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54 comments on Cogeneration At Home: Ceramic Fuel Cells And Bloom Energy
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54 comments on Cogeneration At Home: Ceramic Fuel Cells And Bloom Energy
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You people are behind the times on stirlings vs fuel cells. Why not? There is too little on the web that is up with it, so I will fill you in.
1) stirlings have beaten fuel cells in recent head to head contests on a lot of things like CHP and small battery replacers and such-like little power generators. Stirlings are fuel insensitive ( run fine on diesel, or wood chips) and last a long time- many years -and are fairly efficient (maybe 20% + efficient system fuel to electricity at 100 watts out).
2) They are just metal, no magic membranes or any such $$ stuff needed. Very ordinary kinds of hardware we all know and love. No fundamental reason a stiring should cost more than a couple of times an IC of same power (needs some hot metal the IC does not need)
3) Built right (that is, free piston, not cranks), they are nearly silent and vibration-free.
4) They are way more than just a stop-gap. Anywhere fuel is being burned, a stirling could get a good bit of the available energy from that heat as electricity. This goes for now- and forever.
5) Stirlings are good for solar. Very good. and getting better.
6) "If they are so good, why can't I buy one?" Dunno. Ask the money people. Meanwhile, read the blurbs.
http://www.infiniacorp.com/technology/index.php
http://www.sunpower.com/
You don't believe me. The stuff up there is just company brags. "Where is your reference?" Hey, it's Sunday; I am not being paid for this. I hit a few search questions and didn't get what I wanted. That does not mean I am wrong- just lazy. You do it- it's out there somewhere.
It's a stop-gap because architecture is bound to eliminate most of the need for heat through improved design.
EP. First, thanks again for all your good work.
What I mean here is that if you are using something that generates a lot of available energy and does not use it, such as for example, any combustion process used for mere low temp heating, then you can get some of that available energy by a stirling. I am sure you are fully aware of that.
Of course, to do combustion for just low grade heat is atrocious in the first place, but done all the time. And I completely agree that building heating need not be in the first place, if good design is used. Trouble is, we live in a highly unoptimized world. Wish it were not so.
But my real message, somewhat filppantly delivered, is that stirlings have got pretty good, and deserve a bit more recognition/use than they are getting. And of course, so also for some fuel cells, although I personally believe the merits of fuel cells are not equal to the hype/$ they have received. A wholly prejudiced remark, of course, from one who might, if extremely lucky, get some financial reward from any market success of stirlings.
If you really want to get efficient, you could always use a Stirling engine as a bottoming cycle to recover work from the off-heat from an SOFC. IIRC, this is already being done with small gas turbines on MCFCs (but at a scale much too large for heating individual homes).
SOFCs and MCFCs can do things Stirlings cannot: they can extract electricity at high efficiency and supply the waste heat at temperatures high enough to perform lots of industrial processes (it's hard to bake coatings or anneal metal with the hot water from a Stirling). The difficulty I see with Stirlings is that they're mechanical, and present problems over and above those already solved in combustion engines. I'd love to have one that runs off a wood stove and generates a couple kW, but I don't expect to be able to buy one with anything like the 10-year warranty I'd consider minimal.
Ok, how about 15 years continuous run w/o mantenance? That's what NASA demands and will get from its isotope heated stirlings. By that time, anything is obsolete and should be replaced just for that reason alone.
As for the wood stove, right, just what I have been working on, and actually have got, except its cost is a bit high, maybe 50K for that one-off prototype. But if you take the material cost and multiply by an experience factor, you get a good number mere mortals can afford- around 2K/kW for the whole thing, wood burner included-- with a load of nice dry hardwood as bonus. Smoke free, of course.
But all that is mere fun and games. The real serious target is solar thermal in the desert. I am putting my bets on stirlings to beat all at that application. Fuel cells need not apply.
Just two questions:
I've got nothing against Stirlings, but it looks like the fuel cells are headed for the consumer market faster.
Are you talking about SOFCs? What evidence do you have that they are close to the consumer market? I certainly do not regard the above post as such evidence. At least Whispergen is selling Stirling generators in the yachting market with reasonable warranties. I am not trying to defend Stirlings which I do not believe will make much impact in the CHP market. I just haven't discovered any evidence that SOFCs are close to being ready for prime time.
Among other efforts, Delphi is developing SOFC units for vehicular APUs and other uses. These 2-6 kW units are in the ideal size range.