Author Topic: Heliostat Array Project  (Read 13659 times)

Gabriel

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Heliostat Array Project
« on: July 27, 2009, 04:48:11 PM »
Yes, finally, a decent sized working heliostat. I first started working on this over a year ago and it's finally nearing completion. Woo Hoo!

Here is a 8.5 hour time lapse video of its first run.

First Test of a Larger Sized Heliostat (8.5hr Time Lapse)

You can see that the reflection does drift to the right throughout the day, but it isn't very much, and I'm pretty sure that I can fix it just by changing the settings in the heliostat program I wrote.

Here are a few pictures. I will have a full write up of how I built it later on when I get the chance. It's pretty simple though. I used an old riding lawn motor tire rim for the azimuth's motion and a couple of door hinges for the altitude's motion. The lever arm/ leadscrew arrangement is working out well and so are the soda bottles used to weather proof the stepper motors.





My next task will be to see if I can build an array of heliostats, all controlled with just two motors. (Hopefully) I already started building another mount for a mirror, and they go together pretty quick, so I hope to have it done soon. I will post an update when I've made some progress.

Gabriel
« Last Edit: July 27, 2009, 04:58:08 PM by Gabriel »


Davetech

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Re: Heliostat Array Project
« Reply #1 on: July 27, 2009, 06:12:20 PM »
Awww Yeah!   Now yer cookin' with gas... err... I mean solar!

That's great, Gabe.  Congratulations!

What did you make the actuator part from (on the threaded rod)?  It looks like you might have made it from cast resin?

Interesting weather-proof housings! They almost look like soda bottle lights....  ;D

I haven't gotten back to my "ramp" idea for controlling the tilt. I'm anxiously awaiting delivery of some eBay copper clad that is twice as thick as what I was trying to route. Then I'll make the control board just for Pan and I'll tinker with the ramp idea some.



Gabriel

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Re: Heliostat Array Project
« Reply #2 on: July 28, 2009, 02:09:38 PM »
Yep, I used cast resin to make that actuator part. I wasn't able to find what I needed in town, so I had to make something. I have pictures of the process which I will upload when I get the chance.

I got a second mirror mount up, and I was playing around with controlling them both with just two motors today. I managed to put something together that seems like it will work, but I need to get some steel cable before I can finish it.

One downside that I thought of about the ramp idea is that you wouldn't be able to switch targets without also switching ramps. That, and you would have to go to the trouble of aligning the heliostat every time you wanted to move it.

One advantage with controlling a heliostat with light sensors is that you can put it pretty much wherever you want and it should work, but, with a ramp, it would require some finagling.

The ramp idea is a neat one, but I think it might take a lot of work to get the bugs worked out.

I'll put pictures up if my steel cable contraption works out. (I took everything apart with remembering to take a picture. ::)) It should hopefully work for both my heliostat and yours.

Take Care
Gabriel

Jon

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Re: Heliostat Array Project
« Reply #3 on: July 28, 2009, 09:45:46 PM »
It looks good, less than say 10% drift.    If you were to mount a mirror, say on top/above of your existing mirror - even in theory, and adjusted it to have the same target as the first mirror there, would it still track the sun good along with the other mirror which obviously works in the video?   If it works, and the motors are strong enough with the added weight, it could provide some "extra suns" without needing another complete heliostat system.

Another question.  I know that the sun is not a point source, and the reflection of light "expands" at a slight angle...and is larger than the size of the mirror by the time it is at the target.   I want to try to measure this angle using a small mirror and some trigonometry to find the total angle.  But offhand, do you know the value of this angle?

