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Umbrella solar cooker
A bit of Background
The use of a parabolic shape is not a new invention by any means. There has been use throughout history of focusing the sun’s rays for cooking purposes. Today, many are attracted to the idea of cooking with a renewable resource instead of using expensive and pollutant fuels. Furthermore, I am hopeful that with the use of parabolic solar cookers, third world countries can decrease mortality that is attributed to contaminated water. This is what I look foreword to as I begin my project building a solar cooker.
What an Opportunity!
I have the opportunity of working with Bart Orlando, who is known throughout Humboldt County and other sectors of the Engineering Community for his inventive ideas with solar and bicycle power. With his help I will be making a solar cooker for Engineering 305, Appropriate Technology. I chose this project, because I was very inspired by geographically appropriate places, being able to sanitize drinking water and cook food with a renewable resource. Furthermore, with simple skills of making a solar cooker, individuals would be empowered to improve their own lives.
It seems that it is difficult to get people to use solar cookers if they don't feel they have a need for it, or are unfamiliar with it. That is why I am interested in making an umbrella solar cooker, which presents the idea of a multi-use solar cooker. It seems that if someone had an umbrella that could be easily transformed into a solar cooker, that person would be more likely to convert it into a solar cooker, than buy a whole new apparatus. It is my hope that the idea of a solar cooking umbrella can help solar cooking technology become more adoptable. It could be known as the "Parasol" Para(bolic) Sol(ar cooker)
I will be able to gain hands on experience by making my own solar cooker, which I will construct here in Arcata, with materials that I hope to find locally. I am looking foreword to the development of this project, I hope you come back to visit this site to see my progress..
A look at the Literature
Brief History of the Parabolic Solar Cooker
Solar thermal technologies have been evolving for many centuries. The ancient Greeks, Romans, Aztecs and Chinese used parabolic shapes with reflective material as cookers . There has been documentation dating back to around 1650 where German Engineers harnessed the sun for energy . A Frenchman, Augustin Mouchot designed a portable solar cooker for the French troops in Northern Africa in 1877 . Using basic ideas of reflection, the sun’s energy can be concentrated onto a single spot. The parabolic shape enables the energy to reflect to one point. Getting large populations to adopt solar cookers hasn’t been that successful. In the 1950’s there was a lot of development, however it was an unsuccessful industry because there wasn’t a market for solar cookers . Mr Jerome Johnson is a lighting designer. He made and sold photography equipment. He designed a reflectal umbreall device to diffuse light. In the 1970s he moved towards energy conservation and turned the reflectal design into an umbrella food cooker. .
Basics of the Parabolic Solar Cooker
The sun beams down a huge amount of energy onto the earth every day, enough in just 40 minutes to replace fossil fuels burnt up in one year in the United States . The difficult task is to actually capture and use that energy. There are three different types of harnessing the sun’s thermal energy that i am most interested in; a parabolic trough, tracking mirror, and a parabolic dish. The parabolic dish, which is what I am focusing on, is very efficient if it remains directed at the sun, because the sun’s rays can focus at one point . The parabolic solar dish can be constructed out of a parabolic shape, which can be a recycled product like a satellite dish. You also need reflective material and a mounted rack at the focal point of the parabola with a dark pot to absorb the energy and cook food .
For additional information on parabolics, visit Bart Orlando's webpage at http://www.humboldt.edu/~ccat/solarcooking/parabolic/paraboliccookerwebsection-pg1.htm
There are many advantages to the parabolic solar cooker, like the ability to cook without fuel, eliminating smoke and pollutants while cooking. Furthermore the sun’s rays can be used anywhere where then sun is, even if there is a small amount of cloud cover. Also, the ambient temperature is not an issue, because it is possible to cook with the sun even if it is a cold day, just as long as it is sunny .
There are a few minor setbacks or concerns with the solar cooker; for example it is a slow way to cook; it is unfamiliar to many people, variability of sunshine, wind, and lack of durability depending on the structure .
Examples of Solar Cookers
There are multiple types of solar cookers. They all have the same goal of channeling solar energy, but they are a little bit different. Following are three possible designs.
- Solar Box
- The solar box is a solar cooker that utilizes the greenhouse effect to cook food. Inside the constructed solar box there are reflective materials to reflect the energy and also glass on the top of the box to trap the solar energy inside. This method works well in very sunny situations, and is safe because it is an enclosed instrument. A disadvantage is that it doesn't reflect to a point, like parabolic cookers .
- Solar Dish
- The solar dish is a parabolic shape that reflects the sun energy to a single point. This is advantageous because the structure of the parabola allows the sun to be very intense at one point. The bigger the structure is, the more sun energy it can absorb. Also, it is better if the parabola is deep to protect from the wind. Sometimes if the dish is really big, it can be difficult to transport.
- Solar Umbrella
- The solar umbrella is similar to the solar dish; however it tends to have a more conical shape. Therefore the sun energy focuses on a line, rather than a point. This is a disadvantage because the sun energy is more dispersed, unless one was cooking a long line of hotdogs. An advantage of the solar umbrella is its transportability.
