solar cooker designs
as mentioned here some time ago, the byu benson institute arranged to have several
solar cookers taken to the altiplano in bolivia and tested there.i have just received the
report, results of which follow.
the tests were done by a group of 14 college students at the university of san andreas.
tested were:
- solar box cooker which i purchased from sci then sent on to bolivia;
- large 70-cm diameter (top) solar-cone cooker developed at byu,
with al-foil glued onto cardboard (45-degree opening angle).
- medium, 49-cm diameter (top) solar-cone cooker developed at byu,
with aluminized-plastic glued onto a thicker polyethylene cone (45-deg. again).
- "eleanor's solar cooker. it is a piece of cardboard covered by
aluminum paper. the piece of cardboard is bent to direct solar rays into
the cooker." -- from the report (translated into english)
have asked for details about this cooker -- the nice thing is that
a student looked at what we sent, then designed her own cooker based on
this information. the cooker is evidently just a blackened pot with some
kind of transparent hood around it -- trying to get details.
results:
"the oven pasteurized the water in 110 minutes. the eggs were then added to be
cooked. they were not dooked until noon. this is the reason why the oven was not used in
the other tests."
i sent wapi's to show when water would be pasteurized, that is, when the wax melted in
the wapi, the time elapsed was noted.
"the large cone took 130 minutes to pasteurize the water and did not cook the
eggs. its inefficiency may be a result of the lack of reflection in the surface."
the medium-size cone had a good performance. it pasteurized the water in 50 minutes,
cooked the eggs in 70 minutes (same water), cooked rice in 75 minutes (same water). to
cook rice with water at room temperature will take a little less than 110 minutes."
this shows the importance of higher reflectivity: the smaller cone worked much better
than the larger cone, clearly due to the higher reflectivity of aluminized-plastic.
"eleanor's [cooker] was the best cooker. it pasteurized the water in 50 minutes,
cooked the eggs in 100 minutes with ambient-temperature water, and cooked rice in 160
minutes with ambient-temperature water."
to me, the data seem to suggest that eleanor's cooker was a the same or slower than the
medium-sized solar cone-cooker; but for some reason the students found it to be the best.
i hope to learn why. in any case, i'm pleased that eleanor took the initiative to build
her own solar cooker -- that is key to the successful spread of solar cooking, i think --
personal involvement and enthusiasm. so i'm happy that solar cooking has been experimented
on by university students in bolivia. the byu benson institute will continue to support
and encourage solar-cooking there.
--steven jones
byu physics dept
since 1985 i have had various versions of solar wall oven in
the south wall of my house. an insulated 24" x 24" door in
he wall between my refrigerator and kitchen counter gives
ready access to the oven. it is handy and feels like it
belongs there. i have a microwave oven and a range top, but
do almost all my major cooking in the wall oven.
it gets about 250 degrees f. by 9:30 a.m.
rises to around 300f at noon and slowly
drops until by 4 p.m cooking is over. during
this time i cook several items. a pot of
presoaked beans will take 3 or 4 hours.
brown rice takes about 2 hours. since it is easy, i can save a lot
of money by buying rice and beans in bulk rather than in small
quantities.
bread takes 2 hours. a chicken or a beef roast takes 2 to 3
hours. several pots can be done at the same time. for
recipes that ask for higher temperatures, simply give them
more time at the lower temperatures. most foods will turn
out well cooked and delicious with flavor increased by the
gentle cooking.
if i am going to be away from home, i may put the pots in
before 8 a.m. and let them wait for the oven to heat up.and
since the oven turns itself off, things do not have to be
taken out promptly.
our water is good. but if the water should become
microbiologically contaminated, i would be able to make it
safe to drink by treating it in the wall oven instead of
"boiling for 10 minutes." there are special sensors and
instructions that describe how to do this available through
sci.
please take the plunge. try a solar wall oven. you will be
delighted with the delicious foods and with the savings on
fuel costs as well as savings on air conditioning to cool
the kitchen.
here is a general description of how they are made. they require
a home with an available wall space having solar exposure and the
consent of the homeowner. at least one has been installed through
an adobe wall, but not to my knowledge on circular houses or
thatch walled homes. they are more expensive than
the yard designs (cardboard and wooden solar box cookers and
various solar panel cookers.) so i generally talk about what is
potentially more useful worldwide and on the lowest economic
level.
kerr-cole solar through-the-wall-oven
goal: to place solar cooking apparatus so it is available
permanently and from within the house. also to provide solar
cooking potential for south-facing apartments, including upper
levels.
general description:
the outside portion of the solar wall oven is comprised of the
oven proper and the passageway ending in a frame to hold the oven
securely in place. if the oven is very big, there may be
cantilever props for additional support.
the in-house portion consists of an insulated cabinet door,
usually matching the kitchen cabinets, to provide access to the
passageway. the inner wall should be removed sufficiently far
above the oven door to allow headroom and the opening inside the
passageway is bigger than needed for the oven door. one insulated
door closes the entire wall opening. a second insulated door
built into the oven unit closes the oven proper. the oven is
attached so when the door is laid open, pots will remain level as
they are drawn into the passageway over top of the insulated
metal in the door.
construction
the insulated oven box is lined with galvanized metal, approx. 26
gauge, is shaped and spaced inside the insulation with 1/2 inch
or so clearance from the insulation and 1/4 in.to 1/2 in. from
the glazing. if desired, mirror-finished metal can be used
however, it is very expensive. roof edging or aluminum print
sheets work. the metal shell is painted black on the bottom
segment; the ends and sides are left shiny and may even be
covered with glued-on foil which is quite durable in this usage.
the oven unit is completed in the yard including hinging the
insulated oven door. an oven door that will lay down on the
bottom of the passageway is handier than side-opening doors which
block the entry of pots significantly. the interior of the oven
is finished, but it is left unglazed and screws inserted through
the sheet metal and framing in the back of the oven into the
aperture frame. then glazing is completed.
this design of solar cooker may be installed off a greenhouse,
solarium, dining room, ramada, or other space as appropriately as
off a kitchen. if a south facing exposure is not available, it
may still be advantageous to install a wall oven designed to cook
during the portion of the day when it can be exposed to the sun.
three to four hours of cooking temperatures in the morning or
afternoon can produce quite a volume of cooked food. with the
south facing ovens i have experienced six to seven hours of
temperatures above 250f daily when the sun is out. well braced
units have withstood 70 mile an hour gusts of wind and can
routinely cook during winds, including transient dust storms,
when solar boxes cannot function.
my curent oven size slants from 15 to 12 inches high, 18 inches
north to south and 30 inches wide.
the exterior end of the passageway and the base for the oven are
set out from the wall sufficently to allow noonday sun at mid-
summer to strike the top of the oven and any reflector. if this
is not possible, place the oven out as far as convenient and
compensate by the angle and size of a south reflector. narrow
eaves or no eaves are an asset; existing eaves may be cut back in
an area somewhat wider than the reflector if desired. eighteen
inches from kitchen wall to oven door is maximum even with use of
a wooden paddle. if it must be further out, consider placing a
portion of the black tray on runners or slides so both tray and
pots can be pulled toward the kitchen for easier access.
if anyone makes a wall oven of any design, please be sure to
let us all know what you did and howit did or did not work.
cheers,
barbara kerr
from: "russ hilleke, physics dept (3-6953)", hilleker@citadel.edu
date: tue, 6 aug 1996
subject: backpacking solar cookers
i have been lurking on the list for a couple of weeks and have found the
discussion quite interesting. in a message i received yesterday, barbara kerr
said:
>i suspect that there will be a way found to keep the hood in two
>parts so it can be carried in a backpack, but i have not succeeded
>in getting the necessary stability yet. let me know if you figure
>out how this can be done.
