[UneasyRider]

I have been looking at 3 types of solar cooking, the fresnel lens, parbolic cook top and solar oven. I am looking for anyone with practical advice on which one to do. Any input is appreciated.

[emt1581]

Originally Posted by UneasyRider

I have been looking at 3 types of solar cooking, the fresnel lens, parbolic cook top and solar oven. I am looking for anyone with practical advice on which one to do. Any input is appreciated.

I've never done it but ever since I saw a vid in my thread of that chick with the lens doing it I've wanted to try it. Seems like it'd be near impossible with anything portable/pocketable though from what I've seen. And lugging around a 3-4' wide lens isn't exactly practical for me. At that point I'd like to just start a fire and use that to cook with.

We'll see what people say.

EDIT: Seems that my thread on Fresnel lenses didn't survive so that link someone shared to the site that deals in bulk and huge lenses... that'd be cool to have again.

-Emt1581

[farmer-dave]

When I was a kid I used to cook hotdogs using a suntwist that my brother in law made. I think he built it as a boy scout project. It was basically a 4' diameter reflector cut into spirals that reflected the light to a focal point. Seem's like it took about 5 minutes to cook some dogs, although it was better if you flipped them over and then it took about 8 minutes. That was the extent of using it for cooking except for marshallows.

I've often though of buying a solar oven but for the cost, I could buy a heck of a lot more propane. I think their usefulness depends alot on your climate and how much sun you really get. May work great in Arizona, less so in Washington. I consider them more of a novelty, nothing wrong with them but I haven't spent my money on one yet.

[doktarZues]

I got in on group buy and have one of these about a year ago, the "sport" solar oven I believe: http://www.solarovens.org/ . Admittedly I haven't used it near enough to master it but it will damn sure cook up some food.

So far I've cooked chicken and turkey (chili) and all kinds of non meats which are much easier. It really doesn't seem to need a large amount of sun so the assertion that this would probably only work in notoriously hot/sunny areas I believe is incorrect. Depending on your budget, I think these things are ridiculously cheap since the fuel is so plentiful and free and all preppers should have one.

I know a lot of folks store high quantities of rice and beans and I wonder how many have calculated just how much fuel it would take to cook up say 100lbs of beans over a few months. Re-run those calculations with a solar oven and you'll find they're invaluable.

[emt1581]

Originally Posted by doktarZues

I got in on group buy and have one of these about a year ago, the "sport" solar oven I believe: http://www.solarovens.org/ . Admittedly I haven't used it near enough to master it but it will damn sure cook up some food.

So far I've cooked chicken and turkey (chili) and all kinds of non meats which are much easier. It really doesn't seem to need a large amount of sun so the assertion that this would probably only work in notoriously hot/sunny areas I believe is incorrect. Depending on your budget, I think these things are ridiculously cheap since the fuel is so plentiful and free and all preppers should have one.

I know a lot of folks store high quantities of rice and beans and I wonder how many have calculated just how much fuel it would take to cook up say 100lbs of beans over a few months. Re-run those calculations with a solar oven and you'll find they're invaluable.

They look really simple. Are there any things on them that wear out? Maybe gaskets or plastic parts?

My only complaint about anything solar is winter. During the winter it's nothing but overcast around here. Pretty much zero direct sunlight.

-Emt1581

[doktarZues]

Originally Posted by emt1581

They look really simple. Are there any things on them that wear out? Maybe gaskets or plastic parts?

My only complaint about anything solar is winter. During the winter it's nothing but overcast around here. Pretty much zero direct sunlight.

-Emt1581

The reflectors (which I haven't used yet) look a little flimsy and like they wouldn't last too long getting beat on by the elements (wind)..but the fundamental hardware is 3 pieces: the dark pots with your food in them, the plastic box that you set them in and a clear plastic lid. Not much to wear out.

There of course are all makes and models out there but the one I have is quite sturdy. The metal clips that fasten the lid is probably the weakest link and that could easily be replaced with something makeshift.

[quake]

Before the last server crash, I had several pics posted, but can’t find them now – I’ll see if I can dig them up from photobucket.


Never used the parabolic or Fresnel approach, but we’ve used a couple box-style cookers for 6-8 years now. Haven’t lately as we’ve been silly busy with stuff, but it does work surprisingly well. Made our first one out of wood and it worked great until my then-young son left it open in the rain for two days and it molded irrecoverably before I found it.

First one, made from wood scraps, a mirror, and plain styrofoam insulation. On a cloud-free day it would usually reach 370-380 degrees and more than once broke 400:


Used a table-leg bracket and eye-bolts for the mirror brace and adjustment:


Closed. Prop & all fit down inside for storage:



Don’t have pics of the second one, but when I tried to make better I ended up making it worse. Made it larger and heavier, angled the top to face the sun more directly, and insulated it much thicker with cellulose blow-in type insulation. Turned out to be too much mass and it never got above 200 degrees. Lesson learned – mass is the enemy. Obvious once I thought about it, but I just thought about it too late.


Third one, I made out of an old fire-alarm control backbox. Sealed up the conduit entry holes with sheet metal and epoxy, insulated it with two layers of ductboard, and added the mirror & prop similar to the first one. Actually, the mirror is the mirror from the first one; not an exact fit for this new one, but close enough that I used it. This one reaches 300 pretty regularly, but has never broke 375 afaik. The construction makes it much more durable than the first two wood ones, but more mass to try & heat up and makes it heavier to carry around as well.

