Comments on: Build a heliostat for solar heating and lighting

By: John Bolin

John Bolin — Tue, 02 Mar 2010 18:39:49 +0000

Hey Rob cool idea, currently I’m trying to make a Heliostat that is stand alone…..I have looked at the basic program but would still like to see the formula’s so I can convert easier.

Thanks for your time

By: Eco-Challenge: Plastic Mirrors - EcoRenovator

Eco-Challenge: Plastic Mirrors - EcoRenovator — Thu, 24 Dec 2009 15:52:56 +0000

[...] might be keeping them flat and properly mounted. I saw a great, simple solar technology at: IWillTry.org Build a heliostat for solar heating and lighting It's basically a big reflector that tracks the sun and constantly blasts a beam of light through [...]

By: jon

jon — Fri, 16 Oct 2009 18:11:39 +0000

I used the spa.c program to get an accurate sun position plus a little trigonometry and it works well with an arduino, adafruit motor shield and DC motors.

By: jon

jon — Thu, 24 Sep 2009 15:12:05 +0000

My system is great for putting a very bright rectangle on the wall, but I would prefer something a little more diffused. Something like a pebbled mirror, although I can’t think of where one would get that.

By: jon

jon — Thu, 24 Sep 2009 15:01:56 +0000

The lowest cost control I have found is to use an Arduino with the Adafruit motor shield. It has H bridges, so needs only one power supply to get forward and reverse for two motors. Motors were from http://www.surpluscenter.com.

Rob, I hope I’m not misusing your forum for discussing other systems.

By: jon

jon — Tue, 22 Sep 2009 18:45:10 +0000

On thing I have discovered is that if the heliostat is close to the house, the system is not very sensitive to position. Ie, my 1′x4′ mirror is on a deck, 12′ from the house, facing large windows. I’m not picky about where it hits inside the house. +/ – 15 degrees is ok. So some simple system without feedback or sun position might be fine, even with DC motors.

I expect to use some solid state relays to control four 12VDC/500ma power supplies.

By: jon

jon — Tue, 22 Sep 2009 15:06:37 +0000

Here is the best solar reflective material I have seen:

http://home.att.net/~cleardomesolar/solarflex.html

By: Rob

Rob — Tue, 22 Sep 2009 15:06:23 +0000

Hi Jon,
A webcam with custom software to track the position of the reflected spot is a workable idea for a single heliostat which I think is your plan, but controlling multiple heliostats to reflect sunlight onto a single target would be more difficult. In that case an open-loop positioning system of reasonable accuracy is required, though a camera can still be used for periodic calibration of the open-loop system (ie one heliostat at a time is moved to reflect light onto a calibration target). This is the method used by some friends of mine working on an engineering/art project called The Heliomatrix http://www.heliomatrix.org which consists of an array of independently controlled mirrors that can be programmed to paint a surface with sunlight (like a laser light show… only bigger and slower).

By: jon

jon — Tue, 22 Sep 2009 13:41:37 +0000

The best way to position a heliostat is a good question, especially with DC motors where you aren’t sure how far it moved. I’m leaning towards a low cost webcam to see where on the wall the sun is directed.

By: Marc

Marc — Tue, 22 Sep 2009 01:32:53 +0000

I will try one for a friend. I will use a programmed clock and add motor motion depending on time and month. Kool website!!!

By: jon

jon — Sun, 20 Sep 2009 21:52:31 +0000

Looks like aluminum foil would be a better fit than mylar in terms of temperature expansion. I’ll try some on Hardibacker (using spray adhesive).

By: jon

jon — Thu, 17 Sep 2009 01:42:06 +0000

I should also mention that I have purchased foam insulation boards that already have a reflective film attached. One was white beadboard and was very shiny, the other was a stronger, stiffer foam but not as shiny. Never tried them in the sun, but never saw the surface wrinkle either.

By: jon

jon — Thu, 17 Sep 2009 01:14:57 +0000

Hard to find good data, but I think cheap glass with iron in it actually absorbs about 5% per pass. But I agree, not a big factor.

I wonder if mylar stretched across a flat surface would work? If there is nothing behind the mylar, I would expect the wind to change the shape (ie, depress the center).

A thin sheet of of polished aluminum over some stiff flat surface might also work,

My small heliostat is coming along – uses a glass mirror, vertical pipe, threaded rods, geared DC motors, a hinge, hardibacker.

By: Rob

Rob — Wed, 16 Sep 2009 05:27:03 +0000

Hi Jon,
I think two trips through the glass of the mirror makes little difference to efficiency. I believe you get about 4% reflection at any glass/air interface, but as long as the front surface of the glass is parallel to the back mirrored surface, both surfaces will reflect the light in the same direction, so it doesn’t matter.

