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> How would this work? Surely sunlight can't create enough heat to ionize a gas (creating plasma?). He isn't ionizing the gas, he is increasing the gas pressur

by gvb 16y ago

> How would this work? Surely sunlight can't create enough heat to ionize a gas (creating plasma?). He isn't ionizing the gas, he is increasing the gas pressure by heating it. "Only instead of using those pressure gradients to move an axle or a wheel, he’s forcing ions through a membrane." See next for why that is important. > Why don't the whole hydrogen atoms go through the membrane to the lower pressure area? He uses a semi-permeable membrane http://en.wikipedia.org/wiki/Semipermeable_membrane http://en.wikipedia.org/wiki/Semipermeable_membrane. They also have use in chemical applications such as batteries and fuel cells. The membrane blocks the atoms, but allows the ions (protons) through. It does require a substantial amount of pressure for it to work. That is where the heat -> pressure comes into effect, and why the reconstituted hydrogen on the "cold" size has to be compressed and pumped back into the "hot" side. While this sounds a little like a perpetual motion machine, it isn't because the sun's heat is adding the energy that is being extracted via the electrons. > How does he alternate which side is heated? How does he cool the other side? He heats one side and cools one side, no alternating. The heating (and cooling) cause a pressure differential, which drives the reaction via the semi-permeable membrane. --- I suspect there are some pretty substantial challenges remaining before this becomes a sizable / viable energy source. It sounds like it is related to proton exchange fuel cells, except instead of using the catalyst + oxidant to drive the reaction, it is using pressure. Refs: http://en.wikipedia.org/wiki/Fuel_cell#Proton_exchange_fuel_cells http://en.wikipedia.org/wiki/Fuel_cell#Proton_exchange_fuel_... http://auto.howstuffworks.com/fuel-efficiency/alternative-fuels/fuel-cell2.htm http://auto.howstuffworks.com/fuel-efficiency/alternative-fu...

tocomment 16y ago
So if the sunlit side is under higher pressure, how do the hydrogen atoms return to that side? I must still be missing something. Also, is there really enough hydrogen ionizing at 400C?
- gvb 16y ago
  > So if the sunlit side is under higher pressure, how do the hydrogen atoms return to that side? I must still be missing something. The article says it is compressed in order to move it back to the high pressure side. > Also, is there really enough hydrogen ionizing at 400C? I don't believe (traditional) ionization is occurring. My guess is that it works at the molecular level like reverse osmosis works with salt water to form fresh water. http://en.wikipedia.org/wiki/Reverse_osmosis http://en.wikipedia.org/wiki/Reverse_osmosis The dissociation of the hydrogen atoms into protons and electrons is through heat and pressure, facilitated by the semi-permeable membrane. Note that the membrane is key and is very unique. Johnson [...] proved he could make a ceramic membrane capable of withstanding temperatures above 400 degrees Celsius. A semi-permeable plastic membrane is non-trivial. A semi-permeable ceramic membrane that passes protons, strips electrons, and blocks hydrogen atoms while running at 400^C has to be really, really tough to do.
ajb 16y ago
Electrons are a lot smaller than protons. Why wouldn't they go through the membrane?
- grhino 16y ago
  Apparently, it's an insulated membrane that only lets protons through. A proton can move through the membrane more easily than an electron can. It has more to do with other properties of the material and the ions than the effective size of electrons vs protons.
  - gvb 16y ago
    Assuming my reference to proton exchange fuel cells is in the ballpark, the mechanism is to use the membrane plus pressure to separate the hydrogen into electrons and protons. The electrons are routed through the load, i.e. extracted electrical power, and the protons pass through the membrane. The inactive (non-dissociated) hydrogen molecules are blocked from the "cold" side by the semi-permeable membrane. The electrons and protons recombine on the cold side to reform hydrogen. That hydrogen has to be compressed sufficiently to move it back to the "hot" side of the system. This is probably a pretty substantial compression and will probably limit the efficiency of the system - it also raises the "perpetual motion machine" red flag in my mind, except the sun is adding lots of thermal energy to make it go for real. I'm picturing the system working at a molecular level like reverse osmosis of seawater: http://en.wikipedia.org/wiki/Reverse_osmosis http://en.wikipedia.org/wiki/Reverse_osmosis. Reverse osmosis requires a substantial amount of pressure (~1000 psi) to force the water through the semi-permeable membrane while the salt cannot pass through the membrane and thus stays on the salty side.

by gvb 16y ago

tocomment 16y ago

So if the sunlit side is under higher pressure, how do the hydrogen atoms return to that side? I must still be missing something. Also, is there really enough hydrogen ionizing at 400C?

gvb 16y ago
> So if the sunlit side is under higher pressure, how do the hydrogen atoms return to that side? I must still be missing something. The article says it is compressed in order to move it back to the high pressure side. > Also, is there really enough hydrogen ionizing at 400C? I don't believe (traditional) ionization is occurring. My guess is that it works at the molecular level like reverse osmosis works with salt water to form fresh water. http://en.wikipedia.org/wiki/Reverse_osmosis http://en.wikipedia.org/wiki/Reverse_osmosis The dissociation of the hydrogen atoms into protons and electrons is through heat and pressure, facilitated by the semi-permeable membrane. Note that the membrane is key and is very unique. Johnson [...] proved he could make a ceramic membrane capable of withstanding temperatures above 400 degrees Celsius. A semi-permeable plastic membrane is non-trivial. A semi-permeable ceramic membrane that passes protons, strips electrons, and blocks hydrogen atoms while running at 400^C has to be really, really tough to do.

ajb 16y ago

Electrons are a lot smaller than protons. Why wouldn't they go through the membrane?

grhino 16y ago
Apparently, it's an insulated membrane that only lets protons through. A proton can move through the membrane more easily than an electron can. It has more to do with other properties of the material and the ions than the effective size of electrons vs protons.
- gvb 16y ago
  Assuming my reference to proton exchange fuel cells is in the ballpark, the mechanism is to use the membrane plus pressure to separate the hydrogen into electrons and protons. The electrons are routed through the load, i.e. extracted electrical power, and the protons pass through the membrane. The inactive (non-dissociated) hydrogen molecules are blocked from the "cold" side by the semi-permeable membrane. The electrons and protons recombine on the cold side to reform hydrogen. That hydrogen has to be compressed sufficiently to move it back to the "hot" side of the system. This is probably a pretty substantial compression and will probably limit the efficiency of the system - it also raises the "perpetual motion machine" red flag in my mind, except the sun is adding lots of thermal energy to make it go for real. I'm picturing the system working at a molecular level like reverse osmosis of seawater: http://en.wikipedia.org/wiki/Reverse_osmosis http://en.wikipedia.org/wiki/Reverse_osmosis. Reverse osmosis requires a substantial amount of pressure (~1000 psi) to force the water through the semi-permeable membrane while the salt cannot pass through the membrane and thus stays on the salty side.