My Personal Criteria
- Performance- The ability for the cooker to pasteurize 1 gallon of drinking water at 160 F degrees, to cook food, and ignite paper. 10
- Safety- The cooker should not blind or cause food sickness. 10
- Cost- Monetary spending. 5
- Durability- The length of time or elements it can withstand. 4
- Transportability- The ability to bring the cooker to places by one person with little packaging. 7.5
- Location- Where the materials are found and where structure is built. 7
- Versatile- The other ways this cooker could be useful (shelter, umbrella). 7
- Ease of Operation- The ease at which this cooker can be used. 8
each criteria is weighted on a scale of 1- 10
for a parabolic solar dish or umbrella
When constructing a parabolic solar cooker, you can be very creative with the materials. In regards to reducing the materials embedded energy, it’s great to find local and recycled products to construct this. There are some very essential items that will make your cooker work well. It is important to have durable reflective material and a pot in the middle that is black to absorb the reflected energy. However you go about it, the dish needs to have a parabolic shape. And most importantly, sunglasses need to always be worn to protect the eyes from getting burnt.
Umbrella Materials and Budget
|1||Cloth for Umbrella||Donated||$0|
|4 ft x 23 ft||Roll of Mylar||Donated||$0|
|3(10ft) 3(8ft)||Bamboo Poles||Mad River Nursery||$10|
|4 Tires||Scrap Tire||Adventures Edge (donated)||$0|
|80 ft||Twine||Recycling Center (donated)||$0|
|1 (10ft) 2 attachments||PVC Pipe and Screw Attachments||Ace Hardware||$15|
|34" x 42" (x8)||Cardboard||Adventures Edge (donated)||$0|
|1 roll||Double Sided Tape||Hardware Store (donated)||$0|
|Too many to count||Staples||Found||Free|
|6 ft||Chain||Scrap Salvage Yard||$1.00|
|1||Large Can||The "J"||$0|
|1||Quart Mason Jar||Donated||$0|
|1||Plastic Sleeping Bag Case||Found||Free|
- Why use Bamboo?
Bamboo is a great resource for engineering. It grows very fast, is light weight, and can grow on marginal land. Bamboo is found all over the earth, especially in Africa, Asia, and Latin America. It is easy to work with and can be split with minimal force, which was great for me and my project. This hearty resource has been traditionally used, therefore the growing opportunity for modern bamboo engineering can allow for younger generations to continue on bamboo harvesting.
Proposed time line
|Collect All Materials||Week 9|
|Finish Construction/ and Paper||Week 10-11|
Design and Construction
I was fortunate to have acquired a patio umbrella canvas from Bart to start off my project. We discussed using bike flag poles or fiber glass rods for the umbrella frame, but were unable to find those materials. Bamboo was a very exciting option for the frame. We split the bamboo with a camping knife and a hammer. It split very easily! However, it was difficult to keep the split straight, so we had to whittle down the rest of the piece of bamboo to get it even. After the bamboo was split, we decided to soak it in water to help increase the flexibility. It didn't seem to be a necessary step in the process, because it was flexible enough before the water bath. Once the bamboo was ready, we trimmed them to the correct lengths to fit tightly in the umbrella canvas. Bike tire tubes were used to lash the frame together at the center of the umbrella.
The next task was to figure out what to mount the Mylar onto, to give it more stability. We though about using old linoleum, however, we realized that this didn't fit appropriately into my criteria, because linoleum isn't a local product here. Cardboard ended up being the best bet, because it is a used product that can be found in abundance in most towns. We used bike boxes and a water heater box. The size was measured longer than necessary, in order to allow for the cardboard to overlap. The cardboard was pre-bent, to mimic the shape of the parabola. The Mylar was cut using the same measurements. Double stick tape was used to adhere the Mylar to the cardboard, with staples around the edge for reinforcement.
We had to figure out a way to control the shape of the parabolic curve. With the stiff cardboard in the structure, the umbrella seemed to flatten out. In order to solve this problem, we decided to use draw strings around the umbrella to provide adjustability to the umbrella. Belt loops were made out of old jeans and sewn on with a needle and thread. I highly recommend a thimble when sewing tough materials, ouch! Twine found from the recycling center was used as the draw string, with slipknots to adjust the length. With other types of parabolic cooking, precise measurements are needed, however, with the adjustable twine, it wasn't necessary to calculate the measurements, all we had to do was make the corrections while we were focusing the cooker at the sun.
Finally the umbrella was completed! The next part we needed to figure out was how to mount or hang the cooking container. To continue with the utilization of bamboo, we decided to make a tri-pod out of 8 foot bamboo poles. We used bike tire tubes to tie them together. Chain found from the scrap yard was used to hang the down from the center, with a clothes hanger to hook the tin can to the structure. The large can is used as a water bath/ double boiler, where a mason jar can be put in it to cook. This prevents any plastic or harmful chemicals from the tin can to touch the food. Two holes were hammered into the top sides of the tin can for the clothes hanger to go through. The tin can was painted black to absorb heat, and foil was used to close off the top to prevent heat from escaping.