would someone please direct me to a reference that addresses the
design of solar cookers that can be used for backpacking? information
on other aspects of solar cooking on hikes would also be of interest.
thanks
russ hilleke
charleston, sc
***
from: info@solarcookers.org
date: tue, 6 aug 1996
subject: backpack solar cookers
russ hilleke asked about solar cookers that can be
used for backpacking. solar cookers international
produces and sells the solar cookit at $15, plus $3
for shipping. it weighs about 1 pound and folds into
a package about the size of a loose-leaf binder. it
can be counted on to cook one (approx.3 quart) pot
of food when sun is good, although i am hearing more
reports of people cooking two pots at once with it.
sci also sells the instructions to build your own
solar cooker--both the box type and the cookit type--
for $5 plus $1 shipping.
for more info. request a free brochure and give
your name and postal address.
sci e-mail: info@solarcookers.org
solar cookers international
1919 21st st., suite 101
sacramento, ca 95811
tel: 916-455-4499
fax: 916-455-4498
i believe barbara is working on an even more
portable version of the cookit; hopefully, whe
she will comment on that in response to russ.
sincerely,
kevin coyle
resources coordinator
solar cookers international
***
from: "tom sponheim"
date: tue, 6 aug 1996
subject: re: backpacking cookers
russ,
check out http://solarcooking.org/cookit.htm
for one possibility.
this is the "cookit" model solar panel cooker designed by solar cookers
international. they are pretty light.
tom
***
from: harmon seaver, internet:hseaver@vbe.com
date: wed, 7 aug 1996
subject: re: backpacking cookers
while i realize that much of the emphasis in solar cooker
development has been in providing ultra-cheap tools, i'm interested in
building a cooker for nomadic living and would like something a bit more
rugged than cardboard and tinfoil. has anyone found any available
sources of cheap (or reasonable) aluminum boxes, or even better, folding
units, that can be converted into solar cookers?
somewhere i've seen pictures of what looked to be folding parabolic
reflectors also --- looked like they "fanned out" -- does anyone know
where those are available?
or have any other ideas for building lightweight, portable units with
greater robustness than cardboard? how about materials for insulation?
are the alum/plastic-bubble insulation materials usuable (they use them
for hot water heaters, etc.) or do they off-gas?
--
harmon seaver hseaver@vbe.com hseaver@csd.uwm.edu
***
from: "tom sponheim tomsp@microsoft.com
date: wed, 7 aug 1996
subject: fw: backpacking cookers
one really nice way to do this is to use plastic fluteboard to build a
solar panel cooker (http://solarcooking.org/spc.htm) or a cookit
(http://solarcooking.org/cookit.htm). fluteboard is just like
corrugated cardboard, except it is made from plastic. it is used in the
us a lot to make small signs and to mount posters. it is more expensive
than cardboard, but it is just about the same weight and it is very
durable. i know the serve group in pakistan has used this to build box
cookers as well. jay campbell has experience with it and he is also a
member of this group. maybe he can fill us in on where to buy it, how
much it costs, and his experiences with building box cookers with it.
***
from: barbara kerr, internet:kerrcole@frontiernet.net
date: wed, 7 aug 1996
subject: re: backpacking solar cookers
there are two designs of solar cookers we are aware of that lend
themselves to backpacking: 1) certain of the solar panel designs
such as the seven panel foldable "backpacker" which continues to
be refined and 2) the funnel designs mentioned earlier in the list
and probably also to be found in the solar cooking archive --
http://solarcooking.org
with both of these lightweight designs wind is a problem.
generally they can be braced with rocks, etc. in a 3 ft.x 4 ft.
solar panel design used for big 40 quart pots and pressure
sterilizers, i tie down with lines anchored to cinder blocks.
something like that could be worked for the little solar panel
cookers as well.
these generally use a baking bag or a little jar for a hood, but
both of these are more fragile than we would like. therefore, the
search for a portable hood design from probably polycarbonate or
other heat resistant clear lightweight sheet goes on.
solar cooking is always a partial answer since it depends on the
weather. it is paired with a brief, small fire followed by use of
the retained heat in a sleeping bag, jacket or haybox, etc. to
finish the cooking. it is reported that even relatively recently
the swiss army used this system on night manuevers. to keep from
having to tend the pot as well as to save the expense of fuel, i
personally use it whenever i cannot solar cook and it is ideal for
travelers and backpackers. this system is detailed in "the
sustainable emergency kitchen" in the archives.
if the material in the list archives is not clear, plans for home
building and using a "backpacker" or for "the sustainable
emergency kitchen" are available for $1 and a large stamped
addressed envelop from b. kerr, pob 576, taylor, arizona 85939
usa.
field information on the use of solar cookers in backpacking is
guite valuable so when you start getting out with your choice of
solar cooker, please let us all know how it goes for you.
barbara
from: jan-ellen jones harriman, janellen@usa.nai.net
date: sun, 11 aug 1996
subject: paint
two questions:
1. has anyone ever used chrome spray paint for reflectors?
did it work? any +'s or -'s you could share?
2. how can you tell if a paint will be non-toxic once it is dry?
will it say on the label? are standard spray paints (enamels) ok?
thanks, as always, for all the great postings.
i learn so much here!
je
***
from: renewable news network, rnn@rnn.com
date: mon, 12 aug 1996
subject: paint
> 1. has anyone ever used chrome spray paint for reflectors?
> did it work? any +'s or -'s you could share?
i recently tried a can of chrome spray paint. it did not dry to a
spectrally reflective finish. it did not appear to offer a good mirroring
surface, although i did not test it. other bright, but diffuse surfaces,
have not worked as well, for me, in the past, as reflectors.
what i wanted to try, however, with the "chrome" was to create a
selective absorber surface. the "chrome" would be applied, then dusted
with a black coloring. ...the idea being that the sun would see the
black, and be absorbed at a rate of about 90%, then having changed to heat
and a higher wavelength, the "reflective" (low 10% emissivity) property of
the "chrome" would prevail, and the heat would be retained at the surface
and be further transmitted into the material substrate.
but, i'm not sure the paint is really chrome. it might really be
aluminum. there's no truth in labeling required for this product,
although there should, considering the environmental and possible health
impacts of both.
also, i do not have any facility to carefully control such an
experiment for reliable results, but what the heck...
yours truly,
ross donald
ps. renewable news flash: steve baer, solar pioneer extrodinaire, of
zomeworks, albuquerque, new mexico, usa, tells me he will be reprinting
_the dome cookbook_, out of print for ten (?) years.
