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December 14, 2007



the characteristics you describe for the Solel system make me think that it would be ideally suited for power form the Sahara, perhaps later transmitted to Europe:
Save for a small coastal strip, you have no worries about extensive installations there, as the Sahara is incomparably more vast than the Mohave.
Many of the governments there are interested, and one project combined with Natural gas is already being built in Algeria:
(Sorry, Steve, no disrespect, I know that you will be well aware of this information, but am going into it in a bit more detail for others who may read this blog)
The African coastline in the South of Morocco also has some of the best wind resources in the world, and valueless land - installing wind turbines on a site where you are already going to be building a power plant would greatly reduce costs.
The Germans, who are not renowned for engineering flights of fancy, reckon that by 2020 you might be talking about solar thermal costs equivalent to oil at $15/barrel.
You also mention others jumping into the fray - I reckon e-solar have some nice tech, and certainly loads of backing.
I'd be interested in your comments, and of course that of other folk.


Dave like I said before I am no expert on everything solar and my opinions are only my own. I can only take what I have seen before and apply it to what I see now. I am also a natural skeptic and won’t believe much I read until I can see it in person. Just like the solar projects they have announced in California. I really want to see them break some ground before I truly believe they will build them. The truth is there are only three that have applied to build them as of yet and I have serious doubts about two of them ever getting built. Brightsource does not have a contract yet for the solar towers and they are trying to build a 50 MW solar field attached to 500 MW gas plant in Victorville. Ausra’s plant seems to have a pretty good chance beings it has a contract.

Building power plants in Morocco sounds like an ok idea but since I am a natural skeptic I will point out some problems I see with it. I don’t like the idea of using another country to supply the bulk of your energy. We could be in the same boat we are in today. Using DC lines you could take the electricity any where in Europe but being Morocco I would be a little more worried about terrorism. Pretty simple to knock those lines down. Beings it is a natural wind site that also tends to work against it in my view. Wind sucks and extremely high wind really sucks. In reality most good solar sites have a fair amount of wind but mirror damage can be a costly problem. Ausra’s design, being closer to the ground, looks good but looking at photos of it is still several feet off the ground and not sure how tough the mirrors are. Blowing sand might also be a problem.

Cyril I looked at the California Energy Commissions home page and looked at Ausra’s project in the Central Valley. It does say it uses an “air cooled condenser” I don’t have any idea how it would work but if Ausra’s design can truly use it economically, especially in warmer areas like the Mojave, it would be a great thing. It would solve probably the biggest problem for solar thermal in the desert. The average steam plant uses 800 to 1000 gallons of water per MW . Being a skeptic I want to say they mean air cooled generator, which is pretty common, but I would love to be wrong. Really is an exciting time. Now we just need to build some of the damn things.


Thanks for that Steve.
I did not know that wind could cause so many problems - but after your post I checked up and apparently in Arizona PV panels are usually reckoned to have half the usual rated life due to abrasion!
Ausra have made their design so that you can rotate the mirrors and only expose the steel back in a storm - pretty clever!

Cyril R.

Is misspelling contagious? It's Kramer Junction, not Cramer Junction.

Whatever you say Klee.


Right Steve - let just build them. You of all people know that the SEGS plants have more-less been test beds as they've honed the process. These first Ausra plants will be just the same - test beds where they will hone the process. Neither am I convinced that your employer is without more tricks up it's sleeve. Solel has done a phenomenal job bringing down the cost of the dewar tubes (and Ausra has benefited from that development) so surely cheaper parabolic troughs (maybe a flat-plate assembly) is in order. This is how all industries work - a new company arrives with a superior technology and ultimately someone else capitalizes on it and it just becomes another improvement in a long list of improvements in the industrial record.

Frankly I find it amazing how much money the DOE throws at totally fruitless renewable technologies. It's beyond me why federal and state agencies have done practically nothing to encourage solar thermal development in the last 20 years while throwing billions of dollars into PV incentives and tax breaks. The same goes for geothermal furnaces - you can get a 20K incentive to put PV panels on your roof which still cost you 20K on top of that but you can't get a thing to upgrade to a geothermal furnace which will cut heating/cooling costs more than anything.

Cyril R.

I admit a saturated steam system is different than superheated one and I don’t really know how it would be affected but I am going to assume it will be similar.

