4 ms·

The high temperature needed for industrial processes like making concrete is a perfect fit for concentrated solar furnaces. That's because there is a thermodyn

The high temperature needed for industrial processes like making concrete is a perfect fit for concentrated solar furnaces. That's because there is a thermodynamic loss in taking heat energy to another form like electricity and back again. That's why natural gas heating is roughly 2-4 times cheaper than electric heating. I don't understand why every factory in the world doesn't have one of these attached to it to save close to 100% of their fuel costs for 4-8 hours of the day: https://en.wikipedia.org/wiki/Solar_furnace https://en.wikipedia.org/wiki/Solar_furnace Some formulas on concentrator efficiency: https://en.wikipedia.org/wiki/Concentrated_solar_power#Efficiency https://en.wikipedia.org/wiki/Concentrated_solar_power#Effic... https://www.osapublishing.org/DirectPDFAccess/465BBDC3-CD88-DB70-A7D010CB8BBB020B_198416/oe-18-S1-A5.pdf?da=1&id=198416&seq=0&mobile=no https://www.osapublishing.org/DirectPDFAccess/465BBDC3-CD88-... (PDF): http://www.desware.net/sample-chapters/d06/e6-106-05.pdf http://www.desware.net/sample-chapters/d06/e6-106-05.pdf (PDF): https://core.ac.uk/download/pdf/82769819.pdf https://core.ac.uk/download/pdf/82769819.pdf It looks like the highest temperature achievable for a trough-shaped solar collector is about 400 C, whereas for a parabola, it's closer to the temperature of the sun (at least 2000 C). Note that the maximum possible temperature achievable for any concentrator is the temperature of the source, by the laws of thermodynamics: https://physics.stackexchange.com/questions/279146/what-can-we-deduce-by-the-fact-that-mirrors-cannot-get-a-ray-hotter-than-suns-s https://physics.stackexchange.com/questions/279146/what-can-... I don't have time at the moment, but maybe someone could derive the maximum temperature for a parabolic trough? I feel like it might be approximately the square root of a parabolic dish, but I don't know for certain. I could put together buying ferrock in large quanties (over $1 million) because of the many bike paths and greenbelts that still need to be poured along the river, canals and train tracks in my city. But using concrete or asphalt is perhaps too environmentally unfriendly, and I haven't found a good alternative (say pavers) because we still want people to be able to skate and have a comfortable bike ride. We also have football field-sized piles of glass bottles waiting to be recycled that would be another free input along with solar heat.

Armisael16 8y ago
What are you going to make your crucible out of that is transparent, won’t contaminate the contents and is strong enough at high temperatures to withstand regular use? Also if it wasn’t available 20 years ago there’s your reason.
- zackmorris 8y ago
  My first thought was maybe silicon carbide, since it can be made with readily available silicon and carbon. But there are other caramics which have much higher melting points. Who wants a little hafnium carbide at 3958 C haha: https://en.wikipedia.org/wiki/Ultra-high-temperature_ceramics#Physical_properties https://en.wikipedia.org/wiki/Ultra-high-temperature_ceramic... I'm having trouble finding infrared conductivities: https://global.kyocera.com/fcworld/charact/heat/thermalcond.html https://global.kyocera.com/fcworld/charact/heat/thermalcond.... So looks like aluminum nitride might be best (first made in 1877 so we have the technology!) with a melting point of 2200 C: https://en.wikipedia.org/wiki/Aluminium_nitride https://en.wikipedia.org/wiki/Aluminium_nitride Portland cement (the basic ingredient of concrete) is made at 1450 C: https://en.wikipedia.org/wiki/Portland_cement#Manufacturing https://en.wikipedia.org/wiki/Portland_cement#Manufacturing And looks like any aluminum from the crucible wouldn't contaminate the concrete. Not sure about the nitrogen, but since the air is nitrogen/oxygen, it should be ok: https://www.tandfonline.com/doi/pdf/10.3130/jaabe.10.217 https://www.tandfonline.com/doi/pdf/10.3130/jaabe.10.217 But I think it's important to flip the problem on its head. Since solar thermal energy is essentially free after the solar furnace is manufactured, then we might as well scale it up to provide 2-10x more heat than we need, and then choose a ceramic with the material properties we want, even if its thermal conductivity isn't as efficient as we'd like. Keep in mind that any heat we get from this will be roughly 4 times cheaper than from photovoltaics (running at 25% efficiency) since we avoid the light->electricity->heat conversions.
  - Armisael16 8y ago
    You seem to have a fundamental misunderstanding about how crucibles operate. The outside of the crucible is not supposed to get particularly hot. Heat is applied to the inside; the crucible contains both the material and the heat. If you don’t do this then all the air in the room is also heated up to ludicrous temperatures, and that tends to be bad for any other equipment or people nearby.

Armisael16 8y ago

What are you going to make your crucible out of that is transparent, won’t contaminate the contents and is strong enough at high temperatures to withstand regular use? Also if it wasn’t available 20 years ago there’s your reason.

zackmorris 8y ago
My first thought was maybe silicon carbide, since it can be made with readily available silicon and carbon. But there are other caramics which have much higher melting points. Who wants a little hafnium carbide at 3958 C haha: https://en.wikipedia.org/wiki/Ultra-high-temperature_ceramics#Physical_properties https://en.wikipedia.org/wiki/Ultra-high-temperature_ceramic... I'm having trouble finding infrared conductivities: https://global.kyocera.com/fcworld/charact/heat/thermalcond.html https://global.kyocera.com/fcworld/charact/heat/thermalcond.... So looks like aluminum nitride might be best (first made in 1877 so we have the technology!) with a melting point of 2200 C: https://en.wikipedia.org/wiki/Aluminium_nitride https://en.wikipedia.org/wiki/Aluminium_nitride Portland cement (the basic ingredient of concrete) is made at 1450 C: https://en.wikipedia.org/wiki/Portland_cement#Manufacturing https://en.wikipedia.org/wiki/Portland_cement#Manufacturing And looks like any aluminum from the crucible wouldn't contaminate the concrete. Not sure about the nitrogen, but since the air is nitrogen/oxygen, it should be ok: https://www.tandfonline.com/doi/pdf/10.3130/jaabe.10.217 https://www.tandfonline.com/doi/pdf/10.3130/jaabe.10.217 But I think it's important to flip the problem on its head. Since solar thermal energy is essentially free after the solar furnace is manufactured, then we might as well scale it up to provide 2-10x more heat than we need, and then choose a ceramic with the material properties we want, even if its thermal conductivity isn't as efficient as we'd like. Keep in mind that any heat we get from this will be roughly 4 times cheaper than from photovoltaics (running at 25% efficiency) since we avoid the light->electricity->heat conversions.
- Armisael16 8y ago
  You seem to have a fundamental misunderstanding about how crucibles operate. The outside of the crucible is not supposed to get particularly hot. Heat is applied to the inside; the crucible contains both the material and the heat. If you don’t do this then all the air in the room is also heated up to ludicrous temperatures, and that tends to be bad for any other equipment or people nearby.