Lawn/Garden Convex Mirror in Backyard to reflect sunlight onto the house

[dlgoff]

What's the stuff supposed to do ? Alu foil reflects a lot better I would expect ...

$\$

from: https://www.google.com/search?q=wha...0j0i390l4.11273j0j15&sourceid=chrome&ie=UTF-8
It is a polyester film construction generally made of Polyethylene Teraphthalate (PET). Most films are applied to the interior surface of a glass window in a home, commercial building, or vehicle. They have a scratch resistant coating on the outer surface to protect the film. There are many types of window films.

 

[dlgoff]

@BvU
Here's a page about Window Film Fundamentals:

https://www.wbdg.org/resources/window-film-fundamentals​

 

[BvU]

A nice little gizmo and conversation piece to put in the garden but it hardly needs a "robot" to know where the Sun is, during the day. A synchronous motor and a cam would keep the Sun image where it's wanted (which is over a large back-of-house area). As has been pointed out several times, the pointing is very non critical because an image of the Sun, projected on the wall is not actually what's required. The 'image' needs to be magnified from the half degree spread to 30 to 40 degree spread. The OP doesn't want a solar furnace

Don't understand your comment. This gadget IS a motor and a cam. That some copywriter labels it a robot shouldn't confuse a PFer !

$\$

 

[sophiecentaur]

That some copywriter labels it a robot shouldn't confuse a PFer !

You have a point there but my comment was really for 'The World', rather than just PF.

The ad doesn't seem to say what the gizmo is supposed to do, exactly, or how it does it. Where does "13 lightbulbs" come from? From the photos, the mirror looks about 0.1m² area so there's perhaps up to 100W available. That's radiation, rather than lightbulbs. That could be a lot for just one room but not much for a number of windows plus walls and outside would be pretty bright for comparison.
Setting it up would actually be eliminated with the aid of a bit of on board processing / feedback. Is that what the 'Radar feed' thing on a stick is supposed to do? The focal length of the mirror would need to be appropriate for the OP's situation. It would need to be on the other side of the garden if I've understood the setup.

I'm afraid I took instant dislike to the glossy on the grounds that it would just have to be form over function and very expensive. (Too Saint Tropez for my liking .)

 

[BvU]

I'm afraid I took instant dislike to the glossy on the grounds that it would just have to be form over function and very expensive. (Too Saint Tropez for my liking .)

So did I, but from post #11 I got the impression that the OP (who hasn't been seen since November 15 ...) prefers something with a Saint Tropez look over a rickety DIY with a raspberry and some rubbber bands sticking out ...

@BvU I agree that starting out with a flat mirror might be better but I would rather do this once as I will need to custom make this mirror as well as its swivel with a contractor. I would rather, if I can get everything right from the get go, not go through the hassle of changing the mirrors and the extra costs.

However, I saw a price of 600$ coming by and fell off my chair. Expected 60 to 100 (but then again, the dutch are the scots of the continent )

$\$

 

[Lylehardin]

Buy some cheap wall mirrors ($5 in Walmart here in the US) they flex a little bit (I've made funhouse mirrors with them. Broke a few in the process too so be careful.) so you could experiment by fixing the ends of the mirror to a stiff board and trying different sizes of wedges in the middle to get your convex shape.

 

[jumpjack]

I am studying this topic since a long time... and didn't find a solution yet; not a static one, anyway; for a moving mirror I created a program which calculates the needed orientation of a mirror, given a position in the world, to constantly reflect the sun into a static point:

https://jumpjack.wixsite.com/progetti/ipsun

But it's very hard to find a pan/tilt mechanism which can be easily interfaced to such a software: the camera I used was just a "feasibility study", it's too weak to be useful for a big mirror; and I don't want to spent months on building and testing my own pan/tilt device, so if anybody could suggest a ready-made product wihch can be externally controlled at degree-level precision, I would really appreciate it. I think we should also focus on "RS-485 Pelco D protocol" for remote controlling, and the "key" is "absolute positioning".

In the meantime, I found this static mirror product:
http://cleardomesolar.com/solareflexpanels.html

I tried to reverse-engineer it, currently without success (and without help...)

