"Sun-Brella Greenhouse Effect Cooker": Working Solar Cooker for the Vulnerable, Refugees, Eco-Enthusiasts and Creative Cooks

Why?

From hardships to hobby, for all walks of life, this project provides an "open-source software" of cooking from "easily available materials" which works genuinely "with proof".

Introduction

I have a deep admiration for the do-it-yourself ethos. There's something genuinely inspiring about individuals who take ordinary materials and transform them into innovative gadgets, playful toys, or heartfelt gifts. The ability to tackle a problem with everyday items, powered by a blend of creativity and diligence, is truly commendable.

Driven by this same spirit, I embarked on a quest to create a device capable of preparing "warm food" efficiently, without relying on electricity—a perfect ally for keeping cozy, even in challenging circumstances. My exploration revealed that while some solar cookers available online fall short of reaching high temperatures, others are dauntingly complex to assemble perfectly, or require specialized components not easily replicated outside of a factory setting. This spurred me to delve into the realms of solar power, thermal radiation, greenhouse effects, and culinary arts.

The result is a solar cooker designed with scientific principles at its core. Utilizing an umbrella wrapped in aluminum foil, we concentrate solar energy, while a glass cover exploits the greenhouse effect to retain heat, doubling as an insulator. This method also allows for bottom-up heating, a technique more efficient than the conventional top-down approach used by most solar cookers. For those interested in the nitty-gritty, "Step 1-Theory" breaks down the scientific foundations of our cooker, complete with formulas.

Basic Components

An umbrella, foil, glass, and a black pot. It's essential to use all these components as skipping any might result in the cooker not working.

Who Can Use It

Anyone—regardless of age or gender can learn the knowledge for future use in emergencies. Also good for fun D.I.Y, kids garden cake party, also Survival situations.

My Test Environment Conditions

Ambient: temp 16C low-25C peak , Sunny Day, Humidity 50%, Barometer: 1017 mbar, Winter-spring, Feb-28,29 of 2024, 29 degree N latitude

Supplies

INGREDIENTS:

For Making a Hot Beverage:

Ingredients:

• Umbrella (standard rain umbrella)
• Aluminum foil (kitchen use)
• Charred aluminum soda can (see preparation steps below)
• Glass jar (larger than the soda can, ensuring the can doesn't touch the jar when suspended)
• Copper or iron wire (for creating a handle; avoid plastic or wool materials)
• Small metal rod (to suspend the pot inside the jar)
• Clean water
• Coffee or tea
• Sugar and milk (optional, to taste)

For Cooking Food (Bread, cake or Grilling):

Ingredients:

• Umbrella (standard rain umbrella)
• Aluminum foil (kitchen use)
• Grill plate (approximately 12"x10"x1", suitable for oven use)
• Black plate (for covering the food, such as a cake maker utensil cover)
• Glass box (to contain the plate and food)
• EPDM window sealer tape or high-temperature rubber (optional, for sealing the top)
• Duct tape (for sealing the edges)
• Small ceramic tiles or bricks (4 pieces, to insulate the hot grill from the glass bottom)

Step 1: Theory:

[ (Read only if you are interested to know the theory, skip if you like to jump to the making part! No need to know everything)

1. Sunlight's 1000 Watt per square meter power : This DIY project turns an umbrella into a solar cooker, leveraging the sun's peak energy output of 1000 watts per square meter, known as "Solar irradiance." Capturing an area of 1 square meter with the umbrella can yield a cooker with 700-1000 watts of power. The umbrella's curved shape concentrates the sunlight onto a pot, similar to how a magnifying glass focuses light. (Thanks for giving new reflector ideas in comments: Mylar emergency blanket for ease in folding: by stevedummit3, photographer's old silvered umbrella flash reflector by TwoWindsBear)
2. Black is necessary to absorb sunlight: because it absorbs light from all the colors, ensuring the food absorbs all the light, unlike reflective materials like plain steel or aluminium, which would reflect the heat away.
3. Glass is necessary to trap the heat by greenhouse effect: Glass allows light to penetrate while blocking mid-infrared thermal waves. When any object absorbs light, it also reflects thermal waves in Mid-infrared region. At 100 degree centigrade, the black body radiation wavelength is= b/T. b is Wien's displacement constant 2.897×10^(−3), and T is absolute temperature (373 k). This gives, wavelength= 7.8 nanometer. This is Mid- Infra Red frequency. Glass blocks these wavelengths, trapping thermal energy inside the jar and increasing its temperature. This is similar to the "greenhouse" effect. Without glass, the pot would lose most of this energy. IR Image courtesy: https://www.youtube.com/watch?v=Sth61H7FZSQ
4. If you leave any of these three, it might not work well!

