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Published on April 24th, 2012 | by Susan Kraemer


Interview: Molten Salt Storage is Safe + Could Store Heat for 2 Months

April 24th, 2012 by  


Last week I had the chance to talk on Skype with Kevin Smith, the CEO of SolarReserve, which is building the world’s largest concentrating solar power plant in Tonopah, Nevada. It is the same technology as one that came on line in Spain last year that can ship power 15 hours a day by using molten salt storage – both as the carrier and as the storage. It was developed by (literally) rocket scientists in the 90s with a pilot project that proved it works.

First, I had to know:

SK: I’ve had a commenter who thinks molten salt could explode… ?

KS: There’s a tremendous amount of study work thats been done on molten salt. It’s a combination of potassium and sodium nitrate.  It’s a very safe compound. It’s kind of similar to the kind of garden fertilizer that you’d spread around in your garden and at these temperatures – the only problem is it’s very hot.

But theres no risk of explosion… theres no… It’s not considered a hazardous substance by the U.S. government. It’s no more hazardous than the high temperature steam, which obviously the high temperature; it’s hot…you have to treat it with that kind of caution – but theres no issues with it being hazardous.

SK: How hot do you get at the top?

KS: We’ll heat up to 1,000 degrees which is comparable to the temperatures that you’ll see in a regular power plant. The big difference with utilizing molten salt, is that at 1,000 degrees Fahrenheit it’s still a liquid which means we can store it in a tank. Its low pressure so… it’s not like it’s a high pressure tank or a high pressure system, because it’s a liquid: it’s all still at low pressures, then once we take it to the power project the steam is also at 1,000 degrees.

SK: How about any danger of heating up the surrounding air?

KS: No its completely insulated. the way the system works is what you have is there is a heat exchanger at the top of the tower. The tower is about six hundred feet tall – 550 ft ft tall – its surrounded by huge field of mirrors, and the mirrors heat up the salt as it runs through this heat exchanger and then once its heated up to full temperature it drops back down the tower and its stored in an insulated tank, its a continuos loop like the radiator in your car.

When it comes out the other end it’s at high temperature and then we put it in this tank at the base of the tower – that also is a heavily insulated tank, and its stored in that tank for when we want to generate electricity. Then when we want to generate electricity it goes through another heat exchanger that takes water and heats it into steam, then it goes through a conventional steam turbine just like a regular power plant. So our back end looks just like a conventional power plant with a steam turbine – steam that turns the blade on the turbine.

SK: The 15 hour Gemasolar plant is the same as yours, right? (Along with everything else I learned in this talk, BTW, is the correct Spanish pronunciation: it’s “hemma-solAAR”)

KS: We’ll generate similar to Gemasolar in Spain which uses up all the heat in the salt every single day. Our facility is a similar technology to theirs other than that ours is about six times as large as their project. So their project is really more of a pilot project. They’re I think 17 MW, we’re 110 MW. Ours is the first commercial utility-sized plant.

And we’ll store energy for ten hours. We’ll run during the day, and then we’ll have an additional ten hours that we could run.

SK: Could you store power for more than ten hours?

KS: The molten salt in the tank loses less than one percent of it’s heat overnight. It’s a heavily insulated tank.

If we filled the tank with the hot salt and it just sat there it would stay there in its molten salt state for two months.

SK: Two months!!!???

KS: Now, that’s not the way we use it! We use it on a daily basis because we’re generating electricity here every day.

But because its in a heavily insulated tank and because salt is a bit self-insulating: the salt in the middle sees the salt next to it is hot… only at the exterior walls do you get a little bit of heat that escapes. As a practical matter though, the heat will be used daily.

Storage means the company can produce for exactly the peak times that a utility needs to cover. For late risers in Las Vegas, who are out till midnight, that can mean a customized generation to suit their needs.

For the Nevada project we’ll only run 12 noon till 11-12 oclock at night. With Las Vegas the big load center for Nevada, they are looking for their peak requirements on the utility, which go up to 11, 12 o’clock at night. But we won’t run overnight.

SK: So, Gemasolar’s is 15 hours and Las Vegas wants just those 12 – but you could run solar 24 hours?

KS: Yeah, we could run it overnight but the utility doesn’t really want it overnight.

SK: Any things you can say about the BrightSource non-IPO?

BrightSource is a good company. They’ve got strong projects in construction. They are a different technology than ours. Clearly the markets right now are not very strong, either for Initial Public Offerings, or even just the business climate is weak right now.