Jon

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Re: Heliostat Array Project
« Reply #4 on: July 29, 2009, 07:55:44 PM »
It rained all day today, so no possible experimentation/measurments with the sun and mirrors.  When I find out that value of the "angle" I'll post it.  I put this post here in heliostats rather than in the solar projects catagory, since those don't always include heliostats, hope it's on topic, if not it can be removed and put there.
« Last Edit: July 29, 2009, 07:57:37 PM by Jon »


Gabriel

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Re: Heliostat Array Project
« Reply #5 on: July 30, 2009, 06:08:13 AM »
Hey Jon,

Sorry I wasn't able to post yesterday to answer your question. I've been busy. You're right about the reflection of light expanding at a slight angle. I dug up this page from favorites which I think answers the question. http://www.heliostat.us/howfarcanaheliostatgo.htm

As for your first question, I'm not actually sure yet. For example, if I focus two mirrors at one spot, the target's altitude and azimuth can only be correct for one of them. I am unsure of how much of an issue this will be. I know that the second mirror will drift, but by how much I don't know. I need to experiment with it before I can say anything. I hope to have some information on the subject today, if the sun comes out.

I have two mirrors set up so that they are both controlled with just two stepper motors. The weight of the mirrors is balanced out, and the motors seem to be strong enough.

Oh, and I'm not picky about which topics people post in. You can post wherever you feel it's convenient. 8)

Take Care
Gabriel

Jon

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Re: Heliostat Array Project
« Reply #6 on: July 30, 2009, 10:02:44 AM »
I know that with a parabola made of many small mirrors that they all keep the same focus/target as long as the dish is aimed at the sun.  However, it's not so intuitive with a heliostat if this type of multiple mirrors set to the same target will work correctly as the sun (aparantly) changes position.   I think there is a chance at least that both mirrors will keep the same focus/target.  It seems resonable, but with all the angles and things going on, there is a chance the reflection of one mirror, the "secondary" ones will drift off target.  I think it's a valid question and needs to be answered eventually by experimentations, etc so that others can know if there is any feasability in it.  If it does work, it helps, if not then it indicates some extra complexity of the issues with heliostats.

I think what you are trying to do is "gang" the mirrors to the same steering mechanisms?  Then for each adjustment in one mirror, all the other mirrors will (most likely) receive the same adjustment.  Hence, in a way, that might be similar in some ways to hard mounting a mirror close to the "primary" mirror, and it will be adjusted in the same amounts as the "primary" mirror.

Jon

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Re: Heliostat Array Project
« Reply #7 on: July 30, 2009, 10:19:14 AM »
Thanks for that link!   That does verify that there is dispersion, which is typical as the distance from an energy source increases.   That value of 0.5 degrees or half a degree is the apparant angle that the Sun is in the sky.  It can be found from using a bit of trigonometry with the known values:  the distance to the Sun at 93 million miles and the diameter of the Sun at 865 thousand miles.  I think the Moon is also apparantly 0.5 degrees in the sky, and can be verified during an eclipse...well at least that it has the same apparant angle as the Sun.

I'll try to do an experiment with the value in that link that the dispersion is at an angle of 0.5 degrees, and check it out.  I guess for close distances, say less than 50 feet, the the dispersion is minimal, and for larger distances and systems it needs to be considered even more.

Jon

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Re: Heliostat Array Project
« Reply #8 on: July 30, 2009, 12:40:52 PM »
Ok, I just got back from taking some basic measurements and calculations.  The reflection off the mirror onto a wall was a bit diffuse around the edges. that is, it's not sharply defined, it's "fuzzy" or fades at the edges.  So I had to guestimate the width of the light there.  I measured and then calculated about 0.3 degrees total angle, so it's close to the theorized 0.5 degree total angle of dispersion.  Perhaps my guestimation of the width of the light was a bit short, and maby a bit off with my multiplication of the number of "shoes" and it's corresponding inches used as the distance from the mirror to the target.

I'm not sure how clear on that site the value of about 115 is described.  In general, I think it means it will take 115 of the same units (of measurement = used for measurement of the width or height of the mirror and distance to the target) for the image to expand by one unit.  The units can be inches, feet, meters, etc. but must all be identical to be relevant.
« Last Edit: July 30, 2009, 02:45:44 PM by Jon »

Gabriel

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Re: Heliostat Array Project
« Reply #9 on: July 30, 2009, 06:53:15 PM »
I didn't really do much with the heliostat project today, but I did manage to take some pictures.