[quake]

Most-used pan is a simple aluminum pan with snap-on lid, painted with high-temp flat black grill paint:



Inside the pan, a cooking bag keeps the moisture contained. This is important on a flat-glass-top box cooker, as escaping moisture causes condensation on the glass lid, greatly reducing light entry and cooling the oven down below the cooking point. This is a ~3 lb roast, three potatoes, & half an onion. Usually add carrots, but for whatever reason, not that particular day:


Four & a half hours at ~250 degrees that day; slow-cooked like this, the meat is almost literally too tender to cut. It almost falls apart with just a fork:


I've been intrigued by the commercially-made box cookers, as they should be more efficient than my home-made, but never have taken the plunge on one yet.

[actionshooter10]

I've used solar ovens like Quake pictured many times.

You can bake ANYTHING with them.

No lack of sunlight in Tejas...lol.

[Mr.Pliskin]

Cody Lundins book When All Hell Breaks Loose has directions how to make one out of a cardboard box, aluminum foil and a sheet of glass or plexiglass, and even has the extended cook times. I've been meaning to make one for the past few days since I just got 500 feet of aluminum foil from sams but havent got around to it yet.

I realised I could go cut down fence posts or mesquite trees for fuel to heat food, but thats allot more expended energy for the meal rather than just waiting for the sun to heat it up. An all around good thing to have.

[quake]

Originally Posted by Mr.Pliskin

...I realised I could go cut down fence posts or mesquite trees for fuel to heat food, but thats allot more expended energy for the meal rather than just waiting for the sun to heat it up...

That's one of the big pluses of solar cooking imo. If you can use it every day, then great; but even if the weather is such that you can only use it half the time, that still means that your other (stored) fuel only gets used half as much, and so lasts twice as long.

[sebecman]

Quake - that's a great post, thanks!

[Bolster]

Question for Quake (or whomever): If your solar oven isn't full, does it make sense to put in some mass to fill the empty space, or no? For example, if you had room left over, imagine you put a brick in the oven beside your food, would that help retain heat? (Sort of like how we keep our freezers full of ice, if possible?) Or would you be wasting energy trying to heat the brick, that could be cooking your food?

[RedHaze]

No extra mass needed. It's all shiny in there, if there is open space, it means it's reflecting MORE and whatever you're cooking should be absorbing more of what's being reflected around in there.

[TangoFoxtrot]

I'd be interested in this type of cooking as well. Back up to my propane grill, charcoal grill, and wood firepit.

[quake]

Originally Posted by Bolster

Question for Quake (or whomever): If your solar oven isn't full, does it make sense to put in some mass to fill the empty space, or no? For example, if you had room left over, imagine you put a brick in the oven beside your food, would that help retain heat? (Sort of like how we keep our freezers full of ice, if possible?) Or would you be wasting energy trying to heat the brick, that could be cooking your food?

Just the opposite; pretty much as RedHaze says. Mass is the enemy. A brick will hold btu's better than empty space will, but it also 'consumes' or absorbs btu's in the process of heating up; btu's that would have otherwise gone toward something productive (cooking).

That's the exact mistake I made with my second home-built solar cooker. It was better insulated, had a better glass-to-space ratio, more reflected light into it, and better angling of the glass. It absorbed btu's better, but there was just so much of it that those btu's got spread out over a lot more mass, making it less hot than the lighter, simpler ones I've made. The added mass does kind of seem like a good idea at first glance, but think of your normal kitchen oven, cooking a 15-pound turkey; and adding a dozen bricks in the oven at the same time. It will definitely make the oven retain heat longer once turned off, but it will also mean it either takes more time to cook the turkey since the heating element now has to cook the turkey AND the bricks. Only way to compensate for the bricks and cook in the same time frame is to turn up the oven to a higher setting; and with a solar cooker, the sun is the heating element, so there's just no 'turning up the setting'.

Mass is the enemy in a solar cooker.

All that said, I have seen some that were made pretty massive, out of mud, adobe, etc. But they were near equatorial in location (maximizing the sun's input), and didn't get as hot as a lightweight box cooker either; used mostly in very remote areas for low-temp, slow cooking of things like beans, stews & such.

[Bolster]

Excellent. Thanks for the thoughtful answer. Previously you'd said "mass is the enemy" but I thought that might have been for the box rather than the contents. But mass is the enemy, wherever it is. I get it now.

I have a Global Sun Oven on the way and am trying to learn the ropes before it gets here.

[SFCSMITH(RET)]

Originally Posted by emt1581

My only complaint about anything solar is winter. During the winter it's nothing but overcast around here. Pretty much zero direct sunlight.

-Emt1581

During winter.. you should be doing something for heat.. That is where we cook a lot. On the wood stove.

[UneasyRider]

Originally Posted by Bolster

Excellent. Thanks for the thoughtful answer. Previously you'd said "mass is the enemy" but I thought that might have been for the box rather than the contents. But mass is the enemy, wherever it is. I get it now.

I have a Global Sun Oven on the way and am trying to learn the ropes before it gets here.

Use all black pans and you will do just fine. I have used both and there is a big difference in temperature.

[Devans0]

"Please school me thread" reminded me that aluminum wasn't the best reflector for solar, in past experiments. Reflective mylar doesn't block infrared frequencies as I remember from ancient experiments

[UneasyRider]

Originally Posted by Devans0

"Please school me thread" reminded me that aluminum wasn't the best reflector for solar, in past experiments. Reflective mylar doesn't block infrared frequencies as I remember from ancient experiments

They use polished aluminum which is pretty good. Most of the heat in the oven comes directly from the sun without the need for the reflectors here in Florida.

[UneasyRider]

I looked at solar cooking quite a bit online before buying one and seeing 500,000 people in the desert using them was convincing. That desert used to be forest before all of those people burned it for a fuel supply. Now they walk huge distances to get wood or use solar cooking.