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UnusualAttitude

Mont Louis Solar Furnace

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Hey there. I'm on summer holiday in the Pyrenees at the moment and today I had the chance to visit something pretty darn impressive that I was, until now, almost completely ignorant about: a Solar Furnace.

By reflecting the abundant Pyrenean sunlight onto a concave array of mirrors, which focus the solar energy into a single point, temperatures of more than 3,000°C can be achieved in just moments. This is our guide Thomas demonstrating how if you place a simple wooden plank at the focal point, it instantly bursts into flame...

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A wider view showing just how impressive the concentrating array is, and this is only the small prototype that generates 50kW. It was built in 1949 by Félix Trombe who then went on to design its 1MW big brother in Odeillo, which has also been used for research, including testing aerospace materials for resistance to re-entry.

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The Mont Louis furnace is now mainly used for more mundane activity of pottery firing. On the day of our visit, a short power cut that morning had caused the computer that keeps the heliostat mirrors facing the sun to reboot, and the focal point to shift from its usual spot at the front of the furnace. If you look at the damage to the right of the furnace, you can see how the power of the sun has simply melted through the cast iron. Looks a bit like something Qui-Gon Jinn would do with his light sabre. That's hot.

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Edited by UnusualAttitude

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That... is impressive. Very, very impressive! (Such concentrated energy - and they still need a mains supply!)

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3 minutes ago, softweir said:

That... is impressive. Very, very impressive! (Such concentrated energy - and they still need a mains supply!)

I did ask if such a contraption could be used for generating electricity. Apparently you could, if you put a turbine in place of the furnace. But the focal point is literally just that - a single point - and this would defeat the purpose of having a furnace in the first place.  

The question I should have asked,  I suppose,  was "what would the vacuum ISP of such an array be, if used to heat liquid hydrogen / methane / ammonia and expel it through an exhaust...?" 

But that would have earned me strange looks from the rest of the group of visitors.... :D

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3 hours ago, UnusualAttitude said:

I did ask if such a contraption could be used for generating electricity. Apparently you could, if you put a turbine in place of the furnace. But the focal point is literally just that - a single point - and this would defeat the purpose of having a furnace in the first place.  

The question I should have asked,  I suppose,  was "what would the vacuum ISP of such an array be, if used to heat liquid hydrogen / methane / ammonia and expel it through an exhaust...?" 

But that would have earned me strange looks from the rest of the group of visitors.... :D

You can use this system for producing power, its used some places but having long lines with curved mirrors heating an pipe are cheaper and easier to maintain, also less dangerous :)
Using the heat directly is more efficient but will only work then the sun is shining. 
Vacuum IPS can be up to 1000 s or as an good nerva 


 

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wow.... instant sun tan = instant death!

That is impressive... you could boil water to generate power with a steam turbine... it would be very Green except for the heat it creates.

5 minutes ago, magnemoe said:

You can use this system for producing power, its used some places but having long lines with curved mirrors heating an pipe are cheaper and easier to maintain, also less dangerous :)
Using the heat directly is more efficient but will only work then the sun is shining. 
Vacuum IPS can be up to 1000 s or as an good nerva 


 

Except, water stores heat efficiently so maybe they can figure out a way .... maybe.

 

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3 minutes ago, kiwi1960 said:

wow.... instant sun tan = instant death!

That is impressive... you could boil water to generate power with a steam turbine... it would be very Green except for the heat it creates.

Except, water stores heat efficiently so maybe they can figure out a way .... maybe.

Not at 3000 degree :)
Many solar thermal plants store energy as heat often by melting salt who can then be used to heat water after sunset, benefit of melting salt is that the phase change absorb and release lots of energy and melting point is enough for high pressure steam.
 

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We should build at least one solar thermal rocket. It would have even more sunlight if used near Venus's orbit. Hmmm... Venus-Earth space tug?

Heating up liquid hydrogen could work well. Depends.

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4 hours ago, kiwi1960 said:

 

That is impressive... you could boil water to generate power with a steam turbine... it would be very Green except for the heat it creates

 

It doesn't create any heat. It just focuses what is already there on a larger area and shoves it in one spot.  Total energy is exactly the same.

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2 hours ago, Shpaget said:

It doesn't create any heat. It just focuses what is already there on a larger area and shoves it in one spot.  Total energy is exactly the same.

Exactly,  and on a small tabletop demonstration rig we were shown how you can place your bare hand just a few centimetres behind the focal point and feel just a slight warmth. But at the focal point itself, you can burn a hole through titanium... Freaky. Don't try this at home, kids... 

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A good beginning for a Martian ship.

Spoiler

Korolev's TMK project, with solar concentrators (1964 version)  (in Russian).

