Everything I know about Solar Cooking

Everything I think I know about solar cooking. By Jim La Joie

About the Author: Jim has been solar cooking since the ‘70s. He has used every type solar cooker including parabolic, panel, box, fresnel, and tube. Jim has not used any hybrid solar cookers (electric combined with solar). The designs covered here will cook well without any input other than sunshine.

Lets start with the Sun, which is our power source. Solar power is measured in watts per square meter (Wm2) According to Woods Hole Oceanographic Institute  “Above the earth's atmosphere, solar radiation has an intensity of approximately 1380 watts per square meter (W/m2). This value is known as the Solar Constant”.

I live at sea level and receive less (980 - 1150 W/m2). Your location will be different.

The sun rises in east and sets in the west. This journey takes from 8 hours in winter up to 14 hours in summer - depending on your location.

All solar cookers must account for the movement of the sun. As you will find out below, some designs do better than others in this regard

This is a map of how much sun we get in the USA in January. Is it enough? Some users report baking bread in February in Seattle - so, yes.

Next is sunshine in July

And finally, year round average

No matter where you live, some days will be better than others. Learning your local weather is essential.

Next are the laws of physics. Energy can never be created or destroyed. Energy can only change its form. The more light energy a solar cooker collects, the more heat energy it may develop.

Given two solar cookers of similar design, the one that can collect the most light (larger mirror array) will cook the most food.

Given two solar cookers that are exactly the same, the one that can collect sunlight for the longest duration will cook the most food.

Well designed solar cookers will produce good cooking performance for at least 4 hours a day. Superior solar cookers will produce good cooking performance for more than 4 hours a day, sometimes 6, 8 or even 10 hours a day, thus adding to their usefulness.

A brief look at the types of solar cookers:

Parabolic

A parabolic looks a lot like a satellite TV receiver. It is a concave disk of parabolic shape that collects light and focus’ on a small point where the cooking pot is placed.

Panel

A panel cooker uses one or more panels to reflect light onto the cooking pot.

Box

The box cookers all use an insulated box with a glass door. They may gave anywhere from 0 to 4 reflective panels.

Tube

Tube cookers use a vacuum insulated glass tube and reflectors. The reflectors may be curved or flat

Fresnel

Fresnel cookers use a large Fresnel lens, usually taken from an old flat screen rear projection television.