Hey anons,
So I'm going to build a solar oven as part of a project for this Summer. I'd love to know if any of you have any experience building them?
Unfortunately I have an additional caveat in its design which is that it must be transportable and not to heavy (as I need to fly with it)
I'm thinking:
- Get a large (golf?) umbrella. Remove the handle section, leaving just the ribbed mechanism for opening the umbrella.
- Using the geometry of the umbrella as a template, I can cut out 'petals' of reflective material, which I can then attach between each rib.
- Was thinking of using silver mylar on the roll (20m x 1.2m wide for £25 on the bay: http://www.ebay.co.uk/itm/Silver-Mylar-Reflective-Mirror-Foil-Sheet-Sheeting-20M-Roll-Party-Gift-Wrap-/131701785611?hash=item1eaa09c40b:g:oWcAAOSwFqJWl83w)
Either attach the mylar by adhesive (when on site), or if I can I can bolt it on with small wingnuts which'd allow me to deconstruct it without tearing it apart.
I guess my questions come down to:
- Does the above make sense and do you think it'll work?
- Is Mylar sheeting gonna be good enough? Can anyone suggest a better alternative for this application?
- Is the geometry of an umbrella going to be appropriate to focus the solar energy to the centre point?
I'm going to be using it in desert conditions, average highs of 28-34C, and I intend to use it to make bread. I'm optimistic about reaching 180C, not sure if I can push 230C
I own an IR thermometer and will probably test it here at home (mild summer temps) to see how it might fare.
Here's a good image of what I'm planning, more or less.
>>963259
And heres the image of the umbrella I was looking for.
Crucially it is:
Parabolic in shape
Large - good minimum is 120cm
Has a lot of ribs - apparently you want over 16 to ensure smooth transitions/curves
>>963257
I've made several styles (Fresnel lens, Funnel, Panel, Parabolic, Box, Collapsible, Mylar blanket, etc.) My personal favorite has been a standard insulated box cooker with 4 trapezoid-shaped reflectors. However, the one I use for cooking bread loafs and big meals is rather large, heavy, and required attaching wheels to move it around.
Parabolic cookers are very fussy. You have to get the cooking vessel right in the focal point at all times. This requires lots of babysitting. You will need to adjust the alignment with the sun once every 15-20 minutes for optimal cooking temperatures. They are also hindered by ambient temperatures and wind. They also need cloudless skies to work even remotely well.
Funnel and Panel cookers (like the one in this image and the one in your image) are easier to use and require much less babysitting. They are also less hindered by ambient temperatures since they use a wind break. The cooking vessel is inside the wind break. The on in your image has 2 containers. A clear outer wind break and a black inner cooking vessel. These are "ok" for semi-cloudy skies.
Insulated Box cookers, while bulkier are the easiest to use. You don't need to align them as much (same amount as funnel/panel cookers) and they work in fairly overcast skies (better than funnel/panel cookers). Well-insulated, doubled-glazed ones work in the dead of winter at -10F without trouble.
>>963301
...Continued
Because I like using box cookers and I dislike their bulkiness, but still love them insulated, I decided to design a portable one. I made this one and kept it behind my truck seat for years until someones dogs tore it up. I used it when at remote work sites to cook and warm up food. I was the only person who had hot meals while on those jobs.
One day I'll make another one and it will be even better, smaller, lighter, with higher cooking temps etc.
So, you'd need to weigh your options as to what type of cooker would best fit your cooking style/attention to the cooker while cooking, its portability, and if the construction materials are allowed on the plane (I have no clue at all about the later). However...
>>963303
...Continued.
You can make a functional solar cooker from just about anything. This one, uses a plastic bag as the glazing and has spacers to allow the use of 2 pieces of glazing. It merely lacks insulation, but that is what the towel is for.
>>963303
Another image of the portable one.
>>963310
Emergency blanket funnel/panel style cooker. It worked, but isn't really easy to setup and not easy to reposition. Highly portable.
>>963311
This is the one I use most. It reaches about 380F. I made it to be heavy, it uses lots of insulation, has double-glazing (tempered glass for inner glazing), and as large a set of reflectors as a couple of 4' x 8' sheet of 1/4' plywood could make.
>>963313
Wow
>>963301
>>963303
>>963308
>>963310
>>963311
>>963313
Damn anon, very very impressive. I especially like the second and last [box cookers]. Nice little lesson and the strengths of a box design seem glaring now.
If you'd indulge me I have questions. First I should say that I'll me using it in the south of Spain in July so weather will be 77% chance of sunny days 32C/90F noons. And I'd like to be able to maintain a 180-230C range.
When you refer to insulation I assume you mean the box itself. The petals are more or less similar in design regardless of the solar oven style?
What is your box made of? Is it just black painted wood?
I have some thinsulate boarding kicking about, and I'm sure I could knock up a box, but I'd want to be able to fit four loaves if possible as I'll be cooking for a few.
Are the panels flat?
Guess it's time to look up some designs and figure out how to make one transportable.
>>963515
cont
The tilt and allowing the oven to sit flat seems like a conundrum.
