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Concentrating Solar Energy on Evacuated Thermal Tubes With Stationary Mirror - Page 4

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Posted by daestrom on January 3, 2007, 12:25 am
 


I don't think so.  The theta-max is still pretty narrow compared to how far
the sun moves across the sky on any given day.

With a trough running east-west, you lose a bit of collection on the ends of
the trough when the sun isn't due south.  But much of the collector is
active for several hours. A photon may first enter the collector 1m from the
east end, hit the reflector 1.5 m from the east end, and finally hit the
absorbing tube 2m from the east end.  But when you look at the cross-section
of the compound parabola, it enters nearly 'straight' in and reflects up to
the absorber.

The nice thing about the compound parabola isn't that it tracks the sun
across the sky from sunrise to sunset, but that it works as well in February
as December and January.  That is, the compound parabola does the *seasonal*
tracking, not the daily tracking.

daestrom


Posted by Rob Dekker on January 3, 2007, 4:42 am
 


Winston's compound parabola, then the collector can

d, sticking up, right in the center of the dish.

surprized if we can get to 30 sol or more.

that it has a small focal area which does not change

moves around if the position of the sun changes. So we

the sun moves across the sky on any given day.

the trough when the sun isn't due south.  But much of

collector 1m from the east end, hit the reflector 1.5 m

But when you look at the cross-section of the

absorber.

the sky from sunrise to sunset, but that it works

does the *seasonal* tracking, not the daily tracking.

I realized the same after I sent out the posting.

The theta-max determines the size of the collector, not just in vertical, but
(for a dish) also in horizontal direction.
With the Winston parabola design in 'dish' form is that we can make a different
theta-max for east-west than for north-south, so we
could construct a dish that is somewhat

To keep collecting rays over say 6 hours a day without tracking, theta-max
east-west would need to be 45deg, which translates to an
additional sun-concentration factor of 1.4. That's not a lot, so it is probably
easier just to use a trough.

Thanks for your posting !

Rob



Posted by Morris Dovey on December 21, 2006, 3:16 am
 fossilfreedom@gmail.com (in
1166218400.773868.207840@16g2000cwy.googlegroups.com) said:

| You can concentrate Sol's energy many times over, without tracking
| the sun. The result is that you can capture more energy with your
| surplus solar energy Thermal Collector  tubes!

| Link: http://www.fossilfreedom.com/increase-output.html

The compound parabola reflector geometry is most interesting - thanks
for hosting the page and posting the link!

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



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