Well, not needing a superheating stage, a lower operating temperature would be doable. That's what they are proposing to do with their direct steam turbine. Having a lower operating regime could make dry cooling more viable but I'm not sure about how this will work out in their design. And they'd still need steam seperators and flow controllers, otherwise nasty things will happen to the turbine and tubing. But these devices have improved greatly over the last decades with advances in software and controlling hardware.

One of the reasons I thought Ausra would be going after dry cooling is that they mentioned the system would be closed-loop but maybe that's only for the coal reheater project.

It's also possible that they aren't going after dry cooling right now, in their first plant. However I think electrical generation water use in the Mojave is a serious problem when tens of GW of solar thermal plants are to be deployed.

And, going after dry cooling can give them something to brag about, like how 'green' they are, that would be good PR.

Here's an excellent Comparison of Alternate Cooling Technologies for California Power Plants from the California Energy Commission that you mentioned.

What I've also been reading about dry cooling is that the performance penalty isn't that big when the water use reduction bonus is factored in. That is, economical performance is not lowered that much.

You are right though that dry cooling would be very dependent on location for performance. Mojave is indeed problematic.

I'd like to point out that developments in advanced (triple?) absorption chillers could also lead to efficient and effective dry cooling systems.

An alternate strategy would be to make sure there is enough water so it won't be a problem to use wet cooling. Water could be piped from reverse osmosis desalination plants near the coast (ie using sea water), but that would require a lot of additional infrastructure and osmosis plants, so that would have to be compared against the problems of dry cooling.

It's not so much Ausra that's fascinating me, it's that design. I'm also a skeptic, but it's hard to beat all those little advantages that the compact linear fresnel reflector offers.

Fortunately, we shouldn't have to wait long for results; the first plant is scheduled for operation in April.

Cyril R.

Solel has done a phenomenal job bringing down the cost of the dewar tubes (and Ausra has benefited from that development)

Ausra won't be using evacuated tubes in their low temperature proposal, they have their own inverted cavity receiver design for that.

They mentioned using evacuated tubes for higher temperature operation, but I'm not sure what they've decided to be best yet.


>Ausra won't be using evacuated tubes in their
>low temperature proposal, they have their own
>inverted cavity receiver design for that.

I see. I wonder if that's because dewar tubes wouldn't survive the expansion due to high pressure steam (as they plan on using water as the HTF). That was something I wondered about from the start when I heard they were talking about generating steam while in the array.


DaveMart yes wind is a problem. With the Solel system basically during high winds the outer rows are turned so the backs face the wind and block the wind for the other mirrors. If the winds are too high then the field is simply stowed. The worst time for the mirrors are when they are at 90 degrees. Most of the time winds come from the west and the field does a pretty good job of limiting breakage. Freak winds from the north or south can do some huge damage. The absolute worst is dust devils in the field. Solel’s style mirrors are expensive. They are not only curved they also use high reflectivity glass. There have been recent changes that have limited breakage quite a lot but it is still expensive and may be one of Ausra’s biggest advantages.

Davea I agree that some changes are coming for Solel too. I think Ausra may really be on to something with the flat glass. Cheaper and better land coverage. As Cyril pointed out the Solel system has to be spaced further apart to keep from shading the mirrors. You do need to leave room between rows to be able to clean the mirrors but not nearly as much as the Solel system. They have changed the trough system with the Solargenix plant. I believe it is something called the “Euro Trough”. As I understand it, it is a more bolt together system made out of aluminum. It is supposed to be easier to mass produce but I believe they are having a little bit of trouble with them. Not sure how they are holding up to the wind. I need to make a phone call, to a friend of mine, and find out.

Cyril I actually think you were right when you said that Ausra may be planning on using a dry cooling tower with the first plant in the Central Valley. I hope they can make it work because I believe that lack of water is the major issue facing solar thermal in the Desert Southwest. The website is down now but Harper Lake Energy Park has some interesting information on how much water is in the aquifer beneath Harper Lake. To be honest the people who are pushing that project kind of remind me of snake oil salesmen so I take what I read with more than a grain of salt. I guess with the aqueduct you could buy some water from down the hill but really don’t think you are going to win competing against LA. You and I seem to think alike about using ocean water. Not sure it could ever justify the price but then again they pump water out of the Delta and into the Aqueduct. Really there would be no problem using ocean water in a cooling tower without treatment. I believe the Pacific has a conductivity (mineral content) of around 26,000 and you can run the cooling towers at over 40,000 without any problems. That being said you are going to have to very large ponds to hold the much greater amount of water that would have to be blown down out of the tower to keep the conductivity down. They also have zero discharge cooling towers that all the blow down water is treated and the minerals removed. Most of the cooling water is still lost threw evaporation but it does save some water.

