Roasting Coffee

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Roasting green coffee beans is as easy as on fire using the same traditional instruments: a flat bowl out of sheet-metal and a metal spatula. The taste of the ethiopian coffee is usually even better as the roasting process is somewhat slower at the beginning when the beans are white and the heat is mainly produced by the metall dish. Finally the roasting process speeds up when the meanwhile black beans collect the light from the top themselves.

Using the Jabenna

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In the traditional Jabenna, a water container made out of thin clay a liter of water needs less than 8 minutes to boil and coffee may be prepared in the usuall way. The Jabenna is an ideal heat collector for a parabolic cooker. It is black and the ball-shape can be placed in the focus to collect light from all sides. In the early morning or late evening when the sun is close to the horizon the parabolic mirror has to be positioned nearly vertical so that the light hits the pot from the side and top as well. In a pot with a lid the light from the top heats the lid but not the water.

SK14 Modifications by AMSI

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The original EG-SOLAR SK14 solar cooker which had been copied and slightly modified according to the local requirements and manufacture possibilities to become the AMSI cooker.

 

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The modified AMSI-Solar-Cooker. The modifications are:

• Instead of galvanised flat metal bars, simple and cheap reinforcement bars which are locally available are used. All parts are welded together and not screwed which is cheaper, more durable and form-stable. The cooker can be used on uneven ground as well.
• The parabolic cage for the mirror is assembled and welded on a wooden mould to guarantee for shape precision even with low precision parts.
• The mirror-part can be easyly disconnected from the stand to allow the storage of the cooker in rooms with small doors.
• The pot holder is one part, firmly connected to the mirror. No parts may fall into the mirror and scratch the reflecting surface during transport and operation. The shape of the potholdes has been changed to allow the traditional cooking equipment to be used (The Jabena-jar and the Injerra-plate).
• The mirror panels are fixes with hard aluminium wire to the cage. This makes the fixation of the prefabricated mirror-panels on the usually inaccurate supporting circles easy and durable.

All modifications where made to adopt the SK14 concept to the local constraints of available material, inaccurate production and very rough handling which had to be faced.

Further modifications I want to make are

1. Avoiding the parabolic cage completely by connecting the mirror plates firmly with false (blind?) aluminium rivets. The shape of the mirror sheets has to be optimized for that purpose and the connection holes of overlapping mirror sheets have to be drilled very accurately, but than the right shape is simple and absolutely guarantied. I think of mirror sheets having interchanging trapezodial and triangular shape and arranged in rings.
2. Leaving a hole in the center of the mirror and slightly enlarging the mirror size. In the center of the mirror there is alway shadow made by the pot so removing the mirror there has no negative effect on the cooking energy provided. The hole at the same time replaces the solar gage to adjust the cooker. The cooker will be best adjusted if the shadow of the pot is in the center of the shadow of the mirror-ring on the ground, - very easy!
3. Because the mirror without cage is no longer so heavy the largest ring holding the mirror may be fixed directly to the pot-holder bar. The shape of the parabola has to be changed than so that the focus is in the plane of the largest ring. This again simplifies the construction and reduces weight and material. No pieces of sheet metal are needed any longer, so no drill mashine and sheet metal cutter is needed if the mirror sheets are pre-fabricated.

Constructing the AMSI-Cooker

The following pictures demonstrate the use of the wood model to make a parabolic cage out of reinforcement bars in the proper shape.

First of all the 4 rings have to be formed. They should be exactly round and flat. To check the shape of the rings draw circles with the right diameter on a level concrete floor or on a big peace of plate-wood. To check the rings place them on your drawing on the floor or the plate-wood. They have to cover the line an touch the level ground all over the circumference. If not, bend again and again and again ... because the quality of the cooker depends on it very much.

Then joint the two parts of the plate-wood model to form a cross as shown on the next picture and place all rings on it so that the rings are laying on the model at the positions marked with the small black arrows.

