Solar cooking has been a field of great interest to our sponsor, Earth Trek Gear, for the past 10 years. Solar cooking’s practicality arises from being one of the most environmentally friendly methods of cooking, which translates into a sustainable option for food preparation where traditional methods are inconvenient. In addition, solar cooking can be a great science experiment for children, reinforcing topics such as thermodynamics and environmentalism.
Earth Trek Gear is a wholesaler of hiking and camping equipment. One of their top selling products has been the solar oven. However, they have received complaints that the oven does not cook food hot enough; thus, they have opted for a redesign. Team Solar Chef engineered a new solar oven for Earth Trek Gear, one which outperforms the old model while remaining inexpensive to produce.
Earth Trek Gear’s previous design allowed for fast, inexpensive manufacturing. The oven was made of foam sandwiched between thin layers of foil, a material similar to windshield sun reflectors. Manufacturing was simple: a template was placed on a section of this material, and the shape was cut out. Both the materials and labor were inexpensive, leading to an affordable final product. The other major benefit of this design was its portability–being lightweight and compact is important in hiking, and reduces shipping costs.
However, the oven had difficulties reaching proper cooking temperatures consistently. Its crinkled surface caused much of the sunlight to simply miss the pot of food. This flaw is dangerous, due to the risk of food borne illnesses from the consumption of certain uncooked foods. Its other major setback was its lack of structural integrity. Cooking in the wind was a near impossibility, as the panels would constantly bend, deflecting even more light from the food.
A redesign became necessary–one that matched the existing benefits while rectifying the problems of the old cooker.
To classify the redesign as successful, four major requirements have to be met.
The oven must consistently heat food to temperatures of 74ᵒC or greater. Poultry, which sets the bar for cooking times and temperatures, must reach an internal temperature of 74ᵒC for at least three minutes to ensure it is fully cooked and safe to consume.
The oven must be lightweight and collapsible. This allows it to continue to be a backpacking accessory, and also adds convenience for home storage. Shipping costs are also greatly reduced.
The Sun Chef consists of a single plastic sheet covered in reflective vinyl, with petal shapes cut into the plastic. These petals are bent upwards into a parabolic shape–interlocking tabs cut from the plastic are used to hold the petals in place. The oven’s focal point is near its base, allowing the pot to rest directly on the oven while cooking.
Single Sheet: The parabolic shape of the oven is formed from a single sheet by interlocking the separate petals with tabs (detailed below). The single sheet design minimizes the materials used when compared to a multi-component assembly. Also, this allows for a fast manufacturing process, as well as easy consumer assembly.
Tabs: The tabs utilize the stiffness of the plastic by interlocking in the unfolding direction. Essentially, the harder the petals try to unfold, the more secure the connections become. Tabs were the best solution to holding the oven in its shape, as opposed to something like velcro, because they are cut right from the plastic, eliminating the time and cost induced by having separate components.
Focal Point: The parabolic shape of the oven outperforms the panel geometry of the previous model, due to the increased amount of light focused onto the food. The focal point is near the base of the oven so the container of food can rest directly on it while cooking. This eliminates the need for a pot stand, which reduces the price of the oven.
Plastic: The structural material chosen for the oven, impact-resistant polystyrene, has the perfect compromise between flexibility and rigidity. It is tough enough to withstand “the elements”, its stiffness forms a nice curve, and it is flexible enough to fold nearly in half. On top of these features, it is lightweight, increasing the oven’s portability.
Vinyl: The reflective vinyl is the best choice for both the manufacturing and performance of the oven. It is easily applied with a squeegee, and can be applied even faster with an application roller. Its smooth finish eliminates the problem caused by the surface crinkles in the previous model.
To test the effectiveness of the oven, water was heated in the cooker, and the changes in temperature were recorded. Water was chosen because both it and its properties are readily available. As a standard amount, 1.5 L (about 6 cups) of water was used to simulate the types of food that would be cooked–namely, soups and stews. Tests were conducted outdoors in a variety of weather conditions. A thermocouple was used to measure the temperature of the water, and LabView was used to record this temperature every 30 seconds. The temperature versus time results are shown below, on the left.
After the oven’s ability to heat water was verified, an actual cooking test was performed on a hot dog. The thermocouple was put in the center of the hot dog to be sure it was thoroughly cooked. Its temperature versus time results are also shown below, on the right.
A wide variety of solar ovens exists on the market, and there are many sets of instructions to build one from house hold materials. With so many competitors, it is hard to tell which oven is a good deal. The chart below compares a selection of ovens representative of the market on a “bang for your buck” basis: the average temperature at which each oven operates versus its individual price.
Per-Unit Cost Analysis
Each feature of the oven was designed with cost-effectiveness in mind. The table below lists the costs of the individual components of each oven based on the bulk-purchasing prices.
MEET THE TEAM
Meet The Team (Left to Right)
Nick Keglovits is a senior in Mechanical Engineering at the University of Nevada, Reno and is expecting to graduate in May 2013. His expertise in drafting and web design has greatly influenced the direction of the team when designing and marketing the product.
David Winkler is a senior at the University of Nevada, Reno majoring in Mechanical Engineering. He is expecting to graduate in May 2013. His vast experience in drafting, design and manufacturing were invaluable in creating this product.
Chris Duarte has provided the team’s leadership and organization. He is a senior in Mechanical Engineering at the University of Nevada, Reno and is expecting to graduate in December 2013. His experience in manufacturing and retail have provided leadership and insight in the team’s product development and marketing.
Torry Brashear is a senior in Mechanical Engineering at the University of Nevada, Reno and is expecting to graduate in May 2013. He was responsible for much of the research and development of the product and his experience with LabVIEW and MatLab have proven invaluable to the team.