Cyril R.

Davea0511: as long as they can ensure that a water film covers the entire inside of the tubing at all times it shouldn't be a problem, considering the low pressures proposed. (But maybe, evacuated tubes might need some redesign for this purpose eg thicker tubes.)

One of the reasons saturated wet steam systems for solar thermal plants are more viable now than in the past, is new monitoring software and flow controller technology to manage the water flow through the pipes.

It's possible that a closed cavity receiver with simple steel pipes is actually even cheaper than evacuated tubes, and with lower temperatures they should perform quite well so evacuated tubes wouldn't be much of an improvement then.

Steve: you've got me thinking there about using sea water piped in from the coast. I was actually thinking about desalinating it with an efficient RO plant near the coast, then piping the fresh water to the plants in the Mojave. If sea water can be piped directly, that would be even more interesting. Are you sure the mineralization won't be a problem, especially regarding down-time for extra maintenance? If so, then perhaps that's a good thing: the minerals (various salts) actually have market value so they could be sold as a small byproduct of solar thermal generation plants.

Hmm. Some of the salts could even be used for thermal storage if necessary.

Lots of stuff to think about. Perhaps you could talk to your employer about it? :)

Cyril R.

Regarding cleaning, I think having 360 degree rotational capability could enable cleaning the mirrors from below so no extra horizontal spacing would be needed.

That would be a bit difficult with troughs, because the receiver is tied to the reflector. That's another possible advantage, having a receiver fixed in space.

Cleaning nearly flat mirrors may also be a bit easier to do than strongly curved ones.

Solel is using some sort of cleaning bot right? Ausra says they'll be cleaning manually. Maybe they're using poor interns for this purpose :)

I can already imagine it. New kid in the team, gets a tour around the solar field in the heat of noon, after that, the project leader says "here you go, see you tomorrow" while handing over a bucket of water and some washing equipment :)

Poor interns indeed...

Cyril R.

Another interesting future development would be solar thermal in cold arid places like northern (central) Canada. Right on the polar circle looks like a good spot. The direct beam insulation is much lower there of course but is partially made up by much lower ambient temperatures. You'd need a very different design to deal with the low sun angle there, like an almost vertically mounted array in a long but shallow field. Dry cooling would work very well there, and wet cooling too because of the availability of really cold water nearby.

In the northern summer months, there would be reliable output with the sun shining (almost) the entire day. And in the northern winter months, the ambient temperature is much lower so there should be reasonable performance in winter too especially with dry cooling.

Cyril R.

Steve, I've got a question for you about that cavern storage. They say it can't be taken higher than 680 degrees Fahrenheit. Why would that be the case? I thought there isn't any real barrier here, just how much pressure and temperatures the materials can take, right?

I'm also pretty sure now that they at least plan on using dry cooling, their website has an animation that says "the cooled steam turns to water and is recirculated to continue the process" (number 6).

Cyril R.

I'm also a bit puzzled by that 9 square miles for 553 MW. But I got it from Solel's website so I assumed it to be the correct figure.

Perhaps they mean combined with all the existing plants in already in the Mojave? That would make more sense: 354 + 553 = 907 MW = about 100 MW/square mile. That must be it.


Cyril R. wrote: They say it can't be taken higher than 680 degrees Fahrenheit. Why would that be the case?

I would guess that the problem would be related to the fact that 680 degrees Fahrenheit is close to the critical point of water, which is 705 degrees Fahrenheit and 3,208 psi. There is no such thing as liquid water above 705 degrees Fahrenheit, at any pressure. Material corrosion rates are high at anywhere near or above the critical point.


I have no idea if it would ever be feasible to use ocean water for cooling but you would have no problem using it in a cooling tower. Many power plants use ocean water for cooling . If you were to taste the water in a cooling tower it would taste like very salty ocean water. There are a couple of chemicals used in the water but none that would cause much of an environmental issue. Acid for PH control, chlorine to inhibit algae growth and an inhibitor to limit metal corrosion. It would take more water salt water than fresh simply because you have more salt and calcium in the ocean water. They do have zero discharge cooling towers that eliminate the need for holding ponds. Not sure what the value is of the salt and other dissolved minerals in the water would be.