***
from: barbara kerr, kerrcole@frontiernet.net
date: mon, 12 aug 1996
subject: re: paint
hello jan-ellen,
chrome paint is a mystery to me. flaked aluminum paint and flaked
stainless steel paint, even sprayed so the flakes lay flat, did
not relect well when i tried it. what you are looking for is a
good front surface reflection. let us know how it works relative
to rolled on kitchen foil if you try chrome paint.
there are no clear guidelines on what is toxic and what is not
toxic paint in reference to solar cooking. the heat, moisture and
proximity to food are factors not generally considered in rating.
my personal guidelines are that i start with a paint that has been
commercially advertised for use around food and is rated
non-toxic. then i want to be sure it is stable to the maximum
temperature i might ever get, so i use a high temperature paint.
this generally boils down to some sort of barbecue black or stove
black.
there is always a preheating and seasoning period of several hours
at maximum solar temperatures to drive off any volatile compounds.
it is important to know that almost all
odors are pollutants when close to food. don't use anything that
smells around your food, except spices, etc.
we have also confidence in tempera powder which is labeled
non-toxic since this is used by very young children who could be
assumed to get some in their mouth. used with a non-toxic glue,
this makes a fairly durable dark coating. we keep it out of the
inside of pots and out of food.
i have used a black paint intended for coating motors and rated to
above 1200 degrees f and it never stopped off- gassing. i believe
that the temperatures obtained in the solar cookers was
insufficient to set the compounds used for this motor paint. i
have not experience this problem with barbecue paints. it was for
this reason that i always look for paints that are recommended for
use around food.
keep us informed of what you discover so we can all share in your
work.
and above all, have fun! enjoy the wonder of it all! cheers,
barbara
from: barbara kerr, kerrcole@frontiernet.net
date: fri, 9 aug 1996
subject: re: cooking away
steven,
tom has asked me to respond to your question about patents
possibly impeding the spread of solar cooking in poorer areas.
there is earlier material on patents that was put up on the list.
perhaps tom can tell us how to get to it.
it is a matter of opinion and where one fits in the economic
scheme as to whether or not patents are useful.
my work is on the lowest economic level and i do not intend to
go into business although it would be nice to make some money.
this influences the decision since business people are reluctant
to move without patent rights.
i have obtained two patents. the first was taken out in the
mid-70s on the early cardboard solar box cookers with the
intent that it would prevent the idea from being sequestered
by some corporate interest and never utilized. this was a weak
reason even then, but there seems to be little if any possibility
of the ideas of the various ways of solar cooking getting "lost."
solar cooking is like building a fire. there are so may ways to
do it and so very many variations possible, it is going to be
hard to block this knowledge now that the potential is known.
i understand it would have been just as effective for this
purpose to have published and circulated written material
describing the item. we did that anyway so perhaps that patent
was unnecessary, but it reassured us at the time.
the second patent was on a version of the solar wall oven. since
this appears to me to be ultimately as commercial as air
conditioners i thought maybe this would be a saleable patent.
probably it is not saleable since various details have evolved
which would justify a new patent, which anyone could take.
all this is very expensive and to sustain a patent is getting
increasingly costly. that is without considering that if the
patent is invaded, defending it would require a court fight
which can lead to devastating expenses for most individuals. and
without considering that minor changes can justify a new patent
which can be taken out by anyone. money can usually be put to
better use.
>from my viewpoint, patenting is not useful, particularly for
designs for use in developing countries unless one plans for
mass production and maybe not even then. refer to the situation
within the specific country. or to the organization through which
the circulation may take place -- do they require a patent?
write, publish, and distribute the knowledge through workshops
and so forth, if the goal is simply to assure it is available to
the world as needed. get the idea into libraries, schools,
periodicals, and the hands of individuals and ngos.
and read the earlier material sent to the solar cooking list on
patents. there were some experts who gave us their valued
opinions, including a way to start a patent to get first in
line with an idea, yet not pursue it into the expensive areas.
***
reflectors
from: barbara kerr, kerrcole@frontiernet.net
date: sat, 17 aug 1996
subject: reflectors -- a safety question
potential dangers from solar radiation
sunlight causes no pain in the eyes. yet, even normal bright
sunshine over time can cause cataracts. within a few seconds,
looking directly at the sun can cause retinal damage, resulting in
permanent loss of sight. if there is an after image of a bright
area drifting in the visual field after looking away from a bright
area, this indicates a serious risk. full spectrum sunglasses are
recommended when using devices that throw reflections onto the
operator's face. yet we all realize sunglasses are not universally
available and when available, often not used.
with fire, there is heat and pain to alert the operator of danger
and keep children back. with solar radiation in the eyes, there
is no natural warning. informed caution is required. and i do not
believe we can rely on education to reach far enough and fast
enough to make highly reflective open solar cookers safe in a home
setting. safety must be built in.
the use of stainless steel, polished aluminum and other highly
reflective materials troubles me. some of these are rated as
producing as high as 95% reflection of radiation falling on them.
in an enclosed configuration, these high technology materials may
be an advantage. ln our home and family oriented solar cookers, i
believe they are dangerous.
reflection from one flat panel of 95% reflection is almost like
looking directly at the sun. if one gets into position where
reflections from several panels are converging, the danger
increases.
for the solar panel cookers, there is clearly a problem with
multiple reflections concentrating radiation which may fall on the
face of the operator or anyone looking closely at the pot. the
angle from which one approaches a panel cooker can make a great
difference. with a small panel cooker, approaching from the sunny
side throws a shadow over the area and reduces exposure to
radiation. larger panel cookers differ and need to be studied for
the best approach angle.
parabolic designs, both dish and trough, concentrate solar
radiation to a very high degree and therefore present a particular
danger. those designs that focus below the perimeter of the
device are safer than those that focus out side the perimeter.
when concentrated radiation is focused on a pot and that pot is
removed or the focus migrates, it may jeopardize the eyes of those
in the area. for some such designs, perhaps a barrier could be
integrated that would automatically fall into place when the pot
is removed. still danger remains from the focus migrating off the
pot and in to the yard as the sun moves.
rather than risk promoting solar cookers with these dangers, i
believe we should design with materials that are not maximally
reflective. some efficiency is sacrificed , but this is a safety
matter.
there are probably a number of ways safety can be built in but we
have not particularly searched for them. in my own work on simple
designs, it seems that the level of reflection from kitchen foil
is safe yet effective for cooking, provided units are designed so
sunlight is not thrown on the face of the operator, and the cooker
is used with caution. (i have had some solar wall ovens that
clearly presented a hazard and had to be eliminated from
consideration for this reason.) foil, well glued and rolled on
tightyly and smoothly, is my personal preference. there are many
reflective materials available that may be chosen.
i want to raise an alert. as many more people are designing solar
cookers the first choice seems to be "the brighter the reflector,
the better." this is not necessarily so. we just need sufficient
concentration of solar radiation to cook in a reasonable length of
time. safety is primary.
there are probably better solutions to the hazards of concentrated
solar radiation than relying exclusively on kitchen foil. let's
look for them. and for those who prefer brighter reflective
materials, extra caution is advised.
from: jim arwood, jima@ep.state.az.us
date: mon, 19 aug 1996
subject: re: reflectors -- a safety question
here is a response i received when i put this question out to the engineers
in my office.
there definitely is a hazard anytime you are looking directly at the sun or
it's image. even driving down the street under the right (or wrong, i
guess) conditions can provide a blinding reflection from a rear window on a
pickup. i doubt if a few seconds of exposure constitutes a major hazard,
but if one were to look repeatedly at a solar cooker under the appropriate
conditions, there could be a problem. i remember reading about something
the indians used to do to enemies they captured. they would cut off their
eyelids, then strap them to a tree facing south. by sundown, they were
blind. but it didn't take place instantly.
at the very lease, solar cookers should contain warnings in the packaging
material and on the cooker itself admonishing people not to look at the
reflective surfaces.
----------
from: jonesse@plasma.byu.edu
date: tue, 20 aug 1996
subject: re: reflectors -- a safety question
barbara kerr raised a very important issue: safety in use of solar cookers.
the problem is that the fusion energy of the sun is brought to us via
electromagnetic radiation -- and this can damage the retina in the eye.
i should like to point out that any energy source is hazardous.
half the world's population cooks by burning bio-mass of one form or another.
the statistic i've heard on deaths due to smoke inhalation from this practice,
in children, is 5 million deaths per year. (scientific american article a
few years back. any other refs on this?) women and children are probably
affected more by the smoke than men, i would assume.
this is not to minimize the safety concern of solar cooking -- just to put
it in context. nuclear power faces its greatest problems now not from costs
but from safety issues. i believe that if safety had been the first concern
in the 1950's, then nuclear power might be a more popular energy source today.
this is because "inherently safe" reactor designs are now available, which
cannot result in "china syndrome" meltdowns, nor in explosions -- yet its
too late. the public does not trust nuclear power...
let's not let this happen to solar power!
