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solar PEM generator

solar PEM based electrical generator
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Device composed of a sun concentrator (parabolic mirror or fresnel lenses) and two vessels containing hydrogen and which are comunicated to a PEM (proton exchange membrane) electric conversion device.

The idea is basically to generate differential pressure between the two hydrogen vessels and convert the resulting hydrogen flow into electricity thanks to the PEM device.

The cycle would be:

1) Concentrated sun heats hydrogen filled vessel.

2) Hydrogen heats to high temperature and pressure within the vessel rises several times above 1 bar.

3) Valve is open and high pressure hydrogen passes through a PEM device to a secondary refrigerated vessel. The hydrogen protons pass through the PEM while the electrons pass through a charge from anode to cathode. So, an electric current is generated.

3) The flow stops when pressure in both vessels is balanced, and therefore the current flow drops to zero. Now the hydrogen density is much higher in the refrigerated vessel.

4) We close the communication valve and switch the position of vessels, exposing to concentrated sun the previously refrigerated one and viceversa.

Return to 1)

Notice that after the first cycle the efficiency increases as pressure in the refrigerated vessel will fall well below 1 bar at the end of phase 2.

Similar to stirling cycle without moving parts. Potentially better efficiency compared to solar stirling engine driven generator, as there are just two conversion transitions(radiation-heat-electricity) instead of three (radiation-heat-mechanical-electricity).

Any comments?

rpardell, Sep 01 2003

Whispertech http://www.whispertech.co.nz/
combined stirling engine/gas boilers [scubadooper, Oct 04 2004, last modified Oct 21 2004]

Roof Garden Roof_20garden
Converting heat energy into chemical energy [madness, Jan 25 2005]

PEM fasteners http://www.pennfast...ners+for+Sheetmetal
[normzone, Jan 25 2005]

[link]






       So it's a hydrogen steam engine?
phoenix, Sep 01 2003
  

       PEM must be saturated with water in order to pass protons.
lurch, Sep 02 2003
  

       Where do you get the power to run the refrigerator?
Freefall, Sep 02 2003
  

       a combination of stirling engine and fuel cell?
scubadooper, Sep 02 2003
  

       I maybe explained myself not very well.   

       1) When I said refrigerated i just meant cooled to ambient temperature, so 300K, through a radiator, no energy consumed.   

       2) The problem of PEM water management must be managed somehow, but it doesn't seem to be more severe than in a PEM hydrogen fuel cell. The hydrogen just swaps from one vessel to the other (from hot to cool), so basically a fixed amount of water can be vaporised in the hot side and condensed in the cool one.
rpardell, Sep 02 2003
  

       To scubadooper:   

       Yes , it is something like mixing a solar powered stirling engine with a PEM fuel cell. The technology is at hand. The difference with a stirling is not using a displacer and that there is no working piston but a PEM based electrical generator instead. Maybe a possible derivative would be to use a displacer instead of switching vessel positions, then it would be more like you say.   

       I am thinking about a long cycle, like 10 seconds or more, and very high working temperatures in order to achieve over 60% system efficiency. With switching vessels instead of displacer the heat losses can be much less than in a stirling cycle machine.
rpardell, Sep 02 2003
  

       Hmm, sounds like a lot of development work for not much gain.
scubadooper, Sep 02 2003
  

       To scubadooper:   

       Anything that raises the system efficiency of a solar energy conversion system is worth a world. Mean irradiance is 1kW per square meter, but nowadays you can only get from 100W to 200W out of it, in the best conditions.   

       The main problem of solar energy is that photovoltaics present very low operational efficiency ranges from 10% to 20%. Lots of peopple all around the globe stress their brains in order to find better ways of converting sun to electricity, as the thermodinamical theorethical limit stands very much higher than this poor 20%. Besides this, any concentration system has the advantadge of being more cost efficient, in general.   

       At present, best efficiencies have been obtained with parabolic concentrated stirling systems, reaching between 30% and 40% operational efficiency.
rpardell, Sep 02 2003
  

       Increasing solar energy efficiencies is currently a waste of time, you'd be better off (from an ecological and a power grid reliability point of view) implementing a distributed electrical generation infrastructure (check out the link to whispertech.)   

       The next thing to worry about would be greater efficiency during end use of the generated power.   

       Solar power, in my opinion, doesn't offer any great advantages other than in a couple of specialised locations globally, where they're used with steam turbines. Big containers of extremely hot hydrogen, would not give me much confidence in their reliability.
scubadooper, Sep 02 2003
  

       To scubadooper:   

       I won't argue about the benefits of solar energy, as they are obvious to anyone, in particular for a decentralised energy system, as you propose.   

       My idea is about a small system, that can be constructed in the 1 to 30kW power range, and so the ammount of stored hydrogen would be in the order of 1 MOL. This is as dangerous as having a lighter gas bottle at home, with the difference that the solar device would be over the roof and not inside home.
rpardell, Sep 02 2003
  

       How big do you plan the reflectors to be????
scubadooper, Sep 02 2003
  

       To scubadooper:   

       Good point. I think the best system would be a 3kW system, given 60% efficiency this would mean a 5 square meters of parabolic dish would be needed, this is going to be aprox a 125 cm radius dish. The dish would track the sun automatically, being this technology commercially available.   

       In Europe this system would generate surplus energy (more energy than consumed by a medium household). At least in Spain you can sell to the power company the energy generated at a price over the market.   

       This system has some advantages over photovoltaic pannels:   

       1) You need much less surface than with photovoltaics given the same ouptut.   

       2) It is more efficient as it can track the sun. You get more kWh per annum given the same nominal power.   

       3) It is less dependent on house configuration, as it can work as well on flat as pointed roofs.   

       4) It has an easier installation, being it like installing a big parabolic anthenna. In fact the commercually available tracking mechanisms derive from satellite anthenas.   

       5) It would have a lesser visual impact. This is quite important as many people refuses photovoltacis on this superficial basis.
rpardell, Sep 02 2003
  

       rpardell: I know it has been awhile on this discussion, but I completely agree with you that there needs to be a NEW approach to the generation of useful power from the sun. If you could acheive near 60% efficiency with something like this, you could revolutionize the industry.   

       Where can I learn more about PEMs?
mwoods, Jan 24 2005
  

       You are discussing generation of electricty by using a fuel cell membrane. Is it not possible to use the heat to drive a reversable endothermic chemical reaction? From an ecological point of view the Sabtier process is probably the best since it will scavenge C02 from the atmosphere...
madness, Jan 25 2005
  

       Hmm does the sabatier also work with earth atmosphere? I remember reading something about this as a proposal to produce fuel for rovers on mars.   

       But there is less CO2 in the atmosphere yet than on mars. Maybe we should wait until it gets more...
Fledi, Jan 25 2005
  
      
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