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pengyou

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Reply with quote  #1 
I have been reading about solar energy since I was 13 years old which was....well, more than 10 years ago [wink]  I am now approaching a phase of life where I can "make my dreams come true" and build some of the things I have been thinking about.

One of those things is the construction of a greenhouse. In particular, I am looking into having multiple layers of plants - probably 3 layers.  In order to do that I will need some additional source of light.  LED's are top on the list but also I would like to consider finding a highly reflective surface to place outside the greenhouse at a 45 degree angle to the greenhouse and reflect light to the lower two levels of plants.  The photo below is a crude sketch done in paint to try to illustrate what I am talking about.  The black box with the triangle on top is the greenhouse.  The red lines represent the mirrors/reflective surface I am talking about.  I am building a model now to see if this would be cost effective, especially given a limited amount of space.   This seems to be a little off topic for the others posts I have seen, but I was impressed with the amount of knowledge represented here.  I would like to start a discussion about what kind of material I can use for these mirrors.  I am especially interested in learning: how to describe the effectiveness of materials used for this purpose, and how long materials will last.  The property is most likely to be in Arizona in a climate that has an average winter low of about 35 degrees and a summer high of 100 degrees (F).  The "mirrors" will be mounted on a frame that is mounted on a concrete surface.  I am not sure at this point if they will be fixed or will have the capability to be adjusted for changes in the position of the sun.  More than likely, they will be fixed (cheaper).  GH.jpg 

Garage_Hermit

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Reply with quote  #2 
Hiya, and welcome to the site !

I am not a greenhouse specialist (despite my initials) but am also in the process of building one !

What strikes me with your idea, is, the reflectors *themselves* will block incident light, thus U might end up with no real gain...

In which case, perhaps they need to be further away from the GH walls...
... in which case, maybe some sort of SIMPLE wheeled chassis might be worth considering...
...particularly since you will have a nice concrete base to roll them on !

Hang on a bit, lots of greenhouse specialists will surely respond !

Good luck,

G_H

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pengyou

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Reply with quote  #3 
So perhaps some kind of fresnel lens would be in order?  but not angled to produce high heat but redirect light?
gbwillson

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Reply with quote  #4 
Welcome Pengyou,

What about mylar attached to a board? It's about as low tech as you can get, as is the cost. If nothing else you can use these reflective panels to experiment with different lighting setups and angles. 

Greg in MN[wave]
pengyou

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Reply with quote  #5 
Thanks.  Does mylar come in different thicknesses?
kcl1s

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Reply with quote  #6 
Be careful with the reflectors. We thought it would be a great idea to insulate the north wall of our one acre commercial greenhouse with 4x8 R-max sheets and get the benefit of additional reflected light from the shiny surface. We lost hundreds of young potted plants along that wall in just one sunny day! The extra light just fried the plants. We quickly painted the R-max with flat white paint and solved the problem. I would try to get diffuse reflected light somehow. 

Keith
Garage_Hermit

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Reply with quote  #7 
Does mylar come in different thicknesses?

yea - one mil to ten mil

it is what you would commonly refer to as "space blanket", I believe it was invented for the Apollo program.
Here is a guy awaiting reentry...
Résultat de recherche d'images pour "mylar space blanket"
G_H

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netttech

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Posts: 720
Reply with quote  #8 
Yes Mylar comes in different thickness but don't think you need anything thick for you're needs.

I suggest placing the reflective surface some way inside though. That would only redirect sunlight inside & what was diffused once already. It may not burn any plants as noted previously. Plus you wouldn't need to clean the reflectors, as you would being outside.

Here's where I bought my roll but it may be cheaper to buy foil backed foam as suggested in the other post.

http://www.mirrorsheeting.com/

Jeff
Central IL
Solar air & water
pengyou

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Posts: 9
Reply with quote  #9 
Thanks!  The mylar would be positioned so that it would reflect light to plants that are on the bottom shelf of a 3 tier cabinet. Hopefully that would not present a problem.
Garage_Hermit

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Reply with quote  #10 
Perhaps the cabinets could have transparent (glass...) shelves - that might increase light-transfer ???
OR perhaps the shelves could be slightly inclined downwards, towards the GH glass wall ??
Or perhaps an internal mirror, inside the GH, directed towards the shelves in quesion, reflecting internal light ?

But guess U thought of all of this already [cool]

G_H


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(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilà" unless talking musical instruments...
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