 
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Remarks:

1. The little sun-like mark at the junktion of the two plate-wood pieces is the focal point of the parabola.
2. To make the parabolic cage stronger the largest ring is doubled on this picture, where the hinges of the pot-holder will be placed. This is not needed if the cage is completely welded and not only fixed with wire.

Finally place the connecting sheet-metal piece (Part L in the construction plans) on the top of the wood-model so that the hole in the sheet-metal is exactly on the cross-point of the two model parts (see next picture)

After placing all the rings on the wood model bend the connection bars as described in the construction plans.
Measure the circumference of the biggest ring, divide the length by 6 and mark the six positions of the connection bars on the largest circle. Carefully hold the connection bars close to the final position and check that they just touch all the rings and the sheet metal plate on the top without displacing the positions of the rings on the wood model. If the shape is not absolutely perfect correct the shape again, and again, and again ... the quality of the cooker is depending on the exact shape of the paraboloid!

The next picture shows how the result should look like:

 
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Also you can see on the picture that finally all connection points are bended together by iron-wire pieces like people do to make reinforcement cages for concrete works on construction sites. If you did a good job with it the cage can be lifted of the wood model without any deformations.

 
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But better weld some or all connections point-wise together before removing it from the wood model. But avoid welding clos to the wood!

 
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Weld the sheet metal on the top to one or two bars with a welding point and remove from the cage the wood model
immediately not to burn the wood.

Now the most dificult part is done! The utmost degree of accuracy should be used to make this part of the cooker as it is important for the cooker quality. If the rings have a slightly different diameter or are not placed perfectly in the right position the fixation on the aluminium plates becomes difficult but the shape of the cooker is still perfect as long as all rings are touching the woofmodel at all possible points. This is the big advantage of using the model. (So: Accuracy becomes less important. But for the sake of quality: don't tell that to the metal workers.)

Now the Stand for the cooker is produced in the back you can see the finished pot-holder and the cage:

 
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And here are all may studends of the last solar cooker workshop showing prowdly their diploma.

 
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CONGRATULATIONS!

Teaching Solar-Cooking

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Our Yellow Submarine with the satelite dish is soon well known in the surrounding of Arba Minch and people gather where ever we stop to demonstrate the simple miracle of concentrating sunlight and transfering it to heat.

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At different places the cooker was presented to make people curious to see how it works

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Ato Muise Gipo is demonstrating the use of the AMSI solar cooker and is teaching the principles and advantages of using a solar cooker in this extremely sunny region of the world.

Carrying Firewood

   
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In Ethiopia mainly women and children are spending much time carrying firewood over large distances.
Poor families may spend nearly their whole life with carrying heavy loads on their backs over several kilometer each day, to earn their living.

Firewood is taken from the hillsides of Arba Minch supporting the erosion of fertile soil or even from unique forest around the fourty springs in the protected area of the Nechisar National Park, destroying an other trasure of Ethiopia. When the trees are gone even small thorny bushes are taken as firewood. The fertile soil is drying out becomes unprotected and will be washed or blown away after some time.

The loads are often so heavy that a donkey on four legs would not make a single step with this load on the back. Woman are carrying such loads fixed with thin strings over the shoulders cutting into the flesh. After few years the spine gets deformed leading to back pain.

Due to the increasing demand of firewood more and more trees from the surrounding are ending up as firewood on the market places. This leads to a dramatically increase of deforestation and erosion. Destroying the basis of living for all following generations in this beautiful and extremely sunny region of the world.

Deforestation - Erosion

   

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Due to the increasing population of Arba Minch town the need of firewood becomes more pressing, the transport distances increase so that even small bushes are collected and burned. Firewood becomes more and more expensive. An AMSI solar cooker is about as expensive as the firewood it can save within one year.

 
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Where the forest has been destroyed heavy rain may wash the fertile soil away destroying the country and the living conditions forever.

Due to the increasing demand of firewood more and more trees from the surrounding are ending up as firewood on the market places. This leads to a dramatically increase of deforestation and erosion. Destroying the basis of living for all following generations in this beautiful and extremely sunny region of the world.