I did a lot of experimenting with geogebra, but as of now I didn't yet find a valid geometry. You can find here my million of experiments...
https://www.geogebra.org/u/jumpjack

I think that probably the final outcome of this study won't be a single mirror, but a "tower of mirrors": I imagine a stack of small 20x20cm mirrors, probably at least 4 "floors" (one per season), each one made of 5-6 mirrors with different orientations, each mirror reflecting sun into the window for a couple of hours, but this is just an hypotesis.
Maybe a double-mirror system would be even better: the "tower" reflects the sun in different location inside a window-sized mirror set, which then reflect all the different reflections into one single point.

Can anybody help designing all of this in geogebra?

 

[sophiecentaur]

to constantly reflect the sun into a static point:

Are you sure this is what's required though? I put my Engineer hat on and went back to the basic problem. The sun is bright (obvs) and you don't particularly want to gather all the incident light and aim it somewhere. So an active pointing mechanism would illuminate just a small area. Elsewhere in the garden / house would get no benefit. With a broad beam, the advantage of steering could largely be lost.

The images in that link with the mirrors shows what I mean. The Solareflex AA would look very cool (as long as you keep it very clean) and, being convex, would show an image of the Sun over a wide range of angles (depending on how you curve it). Your source would move over an angle of, say 120 degrees and you desire to illuminate with around 60 (?) degrees. Would such a system be significantly less effective?

An alternative approach could be along the lines of photography reflector which is basically a diffuse reflector for 'filling in' shaded areas of a scene. I have successfully used a small one for outdoor portraits. They are used as a cheap alternative to massive lights in cinematography. A metre square of reflector would be like a very efficient 1kW lamp. Have you actually tried anything as simple as that? Crinkled kitchen foil would be suitable for testing. Not as pretty to look at as a large mirror but very very cheap. A stack of mirrors would also look very nice but would the 'gathering power' be much better than a diffuse reflector / (white wall, even).

I just had a thought. One of the good things about a convex reflector could be that it could produce sharp shadows, if large enough. That could give a good illusion of the 'real sun'.

 

[jumpjack]

Are you sure this is what's required though?

This is what I want. Or at least, if not a point, an user defined area 1x1 meter sized. I think I found a gemetric method with geogebra, using 4 mirrors with 5° difference orientation one w.r.t the adiacent one; once I refine the model I'll post it.

 

[sophiecentaur]

Or at least, if not a point, an user defined area 1x1 meter sized. I think I found a gemetric method with geogebra, using 4 mirrors with 5° difference orientation one w.r.t the adiacent one; once I refine the model I'll post it.

Ah - I was making assumptions. I certainly like the plan for a passive system. If you aren't too happy with the available formulae and data, you could always manually adjust individual mirrors to suit each part of the day. A simple arrangement of just one mirror would give you the positions you need. Would just four mirrors be enough? I was thinking each mirror might only work over 10 degrees - but it would depend on the actual size and the angle subtended from the observer, I guess.
I must say, I really fancy that big cylindrical mirror in the link. Probably cost a fortune to make it look as nice as the photo.

 

[jumpjack]

Point is: is it just cylindrical, or something else?
Continuing my simulation I found the possibly it is cylindrical, but also that a discrete mirror would work better than a continuous one, because each mirror would reflect into the window a "box of light" as large as the mirror itself, without attenuation due to curved surface.
I am now trying to calculate the best curvature of the cylinder and best width of the single mirrors to have several "suns" traveling across the window along the day.

 

[Drakkith]

Just FYI to everyone, the OP hasn't replied in almost a year, so questions may or may not be answered in a timely manner.

 

[jumpjack]

"Caia" heliostat from Solenica is eventually on delivery all around the world! (after 6 years awaiting since its presentation at MakerFaire Rome).
Mine should be shipped around April, I'll report about it here.
Did anybody here purchase it?

 

[berkeman]

"Caia" heliostat from Solenica

Looks expensive! How much did it cost?

 

[Nik_2213]

"You may only need to whitewash the wall." Which is what our neighbours did.
Proved remarkable effective...

FIL lined back of his small, lean-to greenhouse with 'radiator reflector', matte Al foil on expanded polystyrene sheet, stuck to wall with recommended 'non-solvent' tile cement. Sheltered in greenhouse, lasted two decades...

