Scheffler Parabolic Solar Cookers
By J Mc
Barli Development Institute for Rural Women Indore
It was decided that the site and the Institute was a suitable location for the testing of this type of solar cooker. We were
fully committed protecting the environment and in the promotion of non conventional energy system and had skilled and
fully committed people to establishing and maintain it.
The Concept

The solar cooker invented by
Wolfgang Scheffler is designed so
that cooking can be done inside
the kitchen, where as most other
designs of solar cooker the cook
has to stand in the sun. Because of
this there are certain restraints
about the alignment and design of
the kitchen building.

The building needs to have a
north-facing wall, no large
buildings or structures close to the
dish, and sloping roof to allow the
sun to shine on the dish during the
daytime and throughout the year.
The idea of the Scheffler Parabolic Cooker is basically quite simple in practice: it concentrates the solar radiation to one
point through absorption onto the black coloured surface a cooking vessel, this concentrated energy is converted into
heat and used to cook food inside the cooking vessel.
The basic construction consists of a primary reflector of approximately 8 square metres, made form mirrored acrylic
sheets, the rays from this reflector are concentrated to a secondary reflector, made from aluminium strips covered with
household aluminium cooking foil.

especially when we need to cook in larger quantities. The light is concentrated through an opening in the kitchen wall,  
then reflected a second time by a secondary reflector to the bottom of the cooking vessel.
per hour. This mechanical drive uses gears, which are normally used in a manually operated air blower of a small per
hour. This mechanical drive uses gears, which are normally used in a manually operated air blower of a small
blacksmith’s forge, this and all other parts used in the tracking mechanism are available in most local hardware shops.
blacksmith’s forge, this and all other parts used in the tracking mechanism are available in most local hardware shops.
slope of the disk is adjusted by 2
adjustable rods at top and bottom
of the disk. This has to be done
every few days. The construction
of the frame is flexible, so that by
adjusting the seasonal slope, the
shape of the parabolic dish
changes. If the geometry of the
collector were to remain the same,
the focal point would shift up or
down when the slope of the
reflector is changed. As cooking is
done inside the building we need a
fixed focal point throughout the
This drawing attempts to show the angle and shape of the dish during mid winter and mid summer, points A is attached
to the rotating arm and point B to the parabolic dish, between points C and D, is the lower adjusting rod and between
points E and F the upper adjusting rod.
Installation of the Solar Cooker
In April 1998 the cooker arrived from Gardia Solar Enterprises Valsad Gujarat, a foundation had alread been made for
the stand of the dish. The engineers from Gardia assembled the dish, mounted the stand on the foundation, then erected
the dish on the stand. When this was completed, the location of the actual location-cooking place was found. This
cooking place then made, then we erected a shed for cooking in, this was a basis structure , but served the purpose
very well, it was quite simple structure using mostly building materials that left over from other works. Only major
expense being the corrugated iron sheets and the angle iron frame. When it was finally completed, it had a tandoor, and
large fuel-efficient wood burning stove, a place for washing vegetables and utensils.

The area where this shed was located was the best area close to the main building where there we could get maximum
sunshine throughout the day.

The students use to enjoy being there and it was the main focal point for gathering and relaxing after classes. It
resembled the open and airy environment of their own villages.

The Start of Cooking

Now that the basic structure was erected, we began the work of actually using the solar cooker, though the Institute
had been cooking with solar box cookers for more that 13 years, the success of using these for larger scale cooking
was limited, as they were mostly used for cooking dals, etc. Using this type of concentrated cooker was a new
experience for everyone.

When we Installed this cooker the number of students was around 35, and the total number we had to cook for was for
about 45 persons including staff and others. The first experience the cook had was she could cook breakfast without
lighting a fire. Though to get the system going was quite difficult, first was to organize the cooking schedule, the
Institute had a menu already in place to suit the eating style of the students i.e. They would have poha and tea for
breakfast at 9:00 am, rice and dals for lunch at 1:00 p.m. and vegetables and roti for dinner at 7:00 pm.. Normally the
scheduled classes of the Institute would end at 6:00 p.m., so the girls would help the cook make chapattis for dinner.
We decided to stay with this system, in the morning, the onions, spices etc were fried and then the poha cooked,
depending on how fast the poha got cooked, they would put the tea to boil, if there was not enough time then the tea
would be made on the wood stove. Next was to cook lunch again 2 items had to be cooked, and to avoid any idle time
of the cooker and to maximize it use the item to cook next item had to be prepared and be ready to start cooking as
soon as the previous item was removed from the solar cooker. This was to prove the most difficult for the cook.
Traditionally she would finish preparing the food, relax and enjoy having food and some rest after the students had
eaten, but now everything had to be prepared earlier. It was decided that first we cook the rice then the dal for lunch,
this worked fine as the rice normally cooked within 1½ hours, giving time to cook the dal before 1:00 p.m. lunch time,
but there was no fast rule about this. After 1:00 p.m. the vegetable for dinner was cooked, we continued with the same
system of the trainees helping to cook the chapattis on the wood stove after 6:00 p.m.

