Useful Websites

Hello!

Here are some useful websites Jia Yun found them.
http://solarcooking.wikia.com/wiki/Introduction_to_solar_cooking
http://www.solarcooking.org/
http://www.cookwiththesun.com/

For integrated solar cooking:
http://www.integratedsolarcooking.com/
Integrated solar cooking should be worth mentioning in our presentation since I don’t think there will be much space left in our poster to add this. If not Jess can do a brief summary and add this in too. thanks!! Brief background below:

Integrated solar cooking can be used to reduce usage of natural fuels. Integrated solar cooking taps on solar energy when it is available, and also allows usage of wood, charcoal etc when solar energy is unavailable.

When solar energy is available, integrated solar cooker uses the same principles as normal solar cookers. However, the additional features of this solar cooker enhances its feasibility to be used in places w/o cooking gas. When solar energy is unavailable, a ’six-brick Rocket stove’ is used. Wood is used as a fuel for heating, and the advantage of this ’six-brick Rocket stove’ is that it is relatively clean and highly efficent. A hay basket that comes together with this solar cooker allows food to be kept warm for longer periods of time, which might speed up solar cooking and reduce the usage of energy to keep food warm (water heaters).

yup.. that’s all  

PosterPlanning

So i think we should plan what to put in our poster?

I know the guidelines are somewhere but I forgot where.

Post responses etc in comments.

An Idea

Hello!

I think we can try to create a solar cooker in addition to our poster to better explain ourselves during our presentation (if we have one). I’m not sure what other research we will need though…

pei ling

Feasibility of Solar Cooking

Found a good report which contains loads of stuff that we could use.

It’s here. (WARNING! It’s a PDF! Save As if you don’t want major Acrobat browser lag)

Summarized things I’ve got from it so far:

The feasibility depends on many variables. It’s not a catch-all kind of statement you can make, though I think we can make sort-of-generalized-but-not-too-generalized statements for our final product (like, specific to SG)

1. price of fuel, ovens
2. availibility of sunlight
3. cooking techniques
4. household size
5. cooking schedule

Jen can you do some more poking around of this. Thanks.

Depiction of a solar cooker, how it works

Word Document: our-solar-cooker

Advantages of Solar Cooking

 Advantages of solar cooking, compiled from different sources (sources are cited at the bottom.) Since we’re only interested in the environmental (and perhaps some economical) aspect, I left out the social/health/other reasons.

• Independancy from wood – if wood from trees is no longer needed, desertification can be stopped in many regions.
• Independancy from fossile fuels – after the solar cooking device is payd no further costs will burden the users over several years.
• The devices are cheap, robust and can be maintained by the users itself.
• The annual per capita wood consumption for cooking in most parts of the world is about .5 ton (1.32 kg per day), or about 3 tons per family of six people. A solar cooker can save one ton of wood per year.
• The energy for solar cooking is infinitely renewable and entirely non-polluting.
• The World Health Organization reports that cooking with fuel wood is the equivalent of smoking two packs of cigarettes a day. Inhalation of smoke from cooking fires causes respiratory diseases and death. One of the solutions advocated to address this problem is solar cooking which makes no smoke at all. It just uses free and abundant solar energy.

Also, might want to have a look at this which claims to be:

more convenient, much lower-priced, and now competitive with alternatives such as wood, charcoal, and wood stoves. One such model, an open reflector, has been widely tested and has proven useful in the USA, Kenya and Zimbabwe. It pays for itself in fuel savings in two months or less and becomes a recurrent economic benefit to individual households.

It’s called a Cookit.

By the way, here’s instructions on how to build your own solar cooker:

http://www.charityguide.org/volunteer/fewhours/solar-ovens.htm

Sources:

http://solarcooking.wikia.com/wiki/Advantages_of_solar_cooking

http://en.wikipedia.org/wiki/Solar_cooker#Environmental_advantages

http://www.energieinfo.de/eglossar/solar_cooking.html

Equipment needed and the rationale

Firstly, the cooker must have some materials to shape it and give it structure, and to make it more durable. Materials that can be used to give it a box-like shape are wood, metal, clay, cement, almost any material that is stiff, although it must be moisture resistant. This is because when the food is cooked, water evaporates, and may condense on the outside of the box.

