CleanTechnica Exclusive

Published on March 31st, 2016 | by Susan Kraemer

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Crescent Dunes CSP: Cutting Edge Engineering For Solar At Night

March 31st, 2016 by  



Innovating at the lab bench scale is very different from actually building completely new energy technologies that must be pioneered from the ground up, at full scale, in the real world.

Ten hours of solar thermal energy storage now supply Las Vegas with solar power from midday to midnight.

Cresent Dunes solar after dark

SolarReserve’s 110 MW Crescent Dunes Concentrated Solar Power (CSP) plant just came online in Tonopah, Nevada. Its technology was literally invented by rocket scientists, and demonstrated at “lab scale” at the 10 MW Solar Two pilot project with DOE funding.

But part of commercializing a breakthrough technology at full scale is negotiating the difference between technology design and boots-on-the-ground engineering for manufacturing.

As first-of-a-kind, Crescent Dunes was almost handmade

“Molten salt power towers are very new, and especially ones the size of Crescent Dunes. This is the largest one out there with integrated storage,” Dave Morse, Operations Director for Automation at Delta told Cleantechnica in a Skype interview.

“As the first-of-a-kind, Crescent Dunes was almost handmade” added Kevin Smith, CEO of SolarReserve.

SolarReserve created the algorithms controlling the collector field and the pointing of the 10,347 billboard-sized tracking mirror heliostats.

As the go-to firm for industrial automation, Delta’s motion control software supports these algorithms with local control at each heliostat so that each one precisely reflects and concentrates sunlight onto the large 100-foot receiver at the top of the 540-foot tower.

Delta makes high-speed control systems and servo motors for extremely precise motion control for a wide range of applications.

“Most of the engineers in the world know that that’s what we do and they come to us with their motion-control ideas,” Morse said.

With breakthrough technologies there is no help out here. You are on a path nobody has been on; there’s no rule to follow

The thing with breakthrough technologies is that “there is no help out here,” he pointed out. “There is really nothing you can look up; because you actually are trying to invent the wheel. You are on a path nobody has been on; there’s no rule to follow.”

The way trackers are deployed in PV, it is relatively easy to point a tracker at a moving object like the sun.

Similarly, tracking in trough CSP (as opposed to tower) is easy; the rows of parabolic mirrors concentrate sunlight onto a pipe running along right in front of each row. A heat transfer fluid (HTF) in the pipe is heated. It is easy to point the parabolic reflection at the nearby pipe.

“But it is much harder to point a reflection of the sun at something somewhere else; as we did at Crescent Dunes aiming at the distant tower,” he explained.

“It is basically trigonometry that you’re doing, every second of the day; trying to make sure that you hold that position.”

“As the sun is moving, the angle changes. The sun constantly moves, but what you’re trying to point it at doesn’t. It’s very difficult to actually say, okay; where is the sun. It is basically trigonometry that you’re doing, every second of the day; trying to make sure that you hold that position.”

Each heliostat includes its own on-board computer to do the math for its own unique position in relation to the tower all day (and through the seasons as the sun’s angle in the sky changes).

And that is, if all else proceeds according to plan. But in the real world, perfection in meeting a first-of-a-kind spec is not guaranteed.

“If a mirror manufacturer couldn’t hold a previously agreed-upon specification for the high reflectivity required, it would be our jobs at Delta to compensate,” said Morse.

This greatly increased the precision in pointing that Delta had to achieve.

The precision had to be plus or minus a milliradian

“With higher reflectivity, if the precision was plus or minus half a degree it would be okay. But with a lower reflectivity, the precision had to be plus or minus a milliradian,” said Morse.

A milliradian is a much more precise angular measure than a degree. It is 1/6400 of a degree.

“The bottom line is, it’s challenging to manufacture today’s technology to the level that we would expect, because we’re at the cutting edge. Our job is figuring out how to design cutting edge technology for mass production, and that’s really the key difference between what we can dream up in the lab and what’s real.”

These challenges are what made working on Crescent Dunes exciting. “Tower CSP is far more interesting to us. Anyone can do trough. It’s very simple, and we do quote on it, and we do have business in it, but it’s not our focus,” said Morse.

During the process of constructing the 110 MW tower project, both Delta’s and SolarReserve’s engineers were discovering ways to do things better. “Part of our ongoing activities is advanced R&D, including cost analysis,” Smith said.

