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Anyone interested in building cheap DIY parabolic troughs?

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Posted by azuredu on November 13, 2008, 5:39 pm
 
I have got a method to build cheap and efficient parabolic troughs, a
method easy enough to allow me to build one on materials bought from
DIY shops. Cheap but not of bad quality: I've had one with a
concentration ratio of 30 times, and am building an improved one
aiming at 80 times. This is top professional level, the same as the
huge troughs in Californian solar power plants. But I am only using
some plastic plates, a drill and a saw.

The retail materials cost me more than 200$/m^2. But if produced
industrially, the trough may cost as low as 30$/m^2 wholesale price.
Because it is extremely simple. Will publish all the details when
everything is ready, including the trough, a thermal storage unit, and
a thermoelectric unit that will allow you to generate electricity
round the clock.

Everything will be built on my balcony, so you too you can do it.
Solar energy, it's easy and cheap! Interested? Write me to "xiao at
unice.fr".

Posted by Morris Dovey on November 13, 2008, 10:34 pm
 
azuredu wrote:

No - if you post to usenet, that's where the responses will be. Below is
a link to a small DIY parabolic trough with a "concentration ratio" of
44:3/8 with a materials cost of less than $40 for more than 2m^2. It
can produce temperatures in the 725F/385C range.

I would be interested in your mount and tracker designs, and suspect
that these would also interest others here.

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

Posted by azuredu on November 14, 2008, 6:04 am
 

Thanks very much for the link. Nice pictures, although I am afraid
that the rib design gives you some inter-rib deformations which can be
seen from the photos. Cannot judge how severe they are; if you take a
front picture or some tracked pictures, then the severity of the
deformations can be evaluated.

The mount is easy. You have only to add a bearing at each end of the
tube, and whatever you like as chassis. I am using plastic tubes of
used water evacuation as bearings; worked fine.

Tracker is a bit more tricky. I have the circuit design and
microcontroller programming, and will be glad to publish them, but are
you ready to solder circuit boards and burn microcontrollers?

If you really want to go beyond water heating (above 100C), you need
something more than just a bare tube. The tube should be black chromed
(selective coating), and there must be an evacuated insulation layer
enclosed by a glass tube. But if you don't have the means to seal and
evacuate glass tubes, a small vacuum pump will do. See my article on
this. http://wims.unice.fr/xiao/collector.pdf

Once you get there, you still have to make sure that the thing will
last very long and stand to weather. Then it can go into every home.


Posted by Morris Dovey on November 14, 2008, 1:25 pm
 azuredu wrote:

It hasn't been a problem so far - the concentrated band at it widest
point is 3/8 inch (9.525mm) on a 1 inch diameter target. It would, of
course, be better to illuminate the entire bottom half of the target
tube, but we haven't gotten around to adding spacers to lower the tube.


Everything has been easy - until we try to make it idiot-proof. :-)

I'm interested - please post links to photos when you have them. I'm
always looking for better methods...


Probably (I've been working on computer circuitry since the early
1960's) - although my eyes aren't as good as they once were. I think I'd
much prefer a passive pneumatic/hydraulic system to an
electrically-driven system, though.


I'm not interested in water heating at all. I just want to heat air -
and the 725F/325C is about all I need from the trough shown.


I have the ability to CNC cut aluminum ribs up to eight feet wide that
can be used for sandcasting - but I think I'm a long way from being
ready to take that step - and the collector is not the primary focus of
my efforts.

For the testing done over the past two years, the plywood ribs have been
adequate.

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

Posted by azuredu on November 14, 2008, 3:11 pm
 
To me it is not obvious how you can reach the cost, precision and
versatility of electronics.

A microcontroller is just a few dozens of cents wholesale price.
Adding a motor, you get it. And you get things that passive method
doesn't offer, such as emergency resting when the HTF circulation has
a trouble.



No, it is not that you can get 325C at dry burning that you can get
325C real heat output. The efficiency will drop to near zero at this
level. I've also got 300C+ temp for my earlier trough at dry burning,
even damaging the equipement. But with circulation, the only
reasonable thing is to heat water.

Therefore an evacuated receiver is a must for high temperature.


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