 

[phinds]

Guys,

Just FYI to everyone, the OP hasn't replied in almost a year, so questions may or may not be answered in a timely manner.

except that it is now over TWO years since he's even been here

 

[bob012345]

My solution is install skylights. Expensive yes, but if the OP works in Dubai they are likely not poor.

 

[jumpjack]

Looks expensive! How much did it cost?

Around 150$ + shipping. But this was the price for "backers" at the time of first prototypes, I don't know which will be the final retail price. Anyway any other heliostat project I found was in the order of thousands of dollars, it was enormous (1 m2 or more) and you had to build it by yourself.

About "sun capturing" surface, I wonder: if it was possible to design a "multimirros structure" which concentrates the sun light from 1 m2 into a small pipe 10cm wide and 10 meters long, how much of the original light would came up from the other edge, assuming the interior of the tube is a mirror? Of course I don't have enough space for a 1m diameter solar tube!

I am experimenting with this 2d optics simulator to figure out the better "concentrator design":
https://phydemo.app/ray-optics/simulator/

I also found a 3d optics simulator, but I can't get it working, I can't find any object to put into my project:

https://simulation.3doptix.com/index.html#

 

[Drakkith]

About "sun capturing" surface, I wonder: if it was possible to design a "multimirros structure" which concentrates the sun light from 1 m2 into a small pipe 10cm wide and 10 meters long, how much of the original light would came up from the other edge, assuming the interior of the tube is a mirror? Of course I don't have enough space for a 1m diameter solar tube!

Certainly. A concave mirror could focus the light into a narrow mirrored tube. You'd lose a small percentage of light with each bounce off of the mirrors, but should have plenty of light left at the end. Throw in some flat mirrors to track the Sun and you'd have what you're looking for.

But that's a rather convoluted way of getting some sunlight into a building when things like skylights and roof windows exist.

 

[Nik_2213]

Even minimal research will find neat commercial 'light wells' with a domed roof 'catcher' feeding a reflective 'chimney' down to room...

 

[jumpjack]

I live in a flat at ground floor, roof is 3 floors above...

 

[Nik_2213]

"... roof is 3 floors above..."
Fair enough.
FWIW, I'm adding a pair of 60 cm diameter mildly-convex (*) 'security' mirrors between cat-shelves on our garden wall to brighten this side of garden...

*) Reflected objects are closer than they appear, especially T-Rex...
;-)

 

[FOXGLOW]

How did your test go? It's about 2 years later? I am thinking about doing the same and in my situation, trial by error is the best way to go about. I am buying a couple 18" to 24" convex mirrors on Amazon and will mount them in my backyard on my tall fence posts which are always even in winter in the sun until 4:30 pm. A bit of a shade in summer is nice. So maybe I will have to cover the mirrors then. But in any case, the test will cost around $60 USD. And my wife might enjoy the few extra sun beams. Convex rather than flat is in my opinion and in my situation probably better because it will disperse the sun reflection rather than a flat mirror. Yesterday (and it is winter here right now - so a bit cold) I was walking to back of my house and caught a sun reflection right into my face which was actually very warm, almost summer warmth I would guess it was probably around 25 degrees heat in my face - the reflection came of a window from the building. That was enough to start my research. Please let me know. Thanks

 

[BlazyG]

Hello-

I am starting a project to get direct sunlight onto the house by placing convex mirrors on the outside stone fence of the backyard since it is the only place of my property that is not shaded by other houses in the neighborhood. For that, I need to calculate the size of the mirrors, given the distance from the stone fence on which they will be placed (on a swivel) to the house as well as the size of the glass doors that open up from the living room to the garden (I would rather that I cover the entire area of the doors with sunlight!). I tried to do some research on my own but I think I'm way over my head on this one. Is there some kind of formula I can use to calculate the area of the light that is reflected onto the house given the size of the mirror and the distance from the mirror to the house? Is there any other parameters that I have missed? Please feel free to ask me for more information if I have missed providing any!

Your project to use convex mirrors to direct sunlight into your house is quite innovative, but it does involve some complex optics. The behavior of light when it reflects off convex mirrors can be a bit tricky to calculate because convex mirrors diverge light rays, spreading them out over a larger area. This divergence means that the area of light that reflects onto your house from a convex mirror will be larger than the mirror itself, but also less intense.