We realized that the can was exposed to too much wind with the structure we had created. Therefore we needed to construct a dead air space, which is a space of still air that prevents wind from cooling the cooking container. Luckily i had the perfect thing on my porch, a clear plastic sleeping bag case. We lined it with clothes hangers that we bent into circles and taped to the inside. This worked great!
Once the entire piece was put together the last thing we had to do was stabilize it. We used twine and bamboo to steak down the umbrella to prevent it from blowing away in the wind. Yarn was used to tie the chain to each of the bamboo poles of the tripod to prevent the pot from swaying around. One piece of yarn was taped to the plastic dead air container and secured to the middle of the umbrella for stability as well.
After a few cloudy days, the sun finally came out and we were able to test the Para(bolic) Sol(ar cooker). We put a quart of water inside the tin can and a quart of water inside the mason jar. After an hour of direct sun we took the temperature of the water inside both the tin can and the mason jar and we were pleased to see the thermometer reach 160 oF degrees. This means that we were able to pasteurize water!!!
The next time that we tested the Par(abolic) Sol(ar cooker) we were able to cook oatmeal, which was done at 3:00pm, this means we can cook even more kinds of food earlier in the day!
Discussion and Reflection
I thoroughly enjoyed working on this project, and having it be a success was additional excitement! What i really love about this product is that it has multiple uses. What attracted me to working on an umbrella solar cooker was its versatility of function in hopes that it would increase it's societal adoptability. This structure that we created works...
as a solar cooker.
as an umbrella
and as a shelter
The Mylar lining the shelter also works to radiate heat back to the person in the shelter
Bamboo was a very liberating resource to use. Being small and strong myself, I felt empowered to work with such a light and strong material. This resource is found all over the globe, and would provide useful for many different projects. This was the first time Bart had worked with bamboo for a solar cooker, and has been very excited with the progress. We even discovered that we were able to bend bamboo by heating it within other solar cookers. Bart had worked on one other umbrella solar cooker in the past, and noted that this one had made vast improvements from the last. The main distinction is that this Para(bolic) Sol(ar cooker) is able to focus light to a spot, where the last could only focus light to a line. This is because we used bamboo and cardboard, which were materials that could be bent. It should also be noted that since we were able to be successful in the foggy climate of Arcata, it is highly possible to successfully solar cook nearly anywhere else!
I was able to meet many of the initial criteria that I had created before this project.
- Ease of Operation
First of all it was able to pasteurize water, which is the most important of the criteria. This solar cooker has proven to be safe the times that we have tested it. There is always a risk for over heating and fire, however by flipping the structure over to a shelter, that risk is eliminated. The cost of this umbrella cooker was very little at $27.50. It doesn't seem to be very durable, which time has yet to really prove; however that wasn't a very important criteria. We felt it was most important to explore this opportunity and design more than worrying about durability. The transportability ended up being much harder than we had hoped for, with all the supplies that have to be used for it, however I can see the idea of an umbrella cooker being mass produced in the future as something that has little packaging and materials. We were able to use products that weren't necessarily local, but had little embedded energy, like used and recycled materials. We also found that it was very versatile, being able to be a cooker, an umbrella, and a shelter. The set up is a little complex, which decreases the ease of operation. All in all I am very pleased with how well most of the criteria was met.
- Things to do differently
If I were to redo this project, there are a few things that I would do differently or improve on. First of all I wouldn't have used the water bath to soak the bamboo, this wasn't necessary for the bend ability of the bamboo, and also was too expensive and unnecessary at $15. I would also explore using another material than cardboard; however cardboard was the most practical at this time. In the final design, I could tell that the Mylar seemed to wrinkle a bit, if I were to do the project again I would explore more deeply on how to fix this. I would also try to construct more pockets and bamboo rods to fit into the umbrella canvas to increase the amount of facets on the umbrella. By doing this I would be able to tighten the focal point and cook at a higher temperature.
Since this is only the second time that Bart has mentored a student working on the umbrella style solar cooker, it is important to realize the immense opportunity for improvements there are. Even the amount of improvement from the last umbrella to this one is huge! The main difference is the ability to have been able to create a parabola, where the last one was not a parabola. I have even been able to make vast improvements on my own umbrella solar cooker in the last few days. We were able to find some really important parts to create a much sturdier stricter to hang and cook food and water in. We came across a really strong metal rack from the scrap yard, which we used to hang with chain and S hooks. Then we found a large pickle jar that we could put a smaller mason jar, painted with black paint inside. This created a more efficient dead air space than the last we had constructed. Furthermore it is more durable of a cooking container.
|1||Metal Rack||Arcata Scrap and Salvage||$0.50|
|6 ft||Chain||Hensels Ace Hardware||$5.00|
|3||S hooks||Hensels Ace Hardware||$1.50|
- Johansson T B. H Kelly, A Reddy, R Williams. L Burnham Ed. 1993. Renewable Energy: Sources for Fuels and Electricity. Covelo CA: Island Press.
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- Halacy, Beth and Dan. 1992. Cooking with the Sun. Lafayette CA: Morning Sun Press.
- Butti, Ken, and John Perlin. 1980. A Golden Thread: 2500 Years of Solar Architecture and Technology. New York: Van Nostrand Reinhold Company.