I’ve tried gluing silvered mylar to different surfaces in an attempt to make a panel that is lighter and cheaper than using glass mirrors. The issue with that is thermal expansion. Just about anything it might be useful to glue the mylar to will have a different coefficient of thermal expansion and as the temperature outside changes, the mylar will wrinkle scattering the light. An option I’m considering is using mylar bands about 1ft wide stretched across a metal frame with a tensioner (bungy cord) to take up the slack as the mylar expands and contracts. That could reduce the weight a lot, but I’m not sure how it would react in the breeze. It may resonate, scattering the reflected light.

By: jon

jon — Wed, 16 Sep 2009 01:56:41 +0000

I have found Hardibacker to be a fairly stiff, strong, flat, rot proof material.

By: jon

jon — Wed, 16 Sep 2009 01:09:30 +0000

Maybe mylar film glued to the front of a piece of plate glass would work? Certainly two trips through the glass of a normal mirror can’t be helping efficiency.

By: Gabriel

Gabriel — Wed, 01 Jul 2009 00:26:41 +0000

Oh Yeah. You’re right! I didn’t think to mentioned it, but this program wouldn’t work for your particular heliostat design without modification. I need to bring that up somewhere in the program’s documentation (Which still needs some work anyway). Thanks!

I’ve been making my own worm gears out of threaded rod and plastic, so a simple gear ratio would work in my case. My heliostat is based around a gimbal design, so the mirror is pretty well balanced, which is why I can get away with using cheap homemade worm gears.

I will have to look into the lever arm design sometime to see if I can include it in the program somehow. I’m sure that it can move a much heavier load than my worm gears.

Oh, and if someone did want the source code, I can put it up on my site for download. It’s something that I was planning to do eventually anyway. I just need to add some comments in the code and probably clean some things up.

Thanks again!
Gabriel

By: Rob

Rob — Tue, 30 Jun 2009 22:32:08 +0000

Hi Gabriel,
Your program is the most comprehensive I have seen. Thanks for contributing it. One consideration is that depending on the drive mechanics, there may not be a simple constant gear ratio between the stepper motor position and the heliostat angle. In my design, for example, the stepper motor rotation is converted to linear motion via a leadscrew which pushes on a lever arm to rotate the heliostat. The stepper motor position is related to the heliostat angle by a sine function rather than just a constant. Designing a program to meet the demands of ANY drive geometry without allowing modification of the source code is a challenge.
Cheers,
Rob

By: Gabriel

Gabriel — Tue, 30 Jun 2009 18:22:56 +0000

Hey everybody,

I’ve been visiting Rob’s heliostat project and the other projects that he has on and off for the last year. This is a really cool site. : )
For the same amount of time, I have been working on a heliostat of my own and finally have it up and running.

The hardest part was figuring out how to program it. I’ve noticed that a lot of people seem to be stuck at this spot also, so I decided that I would contribute my time in order to write a program that would make it easier for them.

The link to it is http://cerebralmeltdown.com/projects/suntrackprogram/default.htm

This program will do all the calculations necessary for up to two heliostats and will also send signals through the computer’s parallel port for controlling the stepper motors that will adjust them to the correct orientation.

In addition to that, you can hook up limit switches to your machine and the program will automatically seek them out and reset its position at the press of a button.

It’s been working well for me, but it is still just a beta program, so be careful. I think I’m about finished working on it though because I can’t really think of anything else to add. At this point, I mostly just need people to test it out and confirm that it works on computers other than my own. For example, I don’t think it will work on a 64bit Windows OS. If someone needs it, I might be able to fix it, but I don’t have one of my own to test it out on and need someone who does.

Anyway, I hope that someone finds this useful. In the mean time, I will keep working to try and make heliostats more accessible for people. I still have a lot to do though, so I had better run. Right now, I’m off to see if I can’t put together a set of plans for building one. : )

Thanks!
Gabriel

By: from amsterdam (nl)

from amsterdam (nl) — Wed, 03 Jun 2009 19:55:11 +0000

the freon thing spider talked about was an invention of a company called zomeworks, headed by steve baer .
they did some really nice inventions and are still around.
the free program for sun tracking is one of the best things i have seen in many years, perfect!
all i can hope for is to see the day that there is a version for dummies like me.
hope you will put the program and its devopments in many places so that more people can work on it .
looks like you are initiating the solar linux………..btw guess you all know the box by practical solar?