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Solar Energy

Published on February 14th, 2014 | by Tina Casey


Giant Solar Battery Made Of Salt (Almost) Ready To Charge Up

February 14th, 2014 by  

It basically runs on salt but nevertheless Crescent Dunes, the new 110 megawatt solar power and energy storage facility near Tonopah, Nevada, is billed as the “most advanced solar plant in the world” on top of laying claim to being the largest facility of its kind in the world. Now that construction is complete, the commissioning phase is under way so this is a good time to catch up and see what all the excitement is about.

We’re particularly interested in this project because we helped finance it and so did you, if you pay federal income tax. We’re not talking Kickstarter or Indiegogo either. In 2011 we taxpayers backed a $737 million Department of Energy loan to SolarReserve, the project developer.

That puts you and me in the same league as other project investors, the global engineering firm ACS Cobra and the financial services giant Santander, which was named “Sustainable Global Bank of the Year” last year. Not bad, right?

Crescent Dunes molten salt solar power plant

Crescent Dunes courtesy of SolarReserve.

The Salt Battery

Now, about that salt battery. Crescent Dunes represents the next generation of solar power plants, in which integrated thermal energy storage in the form of molten salt enables the plant to keep churning out electricity long after dark.

The storage feature enables the plant to smooth out spikes that are characteristic of solar energy, not only day-night cycles but also smaller bumps like weather and cloud cover.

Go ahead and pat yourself on the back for this one, too. Our Energy Department laid the foundation for cost-effective molten salt energy storage for solar power plants back in the 1990’s with two demo plants using a “solar salt” composed of sodium nitrate and potassium (you can read all about it in this 2013 NREL report on molten salt).

The Crescent Dunes Solar Energy Project

In terms of efficiency, Crescent Dunes represents a step up from the demo plants. More than ten thousand ground-mounted mirrors called heliostats collect solar energy and focus it on a central tower, where molten salt is circulated. The heated salt goes down to power a steam turbine, which generates the electricity.

The molten salt also serves as a “salt battery,” storing energy in the form of heat. When the heliostats are not contributing fresh solar energy, retained heat in the molten salt will continue to produce enough steam to generate electricity for about six hours.

With construction complete, the initial shakedown phase currently under way includes energizing the grid connection and other electrical systems. The heliostats are also undergoing the first stages of calibration for maximum efficiency.

The next steps include a number of stages that are common among conventional power plants, including revving up pathways for water, air, steam, and cooling.

SolarReserve points out, though, that among other differences the dry cooled condenser sported by Crescent Dunes will result in far less water consumption than conventional steam power plants.

The plant is expected to get up to speed later this year and when it does, the utility NV Energy already has dibs on 100 percent of its 500,000 MWh per year, which is enough electricity for 75,000 homes during peak periods.

US Solar Industry Races Ahead While Fossil Fuel Infrastructure Crumbles

Not for nothing, but while we’re on the subject of record-breaking solar power plants supported by us taxpayers, just yesterday the Energy Department held a dedication ceremony for another showpiece for US solar tech leadership, the Ivanpah concentrating solar power plant in California.

Facilities like Crescent Dunes and Ivanpah are not impact free, of course, especially when it comes to the construction supply chain.

However, there is no disputing the fact that once they are up and running, solar facilities do not require the kind of destructive energy harvesting operations required of fossil fuel power plants, and they do not produce the emissions that result from burning fossil fuels.

A recent series of events involving the fossil fuel infrastructure also underscores another indisputable fact, which is that infrastructure crumbles.

There are always going to be infrastructure episodes even under a best case scenario, where ample public and private resources are dedicated to efficient monitoring, troubleshooting, maintainence, and repair.

There is increasing evidence, though, that the US fossil fuel infrastructure has not been attended to, and it’s not getting any younger. Examples from the past few weeks include the Elk River coal washing chemical spill, the Dan River coal ash spill, the Kanawha River coal slurry spill, and a huge gas explosion in a Louisiana-to-New-York gas line that  put an entire rural Kentucky county in a state of emergency (fortunately with no lives lost — imagine if that had happened in a more populated area…).

