Tips for Using the Solar Box Cooker

After following the Instructions for Building a Solar Box Cooker, you have constructed a solar box oven and are ready to use it. The first sunny day after the cooker is complete, heat it empty so it can completely dry.  Recording results of the oven's performance will help you discover which conditions produce the best performance.  Ideas for experiments and using bricks to change the oven’s performance are included in this section.  If the oven doesn’t heat as well as expected, follow the instructions for troubleshooting.

Heat the Cooker Prior to the First Use

It is important to place the solar box cooker in the sun to heat thoroughly before using it to cook. The glue will completely dry in the hot sun. Once the oven is hot, take the inner box and piece of glass off to allow any moisture to dissipate. Select a level area that receives full sun to place the solar box cooker. Place the cooker with the long side centered on the sun’s east-to-west path across the sky shortly before the sun is directly overhead.

Always wear sunglasses when using the solar cooker, especially when positioning the reflectors or checking the cooker’s temperature. The focused sunlight can damage eyes.

Place the thermometer in the inner box of the solar box cooker for this first heating, and check the temperature each half hour. The solar box cooker should reach 180 degrees in the first half hour, 225 degrees by the end of the first hour. If the inner box of solar box cooker doesn’t reach these temperatures on a day with full sun in the summertime, read the suggestions on troubleshooting at the end of this section for more information on improving the cooker’s performance.

What Food Cooks Best?

Mushrooms, red bell peppers, and rice were tasty cooked in the solar oven. Do not try to cook broccoli, cabbage, or any related vegetable. They develop an awful odor. Cookies are fun, but results are mixed. I suggest food that you can place in the oven and take out once.

Results were consistent for the following recipe:
Place 2 1/2 cups of water and 1 cup of brown rice in a pyrex dish. Cut up a red bell peper into strips and layer over the top of the rice. Place six cleaned mushrooms evenly spaced on top of the rice and bell pepper. Cook for 2 hours.

Experiment and record results

Once the solar box cooker is complete, experimenting and cooking with it is the fun part. Recording the results will enable you to accurately predict what temperatures the cooker with experience. Temperature, wind direction and speed, and humidity all affect the oven's performance. The angle at which the sun strikes a particular location, its angle of incidence, changes on a daily basis and affects how much sunlight enters the oven.

Set the solar oven up on an almost daily basis for several weeks in a row. Place a pan of water in the cooker and measure the change in temperature over time of both the cooker and the water to generate data on the oven’s performance. A series of systematic changes is the basis for the experimentation. Change only the initial temperature of the water each day for a week and record the effect on the oven’s performance. Does the choice of pan affect how quickly the water heats? Try using the oven without reflectors, without the glass lid, or without the black cookie sheet to vary the heat gain. Vary the amount of water placed in the oven; how long does it take to heat one cup of water as opposed to three cups?

Use Bricks to Increase Heat Storage

Changing the mass in the oven will change the oven’s performance. You can use bricks to increase the mass inside the cooker and thus increase its potential to store heat. The bricks also increase the mass which must be heated, thus increasing the amount of time for the cooker to reach high temperatures. The heat held by the bricks hold keeps the oven temperature constant. See the background information on page 6 for more information about heat storage.

First, make sure the bricks fit inside the inner box of your oven and leave enough space for your food. Preheat the bricks in direct sun. When they are hot, use oven mitts and place them in the bottom of the inner box, under the cookie sheet. The bricks also move the cookie sheet up towards the glass, leaving a very shallow open space in the oven. This reduces shadows and allows food to cook more evenly. Bricks are useful when you have a long time to preheat the bricks before starting your meal and you are cooking food that fits in a one inch shallow area, such as biscuits or cookies.

Troubleshoot a Cool Oven

If the oven is not reaching temperatures of 225 to 250 degrees in one hour, first check to see if too much heat is escaping from the oven. This problem illustrates convection; hot air is rising and escaping from the oven. Next the check the orientation of your cooker to the sun. The angle of the sun’s rays to the reflector are important to the cooker’s success.

Re-insulate the cooker. Hot air rises, and will push its way out of the cooker where the lid of the inner box cooker seals the glass in place. If the solar box cooker doesn’t hold heat, the box inner box may need more tape or insulation. Place your hand about an inch above the surface of the inner box and glass. If you feel a flow of hot air at the corners, try re-taping the corners of the inner box lid. If the flow of air is greater along the edges, add more weatherstripping on the inside of the inner box lid.

Re-orientate the cooker. The reflectors are used to direct the sun’s rays into the cooker. If the solar box cooker is not heating up, they may be need to be repositioned.

Make sure the cooker is in the full sun, away from any shadows. The sun has to be directly overhead, or the reflectors will block the sun instead of directing it into the cooker.

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