--steven jones
byu physics
from: marge wood, woodm@nicanor.acu.edu
date: wed, 21 aug 1996
subject: re: reflectors -- a safety question
let's just stick to solar energy on this list; lots of people would not
agree with you about safe nuclear power--the waste issues have never been
dealt with. solar is a good alternative, and living at all is dangerous,
so we just have to do the best we can.
marge
cc:solarcooking-l@igc.apc.org
i'm not sure marge understood the thrust of my comments about the importance
of safety in the early stages of an emerging energy source. let me try
again.
early on, fission was recognized as a cheap energy source -- "too cheap
to meter" was the slogan. yet safety was, i think, secondary in the
development of early designs. i raise the issue only as a way to instruct
us that we must avoid repeating this mistake: safety is more important
than cost, that is the lesson.
incidentally, i choose to look at solar energy as a source of controlled
thermonuclear energy, namely fusion. ironically, less developed countries
may end up using fusion energy on a large scale (for cooking) long before
"developed" countries do.
the little solar funnel i've been working on is now being field-tested by
the benson institute on the altiplano in bolivia. i also sent a cookit and
a solar oven for use and testing there. the benson institute is working
with these people (and in other countries) to promote the use of solar
energy. luis espinoza of that institute told me that earlier efforts to
promote solar cooking using parabolic collectors failed -- because the
parabolas were unsafe. it happened more than once that a parabolic collector
was stored near a shed, and moving sun rays focussed on the shed resulting
in a fire. this cannot happen with any of the solar collectors now being
tested. let's just hope that the mistrust level from the earlier experience
is not so high that the people will not try again...
steven jones
byu physics dept.
from: info@solarcookers.org
date: tue, 27 aug 1996
subject: eyelids, sun and blindness
a while back jim arwood wrote about captives
whose eyelids were cut off and who were then
tied to a tree facing the noonday sun and who
would thus be blind by sundown. bev blum,
executive director of solar cookers international
comments:
without eyelids, the cornea does not stay moistened
and blindness follows--with or without sun.
from: barbara kerr, kerrcole@frontiernet.net
to: jonesse@plasma.byu.edu
date: mon, 2 sep 1996
subject: re: reflectors -- a safety question
i agree the earlier we face safety questions the better.
that is why i am raising such an ugly thought. development
can be guided in part by safety concerns when they are
identified.
i see as yet no safety problem with solar boxes, only with
some panel models and some wall models. these problems
involve concentrated radiation striking the eyes.
what about funnel designs?
distribution:
jonesse@plasma.byu.edu
solarcooking-l@igc.apc.org
from: jonesse@plasma.byu.edu
date: wed, 4 sep 1996
subject: re: safety
barbara kerr writes:
"i agree the earlier we face safety questions the better. ... i see
as yet no safety problem with solar boxes, only with some panel models and
some wall models. these problems involve concentrated radiation striking
the eyes.
what about funnel designs?"
the funnel we are using is a truncated cone with a 45-degree opening angle.
actually, a 60-degree angle is optimal, but then the cone would have to
track the sun whereas the 45-degree angle allows the cone to remain fixed
for several hours. the sunlight is concentrated, but this is along an
axis (not to a point -- like parabolic reflectors). importantly, the
"hot axis" is along the bottom 8 inches or so of the cone -- that is, deep
inside the cone. you can stick your arm up into the bottom of the cone and
feel the heat, but it will not burn you. when you bend over the cone, you
more or less automatically block the sun. heat builds up inside the clear
jar or plastic bag which replaces the window on the solar oven -- with
sunlight entering from all sides except the bottom, rather than just from
the top as in the solar oven.
the danger comes when the cone is positioned at an angle to the sun so that
the light reflects back up and can strike the eyes. again, this is not a point
focus, but it is still concentrated. we have made cones with aluminum foil
glued onto cardboard -- easy and cheap. the reflections in this case are
rather scattered and innocuous. we also use aluminized mylar, which is
more reflective -- and more worrisome regarding stray reflections. for long-
term use, the cone is fixed to a wall, or it could be placed in a hole in
the ground -- so that odd angles to the sun can be essentially avoided.
i wear dark, polarized glasses in any case and have avoided problems. i
worry about people neglecting to use dark glasses or to take safety
precautions.
--steven jones
from: "eric johnson", ejohnson@infosel.net.mx
date: wed, 15 jan 1997
subject: glass expansion tolerances?
greetings from mexico,
i have a quick question for you. how much space should i leave between the
frame and the glass for a 3mm (1/8") sheet with the dimensions 130cm (51")
by 60cm (24") for expansion from the heat? i will be mounting two sheets in
a metal frame for my next solar oven. i figure that 5mm (3/16") on each side
should be more than sufficient but would like to have some confirmation from
the experts.
thanks in advance for your help.
eric johnson
***
from: barbara kerr, kerrcole@frontiernet.net
date: thu, 16 jan 1997
subject: re: glass expansion tolerances?
3/16th of an inch looks about right. we usually use 1/4 in.
space and seal glass in lightly, only enough to stop air
leaks. we use silicon sealant from the outside so the seal
can be cut and the glass lifted out if it ever breaks.
probably a hair breadth between the two glass sections would
be a good idea.
this is going to be a big solar oven. can you tell me
eventually how it works out and a bit about the design?
thanks,
barbara
***
from: elfpermacl@aol.com
date: thu, 16 jan 1997
subject: re: glass expansion tolerances?
the metal frame will expand far more than the glass. glass has a very low
coefficient of expansion.
for mother earth, dan hemenway, yankee permaculture publications (since
1982), elfin permaculture workshops, lectures, permaculture design courses,
consulting and permaculture designs (since 1981), and now correspondence
permaculture training by email. copyright, 1996, dan & cynthia hemenway, p.o.
box 2052, ocala fl 34478 usa yankeeperm@aol.com
we don't have time to rush.
***
from: "eric johnson", ejohnson@infosel.net.mx
date: thu, 16 jan 1997
subject: re: glass expansion tolerances?
--- on thu, 16 jan 1997 07:57:42 -0500 (est) elfpermacl@aol.com wrote:
>
>the metal frame will expand far more than the glass. glass has a very low
>coefficient of expansion.
