Guide To Building A Parabolic Solar Cooker

by SolReka - Date: 2008-10-30 - Word Count: 1025 Share This!

Building a parabolic solar cooker really isn't as difficult as it may seem, once the basics are first understood.

There are many popular solar cookers in use today, including the Sun Oven, Sports Solar Oven, and the Cookit, to name but a few. However they all adopt either the box or trough design. Very few designs are actually parabolic, those that are, are generally quite expensive like the SK-14, compared to the more popular designs. The box solar cooker for example, is simply a cardboard box with reflective panels and a pane of glass which traps hot air in a box.

So What is a Parabolic Solar Cooker?

The sun's rays are collected using a reflective surface like a parabola or curved surface. The main difference between a parabolic solar cooker and other solar cooker designs is that the parabolic shape focusses the sun's rays into one point; called the focal point. A small focal point means a greater concentration of solar energy. With a parabolic solar oven, it possible to cook food at the same rate that food is cooked in a conventional. Parabolic solar cookers are considered to be a better alternative for outdoor cooking and camping as they require no firewood or the need for gas stoves and they offer fast cooking times.

Why Build a Parabolic Solar Cooker?

Building a parabolic solar cooker will result in a higher power output than other solar cooker designs. Remember, the smaller the focal point, the higher the cooking temperature. Water can be boiled in seconds using a sufficient sized parabolic cooker. However, due to the high level of accuracy required in the manufacture of parabolic cookers, a minimal focal point is very difficult to obtain.

Very high cooking temperatures can be obtained with a parabolic solar cooker, thus drastically reducing the time taken to cook food and to boil water. The box design solar cookers generally take several hours to cook food.

To summarise, building a parabolic solar cooker offers faster cooking times than other more conventional solar cooker designs. However, please bear in mind that parabolas need more frequent adjusting, pointing to the sun to optimize cooking with the sun.

How Do I Build a Parabolic Solar Cooker?

Several methods are available, one easy and ready-made solution is to use a satellite dish. Then line the inside of the dish with a reflective material such as aluminium foil, or better still Mylar. Anodized aluminium could be used, even small segments of mirror. However, the focal point would become 'scattered' as the mirror and anodized ally would not give a true parabolic shape. Another method for building a solar cooker, is to search online for parabolic calculators, and parabolic solar kits.

After researching and testing countless parabolic and general solar cooking designs, the following conclusions have been made: -

First of all, work out what size parabola you want to build. As a rule of thumb, every one square metre of reflective surface equates to 1kw of solar energy. This isn't quite the case for a paraboloid due to its shape, but the rule will suffice. A one metre diameter parabolic which has been engineered to a high spec will pump out more than enough heat to boil water in a few minutes.

800Watts or more of solar energy is sufficient for cooking your solar food.

Establish a focal point. Let's assume your building a one metre parabolic solar cooker. A suitable focal point would be approximately 20cm.

A focal point of 25cm wouldn't produce the same results as the focal point of 20cm. This is due to factors such as wind, stand design, and cooling effects. With the cooking vessel situated at a focal point of approximately a third of the way down from the top of parabola, this will ensure sufficient wind protection, as well as an area where the heat is 'captured' and retained.

An optimal sized parabolic solar cooker would be in the range of 80cm-1.2m in diameter, with a focal point of 20-30cm.

It is also important to choose the right cooking pot for your solar cooker. It has to be dark in colour and placed in the correct position, namely in the middle of the focal point. It also needs to be oriented to the sun and placed on a small stand that sits at the point of focus for the oven. Parabolic solar cookers can work for 60 to 90 minutes unattended. If you find that the food is not cooked or that another pot has to be heated, then simply adjust the dish to point to the sun every 15-20 minutes or so.

One final note, if the focal point is too low or too shallow, in other words, a deep bowl shaped parabola, then the sun's rays will 'bounce' on the top and sides of the cooking vessel, and not from underneath as they should do. It is also very difficult to manufacture - ref incorporating stand with a deep shaped dish. There is also a smaller surface area, in that the sun's rays only penetrate whatever diameter the dish is set to, irrespective of depth.

A shallow parabolic solar cooker is the ideal solution. A shallow parabola provides a relatively large diameter dish. Factors such as the wind and insulation of cooking vessel must be taken into account for this type of design. Many satellite dishes have a focal point just outside the depth of the dish. This is due to ease of manufacture and optimal threshold for capturing frequency bands.

Suitable Materials for Building a Parabolic Solar Cooker: -

Reflective mirrors - Finished anodised aluminium (expensive).

Mylar - used in hydroponic set ups, creases and tares quite easily but very economic and approximately 95-98% reflectivity.

Aluminium foil - cheap and cheerful, however creases and tares can play a large part in the build. Foil is a great starting point as it's cheap and readily available.

Reflective vinyl - Highly reflective material which also comes with an adhesive backing. For more details visit SolReka website.

So now you have a good understanding of what a parabolic cooker is and the main concepts needed to start building your very own parabolic solar cooker. So, what are you waiting for... It's fun, practical, educational, and very rewarding :-)

Related Tags: solar, oven, cooker, parabolic solar cooker, parabolic, solar cooking

For more information on parabolic solar cookers, please visit: Energy Solutions

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