Crescent Dunes commissioning

The Crescent Dunes heliostat field cost $300 million, almost half of Crescent Dunes’ total cost. For its next project, SolarReserve believes it can get that down to $200 million, a 30 percent reduction, with improvements in pointing accuracy, and with less steel and thinner glass.

Software also had to compensate for any leaning of an individual pedestal supporting its heliostat due to slight settling of the concrete or the backlash

For Delta, accustomed to controlled indoor settings, bringing these kinds of precision controls outdoors bought unexpected real-world challenges. The software had to compensate for any leaning of an individual pedestal supporting its heliostat due to slight settling of the concrete or the backlash.

“Even walking around the five square kilometer site is difficult with equipment in tow. The heliostats are very large and tall, which required us to use a 4-wheel drive scissor lift trucks to gain access to the motors which are higher than four meters in the air,” said Morse. “Our vehicle got stuck on several occasions.”

CSP requires high direct normal irradiance (DNI), with none of the atmospheric losses caused by scattering or absorption from floating particles and gas molecules found around industrial or agricultural zones.

The clear high desert of Tonopah, the stargazing capital in America, with unparalleled views of the Milky Way, makes for ideal DNI nearly 365 days a year. Site manager Brian Painter at SolarReserve recently suggested powering half of Nevada or sending power to California, by building ten more tower CSP projects near Tonopah!

Before permitting, SolarReserve had monitored the site for its weather patterns over several years, and output models account for the relatively seldom dust events.

However, the occasional sand storm sand created its own challenges.

“We had several days where testing was completely halted due to sand storms, as visibility was down to 30 meters; so on those days, we couldn’t see the sun spot on the tower to conduct any calibration,” Morse said. “Even though they were perfectly blue sky days, Sand Devils would sprout and cover the team in sand, or worse, blow sand inside the control cabinets while working on them.”

How molten salt tower technology makes solar power at night:

Highly focused sunlight is reflected off Crescent Dunes’ 10,347 heliostats – aiming thousands of “suns” onto the tower receiver.

Molten salt flowing through piping in the receiver absorbs the heat from this concentrated sunlight – heating from so-called “cold” at 550°F, up to over 1,050°F “hot” – then flows down piping inside the tower into a thermal storage tank.

The tank holds enough in storage to dispatch up to ten hours of electricity at nameplate capacity every day, or 1,100 MWh a day.

To generate electricity, whether the sun is shining or not, stored molten salt is sent through a heat exchanger to boil water for high-quality superheated steam driving a steam turbine.

Storage in molten salt makes a thirty-year supply of solar, dispatchable day or night

Initially heating the solid salts from room temperature up to their molten state took about a month, but it can then be kept within this range of temperatures while circulating in operation daily for thirty years.

If not used, this “stored sunlight” can stay available for months, but SolarReserve’s contract with NV Energy requires each day’s storage be used either that night, or be dispatched on request by the utility as needed.

Coming up, Delta is now moving into the same booming CSP markets overseas as SolarReserve; South Africa, China, Chile, and Australia.

“SolarReserve is an amazing partner and they did everything right,” Morse added. “For those working through these challenges, it is a great sense of accomplishment and we are proud to be part of the Crescent Dunes project.”

Image Credits: SolarReserve





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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.



  • John Ragozzino

    Do you only allow praise and adulation on this Discus site?

  • John Ragozzino

    This is the same type of praise and adulation which was heard when Ivanpah
    started up. The reality was quite different. Lets wait for a couple of years
    of output before we get too optimistic.

    • For Ivanpah’s second year it is operating at 97% of target: http://cleantechnica.com/2016/03/18/cpuc-gets-right-pge-can-keep-ivanpah-contract/

      For completely novel technology to operate within 3% of 2nd year target is actually a much better performance than the first fossil power stations, when that was new technology in the early 20th century.

      • John Ragozzino

        This isn’t new technology. It has been around for 20+ years on a smaller scale. If it was so successful, they wouldn’t be having hearings about cancelling it’s power contract.

        • No, what you’re thinking of 20 years ago: SEGS – is totally different CSP tech: parabolic trough.

          Trough IS the CSP tech that is thoroughly tested, and nobody doing that now has any issues in fine tuning performance: Mojave (2014) and Genesis (2013) used the same parabolic trough tech as SEGS in California and both are performing per specs.