Speaking of gas, hop on over to the Journal of Science and take a look at some research on what’s been leaking out from our aging natural gas infrastructure (h/t: grist.org).

As for oil pipelines, cleanup is still continuing with no end in sight from the 2010 Kalamazoo River oil spill (the largest ever inland oil spill in the US), and last we heard oil is still being found in a 12-acre cove after last year’s Lake Conway oil spill.

And don’t even get us started on fossil fuel disasters related to rail transport.

The point is, when you take infrastructure risks into account, it’s all the more clear that the US cannot sustain a fossil fuel economy for much longer.

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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.

  • John Ragozzino

    Two years later, and that battery has yet to be charged.

  • Mark

    Solar plant and Tonopah Nevada has been commissioning for over a year now.
    If this plan ever gets to run there is no way that will ever pay back the American public.
    The construction practices of the Spaniards Cobra is irregular and does not meet code by no means in the US. Cobra acts like this is Spain and treats Americans like they are junk. Most of the people from Cobra actually push Americans and they still have not lost their visas for being in the United States. I have personally seen Cobra employees yell and touch American citizens. Yet our government accept this as being OK and does not remove them from the US by law they are supposed to be removed from the US for 1to5 years. They threaten American companies by telling them you do it my way or we will not pay you. Most of the companies out there are small companies and if they do not follow their direction they will go bankrupt. Another words are holding them hostage. Cobra Cobras business practices at the Tonopah Nevada site are not acceptable in the US. They do not know how to build anything this is why most of their stuff in Spain does not run correctly in a constantly have people there maintaining and rebuilding what they’ve already built. Somehow this has to be a money laundering scheme somebody in the US is getting rich by having these type of projects going on. There is plenty of large us-based companies that have the experience and the capability of building these types of plants yet we bring people out of other countries this is not helping the US.

    • Bob_Wallace

      OMG! A Spaniard touched an America? Horrors?

      Did the American get cooties?

      And a Spanish company is requiring an American company to perform according to contract specs before it will pay? What sort of ridiculous stuff is that?

      The Spanish company should pay regardless of how badly the American company screwed up. After all ‘Murica is #1!!!

      This is just terrible.

  • The EROEI of solar thermal is even less than photovoltaic. Peer reviewed sources estimate the EROEI of solar PV to be from 4.2 to 5.4. This is, by many well reviewed estimates, significantly below that which can support industrialized civilization. Solar might be fine for some poor island country that only has to support a few thousand individuals who never need to heat their homes, but it cannot support a society with factories, recycling, the internet, space travel, or automobiles.

    • Bob_Wallace

      Andrew, do you not realize that the EROEI issue is important when we’re talking about finite and limited energy sources but has little to no importance when dealing with energy sources which are for all practical purposes infinite?

      Drilling for oil? Better keep an eye on you EROEI to make sure you’re netting energy.

      Installing wind and solar? What matters is cost. Cost is the metric to which you need to attend. Obviously there is energy embedded in wind turbines and solar panels, but it’s ultimately solar energy and we aren’t going to run short of that.

      Now, about you EROEI claims. We know that silicon solar panels pay back their embedded energy in less than two years. Thin film solar pays back in less than one year.

      Twenty years is a very conservative life expectancy for solar panels. Our oldest ones are 40 years old. Let’s do some quick and dirty EROEI calcs based on those numbers.

      20 / 2 = 10
      20 / 1 = 20
      40 / 2 = 20
      40 / 1 = 40

      So pick the numbers you like. The EROEI could be as low as 10. It could be higher than 40. It certainly isn’t between 4.2 to 5.4. One would have to go back in time to find numbers that low. There was even a time at which the EROEI for solar was zero or possibly negative. Those are the olden days. If you want to be taken seriously around here show up with facts, not BS.