Secondly, insulators are needed to retain heat from the sun as food does not cook in a millisecond. Putting the insulators around the box allows for more even heating and also minimizes the heat being conducted from the inside of the box to the outside, thus retaining more heat. Some possible insulators are aluminum foil, feathers spun fiberglass, cellulose, wool, straw, and crumpled newspaper.

The top of the box must be covered by a transparent material to allow the sun rays to pass through and a greenhouse effect can occur in the box, which will raise the temperature in the box. Glass or plastic can be used. Reflectors should also be used to bounce more light into the solar box to increase the temperature.

Lastly, the insulators and the inside surface of the cooker must be moisture resistant too. The water that evaporates from the food when it is heated will condense inside the cooker as it is sealed. The moisture resistance will prevent damage to the materials.

How should the cooker be designed?

Ideally, it should be rectangular shaped and not too deep. This is to maximize the surface area for solar collection to volume ratio. It also makes sure that less heat is lost. Also, it should be easily movable, as it will need to be moved in accordance with the sun’s rays.

Is it feasible?

According to research, the time taken to cook a particular food in a solar cooker would take twice as long as that in a conventional oven, but the food will still cook. However, if there is no sun, the solar cooker will not work. Hence, it is greatly dependent on the weather.

Application of principles in solar cooking (1)

Well now you know the theory. So perhaps you would be wondering how it applies to solar cooking. That is good thinking on your part. But back to the point – in this post, I will explain how refraction, reflection, and radiation apply in solar cooking.In solar cooking, a solar box cooker is sometimes used. It cooks because the interior of the box is heated by the energy of the sun. Sunlight, both direct and reflected, enters the solar box through the glass or plastic top. It turns to heat energy when it is absorbed by the dark absorber plate and cooking pots. This heat input causes the temperature inside of the solar box cooker to rise until the heat loss of the cooker is equal to the solar heat gain. Temperatures sufficient for cooking food and pasteurizing water are easily achieved.Greenhouse effect:  This effect results in the heating of enclosed spaces into which the sun shines through a transparent material such as glass or plastic. Visible light easily passes through the glass and is absorbed and reflected by materials within the enclosed space. Hence, you can see that solar cooking is based on the radiation of visible light waves from the sun into the solar cooking box. The light energy that is absorbed by dark pots and the dark absorber plate underneath the pots is converted into longer wavelength heat energy and radiates from the interior materials. Most of this radiant energy, because it is of a longer wavelength, cannot pass back out through the glass and is therefore trapped within the enclosed space. The reflected light is either absorbed by other materials within the space or, because it doesn’t change wavelength, passes back out through the glass.

Critical to solar cooker performance, the heat that is collected by the dark metal absorber plate and pots is conducted through those materials to heat and cook the food.

 

Reflectors, additional gain:  Single or multiple reflectors bounce additional sunlight through the glass and into the solar box. This additional input of solar energy results in higher cooker temperatures. Again, you see the properties of light being used in solar cooking.

 

However, despite the heat gain from the sun heat is also lost. Radiation is one of the ways in which it is lost: Things that are warm or hot — fires, stoves, or pots and food within a solar box cooker — give off heat waves, or radiate heat to their surroundings. These heat waves are radiated from warm objects through air or space. Most of the radiant heat given off by the warm pots within a solar box is reflected from the foil and glass back to the pots and bottom tray. Although the transparent glazings do trap most of the radiant heat, some does escape directly through the glazing. Glass traps radiant heat better than most plastics.

 Aalfs, Mark (no date). Principles of Solar Box Cooking Design. [on-line]. Available from: http://www.solarcooking.org/sbcdes.htm (Last accessed on 15th March 2008)

Principles behind solar cooking (1)

Refraction

Another property of light is that it refracts, which means that it bends when passing from one medium to another. Moreover, when light enters a more dense medium from one that is less dense, it bends towards a line normal to the boundary between the two media. This is illustrated in the figure below.

