Author Topic: Using one set of LDRs to calibrate sun position  (Read 2103 times)

alobo

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Using one set of LDRs to calibrate sun position
« on: July 31, 2014, 02:19:00 AM »
Hi, Cerebral Meltdown!
You probably have gotten this idea before, but I couldn't find it on the forums ... so let me know what you think.
The heliostat work is incredible, by the way! This is just my 2 cents. (Or 2 rupees, as I am in India).

In a setup with multiple mirrors, you could set up code for an LDR voltage divider on one of the mirrors, and use it to calibrate the Sun position - compared to the calculated position - every now and again? That would almost completely take away any need for adjustment. I say "you", meaning experienced CerebralMeltdowners, because I'm not a particularly useful coder hahah  ;D


Gabriel

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Re: Using one set of LDRs to calibrate sun position
« Reply #1 on: August 02, 2014, 06:18:43 PM »
Hi alobo,

The calculated sun's position should be pretty spot on (if using the Mega calculations). Ideally you shouldn't need to double check them.

What it might be used for is when you first setup the machine you can help orient its position in relation to the sun. I have considered attempting it, but I don't know if I'll ever get around to it. There are so many other things on my list. :)

I don't know if this is exactly what you mean, but there has been some work on heliostats that only use LDRs, no calculations.
http://www.heliostat.us/

Thanks for your input!
Gabriel


alobo

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Re: Using one set of LDRs to calibrate sun position
« Reply #2 on: August 04, 2014, 10:36:48 PM »
Yeah, I figured the Mega would be quite accurate, but I'm trying to get into this sort of thing and I'm trying to save money on the processor. I can buy several standalone ATMega328 chips for the cost of a Mega. More second chances in case I screw up - which I probably will - and have leftovers for other projects, haha. (Also pretty much all the electronics are more expensive in India because of import tariffs  :( )

I think the main issue I'll have with LDR heliostats is getting the gearing precisely right, since the mirror should move at exactly half the speed of the LDRs. I'm not at all a mechanical person, though, so getting a jig like that will take some effort.

This is where I'm taking the inspiration from. Just replacing the analog components with digital - the op-amps/resistors replaced by the ATMega, and the transistors/diodes by an equivalent L293D. Or a stepper motor/driver. It'd only take one analog pin to track each axis, conveniently. That's why I thought of suggesting it here, it seems like it might not be too much to add to the existing Uno heliostat code. (I could be wrong about that, though :P )

Gabriel

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Re: Using one set of LDRs to calibrate sun position
« Reply #3 on: August 07, 2014, 06:03:03 AM »
You may have already seen this, but here is a link to some error checking that I did for the Arduino Uno calculations. http://www.cerebralmeltdown.com/2012/06/18/checking-the-output-error-of-the-arduino-sun-position-calculations/
Depending on what you are doing, it might be good enough.

"the mirror should move at exactly half the speed of the LDRs"
Do you know of anyone who has actually done this? I have heard of it mentioned before, but have always been skeptical of it. It may be that it only works in certain cases. I've never actually looked into it before though, so I could be wrong.

How big of a machine are you planning on making? Does it need to be especially accurate?

alobo

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Re: Using one set of LDRs to calibrate sun position
« Reply #4 on: August 08, 2014, 02:00:11 AM »
I hadn't seen that, thanks for it.

I'm working for an alternative energy startup in India, and we're trying to make a modular CSP system using heliostats and the Arduino platform. The Indian monsoon season throws off the cost-efficiency (and reliability) a bit.
Your heliostat program is quite amazing, but being limited to 16 units does make it a little small for what we'd like to try, while being an excellent proof of concept. I.e. something like a few square meters of mirrors - a larger number of small ones, perhaps each with its own motor, to allow more concentration. The main applications here would be heat, not power generation e.g. steam for a spa. As you can imagine, a lot of electricity goes to use for that. We're still working out the part costs.

We haven't made a model yet, but pure geometry says the LDR-guided heliostats should work, at least in my mind. With the LDRs and mirror normals aiming directly at the target, set that to be the "reset" position in all axes - then set it loose. The mirror normals should always bisect the angle between the line mirror->Sun (dictated by the LDR) and the line mirror->target. The mechanical solution to that should be a simple 2:1 gear reduction between the LDRs and mirror movement in both axes. I could be wrong, but I don't see how.
« Last Edit: August 08, 2014, 02:05:01 AM by alobo »


Gabriel

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Re: Using one set of LDRs to calibrate sun position
« Reply #5 on: August 09, 2014, 07:47:13 PM »
The program isn't necessarily limited to 16 machines. With some modifications it could be made to operate a lot more. I think the real limitation would be in how fast the Arduino is able to update the position of each machine. For example, if you set the machines to update their position every 60sec and it takes 1sec to update each machine's position then the most you could hope to control is 60 machines.

How long each machine takes to update will depend on the gear ratio required on your heliostats. So a big, heavy machine will require more gear reduction and will thus be slower moving.

Using heliostats to provide heat is in my mind the smartest thing that people can do with them. There are so many processes that need heat that it seems silly for anyone to even consider electricity generation as the first option.

Designing a good machine will be the hard part. I personally am still having trouble with it.

alobo

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Re: Using one set of LDRs to calibrate sun position
« Reply #6 on: August 11, 2014, 10:19:53 AM »
You're right, of course. I could add more I/O expander chips (with more ports), or also drive several mirrors in a row/column with one set of signals. I pointed out the time constraint issue to my boss since it updates one mirror at a time. We'll see how it goes  :)

Heat is quite important, indeed! 'Specially in less-developed areas. In the end, even the most sophisticated nuclear power plant ... is a big-ass boiler, hahah. Though electricity generation becomes a much more viable option only if battery power density improves, sadly. That's the real killer in alternative energy, is the storage. Time for someone to come out with an open-source flywheel storage technology - the energy density's supposedly comparable with batteries. ;D

I wish I was a mechanical person, lol. I'd have a much easier time with a lot of things, especially these mirror jigs and such. Speaking of which, I posted a thread in the "Think Tank" forum. Curious to know what you (and others, hopefully) think.  :)
« Last Edit: August 11, 2014, 10:31:37 AM by alobo »