Now as far as mirror cleaning the Solel mirrors are usually hand washed sometime before the peak (summer) season. Temporary workers are hired and the job is basically a hand wash and it does suck. Sometimes really good workers are hired on full time. During the rest of the year they run water trucks at night spraying demin water on the mirrors to clean them. The mirrors can be positioned to clean either the top or bottom. One of the best washes you can get is when it rains. The mirrors will be put at 90 degrees and the whole field will get washed at once. Not that much of that the last year but works well when it happens. I am sure that Ausra’s system must have some space between rows. You would need to get something there to clean them and have to do maintenance too.

I really don’t think there would be a problem using Solel type tubes in an Ausra type system. Basically they are a approximately 2 inch stainless steel pipe cover with an about 5 inch evacuated glass cover. Now some of the problems they have had are they tend to lose vacuum and fluoresce. They get a white coloring that looks like a florescent bulb. It really knocks the hell out of their efficiency. Sometimes the tubes are pulled out and the interior glass is cleaned but now with evacuation and the insulation it provides are gone. Solel claims their latest generation of tubes will not lose vacuum or fluoresce and that would be a huge advantage to the old tubes. I imagine one reason Ausra is not using the tubes is they are expensive.

I did look at the animation, and while I think they may be planning on using a dry tower, there is nothing there that would suggest it to me. It just says water is condensed back to steam which is the same thing a wet system does too.

Krassen Dimitrov

I was thinking yesterday about Ausra in the Arctic/sub-Arctic, too. I love, it's totally crazy, yet it may make perfect sense... It's so crazy, I was sure that no one else was thinking about this, so I was very surprised to see you comment.

Do you know of anyone else to have thought of this? Any papers? Have you done any numbers on it? I'll appreciate it if you dropped me an e-mail at krassend@gmail.com


Cyril R.

Thanks Nucbuddy, that must be it. I recall something about the water triple point which would be that limit. Probably not very economical/practical to go that high with regards to material requirements. It wouldn't fit Ausra's philosophy of cheap and simple either.

Steve thanks for the insider info. I just can't wait till all these new solar thermal plants go on line and show their improved performance and economics.

KD there is one project called SHPEGS which also deals with solar thermal in arctic areas, but they're still working on it.

There certainly would be some advantages in cold arid climates. Some of these tundra climates are as reliable as any hot desert when it comes to direct insulation. Dry, very little cloud cover, predictable climate during most of the year. And that's what you want for a solar thermal electric plant. There will always be considerably less insulation than in places like the Mojave, but much lower ambient temps would make up some of the difference. I noticed a sweet spot in northern central Canada when I looked at some older climatic maps. Not sure if they're still valid. But it's right on the polar circle, just on the continent edge, close to arctic sea water with near-freezing temperatures all the time. The best heat sink you could ever get I'd reckon!

I was thinking it would be possible to use something like freon for a very efficient turbine (freon is liquid under very low temperatures which is perfect because we can cool really good in the arctic). I think more than 50% turbine efficiency would be possible but have to crunch the numbers and look at what turbine would be needed. I've looked into Kalina cycles which are sometimes used for binary geothermal plants using propane as working fluid. They seem suitable as they can operate quite efficiently under lower temperatures and can push the tmin lower.

That all could bring the economics of solar thermal in the arctic very close to those currently in good Mojave locations.

For the design, I think, as Steve has pointed out, that current line-focus designs will be problematic due to it's inability to tilt to the seasonal N-S variations of the sun. It would have to be radically realigned, almost vertically.

Perhaps something like this would be very suitable, with the tower on the south side. The mirrors would be very capable of following the low sun in the south.

I'll work some more on it in the next couple of days.

I have many more crazy ideas. Like, building solar thermal plants in the Tibetian highlands to lower liquid's boiling temps (because of lower vapour pressure in higher altitudes), potentially increasing thermodynamics and also stop most low altitude clouds from impeding output and... well that's a bit too far off right now :)

Cyril R.

One other advantage would be that during the summer the sun wouldn't set or only set for a little while, making power output more steady. Of course that's going to be exactly the problem in the winter with very little sun. But during the winter, air temperature is usually a lot colder so would make up some of that.

But I'll have to run some numbers with regards to radiation and yield.

Kit P

Bakersfield, CA—October 23, 2008—Ausra, Inc. (http://www.ausra.com) and California Governor Arnold Schwarzenegger today launched the company's Kimberlina Solar Thermal Energy Plant in Bakersfield, CA, showcasing the company's "next generation" concentrating solar thermal technology.