>
hmm, so should i make it a tight fit? don't want the glass to fall into the
oven.
barbara,
you asked about the design of this oven. it's a 55 gallon drum cut in half
vertically and welded into a long trough (like the bbqs that they make from
drums). it's 140 cm long and will be inclined 18 degrees (the latitude
here) towards the south. the metal frame with two plates of glass will open
over the top for access to the inside and have one or perhaps two
reflectors of polished aluminum printing plate. it will have a wooden frame
inside the opening upon which the top will rest and seal. this wooden frame
will also hold the foil covered cardboard inner box of the oven. i'm
currently thinking of making the inner box wide and shallow (the bottom will
be about 40cm wide with a depth that varies from about 15 to 30cm high due
to the inclined top). there will be room for lots of shallow porcelanized
pans with black metal covers for efficient cooking.
the airspace between the drum and the inner box will be filled with
insulation. i'm currently thinking of using some cotton material which
carpenters here use to finish furniture called "estopa" which is basically
stringy fibers of cotton. has anyone used poliester batting for insulation?
other ideas? right now the frame will have about 3/8" of space between the
plates of glass. why do you recommend only a hair breadth? wouldn't more
dead air space be better? another question occurs to me. when i talk with
the folks in glass shops, they always say that 3mm glass won't take the heat
and that i need to buy tempered glass. do they just want to sell me
something extra or maybe they don't know?
the whole unit will be welded to the iron railing outside our kitchen door
and will be mounted on a pivot so that it can follow the sun and also be
turned around to facilitate loading and unloading.
the metalsmith is currently finishing up the outer shell with it's mounting
and structure and the frame for the top is done and mounted with hinges.
the next step is buying the glass and doing the inner box.
barbara, you mention in your article about solar cooking (a great help!) to
be careful about black paints and toxicity. could you give me more detail
about the kinds of oil to use for a natural blackening color. what kinds of
oil are low temperature? i can also get some black high temp spray paint
for barbeques, do you think this would be safe to use inside the oven? the
can says it's very toxic when applying. also are there other ways to
blacken sheet metal? perhaps with a welding torch or something?
when i get this monstrosity up and cookin', i'll send photos to tom for the
solar cooking page. then, according to tradition here, i'll have to buy
everybody a coke ;)
this is getting long so i'll close for now. any other ideas or suggestions
would be more than welcomed.
eric johnson
cuernavaca, morelos mexico
michael bonke internet training
millrather str. 22
40591 duesseldorf
tel: 0211 97 79 023
fax: 0211 97 79 025
www: http://www.optimist.com
besuchen sie mich auf der cebit: halle 18, 1. og, stand b12 (global
entrepreneurs network - gen)!
from: elfpermacl@aol.com
date: thu, 26 sep 1996
subject: ceramic parabolic dish stoves
>>the above idea of yours i sent some time ago to our companion in nepal, i
don't know, if he has tried it yet. (it is funny that people have exactly
the same ideas in their minds.)<<
maybe the ideas come from outside our minds or maybe our minds are part of
the same thing or maybe in a recurvsive universe those there is no difference
between the first two maybes.
>>how much have we to pay for a professional potter to do
the job there? where do you live? i live in finland. how can we share
best the information gathered?<<
well, i will pay exactly what i got paid for teaching that first mexican
permaculture design course. love and caring and the opportunity to meet
expenses out of my own pocket. while i can't expect, and see no reason to
expect, other people to pay to help out folks in tight circumstances, i
can't both work for nothing and have money to pay other people to do the
parts that i'm not qualified to do.
by the way, my work with potters was in the mid 1970s and i've lost track of
these folks. i had no idea that i would need them.
i now live in florida, usa, though i do travel a bit to teach. my main
thrust at the moment is in entirely a different direction--adapting
chinampas (an acient swamp gardening technique developed in what is now
called mexico) for use by very hungry folks at the edge of lake victoria in
africa. a pottery stove could well be part of the same program, of course.
i've got a positive response from a potter in south africa and i'm in touch
with an inventor in australia (who doesn't have email) who might add some
ideas if i keep him posted, which i will if we all cooperate. frankly, i
feel that most of my contribution may be done, though i will try to locate a
particularly talented potter who was a good friend 20 years ago and i'll
help keep folks networked. for now, we can email to whoever wants to be on
our group and take the discussion off this mailing list until we have
something to report one way or the other.
how does that sound? any suggestions or improvements are welcome, of course.
as a generalist, my role is integration and now some specialists need to do
their thing i think.
for mother earth, dan hemenway, yankee permaculture publications (since
1982), elfin permaculture workshops, lectures, permaculture design courses,
consulting and permaculture designs (since 1981), and the forest ecosystem
food network. p.o. box 2052, ocala fl 34478.
"we don't have time to rush."
for mother earth, dan hemenway, yankee permaculture publications (since
1982), elfin permaculture workshops, lectures, permaculture design courses,
consulting and permaculture designs (since 1981), and the forest ecosystem
food network. p.o. box 2052, ocala fl 34478.
"we don't have time to rush."
***
from: info@solarcookers.org
date: thu, 26 sep 1996
subject: parabolic cookers in onates and elsewhere
there has been a lot of discussion regarding the parabolic cooker
as described by dan hemenway. he made some good points, but for
me he raised a few questions.
one thing i really liked was that he apparently spent a lot of
time getting to know the people and discussing various aspects of
the design with them. this is great. responsive, two-way
communication between designers and end-users is extremely
valuable and will help avoid situations where know-it-all
technologists try to dictate solutions...which are then abandoned
as soon as the technologists move on. since women do most of the
cooking (and fuel gathering) in most cultures, your concentration
on discussing the topic with women was great, too.
the advantages of solar cooking listed by dan are also generally
on target.
the question, from reasonable skeptics, that always comes up
sooner or later with respect to all solar cooker types is: "will
people really use it?" even with thousands and thousands of
people using solar box cookers and solar panel cookers, that
question continues to be asked over and over again. maybe it
takes 1,000,000 in use, or 10,000,000 before it becomes accepted
as plausible. until you have people making routine use of your
parabolic cooker, you are vulnerable to skepticism.
as someone, i believe it was virtanen, mentioned, technology for
life and/or plants for life have worked on a cooker in nepal that
uses the parabola idea. i think it involves two small parabolas,
and i remember vaguely that the cost of making one was something
like $3. ari lampinen of technology for life was on this
solarcooking-l at one point, and if he is still out there maybe he
could fill everyone in on this cooker.
now on to my questions:
1. wouldn't most of the advantages you discussed be achieved by
other low-cost cooker designs, such as solar box cookers or solar
panel cookers? were these options discussed with the women in
otates? did they actually prefer a very heavy cooker that would
take two people to a operate compared to a cooker that may weigh
only a few pounds?
2. the only advantage in your list of advantages that would
accrue to your parabolic cooker and not to, say, a solar box
cooker, would be the work provided to potters. yet, you
apparently could not find a single potter in a town of
under-employed potters who would work with this, even though you
had all or most of the town's women clamoring in support of the
parabolic solar cooker? i know that women's opinions are
sometimes undervalued in some settings, but this seems extreme.
any solid information, or even informed theories, about what the
problem was?
3. what is your take on the dangers of parabolic cookers? burned
hands? eye damage? a friend of mine recently returned from a
trip where he saw a semi-abandoned parabolic cooker. (the reason
given for disuse was that it took a lot of time with near-constant
need to reorient it toward the sun. he also saw burn marks on a
building where the cooker's focal point accidentally strayed a few
times. imagine that was a retina. if your parabolic is
reflective enough to cook food, won't it be reflective enough to
cause eye damage if the cook is careless?
thanks for all the information you've shared with us.
sincerely, kevin coyle resources coordinator solar cookers
international
***
from: jonesse@plasma.byu.edu
date: fri, 27 sep 1996
subject: ceramic stoves -- try cone-shape instead of parabola
i've been following the discussion on ceramic solar stoves, shaped like
a parabolic dish. we've made a couple of parabolic cookers here -- but
these are very dangerous due to the rather sharp focus. the parabolic dish
is difficult to form, places the focus at a (perhaps diffuse, but still
dangerous) point, and that point is above the dish. eyes can be sizzled in
an instant.
we made a parabolic cooker cheaply using an emergency blanket (al on plastic
film) glued to a wooden frame with a circular hole. opposite this we placed
a clear plastic film on an identical wooden frame, glued the plastic films
together around the perimeter, then screwed the wooden frames together.
a plastic tube allowed air to be inserted between the films. when inflated,
this makes a nice, cheap, nearly parabolic mirror.
