Convex Mirror in Backyard to reflect sunlight onto the house

[sophiecentaur]

reconsidering whether the project is even worth doing in lieu of simply buying a lamp.

I think that, to see actual sunshine when none is available would be significant and worth going for. But not at any price. Leds are no better than leaving the lights on indoors and a string of fairy lights wouldn't be a substitute.
As it's not your or my garden then we can't say what the OP should do. All I can say is that a big enough curved mirror would need to be very costly but a plane mirror would be no more than a few pounds. So it gets my vote.

 

[Drakkith]

@Hadi Remember that this isn't the early morning or late evening Sun we're talking about, this is the blinding midday Sun. Any surface the light falls on is going to be overwhelmingly bright unless the light is highly diffused or spread out. So bright that most people block the direct light with curtains just so they can see the darker areas inside their house.

Also, any time you look outside the window you're going to be looking into the Sun. It's very bright and very uncomfortable to have in your field of view, so you can consider whichever window you're using for this project to be useless to look out of.

 

[sophiecentaur]

@Hadi Remember that this isn't the early morning or late evening Sun we're talking about, this is the blinding midday Sun. Any surface the light falls on is going to be overwhelmingly bright unless the light is highly diffused or spread out. So bright that most people block the direct light with curtains just so they can see the darker areas inside their house.

Also, any time you look outside the window you're going to be looking into the Sun. It's very bright and very uncomfortable to have in your field of view, so you can consider whichever window you're using for this project to be useless to look out of.

That is a good point. Perhaps a security mirror would be an appropriate size and have suitable coverage.
I am reminded of playing with a big, gash mirror when I was a lad. The effect was very localised (of course) and just like the shadow image you would get with the Sun shining through a hole. Good for upsetting neighbours iirc.

 

[persononline]

There is a several years late Kickstarter project attempting to redirect sunlight with a mirror that rotates to follow the sun. Google “Caia” - you may find it interesting.

 

[BvU]

So it's all been done before. More or less an off-the shelf product.
Impossible to think of something original nowadays
Funny to see they can fill whole videos showing the tightening of nuts

 

[sophiecentaur]

Bearing in mind the range of AZ and EL of the Sun when you actually need to see it, it may be that a wide cylindrical reflector would give a wider range of AZ to include most of the day and a more restricted range of EL. The height and width of the cylinder could be chosen independently. Also, it's pretty easy to bend a sheet of SS to any radius you need.
I'm assuming that a round image of the Sun is less important than illumination when it's wanted.
PS if the project turns out to have failed, that sheet of SS could be useful for later projects.

 

[berkeman]

There is a several years late Kickstarter project attempting to redirect sunlight with a mirror that rotates to follow the sun. Google “Caia” - you may find it interesting.

Welcome to PF.

I was worried at first that it might be spam when I saw your post about a kickstarter project, but I see that the funding window is closed and the project is well on its way. Thanks for the interesting info.

 

[sophiecentaur]

So it's all been done before. More or less an off-the shelf product.

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

 

[chemisttree]

Sounds like a real complicated project. Angles, motors, cams, blinding white walls, degrees of latitude.

If only there were something commercially available!

 

[Hornbein]

Painting the interior walls white will brighten a dark room.

 

[Drakkith]

Sounds like a real complicated project. Angles, motors, cams, blinding white walls, degrees of latitude.

If only there were something commercially available!

This seems like a much better solution. No moving parts, no large mirror, and little maintenance.

 

[sophiecentaur]

This seems like a much better solution. No moving parts, no large mirror, and little maintenance.

Can't argue with that really but a bit on the boring side. There is a point about neighbours, who may not appreciate 'light pollution' from a system in the garden. That would need to be born in mind when positioning any reflector.

 

[tech99]

How about trying a sheet of plywood with crumpled Aluminium foil on it?

 

[Tom.G]

How about trying a sheet of plywood with crumpled Aluminium foil on it?

Or cardboard or poster board for a 'Proof of Concept' before buying plywood.

 

[sophiecentaur]

Or cardboard or poster board for a 'Proof of Concept' before buying plywood.

You could re-use the foil for the Christmas turkey afterwards. 1kW per square metre would give in idea of the 'power' of the reflector as an omnidirectional source. Crude but something to start with.

 

[Jonathan Scott]

How about trying a sheet of plywood with crumpled Aluminium foil on it?

I have some pieces of card on walls or window frames with shiny foil hooked over them that was smoothed down over a Lego baseboard, so it is covered with a pattern of bumps that reflect and disperse light. These cards are used to direct some light from a nearby window to darker areas (especially on the same wall as the window). I also have mirror tiles on some window sills for similar reasons; if the sun reaches them, it creates bright patches on the white ceiling that help illuminate the whole room.

 

[chemisttree]

How about trying a sheet of plywood with crumpled Aluminium foil on it?

Try filling your back yard with shiny balloons?

https://img.ltwebstatic.com/images3...7611312fb7ee28d5334137836_thumbnail_750x.webp

 

[dlgoff]

Here's something you might want to consider:

edit: I'm thinking, attaching to a thin (maybe 1/4 inch) curved sheet of plywood.

 

[dlgoff]

Here's something you might want to consider:
View attachment 294979
View attachment 294980
edit: I'm thinking, attaching to a thin (maybe 1/4 inch) curved sheet of plywood.

Since I haven't gotten any response to this, I'm assuming it's not that good of an idea.

 

[BvU]

Since I haven't gotten any response to this, I'm assuming it's not that good of an idea.

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

$\$

 

[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.