Kit P. writes on December 27, 2007 at 02:10 PM:
We will never have too worry about storage since wind and solar will never be more than 1% of US generation. This is based on the practical limitations of project development and maintenance.

And yet it has happened. Wind now accounts for more than 1% of US electricity generation. In 2008, 52 TWH of wind power was generated, out of a total of 4115 TWH generated from all sources. That's 1.2%, up from 0.8% in 2007.

Kit P

Wow, Clee in your zeal to suggest I am wrong you have failed to grasp the concept.

Drive to Ranch Seco and show me the wind and solar generation that has replaced the 900+ MWe of zero emissions from the nuke plant. For thirty years I have been listening to Californians talk about what they are going to do. Californians have a short attention span.

So Clee, has wind and solar grown to the point where storage is an issue? Will it ever? If you add storage, what will be the environmental and economic cost?

Thanks to Bush policies, 2007 and 2008 were very good years for renewable energy. However, demand for electricity is down about 1%. No it is not because Californians did a good job of conserving. What is your unemployment rate?

The CPUC just got done bragging about 500 MWe of new renewable energy as a result of the California RPS. However, 430 MWe was built outside of California. The jobs and new property taxes are welcome in places like Dayton, Washington. This is especially true since the asparagus processing plant shutdown.

Will Oregon and Washington become the eyesore of broken wind turbines that Altama Pass and the delta have become after Californian got bored with renewable energy and failed to maintain them?

Again Clee, I am a very strong advocate of renewable energy. I think we should continue to build renewable energy as fast as possible. I have friends who work in the wind industry. My company has wind and biomass divisions.

So if Clee you want to quibble about the third significant figure fine, if you want to explain why I am wrong about “This is based on the practical limitations of project development and maintenance” give it your best shot.


I'm not defending California. I'm talking about US generation. Yes, the PTC has been good for renewable energy. I don't know if wind or solar will grow to the point where storage will be an issue. Storage is not an issue at 1%. Yes, demand for electricity is down, but the wind generation of 52 TWH in 2008 is also more than 1% of the 4157 TWH consumed in 2007. So even if demand for electricity had not dropped...even if demand for electricity had grown at a brisk 15%, wind generation would still be more than 1% of US generation.

The 1% figure is no more significant or insignificant than when you chose to use it. I don't need to explain why you are wrong that "wind and solar will never be more than 1% of US generation. This is based on the practical limitations of project development and maintenance." because the US (or Bush, if you prefer) has shown in real life that are you wrong about it, not matter what the reason.


Does anyone know where the Aura production plant is located. I know its in las vegas, nv but was looking for the physical address. thanks

Cyril R.

Kit P you better put some suntan on that neck of yours it's getting extremely red.

Kit, if you don't understand the pattern of exponential growth then go back to high school but don't bother us with it anymore.




i think any development of electricity from solar energy is great


Great work on your blog. This article is too interesting. Thank you for sharing.


I can't believe how you people can allow retail pricing for selling excess PV back to the grid, if PV became pervasive. At some point that model just doesn't work economically.

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Nature has given us abundant energy in the form of solar power which is never ending and easily available in the form of Sun. It is best alternative energy to reduce the problem of scare resources.


In http://thefraserdomain.typepad.com/energy/2007/12/ausra-building/comments/page/2/#comment-94974266
Kit P wrote : wind and solar will never be more than 1% of US generation. This is based on the practical limitations of project development and maintenance.

Just one year later he was proven wrong when 2008 wind generation accounted for 1.26% of 2008 US generation, and 1.25% of the higher 2007 US generation.

Now in 2 more years, the US has proved Kit P wrong again by adding another 1% of US generation coming from wind, for a total of 2.30% of 2010 generation and 2.28% of the higher 2007 US generation.

In two short years the US had done a second time what Kit P said would never be done.

Building Material Suppliers

Would love to get something like this going in the UK. But the price of the panels just doen't make it worth implementing. I know that you can sell the power back to the grid, but you need the initial capital to start with.

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I am so glad they're building this facility!

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Did they finish this yet?

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Where in central california are they building this?

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Why are they building that in Vegas?

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Are these built yet?

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Ausra sounds like a good company, what are they doing now?


Seeing solar PV used at this scale is amazing... I wish that it was used in this scale more often. It is great to see this technology, and hopefully others will follow. We have been using Solar Thermal Heating in many of the houses that we build, and we get nothing but good reviews. Saving the environment while saving money!
This blog of ours actually shows how we used it in order to heat a large swimming pool which usually takes a lot of energy.



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