Its improving, we continue to see an improvement in the economy. Our decision was not to look at IPO activity in 2012, we didn’t think the market makes sense right now and its clear from BrightSource’s activity that it’s not.

You know, they’re a good company, they’ve got a nice pipeline of projects and we expect they’ll continue to be successful – we have a different business model, on IPO we’ll probably look at that next year.

(I also had some questions about Desertec too: his answers here.)


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About the Author

writes at CleanTechnica, CSP-Today and Renewable Energy World.  She has also been published at Wind Energy Update, Solar Plaza, Earthtechling PV-Insider , and GreenProphet, Ecoseed, NRDC OnEarth, MatterNetwork, Celsius, EnergyNow, and Scientific American. As a former serial entrepreneur in product design, Susan brings an innovator's perspective on inventing a carbon-constrained civilization: If necessity is the mother of invention, solving climate change is the mother of all necessities! As a lover of history and sci-fi, she enjoys chronicling the strange future we are creating in these interesting times.    Follow Susan on Twitter @dotcommodity.

  • Bob_Wallace

    I’m going to try to keep this short, long day, I’m tired.

    There are things that private money will finance. Things that look like they will probably yield a nice profit. And soon.

    There are things that are too risky for private money. Or which a profit stream is unclear, or too far in the future. But some of those things, if they work, could have huge payoffs.

    Take medical research. Drug companies will pour money into finding a new drug if someone gives them some basic clues about what might work. Those clues come from basic research which drug companies often will not research. So we use public money for basic research into biochemistry, etc. and discover the basics. Then private money takes over.

    Look at the space program. No private company would have financed rocket research. If governments had not provided the money we would not have satellite communication, GPS, etc. Once governments did the basic work, private money jumped in.

    With solar and wind is was not enough to just figure out to get them work. They had to be installed on a large enough scale to bring down manufacturing costs and make them attractive to private money.

    That’s worked. We’ve taken the price of wind-electricity from around $0.38/kWh to under $0.04/kWh and we’re about to end subsidies. We took the price of solar panels from around $100/watt to around $0.50/watt and subsidies will soon end.

    We’ve actually spent only a small percentage of what we spent trying to make nuclear work. Now we have very affordable wind and solar that will mean that our cost of electricity will fall going forward. And we will avoid hundreds of billions of dollars each year in external costs for coal.

    Obviously not all government projects are going to succeed. It would be foolish to expect that. 25% of all businesses fail in the first year, 36% by the end of the second, and 50% by the fourth.


    Out of the entire DOE program that funded Solyndra – here’s some data…

    DOE Loan Programs Status as of May 2013

    Number of Projects – More than 30
    Total Loan / Loan Guarantee Amount – $34.4 Billion
    Disbursed – $18.5 Billion
    Estimate Losses – Up to $799.7 Million. (May be less, pending additional recoveries.)
    Loan Loss Reserve – $10 Billion
    Losses as Percent of Loan Loss Reserve – 8%
    Losses as Percent of Amount Disbursed – 4.3%
    Losses as Percent of Total Loan Amount – 2.3%
    Total Economic Investment Leveraged – More than $55 Billion

    Estimated loss values are based on principal disbursed less any repayments. Actual losses will likely be lower, however, as the government may have additional recoveries on the disbursed loan amounts.

    The DOE did damn good. It took projects private enterprise would not fund and had a <3% loss. Look back at the failure rate for private business.

    Germany had a slight (3%) and temporary increase in coal use following the Fukushima disaster. That incident caused Germany to close down some nuclear ahead of schedule. By 2014 Germany's coal use was at an all time low.

    Germany's wind and solar programs have been outstanding successes, saving Germany billions of dollars per year in fuel purchases.

    Check the rate on T-Bills. The money we borrow we pay back often less than the rate of inflation. And most federal government borrowing is from US citizens, IIRC.

    • DarthGently

      The problem with government market intervention on implementation so that we can, in your words, bring down manufacturing costs, is that the government is canalizing the production process based on central planning which has a historically very poor record compared to the market when placing accurate value on ideas and technology. You are making light of how expensive it is to tool/train up, then re-tool/train, for a specific way of manufacturing PVs, for example, when that technology is in huge flux. Near future re-tooling/training costs will very possibly overrun any publicly funded gains by lowering current production costs. Let’s call these costs required to overcome government induced ossification of ideas and industry an externality also. Now we have subsidized big corporations invested in what is to a large degree outdated wind and solar technology. Entire tracts of land have been taken by eminent domain when 10 years from now the technology requiring that land may be outdated.