  • Too bad this project delivered barely a third of the promised generation. Another failure in a long line of solar promises…

    renewable energy = chasing the wind on a cloudy day!

    Nuclear is the number one form of carbon emissions free energy, yet cleantechnica and other greenies loudly boast when they get nuclear plants shut down through their incessant protesting and litigation. Through market manipulation, in the form of renewable subsidies and net-metering, the value of baseload power is being destroyed. Baseload power is the most cost-effective method of supplying our society’s energy needs. By destroying the market, you destroy our society!

    • Bob_Wallace

      Andrew, your bull doesn’t get a free ride here. Nuclear plants are not being shut down due to activists work but because of economics. Utility companies are closing their most expensive reactors because they are losing money.

      The world has changed, Andrew. Wind and solar are now our low cost, low-carbon providers. Nuclear is so last century….

      • The economics are manipulated you shill! Can you not read?

  • C2shiningC

    I believe they are actually using ammonium nitrate for energy storage because it has a lower melting point (337F) than sodium nitrate (586.4F) or potassium nitrate(633.2F). All three salts are components to make powerful explosives and are serious water contaminants (1ppm considered dangerous to infants).
    The manufacture of all three salts begins with the creation of anhydrous ammonia from methane gas, a fossil fuel. They are highly corrosive, have an extremely low
    viscosity that requires high temperature, corrosion resistant piping (SS) with
    welded joints. The lower melting point of ammonium nitrate means they
    don’t have to keep the pipes as hot to prevent the molten salt from solidifying
    in the pipes at night.
    Safety has to be another concern. One of the worst disasters in US history
    was caused by the explosion of a shipload of ammonium nitrate (Texas
    City). In a molten state it is even more dangerous.

    • Ronald Brakels

      I’m pretty sure no one would be using ammonium nitrate for thermal storage. It’s a bit too blow uppy for that. Instead a mixture of sodium nitrate, potassium nitrate, and calcium nitrate are generally used, all of which are non-flammable and non-blow uppy. While precautions do need to be taken with solar salt, in my country we wouldn’t consider it to be very dangerous as we are completely insane and wedge ourselves between a tank of explosive liquid hydrocarbon and a block of highly machined metal that operates off a continuous series of explosions and zoom around at high speeds. We keep huge tanks of explosive liquid at distribution centers throughout our cities and big machines tow huge tanks of it through our streets to these distribution centers. Personally I think there is something wrong inside our heads.

      • Bob_Wallace

        Do you also do what we do and run pipes full of highly flammable gases underneath your cities and into your building?

        • Ronald Brakels

          Sometimes, yes, but most of the time if we want explosive gases to flow into our homes we need someone to come around with a truck (running off explosive liquid) who will bolt tanks of explosive gas to our houses.

          • Wayne Williamson

            Thanks guys, been a while since I laughed so hard;-)

      • C2shiningC

        I’ve always been a fan of solar ponds which can produce electricity without interruption year round. A small solar pond (1.5 km^2) in Shiraz produced 6.2mw with an efficiency of 16.08% over a three year period. Type of salt is immaterial. Cheaper the better.

        35,200 people were killed last year speeding around sandwiched between tanks of explosives and the highly machined metal exploder chambers. You’re right about something being wrong when people “Choke on a gnat but swallow a camel”.

    • TCFlood

      I agree with Ronald Brakels, ammonium nitrate would never be used since it is an explosive.

      This article appears to confuse molten salt electrical batteries which use molten salts plus molten alkali metals (“sodium nitrate and potassium” mentioned in the article) with molten salt thermal storage which uses only salts which Ronald again correctly identifies as sodium, potassium and calcium nitrates – no liquid metal component would be used.

      • TCFlood

        I just read the NREL Molten Salt link given and it its indeed thermal storage not electric battery storage. Another example of sloppy reporting WITH NO CORRECTION.

