Solar oven problem

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Last week I built my solar box oven. I was quite delighted with the result and was eager to try it. I waited till a really hot day and tried to bake a cake. To my dismay, even after several hours my oven only got up to 170 degrees, enough to pasteurize water (which is good of course) but not enough to cook. Any ideas on where I may have gone wrong? I don't intend to give up of course. Thank you.

-- citygirl (citygirl@idirect.com), July 21, 1999

citygirl, you don't describe your oven, so it's hard to tell.

The areas that could be a problem are:

1. Inside reflectors -- do you have good reflecting walls?

2. Outside reflectors -- are you able to capture enough solar energy by means of outside reflectors?

3. Insulation -- is the interior heating box suffinciently well insulated from the outside box? Do they touch or do you have a good air space between them?

4. Cover -- are you losing heat because air escapes through the transparent cover?

5. Size -- is the oven large enough to capture sufficinet solar energy? Is it large in comparison to whatever you're using to cook food in?

Keep trying. I think most of us have to experiment.

-- de (delewis@inetone.net), July 21, 1999.

Well, I made it according to instructions - about an inch of space, foil lined around inner box, a flap reflector, look bag cover. The box is about 14" high and about 15" by 20" other dimension. I think perhaps I need to refine all the points you made. I may be losing heat through the lid. It was so hard to make it tight. I will try again. Thank you so much for your input.

-- citygirl (citygirl@idirect.com), July 21, 1999.

Where do you live?

I'm working on oven plans, have cooked dinner here in a solar oven, but Seattle takes special effort because we aren't QUITE the sunshine capitol of the world!

Two pieces to the puzzle - you have to capture as much sunlight as possible, and then use it as efficiently as possible. That means square footage and insulation.

Try different designs. A reflector that bounces sunlight onto a pot, with the pot closed in an oven bag, is remarkably efficient. Give it a try.

-- bw (home@puget.sound), July 21, 1999.

Thank you all! I live in Toronto where we get loads of sun in summer, but will have probably 4 months of the year where we can't use it. I will certainly try all the suggestions.

-- citygirl (citygirl@idirect.com), July 21, 1999.

Citygirl- How big are your reflectors? They should each be about the size of the entire top of the solar oven, as a rough guestimate of appropriate size. A few years ago our homechooling support group kids made a half dozen or so cardboard box solar cookers, and they worked fine. We used half a dozen layers of cardboard for insulation between the outer box and the inner "oven" box. Painted the inside of the "oven" box black, lined the reflectors with aluminum foil, glued in place, held the reflectors in place with shoe laces. We used a piece of salvage plate glass for a cover. It works as well as our commercially built "Sun Oven", just not as durable or convenient, but lots cheaper. The "sun Star" at is similar to what we made. Good luck.

-- Jim (jiminwis@yahoo.com), July 21, 1999.

oops--I guess I don't know how to do links. The solar oven site is at "accessone.com/~sbcn/plans.htm" The unit is called "Sun Star".

-- Jim (jiminwis@yahoo.com), July 21, 1999.

accessone.com/~sbcn/plans.htm

Chuck

-- Chuck, a night driver (rienzoo@en.com), July 21, 1999.

I was only able to get from between 200-250 on mine. The inside is lined with mylar with a metal plate in the bottom painted in black. Should the entire interior be painted black?

-- marsh (armstrng@sisqtel.net), July 22, 1999.

Hey marsh--

Nope, depending on the surface areas of the mirrors, any one side or none may be painted. The larger the surface area the greater the focus of radiation. What kind of mylar are you using in the lining?

-- Michael (mikeymac@uswest.net), July 25, 1999.