      The exploration of alternative energy was moving along at a healthy clip long prior to large interventions. The main effect the large interventions had was merely to artificially anoint certain winners in the market and many of those are already becoming ossified barriers to new entries with game-changing ideas.

      Yes businesses fail. But the choice to take on that risk rests on the people taking the risk. Risking money that will have to be paid back by people who aren’t born yet is an astronomically unethical externality.

      Comparing various alternate energy technologies to a moon landing doesn’t work. The moon landing was actually done as I described: it was made to work in a lab setting as much as possible with countless rehearsals to reduce risk. The work was done by private contractors held to very specific deliverable quality and subject to many inspections. As I said, I fully support unborrowed public money being used to research. But implementation needs the the market to sort it out properly. When the government chooses winners and losers in the marketplace of ideas and production it doesn’t make things more fair historically. You just end up with too many models of an old tractor design sitting in storage (reference the USSR) gathering dust and few producing what is needed. Or worse, not enough tractors, even old ones. No one individual or central committee is smart enough to know what ideas will pan out or which will prove valuable and so the best course is to decentralize this decision which inherently reduces systemic risk.

      Are any of the Solyndra executives facing court actions? Were any of their salaries and other compensation recovered? Was there a transparent attempt to post-mortem their failure as a government sponsored company? If that had been a private endeavor in the petroleum industry with similar corruption people would be in jail (reference Enron).

      I’d like to see an independent audit of those German numbers before I fully accepted them. Data gets fluid when so many have so much at a stake. For instance, are projected repair and replacement costs figured into those billions of savings per year by Germany? Is the equipment being depreciated and is that being taken into account on the bottom line? It would surprise me if that were the case.

      “Check the rate on T-Bills. The money we borrow we pay back often less
      than the rate of inflation. And most federal government borrowing is
      from US citizens, IIRC.”

      18 Trillion in debt. There is no way around that figure. And we keep borrowing (I’m not sure it is borrowing if it is involuntary) more from US citizens via inflation (aka quantitative easing, aka “borrowing” from the future). It isn’t the rate on T-Bills that matters. It is the credit rating behind those bills and it is incredibly unlikely living Americans will be able to pay that off debt. Then there is the reality that our credit rating as a nation does not literally guarantee our ability to pay off the debt. It is a persuasive factor, but certainly not a guarantee. One large national level disaster and we could default.

      Via our debt we are taxing the as yet unborn for decisions they have zero control over. These are decisions most living taxpayers have little to no control over also when you come down to it. Most Americans simply do not want to go into further debt and want to get rid of the current debt. They understand, from high school home economics, that this is unsustainable. And they are called crazy nuts for the most part. Taxpayers pay taxes by converting their time and attention into money and paying roughly 1/3 of that “life force” to the various levels of government, which just gets bigger and bigger even when the economy is weak. This is time not spent with their families, not spent keeping kids out of trouble, not spent living their own lives. The only thing we have is time when you come down to it. When we work, we trade our lives, our time, for money. And in the case of the unborn, time that doesn’t even exist yet. When I start seeing people in your position talking about debt placed on unborn taxpayers as an important factor (externality even) to be seriously considered, then I’ll take the line of argument you’ve presented more seriously. Until then there is a hollowness that is impossible to ignore that casts doubt on much of the analysis.

      I grew up in the 70s. I attended a big gathering on the first Earth Day as a teen. I’ve always been fascinated with alternative energy and have followed it since the 70s but I really didn’t seen any overall improvement to the process of its development when government got involved. Not when all costs and externalities were honestly factored in. I just saw money getting raked in from the unwilling and doled out to buddies. Meet the new boss, same as the old boss. Maybe someday we won’t get fooled again.

      Thanks for engaging, it is truly appreciated. Most refuse to engage with anyone who displays an ounce of disagreement these days. As if we are all supposed to think alike.

      • Bob_Wallace

        I generally agree that private industry does a better job of innovation and creating efficiencies than do governments. But there are some things private industry will not undertake. The risk is too high and the possible payoff too far into the future.

        The United States became a world leader because the federal government created universities, offered very low cost education, and funded massive amounts of research. And sometimes ran the big projects that private companies would not have run.

        Without direct federal government involvement how much longer do think it would have taken to build the railroads, the electricity grid, our highway systems, satellite communications?