the solar heating was awesome, but far too dangerous. the diameter was
about 1.2 meters, and the sun was focused to a spot about 5 cm in diameter.
paper ignited in seconds at the focus.
for safety reasons, we abandoned the parabolic dish reflector. our friends
at the byu benson institute had tried such dishes in bolivia -- but when
the sun moved and set wooden structures on fire by accident, the bolivians
would not use the dish-reflectors.
so, we came up with a cone-shaped reflector, which focusses to an axis
deep inside the cone -- rather than to a point above the reflector. to
get into the cooker, one reaches in, blocking the sun. you can put your
arm along the focus -- it will not burn you. but the heat collects on
a black-painted jar (or black pot) which is placed inside another clear
jar, or oven-safe plastic bag. temperatures up to 109 c are reached inside
a pressurized canning jar, safely, in about 45 minutes with our cone cooker.
it could be made of ceramic -- much easier to make a cone than a parabola!
top: about 50 cm diameter; bottom: about 15 cm. opening angle, 40-45
degrees.
aluminum foil inside works well; white glossy paint might be ok too.
place the cooking jar (painted black on the outside) on a piece of wood for
insulation, then put that inside the cooking bag -- blow some air into the
bag to keep it from touching the jar, then use a twist-tie to close it.
i've been cooking potatoes, carrots in about 1.5 hours with this throughout
the summer. rice cooks well too -- water boiling when the canning jar is
opened, releasing pressure. handle the jar with hot-pads, it's hot!
our solar cone-cookers have been field-tested in bolivia, as reported here
earlier -- the folks there liked them.
best wishes,
steven jones
byu physics
***
from: virtanen, hvirtane@cc.jyu.fi
date: fri, 27 sep 1996
subject: re: parabolic cookers in onates and elsewhere
i'll try to answer some of the questions info@solarcookers.org
rised as concerns ptl-life cookers design. i think that ari lampinen will
do quite the same, but maybe we'll manage to say something more if we try
to tell our viewpoints separetely...
on thu, 26 sep 1996 info@solarcookers.org wrote:
> there has been a lot of discussion regarding the parabolic cooker
> as described by dan hemenway. he made some good points, but for
> me he raised a few questions.
>
> one thing i really liked was that he apparently spent a lot of
> time getting to know the people and discussing various aspects of
> the design with them. this is great. responsive, two-way
> communication between designers and end-users is extremely
> valuable and will help avoid situations where know-it-all
> technologists try to dictate solutions...which are then abandoned
> as soon as the technologists move on. since women do most of the
> cooking (and fuel gathering) in most cultures, your concentration
> on discussing the topic with women was great, too.
ptl-life cooker's design was made by cooperation of pfl (of nepal) and tfl
(from finland), also the intended users were involved in the process. the
design uses that kind of skills, which almost anyone adult person in the
area has, so almost anyone can *build* the cooker. on the other point of
view the design is a copy of a chinese cooker model, which the intended
users said to be the most desirable model on the market. shortly pt-life
cooker's idea was to make hand made, local material copy of a good, tested
factory product, which is far too expensive to buy.
>
> the advantages of solar cooking listed by dan are also generally
> on target.
>
> the question, from reasonable skeptics, that always comes up
> sooner or later with respect to all solar cooker types is: "will
> people really use it?" even with thousands and thousands of
> people using solar box cookers and solar panel cookers, that
> question continues to be asked over and over again. maybe it
> takes 1,000,000 in use, or 10,000,000 before it becomes accepted
> as plausible. until you have people making routine use of your
> parabolic cooker, you are vulnerable to skepticism.
>
as far as i know in china (mostly in tibet area) there are about half
million parabolic cookers of similar design as pt-life cooker in use.
i don't know how often the users use the cooker etc. actually i wanted to
have chinese information on that. any chinese specialists of solar cookers
on this list?
> as someone, i believe it was virtanen, mentioned, technology for
> life and/or plants for life have worked on a cooker in nepal that
> uses the parabola idea. i think it involves two small parabolas,
> and i remember vaguely that the cost of making one was something
> like $3. ari lampinen of technology for life was on this
> solarcooking-l at one point, and if he is still out there maybe he
> could fill everyone in on this cooker.
the price is about 3$.
there is a description of pt-life cooker on the web-site of tfl, the
access is possible from the web-site of sci. ari can tell more here on
this list, i think.
>
> now on to my questions:
>
> 1. wouldn't most of the advantages you discussed be achieved by
> other low-cost cooker designs, such as solar box cookers or solar
> panel cookers? were these options discussed with the women in
> otates? did they actually prefer a very heavy cooker that would
> take two people to a operate compared to a cooker that may weigh
> only a few pounds?
i think that the main advantage of a parabolic cooker is the power (and
the speed) of the cooker. you can make it practically as effective as you
want by making the mirror as big as needed. there are disadvantages like
the above mentioned. it must be asked and tested *locally*, which *kind*
of cooker is the most suitable in which *area* and which kind of cooker
the *different people* in the area *actually wanted*, if any at all. it
seems that a box-cooker *simply cannot be made cheap enough* (?) for
nepalese poor people for example. the problem of panel cookers is too low
level of effectiviness, which necessiates big area of the panels, which
leads to high price again... so tfl and pfl ended with parabolic design.
>
> 2. the only advantage in your list of advantages that would
> accrue to your parabolic cooker and not to, say, a solar box
> cooker, would be the work provided to potters. yet, you
> apparently could not find a single potter in a town of
> under-employed potters who would work with this, even though you
> had all or most of the town's women clamoring in support of the
> parabolic solar cooker? i know that women's opinions are
> sometimes undervalued in some settings, but this seems extreme.
> any solid information, or even informed theories, about what the
> problem was?
for pt-life cooker you don't need any potter for the construction. it is
made of clay, but the clay is unfired, the necessary durability is
achieved by using a bamboo frame inside the clay. it is my new idea, that
we might use cheramics for the next design. the advantages would be
1) less time needed for the construction. bamboo-clay model needed about
18 hours man-woman work.
2) better precision of the mirror is easily achieved. much of the time
spent in the construction of pt-life cooker is spent for making the
surfage smooth. by using casting method (mould of gypsum, or concrete) the
right shape is quite easily achieved.
there are many disadvantages with cheramics as well. maybe the biggest
will be that then the price would be again higher... and the low price of
pt-life cooker (as well as the really local production) is the main
advantage of pt-life compared to the chinese original?
>
> 3. what is your take on the dangers of parabolic cookers? burned
> hands? eye damage? a friend of mine recently returned from a
> trip where he saw a semi-abandoned parabolic cooker. (the reason
> given for disuse was that it took a lot of time with near-constant
> need to reorient it toward the sun. he also saw burn marks on a
> building where the cooker's focal point accidentally strayed a few
> times. imagine that was a retina. if your parabolic is
> reflective enough to cook food, won't it be reflective enough to
> cause eye damage if the cook is careless?
i agree with this. there are dangers of misuse always involved. concerning
pt-life cooker this problem was met by using a design which has been
tested by really long time design process by the chinese program. the
design is of that kind where the user is located behind the mirrors and
the focus. of course it is *possible* that someone *can* enter the hot and
dangerous area, whatever iron bars you put there preventing this to
happen. i think that this problem is a relative problem, the danger is
always involved, it is a matter of degree, which must be met by good well
tested design. someone *can* for example put his head inside a box cooker,
which is heated in 150 celsius degrees and keep it there until he dies...
>
> thanks for all the information you've shared with us.
