What materials will I need to build a solar reflector oven?

Materials for a reflector oven

Solar Reflector Ovens all work on the same basic principles and consequently, materials for a reflector oven will all be somewhat similar. The variations will depend on how much an individual is prepared to spend on the project to construct the optimum Solar Reflector Oven.

Let’s break down the components of a Solar Reflector Oven into the various functions that take place within the oven.

• The sunshine gathering function
• The window that allows the sunshine into the oven
• The oven and insulation
• The cooking containers

These components can be divided into essential components and optional components

Sunshine Gathering Components

Solar Reflectors obviously work best when there is the greatest amount of sunshine, those really sunny days, but they will also work when there are some clouds in the sky.

On these cloudy days, in particular, we want to focus as much sunlight on the window to the oven as we can. This is normally done by constructing some kind of reflector. This reflector may be an extension of the box containing the oven, or a separate component.

Reflectors

The reflector is a shiny surface that will redirect the sunshine onto the window. It may be flat or curved. Possible materials are:

• Aluminum foil – Foil is naturally slightly crinkled and to get a true reflective surface it is necessary to fix it to a firm backing. You can use glues to bond it to the hard surface. A soft roller is an ideal tool to flatten the foil onto a hard surface using glue. Just roll the foil removing crinkles, air pockets and lumps. Roll the foil from the center outwards.
• Mylar – Instead of foil, you could use Mylar. This is the material used in making space blankets (those shiny emergency blankets). You stick this to a hard surface in the same way that you stick the foil. Mylar is very reflective and is sometimes used in the construction of mirrors.
• Miro 4 – Miro4 is the material that is often used in aquarium reflectors and if you have access to it, it would make a great reflector material.
• Ultra White Paint – Surprisingly ultra white paint has better reflective qualities than Miro4. Paint is probably the easiest material to use and would also be easily applied to a non-flat surface. You could, for example, paint the inside of an umbrella to create a parabolic shaped reflector which would be even more efficient than a flat reflector.

The Top Window on the Oven

Most designs of Solar reflector Ovens will have a top window through which the sunshine is directed by the reflectors. Your choice of materials for a reflector oven will be directly related to the planned budget for the project and what temperatures you are aiming at.

• Glass – Glass is the most obvious choice for creating the window at the top of the oven. It will handle the heat and is a nice solid material. The only difficulty is getting it cut and the edges ground so that the user does not cut their hands.
• Tempered Glass – A better solution than regular glass would be Tempered Glass. This is the material used in oven doors and coffee pots etc.
• Clear Plexiglas – Plexiglass is a strong material that is easier to cut than glass, you just need a glass cutter tool. However standard plexiglass can emit toxic fumes if heated and it is, therefore, better to choose special “Lexan” plexiglass that can tolerate higher temperatures and does not emit fumes.
• Plastic Wrap – The extreme budget material you can use will be Kitchen Plastic Wrap. This will not tolerate heat from hot ovens and can only be used in demo ovens that reach much lower temperatures. It is also a weak material that will not last long.
• Fresnel Lens – If using glass or plexiglass (a strong window), you may choose to affix Fresnel Lens on top of the surface. These lenses are used as magnifiers and will intensify the light that hits them.

The Oven

The core of the Solar Reflector Oven is going to be the oven itself. The oven needs to be large enough to contain the cooking containers and very well insulated so that it retains the heat that you have created by focussing the light on the absorbent materials inside the oven.

To achieve this the optimum design will be an inner and outer box with insulation in between. Looking at the materials and method of construction the following materials may be appropriate.

• Cardboard – Cardboard is the easiest material to use to create the oven. Cardboard will burn at 450 degrees so it should deal with the temperatures of the oven, the easiest construction method is to get two cardboard boxes, one larger than the other to create the oven. Space between is filled with insulation. I would treat the inside of the inner cardboard box with either a highly reflective material/paint or a material that absorbs heat/black paint.
• Wood – Wood also combusts at 450 degrees. It would be advisable to line the oven with something that has a higher combustion point.
• Aluminum – Aluminum is the perfect material for the inner box in an oven as it is not combustible, and the surface is highly reflective and will reflect any heat back into the oven.
• Clay – Clay is another good material to use for the inner lining of a Solar Reflector Oven. Ideally, it should be mixed with straw. This is the way that cob buildings are made. Try to use dark-colored clay as this will improve the conductivity of heat.
• Bricks – It would be possible to build a permanent solar reflection oven using bricks (double skin). This would certainly be a solid structure and with suitable insulation, it could be quite efficient.

Do you use a dark material to line the oven or reflective material? If you are using dark-colored cooking pots then it is preferable to use a reflective inner service for the oven, as the reflective walls will reflect the heat back onto the dark pot, which will absorb the heat.

If your cooking pots are lighter, then it would be preferable to use darker linings that will absorb the heat and maintain a higher temperature in the oven.

Insulation

In order to maintain the temperature inside the oven, the oven needs to be airtight and the walls, floor, and top should be insulated to keep the heat in. There are a variety of materials that can be used for insulation (placing between the inner and outer walls of the oven).

• Old Newspapers – An easily available source of insulation is old newspapers/ these should be crumpled so that they contain air pockets and then pushed down hard between the skins to form an insulating layer.
• Papier-mache – If you also want to strengthen the structure of your oven, you can make papier-mache and fill the gap between the two skins with this material. It will both make a strong later between the two skins, increasing its strength, and will also add insulation.
• Clay – Clay can also be used as an insulation layer, packing the clay between the two layers of cardboard. This will increase the structural integrity of your oven while making it far more insulated.
• Rammed Earth and Sand – There is no reason why you cannot simply ram earth or sand into the gap between the two skins.
• Wool – Old woolen clothes can be used to fill the gap, ramming them down tightly. It may work better if you cut the clothes up into smaller patches first.
• Straw – In some countries, they build houses with square bales of straw that have a peg hammered through them to keep them straight. They do this because these houses are incredibly well insulated. Straw can be packed into the gap and it will be an efficient insulator.

Cooking Containers

Whilst cooking containers are not a material used in the construction of the Solar Reflection Oven, they are integral to the selection of some of the materials that you will use. You also need to consider the size of the pots that you intend to use when designing the oven.

If you intend to use black colored pots to hold the food that you are cooking then you really should consider choosing a reflective inner skin material or lining so that the sunlight that enters the oven through the top window can be bounced back on the dark-colored pot that will absorb and hold the heat. 

If you plan to use open oven dishes or light-colored pots to cook the food then you are better to choose dark colored linings to the inner oven walls. These skins will absorb heat from the light and radiate it back at the pot or dish

One other point about the cookware you choose is that you should consider the materials from which the pots are made. Cast iron pots will take much longer to heat up than aluminum ones or pyrex open dishes.

I hope that this article has given you ideas on the materials for a reflector oven and allowed you to make informed decisions for your project. The materials can, of course, be substituted for those listed in the “Step by Step guide to building the ultimate solar reflector oven”, that you will find elsewhere on this website.