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Tough Parabola Model - Page 2

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Posted by Morris Dovey on October 12, 2007, 12:01 am
 
Jeff wrote:

|    Living in a hazy area myself, I wonder about the indirect
| fraction of sunlight. I suppose that for a normal geometry absorber
| (ie round) that this would simply be thrown away. Anyone done any
| more looking into those compound parabola reflectors?

|    What do you figure the working temp for your stirling should be
| about? The fact that you are getting 700F almost seems like you
| should be using a different working fluid than water. At any rate,
| it seems like the parabola is a big success!

The working temperature for the fluidyne seems to be in the 115F to
130F above ambient (ambient being the temperature the cool side is
trying to maintain) - but that will probably change as the design is
improved.

[ It's important to remember that Stirlings work off the _difference_
in temperature between their hot side and their cool side - not at
some fixed pair of temperatures.

It's also worth noticing that a measure of the power produced is the
amount of energy transferred from the hot side to the cold side (and
dissipated from the cold side). ]

That we can produce 700+F temperatures doesn't oblige us to run the
hot side at 700F - we're still free to mix that hot air with other air
to run the engine at lower temperatures!

You're absolutely right that we don't want to exceed the boiling point
of our working fluid - but (because of our application) we'd prefer to
stay with water and keep the hot side temperature below 212F.

The trough was built at the start of the project, but probably won't
be used in our final solution. I've more and more strongly favored a
flat panel solution because it can supply the needed energy much more
reliably, safely, and less expensively.

I've kept the trough web page on the site because of the number of
people who seem interested in how one might be built - and because
there are already plenty of photos of flat panel collectors scattered
about the web site. :-)

There are other fluidyne applications for which we're considering
other engine construction materials (concrete and steel are two of
them) and other working fluids.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/



Posted by Jeff on October 12, 2007, 2:57 am
 
Morris Dovey wrote:


   That does sounds like in the range of a good flat plate.

   Thats interesting. But it makes sense.

  I see your point of going with a more conventional collector. I do
like the idea you are thinking of other working fluids.  If you choose
to use    the higher temps of the trough it seems that you could be very
competitive if not above the efficiency of PV. I see that there are some
midscale trough power generation experiments going on. It's nice to see
that you are working on the solution for the 50% or so of the world that
lacks reliable power.

   Jeff







Posted by Morris Dovey on October 12, 2007, 5:31 am
 Jeff wrote:

| If you
| choose to use    the higher temps of the trough it seems that you
| could be very competitive if not above the efficiency of PV.

Actually, the trough is /less/ efficient (more lossy) than the flat
panels I've been building - remember that temperature isn't a synonym
for energy, and that a flat panel with the same area as a trough
intercepts the exact same amount of radiation.

A trough-type concentrator would probably win a water-boiling contest,
but a PV panel is difficult to beat for powering your PC. There's a
real need to maintain a sensitivity to the particulars of the
individual _applications_ of solar energy. AFAICT, there's no single
"magic bullet" that'll let us solve all our energy problems.

| I see
| that there are some midscale trough power generation experiments
| going on. It's nice to see that you are working on the solution for
| the 50% or so of the world that lacks reliable power.

I come at it a little differently. It's not so much that the third
world lacks reliable power, as that they lack water and food (because
of the lack of water). They're obliged to expend all their energy just
to not starve - and too many starve anyway. If subsistance can be made
a non-problem, then they'll be better able to deal with the other
problems (like lack of reliable power). Availability of adequate water
supplies, where and when needed, should help a lot.

I'm not altruistic about all this. There are a _lot_ of potential
applications for solar thermal energy - and there are a lot of
applications for which solar-powered Stirling cycle engines can
provide first rate solutions, and there're a number of these latter
for which solar-powered fluidynes offer significant advantages. I'm
working to solve the pumping problem as a learning exercise - but when
that exercise has been completed, I hope to have learned enough to
tackle some of the more technically demanding - and profitable -
applications.

Maybe I'll get there, maybe not - but it seems worth a try.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/



Posted by no spam on October 11, 2007, 3:58 pm
 
A while back I posted a msg about one with a strange shape, I can't remember
the mathematical equation it was based on, but the article I found it in
said it was the best shape to use if you wanted the most heat without having
to use a tracking system.

It was more aimed (bad pun) at using larger targets such as the type used in
solar water heating.  If you are trying to get the most heat you are going
to need a nearly perfect parabolic reflector with a tracking system to keep
it aimed at the sun.

What kind of temps are you wanting?



Posted by Lee on October 12, 2007, 8:02 am
 
I've used this.    It's very good.


http://mscir.tripod.com/parabola/index.htm

Lee.





Erdemal wrote:


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