DIY Solar Oven

SOLAR COOKING

While waiting for the seeds to sprout, I thought we should discuss another problem...cooking with fossil fuels...

I would definitely like to use the sun to cook...its free...its clean etc etc blah blah blah

I do not know of anyone around me that uses a solar oven, even though Greece has an abundance of sun...we get hot water from the sun for at least 10 months a year...yet no solar cooking.

The attempts I have made so far have not resulted in an acceptable solution.

To buy a new one for 300 to 600 Euros is unacceptable.

Recently, I approached the issue from another angle, which may (or may not) lead to a solution...

What if a solar oven can be assembled from local, easily accessible store bought materials, and put together, without requiring any trade skills...for relatively low cost…and easy to use !!!

These are the parameters…the solution we come up with, if it is to have a chance of being adopted widely, must come close to meeting these requirements!!!

A parabolic satellite dish, covered with sun film (mirror) used in car windows, is a good sun collector/concentrator... is not very expensive (this is relative, I understand this)...the sun film is a peel and stick project...a dish about 1 meter in diameter seems to work...it's a starting point. It's very powerful and impressive...put a piece of wood at its focal point, and it starts smoking in seconds...I am impressed by its demonstration of the power of the sun.

There are other ways to concentrate the sun and we should try them..maybe they will work out better...a parabolic dish may not be for everyone...cardboard reflectors, or similar methods may work out better...we shall try them.

The oven itself, instead of using a metal box, insulation etc, which requires carpentry skills, insulating materials, black paints, silicone, etc...what if we used a Pyrex glass container, such as the glass part of a halogen oven (https://en.wikipedia.org/wiki/Halogen_oven), or large 8 liter Simax or Pyrex containers (glass chicken roasters or similar)..these need to be covered to keep the heat in.

In order for this to work, the food needs to be placed inside a sealed black pot or container, to prevent heat loss, and to collect the sun...a black metal surfaces is essential to absorb the sun. The air in the glass container will be the insulator, instead of insulating materials.

The parabolic dish does not have to be aimed at the sun high up...it can sit up straight, or leaning a bit forward...this allows the sun to bounce of the dish and land on the ground where the cooking apparatus is...this allows the cooking to be done right on the ground, and avoids splattering etc on the dish...I think you loose some of the intensity of the sun, but gain in the ease of use, and eliminate the cost of the apparatus to raise the cooking vessel to the focus point of the dish.

So there are 3 elements...the sun collector....the outer glass container, and the inner cooking vessel...that's it.

I am at the early stages of this journey...but it looks promising...the intention is to come up with a solution, that is simple, to buy/put together, and use, so we all can do a large portion of our cooking using the sun, instead of fossil fuels...

If we can just bake bread, that would make it worthwhile…a major cost of bread making is the energy needed.

This forum has been a great place to exchange ideas...I am sure that "soon" we will have many workable designs, that are easy to use, easy to assemble, and economical.

Here is a photo of the 1st attempt...I cooked mung beans yesterday.

Looking forward to your suggestions.

CAUTION: wear good eye protection when dealing with concentrators...I hear you can go blind...Also we are dealing with heat and glasses...they may shutter at any time, and the heat from the concentrator is !!!

Thank You

Kostas

SOLAR COOKING - 2

Trying to verify the concept of using Pyrex or similar products, for an outer shell of the solar oven.  

Cooking chicken with large potatoes is a good test (hopefully). I set up 3 different arrangements. Two of the 3 worked well…the 3rd, did not cook the chicken enough…not sure why.

Photos tell the story well.

First Arrangement - photos a11 to a14…the satellite dish is around 75 cm …cooking time was 2.5 hours…the outer glass was 8 liter by Simax, and the bread cooking pans are shown in the photos..the food tasted great and was cooked well…it separated easily from the bones.

There is a concern, that it seemed the heat from the reflector, caused some of the paint on the pans to smoke a bit…that may have been from being used the 1st time?  need to keep an eye on that.

Kostas

Photos

1 more photo

Second Arrangement - photos a21 to a24… the satellite dish is around 75 cm …cooking time was 2.5 hours…the outer glass was a glass cake holder (flat bottom)…the round pans were placed one on top of the other as shown. The food was not cooked well and did not reach a temperature of 70 Celsius…the meat did not easily separate from the bones.

I do not know what caused this…it need to be further investigated…This assembly was p[laced for an extra hour in front of the large 1 meter dish…even though the glass is not tempered (at least I think its not), it did not crack under the intense heat, and the food was cooked.