>
> sincerely, kevin coyle resources coordinator solar cookers
> international
>
virtanen
hvirtane@cc.jyu.fi
***
from: virtanen, hvirtane@cc.jyu.fi
date: fri, 27 sep 1996
subject: re: parabolic cookers in onates and elsewhere
on thu, 26 sep 1996 info@solarcookers.org wrote:
> apparently could not find a single potter in a town of
> under-employed potters who would work with this, even though you
> had all or most of the town's women clamoring in support of the
> parabolic solar cooker? i know that women's opinions are
> sometimes undervalued in some settings, but this seems extreme.
> any solid information, or even informed theories, about what the
> problem was?
my first quess, not even an informed theory, is that potter's pots are
quite expensive things... does anyone know, how much a (fired) big
clay pot costs in the area? does anyone know how much an 1 m diameter clay
pot costs in india, in china, in...?
(at least here they cost a fortune and as far as i know there is only one
kiln in the whole country (finland is the place where i live), which is
big enough to take 80 cm diameter mirror-base inside... that means that in
general potters don't even make so big things, whatever the price would
be...)
virtanen
hvirtane@cc.jyu.fi
***
from: barbara kerr, kerrcole@frontiernet.net
date: fri, 27 sep 1996
subject: re: ceramic parabolic dish stoves
ceramic breaks. such a massive production gone in an instant.
in addition, if it is the slightest bit wet, and freezes, it
does not even have to be dropped.
~reply 9/26/96
your history is fascinating and the plight of the families and
the land where you are is quite touching. it is this kind of
situation we have worked to meet since 1974 or so. i have used
the facts that i am a woman who was raise in the appalachian
mountains of north carolina and therefore understand poverty and
making things with what you have. i realized i am fortunately
situated where i have both the interest, the time and the money
to risk working with very low tech solar domestic designs: solar
cookers, solar food dryers, solar water heaters, solar passive
house heating, solar water pasteurization and distillation. i
have put my life to the goal of developing and using the very
simplest methods in my own home. if they past these trials, then
i begin telling people about them. if equipment cannot be
homemade, cheaply of local materials and if it has not work for
me on a regular basis, i keep exploring. my work is on beyond
theory and intuition. only having the device and finding it
useful to me qualifies it for me.
let me offer what i can.
the route of development you will need to explore the ceramic
bowl cooker is very long with endless efforts and testing. in
the end, i believe you will decide that ceramic bowls, unless
they are about 2 feet across and lined with a truly reflective
surface, such as foil, will not cook adequately. even then, with
the slightest breeze, the heat will scatter rather than enter the
food unless there is glazing. but there are solutions that may
fit your needs for solar cooking.
bill lankford had published a picture of a large 5' x 8' flat
topped solar box cooker that reportedly was used to cook pizzas
and to cook for prisons in guyana. it was made of adobe, black
paint, multiple standard windows, and a large reflector. huge but
made locally.
on the other hand, there is a very light, portable family-sized
solar cooker developed by solar cookers international. their
cookit is being used by women in refugee camps in kenya and they
are teaching their neighbors. it is spreading through the camps
naturally from woman to woman. this a cardboard-backed foil
basin about 30 inches or more across, which will fold into a
packet that can be stored in a small crowded home. it requires a
dark pot with a lid and it requires some glazing to enclose the
pot, such as a baking bag.i realize this is far above the
technology you have in mind, but it is the minimum as far as we
have discovered..
truly, many people, including engineers and many handy people
women included, have searched for years for the simplest way to
solar cook and this is considered the best so far in the sense of
being cheap, simple, capable of handbuilding or local
manufacturing. without each component (basin, reflector,
glazing, dark pot with lid), it simply will not produce cooked
food. the problem then boils down to how to get them produced
locally and cheaply and how to help the women obtain them. in
one place, they plant tree seedlings and tend them for 3 months.
if the seedlings survive, the woman receives a solar cooker.
now, if the bowl were not of foil covered cardboard, but of
ceramic, such a cooker would still require the truly reflective
surface. the work i did with white paints and chalks and clays
did not produce anything near enough heat for cooking. and the
heat must be contained around the pot within a clear glazing,
such as being in an insulated box behind a glass or plastic
window, or within a baking bag.
this is just the minimum so far. always, we feel that solar
cooking cannot get any simpler, until the next discovery. many
people are continuing to search for greater simplicity and
economy and harmony with the women, the families and the
environment. together we are moving forward and learning more.
another very simple solar cooker design line are the solar
funnels. you can find out more about them in earlier postings on
this solar cooking list. theyare also minimalist designs.
i wish you well.
***
from: virtanen, hvirtane@cc.jyu.fi
date: fri, 27 sep 1996
subject: re: fwd: from douglas banks
douglas bank wrote:
> i am a potter- and i would be very proud if i could throw a dish that big,
> and fire it successfully (i could probably sell it for a lot too!) large
> flat dishes of that size are very difficult to make. i routinely make pots
> (wash basins) of around 400 mm in diammeter, sometimes just over half a
> metre- they are high fired, so one could apply a good reflective glaze to
> the pots. diam of 600 mm would be feasiable, but much bigger than that- and
> one is i think beyond the realm of regular craft pottery.
for example pt-life cooker uses two mirrors. if you can make two 600 mm
parabolic mirrors of ceramics, it is enough!
> what does the design look like- how easy would it be to adjust the somewhat
> heavy ceramic dish?
the design of pt-life cooker is a copy of a chinese cooker (which uses two
mirrors as well), which is more than 60 kg heavy... and has all the
technology needed to adjust the heavy (made of steel) mirrors. what i had
in my mind was just to try to make new style mirrors for pt-life (or
similar) cooker of ceramics. the design of the frame for mirrors we simply
have to copy from somewhere or to make. but for sure it can be made,
because chinese and nepalese already made it (pt-life cookers mirrors are
really heavy as well)...
> wow- all these questions- , neverthelss- i would be interested in any
> developments! i am always looking to ways of linking my ceramics
> hobby/business more directly with my rural and renewable energy
> research/consultancy work.
it sounds very good indeed.
so, what are we waiting for? we can start working? we will find you the
design for the frame and you'll try to make the mirrors? i must admit that
i don't have the design here at present, but surely we can get to you.
virtanen
hvirtane@cc.jyu.fi
***
from: ari lampinen, ala@cc.jyu.fi
date: fri, 27 sep 1996
subject: pt-life parabolic cooker
i confirm what hannu told about it. it was indeed designed and planned
by the locals. we (tfl, finland and pfl, nepal) noticed that the local
house architecture could be modified for a cooker support system. on the
other hand bamboo baskets made by women could be used as dishes if they
only were big enough and correctly shaped. most men know how to make a
traditional house and most women know how to weave bamboo baskets. our
nepalese partner organization (pfl) found volunteers to make the
construction and took care of all the practical things (we were not
present). the cost $3 came from al folio, al pot and some other small
things, like glue and rope. the price could be reduced to about $1, i.e. the
price of the al folio, because al pot is not needed (the cooker works with
clay pots) and glue and rope can be done in the villages (only labour
needed, no money).
the cooker shown in our web pages (front page www.kaapeli.fi/~tep)
was the first proto in 1995. this year the support system has been
modified to enable easier tracking and dishes are now done a little
differently. the cost has not risen but a few hours more of work (now
about 24 woman-hours total) is needed due to the more complex support
system (made of bamboo and grass ropes) that can turn around two axes.
our purpose was to find a cooker model that people could call their own;
the use could spread without any outside influence and the design would
be improved by the people using it.
anyway, people do not want to use it. the main reason they tell us is
that *the cooker is not fast enough* (1 kg of rice takes 1 hour)! only
cooker that can beat open fire convinces them. the chinese cooker that
boils 3 l of water in 15 minutes or cooks 2.2 kg of meat in 20 minutes is
the only model that they find really impressing.
maybe in some other culture the pt-life cooker concept would have better
acceptance??? the african palm leave baskets would give a good basis
because they are much better than the nepalese bamboo baskets.
regards,
ari lampinen
tfl (technology for life), finland
* solar cooking beyond latitude 62 *
***
from: virtanen, hvirtane@cc.jyu.fi
date: fri, 27 sep 1996
subject: re: ceramic parabolic dish stoves
on fri, 27 sep 1996, barbara kerr wrote:
> ceramic breaks. such a massive production gone in an instant.
yes, it breaks quite easily. but what will professional potters say,
does it break *too* easily? you don't drop the mirrors of your solar
cookers, if they are fixed well.
