Solar cooker, - grill and get electricity

SOLAR COOKER

Cooks also in cloudy weather -- forests will be spared -- the greenhouse effect slows down?
There have been solar cookers in existence before, but not enough attention has been paid to their
development. The solar cooker is the only environment-friendly cooker in village communities in the
developing countries, and its introduction would mean that forests would be spared and desertification
would be prevented. The model presented here is more than a cooker; it can be a frying pan and also
the producer of electricity for the family's battery, which would make possible the small-scale use of
electricity, for example: in lighting fixtures with leds, TV- sets, mobile phones, computer with internet
and perhaps refrigerator. -- Do grill your food with solar-grill ! -- Get electricity for industri and cars.

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The clock turning the mirror Setting of the season The cooking utensil Diagram of a solar cooker:

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The clock turning the mirror (top left-hand corner)

The cooking utensil (in the middle)

1 setting of the season (in the base) and dangers

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The mirror and how to direct it

The mirror of the solar cooker should be 0,5 - 1 sq m in size, and it can be, for example, of bright-coated
aluminium or it can be silver-, gold-, rhodium- chromium-coated or replace aluminum foil. The mirror can
be larger, too, but then it may have to be designed to be easily accessible in cooking situations, for example,
by making a big, asymmetric notch in it. A large mirror makes the device correspondingly a lot heavier,
more expensive and sensitive to wind. A mirror larger than one square metre is not necessary, except when
the cooker is mostly used in cloudy weather.

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Turning clock:
The mirror must follow the sun's course in the sky during the day for which it must have a spring-
operated clock at the other end of a turning axle.

The turning axle is in north-south direction. The mirror must be suspended so that it won't cause a great
torsional moment to the turning axle in order that the clock would manage to turn
the mirror. The spring must
be of solid build. When the
cook comes to the cooker in Electricity for industri and cars
the morning, he/she winds the
spring and sets the mirror in the
direction of the sun. If the sky is
overcast, he/she sets the mirror in the
right direction according to the hour hand.
The spring of the clock must be as strong as
the spring of my grandfather's clock which lasted
a century. The spring must not be allowed to get
rusty in rainy weather. There cannot be any weather-
sensitive plastic parts and electronics. The larger mirror can
be more automatic without spring and produces electricity. Much
larger mirrors produce electricity for industri or community and the system is more
complicated and expensive. People need besides often extra energy both wind power plants and
big batteries. Perhaps 3 m mirror will charge your electric car batteries in the future. (File:PVeff(rev111103).jpg).

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The idea of a battery-operated clock should be forgotten in cookers (0,5 - 1 sq m), because in disaster area, for
example, expensive batteries are not always at hand. Furthermore, it is not in accordance with the idea of environ-
ment-friendly development. Instead, one might perhaps think of a solar-powered electric clock. It would give
energy at about one watt's power to the turning mechanism, also taking care of the right direction in the morning.
Perhaps the clock would even take care of the setting of the season. One must, however, be careful not to make
the equipment too technical in "family" cookers, because nobody can help, and this would make the price too high.
Different versions of the cookers can of course be manufactured for different communities, the wealthy ones too,
but will the right model always find the right place?


Setting of the season:
In addition to the turning axle, there must be another axle for the mirror, because the altitude of the
sun changes with the seasons as well.

In diagram 1 above, the suspension of the mirror is practical and therefore it causes a minor directing error.
The error is unimportant because of the large size of the cooking utensil. As the altitude of the sun changes
10 -15 degrees, i.e. perhaps at an interval of one month (depends on the season), the fastening cotter (1) must
be moved to the next notch, which will alter the inclination of the turning axle. The direction does not have to
be exact at all. The practical suspension is exact enough between the tropics and will work passably everywhere.

The mirror itself of the solar cooker is the shape of a paraboloid mirror with the cooking utensil in the focal
point. Looking from above, the mirror can take other forms than the circle, a rectangle even. Likewise, the
mirror can consist of more than one piece, which have been placed on a plane. The design can be fairly free.
The mirror does not have to be of precision work - small irregularities and lumps do not matter. Nevertheless,
the mirror is still the most important, and expensive, part of the device and the following troubles threaten it:

1. The mirror gets dirty, e.g. by spilled soup.
2. Sandstorms tarnish it.
3. A hard wind threatens to disconnect the whole mirror.
4. It may get stolen.
5. In addition You can break the spring of the clock by accident.
6. While mirrors have not intentionally sharp focus, it can still start a fire or hurt hands: "Focus" ~1 dm2

You must wash and polish the mirror carefully and perhaps coat by reflecting surface from time to time and
You need sunglasses because of dazzle.

The mirror can be cleaned but this may cause tarnishing. A thin plastic foil could protect it. After use it can be
temporarily covered. The whole cooker is mounted firmly with bolts in concrete, a large rock, log frame or the
stock of a tree, in a place sheltered from the wind. It can be placed differently, too, according to the season: one
place for the summer, another for the "winter", under a shelter or even behind windows. The cooking shelter can
also be modified, so that a part of the roof can be taken out or moved. This way the cooker itself does not have
to be moved at all. The cooker should have holes against whirlwinds and in case of spilling soup. To support the
mirror, it could have reinforcements for added rigidity. Solar cooker can also be placed to apartments balcony
or to the roof like a satellite dish.

