Solar Cookers: Cooking with the Sun, History, Theory, Construction, Recipes

By Nicola Ulivieri

An exhaustive manual-essay introducing you to the world of solar cookers that highlights the potential of these practical tools with which you can cook your dishes outdoors with solar energy alone. You will learn the history, development and refinement of solar cookers, but also the theory of apparent motion of the Sun, as well of solar radiation and its conversion into heat. This book is accompanied by an extensive theoretical and practical section that illustrates the working principles of solar cookers: complete with the methods to build them with recycled materials, illustrative examples and advice on recipes.

• Language: English
• Publisher: Lulu.com
• Release date: Apr 19, 2020
• ISBN: 9780244279639

Book preview

REFERENCES

Preface

by Terre di Siena Green – Carbon Free Protagonists.

The reduction of greenhouse gases is a commitment to which all must devote, from businesses to individuals. For this purpose, two Sienese, Simone Bazzotti and Nicola Ulivieri have started to promote cooking with self-built solar cookers, creating various initiatives aimed at raising awareness of the issue of energy saving and the reduction of greenhouse gases.

Nicola Ulivieri is an engineer in Telecommunications and for some time has had a fascinating for the Sun, as evidenced by his book I Segreti degli Orologi Solari (The Secrets of Sundials). Solar cookers are a newer passion inherited from his friend Simone Bazzotti who experimented continually new prototypes for years and with whom he has been pursuing various initiatives carried out in collaboration with organizations including SlowFood Siena, WWF Siena, Erbandando and Cultural Association Murlo.

Together they were awarded the Siena Carbon Free 2015 prize for their project Solar Cookers which emphasized the educational potential of these instruments, in addition to their contribution to CO2 reduction.

These cooking tools, in fact, are powered by solar rays only, allowing a total avoidance of electricity and gas usage; consequently, the production of CO2 for their operation is null.

There are various types of solar cookers. Simone and Nicola have mainly worked with three types: a rectangular box shape, and both paraboloid and parabolic curved reflectors. The materials used are mainly cardboard or plywood, glue and reflective film. Their construction can be done by anyone, and is economical and of high educational value. The temperatures that can be achieved range from 160 °C to 250 °C, depending on the models and materials used. There are no dangers of combustion since the cardboard ignites only at temperatures over 230 °C and cardboard models do not reach such temperatures. Solar cookers are a low-cost technology that uses the most widespread free energy source there is: the Sun.

Their use is spreading, thanks to cooperation with sustainable development organizations, especially in countries where it is difficult and expensive, for local populations, to obtain fuel for cooking food. In Western countries, solar cookers are still little known but arouse every time, to those who participate in the experiments, a lot of interest and amazement highlighting the important educational aspect of these tools and remembering that all advances are obtained starting from small steps.

Simone Bazzotti and Nicola Ulivieri (from right) receiving the Siena Carbon Free 2015 prize, with (from left) President of the Province of Siena Simone Bezzini and the Provincial Councillor for the Environment Gabriele Berni (photo by G. Pizzichi, 2012).

http://www.green.terresiena.it

Introduction

It's been a few years since my friend Simone Bazzotti insisted that I visit him so that he could show me what he had cooked in the sun. For a long time he had been talking about solar cookers that he had discovered by reading some articles on the internet and had started experimenting with. His models were made of cardboard, glue, aluminum foil usually used in the kitchen, cheap or recycled materials. I was not very interested, thinking this was just a hobby without actually functional applications. With the typical mental fatigue of the current hectic life, always looking for time to do something (a time that is always missing), I found - or did not want to find - ten minutes to go and see them, until the day in which Simone persuaded me to go to him to taste his bundt cake made with the Sun. The idea of the sweet, in fact, did struck my curiosity, her appearance was very good, perfect. I savored it and at that moment something changed in my mind. "But how did you do it, with the Sun? And what with?. Simone showed me a cardboard box, with internal insulation and reflective panels covered with aluminum foil. With this? Really?. An excellent bundt cake, delicious, well cooked, cooked in a cardboard box in the sun at a temperature of over 160 °C. I could not believe it. Before long, that which I had thought to be mere toys" became to me objects of extreme interest and utility, and my opinion on these instruments changed radically intuiting their usefulness and potential. I had to build them too! I had to disclose as much as possible their use, with the hope that had happened to me will happen to other people too: an incredible surprise to discover that in the XXI century in a small area you can concentrate a great energy [about 1 kW per square meter] supplied directly from the Sun; a free energy, clean, and able to surprise anyone to observe pots of water boiling in the sun or wooden sticks that burn instantly.

Since that day, the Solar bundt cake day, I started to build my first solar cooker and then continue with other, up to try to invent new and transportable ones and I tried to disseminate their use with articles and initiatives with various associations, including Slowfood Siena, WWF Siena, Cultural Association of my municipality (Murlo, Province of Siena), and others, to show how they work.

The book I wanted to write is meant to be read and used as a manual, and consists of chapters without a forced sequence, where the most difficult sections, more theoretical, if they are not of interest, can be skipped to switch to the more descriptive parts or historical. I wanted to bring back the different aspects of this interesting subject, not only, so, description of types of solar cookers, history, construction, recipes, but also calculations of the savings of CO2, theory of operation of the parabola and calculate the day length, so as to meet readers with interests and different preparation. In short, I wanted to write all that is of interest to me, hoping to convey my feelings on this to you. Enjoy the reading.

