Solar Oven with Heat Storage

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Food is one of the basic needs for human beings. In this modern society, food cooking is carried out using electric power or natural gas. However, rural communities without access to electric power or natural gas in some developing countries are still using traditional way to prepare foods, namely firewood. While the world is struggling with global climate change, climbing cost and shrinking energy supplies, use of firewood could exacerbate global climate change due to deforestation. Hence, alternative energy sources are in dire need and solar energy is considered as one of the most promising sources of energy in food cooking applications. Solar cookers convert solar energy into heat to cook food. It is considered as one of the cleanest modes of cooking because solar energy is a renewable source which is available in abundant and free. However, solar cookers depend on solar radiation to cook food when the sun is available. This limits the use of solar cookers to only the day time. To improve this, some researchers have incorporated phase change material (PCM) in the solar cookers. Again, the PCM temperature is somewhat low (usually below 120 °C) for an effective and efficient cooking application especially when come to baking or frying that needs temperature more than 200 °C.

Therefore, a small scale double-reflector concentrating solar system with PCM heat storage in temperature range 230 – 260 °C is developed and analyzed for cooking application. Many solar heat collection systems are based on transportation of heat from the focal point to the storage by a circulating heat transfer fluid (air/water/oil/molten salt). With a double-reflector arrangement, the storage is heated directly, and no heat transport fluid is needed which on the other hand can be translated into a more simple and low construction cost system. NaNO3-KNO3 binary mixture is selected as the latent heat storage medium because the melting temperature is in a suitable range, widely available in the market and cheap in cost. The main advantage of having PCM heat storage in this system compared to the conventional solar cookers is that cooking can be carried out in the night time or when necessary. In addition, temperature range of the PCM heat storage (> 200 °C) is in suitable range for an effective and efficient cooking application especially for frying or baking purpose.

Cooking tests have been carried out using a thermally charged (? 260 °C) cylindrical heat storage unit with about 8 kg of NaNO3-KNO3 medium. Both the diameter and height were 20 cm. Fins were used to increase the heat transfer rate for thermal charging and discharging processes. The results showed that the thermally charged heat storage can raise at least 6 L of water from room temperature to 100 °C within 2.5 hours. In addition, cooking of eggs and pan cake on a flat pan has been performed with satisfactory results.

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  • ABOUT THE ENTRANT

  • Name:
    Chee Woh Foong
  • Type of entry:
    team
    Team members:
    Ole Jørgen Nydal
    Jørgen Løvseth
  • Profession:
    Student
  • Number of times previously entering contest:
    never
  • Chee Woh's hobbies and activities:
    swimming, reading, skiing
  • Software used for this entry:
    COMSOL Multiphysics
  • Patent status:
    none