Kostas

2 more Photos

Third Arrangement - photos a31 to a35…the satellite dish is around 100 cm (larger dish)…cooking time was 2.5 hours…the outer glass the glass bowl from a halogen oven, and the round pans were placed one on top of the other as shown..the glass on top of the glass bowl was tempered glass…the food tasted great and was cooked well…it separated easily from the bones.

The 1 meter dish is much more powerful than the 75 cm dish, but more difficult to handle.

It was a good day… the system needs more testing and improvements, but it looks promising. Others need to try it and make suggestions for improvements!!!

Kostas

Again, CAUTION: wear good eye protection when dealing with concentrators...I hear you can go blind...Also we are dealing with heat and glasses...they may shutter at any time, and the heat from the concentrator is !!!

2 more photos

Hello Chris,

Sorry it took so long to get back to you…thanks for the info on the almonds and olive trees...growing olives is not easy, maybe it has to do with the weak trees we plant.

Is anyone in your area reproducing olive or carob trees from seed?

Soon I will have an update on this year's seeding project.

I been a bit preoccupied with the solar oven project, but this is coming to a conclusion..sort of.

Kostas

Solar Oven Update…

As we have discussed, trying to grow trees in arid zones, is challenging…the other side of the coin is that we have plenty of sun…6 months of the year, scorching sun…solar cooking should be easy and should be inexpensive (but almost no one is cooking with the sun around us, including my own family.

Here is an update… what I have learned.

The solar dish should be in the 95 cm to 105 cm range (lets say 100cm) …the 75 cm diameter dish is weak, and the 115 and above is to strong.

All glass used to close the pots and pans, and exposed to the sun from the solar dish, should be tempered, or resistant to high temperatures (ceramic glass)…I broke enough of the them…the cake holder is not tempered, and should not be used…the large dish (115cm) will crack even the tempered glass, even the bowl from the halogen oven !!!

Instead of using the halogen oven bowl, or the Pyrex glass containers, I tried enamel pots, which are less expensive and readily available…they worked just as well as the Pyrex glass containers…see the pictures below.

The 1st picture, shows the enamel pots, and the glass lids, which were cut just to fit over the pots…there should be a thin cardboard separating the two pots, to prevent heat loss, and the outside pot should be on a piece of wood (not a cold surface).

The 2nd photo shows this oven in front of the dish…the glasses should be tempered or ceramic glass (which is expensive), otherwise it will break.

This arrangement works, and reaches temperatures of 150 C fairly quickly, and a meal is cooked within an hour to 2 hours.

The cost for this, is approximately 70 Euros, when the materials are bought of the shelve…which I still consider expensive, but this assembly has its advantages over the glass bowls.

I have not tried baking bread yet.

Kostas

Last Solar Oven Design…Less than 10 Euros…

This design is best described by pictures.


Kostas

The last few pictures...

Some notes !!!

***The idea is to construct a super insulated cover for the cooking pot…similar to a wonderbag or a haybox…if this is achieved, it makes cooking with the sun easy.

***Instead of straw, old cloths cut in strips can probably be used…will they provide good insulation ?

***Instead of a T shirt, an old dress or similar can be used, or something like a wonderbag can be constructed to fit around the pot and be easily closed…a belt instead of rope can be used to tighten the bag.

***It’s a good idea to have a piece of wood under the oven, so it can be moved easily.

***We should not over tighten the rope…it may impact insulation

***Insert small strips of clothing if there are gaps at the mouth of the pot near the glass…glass should close easily, and not have any gaps in its contact with the enamel. Glass does not need to be tempered…at least so far they have not cracked…

***The solar reflector used is from a roll of roofing sun reflector material…it just sits vertically behind the oven assembly, and does not need to be moved much. It can be of any reflective material.

I cooked a good meal of potatoes and pork…in 2 hours the temperature was 130 degrees Celsius…in 3 hours the meal was thoroughly cooked, but I kept it under the sun for 4 hours (10 to 2).

Need to try other meals, and especially bread.

This is an inexpensive design, and it appears that it works.

We will be trying it, and posting results, and I hope others try it and make suggestions/share results.

Solar cooking is !!!

Kostas

UPDATE ON SEEDING PROJECTS
Some important lessons learned (or re learned this Year)

***Seeds should be placed in the ground in October or November…the weather is unpredictable, and seeds placed in the ground in early January this year, did not germinate…not enough cold and wet days.