The greater the density difference between the two materials, the more the light bends. One place where this is used is in lenses for a variety of optical devices, such as microscopes, magnifying glasses, and glasses for correcting vision. An example of an image formed from a lens is shown below.

In this case the light from the object passes through the lens and is bent, forming an image on the other side of the lens which is magnified and inverted.

Many types of optical illusions are due, at least in part, to the refraction of light. One such example is the fact that if you look down while standing in a swimming pool, your feet appear closer to the surface than they actually are. This is due to the fact that light is bent when passing from water to air, as indicated below. Note that since air is less dense than water, the light bends away from the normal as it emerges.

The illusion comes from the fact that our eye doesn’t know that the light has been refracted when it comes from water into air, and so thinks that it has originated from a point closer to the surface.

No Author. (1999). Refraction. [on-line] Available from: http://theory.uwinnipeg.ca/mod_tech/node113.html (Last Accessed 1st March 2008)

Total internal reflection

An effect that combines both refraction and reflection is total internal reflection. Consider light coming from a dense medium like water into a less dense medium like air.

 

When the light coming from the water strikes the surface, part will be reflected and part will be refracted. Measured with respect to the normal line perpendicular to the surface, the reflected light comes off at an angle equal to that at which it entered at, while that for the refracted light is larger than the incident angle. In fact the greater the incident angle, the more the refracted light bends away from the normal. Thus, increasing the angle of incidence from path “1” to “2” will eventually reach a point where the refracted angle is 90^o, at which point the light appears to emerge along the surface between the water and air. If the angle of incidence is increased further, the refracted light cannot leave the water. It gets completely reflected. The interesting thing about total internal reflection is that it really is total. That is 100% of the light gets reflected back into the more dense medium, as long as the angle at which it is incident to the surface is large enough.

Fiber optics uses this property of light to keep light beams focussed without significant loss.

The light enters the glass cable, and as long as the bending is not too sudden, will be totally internally reflected when it hits the sides, and thus is guided along the cable. This is used in telephone and cable TV cables to carry the signals. Light as an information carrier is much faster and more efficient than electrons in an electric current. Also, since light rays don’t interact with each other (whereas electrons interact via their electric charge), it is possible to pack a large number of different light signals into the same fibre optics cable without distortion. You are probably most familiar with fibre optics cables in novelty items consisting of thin, multi-coloured strands of glass which carry light beams.

No Author (1999). Total Internal Reflection. [on-line]. Available from: http://theory.uwinnipeg.ca/mod_tech/node114.html (Last accessed 1st March 2008)

Radiation

The third and last form of heat transfer we shall consider is that of radiation, which in this context means light (visible or not). This is the means by which heat is transferred, for example, from the sun to the earth through mostly empty space – such a transfer cannot occur via convection nor conduction, which require the movement of material from one place to another or the collisions of molecules within the material.

Often the energy of heat can go into making light, such as that coming from a hot campfire. This light, being a wave, carries energy, as we saw in the last chapter, and so can move from one place to another without requiring an intervening medium. When this light reaches you, part of the energy of the wave gets converted back into heat, which is why you feel warm sitting beside a campfire. Some of the light can be in the form of visible light that we can see, but a great deal of the light emitted is infrared light, whose longer wavelength is detectable only with special infrared detectors. The hotter the object is, the less infrared light is emitted, and the more visible light. For example, human beings, at a temperature of about 37 ^o Celsius, emit almost exclusively infrared light, which is why we don’t see each other glowing in the dark. On other hand, the hot filament of a light bulb emits considerably more visible light. We shall discuss in more detail the nature of light in Chapter 10.

No Author (Sep. 1999). Radiation. [on-line]. Available from: http://theory.uwinnipeg.ca/mod_tech/node77.html (Last accessed on 1st March 2008)