The Problems

By now the major difficult that we discovered was that the focal point of the reflected sunlight was drifting
downwards, as the dish rotated, original we thought that this was a tracking problem, but when we adjusted the
tracking speed, it did not seem to help and we came to the conclusion that this was fault with the cooker, the tracking
speed is adjusted by length of the pendulum in the clockwork tracking mechanism. To correct this downward
movement of the focal point, we had to reset the seasonal adjustment on a hourly basis resulting in keeping a very
narrow focal point, the result of this was to burn the aluminium foil and then melting the aluminium strips of the
secondary reflector. We asked Gardia Solar to send us another secondary reflector, so that we always had a spare
reflector with the strips and foil replaced, When one reflector got burned we would replace it and there was little or no
loss of cooking time. The other problem that we faced was with the clockwork mechanism, when it was working it
was ok, but when it stopped it took a lot of time and adjustment to get it going properly again.

We were also convinced that we will make this cooker work whatever, because by now we were satisfied with the
cooking ability of this solar cooker, so other problems could get sorted out over time.

The Cook’s Concerns

Main drawback at this time was the attitude of the cook, the main problem being that she has to be on duty for the
entire day, and not just cooking for a couple of hours before each meal. In all 2 cooks left the job only because of this

Collecting Data on Solar Cooking

As this was a project to evaluate the cooking ability of this type of cooker, we started to collect data to be presented to
MNES, in the beginning this proved very difficult, and by the time we had got into the system of cooking with the solar
cooker the monsoon had set in and we had no reliable data. We had also planned to keep a accurate account of wood
and gas used during the monsoon, this also proved difficult and unreliable, and by the time we had a good system in
place to get records the monsoon was coming to the end.

Even after we eventually got back to cooking full time after the rains, it still proved very difficult to get data that we
could rely on. Basically it was not until January 1999 that we could say that we had data that was reasonably correct
Table 1 is sample of the data of the cooking times during April 1999,

Table 1
We had tried different methods of collecting data, not only did we need to record the cooking times but also the quantity
of, and the ingredients being cooked, as the food was issued to the cook from the store each day we decided it was
better to use this measurement and therefore cook only had to record the amount of water etc. she used in every meal
rather than weight the food every time before cooking, as this had proved an unreliable method of getting accurate data.
At this point I should mention that the cooks are also village women mostly, with less formal education.

Table 2 show cooking times for tea from 1st to 10th March 1999, rows in bold italic were not cooked on solar cooker.

Table 2
Table 3 for same period for poha, again figures in bold italic were not cooked on solar cooker.

Table 3
During April we could mostly make the tea and cook the poha for the breakfast before 9:00 am

Table 4 shows the times for cooking rice from 1st to 10 th March 1999

Table 4
Table 5 times for the dals cooked during the same period.

Table 5
Table 6 shows the weight of vegetables and the cooking times recorded for dinner, I had not included the type of
vegetables cooked to save space, the Institute grows its own vegetables and these include most normal seasonable

Table 6
These tables will give the reader a reasonable idea of how the cooker performs, March is a fairly cloudless month with
almost 100 percent cooking time on the solar cooker.

Saving Valuable Fuels and Money

By 13 June monsoon had fully set in and cooker was only used occasionally and mostly only for heating water. Now
we would try to still keep up the same evaluation system but cooking on wood or gas. Below is typical full days
cooking on gas and same using wood, cooking the similar items that were cooked on the solar cooker

Meeting People
DAVV Indore. Here I met Wolfgang Scheffler inventor of the system and Deepak Gardia of Gardia Solar Enterprises
DAVV Indore. Here I met Wolfgang Scheffler inventor of the system and Deepak Gardia of Gardia Solar Enterprises
manufacturer of the cooker. Attending this was also Dr. A.K. Singhal and others from the MNES. Also it was
satisfying to know that our cooker, despite all the trouble we had was performing as well as other cookers installed
elsewhere., and I was the only one to present from the viewpoint of a user, all other papers presented regarding the
cooker were from the technical side.
cooker were from the technical side.