          Nobody has ever done direct steam with the steam drum 500 up feet up a tower at this scale – Ivanpah is nearly 400 MW. The only other direct steam power tower is in South Africa, Abengoa’s Khi Solar One (begun generating 2016), and that is only 50 MW.

          The tower pilots and demos at the 10 MW scale in the US were precursors testing the technology that Crescent Dunes uses, molten salt, these were not trying to do solar with just water like Ivanpah direct steam.

          So, first of a kind.

          And, its first year, yeah, it only did 80% of target. But second year it fixed the problems, and 97%, and that is why PG&E asked to allow them more time.

          • John Ragozzino

            No, I am thinking of the collecting tower in Albuquerque that has been there for at least 30 years.
            I am thinking of the two facilities with mirrors and towers at Daggett Ca, that were recently
            torn down which was built in the 90’s. I am thinking of the Sierra Sun Tower in Ca. built
            10 years ago and found to be unprofitable to operate. No Susan, this is marginal technology, and if you think quibbling about the location of the collector and boiler will make a difference
            in it’s long-term viability as a power producer, give it your best shot!

          • Those were the demos of similar (but NOT identical) technologies: at just a few MW each. The DOE dismantled the two towers after the lessons learned in their demos. SolarReserve tech developed out of one, but not Ivanpah’s tech.

            Demos are a far cry from a nearly 400 MW plant.

          • John Ragozzino

            Yes Susan, but they were UNSUCCESSFUL! Got to ask yourself, if the money wasn’t so free and easy, would Ivanpah have ever been built? If it’s so cutting edge, why not built a test plant????

          • Bob_Wallace

            It is a test plant. A full size test plant. If it works as designed then we should see the next plan to include storage.

            As for the first plants being “unsuccessful” (and you don’t need to shout) they were only unsuccessful in that they did not produce electricity at market prices.

            That’s true for emerging technology. Early versions are often not competitive. Our first wind turbines produced $0.38/kWh electricity. As we’ve built better and better versions, learning as we go, we’ve lower the price to under $0.04/kWh.

          • John

            Now that’s funny Bob, a full size test plant! It’s a failure because it burns a huge amount of natural gas, makes expensive energy, and doesn’t make enough of it. Oh yes,
            and it kills birds.

          • Bob_Wallace

            John, if you can’t tell the truth then you need to go to another site that enjoys lies.

            Ivanpah does not burn a huge amount of gas. It burns a small amount of gas in order to heat up in the morning. Future thermal solar that includes storage won’t need gas to warm up in the morning, they can use some of their stored energy.

            It looks like the cost of electricity from Ivanpah, once it has completed its four year setup period, will be in the range of other sources of electricity. Not as cheap as wind but much cheaper than nuclear.

            It does kill birds, but just a bit over one a day and that number will probably be reduced. Coal is the major killer of birds when it comes to electricity generation.

          • John

            No lies, just the facts Bob. A four year setup period! That sounds funny too. What other industry needs 4 years
            to make their stuff work? You said previously that you aren’t impressed with this technology. What has changed???

          • Bob_Wallace

            Nuclear reactors need time to bring up to full performance.

            I’m not convinced that thermal solar will be competitive, even with storage. But I’m willing to wait to see if it can prove itself.

          • BrightSource did test its direct steam technology in its demo in Israel.

            (If its money for solar innovation that is so upsetting, you’ll be happy to hear the DOE Loan Guarantee Program is now funnelling $8 billion to build tried and tested nuclear technology: for a single nuclear power plant in the South.

          • I wonder whether you would similarly dismiss the long term viability of generating electricity by burning coal.

            The first ever coal power – Edison’s coal plant in NYC – began at only 1% efficiency. It took 15 more years to get that to even 15%.

  • jdeely

    So – what is needed for this to scale? also, what benefit is there from 100MW vs 2 – 50MW projects. Could a 50 MW project be done by newly trained technicians in let’s say 6 months?

    • Matt

      This is a good question and more important the the above “what makes it utility scale”. With PV the sweet spots is ~10MW units, very little benefit of scale past that. So for a 600MW PV farm you do 60 10MW units. What is the sweet spot (cost saving) for CSP. As you increase the radius of the circle you get more mirrors per row (pro) but you increase the require pointing control (con). Area (number mirrors) goes up r**2 pointing control is likely about 4*r and likely several other factors in there.

