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What is ISEC?
The insulated solar electric cooker (ISEC) utilizes solar energy to provide heat to a cooking pot. This eliminates the need for the combustion of coal or natural gas, thus reducing the carbon emissions released into the atmosphere.
Currently, the prototype allows the user to place a pot within a casing which contains Erythritol. Erythritol is a phase-change material (PCM) that is used to store the thermal energy collected by the solar panels so that cooking can be performed at night as well. This material melts at 118 degrees Celsius, allowing for latent thermal energy to be stored. Unfortunately, however, erythritol degrades over a matter of only a couple months, rendering it incapable of storing sufficient energy.
Our goal is to research different methods of flow to prevent the degradation from occurring as well as looking into new PCMs for which we may substitute erythritol.
ISEC Design
A schematic of the ISEC prototype showing a cooking pot inside of a nest and Erythritol in between. The cook pot has a heating element connected to a 100 Watt solar panel, which transfers DC current to the element and is heating the pot as well as the phase change material.
Image: PCM heating-cooling cycle [9]
What makes a good PCM?
High heat of fusion [4]: Materials with a high heat of fusion will absorb energy without undergoing a large temperature change. PCM materials phase change between solid and liquid to absorb energy. [5]
High thermal conductivity [4]: Materials with a high thermal conductivity are easily penetrated by heat, which creates an even melt front and small temperature gradient. If a material has low thermal conductivity, this can be corrected using fins which have a large surface area and high conductivity. [5]
High Specific Heat & Density [4]: The amount of heat stored by a PCM is directly proportional to its density and specific heat. [6]
q = V ρ cp dt
q = sensible heat stored in the material (J, Btu)
V = volume of substance (m3, ft3)
ρ = density of substance (kg/m3, lb/ft3)
cp = specific heat of substance (J/kgoC, Btu/lboF)
dt = temperature change (oC, oF)
Durability (Long Lifespan) [4]: Some PCM materials, like hydrated salts, can become unstable over repeated use cycles [5]. For a solar cooking application this is undesirable because we want to maximize the number of possible use cycles.
Background
Common sources of fuel for cooking are coal, biofuels, and natural gas; however, both of these sources contribute to household air pollution. According to the World Health Organization, over "3 billion people" use cooking sources that contribute to household air pollution, resulting in "3.8 million" deaths [7]. It also contributes to diseases such as "pneumonia,...stroke, ischaemic heart disease, COPD, and lung cancer[7]."
To help contribute to the inclusion of renewable resources, we will provide solutions to improve the state of renewable fuel resources. Insulated solar electric cooking demonstrates one possible solution to these nonrenewable cooking sources, but as it is now, the technology cannot be mass produced due to the erythritol degradation. This will produce both electronic waste and metal debris, damaging the environment. Halting degradation prevents more waste from being produced.
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