Author Topic: Long Range Reflection - Issues?  (Read 600 times)

marcusbehrens

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Long Range Reflection - Issues?
« on: November 03, 2014, 01:59:52 PM »
Hi,

I have been successfully using my first Heliostat mirror across our valley in Heidelberg. The distance is 560m. It worked well over a couple of hours after having done the necessary upgrade from the Uno to the Mega to get enough precision on the sun calculation. If you know a little german you can follow my presetation of the mirror at the maker faire in hannover here: http://www.heise.de/video/artikel/Maker-Faire-Hannover-2014-Klaenge-zuechten-Tetris-Couchtisch-360-Videos-Sonne-umleiten-2250240.html

Now I gave some thought to building a second version of the mirror which is weather proof, solar powered and remote controlled to let it stand in someones garden for a whole year. Ahead of investing into all of the additional hardware I need (expensive pieces is the solar panel, battery and regulator and the xbees for wireless controll) i thought abut the size of this thing that would be right.

Remembering that the sun is half a degree in diameter I calculated how much a ray from the left side of the sun vs. from the right side of the sun would be veering left or right after the reflection. To my horror I cam up with 5 meters of deviation via this effect. This means a mirror of half a square meter would have some of its light spread across around 15 square meters. In average the light intensity would be down by a factor of 30! that would explain why the light entering my living room window of 2x3 meters was not as bright anymore.

I want to calculate more details here but do you have the same experience? Or is most of the light still coming in in the center of the spot I'm aiming at?

I was first worried that a mirror that is not completely flat would be a big problem. But given that the light of the sun could come in with up to .5 degree angle any deviation that is less then a tenth of a degree would be not that big of a problem - so an optical mirror used in video projection is not really required for a heliostat.

Regards, Marcus from Heidelberg


Gabriel

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Re: Long Range Reflection - Issues?
« Reply #1 on: November 05, 2014, 06:03:00 AM »
That's really cool! I wish I could speak German now. :) The heliostat is the third presentation in the video more towards the end of it for anyone else who wants to see Marcus's heliostat.

Wait did you just say 560 meters! That's pretty impressive. Are you using all of the Arduino Sun Harvester program that I wrote, or just parts of it?

Yes the size of the reflection will basically get bigger as it gets further away from the heliostat. The energy from it will also thus be more spread out. You can experiment with this just by taking a mirror outside on a sunny day and seeing how the size of the reflection gets bigger as you shine it on objects that are further away.

I know that some (maybe all) of the large commercial heliostat arrays will actually add a slight bend in the mirror to turn it into a parabolic shape. This helps refocus the light coming from the sun so that it can go a further distance without spreading out.

Naturally, you want to be careful when you do this though because focused light can potentially get things hot enough to ignite!