      • jdeely

        Matt, That is exactly along the lines of what I am thinking. You can also strategically locate two 50MW projects better plus easier to deal with smaller land parcels, could sell the output to a utility(maybe municipal) that does not need larger amount etc.. Interesting question on what is the sweet spot.

        • If the sweet spot was smaller, that would make it easier to scale the technology and lower costs. For example, the CEC in California only requires projects over 20 MW to go through its very arduous several-year (and up to five years with NIMBYs opposition) permitting.

          Unfortunately, while PV is cost effective at small scale like 10 – 20 MW, CSP isn’t, because of the power block. You never see a 10-20 MW coal or gas plant, because the thermal generating power block is not cost effective that small. The back end of a CSP plant is the same, it uses the steam turbine.

          At least 100 MW, and now up to 160 MW is currently considered the optimal size for power tower, the future of CSP. 2015-2016 bids have been in this range.

          • jdeely

            Susan – thanks for that. So the 50MW limitation in Spain actually made the plants more expensive as well. Not very effective.
            When you mention 2015-2016 bids – what are you referring to? any in US?

          • No, there are none in the US now. Chile and South Africa.

      • 160 MW seems to be the ideal.

  • JamesWimberley

    Ridiculous puffery. 24-hour production with CSP was demonstrated by Gemasolar in Spain five years ago, at utility scale (20 MW)(link). Crescent Dunes is a minor improvement on a demonstrated technology. The big progress seems to have been on costs, which is important, but spare us the breakthrough starry eyes. It’s like the American delusions that the USA invented film, computers, space rockets, antibiotics, jet engines, and so on. I’ll grant you duct tape.

    • Spanish CSP was limited by law to 50 MW and under.

      So Gemasolar had only 2650 heliostats to control, not 10,347. So Gemasolar was more like another pilot, like the Solar Two pilot for Crescent Dunes, built with US R&D but at only 10 MW.

      Unfortunately, Spain then clamped down on solar tariffs, so Spain’s CSP got cut short, but Masdar and SENER did a great job with Gemasolar.

      (To me, 100 MW and up is utility-scale for the US with its larger grid than Spain; look at all the PV plants being built at 100 MW and up to 600 MW.)

    • Kevin Smith

      The 110MW Crescent Dunes facility is really the first full scale facility, at almost 6 times the size of Gemasolar. At 18MW design, Gemasolar is not considered “utility scale”, still more pilot scale. The Sener technology was actually derived from Rocketdyne’s technology as well, and they will (or should) openly admit it. Rocketdyne worked with them before participating in the formation of SolarReserve. The 18MW Gemasolar facility is essentially a copy of the 10MW Solar 2 facility built by the US DOE in the late 90’s, also a pilot scale facility.

    • Mary Grikas

      Gemesolar is a great project but it’s only 19.9 megawatts, less than a fifth the size of Crescent Dunes.

    • BernhardSeubert

      When comparing two CSP projects (with storage), the annual yield should be more important than the nameplate capacity. Crescent Dunes is still more than 4 times bigger but GemaSolar has the higher capacity factor 😉

  • Jason Willhite

    Awesome article! Thank you, Susan

  • Mathieu Vaudrin

    A milliradian is not 1/6400 degrees but about half tenth of a degrees, not at all the same number. In maths speaking, 0,001 rad multiply by 180 deg and divide by 3,1416 or Pi, gives you a milliradian in degrees which is exactly 0,057 deg/rad^-3. Still a good news, I see good sights for CSP, next phase : mass production of cutting edge technologies for mass use of renew energies.

    • Larmion

      Interestingly, a steradian is equivalent to about 1/3200 of a square degree. Since they mention ‘plus or minus one’, that might explain where the 1/6400 comes from. Even so, that doesn’t explain where the ‘mili’ prefix comes from.

      Wouldn’t it make more sense to express a 3D mirror position in terms of steradians?

      • JeffJL

        Perhaps. But then only you and Mathieu would understand what you were talking about. 🙂

    • Thanks for the correction. (Can’t edit unfortunately)

    • Matt

      The first sign they were in trouble was when they decide to switch between units (degrees / radians).

  • Lou Gage

    very, very impressive. LV is an excellent test case with high AC loadings through the night. Hope this proves the case for CSP in utility scale to American utilities and investors. Lou Gage

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