To estimate the size of the mirrors needed, we need to understand a few key principles:

Mirror Equation: For convex mirrors, the mirror equation relates the object distance (
u
u), the image distance (
v
v), and the focal length (
f
f). The equation is given by
1
f
=
1
v
+
1
u
f
1

=
v
1

+
u
1

. However, for your purpose, this equation helps more with understanding the formation of images rather than the dispersion of light.
Field of View: The size of the area illuminated by the mirror will depend on its field of view, which is influenced by the mirror's curvature. Convex mirrors have a wider field of view than flat mirrors, allowing them to illuminate a larger area.
Geometry of Light Reflection: The geometry of how light reflects off the mirror and onto a target area (like your glass doors) is crucial. The angle of incidence equals the angle of reflection, but due to the convex nature of the mirror, rays diverge.
Distance and Size Relationship: The further the light has to travel from the mirror to the target, the more spread out (and thus, less intense) it will become. The size of the illuminated area on your house will depend on the mirror's curvature and the distance from the mirror to the house.
To estimate the size of the mirrors, consider these steps:

Mirror's Curvature (Focal Length): The curvature of the mirror determines its focal length, which affects how much it will spread out the light. A mirror with a shorter focal length will spread light more than one with a longer focal length.
Distance to the House: The further the mirror is from the house, the larger the mirror needs to be to illuminate the same area, due to the divergence of light rays.
Desired Illuminated Area: You want to cover the area of the glass doors. Knowing the dimensions of these doors helps in determining how wide the beam of light needs to be when it reaches the house.
A simple way to start is by using a practical approach, considering the angle at which sunlight hits the mirror and the angle needed to reflect it towards your doors. However, without specific measurements (size of the doors, distance from the mirror to the doors, and the amount of sunlight you wish to redirect), it's challenging to provide a precise formula.

As a practical experiment, you could use a small, movable mirror to test how different sizes and angles affect the sunlight's coverage on your doors. This hands-on method could give you a rough idea of the mirror size needed before committing to larger, more expensive mirrors.

 

[phinds]

How did your test go?

The OP has not been here for 2 years

 

[harborsparrow]

I hope you will post here about what kind of thing you end up trying, and how it worked out. I too have a couple rooms that need more natural light, but because I've got neighbors living upstairs, it's impossible to install any kind of sun tunnel.

 

[phinds]

I hope you will post here about what kind of thing you end up trying, and how it worked out. I too have a couple rooms that need more natural light, but because I've got neighbors living upstairs, it's impossible to install any kind of sun tunnel.

The OP has not been here for 2 years

 

[gary350]

Don't use convex mirror you will catch something on fire.

Summer sun is about 420 btu per sq ft. Winter sun is about 200 btu per sq ft. A mirror 2'x3' = 6x420=2500 btu of heat. If your aiming at a patio glass door 5'x6' buy a sheet of foam insulation that has aluminum foil on 1 side this makes a very low cost mirror. You don't get a good quality reflection but it works. 5'x6'=30 sq ft = 30 x 350= 10,000. btu of heat summer sun and 5000. btu winter sun. If you walk past the patio door inside the house you can feel a temperature increase of about 20°f. I turned our house furnace fan ON it circulated heat to the whole house, our house was 1500. ft then.

Build a turn table with the mirror on it. Put a solar cell in the bottom of a deep cardboard box when sun shines down inside the box solar cell has enough voltage to turn on a DC motor to rotate the turn table. When turn table mores our of the sun motor stops. The turn table will more forward little by little all day keeping the mirror reflection on the patio door. Auto return timer send mirror back to the start location at 11 pm.

As the sun elevation change the mirror angle needs to be changed. At my house Dec 21 our sun is at 32°. Then June 21 sun is higher, I can't remember without looking that up but I think our sun is 78°. Once a week manually re adjust the mirror. If you want to get fancy you can build another auto tracker to tilt the mirror from 32° to 78°.

I built this years ago. I had pics once but they are lost.













t

 

[Averagesupernova]

Don't use convex mirror you will catch something on fire.

You are thinking of concave.

 

[gary350]

You are thinking of concave.

YES concave. Time expired I can't correct it.