Also, does the design have to be based off a square? Could I, say, elongate it into a rectangle?
Does bigger panels mean a higher heat?
Is there a certain angle they should be in relation to the oven?
I wonder if I could use tent poles (or similar) to build a mountable frame from the box oven, and then have individual panels that fit on (somehow). Would pack down well.
>>963515
>>963519
>When you refer to insulation I assume you mean the box itself.
>What is your box made of? Is it just black painted wood?
This image shows the box cooker here >>963313 in progress. The layers of insulation in this one from inside to outside is: 1 inch of cardboard, 2 sheets of Celotex blackboard, 2 sheets of Styrofoam, outer cardboard box. Everything is bolted together and the bolt heads were covered with cardboard to help prevent thermal bridging. The door uses the same insulation with additional 1/4" plywood and a later-installed handle. A wooden frame was added when it was apparent it needed wheeled transport. It was painted black inside to help raise ambient air temps for baking.
>The tilt and allowing the oven to sit flat seems like a conundrum.
The bottom has a removable black-painted metal tray. Peg holes in the back wall allow the unit to be tipped and the metal tray to be leveled on them.
If I were to do this again, I would drop money on some aerogel blanket insulation for the sides and airloy for the bottom. That would allow for a very compact design, much lighter, and still have great temperatures.
>The petals are more or less similar in design regardless of the solar oven style?
Pretty much.
>Are the panels flat?
Yes. It is based on this design:
http://www.backwoodshome.com/making-and-using-a-solar-cooker/
>Could I, say, elongate it into a rectangle?
Of course.
>Is there a certain angle they should be in relation to the oven?
Yes, see link above. When fitted together, they angle properly.
>>963519
>I wonder if I could use tent poles (or similar) to build a mountable frame from the box oven, and then have individual panels that fit on (somehow). Would pack down well.
My panels rest on a piece of 1/4" plywood on the top that has wooden lips attached. On the back of the panels I have hooks glued on and use bungee cords to hold it down on the box.
>180-230C range.
Take care to use Tempered Glass for the piece of glazing that will be on the inside. If you don't, it WILL break. My first test broke at 250F/121C.
>>963519
>The tilt and allowing the oven to sit flat seems like a conundrum.
This one I started was intended for winter use when the sun is very low in the sky. That may give you some ideas.
I know that when I did a project like this in university, one group made a really interesting parabolic one - they made a ~30cm deep "ring" of cardboard (I think it was hotglued and multiple layers of it for strength), stretched some mirror film over it, covered the other side, and evacuated the cavity; this resulted in a VERY smooth and very reflective surface. I'm pretty sure they were able to get the highest temps, too - they cooked any foods 3-5x faster than other groups. By the end of the demo, they had churned out little egg-and-bacon sandwiches for half the class.
Whatever you end up doing, make sure you add some sort of way of "levelling" it - all the sun in the world won't do you good if it's not being focused correctly.
>>963552
tempered glass for what exactly? The 'lid' of the oven?
>>963844
The box has a window to allow the sun light to shone through. It uses 2 pieces of glass. The inner piece of glass that experiences high temperatures is made of tempered glass. On my design, the glass section is not a lid. The lid is in the back as seen in >>963544
>>963707
Yeah, if you have the proper setup, parabolas and Fresnel lens are the way to go for fast cooking, like frying things. On a sunny day with a large parabola you can cook up a storm. For baking, you need a larger area, at which point things start to become very cumbersome. I don't recommend either for baking.
Frying with a parabola is a bit frustrating sometimes if the unit is very large. This is due to the fact your shadow is over the parabola when you're flipping the food around. There's also the danger of getting burned or even blinded.
On the other hand, a Fresnel lens is extremely dangerous for burns. More so than the parabola. This is because you can easily cross your hand over the food you are fixing in order to flip it and end up putting your hand right in the focal point. There's more of problem with blinding yourself since the focal point has a chance of reflecting the light depending on what is in the focal point. I suggest wearing strong UV protection when using a Parabola, but more so when using a Fresnel lens (check out the glare in this image from a Fresnel lens cooker).
Moving a non-folding parabola around is a pain and storing it is a pain; same with box cookers. But, you can also accidentally burn things with the parabola. A Fresnel lens on the other hand is even worse. You need to have a cover or pouch for it. Never move it around when uncovered. One simple slip up and you will catch yourself on fire instantly. You have to carry them parallel to the sun's rays to keep the sun from shining through it and hold it as close to your body as possible to prevent accidental fire.
>>963257
I just need something to angle it with and some way to hang a pot in the center. Otherwise, this things just a refrigerator box and some mylar.
https://youtu.be/xbwliZJiHe8
>>963897
That poor CCD.
this is pretty cool ,but as someone who lives in England. I got to say it would be pretty useless for me
>>963897
Didn't know J.J Abrams had a cooking show
>>963934
That's one sad thing about this county. As much as I am interested in solar investment, doing so on these shores will largely be a waste of time.
>>963934
On YouTube some guy cooks a whole chicken on these shores using a box. Weather didn't look the best either.