  • dynamo.joe

    I don’t know why someone doesn’t just bump up the thermal reservoir size and say “hey look, 24/7 solar power”.

    It would defuse so many arguments about dispatchability, etc.

    • Bob_Wallace

      We don’t need 24/7. Thermal solar’s niche is pre- and post-PV solar. That’s where they can make money.

      Take a look at how (cheaper) PV eats away the middle of the day, leaving early and late peaks. Thermal solar with storage is likely to be cheaper than stored wind/solar.

      The other place thermal solar can win is by adding gas burning ability so that they can generate on cloudy days when PV is going to be low.

      • A Real Libertarian

        The point isn’t efficiency.

        The point is shutting up the naysayers.

      • too bad that Ivanpah is delivering LESS THAN A THIRD of the generation they promised. Just another in a line of SOLAR FAILURES!

    • Ronald Brakels

      If they draw less heat it will run 24/7 so feel free to say, “Hey look, 24/7 solar power!”

  • Doug Cutler

    Here in Canada in the province of Quebec in June of 2013 we had the most tragic and entirely avoidable oil train derailment and explosion in the town of Lac-Megantic. 47 lives were lost to the blast and fires and half the town center destroyed when the brakes failed on the train parked outside of town during the lone attending engineer’s break. Back-up supervision could have easily prevented the disaster but train company CEO explained just days later it wasn’t cost effective.

    Now the company is in bankruptcy and a long legal shell game of which mother corporation bares responsibility is underway. Meanwhile, who picks up the multimillion dollar clean-up tab? You guessed it, the Canadian Federal Government thus Joe Taxpayer. CAN Feds are in for 50% with total costs at $400Mil and rising. Once again profits are privatized and loses socialized. The Government pretty well has to pitch in but the move represents one more defacto subsidy/non-accounted cost of fossil fuels.

    • Ronald Brakels

      Heads I win, tails you lose.

      • Surf

        This plant was originally designed to generate 50mW 24 hrs a day. However the utility requested a larger turbine (110mw) so that the plant can handle the high load from sunrise to about midnight. Presumably they have other plants that can handle the late night loads.

        However if the utility changes its mind in the future they can throttle down the turbine to 50mW output and switch to 24hr operation.

        • A Real Libertarian

          That’s MW.

          mW is Milli-watts.

      • Gwennedd

        Huh? What was that comment supposed to mean?

        • Ronald Brakels

          If I run a dangerous fossil fuel transportation and nothing goes wrong then I make money and I win. If there is an accident and I don’t have to pay for the cleanup then you, as in the taxpayer, lose by having to shoulder the cost.

          • sam

            The liberal will fix the RET.

          • Ronald Brakels

            I’ve been rather liberal in my life, dearie, but it never seems to fix anything.

          • Rick Kargaard

            I believe the user of the fuel has to bear some responsibility. Those tanks bolted to your house are not there without your approval. Nor does the fuel industry force you to run around in your dangerous sandwich.

  • Matt

    One of the things that make you go hummmm. We have coal ash spills now, what happens when the coal profit start really dropping. Better get them to fix the issue now, or we need another super fund for cola ash clean up this time.

    • coal ash contains many valuable metals. If america could reindustrialize, we could turn many toxic waste products into valuable resources!

  • jburt56

    Next up thermoPV integration. . .

      • jburt56

        It will end the water use issue of CPV, the complexity of turbines, etc.

      • Zachary, we have build hybrid thermoelectric & photovoltaic systems in our lab. The truth of the matter is that a hot PV cell has terrible efficiency. In order for you to cause a thermal gradient across the expensive thermoelectric element, the PV cell heats up so much that it makes the efficiency of the entire system worse!

        Occam’s Razor cuts renewable energy to shreds. We have very sensible methods of generating thermal energy at high density with little waste. Every dollar spent on wind and solar is a dollar that is NOT getting spent on utilitarian solutions. We need to save the earth and POST HASTE!

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