PS: If you have suggestions, questions or if you notice errors in this book or bad English translation, please email me at [e-mail]

The first solar bundt cake with which Simone transmitted to me his passion, leaving me literally stunned by the perfection of cooking, as well as to the goodness of the cake.

BURNING MIRRORS

"[..] Thou living Aton, the beginning of life! When thou art risen on the eastern horizon, Thou hast filled every land with thy beauty. Thou art gracious, great, glistening, and high over every land; Thy rays encompass the lands to the limit of all that thou hast made: As thou art Re, thou reachest to the end of them; (Thou) subduest them (for) thy beloved son. Though thou art far away, thy rays are on earth [..]"

from The Great Hymn to the Aten.

Aten, the sun god of Egyptian mythology, represented by the bright disk that generates life and whose heat carriers rays ending in the form of hands to symbolize his creative function (public domain image  from Wikipedia).

Already thousands of years ago, man had found a way to concentrate the sunrays by means of mirrors or transparent glass in order to set combustible objects on fire. Since then, we have had to wait many centuries before using the same energy and the same notions with the aim of cooking food with tools able to transform sunlight into heat.

The operating principle of those ancient concentrators - also called burning mirrors - and the solar cookers is substantially the same and consists, in essence, in the conveying in a small area the solar rays falling upon a big surface, so as to increase the energy per unit area. We have to state beforehand that, in the case of some types of solar cookers, it is also made use of the greenhouse effect to retain the heat stored.

In the Universal Dictionary of Arts and Sciences by Ephraim Chambers (1775), we read the nice definition of what a burning glass is:

"BURNING-GLASS, weapon, or machine, by which the sun's rays are collected in one place: and by this mean their strength and effect is extremely magnified, so that they burn the objects placed in it. Burning glasses are of two kinds: the first convex, called caustic lentes, which transmit the light rays, and in their passage they refract or tilt toward the axis, having the properties of the lenses, and by operating according to the laws of refraction. […] The second, which are the most usual, are concave; very improperly called burning mirrors, being ordinarily made of metal; those reflect the light rays, and in such reflection, they incline them to a point in their axis; having the properties of mirrors; and operating according to the laws of reflection […]."

The news certainly more known that we received from the story about the use of burning mirrors is that one concerning Archimedes, mathematician, physicist and inventor in Syracuse, who lived in the third century BC, which is said that he was able to employ these tools to set enemy ships on fire during the Roman siege of Syracuse (214-212 BC approximately). We do not have the historical certainty that the event is true or is a legend but, citing Ephraim Chambers, "Nevertheless it proves enough, that such things were known. The machines used there, were, as no one doubts, metallic and concave; and had their focal point to their reflection: finding and agreeing, that the Ancients did not know the focus refracted by convex glasses."(¹).

The tale of burning Roman ships, thanks to the inventions of Archimedes, inspired the movie Cabiria by Giovanni Pastrone, the great epic Italian film dated 1914 with lyrics and screenplay by Gabriele D'Annunzio, the first movie in history to be screened at the White House. In Cabiria it is shown the destruction of the Roman ships with burning mirrors of Archimedes, thus helping to make real the event in the collective imagination. What is really interesting about this section of the film is the didactic explanation that is done when Archimedes shows the use of a burning mirror model to experimentally verify his intuition. That sequence, from which I report here a few frames, explains better than thousand words the principle that stands at the basis of each solar concentrator. It must be said that an experiment was actually conducted in 1973 by the Greek scientist Ioannis Sakkas to check the veracity of the legend of Archimedes’s burning mirrors; to this end he has used 70 copper coated mirrors, the size of about 1 m to 1.5 m each, to concentrate sunrays. What occurred was that, by pointing the mirrors in a single point of a reproduction plywood of a Roman warship, placed at a distance of about 50 m, it took actually fire in a few seconds (²).

Archimedes experiences its idea of concentration of solar rays by means of a model made of 5 movable mirrors.

(Frames from the film Cabiria by G. Pastrone, 1914).

Archimedes experiences its idea of concentration of solar rays by means of a model made of 5 movable mirrors.

(Frames from the film Cabiria by G. Pastrone, 1914).

Focusing the light reflected from 5 mirrors in a small area of a canvas, Archimedes manages to burn it, demonstrating (cinematically, of course) that his intuition had foundation.

(Frames from the film Cabiria by G. Pastrone, 1914).

Focusing the light reflected from 5 mirrors in a small area of a canvas, Archimedes manages to burn it, demonstrating (cinematically, of course) that his intuition had foundation.

(Frames from the film Cabiria by G. Pastrone, 1914).

Roman ships set on fire by the burning mirror of Archimedes.

(Frames from the film Cabiria by G. Pastrone, 1914).

Roman ships set

Reviews for Solar Cookers

[KurtisT · Rating: 5 out of 5 stars]

Thorough and authoritative. An enjoyable read about how to build and cook delicious food with a variety of solar cookers. Whether you are interested in the history, physics, engineering calculations, do-it-yourself instructions, or the recipes and beautiful photos of solar-cooked food, this book has it all.