        Do you think it wise for the US to now imitate those countries whose governments have not done the same or should we continue to do what made us great?

        Yes, the US has a debt problem. One that won’t kill us, but one we must manage.

        Now, do we keep our economy strong or do we cut back our spending and starve the very institutions and activities that made us a world leader? Do we create new industries or all become part time employees of Walmart?

        And can we put the problem of US dept on those who caused it?

        Look at the presidents who ran up the debt post WWII. The spike for Obama’s early years results from the Bush wars.

        Cutting taxes on the rich and engaging in unnecessary wars has caused our debt.

        We now have a Congress whose idea of good government is to starve the goose that lays the golden eggs.

        I’ll give you a graph for Germany’s coal use. The data source is on the bottom right of the chart.

        “Now we have subsidized big corporations invested in what is to a large degree outdated wind and solar technology. Entire tracts of land have been taken by eminent domain when 10 years from now the technology requiring that land may be outdated.”

        My turn to doubt. Large wind and solar projects mostly pre-sold their electricity (PPAs). Profits will flow to the owners until those projects are paid off. After that those wind and solar farm owners will have some very cheap power to sell.

        I am unaware of any land seized for wind or solar. Do you know of any?

        “Are any of the Solyndra executives facing court actions? Were any of their salaries and other compensation recovered? ”

        I am unaware of any of the Solyndra executives breaking any laws. If you open a store and it fails because Walmart or Starbucks move in would you expect to be sent to jail?

        Solyndra sounded like a good idea at the time. Go back and read what the financial industry had to say about it when it was starting up. Solyndra was undercut by the rapidly dropping price of solar panels.

        Enron execs committed fraud.

  • yeeeeeeeuuuhh!!! crescent dunes!!!!!!!! whut whut!!!!!!!

  • Pingback: SolarReserve Interview: What is Night Solar Power Worth to California?()

  • tibor strausz

    any indication about the price per kWh?

    • Hi tbor, I forgot to ask.
      Generally – from looking at the power purchase contracts that are signed with California utilities, at least (this would be with a Nevada utility though) I notice that concentrated solar thermal from Abengoa and Solar Reserve is usually above MPR, while BrightSource is below it, so I am guessing somewhere above 8-9 cents a kwH which was the average but probably below 14 cents a kwH. But they have been working on storage longer – and they fully proved the tech in the 90s, and storage in itself has a separate value to the grid. (BrightSource only added it in 2011)

      • DarthGently

        I’m a big fan of alternate energy research (though not necessarily subsidized implementation) but why is “how much does it cost” always the question that is asked last if ever? Beyond price per kWh, how much of that price is subsidized or tax credited? In other words, how much are we really paying? I like the idea of using and storing solar energy directly as heat for efficiency reasons. Folks jump to PVs and batteries too quickly when often reducing the number of conversions also reduces the cradle to grave impact (both economic and environmental costs) of the tech.

        • Bob_Wallace

          When we talk about “how much does it cost” subsidies are not included. The standard way costs are compared is via Levelized Cost of Energy formulas which take into account capital cost, financing during construction, fixed and variable operating costs and amount of electricity produced. LCOEs are generally calculated for a 20 year period.

          Now, how much are we paying in subsidies? New wind, solar and nuclear are eligible for federal subsidies. Wind and solar can either take a 30% Investment Tax Credit (ITC) or a Production Tax Credit (PTC) that pays them 2.3 cents per kWh produced for their first ten years of operation.

          Given that wind Power Purchase Agreements (PPA) averaged about 2.5 cents/kWh in 2013 that means the actual cost (LCOE + owner profits) ran about 4 cents per kWh. PPAs for solar have been running about 5 cents per kWh, making the cost of solar about 7.5 cents, LCOE + profits.

          We haven’t had any new nuclear come on line for a long time. The projected LCOE for the new Vogtle reactors is running about 12 cents per kWh. The PTC for nuclear was 2.1 cents per kWh for the first ten years a few years back. It was the same amount as wind then. I don’t know if it’s been updated to 2.5 cents.

          That answer your question?

          BTW, some ways of generating electricity have “external costs” that aren’t included. Coal has very high external cost – health and environmental damage that are covered by taxpayers and never show up in the price paid when we talk about coal. Add in external costs and coal is a very expensive way to generate electricity.

  • Luke

    Great interview. That’s the great thing about concentrated solar thermal with molten salt. It’s essentially 24/7.

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