 

[sophiecentaur]

Don't use convex mirror

YES concave. Time expired I can't correct it.

That's a danger. The 'image' of the Sun that's required is actually a very fuzzy one, spread over the whole window area. What's needed is very much a DIY solution. A number of small plane mirrors, mounted where there's loads of sunlight can synthesise a de-focussing effect. This would be better than what a perfect concave mirror surface produces can be achieved . Choose a broad target area in the room and aim a reflection of the Sun from each mirror in turn at various locations in the target area, spreading the light safely. Each mirror can be adjusted separately by covering all the others.

A plane mirror array can cover a larger area than a single concave mirror, thus getting some sunlight over a longer time. Also, the mounting of small mirrors is much easier to achieve and they can be fitted in between plants and other features. Multiple reflectors are the solution for the very biggest telescopes so it's the way to go.

I know this is an ancient thread but our design brains have ben following it closely all the time. I don't really care that the OP may have moved to a different home by now.

 

[gary350]

That's a danger. The 'image' of the Sun that's required is actually a very fuzzy one, spread over the whole window area. What's needed is very much a DIY solution. A number of small plane mirrors, mounted where there's loads of sunlight can synthesise a de-focussing effect. This would be better than what a perfect concave mirror surface produces can be achieved . Choose a broad target area in the room and aim a reflection of the Sun from each mirror in turn at various locations in the target area, spreading the light safely. Each mirror can be adjusted separately by covering all the others.

A plane mirror array can cover a larger area than a single concave mirror, thus getting some sunlight over a longer time. Also, the mounting of small mirrors is much easier to achieve and they can be fitted in between plants and other features. Multiple reflectors are the solution for the very biggest telescopes so it's the way to go. Sun is at a higher angle June 21 that makes btu be about 47000/2=23000 btu in 90 deg weather.

I know this is an ancient thread but our design brains have ben following it closely all the time. I don't really care that the OP may have moved to a different home by now.

Foam insulation board in 4'x8' sheets is very easy to bend I tested it with, 1", 2", 3" bend it produces a hot spot too warm to put your hand if board is bent too much. 130°f is plenty warm no one will get hurt. I was aiming at a sliding glass patio door. Sun is in the south you can only do this with a reflector on the north side of the house. All you need to do is make the 4'x8' beam of sun light smaller about 4'x4' so none of the light missed the patio door. This cost much less than a 100 glass mirrors I checked prices and glass is too expensive and too much work to mount and aim 100 mirrors.

I painted the 2 garage doors on my work shop flat black 1 winter the 2 doors are 7'x8' each that = 112 sq ft x 200 btu in winter = 22400. btu of heat. WOW that heated up my work shop nice. Summer came it was to hot to go in the work shop sun is producing 47,000. btu in 90° weather I painted the 2 doors white again.

https://www.google.com/url?sa=i&url...ved=0CBMQjRxqFwoTCKDou8KRyYQDFQAAAAAdAAAAABAE

 

[sophiecentaur]

I would just not like the aesthetics of a shiny, white sheet. Mirrors are popular as trompes d’oeil ; white sheets are not. This is with good reason.
But you can do what you like, of course.

 

[jumpjack]

Found a very good, free and online tool to play with rays reflections:

https://phydemo.app/ray-optics/simulator/

I am currently using a couple of parabolic dishes for satellite TV, covered with small mirrors, to succesfully reflect sunlight to my north-facing window for 4-5 hours per day withount need for moving the mirrors; then I figured out that I could get exatly same result with a convex mirror: the only difference bewteen convex and concave is that one mirror turns the image upside doen (concave one), the other does no (jut try it with a spoon); so one could use, rather than a satellite dish manually covered by small mirrors, one of those convex mirrors used to check for incoming cars behind a turn: indeed, if you look at one of this mirror you can see the whole path that Sun will cover along a day!
So I think I will convert my system to convex-type, by moving the mirrors on the back side of the dishes: actually the parabolic mirror can only concentrate sun rays in its focus... but what does it happen if the mirror accidentally falls?!?

 

[sophiecentaur]

convex-type, by moving the mirrors on the back side of the dishes

Experimenting is good value. I would say that a convex mirror would probably be best because it will catch the Sun better throughout the day.
Enjoy yourself.