32-33.jpg

 

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Hmm... Death-rays XD

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For those who think this is "so powerful", a cold shower - just because something is superhot, doesn't mean it's packed with energy. Power is energy delivered divided by the time it has been delivered in. That means that you can get enormous powers if you use short enough timespan during your measuring.

Example - lasers. They can heat up targets at millions of kelvins because they release a certain amount of energy in a very short pulse (picosecond bursts, for example).

 

Temperature ≠ heat :wink:

 

On 25.07.2016. at 2:32 AM, magnemoe said:

Not at 3000 degree :)
Many solar thermal plants store energy as heat often by melting salt who can then be used to heat water after sunset, benefit of melting salt is that the phase change absorb and release lots of energy and melting point is enough for high pressure steam.
 

And it has been determined that such power sources are extremely expensive to the point of complete financial loss. I was surprised, too.

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Australia was leading the research into these kind of solar power plants for a short while.  Australia has some of the hottest and driest places on the planet, so you'd think solar would be a pretty good bet...  But there's also mega-tonnes of coal to be dug up first unfortunately.

Edited by Red Iron Crown
No politics, please.

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On 7/26/2016 at 1:51 AM, lajoswinkler said:

For those who think this is "so powerful", a cold shower - just because something is superhot, doesn't mean it's packed with energy. Power is energy delivered divided by the time it has been delivered in. That means that you can get enormous powers if you use short enough timespan during your measuring.

Example - lasers. They can heat up targets at millions of kelvins because they release a certain amount of energy in a very short pulse (picosecond bursts, for example).

 

Temperature ≠ heat :wink:

 

And it has been determined that such power sources are extremely expensive to the point of complete financial loss. I was surprised, too.

Don't forget that doing such just moves electricity generation from peak need (because air conditioners will be trying to cool buildings that are being heated the same way the furnace is) to less than peak need.  Not such a great idea (although probably necessary to build generators at a reasonable cost).

I'd be more interested in reflecting mirrors into (PV) solar panels.  Since Hawaiian panels get at least twice the power as (non-desert) continental US panels (or at least where I live), I'd assume that concentrating 2-4 mirrors into one PV would make sense (that you can find mirrors cheaper than PVs).  You might have to move the PVs (which would be a pain/cost/whatever) or wildly overprovide on mirrors.  Or you do the same with some sort of cheap fresnel lens (again, expect to "overprovide", especially if you plastic filters important wavelengths), but this should be easier to move (or sufficiently overprovision that it doesn't matter).

Note: if you go the "overprovide and don't bother moving" route, make sure that the concentrated rays that miss the PV aren't melting anything.  Either run hot water lines (for cooling) or reflective surfaces.

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6 minutes ago, wumpus said:

Don't forget that doing such just moves electricity generation from peak need (because air conditioners will be trying to cool buildings that are being heated the same way the furnace is) to less than peak need.  Not such a great idea (although probably necessary to build generators at a reasonable cost).

I'd be more interested in reflecting mirrors into (PV) solar panels.  Since Hawaiian panels get at least twice the power as (non-desert) continental US panels (or at least where I live), I'd assume that concentrating 2-4 mirrors into one PV would make sense (that you can find mirrors cheaper than PVs).  You might have to move the PVs (which would be a pain/cost/whatever) or wildly overprovide on mirrors.  Or you do the same with some sort of cheap fresnel lens (again, expect to "overprovide", especially if you plastic filters important wavelengths), but this should be easier to move (or sufficiently overprovision that it doesn't matter).

Note: if you go the "overprovide and don't bother moving" route, make sure that the concentrated rays that miss the PV aren't melting anything.  Either run hot water lines (for cooling) or reflective surfaces.

Think the problem with mirrors is that it also require that you aim at the sun, you could probably use lenses and strips of PV however this would fast cost as much as more PV material. 

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24 minutes ago, magnemoe said:

Think the problem with mirrors is that it also require that you aim at the sun, you could probably use lenses and strips of PV however this would fast cost as much as more PV material. 

Huh.  Some quick googling implies that even "cheap magnifying glass" lens material might not be cost effective.  I was expecting that to be much cheaper, like "included in a cereal box because it's cheaper than cereal" cheap.  I still suspect that in quantity it would make sense, but only for PV systems not at all constrained by roof size (probably a minority of solar usage).

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Oh, I forgot to mention that giant solar power plants that use single tower to melt salts are not eco friendly. They are actually quite horrible. The insects are attracted to the intense brightness of the focused beams and burned. Same goes for every bird that follows the insects. They burn up in the air.

Long trough type solar concentrators can be very easily made to track the Sun, they require only one axis and multiple rows can use same drive and tracking mechanism.

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