Heliostat

brian

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Jul 1, 2008, 6:39:38 PM7/1/08

to

I made a very small poor model to demonstrate it (on the utube link) and
more info is on the other links.
Anyone want to try it for real? It is radically simpler than any heliostat
design i have seen.
I just do not have time, (work project to be completed by the 6th) to make a
real one.
I think a fixed attachment to the mirror (as in the model) is the way to go
and also, the alternative to rubber bands as suggested in the instructables
site.
Brian White
http://www.instructables.com/id/HELIOSTAT/
http://www.youtube.com/watch?v=WRTX1S7PD-U
http://www.appropedia.org/Heliostat

Duane C. Johnson

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Jul 1, 2008, 10:26:29 PM7/1/08

to brian

Hi Brian;

brian <gaiatechn...@yahoo.com> wrote:

> I made a very small poor model to demonstrate it (on

> the YouTube link) and more info is on the other links.

> Anyone want to try it for real?

Already have several years ago.
At least quite close to it.

> It's radically simpler than any heliostat design
> I have seen.

Although a bit hard to see it's clear enough to
understand.
Your concept is quite similar to the clock drive designs
of Silbermann from 1825 or so. See:
http://www.redrok.com/main.htm#mechanical
The significant difference is the mechanism that causes
the bisector angle between the sun and light target.
Silbermann, see Silbermann6, uses a sliding pantograph
device.

I have done it like you with a pair of springs also.

> I just do not have time, (work project to be
> completed by the 6th) to make a real one.

> I think a fixed attachment to the mirror (as in the
> model) is the way to go and also, the alternative to
> rubber bands as suggested in the instructables site.
> Brian White
> http://www.instructables.com/id/HELIOSTAT/
> http://www.youtube.com/watch?v=WRTX1S7PD-U
> http://www.appropedia.org/Heliostat

Have fun!

Duane

Jeff

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Jul 2, 2008, 3:35:38 PM7/2/08

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Duane C. Johnson wrote:
> Hi Brian;
>
> brian <gaiatechn...@yahoo.com> wrote:
>
> > I made a very small poor model to demonstrate it (on
> > the YouTube link) and more info is on the other links.
> > Anyone want to try it for real?
>
> Already have several years ago.
> At least quite close to it.
>
> > It's radically simpler than any heliostat design
> > I have seen.
>
> Although a bit hard to see it's clear enough to
> understand.

Hi Duane,

I've been meaning to ask you...

You've seen a lot of solar engines. What do you think has been the
most successful? For the concentrator, the engine and for the working
fluid?

Jeff

David Williams

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Jul 2, 2008, 8:29:20 PM7/2/08

to

-> I made a very small poor model to demonstrate it (on the utube link) and
-> more info is on the other links.
-> Anyone want to try it for real? It is radically simpler than any heliostat
-> design i have seen.

The simplest design I have seen (Duane prefers to call it a coelostat),
has two mirrors. One is rotated by a simple clock mechanism about an
axis that is parallel to the earth's axis of rotation. The mirror is
aligned so as to reflect sunlight in the direction of one of the
celestial poles. A second mirror, which is stationary, intercepts this
polar beam of light and reflects it in whatever direction is desired.

If you think about it, the first mirror is stationary relative to the
sun, and the second one is stationary relative to the earth. There's a
nice symmetry about the whole thing.

I have built one of these things, using the works taken from an old
alarm clock and a simple 2:1 gear to reduce the speed from one rotation
every 12 hours, for the hour-hand of the clock, to one rotation every
24 hours, to keep pace with the sun. It works excellently, producing a
stationary output beam of sunlight for the whole day. However, it needs
to be manually adjusted every few days (most often near the equinoxes)
to compensate for the seasonal movements of the sun, north-south and
also east-west. To compensate for these automatically needs something
more complicated.

dow

brian

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Jul 4, 2008, 3:15:49 AM7/4/08

to

I was thinking mostly of solar cooking.
I made a parabolic dish (an off centre paraboloid is necessary) on
equatorial mount that turns at 15 degrees per hour. (They put 2 of my low
tech timer (or tracker) ideas on solarcooking.org).
Its focus is at one spot all day.
I call it a tracking solar accumulator.
I made my dish from plastic material with alu foil as the reflective
material (which is not that great because the dish has slowly distorted
over 3 months and the foil has lost some shine.
The other problem is ballance, the paraboloid must be moved to repoint at
the sun once or twice a week and you have to reballance the thing a little
each time too. (like ballance for a telescope on equatorial mount).
I think it is way easier to make a stationary deep parabolic dish and shine
light onto it from several easier to make (and always ballanced!) flat
mirror heliostats.
In the simplified design, you have 2 pointers, one to the sun and one to the
target. Sure they are on the surface so they will cause slight losses but
it also makes it really easy for the user to reset it as the seasons
change.
The only one you should have to adjust is the sunpointer (with the seasons)
and if the clock stops.
The reason i only have one reflector is that you get losses with each
reflector in series so if 0.85 is the efficiency of one, the efficiency of
2 is 0.85*0.85=0.72 . I am pretty confident that with a dripper tracker
you could control the movement of at least 4 heliostats, either all
pointing at a solar cooker or perhaps all pointing at different windows of
a house for heating/lighting.
Anyway, it is just an idea.
I like it because it might be possible to make it low tech on quite a large
scale. Rubber bands were just for the model! I think 2 strings off the same
tensioned spool would be the start of a durable larger system.
Brian