The next three pictures show how the two mirrors are connected to each other. In the top one is the primary mirror. As the stepper motor lifts it, the steel cable transfers the motion to the second mirror (4th and 5th pictures). It seems to work OK, but I still need to do some adjusting to get it right.
 





The mirrors aren't angled to hit the same spot yet in this picture. I was just testing it out. Five minutes later the sun disappeared, and I couldn't do anything.



I could say a more, but I need to run. It's probably better that I wait until I've tested it anyway to avoid going into detail about a system that might not even work that well.  ;)

Gabriel

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Re: Heliostat Array Project
« Reply #10 on: August 02, 2009, 08:44:27 AM »
I was able to try reflecting the light from both mirrors onto one spot yesterday. It seems like it works without much drift. 

I need to redesign a few things though. The mirrors' tilt/altitude connection is not working quite as well as it could. I think I need to move the pulleys around so that the geometry is the same for both mirrors.

I also bought a few lazy susan's off of Amazon the other day with hopes that I can use them to replace the riding lawn mower parts that I'm currently using. When I just had the one mirror, the wheel mount worked fine, but, now that I have two, the weight tends to shift as the heliostat moves throughout the day throwing the whole thing off kilter.

Another thing I'm going to try is to move the mirrors closer together and also add a third one. Once I have three up and running, I'm calling this project finished. I suppose that I could go for more than three, but that's a lot of heat to be focused on one spot. I'm not too worried about starting a fire, but I did a test with vinyl siding, and it seems like too much heat will cause it to warp. My house is covered in vinyl siding.

Davetech

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Re: Heliostat Array Project
« Reply #11 on: August 02, 2009, 01:11:18 PM »
Lookin' great there, Gabe. 

If I were working for a power utility, they'd demand super precision and it would make a difference in their bottom line. But for me, if I'm able to just keep most of the reflection on target most of the time, I'll be quite happy.

You can usually find just the lazy susan bearings on eBay. Costs less and less shipping if Susan doesn't come along. There's a listing up there right now: LAZY SUSAN BEARINGS -3 INCH-200 lb MADE IN USA  $3.49 with free shipping.

I think it is the same seller I bought mine from.


Gabriel

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Re: Heliostat Array Project
« Reply #12 on: August 15, 2009, 05:13:12 PM »
I think I finished the heliostat array today. I haven't had the chance to test it out in the sun yet, but everything appears to work. The new one moves much easier than the old one. The lazy susan bearings make a big difference. Getting the lawn mower tires that I was using earlier aligned properly was more trouble than it was worth.

Here are a few pictures. You can see that I haven't angled the mirrors yet, but I will once the sun comes out.











« Last Edit: August 15, 2009, 05:20:43 PM by Gabriel »

Davetech

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Re: Heliostat Array Project
« Reply #13 on: August 15, 2009, 09:43:47 PM »
Wow. you've been busy!  And it is looking really good too, Gabe.   Can't wait to see your video of this working!



Brendan

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Re: Heliostat Array Project
« Reply #14 on: August 16, 2009, 09:40:15 PM »
Hi Guys,

Love the work you are doing.  Not sure where to post but this thread looked active so I wanted to ask Gabriel why he abandoned the gimbal design as being too hard to align?  Is it discussed?  I haven't built anything but was planning on using that so that I could use a worm gear and a very low power stepper motor since it's cheap -- same reason you liked it I think.  Is there a place where you discussed it or can you comment?

My interest is to use microcontrollers to control small stepper motors to aim and I'm ultimately interested in an array of heliostats (10-30) for concentrated thermal.  But, if precision aiming is impossible with cheap components the whole idea goes out the window.

Apologies for lacking practical experience.  It's all dreams at this point but you gotta start somewhere I guess. 

Brendan