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Diagram 2: Suspension of the cooking utensil

Cardanic hanging The cooking utensil must stay upright with all positions of the mirror, so it must
have a cardanic suspension (diagram 2). The utensil must be easily changeable.
This means that there will have to be a stand made of wire, and the utensils have
to be of the same type and size (2 litres). They will have to be dark-coated, fairly
roundbottomed "pots" with a handle, designed specifically for this device. Being
roundbottomed is inconvenient, so the cooking utensils require a special mount
on the table, or the pot itself has a protecting wire mesh.

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.Diagram 3: The transparent thermos bottle - Dewar pot

Thermos bottle:
black inside -
outside transparent

The cooking utensils can be of many kinds. One example is the vacuum-cased Dewar (diagram 3)
pot. Its exterior is glass and the interior is a black-coated steel pot with a vacuum between them.
The Dewar pot has its use when the soup has to be kept warm in cloudy times or in the dark. At its
highest, the cooking power given by the mirror is less than a kilowatt, but in cloudy weather and
even in rainy weather the mirror can heat up at 50 - 100 watt's power, which corresponds to the
smallest power of an ordinary electrical hot-plate. Water heats up to boiling temperatures in a
Dewar pot even if the sun was invisible, as long as it's directed towards the sun. The warming
up is caused by long-wave heatrays that are able to penetrate the clouds.
The glass has to be
selective, i.e. the quality of the glass must be chosen in a way which lets through short-wave heatrays,
but holds back only the rays with the longest wavelength (> 8000 nm). A Dewar pot breaks easily and
is perhaps not even completely safe, that's why it may have to be protected with a wire-mesh stand.
Maybe the glass can be replaced by a suitable type of plastic. (Stored in White House 1.18.1999).

Another kind of utensil can be a pressure cooker, which differs from a standard utensil in having a
dark exterior and a somewhat round bottom. It may be possible to combine these two types by making
a pot which is both a pressure cooker and a Dewar pot. In addition, inside it can be placed a vessel
which divides the Dewar pot in three parts. This makes it possible to make three dishes at the same time.

The frying and browning of food requires the temperature of at least 200 oC, and that is not always
possible. At noon the sun shines onto the bottom of the frying pan, and then the temperature may
be high enough in a small area to make it possible to fry food or bake bread. The solar cooker
requires its own type of frying pan.

Water cooling photocell Diagram 4 and 5: Photocells
Production of electricity

A special kind of pot is one that produces electricity.
One cooking utensil can be of a type which has an exterior
covered with photocells (Diagram 4). The photocells can be
multi-layer cells which make possible rather a good efficiency
(20 - 40%). They can also have a thin layer of amorphic silicon.
They are then cheaper to make, with an efficiency of only
5 -15%. The efficiency of GaAs cells is 20% at their best.

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Air cooling photocell

The solar cooker's thermal efficiency is a lot greater than
the electrical efficiency (60 - 80%). When the photocell
pot produces electricity, it can simultaneously heat water.

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Air does cool photocell too (Diagram 5).
The photocell is probably cheaper to make and do not burn
down perhaps so easy. A propeller helps perhaps cooling
like in a prosessor of computers - but bigger.

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Many cookers can connect together electrical sometimes,
transform electricity to alternating current, feed it to general
net and get money.

Finally

The basic equipment uses basic technology with aluminium, stainless steel, Simple grill
chrome etc. as materials. As an example, the clock is a strongly
built spring-clock. The clock should wear normal use
for decades. It must have a winding apparatus for
the spring, an hour hand and a locking switch.
The device looks inconsequential, but its
importance may be great. The costs will
remain relatively small in mass production.

The system works well in summer cottages,
garden parties and camping places for an
environmentally conscious user in the western
world and for grill without coal, electricity
or gas. The cooker can be modified for use in
outings, it can be a basic version with a folding
mirror, like in an umbrella........Simple grill =>

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Many regions on Earth have become desolate because of the gathering of wood, for when trees
disappear, the soil is exposed to the scorching sun. The comprehensive introduction of the solar
cooker might reduce desertification and its consequences, migrations of peoples and the ...

Greenhouse effect:
- global warming
- dryness
- storms,
- floods
- hailstones
- bad snowfalls
- polar ice caps melt
- dead of many species
- distribution of harmful species.

Solar cooker is important for all people and us. Let us design, sell and donate solar cookers!
Forest back!

Tapani Hakonen
Äänekoski Finland Europe
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PS. The original idea came to my mind in the winter of 1985. Thanks to my son Henri for help and
advice on telecommunication matters which have enabled me to bring these pages onto the Internet.
Thanks also to my readers for a great interest in my pages.
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