David Williams

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Jul 4, 2008, 3:27:30 PM7/4/08

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-> I made a parabolic dish (an off centre paraboloid is necessary) on
-> equatorial mount that turns at 15 degrees per hour. (They put 2 of my low
-> tech timer (or tracker) ideas on solarcooking.org).
-> Its focus is at one spot all day.
-> I call it a tracking solar accumulator.
-> I made my dish from plastic material with alu foil as the reflective
-> material (which is not that great because the dish has slowly distorted
-> over 3 months and the foil has lost some shine.

Yes. It's hard to make a mirror that will stay highly reflective over a
long period, especially in a cooking environment, where greasy smoke
leaves deposits on the mirrors. Cleaning tends to damage the surface,
unless it's glass, with the silvering on the back.

-> The other problem is ballance, the paraboloid must be moved to repoint at
-> the sun once or twice a week and you have to reballance the thing a little
-> each time too. (like ballance for a telescope on equatorial mount).
-> I think it is way easier to make a stationary deep parabolic dish and shine
-> light onto it from several easier to make (and always ballanced!) flat
-> mirror heliostats.
-> In the simplified design, you have 2 pointers, one to the sun and one to the
-> target. Sure they are on the surface so they will cause slight losses but
-> it also makes it really easy for the user to reset it as the seasons
-> change.
-> The only one you should have to adjust is the sunpointer (with the seasons)
-> and if the clock stops.

If possible, I think you should make your paraboloid function as the
stationary mirror of the heliostat, too. Have a flat mirror that rotates
every 24 hours, to keep pace with the sun, and reflects light in the
direction of one of the celestial poles. It should be easy to balance.
Then put the paraboloid so it intercepts the polar beam of light from the
first mirror and focuses it directly onto the cooker. So you have two
mirrors instead of three, which will reduce inefficiencies.

As you say, only the rotating mirror has to be adjusted every few days
to follow the sun's seasonal movements. It has to be tilted in the
north-south direction, and also rotated a bit in the east-west
direction. The east-west movement basically means that the clock has to
be set ahead or back a bit. If the clock mechanism is clockwork, so it
has to be wound up every day or two anyway, making these mirror
adjustments adds very little trouble.

-> I am pretty confident that with a dripper tracker
-> you could control the movement of at least 4 heliostats, either all
-> pointing at a solar cooker or perhaps all pointing at different windows of
-> a house for heating/lighting.
-> Anyway, it is just an idea.
-> I like it because it might be possible to make it low tech on quite a large
-> scale. Rubber bands were just for the model! I think 2 strings off the same
-> tensioned spool would be the start of a durable larger system.
-> Brian

If you want to control a lot of mirrors, it becomes economical to use a
computer. A single computer, even a very small one, can control dozens
or even hundreds of mirrors.

There are other possibilities, of course. The position of the sun in
the sky can be determined by sensors. If a single mirror is set up in a
dual-axis mounting with the main axis pointing in the direction of the
target at which light is to be reflected, a very simple mechanism,
controlled by the sensors, can keep the mirror properly aligned.

I think you should consider durability. Rubber bands don't last long,
especially if they are exposed to direct sunlight. And string tends to
stretch or break.

Have fun!

dow

Duane C. Johnson

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Aug 5, 2008, 12:43:39 AM8/5/08

to brian

Hi Brian;

brian <gaiatechn...@yahoo.com> wrote:

> I made a very small poor model to demonstrate it

> (on the YouTube link) and more info is on the other links.

> Anyone want to try it for real? It is radically simpler

> than any heliostat design I have seen.

> I just do not have time, (work project to be completed
> by the 6th) to make a real one.
> I think a fixed attachment to the mirror (as in the
> model) is the way to go and also, the alternative to
> rubber bands as suggested in the instructables site.

I have come up with an alternative to the 2 springs
method of obtaining the half angle mechanism on your
"Receiver Axis" design. This is essentially the same
method as used on the Silbermann clockwork driven
heliostats. See:
http://www.redrok.com/main.htm#mechanical
Silbermann uses a slider mechanism to get the
half angle function. However, this requires fairly
accurate machining.

The 2 springs method suffers from misalignment caused
by offset weight and friction.

See a diagram here:
http://www.redrok.com/heliolighting.htm#heliocable1
This method uses a single spring and cables.
The rest is basically the same as yours.

I'm setting up a model using wooden "Embroidery Hoops"
I got at Michael's craft store. I will take some
pictures when it is done.

> Brian White
> http://www.instructables.com/id/HELIOSTAT/
> http://www.youtube.com/watch?v=WRTX1S7PD-U
> http://www.appropedia.org/Heliostat

What do you think?

Jussi Saily

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Aug 16, 2008, 1:38:48 AM8/16/08

to

On 5 elo, 07:43, "Duane C. Johnson" <red...@redrok.com> wrote:
> What do you think?
>
> Duane

I think that you should return my money or send the solar trackers I
ordered, Duane.

-- Jussi