During this meting we discussed the technical problems with the cooker, and now it seemed clear to me that the
problem of the shifting focus, was an installation problem, and Deepak Gardia and Wolfgang told those present that
they had now changed the method of installing the cooker.

It was during the talks with Wolfgang and Deepak they told me that they had a new invention that would cook in the
night. They said that they would like to send it to Barli for evaluation and testing, because they were quite pleased
with the way we had collected the data and tested the community cooker

The Solar Storage Cooker.

attended this convention, and they decide to stay with us at Barli, this gave me an excellent opportunity to interact
attended this convention, and they decide to stay with us at Barli, this gave me an excellent opportunity to interact
with them and consult about different aspects of the solar cooker, during this time we tried to resolve the problem of
the drifting focal point, and it was decided that it needed complete realignment.
the drifting focal point, and it was decided that it needed complete realignment.

During their visit we discussed the solar storage unit, Deepak had suggested to use the existing dish for a number of
hours each day to charge this unit. I did not like to do this as we had by now become dependant on our solar cooker
and to use the dish for a number of hours every day was going to spoil our solar cooking routine.

As Dr. A.K. Singhal of MNES was also attending this convention, I ask him if MNES could help if I decided to install
another dish. They agreed to give the standard subsidy of 25,000 Rs towards the cost of the dish, this agreed we told
Deepak to supply us another dish for charging the storage unit. A local Charity Kissan Malhotra Charial Trust gave
the other 50% of the cost of the dish to the Institute.

on the day of the workshop. So we would have to make an extension to our existing shed to house the storage
system, and as the dishes need to be about 5 metres apart meant quite a bit of space.

system, and as the dishes need to be about 5 metres apart meant quite a bit of space.

We hastily made a foundation and when the engineers from Gardia solar arrived with the new dish and the storage
unit we were ready to assist them to get the system up and running as fast as possible
The pictures above and above left show the hastily laid foundation and the new alignment frame for the reflector dish.
With the new type of mounting frame, alignment of the dish and
setting the foundation for the dish was much easier with little or no
chances of wrong alignment of the dish.

The picture on the left shows the solar storage system getting its
first rays of sunshine
While doing this installation work we looked at the problem
of misalignment of the earlier dish, and discovered the
problem was with the placement of the cooking area, as
this was built into the shed we decided moving the
mounting of the dish would be the best way to get the
proper alignment.
The picture on left below shows the work
of realignment of the dish mounting
Picture on the right shows the 2 dishes and the work on
the extension to the shed almost complete for the
inauguration of the storage system

Over the next few days we got some walls built on the
New Solar Kitchen

But on this same area we would build a wing of the new dormitory that had been planned
Solar Storage goes up

The solar storage system weighed around 600 kilos, so how to get it on the first floor, we considered hiring a crane, the
there was the problem of getting the crane into the location to get the system where we needed it. As the main staircase
to the first floor was nearing completion I decided that on the students day off we get them all together and make some
rails and roll the storage unit up the stairs on wheels.

We bought some heavy wheels fitted them to the frame and wheeled the unit through what was a building site to the
bottom of the stairway leading to the first floor.
It was hard work getting the storage cooker onto the first floor, but with the help of all the students who were very
excited with the task. They heaved, they pulled and they pushed the unit all the way to its destination, the whole operation
went very smoothly, and was completed in about 1 hour.

had to add a 1-metre cantilever extension to the building to accommodate the supporting frame of the Scheffler dishes.

Next operation was to align the dishes exactly north, this prove not to be too difficult with the new mounting frame and I
also had the use of a transit level with built in compass.

It would take until January the following year that we could have the construction of the kitchen to a stage that we could
cook in it.
In the picture on the right though not very clear, the cantilever extension to the building to accommodate the frame of
the Scheffler dishes can be seen.
The system had by now turned into a very good integrated solar
cooking unit. One dish was used for cooking directly cooking most of
the food for 3 meals a day for the Institute, the other one used for
charging the storage system which was used mostly for cooking
chapaties after sunset and making the morning tea. We also built into
the kitchen a well designed fuel efficient wood burning stove to use
when there was cloud and during the monsoon season.

On the left is a picture of our fuel efficient wood burning stove
One major difficulty that we faced was with the tracking mechanism especially the pendulum that controlled the
speed of tracking, it would work for some time then start to give difficulties and would be very difficult to get back
to effective working state.
On the right is a view of the outside of the solar kitchen. inside the kitchen making, students are making chappatis on
the storage cooker at night.