> in addition, if it is the slightest bit wet, and freezes, it
> does not even have to be dropped.
many things break, if frozen. in many countries and areas nothing is ever
frozen because the temperature is never below zero celsius.
what do professional potters say, is good ceramics wet inside?
i've never seen any of my dishes broken because frozen. (i live in a
country, where the temperature is sometimes 40 degrees celsius below
zero.)
> in the end, i believe you will decide that ceramic bowls, unless
> they are about 2 feet across and lined with a truly reflective
> surface, such as foil, will not cook adequately. even then, with
> the slightest breeze, the heat will scatter rather than enter the
> food unless there is glazing.
pt-life cooker performs quite well, the chinese original with its better
mirrors is better. both of them use foil as surface (as it can be used
with ceramic bowls...). if we use ceramic mirrors, pt-life would be as
good as the chinese original and locally made?
> bill lankford had published a picture of a large 5' x 8' flat
> topped solar box cooker that reportedly was used to cook pizzas
> and to cook for prisons in guyana. it was made of adobe, black
> paint, multiple standard windows, and a large reflector. huge but
> made locally.
our problem has been the price of glass for the box cookers. besides that
glass cannot be made locally. our nepalese partner complains about other
things as well, including the complexity of good design/or low power.
> on the other hand, there is a very light, portable family-sized
> solar cooker developed by solar cookers international. their
> cookit is being used by women in refugee camps in kenya and they
> are teaching their neighbors. it is spreading through the camps
> naturally from woman to woman.
i have built and tested cookits here. it is really good for its intended
use, refugee camps. but our nepalese partner is not satisfied with its
power in home use.
> now, if the bowl were not of foil covered cardboard, but of
> ceramic, such a cooker would still require the truly reflective
> surface. the work i did with white paints and chalks and clays
> did not produce anything near enough heat for cooking.
pt-life and the chinese original use foil. that is the only part necessary
to buy for pt-life cooker.
> another very simple solar cooker design line are the solar
> funnels. you can find out more about them in earlier postings on
> this solar cooking list. theyare also minimalist designs.
i'm aware of that design. is it powerful enough? i haven't tested it, and
have seen only tests of quite small models. the cooker should be able to
cook at least 1 kg of rice in one hour's time.
virtanen
hvirtane@cc.jyu.fi
***
from: marge wood, woodm@nicanor.acu.edu
date: sat, 28 sep 1996
subject: re: ceramic stoves -- try cone-shape instead of parabola
neat! i think i'll pull out that cone-shaped sort of colander in the
cupboard and line it with foil. it even has a three legged stand to hold it.
---------------------------------------------------
marge wood woodm@nicanor.acu.edu (915) 674 2341
***
from: internet:elfpermacl@aol.com, internet:elfpermacl@aol.com
date: sat, 28 sep 1996
subject: re: ceramic stoves -- try cone-shape instead of parabola
hey, steven jones:
did you miss the part where i said that one benefit of the ceramic parobolic
dish would be that the focus, due to imperfections, would be more of a disc
than a point? i don't blame bolivians (or anyone) from avoiding a dangerous
design, particularly one where they can't see the danger. i've seen a
parabolic dish of maybe 8 feet in diamater evaporate a brick at focus in
under five minutes. the sound and smell were awful. the design i've
proposed could not be made to such precisioin, which is the other half of
the criticism. sounds like i've got it about right.
a dish is still a more familiar kitchen item than a cone. but whatever
works. what idiot put his or her head in a working stove? sounds like
natural selection to me. had the person never seen a stove? nobody
instructs people to focus a stove that way. you just position to pot to
receive a bright disk of light. one is positioned to look up at the pot,
not down over the stove.
for mother earth, dan hemenway, yankee permaculture publications (since
1982), elfin permaculture workshops, lectures, permaculture design courses,
consulting and permaculture designs (since 1981), and the forest ecosystem
food network. p.o. box 2052, ocala fl 34478.
"we don't have time to rush."
***
from: marge wood, woodm@nicanor.acu.edu
date: sat, 28 sep 1996
subject: re: ceramic stoves -- try cone-shape instead of parabola
there is something about shiny things. folks need to be made aware of
safety issues, including keeping small children away. but everyone can
learn. making solar cooking easy, affordable, convenient and socially
acceptable seem to me the key issues for getting lots more people to do it.
i need to go get the solar cooker set out and some food in it; today
looks like a perfect day
for it....
---------------------------------------------------
marge wood woodm@nicanor.acu.edu (915) 674 2341
***
from: ari lampinen, ala@cc.jyu.fi
date: sun, 29 sep 1996
subject: parabolic hazards
on thu, 26 sep 1996 jonesse@plasma.byu.edu wrote:
> for safety reasons, we abandoned the parabolic dish reflector. our friends
> at the byu benson institute had tried such dishes in bolivia -- but when
> the sun moved and set wooden structures on fire by accident, the bolivians
> would not use the dish-reflectors...
you can also make a parabolic mirror that has its focus deep inside.
a german sk series (sk-14 is the current version) is an example of
that. about 4000 of them have been distributed and no reports of
accidents are known. i just checked this with the manufacturers at
the eurosun96 conference in freiburg, germany, 16-19.9.
on the other hand, i haven't heard of any accidents by the users of
the chinese 2 m2 cookers (some 200.000 in use) or the swiss 7 m2 ulog
sun tracking community cookers (about 50 in use) that have their focus far
out of the rim. the ulog cooker situation i also checked at eurosun96.
with these cookers the hazard potential is there even though they have been,
of course, purposefully designed to have a wide, > 10 cm, focus.
-ari
***
from: info@solarcookers.org
date: tue, 1 oct 1996
subject: parabolic thanks
thanks to all who responded to my request for more information on
experience with parabolic cookers (and related topics of
dissemination and consultation with end users.) especially
exciting for me were the numbers of parabolic cookers distributed
in china and the growing numbers of sk-14's that have been
distributed. but it is clear that many people are involved in
good and important work in many places; our exchanges on the
solarcooking-l just confirm the value of pooling these varied
experiences. thanks to tom sponheim for hosting.
those interested in more details on china's experience may be
interested to know that at least 5 chinese representatives are
listed among the presenters at the world conference on solar
cooking in india in january. tom will probably be posting more
info. here on solar-cooking-l about the conference soon.
thanks again to you all for your work and for sharing your
thoughts.
sincerely, kevin coyle resources coordinator solar cookers
international
michael bonke internet training
millrather str. 22
40591 duesseldorf
tel: 0211 97 79 023
fax: 0211 97 79 025
www: http://www.optimist.com
besuchen sie mich auf der cebit: halle 18, 1. og, stand b12 (global
entrepreneurs network - gen)!