]

Step 2: The Umbrella

Line the inside of the umbrella with aluminum foil, trimming and shaping the foil to fit the corners. Secure the foil to the umbrella's steel wires and edges with tape as demonstrated. This is the setup we have used in the experiment.

(Version2 update: You can also glue the foil to the umbrella using white glue. Shown in the last picture. It is not used in our experiment. Non-glued version was sufficient )

Step 3: Survival Cookpot (Option 1)

Remove the can's top and ensure there's no plastic inside. Create two holes near the top and attach a copper wire handle as shown in the accompanying picture. Ignite some wood and place the can above the fire, occasionally turning it. A bit of internal blackness is okay but clean off any remaining black powder and wipe the can's interior. Avoid touching its charred exterior. Alternatively, use black paint that can withstand 100°C and has a matte finish to prevent light reflection, though charring is preferred.

Step 4: Cover the Pot

Create a hanging pot with the following steps for efficient energy use:

1. Fill half of the aluminium pot with water.
2. Craft a small metal stick from a cloth hanger or similar material.
3. Create two loops from the wire handles of a can to attach to the stick.
4. Thread the loops through aluminum foil, then insert the stick through these loops.
5. Position the setup in a glass jar, ensuring the jar doesn't touch the can.
6. Cover the jar with another piece of aluminum foil as a lid, sealing it to prevent air flow.

Step 5: Hang the Pot

1. Position the umbrella so that its handle's shadow falls on the pot, indicating it is reflecting sunlight towards the pot.
2. In every hour, slide the pot so it is under the handle's shadow. Or adjust the umbrella. This "shadow method" is an approximation of focus point.
3. To confirm the right focus, check for a hotspot by feeling for warmth and looking for reflected light on the underside of your hand.
4. from 10 AM to 2 PM, the sun will move 360*4/24=60 degrees so you may need to adjust hourly. (Pointed by : Organikmechanic)
5. In my case, I adjusted one/two times so that there is heat beneath the pot because a wide portion felt warm enough.

Step 6: Wait We Shall, Wise One

• If you followed all steps, in 15 minutes or less you should see water evaporation on the walls of the jar.
• Keep the aluminium foil lid tight, Else the heat may go away by air convection. You can make an air proof lid also for better air trapping in the future.

Step 7: Check for Steam and Drink Your Coffee

• In 2-4 hours, You can get hot water by opening the lid.
• I waited for 4 hours till I opened as shown above.
• You can see the visible steam in the picture.
• Remember 100 degree centigrade water without any intervention is no joke. Many solar cookers fail to deliver their promise. But this one seemed to deliver.
• If you glue the aluminium foil to the umbrella then you will get better reflection and better results I think. Keep me posted if you make one.
• Make your coffee or tea.

Step 8: The Griller/baker (Option 2)

• If you want to go a step further, you can use a plate to grill.
• Boiling water has the fixed temperature of 100 degree centigrade. So it will not go above that till all water boils away.
• Theoretically higher temperature is possible but it will take exponentially longer time I think. Let me know what you think in comments.
• Use a black coloured steel plate for covering also. I had a rusty old one.I had to use aluminium foil below the plate to keep rust away from food.
• If you dont have any plates, use aluminium foil to cover completely but char them similarly like the can we used before.