Changes Being Made
A student from Switzerland, Mr. Adrian Kondrad, was planning to come to India to study solar cookers and the spend
some time with Wolfgang Scheffler before coming to India. I suggested that he and Wolfgang look at the spend some
time with Wolfgang Scheffler before coming to India. I suggested that he and Wolfgang look at the problems with the
tracking system.

They had developed a total new tracking system and when he came here, we both agreed that this would be quite
difficult to fit the to our existing system, so instead we looked at redesigning the pendulum of the existing tracking
system. We looked a different ways of doing this and finally came up with a design we would try. After a number of
days of trial, error and different adjustments we came up with a pendulum design that seemed to work much better
and was also simpler to build than the original. This has worked very well up to present thought a time of writing the
pendulum is giving slight problems on both cookers

left is a picture of the storage system and the direct
solar cooker on rails
During the last year we also changed the system of covering the aluminium strips in the secondary reflector with
aluminium foil. And instead we made these strips from highly polished and hardened aluminium sheet, this material is
also used in the construction of SK14 parabolic cooker and other uses such as lighting installations.


Now for the last year or more whole cooking units are being maintained by the cooks and any technical adjustment or
repairs are being done by our garden staff. Recently when the wire rope supporting the weight to drive the tracking
mechanism broke, I did not know about it until a new rope was fitted to the system. The cooks clean the reflectors
make the seasonal adjustments if the tracking clockwork mechanism stops they get started themselves. They have
completely the understood the need to use solar cookers and now even in the monsoon season, when the clouds part
and the sun shines for some time I see the dishes are orientated to face the sun, they make sure that no valuable
sunshine goes to loss.

Hay box
The Results
to the villages and demonstrated how they can use solar cookers in
to the villages and demonstrated how they can use solar cookers in
the villages. As a result the Institute started manufacturing small
parabolic SK 14 parabolic solar cookers invented by another
German inventor Dr.Seifried. During the training programme at the
Institute those trainees who will willing to pay a percentage of the
cost and who during the training at the Institute would learn to
cook, mostly their own recipes on this small parabolic cooker, take
the cooker home with them after the course is complete.the cooker
home with them after the course is complete.
As result we were able to start a process of use of solar cookers in the rural areas where the need for the use of non
conventional energy is greater and the fuel wood is more difficult to obtain. This project is being funded by Intersol in
Austria and the money is being raised by primary school children
Below is a table showing of visitors who came to see the solar cookers and other environment protection work at the
Institute since the installation of the solar cookers.
Self Groups on field visits
and tours
Visitors and Guests of School of Energy
and Environment Studies and others
Other Visitors interested to
see the Solar Cookers

During this period the Institute has trained 602 village women and 476 members of their families visited the Institute

Some Information about Barli Development Institute for Rural Women

being of their families and home villages.

free of charge to women, drawing its trainees mainly from tribal areas throughout the region -- a region marked by
shortage of drinking water and poor soil.
shortage of drinking water and poor soil.

their culture which need to be preserved and strengthened.

The Institute works on these goals through an holistic approach to education, giving each trainee courses in literacy,
leadership training, tailoring, agriculture, artisan crafts-work, human rights knowledge, environmental awareness, self-
esteem and personality development, a sense of social commitment, nutrition and health, and income-generating skills.
Interwoven into the curriculum is an emphasis on art, music and dance.

the environment is a spiritual responsibility, as well as an important service to the community. In practical terms, the
energy conservation techniques such as composting, vermiculture, the use of biodegradable products, and proper energy
conservation techniques such as composting, vermiculture, the use of biodegradable products, and proper waste
management. One of the institute’s earliest health education campaigns freed that area of guinea worm by teaching the
importance of clean water.
importance of clean water.

More specifically, the trainees learn conservation strategies by doing. At the Institute itself, rainwater is caught and
stored rainwater is harvested and the depleted ground water level recharged, and wash-water is re-used for irrigation.
Gardens, tended by the trainees, provide most of the Institute's food. Trainees prepare meals using a state-of-the-art
solar cooker; some become "experts" able to support the use of solar cookers in their villages.

The Author is Manager of :
Barli Development Institute for Rural Women and a committed environmentalist.
Please except my apologies for the absence of the tables, it
was too time consuming to remake them on the transferred
web page.
I will find the original MS excel sheets and replace ASAP

Jimmy McGilligan
Hosting by Yahoo! Web Hosting
Initial Study