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Temperature benefit of Evacuated Solar Tubes


bobbyF
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Hi there,

From what I've read, typical temperatures of Evacuated Solar Tubes used in Steam Turbine Plants (using solar trough linear concentrators), reach about 200 degrees Celsius (392 F).

Is there any benefit to increasing this temperature any further? If for example the temperature was 500C, or 1000C, what would this mean in terms of efficiency or power output capacity for the steam turbine or the plant power generation..?


Cheers.

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2 hours ago, bobbyF said:

From what I've read

Where have you read this and where does one of these run?

Here they run horizontal piping in the focal point of long parabolic reflectors and melt salt, that's around the 500degC mark, then running water piping through the molten salt storage container, creates the steam required. See Bokpoort down the drag from here...

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Hi @Kalahari Meerkat,

Thanks for the reply.

What I meant by Evacuated Tubes, perhaps due to my lack of experise, is this kind of power plant:

http://large.stanford.edu/publications/power/references/docs/Andasol1-3engl.pdf

This is a very detailed article about this kind of tech, but if you search "400" you'll see that they say that the fluid being heated gets to 400C, so my estimate of 200C was actually an error because I was referencing some data about water-heaters that I found that also use this technology of evacuated tubes.

 

In any case, the question is the same. Let's say that you can heat up the fluid in the pipes to 400-500C currently. What happens if you can heat it to 1000C? Do you get more efficiency from the power plant as a whole due to less need to heat the salt? or excess heat that you can use? of higher operating temperature for the steam or fluid and therefore more 'bang for you buck' in terms of power concentration?

 

Thanks

 

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2 hours ago, bobbyF said:

Let's say that you can heat up the fluid in the pipes to 400-500C currently. What happens if you can heat it to 1000C?

I'd guess at that point you need to start looking more critically at the melting point of materials you could use in the construction of the turbine and piping (steel 1500C, copper 1100C), or at least what stresses the materials can withstand at that temperature, and for how long.

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Ok, the troughs in the linked document are probably 3m edge to edge and presumably the temperature zones where these are being deployed are somewhat cooler climate zones, I'm guessing... (only briefly looked at this, didn't really read anything).

The troughs on the installation at Bokpoort, are less than 0.5m edge to edge and the piping in the focal point was probably not more than 50mm diameter, all in stainless steel, I think...

The obvious question is, to what contortions do you have to go to achieve higher temperatures? and is the outcome worth it? Even the steam turbine will have to be engineered to deal with higher temperatures and presumably varying temperatures, since you won't be able to keep temperatures at your higher specified number 24/7. Common sense says that higher temperature should generate higher power, but how much and is it worth it?

There are various other CSP's around this neck of the woods and some have mirrors illuminating the concentrator at the top of a tower, these could well generate higher power, but Bokpoort it the only one I'm aware of that is specced to deliver power nearly 24/7, whereas the others don't go much beyond sunset... if you are looking at this from a commercial perspective, you're probably on the wrong forums and presumably will have to pay some engineers elsewhere to do some calculations and designs for you, if you are doing this for your own use, homebrew styles to generate your own electron stream, cool, keep us up to date, I'm sure lots of people would be interested in this, just I think, it ain't all that practical and achievable to attempt this on a small scale for own use, but I'll happily be proven wrong and would look at an installation myself if it can be shown to be doable without having staff on hand checking on things and making sure nothing goes wrong....

Think water supply, clean water supply, otherwise sludge potentially causing the end of various parts of the steam & turbine chain etc.

Sorry, not an engineer and never worked for the railways neither....

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Hmm..

Thanks for the illuminating answers guys.

A bit of another tangent question - let's take a current trough power plant with 400C tubes now operates with around 8h of sunlight and the rest it tries to make up with salt storage etc..

If we somehow keep the 400C constant (let's just assume this for the thought experiment's sake), does that mean that the power plant can operate 24/7 without the salt storage?

Relatedly, does anyone know what that would mean in terms of upfront costs or operating costs? meaning, what % of the total cost to build the power plant is the linear array and what % is the salt tanks and equipment related to that?

 

 

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9 hours ago, bobbyF said:

Hmm..

Thanks for the illuminating answers guys.

A bit of another tangent question - let's take a current trough power plant with 400C tubes now operates with around 8h of sunlight and the rest it tries to make up with salt storage etc..

If we somehow keep the 400C constant (let's just assume this for the thought experiment's sake), does that mean that the power plant can operate 24/7 without the salt storage?

Relatedly, does anyone know what that would mean in terms of upfront costs or operating costs? meaning, what % of the total cost to build the power plant is the linear array and what % is the salt tanks and equipment related to that?

 

 

Anybody who is event remotely close to implementing this would be able to do this calculations themselves, so I'm not sure what you're after here? Is it just some mental gymnastics?

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Haha,

thanks.

I'm just a curious person without much knowledge on the subject.

I was wondering what can happen if you come up with some innovative way to keep the temperature from falling at night or raise it high enough so that it's still warm during the night until it cools.

I guess if somehow the tube rotated with the Earth (in a thought-experiment scenario) then the sun would keep it heated and therefore the power plant would be simpler in terms of the salt storage process.. right?

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