouds? Well, I found my answer when looking at the Ivanpah Solar Power Facility. []

    To get these things started in the morning takes a lot of natural gas. I understand the need for a power plant, any power plant, to have backup power on site in the case of the need to shut down the primary electric generation when there is loss of a connection to the grid. But the need to do this every morning does sound a bit counter productive. This is a plant that is supposed to reduce our reliance on fossil fuels. That's what I thought the whole point of solar power was supposed to be.

    Perhaps, after we prove molten salt solar can work when the weather agrees, then we can put a small modular thorium reactor on the site to warm up the salt in the morning and provide a base load of power for when the sun doesn't shine. Of course, once you can show that small modular reactors of about 100MW capacity can keep the solar power plant running then people will begin to wonder why they bother with the large expensive solar tower when the reactor keeps running regardless of the weather. At some point they'll tear down the tower to make room for more reactors.

    That's the whole point to me, moving towards small modular thorium reactors. Of all the technologies we have out there right now I see that as the one true solution. We'll still see wind, solar, hydro, geothermal, and so on in the times and places where it is cheap but small thorium molten salt reactors can be used in so many places. Make them on an assembly line like a Boeing airliner and we should see a new one built every month. In twenty years we should see the grid powered by more than 50% nuclear fission.

    I still think that nuclear fusion will prove viable within my lifetime, but only when done on a multi-gigawatt scale. That is going to be very expensive to build initially but once built it should run for a long time using common elements as fuel. Until we have a leap in technology like that we have three choices:
    - Nuclear fission
    - Continued fossil fuel use, with all its pros and cons
    - Expensive unreliable wind and solar

    So, go build your concentrated solar power plants, those would make great sites for a future thorium fission power plant.

  • Molten salt is terrible for electricity storage.

    Thermal energy capacity: 0.13 kWh/kg []
    Electrical conversion efficiency: 25% [] at best
    Electrical storage capacity: 0.03 kWh/kg
    Amount of mass to store 12 kWH (one household overnight): 400 kg
    Amount of mass to power a large city overnight (1 million households): 1 Empire State Building

    Sodium-sulfur battery electrical storage capacity: 0.5 kWh/kg
    Charge/discharge efficiency: 80%
    Useful storage capacity: 0.4 kWh/kg
    Amount of mass to store 12 kWh (one household overnight):

  • Seems to me that you'd obviously want enough heat capacity that you could provide power around the clock. Add heat whenever you have sunlight, draw power whenever you need it. Ten hours of reserve shouldn't be that much cheaper than 14 hours of reserve. We're just talking bigger tanks, right?


  • How about setting up solar power plants around the globe an exchange power. Get the power from the plants that are currently basking in the sun. A kid can think of that. Electric energy trading is already a reality.

"You can have my Unix system when you pry it from my cold, dead fingers." -- Cal Keegan