Step 9: The Glass Box

To make the glass box you can go ask a glass-cutting shop. It is risky to cut glass by yourself. Make sure the box is 2" bigger than the plate sides. The box I used was 14"x 12" x3" for a 12" x10" x 1" grill plate.Or you can use a similar sized aquarium also I believe in emergencies. Glass box is preferred as it does not have a lot of gap from the plate. To make the box you will need:

1. Glass pieces (Cut accordingly)
2. Glass cutter
3. Plier
4. Glass Glue that can survive high temperatures (eg. Ultraviolet Glue).
5. UV light to solidify the glue in minutes.

• Then use duct tape to seal all the edges.
• Use a EPDM tape to seal the top. ( You may instead use flour dough to seal. Or just rest the glass cover on the top. It will still work. But will be much less efficient because hot air will vent away)

-Don't forget to put the ceramic tiles as shown before putting the grill plate. I just broke a small wall tile for bathrooms made from ceramic.You can use pieces of brick or concrete also. This will make sure the glass does not crack.

-If there are any queries fill free to ask in the comments.

Step 10: Bread Master Recipe

Let's simplify the process of making bread for emergency situations, stripping away all the complexity often suggested. Here's a straightforward approach:

First, you'll need flour - any kind works, but I personally used simple wheat flour.

For creating the necessary bubbles in the bread, you have two options:

• Combine something sweet like sugar or honey with "active dry yeast," then add warm water to produce CO2 in time.
• Or, mix an acidic food (like vinegar, lemon, yogurt, or egg) with baking soda to generate CO2. (Short time)

It's important to mix these agents into the flour at different stages to ensure the chemical reactions happen within the dough, not beforehand. Adding salt enhances the flavor. If you want to include herbs and seasonings, incorporate oil/butter into your dough to help carry these flavors, as water may not be as effective.

Here's my go-to, basic recipe:

• Start by mixing 2-3 cups of wheat flour with 2 teaspoons of baking soda. (Update: 2 tsp baking soda is too much, use 3/4 tsp instead)
• Gradually add water until you form a dough.
• Next, incorporate 2 teaspoons of vinegar, folding the dough several times to mix.
• Flatten the dough by hand as shown.
• To retain moisture and achieve a nice browning, lightly coat top and bottom surfaces with mustard or olive oil.
• Finally, cover the dough with aluminium foil and lid.

(If there are any good cook who can suggest better recipes of simple and delicious cake or bread in the comments that will be great. The cooking time is 4 hours under 100C temperature.)

Step 11: Place and Wait

1. Position the umbrella so that its handle's shadow falls on the plate, indicating it is reflecting sunlight towards the pot.
2. In every hour, slide the plate so it is under the handle's shadow. Or adjust the umbrella. This "shadow method" is an approximation of focus point.
3. To confirm the right focus, check for a hotspot by feeling for warmth and looking for reflected light on the underside of your hand.
4. from 10 AM to 2 PM, the sun will move 360*4/24=60 degrees so you may need to adjust hourly. (Pointed by : Organikmechanic)
5. In my case, I adjusted one/two times so that there is heat beneath the plate because a wide portion felt warm enough.

Step 12: Birds!

• Birds may make rounds after seeing the shiny reflection from the umbrella or food. That is why you should cover your food with the top plate not to tempt them.
• You can see the pigeons from a local pigeon owner making rounds above.
• I did not face any trouble since I covered the food after knowing this.
• An Eagle can see its tiny food from 2 miles away!

(Did you see the kite in the picture hovering just above me in the second picture? )

Step 13:

Inspect the bread between 2 to 4 hours. I waited 4 hours, but gluing aluminum foil to the umbrella for a more uniform reflective surface could shorten this time. I measured the bread's temperature with a high temperature food thermometer, which read 87°C, not 100°C. However, this likely indicates a calibration error, as it also read 87°C in boiling water, suggesting the bread's actual temperature was 100°C. Evidence of steam in the final image supports this conclusion.

Step 14: Final Product

Ready for you to eat, the final product is.

Njoy, you must!

Kindly do not forget to like if you find it useful as it will inspire your friend to keep inventing. Also I urge readers to try this at least once in free time. This was a surprising experiment for me at least.