***Small clay cubes (3 cm or less) did not sprout at all…they survived the rainstorms intact, but the seeds inside them failed to sprout. Rains followed by warm weather or wind dried the clay cubes…5 or 6 cm (2 to 2.5 inch) is more appropriate… we had success with this sizes before on a small scale…we will make more of them this year, and see how they do. When plums or other seeds in the ground germinate, and next to them the same seeds in clay, do not, there is something wrong with the recipe for the clay cubes, that needs correcting.

*** There is nothing that can be done about the ever changing weather…it’s the end of April, and the high winds and lack of rain have dried out the soil, consequently trees that sprouted this year, are showing signs of stress already…if May comes and goes with little or no rain, we can expect most of these young trees to perish…we need to accept this fact of life and keep trying again and again until the desired forests/food forests are established…PERSISTENCE is the key word, and optimism that it will get done.

***The carob seeds that were fed to a goat, sprouted…some of them !!! we fed a friends goat with carobs…she digested most of them, but we collected about 10, that were soft and doubled in size…they buried in the ground, and they all sprouted…this is a start, on the road to using this magnificent trees for reforestation purposes.

***The wild olives we collected, were placed in the ground late…so they did not germinate…will try again this year, and hopefully we will have good results…I collected about a kilo of them, so I will also be putting them in clay cubes.

***The are four pieces of land near Thessaloniki and two pieces of land 1/2 hour South of Thessaloniki, that I decided to concentrate to reforest. A piece of land in Crete that a friend owns will also be seeded.  Here is a brief update/description on each. I have not visited the seeding area, around Sparta, so I cannot provide updates.

Crete: We seeded in mid January, about 1000 to 1500 square meter parcel of land…the land has already olive trees, spaced far apart, but the owner is excited about creating a food forest. It was a mistake to place seeds in the ground that late, we will revisit the area in October or November this Year and try again…Crete is much more difficult than Thessaloniki

Thessaloniki:
Some general comments…there are wild pigs in the area, and some stray dogs…they are digging up the soil and causing some damage..It's important to note that we do not have a problem here with the "pest" digging up and eating the almond seeds like we have in the Petra seeding areas (1/2 hour South of Thessaloniki). The wild rabbits in the area, in the past have been eating the young trees, but it appears the trees re grow and survive the rabbits.

EK-1  Approximately 250 square meters…the soil appears to be rich, and all round there are pine trees, so the land is protected somewhat from the scorching sun. Last year we had placed around 10 almonds seeds here, and they sprouted. This year, we seeded 500 almonds, 300 apricots, 500 plums, 100 crataegus 125 apples, and "some" wild pears…will provide a video of the area soon…there are signs of distress on the young trees due to the lack of rain.

EK-2 Approximately 2000 square meters…the soil appears to be rich..the area was burned about 20 years ago. The new trees are growing fast, some almonds have reached 15 to 20 cm height…some are showing signs of stress due the rain situation. This is the 1st time we seed in this area…it looks like an ideal place for a food forest…I hope we succeed. This year, we seeded 500 almonds, 700 apricots, 500 plums, 400 crataegus 250 apples, and "some" wild pears.

TR-1 Approximately 1500 square meters…the land is partially covered by pines (about 60%), and has steep south facing slope…the land has a thin layer of rich soil, and it appears the subsoil is clay. We have placed seeds in the ground in the last 2 - 3 years, and many trees have survived and are growing. This year, we seeded 1000 almonds, ? apricots, 250 plums, 400 crataegus 250 apples, and "some" wild pears. It will be interesting to see how these trees will do next to the pine trees…this may guide us towards reforesting pine forests that get damaged by insect infestation or are burned.

MK-1 Approximately 5,000 to 6,000 square meters…this is a good size piece of land, with decent soil, and south facing slope, the top is partially covered by pine trees. Most of the area was burned 20 years ago. We placed some seeds in the ground in the last 3 years, so we have some trees growing…now we will try to place many more, so we will develop a dense forest. This year, we seeded 1000 almonds, 1000 apricots, 1500 plums, 750 crataegus 500 apples, and "some" wild pears.

We also have 2 areas, that we concentrate on, in the Petra area (about 1/2 hour south of Thessaloniki)…will provide info on this soon.

Kostas

If you haven't seen builditsolar.com, there are a lot of DIY solar and energy saving ideas and builds including some solar cooking concepts.